Design & Fabrication of Screw Conveyor
INTRODUCTION
1.1 GENERAL
SCREW CONVEYORS are one of the oldest and simplest method of
moving bulk material and consist primarily of a conveyor screw rotating in a stationary
trough.
Conveyors find application mostly in productive factories where
transportation is fairly of continuous and uniform character, the individual loads being very
high.
Screw conveyors are compact, easily adapted to congested locations and
can be mounted horizontally, vertically and inclined. Their supports are simple and easily
installed.
These versatile conveyors can be used to control the flow of material in
processing operations which depend upon accurate batching or as a mixer, agitator or
stirrer to mix and blending dry or fluid ingredients provide crystallization or coagulation
action or maintain solutions in suspension.
Screw conveyors can be effectively sealed to prevent dust or fumes from
escaping or dirt or moisture from entering. They can be jacketed to serve as a dryer or
cooler, or furnished in a wide variety of materials to resist corrosion, abrasion or heat.
Screw conveyors are used as a earth augers to dig past holes or to bore
under highways for installation of culverts. They are also used extensively on threshing
machines hay balers fodder blowers and many other farm machines.
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Design & Fabrication of Screw Conveyor
1.2 SCOPE
This manual is helpful in designing of screw conveyors using calculations in metric
units.
Saving of labour and time.
To increase the output:
With the help of conveyors more work can be done with a given floor space, blocks are
avoided.
To utilize existing building for new purposes:
Conveying plant enables two or more detached building to be connected together and
used for several operations in propersequence.
Reducing personal hazardous:
The enclosing trough can be made tight enough to contain toxic dust and vapours.
Material in transit can be heated or cooled by jacketing the trough.
1.3 OBJECTIVE
The aim of this project is to "design and fabricate a screw conveyor" to convey cement
at 7 TPH for a distance of one meter.
This design is in accordance with CEMA HANDBOOK NO .350
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Design & Fabrication of Screw Conveyor
LITERATURE REVIEW
2.1 DIFFERENT TYPES OF CONVEYING EQUIPMENT FOR BULK
MATERIALS
2.1.1 BELT CONVEYOR
Belt conveyors are the most versatile and widely used of all conveyors.
They are capable of handling higher tonnages over greater distances at lower costs per ton
then any other type of conveyor – and often at lower cost per than any other means of
transportation. Yet, they are used extensively for small and moderate capacity systems
because of their ability to handle practically any kind of material economically and
dependably. Since the material is carried on the belt, tees conveyors are suitable for
handling certain corrosive materials that would quickly attack the vital parts of all metal
conveyors.
The range of the sizes, which may be handled on belt conveyors limited
only by the width of the belt.
Materials may vary from extremely fine Chemicals to lumpy ore, stone,
coal or pulpwood logs. Since belt conveyors are relatively self cleaning to or more
dissimilar materials may be handled at different times by the same conveyor.
Belt conveyor systems are capable of operating around the clock without
loss of time for empty return trips or delays for loading and unloading. Belt conveyors are
adaptable to the parts of material flow in any plant. They occupy comparatively little space
and can avoid existing equipment and structure. Long distance belt conveyors systems will
negotiate terrain and paths of travels that are not practical or economical for more other
method of transportation.
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Design & Fabrication of Screw Conveyor
Bulk materials, flowing continuously and uniformly from belt conveyors,
may be distributed to desired location. In addition to transportation and distribution, belt
conveyors may be used to perform many other functions such as weighing, blending,
sampling and stock piling. Also belt conveyors may be supported and housed at lower cost
then most other facilities for transporting similar large volumes.
The principal factors contributing to comparatively low operating costs of
belt conveyors systems are low power requirements, long life of wearing parts, low lab
our cost of replacing parts, low cost of inspection and attendance, low cost of loading and
unloading per ton handled and maximum safety of personnel.
BELT CONVEYOR
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Design & Fabrication of Screw Conveyor
OSCILLATING CONVEYOR
2.1.2 OSCILLATING CONVEYORS:
Oscillating conveyors move materials in a uniform flow by the upward and
forward oscillating motion of a continuous metal trough mounted on sturdy, inclined
reactor legs. This conveyors are ideal for handling all granular, free flowing materials as
well as hot, abrasive, dusty, stringy and other difficult- to- handle materials or where
contamination or corrosion is a problem. Oscillating conveyors are also used cooling,
heating and drying. They have leak proof trough in which there are no moving parts, and
can be enclosed and sealed for dustproofor a gas-tight operation.
Oscillating conveyors can be modified for many special uses. Trough can be
made in a special widths or they can be constructed of tubes or pipes; they may also be
divided lengthwise for simultaneous handling of different materials or parts. Oscillating
conveyors can also be used as picking and sorting tables. Standard
conveyors can also be use on modify to suit many process applications such as drying,
Cooling, screening, etc.
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Design & Fabrication of Screw Conveyor
BUCKET ELEVATORS
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Centrifugal discharge elevator
bucket elevator
Positive discharge bucket elevator
Design & Fabrication of Screw Conveyor
2.1.3 BUCKET ELEVATORS:
The typical bucket elevator consists of series of buckets mounted on a chain
or belt operating overhead and foot wheels. Take-ups are provided as a means to
compensate for variations in length of chain or belt due to temperature changes,
atmospheric conditions, or wear. A steel casing usually encloses the bucket line and the
head and put machinery. The type of elevator and material handled determine the bucket
selection.
Chain is used on elevators caring heavy loads, hot materials, or those, which
pack between the buckets and a belt. Rubber covered or treated fabric belts are used an
elevators handling grains, cereals, and many other, free - flowing, abrasive materials. The
head and the foot machinery components have been selected to best suit the service
requirements of the individual's elevator.
Selection of the proper type of bucket elevator depends largely on capacity
requirements and the characterstics of the materials to be handled.
CENTRIFUGAL DISCHARGE BUCKET ELEVATOR
Elevator of this design predominates in the bulk handling of free flowing,
fine and loose materials with small to medium size lumps. Buckets, mounted at spaced
intervals, are loaded by scooping up materials from the boot or by feeding the material into
them.
Material is discharged by centrifugal action as the buckets pass over the
head wheel. These elevators are made in several types and are suitable for many
requirements.
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Design & Fabrication of Screw Conveyor
POSITIVE DISCHARGE BUCKET ELEVATORS
Elevators of this design operate at low buckets speeds suitable for handling
light, fluffy, fragile materials and those having a tendency to stick in the buckets. Buckets,
at spaced intervals, are loaded by scooping up material from the boot or by feeding the
material into them. After passing over the head wheels, the buckets are inverted over the
discharge spout, providing a positive discharge of material.
CONTINUOUS BUCKET ELEVATORS
Elevators of this design are made in a number of types for handling many
bulk materials ranging from light to heavy and from fines to large lumps. Buckets are
spaced continuously and loaded by direct feeding. Their close spacing prevents spillage
between buckets. As buckets discharge, the material flow over the preceding bucket, who's
front and projecting sides form a chute, to the discharge spout.
INTERNAL DISCHARGE BUCKET ELEVATORS
Internal discharge elevators provide excellent means for the continuous,
gentle handling in bulk of relatively small articles such a stampings, castings, plastic chips,
pallets, bolts, nuts, rivets, granule chemicals, seeds, shelled nuts and similar materials.
Discharge can be on either side of casing through a chute or directly to a conveyor.
2.1.4 GRAVITY-DISCHARGE CONVEYOR ELEVATOR
The gravity – discharge conveyor – elevator is used to handle non-abrasive
bulk materials in vertical, or combination of horizontal and vertical paths. It derives its
name from the fact that material discharges from the buckets by gravity. Gravity conveyor
is easy to setup, as it does not involve any power drive.
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Design & Fabrication of Screw Conveyor
Because of the gentle pick-up and discharge of material the gravity-
discharge conveyor- elevator is primarily intended for use where breakage or degradation
of conveyed material is an important consideration. It is also suitable for lumpy materials
relatively large capacities and many other applications where comparatively economical
equipment is desired.
