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Manufacturing Engineering Thesis

2020-05-27

Adaptation, Design and Fabrication of

Multipurpose Threshing Machine

Wondmagegn, Wudu

http://hdl.handle.net/123456789/10857

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BAHIR DAR UNIVERSITY

BAHIR DAR INSTITUTE OF TECHNOLOGY

Faculty of Mechanical and Industrial Engineering

Adaptation, Design and Fabrication of Multipurpose Threshing

Machine

Master Thesis

By

Mr. Wudu Wondmagegn

Advisor: Dr. Assefa Asmare

Bahir Dar, Ethiopia

January, 2017

BAHIR DAR UNIVERSITY

BAHIR DAR INSTITUTE OF TECHNOLOGY

FACULTY OF MECHANICAL AND INDUSTRIAL ENGINEERING

Adaptation, Design and Fabrication of multipurpose threshing machine

A Thesis Submitted to Faculty of Mechanical and Industrial Engineering of Bahir

Dar Institute of Technology in Partial Fulfillment of the Degree of

Master of Science in Mechanical Engineering

(Manufacturing Engineering)

By

Mr. Wudu Wondmagegn Wondifraw

Advisor

Dr. Assefa Asmare

Bahir Dar, Ethiopia

January, 2017

Student’s Declaration

I, undersigned, declare that the thesis comprises my own work. In compliance with internationally

accepted practices, I have dually acknowledged and refereed all materials used in this work. I

understand that non-adherence to the principles of academic honesty and integrity, misrepresentation/

fabrication of any idea/data/fact/source will constitute sufficient ground for disciplinary action by the

university and can also evoke penal action from the sources which have not been properly cited or

acknowledged.

Signature: __________________

Name: Mr. Wudu Wondmagegn

Date: ______________________

Advisor declaration

I hereby declare that I have consulted the researcher in and out of the progress he made and checked

the thesis judge that the work is adequate in terms of scope, quality for the award of the degree of

Master of Science in Mechanical Engineering with Manufacturing Engineering.

Signature: _______________

Name: Dr. Assefa Asmare

Position: Assistance Professor

Date: _________________

The thesis titled “Adaptation, Design and Fabrication of multipurpose threshing machine by Mr. Wudu

Wondmagegn is approved for the Degree of Master of Science in Mechanical Engineering with

Manufacturing Engineering

.

APPROVAL BOARD OF EXAMINER

Name Signature Date

Advisor

Dr. Assefa Asmare ___________ __________

Manufacturing Engineering Chair holder

Dr. Teshome Mulatie Bogale ___________ __________

________________________ ______________ __________

External Examiner

Dr. Teshome Mulatie Bogale ___________ __________

Internal Examiner

Adaptation, design and fabrication of multipurpose threshing machine

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Abstract

Ethiopia has a highly diversified agro- ecological condition, which makes possible the

production of a wide range of agricultural products. Threshing of cereal crops by hand or

manually or simple tools is a time consuming and a tedious process and leads to high post

harvesting loss. The drudgery involved in the manual threshing or shelling of the cereal crops has

discouraged the mass production and commercialization of the cereal crop and this necessitates

the development and evaluation of a motorized operated crop threshing or shelling machine

using impact method. In order to help small scale agriculture, increase its contribution ensure

food security, threshing operation and its subsequent loss followed is among points requiring

proper attention and that gently account about 30% of cereal crop loss in Ethiopia. In rural area

like in Ethiopia is done by traditional methods. This method is the time wasting, energy supping

and often the grain is broken or damage. In developing world, crop threshing is done by various

PTO operated machines, but in rural areas the farmers who lacks in financial condition cannot

afford this machine. To overcome this problem, this research deals with adaptation, design and

fabricate a multipurpose threshing, for threshing of variety of cereal crops. This machine was

constructed to thresh cereal crops and separate the cobs or chaffs from the grains. The thresher

was constructed from locally available materials made from mild steel and its operation does not

require any special skills. The test was carried out at speed 450, 540, and 730 rpm, 1100 and

1440 rpm, 1200 and 1440 rpm for maize, wheat and Teff respectively and the moisture contents

of 15,2, 10 and 8 %(wb) for maize, wheat and Teff respectively. Its threshing efficiency around

99.98 for maize%,99.9% for wheat, and 100% for Teff and the threshing capacity 2500kg/hr-

3000kg/hr, 750.53kh/hr and 280kg/hr for maize, wheat and Teff respectively and breakage is

very insignificant, as well as losses for all. The machine, threshing action are done by using

replaceable drum, it depends on the type of crop, for maize twisted rasp bar type drum but for

wheat and Teff raspbar drum. It is also capable of reducing time wastage, reduction of breakage

of the grain, increase the efficiency of threshing, separation of stalk from the grain and also

increase the winnowing action during threshing, in order to increase the quality of the threshing

crops. The results of the analysis showed that increase in the speed of the threshing unit increases

the threshing and cleaning capacities of the thresher. However, breakage of the threshed crops

seeds also increases with an increase in the speed of the threshing unit. When the moisture

content of the crops seeds was increased from 13% -18% there was drastic reduction in the

amount of broken seeds from 0.3 to 0.15 % for maize.

The thresher performed satisfactorily and is suitable for domestic and commercial threshing of

cereal crop seeds.

Key words: Replaceable drum, multipurpose threshing, through put capacity, Efficiency


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Acknowledgments

I will forever be grateful to my advisor, Assefa Asmare Phd). He has been helpful in providing

advice many times during my post graduate career, including directing my attention to

opportunities within Bahir-dar institute of technology (BIT) simply for the love of adventure and

the learning experience, thanks Dr. Assefa Asmare. A special thanks to Mr. Gessessew Likeleh,

who has been very supportive to me throughout the research and thanks to Mr. Negese Y. for all

of his support, and for constantly broadening my intellectual horizons. Generally, I would like

thanks during practical work Mr. Getaneh M., Mr. Yitayew T., Mr. Tesfahun and Mr. Biresaw. I

also thank my friends them both for their helpful advice and suggestions in general and thanks

our faculty dean Mr. muluken Z. to facilitate everything during the practical work.


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Table of Contents

ABSTRACT ..................................................................................................................................... I

ACKNOWLEDGMENTS .............................................................................................................. II

TABLE OF CONTENTS ......................................................................................................... III

LIST OF FIGURES ................................................................................................................... VIII

LIST OF TABLES ........................................................................................................................ IX

ABBREVIATION.......................................................................................................................... X

ACRONYMS ................................................................................................................................ XI

1. INTRODUCTION .................................................................................................................. 1

1.1 Back ground of agricultural mechanization ..................................................................... 1

1.2 Problem statement and problem analysis ......................................................................... 4

1.2.1 Problem statement ..................................................................................................... 4

1.2.2 Problem analysis ....................................................................................................... 4

1.3 Objectives ......................................................................................................................... 5

1.3.1 General objective ...................................................................................................... 5

1.3.2 The specific objectives .............................................................................................. 5

1.4 Site Analysis and inventory.............................................................................................. 5

1.5 Justification ...................................................................................................................... 6

1.6 Statement of the scope...................................................................................................... 6

1.7 Limitation ......................................................................................................................... 7

2. LITERATURE REVIEW ....................................................................................................... 8

2.1 Agricultural mechanization .............................................................................................. 8

2.2 Overview of Ethiopia agriculture ..................................................................................... 9

2.2.1 Agricultural mechanization in Ethiopia .................................................................... 9

2.2.2 Harvesting and threshing ........................................................................................ 10

2.3 Maize growing in Ethiopia ............................................................................................. 12

2.3.1 Importance of maize ............................................................................................... 12


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2.3.2 Status of agricultural mechanization in Ethiopia .................................................... 13

2.3.3 Maize threshing (shelling) ...................................................................................... 14

2.4 Threshing Operation of maize ........................................................................................ 15

2.5 Maize shelling techniques .............................................................................................. 16

2.5.1 Hand shelling .......................................................................................................... 16

2.5.2 Maize-shelling with rotary equipment .................................................................... 17

2.5.3 Mechanized threshing or shelling with motorized equipment ................................ 19

2.6 Threshing of Teff in Ethiopia ......................................................................................... 19

2.6.1 Teff and Ethiopia .................................................................................................... 20

2.6.2 Teff grown area ....................................................................................................... 21

2.7 Winnowing of Teff ......................................................................................................... 23

2.8 Threshing of wheat ......................................................................................................... 24

2.8.1 Harvesting and threshing of wheat ......................................................................... 25

2.9 Different parts of a thresher and their functions ............................................................ 27

2.10 Different type of thresher and their suitability for crops ............................................ 29

2.11 Mechanics of grain threshing ..................................................................................... 32

2.12 Determination of mechanical kernel damage ............................................................. 33

2.13 Factors influencing kernel damage ............................................................................. 34

2.13.1 Machine parameters ................................................................................................ 34

2.13.2 Plant parameters ...................................................................................................... 34

2.14 Kernel detachment ...................................................................................................... 36

2.15 Competitive design ..................................................................................................... 42

2.16 Decision matrix........................................................................................................... 44

3. DESIGN ANALYSIS ........................................................................................................... 47

3.1 Selection and design criteria .......................................................................................... 47


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3.2 Methodology .................................................................................................................. 47

3.2.1 Literature review and data collection ...................................................................... 48

3.2.2 The methods used in this design ............................................................................. 48

3.3 Materials and methods ................................................................................................... 48

3.4 Design of machine components ..................................................................................... 49

3.5 Rotational motion and centrifugal force......................................................................... 50

3.6 Rotational Torque ........................................................................................................... 51

3.7 Work done by a torque ................................................................................................... 51

3.8 Pulley and Belt Drive on pulley 1(Power transmitted on main shaft) ........................... 52

3.9 Tensions on belt ............................................................................................................. 55

3.10 Tensions on belt on pulley 2 for cleaning action ........................................................ 57

3.11 Belt selection .............................................................................................................. 58

3.12 Design of hopper ........................................................................................................ 60

3.13 The main frame ........................................................................................................... 61

3.14 Design of shaft ............................................................................................................ 64

3.14.1 Shaft Design Procedure........................................................................................... 64

3.15 Key selection .............................................................................................................. 72

3.15.1 Stress concentrations ............................................................................................... 72

3.15.2 Preliminary design .................................................................................................. 72

3.16 Keyseats ...................................................................................................................... 73

3.17 Selection of anti-friction bearing ................................................................................ 74

3.18 Life of bearing calculation methods ........................................................................... 75

3.18.1 Load analysis .......................................................................................................... 75

3.18.2 Belts ........................................................................................................................ 76

3.19 Design of screw thread ............................................................................................... 79


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3.19.1 Screw thread fundamentals ..................................................................................... 79

3.19.2 Determination of belt length ................................................................................... 82

3.20 Material selection of Bolt and nut .............................................................................. 84

3.20.1 Fastener material selection ...................................................................................... 84

3.20.2 Classification of bolting material ............................................................................ 84

3.21 Total weight of the machine ....................................................................................... 85

3.22 Moisture content of grain ........................................................................................... 86

3.23 Feed rate ..................................................................................................................... 87

3.24 Designing of blower ................................................................................................... 88

3.24.1 Difference between Fans, Blowers and Compressors............................................. 88

4. PERFORMANCE EVALUATION ...................................................................................... 91

4.1 The evaluation of Physical Parameters .......................................................................... 92

4.1.1 Grain moisture content ............................................................................................ 92

4.1.2 Broken/damaged grain ............................................................................................ 92

4.1.3 Grain-Straw Ratio ................................................................................................... 92

4.1.4 Drum speed ............................................................................................................. 93

4.2 Results and discussion .................................................................................................... 95

4.2.1 Threshing capacity and kernel damage of multi-crop thresher ............................... 95

4.2.2 Threshing efficiency and total grain loss of maize crop ......................................... 96

4.2.3 The expected output of wheat crop ......................................................................... 97

4.2.4 Threshing efficiency and total grain loss of wheat crop ......................................... 98

4.2.5 The expected output of teff crop ............................................................................. 99

4.2.6 Threshing efficiency and total grain loss of Teff crop .......................................... 100

5. MANUFACTURING PROCESS AND COST ANALYSIS ............................................. 102

5.1 Manufacturing process ................................................................................................. 102

5.2 Assembly procedure ..................................................................................................... 116


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5.3 Total manufacturing cost .............................................................................................. 117

5.4 Calculate a labor rate .................................................................................................... 118

5.5 Direct Costing Overview .............................................................................................. 119

5.6 Direct materials cost ..................................................................................................... 120

5.7 Direct labor cost ........................................................................................................... 120

5.8 Cost analysis ................................................................................................................. 120

5.8.1 Raw material cost .................................................................................................. 120

5.8.2 Standard components costs ................................................................................... 121

5.8.3 Manufacturing processes cost ............................................................................... 123

5.8.4 Cost of summary ................................................................................................... 129

6. CONCLUSION, RECOMMENDATION AND FUTURE WORK ................................... 131

6.1 Conclusion .................................................................................................................... 131

6.2 Recommendation .......................................................................................................... 132

6.3 Future work .................................................................................................................. 133

7. REFERENCES ................................................................................................................... 134

8. APPENDIXES .................................................................................................................... 140

9. PART DRAWINGS ............................................................................................................ 145


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List of figures

Figure 2.5-1Shelling maize by hand and simple rotary equipment .............................................. 17

Figure 2.5-2Varieties of hand held devices for maize shelling made from different materials and

methods ......................................................................................................................................... 17

Figure 2.5-3Hand rotary and pedal type maize sheller ................................................................. 18

Figure 2.5-4Manual hand operated sheller ................................................................................... 18

Figure 2.7-1Traditional threshing of tef........................................................................................ 23

Figure 2.7-2 Productions of Teff or kimir and preparing the floor for threshing of Teff ............. 23

Figure 2.7-3After threshing winnowing of Teff for separating straw to Teff .............................. 24

Figure 2.8-1Threshing of wheat by using traditional and mechanical .......................................... 25

Figure 2.8-2Threshing of wheat by traditional and mechanization .............................................. 26

Figure 2.9-1Sieve clearance .......................................................................................................... 29

Figure 2.10-1Spike tooth drum ..................................................................................................... 30

Figure 2.10-2Rasp bar drums ........................................................................................................ 30

Figure 2.10-3 Wire –loop drum .................................................................................................... 31

Figure 2.14-1 Schematic diagram of kerenel attachment showing kernel, rachis and pith ......... 37

Figure 3.5-1 Body experiencing circular motion .......................................................................... 50

Figure 3.8-1 Diagram showing two pulleys connected by a belt. ................................................. 52

Figure 3.8-2Larger pulley ............................................................................................................. 53

Figure 5.8-1Twisted bar drum .................................................................................................... 123

Figure 5.8-2 Cylinder drum for wheat and teff ........................................................................... 124

Figure 5.8-3 Lower concave ....................................................................................................... 124

Figure 5.8-4Left and right support and cover ............................................................................. 125

Figure 5.8-5 Different size pulleys ............................................................................................. 125

Figure 5.8-6Manufacturing of drum beater ................................................................................ 126

Figure 5.8-7 Assembly of multipurpose thresher ....................................................................... 126


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List of tables

Table 2-1Area and Production of Main Cereals in Ethiopia 2012-2013 ...................................... 22

Table 2-2Existing threshing machine, written by differentabroad researchers ............................ 39

Table 2-3Existing threshing machine, written by in Ethiopian researchers ................................. 41

Table 2-4 Competitive design ....................................................................................................... 43

Table 2-5 Decision matrix for Key Characteristics and competitive designs ............................... 46

Table 3-1 Recommended life value of bearings ........................................................................... 78

Table 3-2 Technical and working parameter of the thresher ........................................................ 86

Table 4-1 Factors and level values considered on threshing different crops. ............................... 91

Table 4-2 Effect of cylinder speed on performance of multi-crop thresher on maize crop .......... 96

Table 4-3 Effect of cylinder speed on performance of multi-crop thresher on wheat crop .......... 98

Table 4-4 Effect of cylinder speed on performance of multi-crop thresher on teff crop ............ 100

Table 5-1Manufacturing process of blower and blower casing .................................................. 103

Table 5-2Manufacturing process of screw and screw casing ..................................................... 104

Table 5-3Manufacturing process of shaft and key way .............................................................. 106

Table 5-4Manufacturing process of left and right support and cover ......................................... 108

Table 5-5Manufacturing process of front and side cover ........................................................... 110

Table 5-6Manufacturing process of upper and lower concave ................................................... 112

Table 5-7Manufacturing process drum or cylinder beater .......................................................... 114

Table 5-8Raw material cost ........................................................................................................ 121

Table 5-9 Cost of standard components ...................................................................................... 122

Table 5-10 Machining process cost ............................................................................................ 127

Table 5-11Labor cost .................................................................................................................. 128

Table 5-12Cost of summary........................................................................................................ 130


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Abbreviation

CSA Central Statistical Agency

EATA Ethiopian Agricultural Transformation Agency

ECSA Ethiopian Central Statistical Agency

EIAR Ethiopian Institute of Agricultural Research

FAO Food and Agricultural Organization of United Nations

GDP Gross domestic product

GTP Growth and Transformation Plan

IRRI International rice research institute

JICA Japan International Cooperation Agency

MoA Ministry of Agriculture

MOFED Ministry of Finance and Economic Development

NRC National Research Council

PAA Africa-purchase from Africans for Africa

SAA/SG2000 Sasakawa Africa Association

PTO Power tractor operated

UNDP United Nations Development Programme

USAID United States Agency for International Development

USD United state dollar

WDM Weight decision matrix

WFP World food programme


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Acronyms

Symbol meaning

a Acceleration

C Center distance

Cd basic dynamic load rating (N)

D Diameter of pulley

d Diameter of shaft

𝐷𝑥 Diameter of smaller pulley

𝐷𝑦 Diameter of larger pulley

Fa Actual axial bearing load (N).

F.O.S Factor of safety

𝐹𝑔 weight

Fr Actual radial bearing load (N).

g Acceleration due to gravity

K exponent for life equation

Kb Suddenly applied load for bending

𝐾𝑝 no preloaded bearing

Kr outer race fixed inner race rotating

𝐾𝑟𝑒𝑡 reliability

𝐾𝑠 moderate shock load

Kt Suddenly applied load for torsional

L required life of bearing

𝐿𝑐 Length of correction

𝐿𝑝 Length of pulley

L10 life of bearing

M (max) Maximum bending moment

m mass

𝑀𝐴𝑉 the vertical bending moments at point A

𝑀𝑏 Bending moment

𝑀𝐵𝐻 Horizontal bending moment

𝑀𝐵𝑣 the vertical bending moments at point D

𝑚𝑐 Mass of crop


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𝑀𝑐 𝑤𝑏 Moisture content wet bases

𝑚𝑐𝑦 Mass of cylinder

𝑚𝑝 Mass of pulley

𝑀𝐷𝑉 Vertical bending moment

𝑀𝑡 Torsion moment

N Speed, Rpm( revolution per minute)

n rotational speed (rev/min)

P power

P equivalent dynamic bearing load (N);

r Radius of the object

𝑅𝐵𝑉 Vertical Reaction at B

𝑅𝐶𝑉 Vertical Reaction at C

T Rotational torque

𝑇1 Tension in tight side

𝑇2 Tension in slack side

𝑇𝑐 Centrifugal tension

𝑇𝑑 Twisted moment

𝑇′1 Tension in tight side for lead screw

𝑇′2 Tension in slack side for lead screw

V volume

v velocity

Vd Volume of thread

𝑉𝑅 Velocity ratio

Vs Volume of shaft

VT Total volume of lead screw

𝑊1 Weight of pulley one

𝑊2 Weight of pulley two

𝑊𝑑 Dried weight of sample

𝑊𝑖 Initial weight of sample

𝑊𝑝 Weight of pulley

X radial load factor for the bearing

Y Axial load factor for the bearing

Adaptation, design and fabrication of a multipurpose threshing machine

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Greece symbol Meaning

θ angle

ρ density

𝜇 Coefficient of friction

𝜔 Angular velocity

Ѳ Angle of lap in rad

𝜏𝑚𝑎𝑥 Maximum sheer

𝑆𝑦𝑡 Yield strength

Su Ultimate strength


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CHAPTER ONE

1. INTRODUCTION

1.1 Back ground of agricultural mechanization

Ethiopia is one of the largest countries in Africa, with a total geographical area of 440,284 square

miles (1.14 million square kilometers) and an estimated population of about 92 million (2007

estimate). It lies wholly within the Eastern part of Africa (Horn of Africa). Ethiopia has a highly

diversified agro- ecological condition, which makes possible the production of a wide range of

agricultural products. Hence, agriculture constitutes one of the most important sectors of the

economy. The sector is particularly important in terms of its employment generation and its

contribution to gross domestic particularly important in terms of its employment generation and

its contribution to gross domestic product (GDP) and export revenue earnings. Highest (85%)

contribution to foreign exchange earnings. Share of 41% of GDP and more than 50% of raw

material to industries. The struggle for food security for Ethiopia and other West African

countries through the adoption of concerted policies and actions at both national and

international levels points to the need for Ethiopia and other West African countries to evolve

viable international agricultural production options that will ensure sustainable production of

food and raw materials for human consumption, agro-based industries and export. Production

systems involve the conversion of inputs through the application of energy to useful outputs. In

agricultural production, this involves a series of operations from production to processing and

which invariably necessitates the use of machines and equipment at every stage. Increased land

productivity (greater output/unit area of land) generally depends on the application of higher

technology and a higher level of knowledge and management ability. Agricultural mechanization

is an instrument of farm management and as such changes in mechanization level can have a

multiplier effect on output per unit of land [2]. Agricultural mechanization has now been

accepted as the most crucial input not only to increase agricultural productivity and promote

industrialization of the rural sector but also to promote the overall economic development of

nations. Historically, increase in productivity can be linked with technological changes. To

promote agricultural mechanization, therefore, it is necessary that appropriate levels of

agricultural mechanization technology are identified, introduced and managed in each agro-


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climatic zone. It was based on the need to develop “home grown” mechanization technologies

that the then Federal Ministry of Agriculture and Natural Resources, when it realized that only

indigenously developed mechanization technologies manufactured and maintained with our local

know-how and facilities could best sustain agricultural development in Ethiopia. The policy on

agricultural mechanization was to encourage the development of efficient home grown tools,

equipment and systems which improve agricultural production and productivity, relieve the

continuously increasing labor constraints, enhance farmer's income, reduce food imports,

increase food export and save foreign exchange. It was envisaged that mechanization

technologies would accomplish these tasks through carrying out, among other functions, the

standardization and certification of agricultural tools, machines and equipment in Ethiopia, as

well as testing and evaluating the suitability of all types of imported and locally developed

agricultural tools, machines and equipment already in use and those proposed to be used in

Ethiopia. Thus, there has been a long felt need in Ethiopia by the government, concerned

institutions, and individuals to use standardization to promote the evolution of appropriate

agricultural mechanization through a rapid development of indigenous agricultural tools,

machines and equipment, since it has been realized that standardization represents the fastest

vehicle' to integrate agricultural mechanization to technological and economic development of

the nation. Therefore, this research point out, the role of design, fabrication and adaptation of

multipurpose threshing machine and in promoting appropriate mechanization technologies for

improved agricultural productivity in Ethiopia.

The primitive people harvested their corn by hand, and hand harvesting is still the rule in areas

where farms are small, labor is inexpensive, and few hectares are planted to corn. In the

developed countries, the harvest of corn has progressed from hand picking of the ears, through

machine picking ears for storage in cribs, to field shelling by picker Sheller and more recently by

combines. Field shelling of high moisture corn results in damage to a high percentage of the

kernels, À field survey in Iowa indicated that in typical combine harvesting systems from16.4 to

79.4% of the kernels were damaged. The average damage found in corn samples from combines

was 34.4% [84]. Mechanical damage of corn has adverse economic effects on the farmer,

processor, and eventually the consumer. The economic loss from damaged kernels starts in the

field during the harvesting operation. This loss consists of the corn chips and meal that pass out

the rear of the combine and the kernel tips left in the cob. Beside, these invisible losses,


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mechanical damage of corn costs Ethiopia farmers lost cents per bushel on all the corn sold. The

average amount of screening cleaned out before grain gets to the consumer is over 3%. Kernel

mechanical damage during shelling can be reduced by either improving the thresh ability of the

ears or by building machinery that handles the ears and kernels in a gentler manner and hence

causes less damage. The research believes that one feasible way to handle the ears gently and

control them effectively is by threshing them one by one in line instead of in random groups as is

now being done in the conventional shelling machines. Also the kernels of each ear should be

shelled individually so that only very small forces are needed to remove the kernels. During

shelling at 32% moisture content by conventional methods, kernel tip losses amount to about

0.3% of the sample weight [84].

Advantages of agricultural mechanization

To increase efficiency of production

To reduce farm drudgery

To encourage farmers to practice large scale farming

To increase yield of farm produce

To reduce farm hazards

To enhance the quality of farm produce

To ensure that farm work is carried out very fast. i.e. to encourage timeliness offarm

operations

To enable farmers, maximize their profits

To reduce poverty and facilitate farmers to increase their incomes thusimproving their

standard of living

To save labour through human labour replacement with machines. In doing this,

labour is released to other services and industries

To make farm work easy, interesting and attractive to youths

To bridge the gap between the demand for and the supply of good quality food

To supply agro-based industries with adequate and good quality raw materials

To encourage investment in agriculture


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1.2 Problem statement and problem analysis

1.2.1 Problem statement

For a long time now, threshing or shelling of cereal crops to remove the grain from the cobs or

straw has been a time consuming and tedious process especially to the small scale farmers in the

country who basically practice subsistence crop farming. However, traditional threshing or

shelling methods do not support large- scales threshing or shelling, especially for commercial

purposes. Hand threshing or shelling takes a lot of time, even some hand operated simple tools.

In this research study area, most mechanized thresher or shellers designed for maize, wheat and

Teff threshing or shelling are tractor PTO shaft operated and cause great damage to cereal crops

seeds likewise breaking the cob or the straw to pieces, such thresher or shellers are equipped

with rotating threshing drum with beater or teeth, which cause damages to the seeds. Besides, the

cost of purchasing such thresher or sheller are high for the rural farmer and therefore call for the

need of a relatively low cost maize, wheat and Teff threshing mechanism that will be affordable

to such farmers not only to meet their threshing or shelling requirement but also improve the

threshing efficiency and reduce damage to the seed.

1.2.2 Problem analysis

Many small scale cereal crop farmers to shell or thresh their crop produce by use of hand,

something that is time consuming and tedious. Threshing the annual harvesting by hand typically

takes weeks with children sometimes kept out the school to help with the work of threshing the

cereal crop to meet their daily food requirements. This is because processing food for survival

takes priority over education in subsistence farming households since the staple food in the

country maize, wheat and Teff meal. In addition, the hardened, dry cereal crops can also be

painful to thresh or shell and lead to hand injuries. For this reason, other such farmers choose to

use simple hand held tools which are strenuous as well as slow.

For the large scale cereal crop farmers, who tend large hectare of cereal crops for commercial

purpose, threshing their produce has not really been a big problem majority because they have

sufficient capital to hire combined harvester from well established companies and organizations.

It is in this regard that this research presents the adaptation, design and fabrication multipurpose

threshing which typically a thresher for small scale farmers who tends to cereal crop farms.


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1.3 Objectives

1.3.1 General objective

The broad objective of this project is to adaptation, design and fabricate multipurpose threshing

machine, document the challenges and prospects of promoting agricultural threshing

technologies for reducing post-harvest losses which increases productivity and quality of

agricultural commodities in the country.

1.3.2 The specific objectives

To design and test new adaptation threshing or shelling devices that results in less

damage and grain loss.

To establish energy requirement for operating the machine.

To analyze the threshing or shelling proposed by different research

To increase the efficiency.

To reduce the hard work.

To reduced time to thresh or shell different cereal crops

It satisfies the need of rural farmers to earn more money.

To modify the small scale stationary threshing machine to suit separation of different

cereal crops.

To reduce the grain damage, grain losses and increases grain separation.

To evaluate the performance of the adapted threshing machine under different

opretion condition.

1.4 Site Analysis and inventory

The study area in this research is around Bahir Dar region. Due to increasing levels of poverty as

well as poor cultivation techniques that result to low yields during harvesting, large scale cereal

crops farming in this area is carried out by the rich including local farmers and middle class

farmers. However, a bigger portion of cereal crops cultivation is carried out on small scale and

mostly by women and is done on farm.

Existing alternatives to threshing or shelling by hand are often unaffordable or difficult to obtain

for subsistence farmers. An estimated two- third of smallholder farmers in the world lack access

to mechanized agricultural technology. Industrial tractor PTO operated cereal crops thresher or


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shelller are prohibitively expensive, with a cost range 65,000br motorized threshers available in

the market cost up to 85,000br depending on the horse power capacity of the motors.

Multipurpose small scale mechanical powered thresher or shellers cost up to 45,000br, but

technically of their operation limits their use.

While industrial thresher is highly productive, their energy infrastructure requirements can

render them unusable in rural villages. Furthermore, mechanized equipment and stationary

powered operated devices are difficult to transport to the user area. As a consequence, farmers

may be required to travel long distances to process their crop or the technology may not be able

to reach the communities who need it most.

1.5 Justification

Our area requires a conventional threshing or shelling technique that would significantly cater

for the farmers harvesting capacity and which many householders can afford. This is with due

consideration to the following reasons:

Most of the cereal crops grown by such rural farmers is for food rather than for

commercial purpose.

Industrial cereal crops thresher or shellers are too expensive to be purchased by such rural

farmers.

For most of the farmers, the cost of hiring the service of industrial threshers is high with

respect to the amount of grain output at the end of the farming season.

Rotary and pedal- powered cereal crops thresher require too much energy inputs which

limits their adoption by most of the farmers since become cumbersome to use and result

to too much fatigue.

1.6 Statement of the scope

This adapted or manufactured thresher or sheller is to be a power driven operated equipment. Its

work out put will depend on the feed rate and speed of drum as well as on the machine itself. The

operator is to perform the cereal crops threshing by rotating a motor and therefore, proper feed

rate andspeed would be necessary for efficient operation of the multipurpose machine. Improper


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feeding and speed will result discomfort to the machine and difficulties in the smooth operation

of the equipment, thus resulting in lower work efficiency and through put capacity.

In the view of the above, this research focuses on energy consideration which arises from among

other factors. The physiological and psychophysical response of the rural farmers during

operation of the cereal crops thresher or sheller at different distance and length of belt and carry

out design modification in work system so as to have higher machine system efficiency and

through put capacity.

1.7 Limitation

Lack of machines for bending, rolling and shearing.

During the machining of different operation, lack of cutting tool and drilling chuck tool

are one of the challenges during the practical work.

Lack of different cereals crop for testing the machine, because the awareness of our rural

area farm mechanized threshing of different crops were very low.

Challenges in threshing technology generation and development.

Limited emphasis given agricultural mechanization research.

Lack of full agricultural mechanization document in our region.

Challenges in threshing technology multiplication to limited capacity.

Challenge in threshing technology delivery system.


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CHAPTER TWO

2. LITERATURE REVIEW

2.1 Agricultural mechanization

Agriculture in Ethiopia is characterized by small holdings, due to high population density with

nearly two-third of the population residing in rural areas. There are 111.5 million hectares of

land in Ethiopia, 74.5 million hectares of which is suitable for agriculture, and 13.6 million

hectares of which is currently under production. Farmers produce cereal crops (wheat, barley,

maize, and rice), oil seeds (sesame, Niger seeds, canola, linseed, ground nuts and sunflower,

lentils), pulses (soya beans, haricot beans, chickpeas, beans and lentils), beverage crops (coffee

and tea), cotton, horticulture and apiculture.

Large scale commercial agriculture has expanded partly due to foreign direct investment. The

Ethiopian government is seeking private sector investors to help modernize the agricultural

sector and help it produce more efficiently, particularly with large-scale commercial farming and

agro industrial activities. Ethiopia has created a more attractive investment climate in recent

years by providing potential investors with various tax breaks, access to affordable land, and a

relatively efficient investment process.

The government plans to spend about USD 4.4 billion in agriculture during the GTP period

2010/11- 2014/15. Initiatives will be undertaken such as the importation and adaptation of

existing and proven technologies, including agricultural mechanization, research on crop,

livestock and natural resources. The agricultural sector suffers from poor cultivation practices,

overgrazing, deforestation, underdeveloped water resources and drought. According to the

Ministry of Agriculture, Ethiopia is estimated as having one of the highest rates of soil nutrient

depletion in Sub-Saharan Africa [1].

Agricultural Mechanization is an important link in achievement of effective growth in production

and it needs to be addressed in larger context. Despite the big potential of agriculture in Ethiopia,

the low level of engineering technology input in agriculture has been one of the main constraints

hindering the modernization of the country‟s agriculture and food production systems. One of the

major causes for the disappointing performance and low contribution of agricultural

mechanization to agricultural development has been the fragmented approach to mechanization


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issues [3]. This often arises from poor (or no) planning and over-reliance on unpredictable or

unsuitable aid-in-kind for many mechanization inputs, as well as limited co-ordination within

and between government and private sector agencies dealing with mechanization. Thus,

developing appropriate mechanization technology will improve production and productivity,

reduce the huge production losses and it has a great contribution to food security. Moreover, it is

only when the environment is made conducive through proper use of appropriate energy and

improved implements, will there be an improvement in the working conditions and performance

of jobs that would otherwise be difficult to accomplish in the traditional way.

2.2 Overview of Ethiopia agriculture

2.2.1 Agricultural mechanization in Ethiopia

Agriculture is the second largest contributor to the overall economic growth and a significant

contributor to reducing poverty. In 2012-13, it accounted for about 42.9% of national GDP (only

slightly behind the service sector at 45.2%, almost 90 of foreign exchange earnings and 85% of

employment. While agricultural productivity in Ethiopia is improving, there are still major gaps

in productivity when compared with the rest of Africa in some crop areas, and almost

universally, when compared with the global output level [25]. For example, the African average

production of wheat is approximately 10% more per hectare, and the global average is about

50% higher than Ethiopia. In countries like China, there have been significant correlations

between increased use of agricultural mechanization and increased productivity. Even with

significant improvement in productivity in recent years, Ethiopia is still a net wheat importer. In

addition to this, approximately only 12% of the total arable land is utilized for agriculture, with

an expectation that this percentage will grow, both in relative and absolute terms.

Ethiopian farmers are also diverse; agriculture is dominated by smallholder farming. There are

about 14.7 million households [4] of which about 60%, which operate on less than one[1, 2, and

3].


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2.2.2 Harvesting and threshing

Harvesting is commonly practiced using scythes/sickles, which takes on average 40 person-days

per hectare and another 16 person-days for collection and piling. Threshing is accomplished by

trampling a number of oxen or donkeys, treading around on a pile of the materials, or beating the

panicles on the ground covered with mat or canvass. It requires four to six oxen working for

three to four days to thresh crop harvested from a hectare. Extended period of exposure of paddy

in the field results in quality deterioration and higher loss due to microbial effects, physical

losses from repeated handling, insect infestation, and direct consumption by cows, goats,

chicken, etc. These are some of the bottlenecks during the harvesting season as human and

animal labors are not easily available. Improved harvesting and threshing techniques are required

to minimize the loss [4].

In Ethiopia, most crops are typically harvested by manual uprooting, resulting in loss of quality

and reduced nitrogen-fixing benefits due to sticky soils attaching to the roots and being harvested

with the crop. After harvesting, the crop is left to air dry, and then threshed on poorly-prepared

ground with animals, leading to further loss in quality and the introduction of foreign matter.

Mechanizing both harvesting and threshing operations will improve the quality of produce,

reduce post-harvest loss, and replace manual labor. Two types of mechanical harvester – the

swathe, which cuts crops off at the stem and deposits the cut crops into a windrow, and the

combine harvester, which combines harvesting operations of reaping, threshing, and winnowing

may be adopted for different crops. Hence, there will be an increasing need for mechanized

harvesting and threshing to meet productivity and quality standards. The cost of mechanized

harvesters and threshers is prohibitively high for smallholder farmers, but there is potential to

provide access to post-harvest implements through rental schemes administered by cooperatives

to members. Further research and technology development efforts are required to evaluate the

technical and economic feasibility of adapting mechanized harvesters and threshers in the

Ethiopian context.

Harvesting is the process of obtaining plant parts or component of plant-parts that has reached its

physiological maturity or at the stage of growth ideal for separating it from the stock plant. The

act of harvesting can be picking, pulling, plucking, slashing, cutting, stripping and shaking the

economic part of the plant that is of interest to the harvester.


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Threshing or shelling is the process of separating the grain from the seed heads, panicles, or

cobs. It is important to minimize the damage done to grain during this process as damaged grain

is much more prone to attack by insects and fungi. Consequently, techniques that crush and

damage grains such as beating with sticks or trampling by cattle, are not recommended. Also, the

grain should be neither too moist (soft) or too dry (brittle) at the time of threshing; it is best done

when grain is around 14 to 16% moisture content, although crops or cereals is commonly

threshed at around 18-20%.

With cereal crops and beans, the small farmer has several options as to when to thresh the crop.

If the matured crop has stood in the field for some time during dry weather, the seeds may be low

enough in moisture content to be threshed without damage right after harvest. However, the

farmer may still prefer to delay threshing for two reasons:

The grain may still be too high in moisture content to escape spoilage if stored as loose

seed. Grain stored in unthreshed form on the cob, on the seed head or in the pod can be

safely stored at a much higher moisture content since there is much more air space for

ventilation and further drying.

Maize stored as unhusked ears and pulses stored in their pods are more resistant to

storage insects.

Winnowing follows threshing and consists of separating chaff and other light trash from the

grain using wind, fan-driven air or screens winnowing may need to be repeated several times

before consumption or marketing and is usually supplemented by manual removal of stones,

clods, and other heavy trash.

Threshing or shelling is the process of separating the grain from the seed heads, panicles, cobs or

pods of the crops [5, 6]. It is important to minimize the damage done to grain during threshing as

damaged grain is much more prone to attack by insects and fungi. Consequently, techniques that

crush and damage grains such as beating with sticks or trampling by cattle are not recommended.

Traditional threshing of crops like wheat, barley and sorghum is one of the time consuming,

laborious and in which grain loss occurs [5].

To solve this problem a number of appreciable works have been done by different bodies among

which Bako maize sheller and Asella [85] wheat barley threshers are the prominent one since


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long time. However, the high cost of the machines and their engines together with their weight

which is as heavy up to 302 kg compared to 107 kg with peg type drum and 121 kg with bar type

of the currently developed replaceable drums multi-crop thresher was reported to have affected

its adoption rate. In addition, the undulating topography of south-western Ethiopia and small and

fragmented land ownership of the farmer of this area plays a great role in limiting the adoption

rate of the mentioned technologies. Maize, Teff, wheat, barley and sorghum are among crops

produced in south western Ethiopia and farmers are obliged to have one machine for maize and

the other for Teff, sorghum, wheat and barley threshing.

Accordingly, a multi-crop thresher was developed with the following advantages:

Smaller in size, so that it can be transported to the needed area with 2-4 persons

comfortably

Can thresh Teff and wheat using only cylindrical drum and

Can shell maize using replaceable twisted angular bar or triangular bar type open drum

interchangeably?

Can be powered using engine power (5.5hp) which are available on the market at

reasonable prices (currently at about 6,000 to 8,000 ETB)

It can be manufactured at small scale manufacturer level.

2.3 Maize growing in Ethiopia

2.3.1 Importance of maize

In Ethiopia, maize grows under a wide range of environmental conditions between500 to 2400

meters above sea level. Maize is Ethiopia‟s leading cereal in terms of production, with 6 million

tons produced in 2012 by 9 million farmers across 2 million hectares of land [4]. Over half of all

Ethiopian farmers grow maize, mostly for subsistence, with 75 % of all maize produced being

consumed by the farming household. Currently, maize is the cheapest source of calorie intake in

Ethiopia, providing 20.6 % of per capita calorie intake nationally [5]. Maize is thus an important

crop for overall food security. Maize is also used for making local beverages. Additionally, the

leaves and stokers are used to feed animals and the stalks are used for construction and fuel. A


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small quantity of the grain produced is currently used in livestock and poultry feed, and this is

expected to increase with the development of the livestock and poultry enterprises in the country.

The green fodder from thinning and topping is an important source of animal feed and the dry

fodder is used during the dry season. Moreover, the crop has potential uses for industrial

purposes, serving as a starch, a sweetener for soft drinks, an input for ethanol fuel production and

oil extraction, etc as compare to other cereals; maize can attain the highest potential yield per

unit area. In Ethiopia the national yield is about 3.0 t/ha [4]. While significant gains have been

made in maize production over the past decade, there remains large potential to increase

productivity. From 2001 to 2011, maize production increased by 50%, due to increases in both

per hectare yields (+25%) and area under cultivation (+20%). However, estimates indicate that

the current maize yield could be doubled if farmers adopt higher quality inputs and proven

agronomy best practices. At present, only 17% of maize farmers representing 30% of maize

planted area make use of improved varieties of seed[6] and only 30% of farmers use the

recommended rates for fertilizer application. Ethiopia is already a significant maize producer in

Africa, and this role could be further enhanced. Currently, Ethiopia is the fourth largest maize

producing country in Africa, and first in the East African region [7].

2.3.2 Status of agricultural mechanization in Ethiopia

Despite the long history of agriculture in Ethiopia and the start of using some sort of

mechanization, still the country‟s agriculture is characterized by the use of traditional farming

implements and practices with very low energy inputs. The entire field operations at small scale

agriculture is performed with very simple farm tools with mainly human and animal power

sources.

Animal traction is the main farming technology of the smallholder farmers who, in terms of total

arable land, dominate crop production in Ethiopia. The introduction of drought animal power

into the smallholder farming system dates as back as century ago. However, in recent years, the

use of tractor farm technology is increasingly becoming important among the smallholder

farmers at the expense of drought animal. While in the early 1970s only 4% of total smallholder


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farming households used tractors for ploughing, this figure rose dramatically to 17% and 39%,

respectively, by 1980 and 1990s [1].

2.3.3 Maize threshing (shelling)

In Ethiopia, maize was threshed originally by bare hands. Other popular method was the use of

pestle and mortar. This method is still used in the rural areas today. The above methods became

unsatisfactory because of their low output, tediousness and their requirement of extra strength.

The performance of a thresher depends upon its size, cylinder speed, cylinder concave clearance,

fan speed and the sieve shaker speed [9]. The factors influencing the thresh ability of maize in

Ethiopia are field drying, maize varieties, ear size, cylinder speed and feed rate. The properties of

the crop that affect the thresher performance are crop variety, shape and size, hardness of the

seed, the moisture content of the seed and the density [9].

Maize is the most important cereal grain in the world, after wheat and rice, providing nutrients

for humans and animals and serving as a basic raw material for the production of starch, oil and

protein, alcoholic beverages, food sweeteners and, more recently, fuel. Maize shelling involves

detaching of the maize grain from its cobs [10, 11]. Maize shelling is among the major activities

involved in the processing of maize like harvesting, drying, de-husking, storing, and milling [11].

All these processes are costly and for the rural farmers to maximize profits on their produce,

appropriate technology suiting their needs must be used. Maize shelling is a necessary process

subsequent to harvesting because the maize kernels when harvested are firmly attached to the

hard cob [12].

Shelling of the dried cobs by majority of farmers (about 96%) in the study area is carried out by

repeated beating of the cobs with a club while held inside Sacks, open barrels or spreading it

over plastered ground floor in the house or outdoor [13]. This method cause damage to the

kernels and are time consuming involving drudgery [10, 11, and 12]. Other traditional maize

shelling technique is rubbing the maize cobs against one another by hand or by direct removal of

kernels pressing it between thumb and hand palm. This option is being used and known for low

shelling capacity of about 8 kg/hr to 10 kg/hr [12, 14].


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Maize is one of the most important staple crops in the world. Maize is the most important cereal

grain in the world, after wheat and rice, providing nutrients for humans and animals and serving

as a basic raw material for the production of starch, oil and protein, alcoholic beverages, food

sweeteners and, more recently, fuel. It is because of the important place of maize that its

handling, processing and preservation within the optimum conditions must be analyzed. The

major steps involved in the processing of maize are harvesting, drying, de-husking, shelling,

storing, and milling. All these processes are costly and for the rural farmers to maximize profits

on their produce, appropriate technology that suites their needs must be used. Maize processing

not only prolongs its useful life but also increases the net profit farmers make from

mechanization technologies. It is in this line that one of the most important processing operations

done to bring out the quality of maize is shelling or threshing of maize. It is basically the

removal of the maize kernels from the cob. This separation, done by hand or machine, is

obtained by threshing, by friction or by shaking the products; the difficulty of the process

depends on the varieties grown, and on the moisture content as well as the degree of maturity of

the grain [16].