This conveyor - elevator consist of a conveying medium of modified v-
shaped buckets rigidly mounted at regular intervals between two strands of long pitch steel
roller chain, operating over suitably located comer sprockets and in open troughs or
enclosed casings as determined by the requirements of the installation.
Loading can be accomplished by means of a comer boot, or material can be
fed into the conveyor at any point along a lower horizontal run-in the latter instance the
buckets act as a scrapers, pushing the material forward to a corner where it is carried
around a curved trough and picked up by the buckets.
On vertical runs this machine functions as an ordinary bucket elevator.
Upon reaching an upper comer the conveyor line again assumes a horizontal position and
the buckets operate as scrapers. Material is restrained from spilling at corner by specially
constructed curved troughs.
Discharged from the conveyor can only be effected on horizontal runs
where opening occur in the trough bottom. Gates can be provided or the trough bottom
omitted to properly distribute material along the line of travel of the upper run.
2.1.5 FLIGHT CONVEYOR :
A flight conveyor consists of one or two endless power driven chains
carrying properly spaced scrapers or flights for moving material along the length of a
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Design & Fabrication of Screw Conveyor
stationary trough. Material fed into this trough is there by pushed along its length for
discharge at the end of the trough or trough intermediate discharge gates.
Typical materials, which can be satisfactorily handled with a flight
conveyor, are those, which are granular; lumpy; very free flowing; non-abrasive, and
mildly corrosive.
Flight conveyors are used for either horizontal or inclined paths and are
frequently installed where the angle of inclination is comparatively step.
Link - belt flight conveyors are simple in design, sturdily constructed of
durable materials, and provide an efficient, economical and dependable conveying
medium, reflecting the benefits of sound engineering experience.
Single strand flight conveyors with scraper flights are ideal for conveying
hot materials such as cement clinker and lime.
Double strand flight conveyors with sliding chain –suspended flights are
used for larger capacities and longer paths than single strand flight conveyors and can be
made to convey on both runs. The chain operates on flat renewable steel bars attached to
the trough.
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Design & Fabrication of Screw Conveyor
SKIP HOIST
2.1.4 SKIP HOISTS
Skip hoists are particularly adaptable to very high lifts and may be used to
elevate any bulk materials that can be handled in batches, including materials with large
lumps.
The skip hoist will convey virtually all materials with the exception of those
which are very fine, light or fluffy, contaminable, highly corrosive, or those having
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Design & Fabrication of Screw Conveyor
harmful, dusty or explosive properties.
The skip hoist consists of a bucket with or without counter weights or two
buckets balancing each other, a winding machine, wire rope, a steel structure with tracks,
means for loading and unloading the buckets and the necessary electrical apparatus and
lead sheaves.
As an effective method of unloading bulk materials, the skip hoist is
especially applicable to high lifts. The sip hoist is suitable for various combinations of
vertical and inclined paths of travel. It has few moving parts and the material being carried
does not contact these parts; therefore, maintenance is infrequent and simplified.
The link -belt hoist is known for its simplicity of construction, its
dependability and economy in operation. Operation may be manually controlled or fully
automatic.
There are three general types of skip hoist- the single non-counter-weighted
bucket, the single counterweighted bucket, and the type with balance buckets.
2.2 TYPES OF SCREW CONVEYORS
2.2.1 INCLINED UNITS:
Inclined screw conveyors, in general handle products that can be conveyed
in horizontal screw conveyors. Being compact, say contained and fully enclosed they can
be readily applied in congested areas. Feature insuring sanitation and ease of cleaning are
available.
For inclines of about 20 degrees or less, conveyor screws of regular pitch
operating in troughs are usually employed. Inclines above 20 degrees ordinarily require the
use of short pitch conveyor; screw operating in a tabular or shrouded trough.
2.2.2 VERTICAL UNITS:
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Design & Fabrication of Screw Conveyor
A vertical screw elevator is a unit that conveys material vertically. These
units can satisfy many conveying problems and have the further advantage of being
compacted, requiring less space than other forms of elevating equipment.
These units find it difficult to handle materials containing large lumps and
materials that are very dense or extremely abrasive.
Since we do not want to convey cement vertically, we consider either
inclined or horizontal screw conveyors.
“Draw backs of inclined screw conveyors”
The capacity of a given screw conveyor decreases with the increase of incline.
As the angle of inclination increases, there is reduction of flight (i.e. effective angle) as
it pushes against the material. Depending on angle of incline a certain portion of helical
flight does not urge the material forward. This causes material turbulence and
tumbling.
The 'U' shape of the conveyor trough is such that the material is allowed to fall back on
the top of the rotating screw. Again this increases the turbulence and cross sectional
loading.
Due to turbulence and tumbling of material, more horsepower is required than the
power required to normally conveying the material.
Due to the above -mentioned factors we select Horizontal Screw Conveyor, which
conveys cement horizontally.
2.3 CLASSIFICATION OF SCREW CONVEYOR DEPENDING UPON
TYPE OF FLIGHT USED
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Design & Fabrication of Screw Conveyor
1) Paddle conveyor screw.
This consists of a series of cut and folded flights mounted on the central
revolving shaft or pipe. In this the material is intentionally tumbled and sheared as it is
advanced along the casing by the pitch of the screw at every revolution. Friction between
the material and the revolving spiral tends to carry the material up one side and around
with the blade.
The capacity averages about 15% less than that of standard screw
conveyors, due to retarding action. Adjusting the angle of paddles can control conveying
action. They are used for mixing, blending, or stirring dry or fluid materials.
PADDLE CONVEYOR SCREW
RIBBON FLIGHT CONVEYOR SCREW
2. Ribbon flight conveyor screw:
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Design & Fabrication of Screw Conveyor
In this type of conveyor screw a steel bar rolled to form a continuous helical
ribbon flight fastened to the pipe or shaft by steel supporting lugs welded at spaced
intervals.
Variation of diameter, pitch, flight width or thickness can be furnished.
Also, this screw can be furnished with either continuous or sectional flights, lap or butt
welded together.
These are recommended for handling, sticky materials such as molasses, tar
or substances likely to build upon screw. The tendency of materials of this nature to adhere
and build up at the juncture of solid flight with the pipe is over corned by the open
construction of the ribbon flight.
Providing the periphery of ribbon flights with beveled edge improves
operation and reduces power consumption when handling materials which tend to pack or
trowel between flights and troughs. Consequently, beveled edge ribbon flight conveyor
screw is usually subjected to extremely heavy loads and construction is extremely
accordingly heavy loads and construction is extremely accordingly heavy and rugged. The
ribbons are supported on the pipe or shaft by steel lugs, generously proportional to resist
bending.
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Design & Fabrication of Screw Conveyor
HELICOID FLIGHT CONVEYOR SCREW
SECTIONAL FLIGHT CONVEYOR SCREW
To provide moderate mixing or stirring of materials being conveyed,
paddles can be furnished, spaced at intervals and set to partially oppose the forward flow,
called ribbon flight conveyor screw with paddle. Paddles are adjustable and may be set at
any angle, to produce the desired degree of agitation. They are used for light or medium
weight, fine, granular materials.
In multiple ribbon flight conveyor screw, the screw consists of two or more
ribbon flights of different diameter and opposite hand, mounted one within the other on the
same pipe or shaft by rigid supporting lugs. The other, thereby inducing positive and
through mixing moves material forward by one flight and backward.
3. Sectional flight conveyor screw:
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Design & Fabrication of Screw Conveyor
Sectional flight conveyor screws are made of individual flights; each
blanked from a flat steel plate and formed into helix. The flights are butt welded together
and fastened to the pipe, or shaft by intermittent or continuous welds with or without
formed steel end lungs. Sectional flights are formed with regular pitch approximately equal
to the diameter.
The pipe of a size carefully selected for adequate torsion strength and
resistance to excessive deflection, has internal collars at each end. These collars are
permanently inserted and have appropriate inside diameter to accept coupling or end
shafts.
Sectional flight conveyor screws are interchangeable with helical flight
conveyor screw of the same diameter and shaft size.