The different methods of maize shelling can be categorized based on various mechanization

technology used. These includes: hand-tool-technology, animal technology, and engine power

technology. (FAO Corporate Document Repository on Agricultural engineering in development -

Post-harvest operations and management of food grains) [15].

2.4 Threshing Operation of maize

Traditional maize shelling is carried out as a manual operation: maize kernels are separated from

the cob by pressing on the grains with the thumbs. According to the operator's ability the work

rate is about 10kg per hour. Outputs up to 20kg per hour can be achieved with hand-held tools

(wooden or slotted metal cylinders). To increase output, small disk shellers such as those

marketed by many manufacturers can be recommended. These are hand-driven or powered

machines which commonly require 2 operators to obtain 150kg to 300kg per hour. Another

threshing method, sometimes applied in tropical countries, involves putting cobs in bags and

beating them with sticks; outputs achieved prove attractive but bags deteriorate rapidly.


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Nowadays many small maize shellers, equipped with a rotating cylinder of the peg or bar type,

are available on the market. Their output ranges between 500 and 2000kg per hour, and they may

be driven from a tractor power take off or have their own engine; power requirements vary

between 5 and 15hp according to the equipment involved. Whatever the system used, it is very

important that threshing be done with care. Otherwise, these operations can cause breakage of

the grains or protective husks thus reducing the product‟s quality and fostering subsequent losses

from the action of insects and moulds. Transportation of the product from the field to the

threshing place must also be handled with special care, since it can bring about severe losses.

Depending on the influence of agronomic, economic and social factors, threshing or shelling is

done in different ways:

threshing or shelling by hand, with simple tools;

threshing with the help of animals or vehicles;

mechanical threshing or shelling, with simple machines operated manually;

Mechanical threshing or shelling, with motorized equipment.

2.5 Maize shelling techniques

Depending on the influence of agronomic, economic and social factors, threshing or shelling is

done in different ways:

Threshing or shelling by hand, with simple tools;

Mechanical threshing or shelling, with simple machines operated manually;

Mechanical threshing or shelling, with motorized equipment.

2.5.1 Hand shelling

The easiest traditional system for shelling maize is to press the thumbs on the grains in order to

detach them from the ears. Another simple and common shelling method is to rub two ears of

maize against each other. These methods however require a lot of labour. It is calculated that a

worker can hand-shell only a few kilograms an hour. Shelling of maize, as well as of sunflowers,


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can be more efficiently accomplished by striking a bag full of ears or heads with a stick. Maize

and sunflowers can also be shelled by rubbing the ears or heads on a rough surface [16].

Figure 2.5-1Shelling maize by hand and simple rotary equipment[85]

Figure 2.5-2Varieties of hand held devices for maize shelling made from different materials

and methods[85]

2.5.2 Maize-shelling with rotary equipment

Manual shellers, which are relatively common and sometimes made by local artisans, permit

easier and faster shelling of ears of maize. These come in several models, some of them equipped

to take a motor; they are generally driven by a handle or a pedal. Use of manual shellers

generally requires only one worker. A good example is the Antique maize shellers. The major


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setbacks with these shellers are that their threshing capacities are low and most of them require

to be fixed on benches before operation. Also their method of operation is too cumbersome from

the fact that the crank handle is directly connected to the threshing chamber and therefore the

effect of friction is too vigorous during the threshing process [16].

Figure 2.5-3Hand rotary and pedal type maize sheller

Figure 2.5-4Manual hand operated sheller[88]


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2.5.3 Mechanized threshing or shelling with motorized equipment

Nowadays many small maize shellers, equipped with a rotating cylinder of the peg or bar type,

are available on the market. Their output ranges between 500 and 2000kg per hour, and they may

be driven from a tractor power take off or have their own engine; power requirements vary

between 5 and 15hp according to the equipment involved. For instance, the French Bourgoin

"Bamba" model seems well-suited to rural areas in developing countries because of its

simpledesign, easy handling and versatility (maize, millet sorghum, etc.) [16].

It is also important to consider the fact that the operations of harvesting and threshing or shelling

can be carried out simultaneously, by combine-harvesters or picker-shellers. Whatever the

system used, it is very important that threshing or shelling be done with care. Otherwise, these

operations can cause breakage of the grains or protective husks thus reducing the product's

quality and fostering subsequent losses from the action of insects and moulds. Transport of the

product from the field to the threshing or shelling place must also be handled with special care,

since it can bring about severe losses. Maize grain losses contribute to food insecurity and low

farm incomes not only in Ethiopia but also in other SSA countries. Therefore, efficient post-

harvest handling, storage and marketing can tremendously contribute to social economic aspects

of rural communities in Ethiopia as stipulated

The losses are directly measurable in economic, quantitative, qualitative, (nutritional) terms.

Economic loss is the reduction in monetary value of maize grain as a result of physical loss.

Quantitative maize loss involves reduction in weight and therefore can be defined and valued.

Qualitative loss although difficult to assess because it is frequently based on subjective

judgments (like damage), can often be described by comparison with locally accepted quality

standards. Such losses lead to lower levels of food security, hunger and low on farm incomes

[16].

2.6 Threshing of Teff in Ethiopia

Ethiopia experiences high levels of both chronic and acute food and nutrition insecurity,

particularly among rural and urban poor populations and smallholder farmers. According to the


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Ethiopian Central Statistical Agency and United States Agency for International Development

approximately 44 percent of children under the age of 5 years are chronically malnourished

[17,18]. Ethiopia is considered a least developed Country ranked 173 out of 187countries in the

UNDP Human Development Index for 2013 [19]. As of January 2014, the Government of

Ethiopia reported that up to 2.7 million people in Ethiopia were acutely food insecure and

required assistance to meet their basic nutritional needs [18, 20]). “The long-term effects of

chronic malnutrition are estimated to cost the Government of Ethiopia approximately 16.5

percent of its GDP every year”. The World Food Program (WFP) plans to help approximately

6.5 million vulnerable Ethiopians with food and nutritional aid needs in 2014 [21].

Teff, Eragrostis Teff, Ethiopia‟s most ancient indigenous staple food, is one of the most

important crops for farm income, food and nutrition security in Ethiopia. Teff is highly nutritious

and is an important part of Ethiopia‟s cultural heritage and national identity. Being labeled as one

of the latest super foods of the 21st century, like the ancient Andean grain quinoa, Teff‟s

international popularity is rapidly growing [22]. This presents a growing economic opportunity

for Ethiopia and its farmers. It also presents a challenge to Ethiopian food security and the

correlating issue of reducing chronic malnutrition, poverty and hunger.

2.6.1 Teff and Ethiopia

Ethiopia is a landlocked country in the horn of Africa. The country occupies a total area of 1.2

million square kilometers (420,000 square miles). Its principal natural resource is its arable land

of which 35.68 percent is farmed at present. In terms of production, Teff is the dominant cereal

crop by area planted [23]. Ethiopia is the second most populous country in Africa with a total

population of 87 million and an annual growth rate of 2.9% [24,25]. Its largest city and capital is

Addis Ababa. Ethiopia was the only African country to defeat European colonial powers and

maintain its sovereignty as an independent country. However, the country was briefly occupied

by Italy for five years during 1936-1941[25]. Ethiopia generated international attention when it

endured a series of famines in the 1980s, which were exacerbated by drought, adverse

geopolitics and civil war.


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Ethiopia is rich in cultural diversity, having more than 80 different ethnic groups. The food

culture of Teff in Ethiopia is both historical and a part of Ethiopian antiquity, being a significant

part of the country‟s national identity. Teff, the grain used to make the Ethiopian staple bread

injera, is an ancient, self-pollinated warm season annual grain [26].

Teff originated and was domesticated in Ethiopia between 4000 – 1000 BC [29, 30]. Teff is one

of the African grain crops that made the transition from wild grasses to domesticated food at the

hands of Africans, who collected the seed grains of local wild grasses as food and chose the

characteristics best suited to their tastes, farming practices and growing conditions [29, 30].

Teff grain is very tiny and comes in a variety of colors, from pale white to ivory white, light tan

to dark brown to reddish-brown purple. Depending on variety, Teff is ready for harvest two to

five months after sowing [43]. It is the smallest grain in the world, and it takes 150 grains of Teff

to equal the size of one kernel of wheat [31, 32, and 33].

Teff is often lost in the harvesting and threshing process because of its size. In their study on the

Teff value chain, reported that Teff yields are relatively low (around 1.2 t/ha) and high loss rates

(25-30% both before and after harvest) reduce the quantity of grain available to consumers by up

to 50%. Lodging is also another problem associated with Teff. Teff is susceptible to lodging, and

this could account for up to 30% of the potential loss of Teff yields.

2.6.2 Teff grown area

Within Ethiopia, the regions of Gojam and Shewa (located in the central highlands), Gonder,

Wello and Welega are the major Teff production areas [43]. While Teff is most commonly

grown in the Ethiopian highlands, it is now being cultivated to grow in a wider range of

conditions, from marginal soils to flood conditions. This versatility could explain why tef is now

being cultivated in areas as diverse as the dry mountains of Idaho and the low wetlands of the

Netherlands. According to the NRC, Teff was first introduced to the United States by Wayne

Carlson in the 1980‟s (NRC, 1996) and is currently being grown in Idaho, for use by the large

Ethiopian Diaspora communities. However, Streetman (1963) stated: “Species of Eragrostis were


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first introduced into the United States in the early 1930s and several of these have been used

extensively for reseeding the arid and semi-arid range lands of the southwest” (as quoted in

Costanza, 1974). Teff has been on the international radar for some time. For example, Stewart

and Getawa (1962) noted that Teff injerawas superior to wheat bread with potential international

importance as a food source.

Traditionally, Teff is grown in Ethiopia predominately for food, where it is primarily used to

make the Ethiopian staple injera, which provides approximately two-thirds of the diet in

Ethiopia[43]. Other traditional Ethiopian preparations from Teff flour include porridge and local

alcoholic beverages called tela and katikala. Teff straw is used as animal feed, to plaster mud

huts and to make local grain storage silos called goteras [35]. The published accounts on the use

of teff in the late 1800s reported that upper class people consumed white Teff grain, and dark

grain Teff was the food of soldiers and servants, while Teff was consumed by animals [27].

Teff is a very important crop in Ethiopia, both in terms of production and consumption. In a

country of nearly 90 million people, approximately 6 million households grow Teff. As shown in

table 2.1., Teff is the dominant cereal by area planted and second only to corn in production and

consumption [25].

Table 2-1Area and Production of Main Cereals in Ethiopia 2012-2013

Crop Area (1000/hectars) Production (1000/MT)

Teff 3760 3769

Corn (maize) 2150 5500

Wheat 1780 3570

Sorghum 1510 3200

Barley 1015 1620

Total 10,215 17,659


23 | P a g e

2.7 Winnowing of Teff

Once the Teff has been harvested the next stage is to separate the grain from the rest of the plant.

We can see this happening all around the countryside in recent weeks. It is very interesting to be

able to watch the process which follows traditional methods.

First, the farmers take their harvest to a threshing floor a flat circular area marked out by stones.

These seem to be communal areas and farmers take their turn to use them. The Teff is laid out on

the ground and oxen are driven round and round for hours, crushing the plant and releasing the

grain this is threshing. The oxen are driven around by one or two men who sing, make loud

trilling noises and occasionally use sticks to get the cows to move and to stop them eating the

Teff. Another man lifts up the Teff in the air using two-pronged wooden pitchforks to turn and

mix the pile.

Figure 2.7-1Traditional threshing of Teff

Figure 2.7-2 Productions of Teff or kimir and preparing the floor for threshing of Teff[30]

http://en.wikipedia.org/wiki/Threshing_floor

http://en.wikipedia.org/wiki/Threshing


24 | P a g e

Towards the end of the day the crushed Teff is then sifted this is called winnowing. Two men lift

up the Teff in flat wicker baskets above their heads and slowly let it fall to the ground. The grain

falls straight down and the chaff float of to the side. Another man is sweeping and wafting any

remaining stalks off of the pile of Teff grain. In this picture you can see the tef grain in a small

mound by the men‟s feet, looking a little like sand.

Figure 2.7-3After threshing winnowing of Teff for separating straw to Teff[30]

Grains are fruits of cultivated grasses belonging to the monocotyledonous family, Gramineae.

The principal cereal grains of the world include wheat, barley, rye, sorghum, rice and maize. The

last has become a popular staple in West Africa [17].

The performance of a thresher and cleaning depends upon its size, cylinder speed, cylinder

concave clearance, fan speed and the sieve shaker speed [9]. The factors influencing threshability

of crops in Africa are field drying, maize varieties, ear size cylinder speed and feed rate[8]. The

properties of the crop that affect the thresher performance are crop variety, shape and size,

hardness of the seed, the moisture content of the seed and the density.

2.8 Threshing of wheat

Agricultural practices used in Ethiopia are still common and appreciated throughout the country.

Most of the farmer plant seeds by hand, harvest crops by hand, feed them manually into

stationary threshers being operated by tractors for wheat and rice instead of combine harvesters.

The local farm machinery industry was dominated by small enterprises most of them operating

from their backyards in small and medium workshops using century old conventional techniques.

http://en.wikipedia.org/wiki/Winnowing


25 | P a g e

The agricultural machinery industry is quite large but disorganized. Various types of horticulture

and agriculture based products are being produced including ploughs, disc harrows, laser

levelers, planters, seeding drills, rotary tillers, etc., whereas, harvesting systems and threshing

machinery like paddy threshers, pick up balers, mowers, straw balers including cuter bars are

also produced in a country wide manner. Lack of standardization, malfunctioning of design

parameters, deficiency of engineering solutions, feeble management systems, low quality and

weak finance availability are some reasons that has always hampered the development of the

discussed industry. To compound the situation, unawareness with standards, low equipment and

labor efficiency has always the underpinned the industry, sometimes being prudently affected by

unskilled or low skilled manpower. Moreover, prevalence of preset nut obsolete technology and

production assets has always red taped the development criteria, if ever struggled (Anonymous,

2011).

The design and performance evaluation of a stationary wheat thresher depends on one‟s

knowledge of its working capacity (Kg/hr/day), power requirement, threshing effectiveness and

grain loss.

2.8.1 Harvesting and threshing of wheat

Most of the harvesting remains done by hand, with the cut grain often stacked for up to two

months before threshing. The threshing remains mostly done by animal trampling, which leave

up to 30% of the crop on the ground and contaminates the remainder with urine and feces that

could reduce the market value (Figure 2.8-1). This is a major area that innovations might be

possible to improve the grain recovery and reduce the drudgery.

Figure 2.8-1Threshing of wheat by using traditional and mechanical[83]


26 | P a g e

The actual use of combines is very rare, as there just aren‟t enough available in country. An

alternative that appears to be slowly becoming available in Ethiopia is the mechanical threshers

modeled after the IRRI axleflow thresher. These are currently being manufactured by Selem

Children‟s village as part of their vocational training for adolescent residents (Fig. ). Perhaps

other organizations are or could manufacture similar thresher. Since the thresher was developed

by IRRI with international funding, the blueprints are public domain and freely available directly

from IRRI.

While the original design was developed nearly 40 years ago for rice, it has been adopted and

adjusted for different crops. It also appears to work reasonably well on Teff, perhaps the world‟s

smallest grain, for which one would expect considerable grain to be blown out with the straw.

Thus it might be desirable as a follow-up on this assignment to look at way these threshers

available in smallholder communities. At this point Ethiopia might be better off emphasizing the

axle-flow thresher instead of the combines for enhancing the harvesting and processing of grains.

They are independent of field size, less expensive and will be easier to distribute to private

community based family enterprises living and working within the smallholder communities

[80].

Figure 2.8-2Threshing of wheat by traditional and mechanization

Women separate the grain from the ears with a mortar and pestle, as it is needed for consumption

or for marketing purpose. The threshed grain is cleaned by tossing it in the air using gourds or

shallow baskets.


27 | P a g e

These traditional methods are arduous and slow (10kg per woman-day). Consequently, research

has been conducted for some years on how to mechanize it.

The mechanical threshing of wheat ears does not raise any special problems: conventional grain

threshers can be used with some modifications; such as adjustment of the cylinder speed, size of

the slots in the cleaning screens, etc. On the other hand, the dense arrangement of spike lets on

the rachis and the shape of millet ears (especially pearl millet), make their mechanical threshing

excessively difficult.

2.9 Different parts of a thresher and their functions

A mechanical thresher consists of the following parts

Feeding device (chute/tray/trough/hopper/conveyor)

Threshing cylinder (hammers/spikes/rasp-bars/wire-loops/syndicator)

Concave (woven wire mesh/punched sheet/welded square bars)

Blower/aspirator v. Sieve-shaker/straw-walker.

I. Working principle of a thresher

During operation, the crop material is slightly pushed into the threshing cylinder through the

feeding chute, which gets into the working slit created between the circumference of the

revolving drum having attached spikes and the upper casing. The speed of the spikes is greater

than the plant mass due to which they strike the latter which results in part of the grain being

separated from straw. Simultaneously, the drum pulls the mass through the gap between the

spikes and the upper casing with a varying speed. The angle iron ribs on the other hand, restrain

the speed of the travelling of stalks clamped by the spikes. Due to this the spikes move in the

working slit with a varying speed in relation to the shifting mass of material, which is

simultaneously shifted, with a varying speed with respect to the upper casing. As a result, the

material layer is struck several times by the spikes against the ribs, causing threshing of the

major amount of grains and breaking stalks into pieces.


28 | P a g e

As the material layer shifts towards the progressively converging slit of lower concave, its size

reduces.The vibration amplitudes, therefore, decrease whereas the speed of the layer increases.

This causes mutual rubbing of the ear stalks, as well as rubbing of the ears against the edges of

the concave bars and causes breaking of stalks depending on the concave clearance. Since the

system is closed, the thicker stalk, which cannot be sieved through the concave, again joins the

fresh stalk and the same process is repeated until the stalk size is reduced to the extent that it can

pass through the concave apertures. Thus fine bruised straw is produced. The effective threshing

process means that the loss of un-threshed kernels ejected with the straw through the concave

and the loss of grain damage should be low and the amount of the material passed through the

concave should be high.

II. Adjustments of thresher

Various adjustments are required before starting threshing operation. The machine is to be

installed onclean level ground and is to be set according to crop and crop conditions. The

adjustments necessary to get best performance from the machine are:

Concave clearance,

Sieve clearance,

Sieve slope,

stroke length and

Blower suction opening.

Besides these, cylinder concave grate, top sieve hole sizeand cylinder speeds for threshing

different crops are important for a multi-crop thresher.


29 | P a g e

Figure 2.9-1Sieve clearance[84]

2.10 Different type of thresher and their suitability for crops

The type of thresher is generally designated according to the type of threshing cylinder fittedwith

the machine shown below. The major type of threshers commercially available is as follows:

1. Drummy type

It consists of beaters mounted on a shaft which rotates inside a closed casing and concave.

2. Hammer mill type

It is similar to dummy type but it is provided with aspirator type blower and sieve shaker

assembly for cleaning grains.

3. Spike-tooth type

Spikes are mounted on the periphery of a cylinder that rotates inside a closed casing and

concave. It is provided with cleaning sieves and aspirator type blower.


30 | P a g e

Figure 2.10-1Spike tooth drum

4. Raspbar type

Corrugated bars are mounted axially on the periphery of the cylinder. It is fitted with anupper

casing and an open type concave at the bottom of the cylinder. The cleaning system isprovided

with blower fan and straw walker.

Figure 2.10-2Rasp bar drums

5. Wire-loop type

Wire-loops are fitted on the periphery of a closed type cylinder and woven wire mesh type


31 | P a g e

concave is provided at the bottom.

Figure 2.10-3 Wire –loop drum

6. Axial flow type

It consists of spike tooth cylinder, woven-wire mesh concave and upper casing provided with

helical louvers.

7. Syndicator type

The cylinder consists of a flywheel with corrugation on its periphery and sides, which rotates

inside a closed easing and concave. The rims of the flywheel are fitted with chopping blades.

Factors affecting thresher performance

The factors which affect the quality and efficiency of threshing are broadly classified in three

groups:

Crop factors: Variety of crop, Moisture in crop material.

Machine factors: Feeding chute angle, Cylinder type, Cylinder diameter, Spike shape,

size, number Concave size, shape and clearance.

Operational factors: Cylinder speed, Feed rate, method of feeding, Machine

adjustments.


32 | P a g e

General Features of Thresher

Most, if not all powered paddy threshers are equipped with one of the following types of cylinder

and concave arrangement:

Rasp bar and concave

Spike tooth and concave

Wire loop and concave

Wire loop without concave.

Tests by the, IRRI indicated that the spike tooth cylinders performed well both with the hold-on

and the throw-in methods of feeding and its threshing quality is less affected by changes in

cylinder speed. In the axial-flow thresher, the harvested crop is fed at one end of the

cylinder/concave and conveyed by rotary action on the spiral ribs to the other end while being

threshed and separated at the concave. Paddles at the exit end throw out the straw and the grain is

collected at the bottom of the concave after passing through a screen cleaner. Several versions of

the original IRRI design of the axial-flow thresher have been developed in most countries to suit

the local requirements of capacity and crop conditions. Thus, there are small-sized portable ones

and tractor PTO-powered and engine-powered ones.

2.11 Mechanics of grain threshing

The process of mechanical threshing involves the interaction of machine and crop parameters for

the separation of the seed from the pod. Threshing is carried out between a stationary concave

and a rotating cylinder. Different configurations of threshing devices have been used. The two

types generally employed in present day stationary threshers and combines are rasp bar cylinders

and spike tooth cylinders. The latter are used almost exclusively in pea threshers. Also, rubber

covered flat bars have been employed on cylinders and concaves for threshing small seed

legumes such as crimson clover, giving less damage and less unthreshed loss than the

conventional spikes.

High-speed motion pictures have shown that the main threshing effect in crops or cereals results

from the impact of the cylinder bars at high speeds with the pods. The primary function of the


33 | P a g e

concave appears to be that of holding and presenting the material to the cylinder bar for repeated

impaction. A spike tooth has been shown to have a more positive feeding action than a rasp bar

cylinder does not plug easily, and requires less power. However, rasp bar cylinders are readily

adaptable to a wide variety of crop conditions; are easy to adjust and maintain, and relatively

single and durable.

Various parameters are in use for evaluating the performance of threshers and determining and

retaining the quality of the through-put. The parameters include; threshing effectiveness, grain

damage, sieve effectiveness, cleaning efficiency and seed loss. Studies have shown that threshing

effectiveness is related to the peripheral speed of the cylinder, the cylinder-concave clearance,

the number of rows of spikes, the type of crop, the conditions of the crop (in terms of the

moisture content and stage of maturity), and the rate at which material is fed into the cylinder.

Cylinder speed is the most important machine operating parameter that affects seed damage.

Increasing the speed substantially increases seed damage. Reducing the cylinder concave

clearance tends to increase seed damage but the effects are generally rather small in comparison

with the effect of increasing cylinder speed. Susceptibility to damage varies greatly among crops.

2.12 Determination of mechanical kernel damage

Determination of Mechanical Kernel Damage Most researcher‟s express mechanical damage as

percent damaged kernels by weight. Damaged kernels include all kernels with ruptures or breaks

in the seed coats. The official grain standards of the United States Department of Agriculture

[68] define broken corn as that portion which will pass readily through a 12/64 inch round hole

sieve.

In laboratory studies of the effect of cylinders and concave bars and cylinder adjustment on

kernel damage, used the material passing through a 12/64-inch sieve as a measure of relative

damage [68]. This screening process was also used in corn harvest field tests with rasp-bar

cylinder equipped combines in California [67].

The common method of determining mechanical of seed is by visual inspection. This method is

time consuming and the accuracy of the estimate of mechanical damage depends on sample size

and the skill of the person making the determination.


34 | P a g e

Corn shelling studies with combine cylinders and cage type shellers [49]. Kernel damage was

determined on a weight basis by visual detection of mechanical damage to the seed coat

Mechanical damage as any rupture or break in the seed coat of the corn kernel and emphasized

the difference between this definition and the broken kernel definition of the official grain

standards [70].

2.13 Factors influencing kernel damage

The factors influencing the amount of kernel damage may be divided into two major groups:

machine parameters and plant parameters. The machine parameters include all characteristics of

the machine contributing toward damage. The plant parameters include morphological, physical

and biological characteristics of the corn ear.

2.13.1 Machine parameters

1. Cylinder bar speed

2. Cylinder-concave clearance

3. Type and number of cylinder bars.

2.13.2 Plant parameters

1. Kernel strength

a. Compressive strength

b. Tensile strength

c. Shear strength

2. Modulus of elasticity of the kernel

3. Kernel detachment resistance

a. Rachilla strength

b. Glume-kernel bond strength

4. Cob characteristics

a. Compressive strength

b. Deformation


35 | P a g e

Machine parameters

Several researchers have studied the effect of various machine characteristics on grain damage

during the threshing process. In tests done on barley with rasp-bar, angle-bar, and spike-tooth

cylinders, [44] found that the rasp-bar cylinders did the most damage and the spike-tooth

cylinders did the least damage.In laboratory tests with corn, obtained less damage with rasp bars

than with rubber-faced angle bars [68]. Similar results were obtained, in threshing studies with

corn [69].

One of the most extensive studies with rasp-bar cylinders, He investigated the effect of cylinder

speed and diameter, rasp-bar spacing, concave clearance, feed rate and direction of feed on

threshing efficiency and grain damage. It was concluded that the reduction of damage and its

possible elimination, depended mainly on the use of lower cylinder speeds. Lowering the

cylinder speed also decreased the threshing efficiency [44].

Reduced grain damage by using a two stage threshing mechanism consisting of two cylinders

with concaves. The first cylinder was operated at reduced speeds, while the second cylinder was

run at a normal speed of6000 feet per minute peripheral speed. The largest part of the grain was

removed by the first cylinder and was practically damage-free. The remaining portion, removed

by the high impact forces of the second cylinder, received more damage [45].

Research data showing that high cylinder speed was the chief factor causing grain damage was

also reported for wheat and peas, for wheat, for corn [48,67, 68 and 69]. An increase in corn

kernel damage from 6 percent at 2000 feet per minute to 21 percent damage at 5000 feet per

minute. Relatively little effect on damage has been obtained by varying the cylinder-concave

clearance.

Plant parameters

Moisture content of the cobs and kernels was found to be a major factor affecting mechanical

damage. One reason given for increased damage is higher detachment force requirements at

higher moisture contents. Using a strain gauge force transducer, the forces required to remove

corn kernels from the cob and found that the force decreased as the moisture content decreased.


36 | P a g e

Normal detachment force or pull along the axis of the kernels and forces perpendicular to the

normal forces, were determined for a range of kernel moisture contents [67,68 and 69].

In compression and shear tests conducted by [42], smaller loads were required to rupture kernels

at higher moisture contents. In shear tests, however, higher rupture energies were required at the

higher moisture contents because much more deformation was required before failure occurred.

Generally, the force required to damage a high moisture grain was less than that required for one

with lower moisture content. Deformation, however, was greater for high moisture grains,

resulting in higher energy absorbed.

An investigations done by corn plant parts investigated were cutting energy and tensile strength

of stalks, force required for tearing the ears from the stalks and the husks from the ears.

Compression tests were performed on stalk sections and kernels. For kernels, the slope of the

force-deformation diagram increased with kernel maturity. At the "waxy" stage (approximately

35 percent kernel moisture) the slope was one kilogram per percent kernel deformation. At the

"beginning of ripeness" to"full ripeness" stage (from about 18 to 14 percent moisture content) the

slope was two kilograms per percent kernel deformation [40].

2.14 Kernel detachment

The process of detaching corn kernels from their supporting structure, the cob, is defined as

shelling. Shelling occurs when forces applied to the kernels overcome the holding strength of the

kernel attachment. Figure 2.14 shows a schematic diagram of a kernel and its attachment to the

cob. The force required to break the rachilla and to overcome the glume-kernel friction can be

designated as detachment.


37 | P a g e

Figure 2.14-1 Schematic diagram of kerenel attachment showing kernel, rachis and pith [67]

The moisture content of grain is one of the major physical factors for the design and operation of

the threshing machine that affect the mechanical damage to grains and the threshing efficiency of

machines. The effect of moisture content on hardness and strength of several grains indicates that

greater energy is required to break grains having higher moisture content by impact compared to

those having lower moisture content [61]. The seed separation from stalks and passage of seed

through the concave gate is a function of some variables such as feed rate, threshing speed,

concave length, cylinder diameter and concave clearance. These variables are also related to the

threshing losses and seed separation efficiency.An optimum speed is desirable to get an optimum

performance of a thresher as excessive speed can cause the grain to crack, and too low a speed

can give unthreshed heads [9]. The important factors affecting the efficiency of mechanical pod

stripping element are operation speed and crop conditions. Percentage of stripping pods

increased by increasing of peripheral drum speed which ranged from (473 rpm) 0.1m/s to (675

rpm) 3 m/s[59]. The moisture content of the crop influenced the material capacity of a locust

bean thresher. Threshing effectiveness was also found to be affected by the cylinder speed[52].

The feeding rate increasing linearly by increasing drum speed. Also feeding rate depends on the

experience of the thresher labour. The straw sizes decreased by increasing drum speed while the

grain losses decreased [55]. He used three drum shapes (peg-teeth, beaters, and peg-teeth with

beaters). The results showed that the drum with beaters recorded threshing efficiency of96.52 %,


38 | P a g e

separation efficiency of 98.21 %, cleaning efficiency of 95.79 %, stripping efficiency of 99.35

%, threshing capacity of 1.01 t/h, energy, 2.79 kW/h/ton [51].

The threshing efficiency increased with increasing drum speed and decreasing feed rate. The

maximum threshing efficiency was 99.76 % at drum speed of 21.25 m/s (1400 rpm), and feed

rate of 15 kg/min. The maximum amount of visible grain damage was 0.90 % under these

conditions [56]. The machine power requirement was directly proportional to the drum speed,

moisture content and grain damage. Studies on the effect of swinging hammer, spike tooth and

rasp bas cylinders on threshing effectiveness and damage of wheat revealed that the cylinder

speed and concave clearance were found to be important variable in unthreshed grain and

damage model. Increase in cylinder speed and decrease in concave clearance decreased the rate

or unthreshed grain and increased grain damage and power requirement. They found out that the

swinging hammer type cylinder consumed more power than the rasp bar and spike cylinders

[57]. Threshing effectiveness was also found to be affected by the cylinder speed, the concave

clearance for wheat, feed rate of crops, the number of rows of concave teeth used with spike

tooth cylinder, and the type of crop [60].There is an increase in threshing with decrease in

moisture content [62].

Threshing effectiveness was also found to be affected by the cylinder speed. The highest

threshing efficiency was 97.17 % drum speed from 9.28 to 15.33 m/s the capacity increased from

1800 to2400 kg/h[53]. The energy requirements were 3.19, 3.4, and 1.6kW.h/ton for complete,

partial mechanized and conventional systems, respectively. Developed the threshing chamber in

a wheat thresher by removing the feeding auger to increase the feed rate and production rate. The

machine was tested and evaluated under different operating conditions. The results showed that

the purity efficiency of 99.30% and total grain losses of 0.16 % were achieved at drum speed of

870 rpm, feed rate of 1200 kg/h, air speed suction of 32 m/s, blower air speed of 6 m/s, and sieve

tilt angle of 5°[58].

Developed the threshing drum in a local stationary thresher to suit separation of flax capsules.

The machine was tested under feed rates of 8.57, 12.86, 17.14 and 21.43 kg/min, and four drum

speeds of24.25, 25.81, 27.33, and 28.85 m/s. The results showed that the optimum performance

was at drum speed of 28.85m/s, feed rate of 8.57 kg/min, drum fingers of 12 and separation time

of 15 seconds where the threshing efficiency was 96.92 % [63, 64].


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Table 2-2Existing threshing machine, written by differentabroad researchers

No Researcher

Cylinder

speed(RPM

)or m/s

Type of

beaters

Feed rate

(Kg/min.)

Efficiency

(%)

Cleaning

Efficiency

(%)

Grain loss

or damage

(%)

Capacity

Kg/hr Remark

1 Abdulkadir A. 830 - - 99.2 - Negligible - Maize

2 Oriaku.C Rasp bar 2.06 78.93 56.06 - 123.6 Maize

3 Shahid 2006 500-600 Replaceabl

e 37.2 99.6 - 0.30/0.2 460

Multi-

purpose

4 Irtwange

(2009) 500 Star shaped 97.30 95.78

3.70/

4.54

5 Sudagan

2005 750 Rasp bar 99 - - 3000

6 Singha

2008

339.46m/

min Wire loop - 96.4 - - 64.6

39.1

clearance

7 Saeed

1995 550

Paddy

thresher 44

Increase

in speed - 0.4-1.2


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8 Anwar 350 Rasp bar - 98.74 95.88 2.63 900 max Multi-

purpose

9 Afify

1998 5.23m/s Peg tooth - 96.52 95.79 - - 2.79kw/hr

10 Shahid

2006 600max. - - 99.6 - 0.3/0.2 372Kg/hr

Multi-

purpose

11 Ukatua

2006 300-550 Peg tooth -

Speed inc.

damage

inc.

99.26 1.95 -2.44 412-

506.1


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Table 2-3Existing threshing machine, written by in Ethiopian researchers

N

o.

Researcher Beater

type

Capacity

Kg/hr

Efficiency

%

Separation

loss %

Speed

RPM

Cylinder

loss

Breakage

%

Feed

rate

Remark

1 Hussen/Dubal - 26.76 99.67 - Deepened

on human

power

no 0.21 - Hand

operated

2 Hussen/dubal 55 98.77/99.7

9

- 910/1550 - 0/0.35 5/55 Multi crop

3 Oromia

Agri.research.

center

Peg

tooth

62.6 87.8 2 - 8 3.3 - Multi crop

4 Oromia

Agri.research.

center

Peg

tooth

32 48 25 - 0 29.03 Multi crop

5 Oromia

Agri.research.

center

Peg

tooth

62 85 9 - 8 4 Multi crop

In the above table Researcher written by Ethiopian researchers, in number 3, 4 and 5 are written by Teka Tesfaye and Tamiru

Dibaba in Oromia Agricultural Research Center, the name of the thresher is Assela model 2 axial flows, Fadis Research Center and

Jimma Replaceable Multi crop threshing machine respectively.


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2.15 Competitive design

In this research, for the design of multipurpose crop thresher machine, by comparing different

types of criterion that is, feed type, crop flow and threshing cylinder or drum types and power

transmission mechanism.

Given the high labor requirements of manual threshing, in many countries threshing of crops are

now mechanized by use of small stationary machine threshers. Depending on farming systems,

post-harvest practices and infrastructure, threshers come in different sizes and range from small

portable units without cleaner to large scale. Threshing is either done in the field, near the field

or at the nearest road. Threshers can be classified using different criteria such as feeding type,

crop flow inside the machine, type of threshing elements:


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Table 2-4 Competitive design, their Criteria, Type, Description, Advantage and

Disadvantage of threshing machine

Criteria Type Description Advantage Disadvantage

Feeding

type

Hold-on (or head

feed)

Only the panicle is

fed into the

machine

Straw remains

intact

Lower throughput

Complex

machine

Feed-in The hole crop is

fed into the

machine

Higher throughput Clogging with

very wet or long

straw. Higher

power

requirement

Crop flow

Axial-flow

Whole crop moves

axially around the

drum periphery

Low weight

Does not need

straw separators

Good performance

with wet crop

Higher power

requirement

Conventional

Crop flows

tangentially

through gap

between drum and

concave

Lower power

requirement

Concave clearance

easy to set

Needs straw

walker for

separating grains

from straw

Problems in wet

crop

Threshing

elements

Open Peg teeth

Open twisted bar

Rows of peg teeth

attached to

threshing drum

Typical axial flow

thresher drum

Grinds up the straw

Performs well with

wet straw

Simple design

Cheap

Open Rasp bar

Rasp bars attached

to threshing drum,

usually used in

tangential flow

threshers

Lower power

requirement

Problems with

wet straw.

Wire loop

Typically used in

hold-on threshers

and head feed

combines

Lowest power

requirement

Thin wire loops

comb grain and

thresh through

impact

Wears quicker


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From the above different criterion, the best suitable threshing element will select by using a

decision matrix.

2.16 Decision matrix

Making decisions is both important and difficult. I must make decisions that are justified and in

which all stakeholders have confidence. It is also important to document decisions in clear,

structured ways to ensure that others will understand my reasons for having made a decision,

long after the decision is made.

There are often many different criteria that need to be considered in making a decision. It is

essential to identify the criteria, and to make the decision with respect to those criteria as

precisely as possible. The matter is further aggravated when there are many alternatives from

which to choose; in these cases, not only does each alternative need to be examined, but all the

alternatives must be treated consistently to ensure that a final comparison of all the alternatives is

justifiable.

A weighted decision matrix (WDM) is a simple tool that can be very useful in making complex

decisions, especially in cases where there are many alternatives and many criteria of varying

importance to be considered.

WDMs are often used in design engineering as a qualitative tool to evaluate alternatives. This

page explains how they work in general; other topics will show how they are used in specific

design tasks.

To use a WDM, you need certain information:

a set of well-defined criteria;

a set of weights that define the relative importance of the criteria;

a reference against which comparisons will be made; and

a well-defined set of alternatives to be ranked.

How you generate these required data will depend on what you want to use the WDM for. In

engineering design, the required data are typically developed during design stages leading up to

concept evaluation.

The decision matrix the following process:

http://deseng.ryerson.ca/dokuwiki/design:concept_evaluation


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Define your ideal solution. Spend a few minutes thinking about the ideal solution. How

does it look and feel? Try it on for size. Make a list of the key characteristics for your

ideal solution.

Set Your Priorities. Which of these characteristics of your ideal solution are the most

important? Assign a weight (percent) to each key characteristic. The weight establishes

your priorities.

Assign The Points. Evaluate each option and give it a column score for each key

characteristic. You look at each option by itself and rate it according to how it meets your

key characteristics.

Calculate the weighted scores. Use the Column score and the key characteristic weight

(percent) to calculate a weighted score. This combines the facts from your option with

your priorities for the decision to give you an objective measurement.

Add up the total scores. Add up the weighted scores to get the total score for each option.

The option with the highest score is closest to your ideal solution. I‟m going to walk me

through using the decision matrix to decide on a multipurpose thresher machine

destination, so I can see how to perform each step.

The Key Characteristics

For this multipurpose thresher machine example, here are some things you might consider to be

the key characteristics of my ideal multipurpose thresher machine.

1. Assembly 2. Maintenance

3. Material handling 4. Labour requirement

5. Cost 6. Manufacturability

7. Efficiency 8. Durability

9. Ease of operation 10. Thresheablity

From above Key Characteristics, I will learn how to use the decision matrix for your own

choices. After, I make my list, review it with your partner and incorporate her expectations of the

ideal of multipurpose thresher machine. This is the time to compromise and negotiate a solution

in very general terms.


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Table 2-5 Decision matrix for Key Characteristics and competitive designs

Cylinder drum types Power transmitted

mechanisms

No. criterion Weight

(%)

Peg

teeth

Rasp

bar

Wire

loop

Gear

drive

Chain

drive

Belt

drive

1 Assembly 10 8 10 5 5 7 10

2 Material handling 5 3 4 2 2 3 5

3 Maintenance 10 8 8 7 9 9 13

4 Cost 15 7 12 5 4 4 8

5 Manufacturability 10 10 12 10 11 11 13

6 Labour

requirement

5 3 3 2 3 3 4

7 Efficiency 15 12 14 9 13 12 11

8 Durability 10 7 7 5 7 6 5

9 Ease of operation 10 7 7 7 6 6 8

10 Thresheablity 10 7 10 5 6 7 8

Total Sum 100% 63 75 57 66 68 85

Rank 2 1 3 3 2 1

In the end, my list looks like this: From the above decision matrix, I decide from the three

competitive design and The Key Characteristics, that is type of threshing cylinder, feeding

mechanism and type of power transmission, and then finally, selected pig tooth and twisted bar

type threshing cylinder, Axial flow feeding mechanism and a belt drive power transmission and

after this, the design analysis will be carried out.


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CHAPTER THREE

3. DESIGN ANALYSIS

3.1 Selection and design criteria

General Requirements of Machine Design

High productivity.

Ability to produce and provide required accuracy of shape and size and also necessary

surface finish.

Simplicity of design.

Safety and convenience of control

Low Cost.

Easy of material handling

Design principles

The design consideration of this machine is based on three principles namely:

The gravitational dropping of the whole crop through the inlet hopper to the rotating

spikes and exit of the grains to the receiver.

The impact force delivered by the rotating spikes to the whole maize and motion of this

whole maize along the length of the de-cobing barrel

The air generation and supply by the blower

3.2 Methodology

This research will explain the major methods used to solve the problems that are identified in the

statements of the problem. Therefore, this reaearch planned to address the problems in different

ways which are explained below:


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3.2.1 Literature review and data collection

Review relevant past thesis works and journals on designing related in maize, wheat and

Teff Sheller.

Review different books related with design and modification of maize, wheat and teff

thresher machine.

Collect data about the previous design and manufacturing of maize, wheat and teff

thresher.

3.2.2 The methods used in this design

The collection of rural farmer thresher or Sheller needs associated with agricultural

operation.

The design of an appropriate system to meet their needs.

The determination on whether their problem will be solved.

By interview different sector like, agricultural Mechanization, poly technique institute,

and privet related to for this research.

By interview different rural farmer, comparing the last manufactured or previous adapted,

their cause and effect.

3.3 Materials and methods

Field experiments were carried out the growing season of 2008/2009 e.c in the Bahir Dar

institute of technology faculty of mechanical and industrial engineering, maintenance shop.

Cereal crops were planted by different rural farmers.

Materials

Threshing machine: the threshing machine was designed and manufactured for threshing or

shelling of different cereal crops.

Engine: type of robin (carburetor), one cylinder, air cooling, gas fuel and power of 5.5 hp at

2900 rpm to operate the multipurpose thresher.

Stop watch: of 0.02 sec. to record the threshing time.

Tachometer: to check the rotational speed of drum.

Electric oven or moisture content device: to estimate the moisture content.


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Machine description: the adapted multipurpose machine consists of the following components:

Left and right support and cover Fan blower

Shaft with twisted bar for maize Pulleys

Shaft with rasp bar for wheat and Teff V-belts

Bearings Front and side cover

Inlet hopper Lead screw

Exhaust chat straw and cobs Pedal blower

Cereal crop discharge Air flow channel

Bolt and nut Key and key sets

Cart wheel

The shaft carrying the spikes is suspended on two ball bearings. The spikes are arranged in spiral

form (a screw conveyor) with a uniform pitch. The bearings carrying the shaft are mounted on

the structural frame work. The barrel cover carrying the inlet hopper houses the de- cobbing

cylinder. The throat of the inlet hopper fits into a square hole created at one end of the de-

cobbing cylinder. Both the barrel cover and the de- cobbing barrel are static. the barrel is split in

to two halves but held at one side with hinges so that it can be opened and closed.The electric

motor or engine is mounted at one lower end of the structural frame. The assembled blower is

mounted to the side of electric motor. The air exit channel of the blower is connected against the

cereal crops exit spout. V-belts are used to connect the shaft carrying the beaters, the blower

shaft to electric motor shaft via pulleys. All the components of the machine are hole mounted on

the rigid structural support and cover. The assembled machine has the following dimensions:

Overall length 1.40m, width= 0.95m, height 1.4m, diameter of upper concave 0.23m, Diameter

and length of cylinder drum 0.32m and 1m respectively.

3.4 Design of machine components

The criteria adopted in the design of the components of the multipurpose threshers are aimed at

constructing the machine at lower cost compactable with efficiency to ensure durability of

component part.


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In the design, machine parameters that include the power requirements, machine torque, shaft

diameter, pulley design for the blower, design for the feeding tray, design of the threshing unit

and belt sizes and electric motor specifications were determined.

The dropping of the whole maize through the hopper to the rotating spikes is governed by

gravitational force (𝐹𝑔) which is given as; (Ryder and Bennet, 1982) [78]

F= mxg (1)

Where:

m = mass of whole crop

g = acceleration due to gravity

The impact principle and air generation by the blower is achieved through the dynamics of the

machine components namely: pulleys, belt, bearings and shaft. Circular motion of these

components and gravitational motion of the whole Crop through the inlet hopper and exit of

grains through the exit spouts are employed to achieve the desired result.

3.5 Rotational motion and centrifugal force

The rotational motion from the shaft of the prime mover (electric motor shaft) is transmitted to

the driven shaft carrying the rotary spikes.

Figure 3.5-1 Body experiencing circular motion

For any object of mass m moving in a circular motion, its acceleration is directed towards the

centre of the body and its linear velocity is tangential to the radius of the object. The

displacement which starts from point A, then to B and continues is in terms of θ. The angular

velocity is designated ω. The acceleration (a) of the rotary body is given as


51 | P a g e

a = 𝜔2𝑥r. (2)

Where

r = radius of the object.