Sectional flight affords flexibility in choice of diameters, pitches and
thickness. When desired, sectional flights may be continuous welded to the pipe on one or
both sides, thus providing exceptionally rugged construction for the most severe conveying
application.
4. Helicoids type:
The helicoids flight conveyor screw is made of a helix, formed by flat steel
bar and mounted on a pipe or shaft. The helix, formed by special rolling equipment to the
required diameter, pitch and thickness, is a smooth, continuous one- piece flight.
By virtue of its one-piece construction, it possesses superior strength. The
absence of laps, rivets or welds on the carrying face of the flight promotes and maintains
cleanliness and reduces wear. The rolling process affects a hardening and smoothing of the
flight surface, which increases resistance to wear and reduces friction and power
consumption.
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Design & Fabrication of Screw Conveyor
The flight is fastened to the pipe, or shaft, by intermittent or continuous
welds and with or without formed steel end lungs. The pipe, of a size carefully selected for
adequate torsion strength and resistance to excessive deflection, has internal collars at
each end. These collars are permanently inserted and have appropriate inside diameters to
accept coupling or end shafts.
The assembled helicoids flight conveyor screw is solidly constructed and
exceptionally sturdy, and inherent balance permits operation at high speeds. Its distinctive
characteristics contribute in maximum efficiency, durability and economy.
Helicoids flight conveyor screws are interchangeable with sectional flight
conveyor screws of the sane diameter and shaft size.
Helicoids flighting is made with regular pitch approximately equal to the
diameter. It can also be furnished with other than regular pitch and in a wide range of
diameter, thickness and lengths to meet the most exacting requirements. For extremely
heavy duty the flighting may be continuous welded to the pipe or shaft on one or both
sides.
We select helicoids type of screw conveyor flighting.
METHODOLOGY
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Design & Fabrication of Screw Conveyor
3.1 DESIGN CONSIDERATIONS
The key to any successful screw design is, firstly through a thorough under
standing of the characteristics of the material to be handled.
Secondly the action of a screw conveyor is important to understand. It is
most important to have thorough knowledge of, and understanding of the way material
flows and effects of variation in the flow.
Capacities are usually given in TPH. Also the apparent density in the
material could vary. The conveyor size and speed must be based on maximum volume and
the apparent conveyed density of the material.
Surge loads should be taken in account.
3.2 DESIGN CALCULATIONS
Material Handled: Portland cement
Lump Size: Powder
Capacity required: 2.654 TPH [Tons Per Hour]
Length of conveyor: 0.75 c/c [Inlet Center To Outlet Center]
Referring to table get the following data:
1) Bulk Density: 65 -85 lbs per cubic feet
2) Material Class: A 2 7 Y
3) H.P. Factor F: 1.0
Taking the lower value of bulk density and converting it into tons per meter cube.
Bulk Density = 65 lbs per cubic feet
= l.0404 tons per meter cube
4) Component:2 D_From Table No. 1, we get
Now material class = A 27 Y where,
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Design & Fabrication of Screw Conveyor
A- Very fine, 100 mesh under
2- Free flowing - angle of repose 30 to 45 degrees
7- Mildly abrasive
Y-Aerates and becomes fluid.
By deleting last letter in material class, we get A 27
Locating this material class tables we find material Class A 2 7 comes in
Table no 2
This table No: 2 corresponds to Graph G-5
Capacity: 2.654 TPH
For converting TPH into cubic feet per hour we divide the capacity by the
lower bulk density.
Therefore,
Capacity = (2.654 TPH)/ (1.0404 Tons per meter cube)
= 2.55 meter cube per hour
Therefore,
Capacity in cubic feet per hour = (2.55 * 35.28)
Where, (35.28) is conversion factor.
Capacity = 90 cubic feet per hour
For finding the diameter of screw conveyor we refer the graph G-5
From the graph we select 6 inches diameter screw
Curve = 153 mm = 160mm (modified)
From table 12 standard pitch = 125
Putting these values in the formula for capacity
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Design & Fabrication of Screw Conveyor
C = 3.142/4*[(D*D-d*d)*p*k*B.D*(r.p.m.)*60
2.654= 3.142/4 * [(0.160 * 0.160-d*d)] 0.125
0.3*1.0404*60*60
Therefore d = 0.039m
= 39mm
Therefore taking "d = 40 mm".
We select an electric resistance welded (ERW)
A -class pipe. (Since the pipe is being used for light- duty work)
Standard available pipe outer diameter is "42.5" with 2.5mm wall thickness.
Therefore pipe inside diameter is 42.5-5 =37.5mm
Now c/c length of convey or is 0.75 meter
Adding the distance between the trough end inlet and outlet centers (i.e. pitch)
We get,
Conveyor overall length = 750+2*125
=1000mm
ESTIMATING THE HORSE POWER REQUIRED
We assume 100% loading and thus calculate the capacity. Using this
calculated capacity we calculate the required horsepower.
C=3.142/4*[(D*D)-(d*d)]*p*k*r.p.m*60
C=3.142/4*[((0.160*0.160)-(0.04)*( 0.04))*0.125*1* 60*60
C=8.48 TPH
Converting it into lbs per hour
C=8.48 *2205
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Design & Fabrication of Screw Conveyor
=18703.472 LBS PER HOUR
Now H.P. = L*[(D*S+Q+F)]/1,000,000 where,
L=c/c length of conveyor in feet
D = Bearing factor
Q = Capacity in lbs per hour
F = Horse power factor (F = I for cement Portland)
S = Conveyor speed in r.p.m.
H.P. = 2.459 * 18713 * 1 / 1,000,000
H.P. = 0.046
Since the length of conveyor c/c is one meter therefore no hanger bearing is required and
hanger bearing factor, D =0
Brake horse power (B.H.P)
B.H.P. = H.P. * P
The value of “p” for H.P. less than one is “2”
B.H.P. = 0.046*2
= 0.092
Actual B.H.P. = 0.092 / efficiency of gear wheel
= 0.092/0.85
= 0.108
= 0.125 (Standard value)
= Required motor H.P
3.3 SELECTION OF MOTOR
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Design & Fabrication of Screw Conveyor
As seen in catalogue of Hindustan Electric Motors we select a 4 - pole
motor.
The Frame size is 71 for 0.5 H.P. Motor as seen from table no. 3 Looking in
motor dimensions for frame 71 we get the input diameter of motor " d " =9mm. As seen
from table no. 4
Motor rating 0.125H.P/1380 r.p.m.
We have got motor r.p.m. = 1380 and required speed =60 r.p.m (max)
Therefore reduction ratio is 1380/60 =23 = 25 (approx)
We reduce the speed from 1380 r.p.m to 60 r.p.m or lesser in two stages.
We use a gearbox.
3.4 SELCETION OF GEAR BOX
We take a reduction ratio of 25:1
Therefore output of gear box = 1380 /25 = 55.2 r.p.m.
Motor h.p. = 0.125
Multiplying motor h .p by service factor i.e. 1.5
We get h.p. = 0.1875
Taking h .p. = 0.23
The catalogue for selection of gearbox is shown in table no: 5
We select the size of gearbox unit as 112 based on the reduction ratio required 25/1
3.5 SELECTION OF COUPLING
Screw conveyors are limited in overall length by the amount of torque that
can be safety transmitted through the coupling.
Thus we calculate torque to be transmitted and select the coupling on the
basis of this torque.
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Design & Fabrication of Screw Conveyor
Torque T = 716* motor h. p *service factor / motor rpm
=716*0.25 *l.5/1320
= 0.203 kg-cm.
We select a "LOVEJOY" coupling from table no: 7
Having the following specifications:
COUPLING TYPE - L
COUPLING SIZE -050
The selected coupling should fit on the shafts of motor and gearbox.
The dimensions of type -L love joy flexible coupling are as given in the table no: 8
For coupling size-L 050 we get,
MATERIAL - CAST IRON (C 1)
MINIMUM BORE = 5mm.
MAXIMUM BORE = 16mm.
Now, motor shaft diameter = 9mm
And, Therefore coupling is acceptable.