The acceleration is centripetal. The radially inward, or centripetal force required to produce

acceleration is given as [80,81]

𝐹𝑐 = ma = m𝜔2r =𝑚𝑥𝑉2

𝑟 (3)

If a body rotates at the end of an arm, this force is provided by the tension on the arm, the

reaction to this force acts at the centre of rotation and is centrifugal force. It represents the inertia

of the body resisting the change in the direction of motion. A common concept of centrifugal

force in engineering problems is to regard it as radially outward force which must be applied to a

body to convert the dynamical condition to the equivalent static condition.

3.6 Rotational Torque

The value of torque developed by a rotational body is given as the product of the force causing

the motion multiplied by the radius of rotation

T = 𝐹𝑐xr or = pxv (4)

3.7 Work done by a torque

If a constant torque T moves through an angle θ

Work done = T x θ (5)

If the torque varies linearly from zero to a maximum value T

Work done = 1

2Txθ (6)

The power (P) developed by a torque T (N.m) moving at ω rad/sec is

P = Txω (7)


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= 2π𝑵𝟏T (watts)

Where N is the speed in rev/min and

ω =𝟐𝝅∗𝒙

𝟔𝟎 Or

Determination of Power Delivered by Shaft along the Length of Threshing Bars

The power is given by

Power = energy/time = (work done)/time = (force x distance)/time = force x velocity,

Velocity = ωxr (8)

Where:

ω = angular velocity;

r = radius.

Therefore,

power = Fxωxr (9)

3.8 Pulley and Belt Drive on pulley 1(Power transmitted on main shaft)

Figure 3.8-1 Diagram showing two pulleys connected by a belt.


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Figure 3.8-2Larger pulley

Pulley

1. Driver pulley

Gives the horse power rating at a maximum pitch diameter of pulleys and the corresponding

speeds. The horsepower rating of the electric motor will therefore determine the diameter of the

driver pulley.

2. Driven pulley

The spindle speed and the spindle of the prime mover are related by the expression [77].

𝑁1𝐷1=𝑁2𝐷2 or𝑁1 / 𝑁2=𝐷2/ 𝐷1 (10)

i.e.,

(The speed of driver/the speed of driven)=(Diameter of driven/diameter of driver)

The following factors determined the centre distance of pulleys:

the class of V-belt used;

the configuration of the machine;

the space available

However, the two pulleys must be near to each other.

2 Weight of pulley

The weight of pulley on a shaft can be determined as follow:


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Weight of pulley,

𝑊𝑝=mxg (11)

m=ρxV (12)

V = A x𝐿𝑝= (π𝑑2/4) x𝐿𝑝 (13)

Where:

𝐿𝑝= length of pulley

=πxr

=439.6mm

V = π𝑑2/4𝑥𝐿𝑝

=3.14x752/4𝑥𝐿𝑝

=4.41𝑚𝑚3

m = ρ x ( π𝑑2/4) x𝐿𝑝

=7530x3.14x752/4𝑥𝐿𝑝

=23.93Kg

𝑊𝑝= ρ x (π𝑑2/4) x𝐿𝑝𝑥g,

=7530x(3.14x752/4)x439.6x9.81

=143.38N

The velocity ratio between two pulleys transmitting torque is given as:

𝜔1/ 𝜔2 = 𝑁1/𝑁2 = 𝐷2/𝐷1

Where:

𝜔1= angular velocity of driver pulley

𝜔2 = angular velocity of driven pulley

𝑁1= rpm of driver pulley (1440rpm)

𝑁2 = rpm of driven pulley

𝐷1 = diameter of driver pulley (75mm)

𝐷2 = diameter of driven pulley (280mm)

Ѳ = angle of lap between belt and pulley


55 | P a g e

𝑁1/ 𝑁2 = 𝐷2/𝐷1,𝑁2 =𝑁1∗𝐷1

𝐷2

=540Rpm

ω1/ ω2 =N1/N2

ω1=2𝜋𝑁1

60=

2𝑥𝜋𝑥 1440

60= 150.72𝑟𝑎𝑑/𝑠

𝜔1/ 𝜔2 = 𝑁1/𝑁2

308.53/𝜔2=1440/540

𝜔2=150.72x540/1440

=56.52rad/s

3.9 Tensions on belt

For belt transmission between two pulleys, the following equations by [52] are used

𝑇1 − 𝑇𝑐

𝑇2 − 𝑇𝑐= eμѲ

(14)

𝜇= Coefficient of friction = 0.3

𝑇1 = Tension in tight side

𝑇2= Tension in slack side

𝑇𝑐 = mv² (15)

Where:𝑇𝑐 = 𝑐𝑒𝑛𝑡𝑟𝑖𝑓𝑢𝑔𝑎𝑙 𝑡𝑒𝑛𝑡𝑖𝑜𝑛 𝑓𝑜𝑟𝑐𝑒

V= 𝜋𝑥𝐷𝑥𝑁

60

V=3.14x75x1440/60

=5.652m/s

𝑇𝑐=mxv²

=23.93x5.5632

=732.85N

𝑇𝑐= 𝑇1/3 i.e. 3𝑇𝑐 = 𝑇1 (16)

𝑇1=2198.57N


56 | P a g e

𝑇1 − 𝑇𝑐


μ= Coefficient of friction (0.3)

Ѳ= Angle of lap (in rad)

Where:

𝜃𝑑=angle of wrap in radian

D=driven pulley diameter

d= driver pulley diameter

𝜃𝑑=2.93rad

𝑇1 − 𝑇𝑐=1.336(𝑇2-Tc)

𝑇2=(𝑇1-0.334Tc)/1.334

Appendix A4

The power transmitted with the belt is given as

P= (𝑇1 –𝑇2)x v (17)

In this equation the power (P) is in watts, when 𝑇1 and 𝑇2 are in Newton and belt velocity is in

metre per second.

Peripheral Velocity,𝑉𝑝 =𝜋𝐷1𝑥𝑁1

60

𝐷1 = Diameter of smaller pulley i.e. electric motor shaft pulley, 75mm

𝑁1 = Speed of electric motor shaft pulley, 1410rpm

𝑉𝑝 =𝜋𝑥𝐷1𝑥𝑁1

60=𝜋𝑥75𝑥1410

60𝑥1000=5.534m/s

If this velocity i.e. 𝑉𝑝 is in range then, Ok.

Now, assuming Velocity Ratio, 𝑉𝑅 to calculate speed of driven pulley.

𝑁1/𝑁2= 𝑉𝑅 (18)

By using velocity ratio with neglecting slip,

𝑁1

𝑁2=

𝐷2

𝐷1

Angle of lap or contact on smaller pulley,

𝜃1 = 𝜋 −𝐷2 − 𝐷1

𝑐

(19)


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Angle of lap or contact on larger pulley,

𝜃2 = 𝜋 +𝐷2 − 𝐷1

𝑐

(20)

See in appendix A1

Since the smaller value of 𝜃for the pulley will governs the design.

Then,

P= (𝑇1 –𝑇2)x v power transmitted to the main shaft

Appendix A1- A5 for the above calculation

3.10 Tensions on belt on pulley 2 for cleaning action

𝑇′1 /𝑇′2 = eμѲ (21)

𝑇′1 − 𝑇𝑐

𝑇′2 − 𝑇𝑐= eμѲ

𝜇= Coefficient of friction = 0.3

𝑇′1 = Tension in tight side

𝑇′2= Tension in slack side

𝑇1= 𝑇′1

𝑇2=𝑇′2

𝑇𝑐 = mv² (22)

And

V=3.14x75x1410/60

V= 𝜋∗𝐷∗𝑁

60

(23)

𝑇𝑐=mxv²

𝑇𝑐= 𝑇′1/3 i.e. 3𝑇𝑐 = 𝑇′1 24


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𝑇′1 − 𝑇𝑐

𝑇′2 − 𝑇𝑐= eμѲ

μ= Coefficient of friction (0.3)

Ѳ= Angle of lap (in rad) for pulley 2

Where

𝜃𝑑=angle of wrap in radian

D=driven pulley diameter

d= driver pulley diameter

𝑇′1 − 𝑇𝑐=1.336(𝑇′2-Tc)

Then,

The power transmitted with the belt is given as

Since the smaller value of 𝜃for the pulley will governs the design.

Then,

P= (𝑇′1 –𝑇′2)x v, power transmitted to the main shaft

See in appendix A1- A5 for the above calculation

3.11 Belt selection

Diameter of drive pulley d = 75mm

Diameter of driven pulley D = 280mm

(To reduce input from 1440 rpm to 540 rpm)

𝑁1=1440rpm

𝑁2=540rpm

First calculate𝐿𝑝 , length of pulley[73,74,75]

L= 𝜋

2(𝐷𝑋+𝐷𝑦 )+ 2C+ (𝐷𝑋 − 𝐷𝑦)2/4C (25)

Where

C=center distance (600mm)

𝐷𝑦=Diameter of large pulley (280mm)

𝐷𝑋 =Diameter of smaller pulley (75mm)

L=1774.86mm


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Based on power input possible Belt type is A or B

Assumption belt Type A, Minimum sheave = 75mm

See in appendix 1

L =𝐿𝑝 - 𝐿𝑐 (26)

= 1774.86– 32 = 1742.86 mm

𝐿𝑐= length correction factor

From Table 17-10 Choose A2250 -1775 mm

L = 𝐿𝑝 − 𝐿𝑐 =1774.86-32 = 1742.86mm

𝐿𝑝=1775+32=1807mm

Recalculate new C

C=0.25 𝐿𝑝 −𝜋

2 𝐷 + 𝑑 +

𝐿𝑝 −𝜋

2(𝐷 + 𝑑

2

− 2(𝐷 − 𝑑)2)

(27)

C = 616.31mm

Verify the value C to satisfy D < C < 3(D+d) 280 < C < 3(355) OK

Note: if the C is out of range, you have to choose other belt size…

If the value is smaller than D, repeat step 1) by setting𝐿𝑝 = D

If the value is larger than 3(D + d), repeat step 1) by setting𝐿𝑝 = 3(D+d)

At the end of this stage, the final configuration of the belting is confirmed

Type A1775

Input sheave, d = 75mm Output sheave, D = 280mm

𝑁1= 1440 rpm ,𝑁2= 600 rpm

Center to center distance = 600mm

𝑉 =𝜋𝑥𝐷1𝑥𝑁1

60

(28)


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=5.562m/s

Advisable speed in between 5m/s to 25m/s

Eliminate vibration: D < Center distance < 3(D+d) as excessive vibration will shorten the

belt life

Then, the speed is safe or Ok

For more information, see appendix A6- A10

Belt Length (L)

The belt length equation is given as[86]:

L= 𝜋

2 𝐷1 + 𝐷2 +

(𝐷1−𝐷2)2

4𝐶+ 2𝐶 (29)

=𝜋

2 75 + 280 +

(75−280)2

4∗600+ 2 ∗ 600

=1774.86mm

Where:

C = centre distance between two pulleys

3.12 Design of hopper

The hopper is designed to be fed in a vertical position only. The material used for the

construction is mild steel sheet metal, which is readily available in the market and relatively

affordable. The hopper has the shape of a frustum of a pyramid truncated at the top, with top and

bottom having rectangular forms. This is illustrated by the following diagram.


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Figure 3.12-1 Hopper Construction[16]

From the principle of similar triangles, for triangles PMG and POC with M and O being the

centres of EFGH and ABCD respectively:

PM/MG = PO/OC, or PM = PO x MG/OC.

Then the volume of the hopper is given by:

𝑉𝑕𝑜𝑝𝑝𝑒𝑟 = [(Area of Base) x height]/3 (30)

= [(AB x BC) x h – (EH x HG) x x]/3,

Where,

h= overall height

x =height of the truncated top

3.13 The main frame

The main frame supports the entire weight of the machine. The total weights carried by the main

frame are:

Weight of the hopper and housing;

Weight of the threshing chamber;


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The collector and pot; and

The bearings, pulley and belt.

Different loads/weights on the shaft

Mass of designed cylinder beater =20 kg (physically measured)

Mass of designed electrical blower =2 kg (physically measured)

Mass of designed the two pulley =6 kg (physically measured)

Loads of cylinder drum beater, flywheel, pulleys and electrical blower on the shaft were

calculated as:

Follows:

W = mxg

=28x9.81

=274.68N

Where;

W= weight of the component in, N, m= mass of the component, kg and

g= gravitational acceleration m/𝑠2

Weight from P1 on the Shaft, 𝑊1= 𝑇𝑡𝑖𝑔𝑕𝑡𝑠𝑖𝑑𝑒 + 𝑇𝑠𝑙𝑎𝑐𝑘𝑠𝑖𝑑𝑒 + 𝑊𝑝𝑢𝑙𝑙𝑒𝑦 = 538.09 N

Weight from P2 on the Shaft, 𝑊2= 𝑇𝑡𝑖𝑔𝑕𝑡𝑠𝑖𝑑𝑒 + 𝑇𝑠𝑙𝑎𝑐𝑘𝑠𝑖𝑑𝑒 +𝑊𝑝𝑢𝑙𝑙𝑒𝑦 =538.09 N

Where;

Weight of the pulley = 𝑊𝑝𝑢𝑙𝑙𝑒𝑦𝑠 = 6.64x9.81 = 65.13N

From above calculation:

𝑇𝑡𝑖𝑔𝑕𝑡𝑠𝑖𝑑𝑒 + 𝑇𝑠𝑙𝑎𝑐𝑘𝑠𝑖𝑑𝑒 , for the pulley=T=𝑇1+𝑇2 =304.53+201.34=505.53N

Weight from blower on the Shaft, 𝑊𝑏𝑙𝑜𝑤𝑒𝑟 = 2.1x9.81=20.60 N

Weight from cylinder beater on the Shaft, 𝑊𝑐𝑦𝑙𝑖𝑛𝑑𝑒𝑟𝑏𝑒𝑎𝑡𝑒𝑟 =10*9.81=98.1 N

The two design factors considered in determining the material required for the frame are weight

and strength. In this design work, angle steel bar of 40mm by40 mm and 2mm thickness is to

used to give the required rigidity. The Threshing Bars:

Weight, W, of threshing bar is given by:

W = mg =(mc +ms +mcy +mp)xg (31)

where:


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m = mass of threshing bar;

g = acceleration due to gravity.

𝑚𝑐=mass of crop(10kg) - fiscally measured

𝑚𝑠=mass of shaft(5kg)-fiscally measured

𝑚𝑐𝑦= mass of cylinder (threshing cylinder)(20kg) -fiscally measured

𝑚𝑝= mass of pulley(3kg)-fiscally measured

Mass, M, of threshing bar:

M= 20+5+6+3=34kg

Or

m = ρ x V, (32)

Where:

ρ = density of mild steel;

V = volume of threshing bar.

Volume, V, of threshing bar:

V = l x b x h, (33)

where:

1 = length;

b = breadth;

h = height.

W = mxg

=34x9.81

=333.53N


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3.14 Design of shaft

A shaft is the component of a mechanical device that transmits rotational motion and power. It is

integral to any mechanical system in which power is transmitted from a prime mover, such as an

electric motor or an engine, to other rotating parts of the system.

A shaft is a rotating or stationary member, usually of circular cross-section having such elements

as gears, belt, pulleys, flywheels, cranks, sprockets and other power transmission elements

mounted on it [85]. Shafts are either solid or hollow.

3.14.1 Shaft Design Procedure

Because of the simultaneous occurrence of tensional shear and normal stresses due to bending,

the stress analysis of a shaft virtually always involves the use of a combined stress approach. The

recommended approach for shaft design and analysis is the distortion energy theory of failure.

Vertical shear stresses and direct normal stresses due to axial loads may also occur. On very

short shafts or on portions of shafts where no bending or torsion occurs, such stresses may be

dominant.

Procedure:

1. Determine the rotational speed of the shaft.

2. Determine the power or the torque to be transmitted by the shaft.

3. Determine the design of the power-transmitting components or other devices that will be

mounted on the shaft, and specify the required location of each device.

4. Specify the location of bearings to support the shaft. Normally only two bearings are used to

support a shaft. The reactions on bearings supporting radial loads are assumed to act at the

midpoint of the bearings.

Bearings should be placed on either side of the power-transmitting elements if possible

to provide stable support for the shaft and to produce reasonably well-balanced loading

of the bearings.

5. Propose the general form of the geometry for the shaft, considering how each element on the

shaft will be held in position axially and how power transmission from each element to the shaft

is to take place.


65 | P a g e

6. Determine the magnitude of torque that the shaft sees at all points.

It is recommended that a torque diagram be prepared.

7. Determine the forces that are exerted on the shaft, both radially and axially.

8. Resolve the radial forces into components in perpendicular directions, usually vertically and

horizontally.

9. Solve for the reactions on all support bearings in each plane.

10. Produce the complete shearing force and bending moment diagrams to determine the

distribution of bending moments in the shaft.

11. Select the material from which the shaft will be made, and specify its condition: cold-drawn,

heat-treated, etc

Plain carbon or alloy steels with medium carbon content are typical, such as AISI 1040,

4140, 4340, 4660, 5150, 6150, and 8650.

Good ductility with percent elongation above about 12% is recommended.

Determine the ultimate strength, yield strength, and percent elongation of the selected

material.

P = F × V (34)

Where

P = power (Nms−1),

F = Force of threshing (N), and

V = velocity (m/s).

Force required to thresh the crop is given by:

F = m𝑥𝜔2𝑥r (35)

Where:

F = force required to thresh crop,

m = mass of threshing bars,

𝜔= the angular Velocity of shaft. The angular velocity 𝜔is determined by the equation

𝜔 =2𝜋N/60 (36)

Where:


66 | P a g e

N is the speed of threshing (RPM)

𝜔 =2𝜋1440/60

=150.72rad/s

F = m𝜔2r (37)

=24x(2𝜋𝑥1440/60)2)x30

=1620N

The power delivered by the shaft:

P= F𝜔r (38)

=15.45x150.72x0.003

=7324.99Watt

The appropriate electric motor is determined or selected when the total power requirement for

threshing in determined at an appropriate threshing speed.

The relationship between the driven pulley speed and the speed of the prime mover is as

flywheel

RA RB

P2 w N.mP1

Figure 3.14-1 The free body diagram of shaft exerted distributed load and pulley


67 | P a g e

RA RB

P1 P2 w L/2

Figure 3.14-2 overall free body diagram of drum

Where;

𝑊𝑝1= weight of pulley 1, tension 1 and 2

𝑊𝑝2= weight of pulley 2 for blower, tension 𝑇′1𝑎𝑛𝑑 𝑇′2

𝑇1+𝑇2=Weight of belt

P= load applied on cylinder (Weight of crop and cylinder drum)

𝑅𝐶= 𝑊𝑝1+𝑇1+𝑇2

RD=Weight of pulley 2

𝑅𝐷 = 𝑊𝑝2+𝑇′1+𝑇′2

Design Torque, 𝑇𝐷 = 60𝑥𝑃𝑥𝐾𝐿

2𝜋𝑁 (39)

Load Factor, 𝑘𝐿 = 1.75 (For Line Shaft) Selecting material of shaft SAE 1030,

𝑆𝑢𝑙 = 527MPa , 𝑆𝑦𝑡 = 296 MPa

Considering F.O.S. = 2

For ductile material with dynamic heavy shocks for machines like forging, shearing and

punching etc

𝜏𝑚𝑎𝑥 ≤ 0.30 Syt, 𝑎𝑛𝑑 𝜏𝑚𝑎𝑥 ≤ 0.18 Su

𝜏𝑚𝑎𝑥 ≤ 0.30 Syt, = 0.30x296/2 =44.4 N/mm2

𝜏𝑚𝑎𝑥 ≤ 0.18 Su=0.18x527/2=47.43 N/mm2


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Considering minimum of it i.e𝜏𝑚𝑎𝑥 =44.4 N/mm2

Consider Shaft under loading

Calculation of the Shearing Force and Bending Moment of the Shaft at Different Sections of the

Shaft

Figure 3.14-3Vertical Shear Force Diagram

Resolving all the force vertically, 𝐹𝑦=0

𝑅𝐵𝑉 + 𝑅𝐶𝑉 = WPA +WSH + WPD

Where:

WPA=𝑅𝐶 = 𝑊𝑝1+𝑇1+𝑇2

WSH- load applied on cylinder (Weight of crop and cylinder drum)= PL/2=WL/2

WPD=𝑊𝑝1+𝑇′1+𝑇′2

𝑅𝐵𝑉 = Vertical Reaction at B

𝑅𝐶𝑉= Vertical Reaction at C

Taking moment about B, 𝑀 = 0

As we know that bending moment at A and D will be Zero. 𝑀𝐴𝑉 = 𝑀𝐷𝑉 = 0

𝑀𝐴𝑉 and 𝑀𝐷𝑉 are the vertical bending moments at point A and D respectively.

B. M. At C = 𝑅𝐴𝑉 × 1000mm=462.43Nm, for maize

B. M. At C = 𝑅𝐵𝑉 × 1000mm=462.432Nm

First find reactions 𝑅𝐵and 𝑅𝐶 of simply supported beam.

Reactions will be equal. Since, beam is symmetrical.

R1 = R2 = W/2 = (563.33 +563.33 + 29.43)/2 = 578.04N


69 | P a g e

Hence, 𝑅𝐵=𝑅𝐶= 578.04N

Shear Force

Shear force between section A – B = S.F (A – B) = 563N

Shear force at right side of point B = S.F (B) = 563 – 441=122N

S. F (B) right = 122N

Now shear force at left side of point C.Because of uniform distributed load, value of shear

continuously varies from point B to C.

Shear force at point C (Left) = S.F (L) = 441-563=-122

Shear force at point C (Left) = S.F (L) = -122N

Shear force between section C – D = S.F (C-D) = -122 – 441

Shear force between section C – D = S.F (C-D) = -563N

Shear Force Diagram

Figure 3.14-5The sheer force diagram


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Bending moment

B.M will be zero at supports. i.e.,

M(B) = M(C) = 0

B.M at points B and C = M(A) = M(D) = 563 x0.2 = 112.6 N.m

Figure 3.14-6Bending moment diagram

Now, for diameter of shaft,

𝑀𝑐= 𝑀𝑐𝑣

2+𝑀𝑐𝐻2

= −462.43 + 02

=462. 43N.m at mid-point

𝑀𝐵= 𝑀𝐵𝑣

2+𝑀𝐵𝐻2

𝑀𝐵= −462.432 + 02

= 462. 43N.m


71 | P a g e

Bending moment will be maximum at point, where shear force is zero. Hence, bending moment

will be maximum at mid-point.