3.6 FLIGHTS
CONVEYOR SCREW FLIGHTING
Screw conveyor flighting is made in either of two ways, as “helicoids” or
“sectional” flights. Helicoids flights are formed from a flat bar or strip into a continuous
helix. This flighting is thinner on the outer edge then on the inner edge. This process
provides a continuous one – piece construction with a work hardened, smooth finished
flighting surface. Sectional flights are formed from a flat disc and the thickness of the
flight is uniform. The lead of a sectional flight is slightly greater then one pitch. A joining a
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Design & Fabrication of Screw Conveyor
number of sectional flights together on a piece of pipe and butt-welding them together
make continuous helix.
LEFT HAND RIGHT HAND
"RIGHT HAND AND LEFT SCREWS"
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Design & Fabrication of Screw Conveyor
A conveyor is a right hand or left hand as determined by how the helical
flighting is formed .The hand of the screw may be clearly and easily ascertained by looking
at the end of the screw, as shown in the fig 4.6.
The screw pictured to the left has the helical flighting wrapped around the
pipe in a counter- clockwise direction. This is arbitrarily termed a Left- hand screw.
The screw pictured to the right has the helical flighting wrapped around the
pipe in a clockwise direction. This is termed a RIGHT hands screw.
A conveyor screw viewed from either end will show the same
configuration. If the end of the conveyor screw is not readily visible, then by merely
imaging that the flighting has been cut and the cut end exposed, the hand of the screw
readily may be determined.
The arrows in the Fig. 4.7 indicate which way the material will move if
right or left hand screws are rotated as indicated.
It will be obvious to the attentive observer that the HAND of conveyor
screw is a most important consideration in the design, application and ordering of a
conveyor screw. Once a screw conveyor is built and installed with a certain hand,
direction of the rotation is fixed for the desire direction of material transport. Any
replacements must be of the same HAND to avoid disastrous results.
If the hand of the screw isn't specified, the screw manufacture will normally
supply a RIGHT HAND screw.
We select sectional flights with both RIGHT HAND and LEFT HAND
flights on a single screw.
"CALCULATIONS"
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Design & Fabrication of Screw Conveyor
The screw shaft with the profile of the helix of flight and is development is
as shown in figure –
After development we get a right-angled triangle.
The disc internal diameter calculated is a internal diameter of flat disc
from which a section flight is to be formed.
Therefore we get,
Disc I. D * 3.142 = [(PIPE O. D* 3.142) 2] 1/2
= [(42.5* 3.142) 2+(125) 2] 1/2
= 182.84
DISK INTERNAL DIAMETER = 58.2
= 60 mm
DISC OUTER DIAMETER = DISC INTERNAL DIAMETER + CONSTANT
CONSTANT = Screw diameter + pipe outer diameter
= 125 + 42.5
= 167.5
= 168
DISC OUTER DIAMETER = 167.5 + 58.2
= 225.7
= 226
This disc internal diameter 60mm and outer diameter 226mm will be cut
radically and then bent in the form of flight over the pipe. This flight section will be butt-
welded to form the complete screw. Now over all
conveyor length = 1m + 2 * pitch
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Design & Fabrication of Screw Conveyor
=750+2 * 125
= l000 mm.
No. of flights = 1000/125
= 8 flights
We take five right handed flights from inlet end of trough to outlet, and one
left handed flight from the end plate of trough at outlet side to discharge.
Thickness of flight = 3.25mm.
Material = Mild steel (ms).
TROUGHS
The trough not only confines and guides the flow of material, but also
serves as the housing in which all operating components are supported and held together in
there proper functional relational ship.
Corrosive or high temperature applications may require the specific
qualities that make stainless steel and non-ferrous metals well adapted to this service. In
general, any type of troughs that can be fabricated of mild steel also be made of stainless or
aluminum, brass, bronze, copper, monumental, nickel, etc.
FLANDED TROUGH
By forming the top flanges integrally with the trough sides from a single
steel sheet, ad equal strength and rigidity is obtained without super fulvous bulk or wait.
ANGLE FLANGED TROUGH
This trough is identical in construction to the flanged trough; accept that top
flanges are obtained by securely welding structural steel angles to the troughs.
RECTANGULAR TROUGH:
C.O.E. & T.,Akola 28
Design & Fabrication of Screw Conveyor
Rectangular trough may be made from a single steel sheet or with sides and
bottom of separate pieces, dependent on size and gauge of metal .It is frequently used to
handle abrasive materials capable of forming a layer of material on the bottom of the
trough. The material thus move on it's self, protecting the trough from undo wear.
We select single flanged trough.
TROUGH COVERS
The functions of trough cover are
(1) The personal are not protected by the Inaccessible location of moving parts of a
conveyor, to protect personal from contact with the rotating screw and
(2) To keep the conveyed material and dust within the conveyor housing, and to exclude
foreign materials there from. The degree to which the cover feeds the trough depends
upon circumstances attending the particular conveying problem and so thus the means
of securing the cover.
Since our project is for demonstration purpose we use a transparent acrylic
trough cover so that the different components are usually visible for better understanding
and fitted to the trough with the help of bolts.
We provide clearance of 3 mm bet-screw flight and trough.
Therefore radius = screw diameter /2+3=62.5+3=65.5mm
We select trough end thickness= 3m
We take a clearance of 25mm between trough cover plates and screw flight.
Therefore depth=25=screw diameter
Trough thickness = clearance.
= 25 +125 + 3 + 3 = 156mm
C.O.E. & T.,Akola 29
Design & Fabrication of Screw Conveyor
Normally the trough cover plate is of 5.8mm thickness material mild steel.
Based on experience the spacing between the boards provided on troughs is 150mm.
"INLET AND OULET"
We select square inlet and outlet points.
Normally the dimensions of this square is,
= Pitch +2 *clearance
= 125 +2 *3 = 131mm.
The inlet and outlet centers are at a distance of 0.75m and are pitch distance
away from respective ends.
3.7 SCREW CONVEYORS END THRUST
Most screw conveyor can be design with little thought given t<thrust as the
thrust force in an ordinary screw conveyor is moderate and commonly used screw
conveyor drives will accommodate thrust in either direction. However, in screw feeders
with long inlet opening and in screws used to compressed materials (either by design or by
accident when discharge openings are plugged). Thrust can be very severe. Sever thrust
forces can strip the flights from the pipe, stall the drive, and result in sheared coupling
bolts or fractured couplings and shafts.
The thrust force is a function of the weight of the product in the trough, the
angle of the flight helix, and the products friction factor.
Due to the clearance between the flighting o.d and inside of the trough, the
product mostly slights on itself and therefore the friction factor for the product on itself
is more significant than the fraction then the friction factor of the product sliding on steel.
For screw feeders the thrust forces results both from reaction of product
friction on the trough and also from the reaction of the product friction against itself in the
C.O.E. & T.,Akola 30
Design & Fabrication of Screw Conveyor
area over the screw at the inlet. For short conveyor it is not significant but for the long
conveyor it is not significant but for long conveyors it is usually not advisable to have the
screw section in compression, as at every connection there could be a side force that would
tend to cock the connection of the coupling to the pipe.
The most common dives in use today are so called screw conveyor drives
that are adaptation of shaft mounted reduces. This includes drive shafts that are secured in
the reducer so to take thrust in either direction and transfer the thrust force to one of the
hollow shaft bearings of the reducer.
Usually when selecting the end bearing for screw conveyor that has a large
amount of thrust it may be necessary to consider the overhung load in using a roller chain
device.
3.8 CONVEYOR SCREW DEFLECTION
Deflections of conveyor screw of standard length are not usually a problem.
However, if longer than standard sections of screw are to be used, without intermediate
hangers bearings, care should be taken to prevent the screw flights from contacting the
trough because of excessive deflection.
Very often using a conveyor screw section with the large diameter pipe can
solve a problem.
3.9 SELECTION OF END- SHAFT AND BEARING.
BEARING SELECTION
Bearing are deep grove ball bearing 2 bearings of dia.20mm are selected i.e.
2 bearings of SKF6204 are selected based on shaft dia. = 20mm & checked as follows:
Assuming life required =10,000hrs.
C.O.E. & T.,Akola 31
Design & Fabrication of Screw Conveyor
Assuming 90% probability of survival.
Life in million revolution = L*60*N/1000000
= 10,000*60*52.5/100000
= 31.5mR
Bearing load for one bearing P = (x*Fr+Y*Fa) S
Neglecting 'Fa' as there is no axial load coming on to bearing theoretically. Therefore, P =
x*Fr*S
= 1*140*1.2 (Fr=Ra=Rb)
= 168N
= 16.8kg.
Assuming 50% overloading P~25kg
Dynamic capacity C = (L10)*P
= (31.5)*25
=78.95
~80kg.
Bearing of SKF6204 are selected be reducing shaft dia from 37mm 20mm.
For deep groove ball bearing SKF6204
Dynamic capacity =1000kgf (from psg 4.13)
& Max permissible in rpm= 1600rpm(from psg 4.13)
In our case dynamic capacity =80kgf & Rpm-52.5
Therefore bearing is very well safe.
CHECK THE DESIGN
C.O.E. & T.,Akola 32
Design & Fabrication of Screw Conveyor
CALCULATION OF VARIOUS LOADS ACTING ON BEARINGS (SKF6204)
1) Load due to cement
Cement bulk density=1040.4kg/metre cube.
Let V=volume in which cement loads acts down wards (i.e. on center pipe) i.e. cement of
upper part of trough volume acts on shaft.
V= [(width of trough * height of end plate above center pipe)] - [0.5*volume of hollow
pipe)]
Where do >> outer dia of central E.R.W. PIPE
V = 0.140 * 0.070 -3.142[0.0424*0.0424/2]*l
= 9.094* *1040.4=9.461kg
WI~10kg = 100N.
This is for one-meter pipe. Length. Of pipe.
This may be considered as UDL (universally distributed load) over 1 meter
i.e. 100 Newton per meter.
2) Load due to flights
Volume of one flight = 3.142/4 *(Do*Do - Di*Di)*thickness
= 3.142/4*(0.142*0.142-0.060*0.060)*0.0125
= 1.626*
Where Do, Di >> dist O.D & I.D from which flights are made .
Mass of flight = 8*density *vol.
W2 = 8*7800*1.628*
=1.0147kg.
Therefore weight acting 1 .1 kg/m.
= 11 kg/m.
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Design & Fabrication of Screw Conveyor
Adding l& 2
Total udl. on 1 m length =l11 N/m
Taking 50% overload to be on safe side
udl=1.5*111=166.5N/m.
Load fluctuations may come due to dynamic loading
Therefore further increasing udl.
Say udl =200N/m.
3) Load due to each solid shaft
a. Shaft of dia 20mm
W3 = volume* density
= [3.142*(0.020)*(0.020)*0.075]*7800
= 0.184kg.
= 2 Newton. (Approx)
Assuming load acts on bearing
b. Shaft of diameter 57mm
W4 = 3.142[(0.037)*(0.037)*0.050]*7800
= 0.41kg = 5N.
Taking more load for safer design
Let, load due to shaft of dia 20mm be 5N & load due to shaft of dia 20mm be 10N.
4) Load due to hollow pipe (udl)
w5 = volume * density
= [(do*do-di*di)*length]*7800
= [(0.0424*0.0424-0.037*0.037)*l]*7800
C.O.E. & T.,Akola 34
Design & Fabrication of Screw Conveyor
= 2.6266 kg.
Taking 60% overload to be on safer side.
W5 = 5kg.(approx)
Considering this also as a udl of 50 Newton/ meter
Total UDL = 200 + 50 = 250 Newton/meter
Distance of the center from LH bearing = 0.525
Therefore, maximum bending moment.
M = 140*0.525-10*(0.525-0.05)-[((0.525-0.025)^2)/2)*10
M = 67.5 Nm.
M = [3142/32*(d2^4 –dl^4)d211 *fs
67500 = [3.142/32 (42.4^4 – 37^4)/42.4]*fs
fs = 21.47 N/mm^2
The value of shear stress is less than 50N/mm^2
HENCE THE DESIGN IS SAFE.
FINDING THE DEFLECTION OF HOLLOW PIPE
Taking only hollow beam & span 1m (approx.)
Deflection = (5*W*L^4)/(384*E*I)
Deflection = (5*0.25*1000^4)/(384*2.1*100000*66.65*1000)
Deflection = 0 232573 mm
This is quite low deflection, hence tolerable.
HENCE THE DESIGN IS SAFE.
C.O.E. & T.,Akola 35
Design & Fabrication of Screw Conveyor
INSTALLATON OPERATION AND
MAINTAINANCE
4.1 GENERAL
Because of variations in length and installation conditions, screw conveyors
are usually complete units, shop assembled and match marked before shipping, or as
individual components to be aligned and assembled in the field. When the manufacturer
engineers the conveyor, complete specification drawings are generally famished.
Manufacturers instructions should be followed.
SAFETY
Conveyor assemblies or components must be installed and operated in such
a manner as to comply with the occasional safety and health act, all state and local
regulations, and the Indian standard institute safety code.
4.2 GENRAL SAFETY PRECAUTIONS
Taking in to consideration all of the physical aspects of the installation, any
or all of the following safeguards may be required to protect the operators and those
working in the immediate area of the conveyor.
1. COVERS AND GRATINGS use rugged gratings in all open loadings areas and the solid
covers in other areas. Covers guards gratings at the inlet points must be such that the
screws cannot injure personnel.
2. LOCKOUT AND TAG-OUT. A formalized lock-out or tag-out procedure must be
followed when a conveyor is stopped for maintenance or repairs and before conveyors or
guards are removed .all safety devices, conveyors and guards shall be replaced before
starting equipment for normal operation.
C.O.E. & T.,Akola 36
Design & Fabrication of Screw Conveyor
3.GUARDS. For protection of the operator and other persons in the working area,
purchaser should provide guards for all exposed equipment such as drives, gears, shafts,
couplings.
NOTE : DO NOT STEP OR WALK ON CONVEYOR COVERS OR GRATING OR
POWER TRANSMISSION GUARDS.
4.3 PRECAUTION FOR HAZARDOUS OPERATIONS
Standard screws conveyors are not equipped to operate; under conditions
are not equipped to operate under conditions, which may be hazardous, nor with hazardous
materials. The manufacturer should be consulted if there is any indication that a hazardous
condition or material is involved. Several situations may create these conditions. A few of
the more common follow:
Hazardous conditions
Where the product area is under pressure or vacuum, or the trough is
provided with jackets for heating or cooling, special precautions are required. Standard
components are not designed for this service.
C.O.E. & T.,Akola 37
Design & Fabrication of Screw Conveyor
Hazardous materials
These may be explosive, flammable, toxic, noxious, etc. special provisions
for safety are required -Do not use standard components.
4.4 ELECTRICAL
Conveyor components manufacturers generally do not provide electrical
equipment to control the conveyors. In the conveyor installation, the purchaser must used
with any conveyor installation, the purchaser must use equipment confirming to the
national electrical code, and the other local or national codes.
All devices such as those listed below are intended the safety and/or overall
performance of the equipment. Consideration must be given to their use as secondary
safety devices as they might present a false sense of security to the operator or other
personnel safety precaution around the equipment .in no case are they intended to replace
or reduce the importance of lock-Out and Tag-out procedures, the primary.
1. Overload protection. Devices such as shear pins, torque limiters, etc to shut off power
whenever operation of conveyor is stopped as result of excessive material, foreign
objects, excessively large pumps, etc.
2. No-speed protection. Devices such as zero speed switches to shut off power in the
event of any incident that might cause conveyor to cease operating.
3. safety shut off switch with power lockout provision at conveyor drive.
4. emergency stop switches readily accessible wherever required.
5. electrical interlocking to shut down feeding conveyors whenever a receiving
conveyor stops.
C.O.E. & T.,Akola 38
Design & Fabrication of Screw Conveyor
6. signal devices to warn personnel of imminent start up of conveyor, especially if started
from a remote location.