Resultant Bending Moment,

M (max) = -578.04×0.8 +122×0.2 +29×.3

M (max) = -462.43.N.m

Twisting moment on main shaft due to pulley,

Twisting Moment 𝑇𝑑 (N-m) = (P x 60)/ (2 πN) (40)

Twisting Moment 𝑇𝑑 (N-m) = (P x 60)/ (2 πN) [86]

Where;

P is Power at driven Pulley

𝑇𝑑=(2.2x103x60)/(2x3.14x146.53)

=42.30N

𝜏𝑚𝑎𝑥 =16

𝜋𝑑3 (𝐾𝑏 ∗ 𝑀)2+(𝐾𝑡∗𝑇𝑑)2

(41)

𝜏𝑚𝑎𝑥 =44.4 N/mm2

Now, Recommended value for Kb and Kt

For rotating shaft, suddenly applied load (Heavy shocks) Kb = 2 to 3 = 2.5 Kt = 1.5 to 3 = 2.3

𝜏𝑚𝑎𝑥 = 44.4 N/mm2

Now, diameter of shaft,

From the evaluation of the forces and determination of the bearing reactions, the maximum

bending moments (Mmax) for the shaft is evaluated. The shaft diameter (D) is calculated using

the ASME code standard for shafting. The ASME code equation for shafting is given as

For rotating shaft Suddenly applied load (Heavy shocks) Kb = 2 to 3 = 2.5 Kt = 1.5 to 3 = 2.3

=𝜏𝑚𝑎𝑥 44.4 N/mm2


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The minimum shaft diameter is determined using the [10] code equation which states that

𝜏𝑚𝑎𝑥 =16

𝜋𝑑3 (𝐾𝑏𝑥𝑀)2+(𝐾𝑡𝑥𝑇𝑑 )2

Where:

d - The diameter of shaft,

𝑇𝑑 - The overall torsional moment,

M -The bending moment

𝐾𝑏 - The combined shock and fatigue factor applied to bending moment,

Kt - The combined shock and fatigue factor applied to torsional moment, Ss is the allowable

shear stress. According to [10], the Kb and Kt factors when shock is applied suddenly to a

rotating shaft are 1.5 to 2.0 and 1.0 to 1.5 respectively. For shaft without key-way and with key-

way, the allowable stress (Ss) is 55 MN/𝑚2 and 40MN/𝑚2 respectively.

𝑑3 = [16/( 𝜏𝑚𝑎𝑥)]×[(𝐾𝑏𝑀𝑏)2+(𝐾𝑡𝑀𝑡)2]1/2,

=28.44mm

From standard select 30mm diameter

3.15 Key selection

3.15.1 Stress concentrations

In order to mount and locate the several types of machine elements on shafts properly, a final

design typically contains several diameters, key seats, ring grooves, and other geometric

discontinuities that create stress concentrations. These stress concentrations must be taken into

account during the design analysis. But a problem exists because the true design values of the

stress concentration factors, Kt, are unknown at the start of the design process. Most of the

values are dependent on the diameters of the shaft and on the fillet andgroove geometries, and

these are the objectives of the design.

3.15.2 Preliminary design

Values for Kt

Considered here are the types of geometric discontinuities most often found in power-

transmitting shafts: key seats, shoulder fillets, and retaining ring grooves.


73 | P a g e

In each case, a suggested design value is relatively high in order to produce a

conservative result for the first approximation to the design.

Again it is emphasized that the final design should be checked for safety.

3.16 Keyseats

A keyseat is a longitudinal groove cut into a shaft for the mounting of a key, permitting

the transfer of torque from the shaft to a power-transmitting element, or vice versa.

Two types of keyseats are most frequently used: profile and sled runner.

Figure 3.15-1 Different types of keyseats

The profile keyseat is milled into the shaft, using an end mill having a diameter equal to

the width of the key.

The resulting groove is flat-bottomed and has a sharp, square corner at its end.


74 | P a g e

The sled runner keyseat is produced by a circular milling cutter having awidth equal to

the width of the key.

As the cutter begins or ends the keyseat, it produces a smooth radius.

For this reason, the stress concentration factor for the sled runner keyseat is lower than

that for the profile keyseat.

Normally used design values are:

– Kt = 2.0 (profile)

– Kt = 1.6 (sled runner)

Due the above reason, sled runner keyseat because of to resist stress concentration.

3.17 Selection of anti-friction bearing

The prime factors in bearing selection are a total system reliability for its design life and the cost

effectiveness. To achieve such reliability, the bearings must be of the proper type and size. The

selection process must consider all factors which will affect bearing performance and cost. These

factors include:

Magnitude and direction of loads

Speed of rotation

Required life

Available Space

Lubrication

Shaft and housing designs

Alignment

Adjustment

Temperature

Environment

It is impossible to select any one of these factors as being the most critical. All must be

considered in every bearing application.


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Figure 3.17-1 Bearing with house

3.18 Life of bearing calculation methods

Standard methods for estimating bearing lives havebeen developed for most applications.

Include:

Maximum horsepower

Skid torque

Tractive effort

Design load

Work schedule

3.18.1 Load analysis

In many applications, the load and speed considerations are critical to the bearing selection.

Methods of analyzing load sources and the resolution of these loads into bearing reactions are

presented below. Frequently, the methods to evaluate the magnitude of the load and the speed are

based on a history of performance of similar equipment. Such standard approaches are essential

when the bearings are exposed to a full spectrum of loads and speeds and/or a wide variety of

work schedules.


76 | P a g e

The first step in the process is to determine the magnitude and direction of the loads which the

bearings are required to support. Loads may originate from variety of sources including dead

weight, belts, chains, sprockets, gears, imbalance, etc. Each load source is discussed below.

3.18.2 Belts

Are encountered in a wide variety of industrial applications. They are used for both power

transmission and conveyor systems. Power transmission belts maybe flat, “V” sectioned, or

cogged for timing applications. Conveyor belts are normally flat for moving palletized loads or

contoured to a trough shape for bulk materials. Friction between the drive pulley and the belt

transmits the motive power in all applications except for cogged timing belts. To assure that

sufficient frictional forces exist, the belts must be installed with the proper amount of preload

tension. Belt manufacturers provide guidelines to establish the correct value for the preload.

The resultant force created on the drive and idler pulleys in any belt system must include the

preload tension, the forces caused by the driving horsepower, and the weight of the material

being transported in the case of conveyor systems. When the belt wrap is around 180°, formula

(1) approximates the force which must besupported by the pulley bearings

Figure 3.18-1Tension on the tight and slack side

F=T1 +T2=126050𝑥𝐻𝑝𝑥𝑓𝑝𝑙

𝑁𝑥𝐷 (42)

Where:

T1-tension on the tight side

T2- tension on the slack side


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Hp -horse power

N-speed in Rpm

D-pulley pitch diameter

𝐹𝑝𝑙 -preload factor

=1.1 to 1.2 Cogged belts

=1.5 to 2.0 V-belts

=2.0 to 4.0 Flat belts

C = [L/L10]1/KP, or C/P = [L/L10]1/K (43)

, that is;

[C/P]K = L/L10, or L10 = [C/P]K/L.

But L = 60n/106 million revolutions, therefore, L10 = (106/60n) x [C/P]K,

Where:

L10 = life of bearing for 90% survival at one million revolutions;

L = required life of bearing in million revolutions (mr);

n = rotational speed (rev/min);

C = basic dynamic load rating (N);

P = equivalent dynamic bearing load (N);

K = exponent for life equation with:

K = 3 for ball bearing;

K = 10/3 for roller bearing.

There are two antifriction bearings 𝐵1 and 𝐵2used in the experimental setup. The maximum

reactiondeveloped at bearing 𝐵2 i.e. R = 667.33 N is considered for designing the bearing.

Equivalent load coming on bearing,Fe, N

Also, P = radial load + axial load [16,86],

P = (XFr + YFa) (44)

where:

X = radial load factor for the bearing;

Y = axial load factor for the bearing;


78 | P a g e

Fr = actual radial bearing load (N);

Fa = actual axial bearing load (N).

Fe = (XFr+ YFa) Ks*Ko*Kp*Kr,Fr= 667.33 N

Fa= 0, Ne = Fa/ Fr, Ne = 0

Selecting self aligning ball bearing,X = 1, Y = 2.3

𝐾𝑝 = 1 (no preloaded bearing),Kr = 1(outer race fixed inner raceRotating).

𝐾𝑠 = 2 (moderate shock load),𝐹𝑒 = (X𝐹𝑟+𝑌𝐹𝑎 ) KsxKoxKpxKr = (1x 667.33 + 0) x 1 x 1 x 1 x 2=

1334.66 N

Life of bearing, L (million revolutions) = L = (C/Fe) n𝐾𝑟𝑒𝑡

𝐾𝑟𝑒𝑡 = 1 (reliability = 90%), C =(500)(1/3) x 𝐹𝑒 ,C = 10818.138 N

Dimension d 𝐷1= 75 mm, 𝐷2 = 150 mm, B = 15 mm

Table 3.1: below shows the recommended life value in operation. It is assumed that this machine

will be designed to operate for 8 hours per day intermittently and whose breakdown will have

serious consequences.

The bearing life in operating hours is chosen to be 8,000 as illustrated by the table below;

Table 3-1 Recommended life value of bearings[16]

Type of operation Life in operation

Infrequently operated 500

Brief operation only 4,000 -8,000

Intermittent operation 8,000 -15,000

One shift operation 15,000 -30,000

Continuous operation 30.000- 60,000

Continuous operation with high production

capacity

100,000


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3.19 Design of screw thread

3.19.1 Screw thread fundamentals

A screw thread is defined as a ridge of uniform section in the form of a helix on either the

external or internal surface of a cylinder. Internal threads refer to those on nuts and tapped holes,

while external threads are those on bolts, studs, or screws.

The thread form is the configuration of the thread in an axial plane; or more simply, it is the

profile of the thread, composed of the crest, root, and flanks. At the top of the threads are the

crests, at the bottom the roots, and joining them are the flanks. The triangle formed when the

thread profile is extended to a point at both crests and roots, is the fundamental triangle. The

height of the fundamental triangle is the distance, radially measured, between sharp crest and

sharp root diameters.

Figure 3.19-1 Threaded Screw Shaft

The length to diameter ratio (L/D) of screw thread according to (Fayose et al. 2009) is 15.


80 | P a g e

Figure 3.19-2 Screw thread

Handling capacity of the expeller

Capacity = 0.231m3/h = 0.00385m3/min. In one revolution, the screw will handle

0.000385/60=0.0000642𝑚3/𝑚𝑖𝑛/𝑟𝑒𝑣

Determination of Pitch

To determine the pitch, the volume of the expression chamber is required and is calculated as;

𝑉𝑐=

π×Dc 2×P

4

(45)

=0.0190p

VT= Volume of shaft + Volume of thread

Volume of shaft =𝜋×𝐷𝑖𝑜2×𝑃/4 (46)

= 0.004524P

Volume of thread is gotten by assuming an unwrapped section of the thread;

Volume of thread =𝜋((𝐷𝑖 + 2𝑏)2−𝐷𝑖2)𝑏/4 (47)

=0.0001629

VT= 0.004524P + 0.0001629

VG=VC – VT

= 0.001590P -0.004524P – 0.0001629

0.002042P – 0.00002271=0


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P= 0.111m = 111mm=11.1cm

Figure 3.19-3Lead screw during conveying the crops

Determination of Number of threads (n) on the screw

The number of thread considered here is found to be the minimum push worm required for the

machine.

𝑛=𝑙𝑒𝑛𝑔𝑕𝑡𝑜𝑓𝑠𝑐𝑟𝑒𝑤𝑡𝑕𝑟𝑒𝑎𝑑𝑒𝑑𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑝𝑖𝑡𝑐𝑕/pitch=8

Power Required by the Screw Shaft

With a chosen speed of 60rpm for the expeller shaft and 25:1 revolution of electric motor to

expeller shaft. An electric motor capable of producing [76]

W=60*25=1500rpm

W=2𝑥πxN

60 (48)

W=2𝑥πxN

60=1440rpm

T=𝑃

𝑊

(49)

𝑁1

𝐷1=𝑁2

𝐷2,

𝑁1 = 1440𝑟𝑝𝑚,𝑁2=150.72𝑟𝑝𝑚

𝑠𝑖𝑛𝑐𝑒𝑟𝑎𝑡𝑖𝑜𝑜𝑓𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟𝑜𝑓𝑑𝑟𝑖𝑣𝑒𝑟𝑡𝑜𝑑𝑟𝑖𝑣𝑒𝑛𝑖𝑠 1:2,𝐷1=100m𝑚 ,𝐷2=200mm


82 | P a g e

Where;

w= angular speed of screw shaft, rad/s

T= torque transmitted by worm, Nm

Nw=number of revolution per minute of worm action, rpm

P=power transmitted by worm action, W

𝑁1=speed of driving shaft, rpm

𝑁2=speed of driven shaft, rpm

𝐷1=diameter of driver pulley, m

𝐷2=diameter of driven pulley, m

3.19.2 Determination of belt length

To get the angle of contact or lap for both pulleys, Khurmi and Gupta (2009)

Figure 3.19-4 Pulley-Belt Cross-sectional View

𝑠𝑖𝑛 ∝=𝑟1−𝑟2

𝑥= 0

Hence ∝=0

Angle of wrap,

𝜃= 180 – 2α

𝑇1=Tension in the tight side of the belt

𝑇2=tension in the slack side of the belt


83 | P a g e

Ratio of belt tension is given by,

2.3𝑙𝑜𝑔𝑇1/𝑇2=𝜇𝜃𝑐𝑜𝑠𝑒𝑐 β

𝑙𝑜𝑔𝑇1/𝑇2=3.01/2.3

𝑇1/𝑇2=203.6

Velocity of the belt, v,

𝑣=𝜋×𝑑2𝑁1/60= 3.55𝑚/𝑠

Power Transmitted by belt, 𝑃𝑠=𝑇𝛾𝑤 according to Khurmi and Gupta (2009)

Tγ=shear stress of agro materials, given as 5.995

w=required angular speed of expeller shaft, 60rpm

𝑃=5.995×157.1=785.5𝑊=0.786𝑘𝑊

𝑃=(𝑇1−𝑇2)v

At maximum power condition, maximum tension, T is

𝑇1=2𝑇

3

T=3𝑇1

2

Centrifugal tension in belt, 𝑇𝑐

𝑇𝑐=𝑇

3

Cross sectional area of the belt, A

A=𝑇

σ=33.4*10−6𝑚2

σ =permissible stress in belt material, given as, 1.75 x 10-6

Required Belt Length L,

L=2xc+π

2(𝐷1−𝐷2) +

D2−D1

4𝑐

c- Center diameter between the pulleys = 0.55m

L=2x0.4+ π

2(𝐷1−𝐷2) +

D2−D1

4𝑐=1575mm

For more information, see in appendix A1- A5


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3.20 Material selection of Bolt and nut

3.20.1 Fastener material selection

There is no one fastener material that is right for every environment. Selecting the right fastener

material from the vast array of materials available can be appear to be a daunting task. Careful

consideration may need to be given to strength, temperature, corrosion, vibration, fatige and

many other variables. However, with some basic knowledge and understanding, a well thought

out evaluation can be made.

Figure 3.20-1Bolt and nut designation

3.20.2 Classification of bolting material

Since bolting material does not come in contact with fluid, its material compatibility with fluid is

not important. The selection of bolt material is determined based on service conditions and it is

wasteful to specify expensive alloys when carbon steel material is entirely suitable. It is

important for bolting material to have good tensile stress.

As per ASME B16.5, bolting material has been divided into three categories as follows:


85 | P a g e

i. High strength bolting:

Bolting materials having allowable stresses not less than those for ASTM A193 grade B7 are

listed as high strength bolts. ASME B16.5 Table 1B is enclosed for reference. These and other

materials of comparable strength may be used in any flanged joint.

ii. Intermediate strength bolting:

Bolting materials listed as intermediate strength, and other bolting of comparable strength, may

be used in any flanged joint, provided the user verifies their ability to seat the selected gasket and

maintain a sealed joint under expected operating conditions.

iii. Low strength bolting:

Bolting materials having not more than 30 ksi specified minimum yield strength are listed as

low strength. Selected from standard medium carbon steel AISI 1030, 1035, 1038 and 1541 and

ASTM A325, ASTM A449.

From the above point of view, select M14*10 for lower and upper concave

M12*8 for all bearings

M10*8 for left and right support

M8*6 for hopper and

M16*12 main drum

3.21 Total weight of the machine

Mt = mass of cover + mass of left and right cover +mass of lower and upper concave +mass of

screw thread with cover +mass of blower

Mt =the total mass of the machine takes four sheet metal, one round bar, one angle iron and one

flat sheet metal

From standard weight per meter cube [86],

2000*1000*4mm =31.4kg/𝑚2= 62.8kg/𝑚2

2000*1000*3mm =23.55kg/𝑚2=1.5*23.55=35.325kg/𝑚2

2000*1000*2mm =12.56kg/𝑚2=1.5* 12.56=19.275kg/𝑚2

2000*1000*1mm =7.85kg/𝑚2=1.5*7.85=11.775kg/𝑚2

40*40*4mm =kg/𝑚2=9.312kg/𝑚2

40*40*4mm =11.616kg/𝑚2


86 | P a g e

Mt= 150.103kg

3.22 Moisture content of grain

Moisture content of grain and crop straw directly affect the grain breakage and threshing

efficiency of crop thresher. Three grain samples of 50 g each were taken for moisture content

determination. Samples were placed in an oven at 130˚C for 19 h (ASAE, 2009). After drying,

the samples were reweighed and percent moisture content was determined as follows;

GMC = [(WGW-WGD)/WGW] x 100

Where;

GMC = Grain moisture content, %; WGW = Wet weight of grain, g; and WGD= Ovendried

weight of grain, g.

Table 3-2 Technical and working parameter of the thresher

Contents Value

Angle of drum belt 168°

Clearance, mm

Inlet

Out let

55-70

40-50

Threshing speed, RPm 540-730

Length diameter, mm 1400

Drum diameter, mm 450

Number of twisted rasp bar, pcs 3

Engine power, Kw 5.67

The speed of threshing drum was well chosen on the basis of the author‟s researcher and

literature. The clearance between drum and threshing floor was determined in dependence of

mean cob diameter (Figure 3.21-1).


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Figure 3.21-1The schema of corn cobs

The inlet clearance (𝑆𝑜) was counted according to the equation:

𝑆𝑜 = 𝑑𝑧 – 𝑑𝑤 , [mm] (50)

The outlet clearance (Si) according to the equation:

Si=Dz-2

3*So[mm] (51)

Where:

𝑆𝑜 – Inlet clearance [mm],

𝑆𝑖 – Outlet clearance [mm],

L – Length of cob [mm],

𝑑𝑍 – Diameter of cob [mm],

dw – diameter of cob pith [mm].

The clearance between the drum and the concave should be from 10 to 15 mm smaller than the

cob diameter.

3.23 Feed rate

Feed rate was the weight of un-threshed whole crop (grain and straw) fed to the thresher. It was

very important parameter from the standpoint of machine threshing capacity, cleaning efficiency,

grain breakage, and grain loss with straw. It was determined by taking crop bundles of three

different weights (12 kg, 15kg, and 20 kg) and was fed into the threshing unit of the thresher for

the given time. Feed rate was determined as follows.


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FR=QMF/T (52)

Where;

FR=Feed Rate, 𝐾𝑔/𝑕 ; QMF=Weight of whole crop material fed into the thresher, kg

and T=Feed time, h

3.24 Designing of blower

Fans and blowers provide air for ventilation and industrial process requirements. Fans generate a

pressure to move air (or gases) against a resistance caused by ducts, dampers, or other

components in a fan system. The fan rotor receives energy from a rotating shaft and transmits it

to the air.

3.24.1 Difference between Fans, Blowers and Compressors

Fans, blowers and compressors are differentiated by the method used to move the air, and by the

system pressure they must operate against. As per American Society of Mechanical Engineers

(ASME)the specific ratio - the ratio of the discharge pressure over the suction pressure is used

for defining the fans, blowers and compressors (see table 3.24-1) [88].

Table3.1: Difference between fans, blower and compressor

Equipment Specific ratio Pressure rise (mm wg)

Fans Upto1.11 1136

Blowers 1.11 to 1.20 1136-2066

Compressors More than 1.20 -


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Figure 3.24-1Blower overall dimension

The fan inlet area-Is the inside area of the fan inlet collar.

The fan outlet area-Is the inside area of the fan outlet.

The linear velocity of blower as well as crop straw chaff

V (at inlet with eye)

=r 𝜔 (53)

= 0.2x 85.30

= 17.06 m/sec

V (at blade tip)

= r 𝜔= 0.450 x 85.30

= 38.385 m/sec

Area of blower at the inlet for air and crop straw chaff

Area at the eye of developed blower,

A (inlet)

=2 x π x r x L (54)


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= 2x3.14x120mm x120mm

A (inlet)

=0.09043 m2

Area at the exit for air and crop straw chaff

Area at the exit end of developed blower,

A out = 200mm × 200mm = 40000 mm2

= 0.0400 m2

It was found that at feed rate 2430 kg/hour there was 1318 kg/h crop chaff.

Straw grain ratio = 1318/1112 = 1.1852

The centrifugal force of fan blower paddle to throw the chaff

Fc = mxrxω2

(55)

= 0.36kg/sec x 0.4945 m x (85.33 rad/sec)2

= 1296 N


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CHAPTER FOUR

4. PERFORMANCE EVALUATION

This machine was tested on flat level surface and sufficient quantity of crop materials were taken

for evaluation. A combination of feed rate and cylinder speed at two levels for Teff, wheat and

maize crop was employed. Wheat and Teff bundles, and maize cob were fed in to threshing unit

and the threshed materials was collected at the outlet which was cleaned and weighed. The

portion of the material containing un threshed grain was separated from straw and weighed after

hand threshing and cleaning in order to determine the threshing efficiency in terms of percentage

of the total grain recovered. The thresher was evaluated at three different levels of cylinder speed

and feed rate, fixed concave clearance of 3-4.5mm for wheat and Teff crops and 7-8mm for

maize at moisture contents of 15.2, 10, and 8% (w.b.) for maize, wheat and Teff crops

respectively. The machine was driven by 4.125kw 0r 5.5hp diesel engine at a varying cylinder

speed ranging from 450 to 1440rpm for different test crops. Threshing efficiency, output

capacity, cleaning efficiency and kernel breakage were evaluated.