7. special enclosures for, motors and controls, in hazardous atmospheric conditions.
4.5 INSTALLATION
1. All assemblies and parts are checked against the bill of materials.
2. place the screw inside the trough .Fix the trough end plates with bolts provided . A thin
lining of rubber is placed between the trough and it's end plates. Do not tighten the
bolts. Align trough bottom and centerline, and then tighten the bolts.
3. now assemble bearings inside the Plummer blocks
4. installing stuffing box on the screw shaft.
5. slide the Plummer block on the screw shaft and rest it on the base plate using bolts.
Ensure that the Plummer block slides smoothly over the plate.
6. fix the handle on the screw shaft.
7. place the acrylic cover on the trough and fix it using bolts.
4.6 OPERATION
Only persons familiar with the following precautions should be permitted to
operate the conveyor. The operator should thoroughly understand these instructions before
attempting to use the conveyor.
WARNING
Guards, access doors, and covers must be securely fastened before operating
this equipment. Lock out power before removing guards, access doors and covers. Failure
to follow these instructions may result in personal injury or Property damage.
C.O.E. & T.,Akola 39
Design & Fabrication of Screw Conveyor
1. Always operate the conveyor in the accordance with these instructions.
2. Do not place hands or feet in the conveyor opening.
3. Never walk on conveyor covers or gratings.
4. Do not put conveyor to any other use than for which it is designed.
5. Avoid poking or prodding material in the conveyor with bar or stick inserted through
openings.
6. Always have a clear view of conveyor loading and unloading points and all safety
devices.
7. Keep area around conveyor drive and control free of debris and obstacles.
8. NEVER operate conveyor without covers, grating, guards and other safety devices in
position.
C.O.E. & T.,Akola 40
Design & Fabrication of Screw Conveyor
INITIAL STARTUP (WITHOUT MATERIAL)
1. REMEMBER - Screw conveyor drive is generally shipped without oil. Add oil to drive
in accordance with manufacturers instructions.
2. MAKE SURE before initial start-up that conveyor is empty, that end bearings and
lubricated, and that all cover guards, safety equipments are properly installed.
3. If conveyor is part of a material handling system, make certain that conveyor controls
are interlocked electrically with those for other units in system.
4. Check direction of rotation of each unit to assure correct flow of material.
5. Operate conveyor while empty for several hours, making a continuous check for
heating of bearings, misalignment of drive, and noisy operation, if any of these occur
proceed as follows:
a. If anti-friction bearings are used, check supply of lubricant. Either too much or too less
lubricant can cause high operating temperatures.
b. Lock out power supply and check for misalignment in trough ends, screws and
hangers. Loosen and readjust or shim as necessary. If unable to eliminate
misalignment, check parts for possible damage during shipment.
c. Check assembly & mounting bolts.
INITIAL STARTUP (WITH MATERIALS)
1. Check that the conveyor discharge is clear before feeding material.
2. Increase feed rate gradually until rated capacity is reached.
3. Stop & start conveyor several times & allow to operate for several hours.
4. Shut off conveyor and lock out power supply. Remove covers and check coupling bolts
for tightness. Check hanger bearings, realign if necessary and retighten mounting bolts.
5. Replace covers.
C.O.E. & T.,Akola 41
Design & Fabrication of Screw Conveyor
EXTENDED SHUT DOWN
If conveyor is to be inoperative for a long period of time, it is advisable to
permit it to operate for a period of time after the feed has been cutoff in order to discharge
as much as possible from the trough. However there is a nominal clearance of 1/2
"between the screw & trough and this procedure will allow amount of material to remain in
the trough. Therefore if the material is corrosive or hygroscopic or has a tendency to
harden or setup, the trough should be cleaned completely after the4 conveyor is shut down
and power locked out.
4.7 MAINTENANCE
Establish routine period inspection of the entire conveyer to insure
continuous maximum operating performance. Keep the area around the conveyor drive
clean and free of obstacle to provide easy access and to avoid interference with the
function of the conveyor or drive.
1. lock out power to motor before doing any maintenance work preferably with a padlock
on control.
2. Do not remove padlock from control nor operate conveyor until covers and guards are
securely in place.
SERVICING OF CONVEYOR COMPONENTS
In most cases this involves removing an unserviceable part and installing a
replacement. The installation procedures are outlined in the section entitled ERECTION.
Specific instructions for the removal of various conveyer components follows.
C.O.E. & T.,Akola 42
Design & Fabrication of Screw Conveyor
CONVENTIONAL CONVEYOR SCREWS
To remove a section or sections of conventional conveyor screw from end
opposite the drive. Remove trough end, conveyor screw sections, coupling shafts, and
hangers until damaged or worn section is removed.
To reassemble, follow above steps in reverse order.
Sections of conventional conveyor screw equipped with slights flight
couplings may be removed individually with a minimum of disturbance of adjacent
sections.
COUPLINGS
Replace couplings when wear exceeds 1/8 inch. Replace coupling bolts
when excessive wear causes play.
LUBRICATION
Frequency of lubrication will depend on factors such as the nature of
application, bearing materials and operating conditions. Weekly inspection and lubrication
is advisable until sufficient experience permits establishment of a longer interval.
DRIVE.
Lubricate the drive following manufacturers instructions provided for the
speed for the speed reducer and other drive components requiring lubrication speed
reducers are generally shipped without oil.
BALL OR ROLLER BEARINGS.
Ball and roller bearings may be furnished in trough ends. Lubricate in
accordance with manufactures instructions provided.
C.O.E. & T.,Akola 43
Design & Fabrication of Screw Conveyor
CONCLUSION
This project titled "DESIGN AND FABRICATION OF A SCREW
CONVEYOR " explains the design and manufacturing of a screw conveyor, basic
application of which is to transport cement for a distance of one meter horizontally.
This project gives detailed information about the various factors that me
taken into account before designing and selecting different components, which form a part
of screw conveyor, it also gives the details of be assembly as per the standard procedure
employed in the industry.
Moving ahead from designing stage this project gives a detailed count of
the fabrication of the screw conveyor, its installation and its maintenance for a better
performance and a longer life.
Finally the project highlights the major advantages of the screw conveyor
and its superiority over other conveyor designs.
C.O.E. & T.,Akola 44
Design & Fabrication of Screw Conveyor
BIBLIOGRAPHY
1. Link Belt - Screw conveyor & screw feeder
FMC Corporation - Material Handling Equipment division
MISSISSIPPI-38801
2. Stephen-Adamson
Material Handling Equipment Division, Chicago.
3. American Society of Mechanical Engg.
3. Material Handling Hand Book.
4. www.theshathigears.com
5. www.rediff.com
6. www.google.com
7. www.howstuffworks.com
8. www.altavista.com
C.O.E. & T.,Akola 45
Design & Fabrication of Screw Conveyor
The Proposed Estimation of Our Project is as follows
Particulars Qty Amount
1) Screw pipe, Flight 01 1075.00
2) Shaft (in 2 parts) 02 0200.00
3) Bearings 02 0175.00
4) Hub 02 0100.00
5) Cover plate, Side plate 02 0200.00
6) Trough 01 0225.00
7) Coupling 02 0300.00
8) Reduction Gear Box 01 2475.00
Total 4750.00
C.O.E. & T.,Akola 46
Design & Fabrication of Screw Conveyor
APPENDIX
This gives a program in C++, which calculates the various proportions for the screw conveyor for
the given input capacity desired. The program also gives the assembly of screw conveyor in pictorial view.
//THIS PROGRAMME GIVES THE DESIGN OF A SCREW CONVEYOR AND
//GIVES ITS VARIOUS PROPORTIONS WITH SCEMATIC DIAGRAM.