Factors and level values considered on threshing different crops.

Table 4-1 Factors and level values considered on threshing different crops.

Factors Crop types and factors value

maize Teff wheat

Drum

speed(rpm)

450,540,730 1100,1440 1200,1440

Feed rate

(kg/min)

50 10 20

Grain moisture

content (%w.b)

13-18 7-8 9-10

Concave- drum

clearance(mm)

5.5-7 3-4.5 3-4.5


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4.1 The evaluation of Physical Parameters

4.1.1 Grain moisture content

The moisture content of maize, wheat, and teff grain was determined using drying oven. The

grain samples were dried at 130°Cfor some hours. The weight loss of the samples was recorded

and the moisture content determined in percentage. This was replicated twice and mean was

taken. The moisture content was then calculated as:

𝑀𝑐 𝑤𝑏 =

𝑊𝑖−𝑊𝑑𝑊𝑖

𝑥100 (56)

Where

𝑊𝑐wb = Moisture content, wet basis, %.

𝑤𝑖 = Initial weight of sample, kg.

𝑊𝑑 = Dried weight of sample, kg

4.1.2 Broken/damaged grain

From each of the threshed crop sample of about 550g kernels were randomly selected. All

physically damaged/broken grains were visually observed, manually sorted and weighed using

digital balance. Damage due to mechanical threshing was determined as the ratio of weight of the

actual damaged kernels to the weight of a sample taken.

Broken grain (%) =

𝑊𝑒𝑖𝑔𝑕𝑡𝑜𝑓𝑏𝑟𝑜𝑘𝑒𝑛 𝑑𝑎𝑚𝑎𝑔𝑒𝑑 𝑔𝑟𝑎𝑖𝑛𝑠 (𝑔𝑚 )

𝑊𝑒𝑖𝑔𝑕𝑡𝑜𝑓𝑠𝑎𝑚𝑝𝑙𝑒𝑡𝑎𝑘𝑒𝑛 (𝑔𝑚 )

(57)

4.1.3 Grain-Straw Ratio

Grain-straw ratio was determined following procedures. From the material which is to be

threshed, 3 samples were randomly taken of approximately 1 kg for maize, 0.5kg for wheat and

0.25kg for Teff. The maize and wheat crop were measured by moisture contents measuring

instrument. The instrument can get from chemical and food engineering faculty. The samples


93 | P a g e

were placed in containers where the grains and straw were separated by hand. The straw and

grains from each sample were kept paired. After weighing, the samples were oven dried at 130°C

for 2 hours and then reweighed for Teff crops. The moisture content (M) on dry basis, %:-

M =𝑊𝑒𝑖𝑔 𝑕𝑡𝑜𝑓𝑠𝑎𝑚𝑝𝑙𝑒 𝑔𝑚 −𝑊𝑒𝑖𝑔 𝑕𝑡𝑜𝑓𝑑𝑟𝑦𝑠𝑎𝑚𝑝𝑙𝑒 ((𝑔𝑚 )

𝑊𝑒𝑔𝑕𝑡𝑜𝑓𝑑𝑟𝑦𝑠𝑎𝑚𝑝𝑙𝑒 (𝑔𝑚 )x100 (58)

After determining the weight of dry samples the results of the paired samples were used to

calculate the mean Grain/Straw-ratio.

The Grain-Straw ratio (K) was calculated as follows:-

K=𝑊𝑒𝑖𝑔 𝑕𝑡 𝑜𝑓 𝑑𝑟𝑦 𝑔𝑟𝑎𝑖𝑛 (𝑔𝑚 )

𝑊𝑒𝑖𝑔 𝑕𝑡 𝑜𝑓 𝑑𝑟𝑦 𝑠𝑡𝑟𝑎𝑤 (𝑔𝑚 ) (59)

The moisture content on dry basis, %:-

M=𝑊𝑒𝑖𝑔 𝑕𝑡 𝑜𝑓 𝑤𝑒𝑡 𝑠𝑎𝑚𝑝𝑙𝑒 𝑔𝑚 −𝑤𝑒𝑖𝑔 𝑕𝑡 𝑜𝑓 𝑑𝑟𝑦 𝑠𝑎𝑚𝑝𝑙𝑒 (𝑔𝑚 )

𝑤𝑒𝑖𝑔 𝑕𝑡 𝑜𝑓 𝑑𝑟𝑦 𝑠𝑎𝑚𝑝𝑙𝑒 (𝑔𝑚 )*100 (60)

After determining the weight of the dry samples, the cobs and maize grains are manually

separated and weighed. The grains-Spent Cob Ratio (K):-

4.1.4 Drum speed

During the test period, by varying the pulley diameter at the driver and driven pulley was used to

measure the threshing cylinder speed (rpm).

Determination of output capacity, Threshing and cleaning efficiency and percentage grain loss

Threshing capacity, threshing and cleaning efficiency of the thresher were calculated following

the procedure of.

Total Grain Input

Total grain in put (Kg) = A+B+C

Where;

A= Weight of threshed grain at main outlet per unit time (kg)

B= Weight of threshed grain at all other outlets per unit time (kg)

C= Weight of un-threshed grain at all outlets per unit time (kg)

Output Capacity (kg/h)

Output capacity (Kg/hr) = Weight of threshed grain at main outlet per unit time (kg )

𝑡𝑖𝑚𝑒 𝑜𝑓 𝑡𝑒𝑠𝑡 𝑟𝑢𝑛𝑠 (min −1) x60 (61)


94 | P a g e

=50 (kg )

𝑡𝑖𝑚𝑒 𝑜𝑓 𝑡𝑒𝑠𝑡 𝑟𝑢𝑛𝑠 (min −1) x60=3000kg/hr for maize at maximum speed

Output capacity (Kg/hr) = 50kg/min for maize crop

=20kg/min for wheat crop

= 10kg/min for teff crop

Percentage of Un-Threshed Grain

There is un threshed grain during threshing of maize, wheat and Teff. To calculate un threshed

grain can use this formula:

% Unthreshed grain (%) =weght of unthreshed grain at all outlets per unit time (kg )

𝑡𝑜𝑡𝑎𝑙 𝑔𝑟𝑎𝑖𝑛 𝑖𝑛𝑝𝑢𝑡 (𝐾𝑔) x100 (62)

=50gm unthreshed grain in side drum /50kg/min= 0.1 % for maize

% Unthreshed grain= 435gm for wheat at 1440rpm= 0.97%

=90gm for teff at 1440rpm= 0.9%

Threshing Efficiency

Threshing efficiency = 100- Percentage of unthreshed seeds (63)

=100-0.1 = 99.9% at drum speed 540 rpm for maize

=100-0.97=99.03% at drum speed of 1440rpm for

=100-0.9= 99.1% at drum speed of 1440 rpm for teff

Cleaning Efficiency

Cleaning efficiency (%) =𝑤𝑒𝑖𝑔 𝑕𝑡𝑜𝑓𝑤 𝑕𝑜𝑙𝑒𝑔𝑟𝑎𝑖𝑛𝑎𝑡𝑚𝑎𝑖𝑛𝑜𝑢𝑡𝑙𝑒𝑡𝑝𝑒𝑟𝑢𝑛𝑖𝑡𝑡𝑖𝑚𝑒 (𝐾𝑔)

𝑊𝑒𝑖𝑔 𝑕𝑡𝑜𝑓𝑤 𝑕𝑜𝑙𝑒𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙𝑎𝑡𝑚𝑎𝑖𝑛𝑜𝑢𝑡𝑙𝑒𝑡𝑝𝑒𝑟𝑢𝑛𝑖𝑡𝑡𝑖𝑚𝑒 (𝑘𝑔) x100 (64)

=49.55𝑘𝑔/𝑚𝑖𝑛

50𝑘𝑔/𝑚𝑖𝑛 x100=99.78% for maize at drum speed 540rpm, the other

crops can calculated in this way.

= 19.23𝑘𝑔/𝑚𝑖𝑛

20𝑘𝑔/𝑚𝑖𝑛x100=96.15% for wheat at drum speed of 1200rpm

= 9.80𝑘𝑔/𝑚𝑖𝑛

10𝑘𝑔/𝑚𝑖𝑛x100=98.0% for teff at drum speed of 1100rpm

Percentage of Blown Grains

% Blown grain = 𝐰𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐰𝐡𝐨𝐥𝐞 𝐠𝐫𝐚𝐢𝐧 𝐜𝐨𝐥𝐥𝐞𝐜𝐭𝐞𝐝 𝐚𝐭 𝐜𝐡𝐚𝐟𝐟 𝐚𝐧𝐝 𝐬𝐭𝐫𝐚𝐰 𝐨𝐮𝐭𝐥𝐞𝐭𝐬 𝐩𝐞𝐫 𝐮𝐧𝐢𝐭 𝐭𝐢𝐦𝐞 (𝐊𝐠)

𝒕𝒐𝒕𝒂𝒍 𝒈𝒓𝒂𝒊𝒏 𝒊𝒏𝒑𝒖𝒕 (𝒌𝒈) (65)

0% blown grain for maize

0.12% blown grain for wheat

0.33% blown grain for Teff


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Percentage Grain Loss (66)

% grain loss= wt .of whole ,damaged and unthreshed grains at chaff and straw outlets per unit time (Kg )

𝑇𝑜𝑡𝑎𝑙𝑔𝑟𝑎𝑖𝑛𝑖𝑛𝑝𝑢𝑡 (𝑘𝑔) x100

=(740gm Out the cylinder +10gm grain damage +5gm in the cylinder )/50kg/min

=1.5% for maize

4.2 Results and discussion

The performance of this multi-purpose thresher was evaluated at fixed concave clearance of 30-

45 mm for Teff and wheat and 50-70mm for maize and the moisture contents, varying threshing

drum speeds and feed rates in terms of threshing capacity, threshing efficiency, cleaning

efficiency, kernel damage and grain loss. Tables 4.2, 4.3, and 4.4 give the results of the

performance tests.

4.2.1 Threshing capacity and kernel damage of multi-crop thresher

Expected output of maize crop

The effect of drum speed on threshing capacity and grain damage of maize crop is showed in

Table 4.2. The result on effect of drum speed on the capacity indicated that the threshing

capacity was significantly affected by drum speeds (Table 4.2). Mean values of threshing

capacity obtained at 450 rpm and 730 rpm were different. The capacity increased from 2150.5

kg/hr at drum speed of 450 rpm to 24902 kg/hr and 2500-3000 kg/hr at 540 rpm and 730 rpm.

Maximum threshing capacity of 3000 kg/hr was obtained 730 rpm and feeding rate 50kg/min-55

kg/min at an average grain-cob ratio of 1:3.05. With an increase in drum speed to 450 rpm

and730 rpm, the threshing capacity increased which might be due to increase in impact force

required for crop threshing with increase in drum speed. Table 4.2 shows drum speed had highly

significantly affected grain damage. Seed damage increases from 0.15% at drum speed of 450

rpm to 0.2% at 540 rpm. Table 4.2 shows, the higher the drum speed the higher was the grain

damage. Increment in grain damage could be due to increased beating/impact of the seeds by a

rotating twisted rasp bar beater of the drum. The maximum grain loss of 4.55% was recorded at

drum speed of 730 rpm.


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Table 4-2 Effect of cylinder speed on performance of multi-crop thresher on maize crop

Cylinder

speed(rpm)

Threshing

capacity(kg/hr)

Threshing

efficiency

(%)

Cleaning

efficiency

(%)

Kernel

damage (%)

Grain loss

(%)

450 2150.5 90.0 85.3 0.15 1.5

540 2490.2 99.78 90.5 0.20 2.15

730 2500-30000 99.98 99.5 0.30 4.55

Figure 4.2-1 Maize crop before threshing

4.2.2 Threshing efficiency and total grain loss of maize crop

Table 4.2 shows the effect of drum speed on threshing efficiency and total grain loss of maize

crop. Drum speed showed highly significant effect on threshing efficiency. Comparison among,

showed that at all drum speeds the threshing efficiency was significantly different throughout

changes in drum speed. The threshing efficiency increased from 90% at 450 rpm to 99.98% at

maximum drum speed of 730 rpm. The efficiency then decreased to 99.8% at 540 rpm. With an

increase in drum speed the threshing efficiency kept increasing till 730 rpm after which it

showed a slight reduction to 99.78% at 540 rpm. Drum speed had significantly affected grain


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losses (Table 4.2). The grain losses increased from 1.5% to 4.55% at an increased drum speed

from 450 rpm to 730 rpm.

Therefore, the optimum grain damage and grain loses at drum speed 540 rpm and kernel

damaged of 0.2, the threshing efficiency of 2490.2 Kg/hr and the threshing efficiency99.78%is

selected.

Figure 4.2-2Maize crop cob and grain after threshing

4.2.3 The expected output of wheat crop

The effect of drum speed on threshing capacity and grain damage of wheat crop is presented in

Table 4.3. The drum speed showed highly significant effect on threshing capacity. Comparison

among showed that at all drum speeds the capacity was significantly different throughout. The

capacity increased from 475.61 kg/hr at 1200 rpm to 750.53 kg/hr at maximum drum speed of

1440 rpm and average grain-straw ratios of 1:3.43. Maximum threshing capacity of 750.53 kg/hr

was obtained 1440 rpm and feeding rate 20 kg/min. With an increase in drum speed the threshing

capacity kept increasing. This is due to increase in impact force required for crop threshing with

increase in drum speed. Table 4.3 shows drum speed had significantly affected grain damage.

Seed damage increases from 0.67% at drum speed of 1200 rpm to 1.83% at 1440 rpm. The

higher the drum speed the higher was the grain damage (Table 4.3). Increment in grain damage


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could be due to increased beating/impact of the seeds by a rotating rasp bar beater of the drum.

The maximum damage of 1.83% occurred at drum speed of 1440 rpm.

Table 4-3 Effect of cylinder speed on performance of multi-crop thresher on wheat crop

Cylinder

speed(rpm)

Threshing

capacity(kg/hr)

Threshing

efficiency

(%)

Cleaning

efficiency

(%)

Kernel

damage (%)

Grain loss

(%)

1200 475.61 97.8 96.33 0.67 3.55

1440 750.53 99.9 97.5 1.83 4.25

Figure 4.2-3 Wheat crop before threshing

4.2.4 Threshing efficiency and total grain loss of wheat crop

Table 4.3 shows the effect of drum speed on threshing efficiency and total grain loss of wheat

crop. Test results showed that the mean threshing efficiency recorded for the effects drum speed

was statistically highly different. Maximum and minimum means of threshing efficiency were

99.9and 97.8 % respectively at 1440 and 1200 rpm. Threshing efficiency was increasing with

increase in drum speed. Test results indicated that the grain losses had not significantly affected


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by drum speed throughout. However and increasing trend of total grain loss was observed as

drum speed increased from minimum of 1200 rpm to maximum of 1440 rpm.

Therefore, the optimum grain damage and grain loses at drum speed 1440rpm and kernel

damaged of 1.83, the threshing capacity of 750.5 Kg/hr and threshing efficiency of 99.9% is

selected.

Figure 4.2-4 Wheat crop after threshing, straw and grain manual separation

4.2.5 The expected output of teff crop

The effect of drum speed on threshing capacity and grain damage of teff crop is presented in

Table 4.4. The drum speed showed significant effect on threshing capacity. Comparison among

means using showed that at all drum speeds the capacity was significantly different. The capacity

increased from 130 kg/hr at 1100 rpm to 280 kg/hr at maximum drum speed of 1440 rpm and

average grain-straw ratios of 1:2.56. Maximum threshing capacity of 280 kg/hr was obtained at

1440 rpm and feeding rate of 10 kg/min. With an increase in drum speed the threshing capacity

kept increasing. This is due to increase in impact force required for crop threshing with increase

in drum speed. The result also shows drum speed had no effect on grain damage. Seed damage

was found to be 0% at both drum speeds (1100 and 1440 rpm). This could have been due to

smallness of size and mass of teff grain.


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Table 4-4 Effect of cylinder speed on performance of multi-crop thresher on teff crop

Cylinder

speed(rpm)

Threshing

capacity(kg/hr)

Threshing

efficiency

(%)

Cleaning

efficiency

(%)

Kernel

damage (%)

Grain loss

(%)

1100 130 99.9 97.5 0 12.5

1440 280 100 98.75 0 1.95

Figure 4.2-5 Teff crop before threshing

4.2.6 Threshing efficiency and total grain loss of Teff crop

Table 4.4 shows the effect of drum speed on threshing efficiency and total grain loss of Teff

crop. Test results showed that the threshing efficiency was highly significantly affected by drum

speed. Maximum and minimum means of threshing efficiency were 98.97% and 97.43 %

respectively at drum speeds of 1440 and 1100 rpm respectively. Threshing efficiency was

increasing with increase in drum speed. The drum speed had significantly different effect on

grain losses. The grain losses decreased from 12.5%at 1100 rpm to4.05% at 1440 when drum

speed increased from 1100 rpm to 1440 rpm. Decrease in grain loss could be due to reduction in

percentage of unthreshed and blown grains (which are components of total grain loss) with

increase in drum speed.


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Therefore, the optimum grain damage and grain loses at drum speed 1440rpm and kernel

damaged of 0%,the threshing efficiency of 2490.2 Kg/hr and the threshing efficiency 100% is

selected.

Figure 4.2-6 Teff crop after threshing, straw and grain manual separation


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CHAPTER FIVE

5. MANUFACTURING PROCESS AND COST ANALYSIS

5.1 Manufacturing process

A manufacturing process is a designed procedure that results in physical and /or chemical

changes to a starting work material with the intention of increasing the value of that material. A

manufacturing process is usually carried out as a unit operation, which means that it is a single

step in the sequence of steps required to transform the starting material in to a final product.

Manufacturing operations can be categorized in two basic types:

1. Processing operations

2. Assembly operations

A processing operations transforms a work material from one state of completion to a more

advanced state that is closer to the final desired product, while an assembly operation joins two

or more components to create a new entity, called assembly, subassembly, or some other term

that refers to joining the process (e.g. welding, fastener assembly).


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Table 5-1Manufacturing process of blower and blower casing

Operatio

n

number

Items Materia

ls

Sketch Type

operation or

description

Type of

machine

Cuttin

g tools

Measurin

g tools

01 Blowe

r and

blowe

r

casing

Mild

steel

Sheet metal

cutting

2000*1000*2m

m

Shearing

machine

Shear

blade

Tape

meter

02

Sheet metal

cutting

942*500*2mm

Shearing

machine

Shear

blade

Tape

meter and

v- caliper

03

Rolling

942*500*2mm

Rolling

machine

Rolling

die

Tape

meter

04

Bending,200m

m at the

exhaust chat

and drilling

both side eye

cover

Bending

and electric

drilling

machine

Bendin

g die

and

drill bit

Tape

meter

05 Grinding and

fillet corners

Grinding

machine

Grindin

g disc

Tape

meter

06 Finishing Polisher

machine

Polishe

r


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Table 5-2Manufacturing process of screw and screw casing

Operation

number

Items Materials Sketch Type operation or

description

Type of

machine

Cutting

tools

Measuring tools

01 Screw

and

screw

casing

Mild steel Sheet metal cutting

2000*1000*2mm

Shearing

machine

Shear blade Tape meter

02

Sheet metal cutting

753*800*2mm

Shearing

machine

Shear blade Tape meter and v-

caliper

03

Rolling and cutting Rolling

and hand

cutting

machine

Rolling die

and disc

cutter

V-caliper

And tape meter

04

Sheering, drilling

and electric arc

welding

Shearing,

drilling and

arc welding

machine

Shear blade,

drill bit and

welding

electrode

Tape meter

05 Grinding , fillet file

sharp corners

Grinding

machine

Grinding

disc


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machine

Polisher


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Table 5-3Manufacturing process of shaft and key way

Operation

number


description

Type of

machine

Cutting

tools

Measuring

tools

01 Shaft and

key way

Mild steel Round bar cutting

6000*dim.30mm

Circular disc

cutter

machine

Disc cutter Tape meter

02

Round bar cutting

1400*dim.30mm

Circular disc

cutter

machine

Disc cutter Tape meter and

v- caliper

03 Facing and rough

turning from dim. 30mm

to dim. 29.89mm

Lathe

machine

Facing and

turning

tools

V-caliper

04 Key way both side

making,#3 shaft

End milling

machine

End mill

cutter, dim.

8mm

V-caliper

05 Chamfering each corner Lathe

machine

Forming

tool

Tape meter


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machine

Polisher


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Table 5-4Manufacturing process of left and right support and cover

Operation

number


description

Type of

machine

Cutting

tools

Measuring

tools

01 Left and

right

support and

cover


2000*1000*4mm

Shearing

machine


02

Sheet metal cutting

1050*950*4mm

Shearing

machine


and vernier

caliper

03

Drilling M12*10 Drilling

machine

Drill bit V-caliper

04

Bending left, right and

bottom 50mm each side

Bending

machine

Bending

die

Tape meter

05 Grinding and fillet

corners

Grinding

machine

Grinding

disc

Tape meter


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machine

Polisher


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Table 5-5Manufacturing process of front and side cover

Operation

number


description

Type of

machine

Cutting tools

01 Front

and side

cover


2000*1000*1mm

Shearing

machine

Shear blade

02

Sheet metal cutting

1000*640*1mm

Shearing

machine

Shear blade

03

Bending front and side

cover

1000*640*1mm at 120° at

340mm length

Drilling

machine

Drill bit

04

Cutting in let blower and

exhaust dust

chat,120*500mm and 120*

500mm for each

Hand held

disc cutter

Disc cutter

05 Grinding and fillet corners Grinding

machine

Grinding disc


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machine

Polisher


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Table 5-6Manufacturing process of upper and lower concave

Operation

number


description

Type of

machine

Cutting

tools

Measuring

tools

01

Upper and

lower

concave


1000*1000*3mm

Shearing

machine

Shear

blade

Tape meter

Sheet metal cutting

1000*822*3mm

Shearing

machine

Shear

blade

Tape meter

and V-

caliper

02

Sheet metal Rolling,

C=2*3.14*230/2mm

C=722.2mm

Rolling

machine

Rolling

die

Tape meter

03

Bending and drilling ,

Upper and lower

concave, 50mm each side

Bending and

drilling

machine

Bending

die

Tape meter


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04 Cutting of lower concave

at middle 760*480mm

Hand

operated

cutter

Cutter

disc

Tape meter

05 Cutting of upper concave

at inlet and exhaust chat

300*340mm

&200*200mm

Hand

operated

cutter

Cutter

disc

Tape meter

06

Welding of lower and

upper concave for

making sieve and hopper

former

Welding

machine

Electrode

dim.2.5 &

3.2 mm

07 Grinding sharp corners

and fillet

Hand

grinding

machine

Grinding

disc

O8 Finishing machine Hand

polisher

Polisher

disc


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Table 5-7Manufacturing process drum or cylinder beater

Operation

number


description

Type of

machine

Cutting tools Measurin

g tools

01 Drum or

cylinder

beater

Mild steel Flat sheet metal

6000*50*4mm

Shearing

machine

Shear blade Tape

meter

Flat sheet metal

cutting

1193*50*4mm and

cutting 80mm, #45

pieces and

triangular plate

sheering

Shearing

machine

Shear blade Tape

meter and

V- caliper

02 Sheet metal

Rolling,

C=2*3.14*190mm

C=1193mm

Rolling

machine

Rolling die Tape

meter

03 Rolling of former

drum 4*1193mm,

Rolling

machine

Rolling die Tape

meter


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04 Welding drums

For maize

Welding

machine

Electrode dim.2.5

& 3.2 mm

Tape

meter

05 Cutting of rods for

reinforcing bar

6000* dia.

30mm,#16 , 80 mm

length each

Rotating disc

cutter

Cutter disc Tape

meter

06 Welding twisted

rasp drum for teff

and wheat

rhs,40*40*4mm

Welding

machine

Electrode dim.2.5

& 3.2 mm

07 Grinding sharp

corners and fillet

Hand

grinding

machine

Grinding disc

O8 Finishing machine Hand polisher Polisher disc


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5.2 Assembly procedure

1 Assemble the bed using bolt and nut

2 Assemble right and left support and cover to main

bed, using bolt and nut

3 Assemble lower concave to main support using

bolt and nut

4 Place the cylinder beater up, to the lower concave

5 Place the upper concave and joined to the lower

concave using bolt and nut

6 Place blower to the back side of cover

7 Assemble the lead screw and lead screw casing

lower place the lower side of the sieve

8 Tight bolt and nut at all fittings


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Principle of operation

The electric motor or engine provides the primary motion required to power the machine. The

motion and torque are transmitted via pulleys, V- belts and bearings to the shaft carrying the

beater, blower shaft and lead screw conveyor connected to the blades. Both the drum beater and

blower blades rotate in clockwise direction. The whole cereal crops (together with stems) are

introduced into the machine through the inlet hopper. They reach the rotating drum inside the

shelling barrel by gravity. The drum gives continuous impact force on the whole cereal crops,

thereby removing the grains and the chaff. Because the beater are arranged in a spiral form. The

whole cereal crops moves along the length of the barrel in the forward direction until they reach

the chaff exit spout. Before the whole cereal crops reaches this point, almost all the grains (

seeds) are removed thereby letting the chaff go out of the machine clean. Due to the impact of

the beaters some of the chaff or cobs may broken, through both broken and whole exit through

the exit spout. The air generated by the blower blades is channeled to flow against the cereal crop

grain exit spout via a wire mesh. The air blows off unwanted chaff that exit together with cereal

crop grains thereby keeping the cereal cropgrains very clean. The clean cereal crop then run into

the reciver where they are collected for further processing operations.

5.3 Total manufacturing cost

Total manufacturing cost is the aggregate amount of cost incurred by a business to produce

goods in a reporting period. The term can then be defined in two ways, which are:

The entire amount of this cost is charged to expense in the reporting period, which means

that total manufacturing cost is the same as the cost of goods sold; or

A portion of this cost is charged to expense in the period, and some of it is allocated to

goods produced in the period, but not sold. Thus, a portion of total manufacturing cost

may be assigned to the inventory asset, as stated in the balance sheet.

Charged to expense in the reporting period. For this situation, the calculation of total

manufacturing cost is as follows:


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Direct materials. Add the total cost of materials purchases in the period to the cost of

beginning inventory, and subtract the cost of ending inventory. The result is the cost of

direct materials incurred during the period.

Direct labor. Compile the cost of all direct manufacturing labor incurred during the

period, including the cost of related payroll taxes. The result is the cost of direct labor.

Overhead. Aggregate the cost of all factory overhead incurred during the period. This

includes such costs as production salaries, facility rent, repairs and maintenance, and

equipment depreciation.

Add together the totals derived from the first three steps to arrive at total manufacturing cost.

The calculation of this cost is somewhat different if we use the second definition, where some of

the cost may be assigned to goods that are produced, but not sold. In this case, use the following

steps (assuming that standard costing is used):

Assign a standard materials cost to each unit produced.

Assign a standard direct labor cost to each unit produced.

Aggregate all factory overhead costs for the period into a cost pool, and allocate the

contents of this cost pool to the number of units produced during the period.

When a unit is sold, charge to the cost of goods sold the associated standard materials cost,

standard direct labor cost, and allocated factory overhead.

5.4 Calculate a labor rate

In general terms, a labor rate is either the cost or price of labor. To expand on these two

concepts:

Cost based. A labor rate is the cost of labor that is used to deriving the costs of various

activities or products within a business.

Price based. A labor rate is the rate charged to customers for services performed by

company employees.


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When a labor rate is used for defining the cost of labor, it can be further refined into the

incremental cost of labor or the fully-loaded cost of labor. Consider the following differences

and usages:

Incremental labor rate: This rate is the cost of labor that will be incurred if a specific action is

taken. For example, if an employee is asked to work one additional hour, the incremental labor

rate will likely include the person's base wage, any associated shift differential, and payroll taxes.

The concept can yield widely differing results, since asking someone to work overtime yields a

50% higher incremental labor rate. This information is most commonly used when a customer

asks for a special production run at a reduced price, and the incremental profit must be

calculated.

Fully loaded labor rate: This rate contains every possible cost associated with an employee,

divided by the total number of hours worked by the employee. For example, the cost may include

the company's contribution to the employee's pension plan, all benefit costs, payroll taxes,

overtime, shift differential, and the base level of compensation. This rate is typically aggregated

for entire classifications of employees, so that (for example) the fully loaded labor rate for an

average machine operator may be commonly available.

When a labor rate is to be used as the billing rate for an employee to a customer, a number of

considerations must go into its calculation. At a minimum, the labor rate cannot be lower than

the incremental cost of the employee, since the employer would otherwise lose money for every

hour worked by the employee. Instead, it is customary to build into the labor rate an

apportionment of company overhead and a standard profit percentage, so that a long-term, fully-

loaded cost is set as the minimum possible labor rate to charge. A further option is to simply set

the labor rate at what the market will bear, which may be substantially greater than the cost of an

employee. In this latter case, the amount of profit earned by the employer may be outsized, if the

demand for an employee is substantial.

5.5 Direct Costing Overview

Direct material cost

Direct material cost is the cost of the raw materials and components used to create a product. The

materials must be easily identifiable with the resulting product (otherwise they are considered to


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be joint costs). The direct material cost is one of the few variable costs involved in the

production process; as such, it is used in the derivation of throughput from production processes.

Throughput is sales minus all totally variable expenses.

In brief, direct costing is the analysis of incremental costs. Direct costs are most easily illustrated

through examples, such as:

The costs actually consumed when you manufacture a product

The incremental increase in costs when you ramp up production

The costs that disappear when you shut down a production line

The costs that disappear when you shut down an entire subsidiary

5.6 Direct materials cost

Direct materials are the raw materials that become a part of the finished product. Manufacturing

adds value to raw materials by applying a chain of operations to maintain a deliverable product.

There are many operations that can be applied to raw materials such as welding, cutting and

painting. It is important to differentiate between the direct materials and indirect materials.

5.7 Direct labor cost

The direct labor cost is the cost of workers who can be easily identified with the unit of

production. Types of labor who are considered to be part of the direct labor cost are the assembly

workers on an assembly line.

5.8 Cost analysis

5.8.1 Raw material cost

Raw materials cost identifies the price of each initial raw material which will be used in the

manufacturing of the parts and features of the adaptation, designed and manufacturing of

multipurpose threshing machine. The table below gives estimation of the unit and total prices of

each required raw material in accordance with their existing market price.


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Table 5-8Raw material cost

No. Material type Dimension/

specification

unit quantity Unit

price

Total

price

remark

1 Sheet metal 2000*1000*4mm pcs 1 2000.00 2000.00




5 Round bar ∅30 ∗ 6000 pcs 1 2000.00 2000.00

6 Round bar ∅20 ∗ 6000 pcs 1/5 600.00 120.00

7 Round bar ∅8 ∗ 6000 pcs 2 120.00 360.00

8 bar ∅8 ∗ 6000 pcs 2 90.00 180.00

9 RHS 40*40*4mm pcs 1 400.00 400.00

10 RHS 60*60*3mm pcs 1 600.00 600.00

11 Angle iron 40*40*4mm pcs 1 500.00 500.00

12 Flat iron 40*40*4mm pcs 1.5 400.00 600.00

Total raw material cost 12,400.00

5.8.2 Standard components costs

The competitive nature of the manufacturing industry means that companies are constantly

looking for ways to increase the efficiency and productivity of their systems.

Standard components

It is common practice in modern manufacturing for the production of the components that make

up a product to be outsourced to other companies.

The advantage with using standard components is that it speeds up manufacturing and reduces

manufacturing and maintenance costs, as the same units can be purchased and used all around

the world.

Advantages of using standard components

1. Standard components can be manufactured in vast quantities, keeping costs down.


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2. Standard components are supplied in standard sizes. Consequently, they are easy to order.

Ordering of standard components is relatively straightforward, sizes / dimensions etc... are

available in table or index form.

3. Buying directly from suppliers, over the counter, at hardware stores such as B & Q, is easier as

standard components such as screws, bolts, nails and fixings are often displayed in order. This

makes it easier to find the component the customer requires.

4. Safety / quality testing is easier when dealing with standard components. Often a number of

standard components, from a batch will be tested. Faulty components can be withdrawn from

sale, if detected.

5. Manufacturers of „complex‟ products (computers TVs, etc....), usually assemble their

products from standard components. This allows them to concentrate on the development of their

specialised product, rather than having to design each individual component. This speeds up

product development.

6. Setting up a mass production line is easier if standard components are used. It is easier to train

staff / the workforce, as they are dealing with the same standard components, when assembling

products.

Purchasing of standard elements which does eliminate the effort to design and manufacturing of

them, the standard components used in adapting, design and fabrication of multipurpose machine

are listed below as the current market cost.

Table 5-9 Cost of standard components

No. Part name Quantity Unit cost Total cost Remark

1 Bolt and nutM14*10 10 12.00 120.00

2 Bolt and nutM12*10 10 11.00 110.00

3 Bolt and nutM10*10 10 10.00 100.00

4 Bearing with house∅30 8 220.00 1760.00

5 Drill beat∅30 2 30.00 60.00

6 Drill beat∅13 2 13.00 26.00

7 Drill beat∅12 2 12.00 24.00

8 End mill cutter∅8 2 30.00 60.00

9 End mill cutter∅6 2 25.00 50.00


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10 Belt AA68 1 60.00 60.00

11 Belt A65 1 50.00 50.00

12 Belt A40 1 40.00 40.00

13 Electric/engine motor 9hp 1 20,000.00 20,000.00

Total cost of standard 22,410.00

5.8.3 Manufacturing processes cost

Manufacturing process cost in this adaptation, design and fabrication of multipurpose machine

can be categorized in to two groups:

1. Machining process cost and

2. Labor cost

Machining process cost

The Manufacturing of the designed, manufacturing and adaptation of multipurpose threshing

machine involves a rolling, bending, drilling and welding as well as various machining

operations, and then the manufacturing cost must also involve the machining operation costs.

Figure 5.8-1Twisted bar drum


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Figure 5.8-2 Cylinder drum for wheat and teff

Figure 5.8-3 Lower concave


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Figure 5.8-4Left and right support and cover

Figure 5.8-5 Different size pulleys


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Figure 5.8-6Manufacturing of drum beater

Figure 5.8-7 Assembly of multipurpose thresher


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Table 5-10 Machining process cost

No. Type of

components

Type of

operation

Average

total

time(hr)

Cost per

hour

Total cost

1 Right and left cover

and support plate

Sheering, drilling,

and bending

2 100.00 200.00

2 Upper and lower

concave

Sheering, drilling,

bending, welding

and rolling

6 100.00 600.00

3 Drum for maize Cutting, rolling,

sheering ,welding

and drilling

4 100.00 400.00

4 Drum for wheat and

the like

Rolling and

cutting

1.5 100.00 150.00

5 Pedal blower casing Rolling and

sheering

1 100.00 100.00

6 Blower for cleaning

action

Cutting, rolling,

sheering and

drilling

2 100.00 200.00

7 Screw casing Cutting, rolling,

sheering and

drilling

1.5 100.00 150.00

8 Triangular plate Sheering, drilling

and welding

4 100.00 400.00

9 Key way making Slotting 4 100.00 400.00

10 Reinforcing rhs Cutting and

drilling

1 100.00 100.00


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12 All components

grinding and

finishing

Cutting, grinding

and finishing

4 100.00 400.00

Total cost 3,000.00

2. Laboring cost

The cost of labor is the sum of all wages paid to employees, as well as the cost of employee

benefits and payroll taxes paid by an employer. The cost of labor is broken into direct and

indirect (overhead) costs. Direct costs include wages for the employees that produce a product,

including workers on an assembly line, while indirect costs are associated with support labor,

such as employees who maintain factory equipment.

In the current situation, the corresponding rating costs of operators for welding, cutting, drilling and

grinding in Bahir Dar city is obtained as; for machine operators = 100-250 birr/hour and for

assembling = 90-150 birr/hour respectively.

Table 5-11Labor cost

No. Type of

components

Type of

operation

Average

total

time(hr)

Cost per

hour

Total cost

1 Right and left cover

and support plate

Sheering, drilling,

and bending

3 100 300.00

2 Upper and lower

concave

Sheering, drilling,

bending, welding

and rolling

4 100 400.00

3 Drum for maize Cutting, rolling,

sheering ,welding

and drilling

4 100 400.00

4 Drum for wheat and

the like

Rolling and

cutting

3 100 300.00


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5 Pedal blower casing Rolling and

sheering

2 100 200.00

6 Blower for cleaning

action

Cutting, rolling,

sheering and

drilling

3 100 300.00

7 Screw casing Cutting, rolling,

sheering and

drilling

2 100 200.00

8 Triangular plate Sheering, drilling

and welding

4 100 400.00

9 Key way making Slotting 3 100 300.00

10 Reinforcing rhs Cutting and

drilling

3 100 300.00

12 All components

grinding and

finishing

Cutting, grinding

and finishing

6 100 600.00

Total cost 3,700.00

5.8.4 Cost of summary

Cost of summary here provides the sum of all required raw material, manufacturing, assembling,

and also included labor costs to summarize the total cost of the Adaptation, designed and

manufacturing of multipurpose threshing machine.


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Table 5-12Cost of summary

No. Type of cost Total cost (birr)

1 Raw material cost 12,400.00

2 Manufacturing process cost: Machining cost 3,000.00

Labor cost 8,900.00

3 Standard cost 22,410.00

Total cost 46,310.00


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CHAPTER SIX

6. CONCLUSION, RECOMMENDATION AND FUTURE WORK

6.1 Conclusion

The multipurpose threshing machine has been designed, developed and fabricated keeping in

mind the constraints and requirement of the Ethiopian rural farmers. The manufacturability of the

machine is quite good and the handling is quite simple. The crops or cereals discharging

mechanism are effective and crop or cereal seeds can be discharged off very easily.The machine

was tested in maintenance machine shop and later to taken to the field. It is clear that the

manufacturing of multipurpose threshing machine was successfully completed. The actual

through put capacity which was determined to be 2490.2kg/hr, 750.51kg/hr and 280kg/hr for

maize, wheat and Teff respectively. The threshing efficiency increased with an increase in

cylinder speed. It was found in the range of 90% to 99.98%, 97.8% to 99.9%, and 99.9% to

100% for maize, wheat and Teff respectively. At optimum speed of 540 rpm, 1440rpm and 1440

rpm. The output capacity, threshing efficiency, grain damage and grain losses significantly

affected by cylinder (drum) speed and the feed rate capacity of each crops 50kg/min, 20kg/min

and 10kg/min for maize, wheat and Teff respectively. The maximum value grain damage was

recorded 0.3 and 1.83 on maize and wheat crops at drum speed 540rpm and 1440rpm. The

thresher performance better, can get an increase drum speed and feed rate, this means the

through put of the thresher was best at the highest threshing/ shelling speed and it requires at

least four persons to operate during threshing. Because an increase engine or motor power it also

through put capacity. That means it depends on the feed rate of the person who put the weight of

whole crop material fed into the thresher hopper. For commercial purpose can improve the

efficiency of the device effectively by increasing the size of the machine and providing it

multiple heads.

Generally, the cause of the grain damage it depends on the drum (cylinder) speed and the highest

percentage losses occur in Teff crops, due to smallness of the grain.


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6.2 Recommendation

I have the following recommendation:

The thresher should be operated at around cylinder(drum) speed of 540rpm, 1440rpm

and 1440rpm for maize, wheat and Teff crops respectively. The above recommended

speed results in higher threshing capacity, threshing efficiency and cleaning with

reasonable grain damage and grain loss wheat, maize and Teff crops.

After this, I am interested to develop based on the tested result. That means after this I

will test the other crops like rice, sorghum and barely.

The thresher should be operated at recommended speed and do not drop the cereal when

the machine is not running because it may happen grain damage and power interruption.


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6.3 Future work

Field testing and promoting rural farmers the awareness of the machine

Testing of other cereals crop like rice, sorghum, barely and Degussa

Reducing the size of the machine will affordable to individual farmers and lower the cost

of the machine

For the future, this machine duplicated by three times there is an agreement between

technology transfer and me


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8. APPENDIXES

Appendix A1: Diameter, RPM, and distance between interconnected pulleys of a

multipurpose thresher

Pulley

number

Designated

diameter(mm)

Size

diameter

(mm)

RPM formula

for all pulleys

Calculated

value

(RPM)

Pulley

interconnection

Distance,

C

Or center

distance

1 𝐷1 75 1440 pto 540 Open belt drive 600

2 𝐷2 280 𝜋𝐷1𝑁1 =𝜋𝐷2𝑁2 385 Open belt drive 600

3 𝐷3 100 𝑁2=𝑁3 385 Open belt drive 500

4 𝐷4 200 𝜋𝐷3𝑁3=𝜋𝐷4𝑁4 192.5 Open belt drive 500

5 𝐷5 100 1440 1440 Open belt drive 550

6 𝐷6 75 𝜋𝐷5𝑁5=𝜋𝐷6𝑁6 1920 Open belt drive 550

RPM were calculated using formula 𝜋𝐷𝑥𝑁𝑥=𝜋𝐷𝑦𝑁𝑦 (khurmi 2009)


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Appendix A2: Angle of contact, angular, liniar velocities and coefficient of friction for belts

of thresher

Pulley

interconnection

Sin

𝛼=(𝐷𝑥−𝐷𝑦

2𝐶)

𝜃𝑥=Angle of

contact

(degree)

Angle of

contact in

radian

Angular

velocity

𝜔(rad/sec)

Liniar

velocity

V(m/s)

Open belt 1&2 -0.17/0.17 199.6/160.34 3.48/2.79 150.72/40.29 5.652/5.64

Open belt 3&4 -0.1/0.1 191.46/168.54 3.34/2.94 40.29/20.14 2.014/2.014

Open belt 5&6 0.02/0.02 177.39/177.39 3.09/3.09 150.72/200.96 7.536/7.536

𝜃𝑥=180 -2𝛼 for open belt drive (degree), 𝛼=𝑠𝑖𝑛−1(𝐷𝑥−𝐷𝑦

2𝐶), 𝜔= 2𝜋N/60(rad), and V= r𝜔 (m/s)


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Appendix A3: Length, weight and centrifugal tensions of all belts for thresher

Pulley

interconnection

Length of the

belt (mm)

Coefficient of

friction, 𝜇

Weight per

meter (N)

Mass per

meter (Kg)

Cross

sectional area

of belt (𝑚2)

1&2 1607.55 0.3 2.48 0.253 0.997

3&4 1571 0.3 2.42 0.246 0.969

5&6 1375.31 0.3 2.122 0.216 0.851

L=𝜋

2(𝐷𝑋+𝐷𝑦 )+ 2C+ (𝐷𝑋 − 𝐷𝑦)2/4C, weight( N) per meter length of the belt taken from

(Khurmi 2005)

Centrifugal tension for a belts used in thresher, 𝑇𝑐= m𝑣2 (N), 𝜇= 0.3 (Khurmi 2005)


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Appendix A4: Size and tensions for belts used in thresher.

Pulleys Maximum

tension (N)

Centrifugal

tension, (N)

Tight side

tension per

pulley (N)

Tension in the

slack per

pulley (N)

Total tension

𝑇1 +𝑇2 (N)

per pulley

1 & 2 1082.28/1082.28 764.71/764.71 322.50/322.5 214.83/214.83 537.33

3 & 4 314.83/314.83 30.42/30.42 93.63/93.63 62.37/62.37 156.00

5 & 6 2546.14/2546.14 312.35/312.35 757.2/757.2 504.42/504.42 1261.62

Cross sectional area A of belt to with stand the tensions =Mass of the belt/ (total length of belt x

density of belt )Density of rubber belt = 1140kg/𝑚3 (Khurmi 2005), The mass of the pulley can

get fiscally measured. 𝑚1=23.93Kg, 𝑚2=7.50Kg,𝑚3=2.50Kg,𝑇𝑐=mv², 𝑇𝑐= 𝑇1/3,

𝑇1 − 𝑇𝑐



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Appendix A5: Tension, power and torque produced due to belts on pulleys

Pulleys

interconnection

Power

transmitted /belt

,(watts)

Power

transmitted per

pulley, (hp)

Torque on the

shaft, (Nm)

Pulley drive 1 608.65 0.811 10.76

Pulley drive 2 608.11 0.811 15.10

Pulley drive 3 62.95 0.083 1.56

Pulley drive 4 62.95 0.083 3.12

Pulley drive 5 2539.93 3.38 16.85

Pulley drive 6 2539.93 3.38 12.63

P= power transmitted by the belt per pulley (watts) =P= ( 𝑇𝑡𝑖𝑔𝑕𝑡𝑠𝑖𝑑𝑒 -𝑇𝑠𝑙𝑎𝑐𝑘𝑠𝑖𝑑𝑒 ) * velocity

Torque was calculated, T= P*60/2𝜋*N


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9. PART DRAWINGS


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Adaptation, Design and Fabrication of Multipurpose Threshing ...

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