# include<stdio.h>#include<conio.h>#include<graphics.h>#include<math.h>#include<iostream.h>#include<stdlib.h>void draw();void design();void start();void main(){ start(); design(); draw();}void start(){ int gd=DETECT,gm; initgraph(&gd,&gm,"C:\\TC\\bgi"); setbkcolor(BLACK); setcolor(2); settextstyle(7,HORIZ_DIR,3); outtextxy(180,20,"WELCOME TO PROJECT"); outtextxy(280,50,"OF"); outtextxy(0,80," DESIGN AND FABRICATION OF SCREW CONVEYOR"); settextstyle(7,HORIZ_DIR,2); outtextxy(30,240," ....SUBMITTED BY...."); outtextxy(30,260,"1)SHASHANK KAPLE"); outtextxy(30,280,"2)ANANT NAGNE"); outtextxy(30,300,"3)RAKESH RODE"); outtextxy(30,320,"4)SHAHID FAIYAZ"); outtextxy(30,340,"5)VINOD JAYLE"); outtextxy(30,360,"6)DEBASIS BARUA"); outtextxy(200,180,"*GUIDED BY...."); outtextxy(220,200,"PROF. P.R. WADNERKAR"); outtextxy(200,140,"*H.O.D....."); outtextxy(220,160,"PROF. C.V. DESHMUKH"); outtextxy(0,380,"***********************************************************************"); outtextxy(0,220,"***********************************************************************"); outtextxy(0,120,"***********************************************************************");
C.O.E. & T.,Akola 47
Design & Fabrication of Screw Conveyor
outtextxy(0,10,"************************************************************************"); outtextxy(5,400,"PRESS ENTER <---- FOR FURTHER CALCULATION"); getch(); closegraph(); } void design() { clrscr(); int inc,cd,j,d,t,f,n2,did,did1; f=1; long n1,fs; float d1,d2,n,p,c,x,y,l,rr,c1,cdf,hp,bhp,c2,dod,pid; float stdpitch[]={100,125,160,200,250,315,355,400,450,500,560,630}; clrscr(); cout<<"ENTER THE CAPACITY DESIRED IN TONS PER HOUR:"<<endl; cin>>c; c=c*35.28/1.0404; cout<<"ASSUMING CENTRE TO CENTRE DISTANCE=1000 MM:"<<endl; cd=1000*1; cout<<"SELECT THE SCREW DIAMETER FROM FOLLOWING STANDARD SIZES:"<<endl; cout<<"6,9,10,12,14,15,16,20:"<<endl; cin>>inc; ////////////////////////////////////////////////////////////////////// switch(inc) {
case 6: { cout<<"YOU HAVE SELECTED A 6 INCH CONVEYOR FOR WHICH FROM
GRAPH"; n=c*6.66*0.1; cout<<",FOR THE GIVEN CAPACITY , THE VALUE OF RPM IS:"<<n; cout<<endl; break; }
case 9: { cout<<"YOU HAVE SELECTED A 9 INCH CONVEYOR FOR WHICH FROM
GRAPH"; n=c*1.75*0.1; cout<<",FOR THE GIVEN CAPACITY , THE VALUE OF RPM IS:"<<n; cout<<endl; break; }
case 10: { cout<<"YOU HAVE SELECTED A 10 INCH CONVEYOR FOR WHICH
FROM GRAPH"; n=c*1.25*0.1; cout<<",FOR THE GIVEN CAPACITY , THE VALUE OF RPM IS:"<<n; cout<<endl; break; }
case 12: { cout<<"YOU HAVE SELECTED A 12 INCH CONVEYOR FOR WHICH
C.O.E. & T.,Akola 48
Design & Fabrication of Screw Conveyor
FROM GRAPH"; n=c*0.08; cout<<",FOR THE GIVEN CAPACITY , THE VALUE OF RPM IS:"<<n; cout<<endl; break; }
case 14: { cout<<"YOU HAVE SELECTED A 14 INCH CONVEYOR FOR WHICH
FROM GRAPH"; n=c*14/30; cout<<",FOR THE GIVEN CAPACITY , THE VALUE OF RPM IS:"<<n; cout<<endl; break; }
case 15: { cout<<"YOU HAVE SELECTED A 15 INCH CONVEYOR FOR WHICH
FROM GRAPH"; n=c/30; cout<<",FOR THE GIVEN CAPACITY , THE VALUE OF RPM IS:"<<n; cout<<endl; break; }
case 16: { cout<<"YOU HAVE SELECTED A 16 INCH CONVEYOR FOR WHICH
FROM GRAPH"; n=c/45; cout<<",FOR THE GIVEN CAPACITY , THE VALUE OF RPM IS:"<<n; cout<<endl; break; }
case 20: { cout<<"YOU HAVE SELECTED A 20 INCH CONVEYOR FOR WHICH
FROM GRAPH"; n=c*0.017; cout<<",FOR THE GIVEN CAPACITY , THE VALUE OF RPM IS:"<<n; cout<<endl; break; } default: { cout<<"YOU HAVE NOT SELECTED A STANDARD VALUE "<<endl; break; }
} cout<<endl; /////////////////////////////////////// cout<<"MATERIAL CLASS MEANS FOLLOWING:"<<endl; cout<<"A-VERY FINE ,100MESH:"<<endl; cout<<"2-FREE FLOWING ANGLE:"<<endl; cout<<"7-MILD ABRASIVE:"<<endl; cout<<"Y-AERATED AND BECOMES FLUID:"<<endl;
C.O.E. & T.,Akola 49
Design & Fabrication of Screw Conveyor
d2=25.5*inc;//CONVERTING INCHES INTO MM cout<<"SCREW DIAMETER="<<d2<<endl; cout<<"MODIFY THE SCREW DIAMETER TO STANDAED VALUE
WHICH IS EQUAL TO PITCH"<<endl;for(j=0;j<12;j++){cout<<stdpitch[j]<<endl;}cout<<endl;cout<<"SO ,GIVE THE STANDARD VALUE WHICH YOU HAVE
SELECTED NOW (FROM TABLE):"<<endl;cin>>p;
///////////////////////////////////////////////////////// cout<<"CALCULATING THE DIAMETER OF HOLLOW SHAFT WHICH IS
LOCATED AT THE CENTER:"<<endl;
cout<<"*************************************************************************"<<endl; cout<<"c=3.142/4*(d2*d2-d1*d1)*p*k*BD*RPM*60"<<endl; x=((d2*d2)/(1000*1000))-((4*c)/(3.142*p*0.001*0.3*1.0404*n*60)); d1=sqrt(x); d1=d1*25.5; cout<<"HOLLOW SHAFT OUTSIDE DIAMETER="<<d1; cout<<endl; cout<<"'k'IS 0.3 FOR 30%LOADING "<<endl; cout<<endl; cout<<"'d1' IS SHAFT DIAMETER"<<endl; cout<<endl; cout<<"'BD' is BULK DENSITY"<<endl; cout<<endl; cout<<"WE SELECT AN ELECTRIC RESISTANCE
WELDED(E.R.W.)PIPE"<<endl; cout<<"TYPE :'C' CLASS BECAUSE IT HAS MORE THICKNESS,WHICH
WILL AVOID BENDING"<<endl; cout<<"SELECT STD VALUE OF THE PIPE O.D. WITH THE HELP OF
FOLLOWING TABLE:"<<endl; cout<<"PIPE O.D. * THICKNESS "<<endl; cout<<"33.7 * 2.5 "<<endl; cout<<"42.4 * 2.5 "<<endl; cout<<"48.3 * 3.5 "<<endl; cout<<"60.3 * 4.0 "<<endl; cout<<"76.1 * 5.0 "<<endl; cout<<"88.9 * 5.0 "<<endl; cout<<"114.3 * 5.5 "<<endl; cout<<"139.7 * 6.0 "<<endl; cout<<"152.4 * 7.0 "<<endl;
cout<<"#######################################################"<<endl; cout<<endl; cout<<"NOW , GIVE THE VALUE OF STANDARD PIPE O.D. FROM ABOVE
TABLE:"; cin>>y/1000; cout<<endl; d1=y; cout<<"SELECT THE STANDARD WALL THICKNESS FROM THE
TABLE:"; cout<<endl;
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Design & Fabrication of Screw Conveyor
cin>>t; pid=d1-2*t; cout<<"PIPE INSIDE DIAMETER IS"<<pid; cout<<endl; l=2*p+cd; cout<<"CONVEYOR OVERALL LENGTH WOULD BE ="<<l; cout<<endl; /////////////////////////////////// cout<<"ESTIMATING THE HORSE-POWER REQUIRED:"<<endl; cout<<"***********************************"<<endl; cout<<"IN ORDER TO CALCULATE THE POWER REQUIRED WE SHALL
ASSUME 100% LOADING"<<endl; c1=3.142/4*(d2*d2-d1*d1)*0.125*l*n*60; cout<<"CAPACITY AT 100% LOADING ="<<c1; cout<<endl; cout<<"CONVERTING INTO LBS/HOUR"<<endl; c1=c1*2205; cout<<"SO,THE VALUE OF CAPACITY IN LBS/HOUR IS ="<<c1; cout<<endl; cout<<"H.P. =l*(c1*F)/100000"<<endl; cout<<"'l' IS THE LENGTH OF CONVEYOR IN FEET"<<endl; cout<<"'f' IS THE H.P. FACTOR=1 FOR PORTLAND CEMENT"<<endl; cdf=0.003268*cd;//cross section distance in feet hp=(cdf*c1*f)/100000; cout<<"H.P. IS ="<<hp; bhp=hp/0.75; cout<<"REQUIRED MOTOR H.P. IS BHP="<<bhp; clrscr(); ///////////////////////////////// cout<<"MOTOR SELECTION"; cout<<endl; cout<<"***************"; cout<<endl; cout<<"FOLLOWING TABLE SHOWS STANDARD HP,FRAME SIZE
& RATED RPM OF MOTORS"<<endl; cout<<"FRAME H.P. RATED RPM"<<endl; cout<<"#######################################"<<endl; cout<<"56 0.125 1320 "<<endl; cout<<"56 0.16 1340 "<<endl; cout<<"63 0.25 1350 "<<endl; cout<<"71 0.33 1370 "<<endl; cout<<"71 0.50 1380 "<<endl; cout<<"80 0.75 1400 "<<endl; cout<<"80 1.00 1400 "<<endl; cout<<"90S 1.50 1410 "<<endl; cout<<"112 5 1440 "<<endl; cout<<"132 7.5 1440 "<<endl; cout<<"132 10 1450 "<<endl; cout<<"160 15 1450 "<<endl; cout<<"160 20 1455 "<<endl; cout<<"#######################################"<<endl; cout<<"SELECT STANDARD FRAME SIZE FROM ABOVE TABLE: "<<endl; cin>>fs; cout<<"FRAME SIZE SELECTED ="<<fs;
cout<<endl;
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cout<<"ENTER THE SELECTED RPM FROM TABLE ONLY:";
cin>>n1; rr=n1/n; cout<<endl<<"REDUCTION RATIO IS ="<<rr; cout<<endl; cout<<"WE USE THE GEAR BOX TO REDUCE THE SPEED FROM "<<n1; cout<<" RPM TO "<<n; cout<<" RPM "; cout<<endl;
getch(); /////////////////////// cout<<"FLIGHT SELECTION"<<endl; cout<<"****************"<<endl; cout<<"FLIGHT IS MADE FROM A HOLLOW DISC WHICH IS RADIALLY
CUT AND PULLED TO FORM A FLIGHT"<<endl; cout<<"SEVERA SUCH FLIGHT ARE BUTT WELDED TO FORM THE
COMPLETE SCREW"<<endl; cout<<"THE PROPORTIONS FOR THIS HOLLOW DISC ARE AS FOLLOW
:"<<endl; did1=(d1*d1*3.142+0.125*p)/3.142; did=did1^(1/2); cout<<"DISC INSIDE DIAMETER="<<did; cout<<endl; cout<<"CONSTANT =SCREW DIAMETER+PIPE O.D."<<endl; c2=d1+d2; cout<<endl; cout<<"CONSTANT="<<c2; dod=c2+did; cout<<endl; cout<<"DISC OUTSIDE DIAMETER="<<dod; cout<<endl; n2=1000/p; cout<<"NUMBER OF FLIGHTS="<<n2; cout<<endl; cout<<"WE TAKE ONE HANDED FLIGHT"<<endl; cout<<"THEREFORE NUMBER OF RIGHT HANDED FLIGHT="<<(n2-1); cout<<"THICKNESS OF FLIGHT :2 TO 5 MM"<<endl; cout<<"MATERIAL OF FLIGHT IS MILD STEEL"<<endl; /*getch();*/
/////////////////////////////// cout<<"TROUGH SELECTION:"<<endl; cout<<"*****************"<<endl; cout<<"WE SELECT A FLANGED TROUGH."<<endl; cout<<"THE TOP FLANGES ARE FORMED INTEGRALLY FROM A SINGLE
STEEL SHEET."<<endl; cout<<"WE SELECT SQUARE INLET AND OUTLET POINTS ON THE
TROUGH."<<endl; ///////////////////////////////////////////////////
cout<<"BEARING SELECTION:"<<endl; cout<<"*******************"<<endl; cout<<"DEPENDING UPON THE END SHAFT DAIMETER'SKF' BEARINGS
MAY BE SELECTED."<<endl; cout<<"UNTILL THIS WE HAVE BEEN DISCUSSING THE DESIGN"<<endl; cout<<"NOW WE SWITCH ON TO THE GRAPHICS FUCTION WHICH
WILL GIVE US THE VIEW OF THE CONVEYOR."<<endl;
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getch(); } void draw() { int gd=DETECT,gm;
float i,j,k=0,l=0,midy,x=35,y,od,id,t; float sd,sd1; char sdc[15];
clrscr(); cout<<"ENTER THE SCREW DIAMETER SELECTED IN INCHES(in betwee 1 to 50) :"<<endl; cin>>sd1; cout<<"ENTER THE STANDARD SHAFT DIAMETER SELECTED IN mm :"<<endl; cin>>od; cout<<"ENTER THE STANDARD THICKNESS IN mm :"<<endl; cin>>t; sd= (sd1* 25.5)/4; initgraph(&gd,&gm,"C:\\TC\\bgi"); setbkcolor(BLACK);
setcolor(WHITE); midy=getmaxy()/2; line(x,midy-5,x+39,midy-5); line(x,midy+5,x+39,midy+5); rectangle(x+35,midy-(sd+12),x+535,midy+(sd+12)); line(x+35,midy-(sd+14),x+35,midy+(sd+22+25)); line(x+35,midy-(sd+14),x+17,midy-(sd+14)); line(x+17,midy-(sd+14),x+17,midy-(sd+10)); line(x+17,midy-(sd+10),x+32,midy-(sd+10)); line(x+32,midy-(sd+10),x+32,midy+(sd+19+25)); line(x+32,midy+(sd+19+25),x+17,midy+(sd+19+25)); line(x+17,midy+(sd+19+25),x+17,midy+(sd+22+22)); line(x+17,midy+(sd+22+25),x+35,midy+(sd+22+25));
line(x+535,midy-(sd+14),x+535,midy+(sd+22+25)); line(x+535,midy-(sd+14),x+535,midy+(sd+14)); line(x+535,midy-(sd+14),x+535,midy-(sd+10)); line(x+535,midy-(sd+10),x+538,midy-(sd+10)); line(x+538,midy-(sd+10),x+538,midy+(sd+19+25)); line(x+538,midy+(sd+19+25),x+535,midy+(sd+19+25)); line(x+553,midy+(sd+19+25),x+535,midy+(sd+22+25)); line(x+553,midy+(sd+22+25),x+535,midy+(sd+22+25));
line(x+531,midy-5,x+570,midy-5); line(x+531,midy+5,x+570,midy-5); line(x+17,midy-(sd+14),x+535,midy-(sd+14)); line(x+32+27,midy-(sd+12),x+32+27,midy-(sd+35)); line(x+32+97,midy-(sd+12),x+32+97,midy-(sd+35)); rectangle(x+32+12,midy-(sd+37),x+32+112,midy-(sd+35)); rectangle(x+32+12,midy-(sd+18),x+32+112,midy-(sd+20));
rectangle(x+17,midy-(sd+17),x+553,midy-(sd+14)); line(x+531-27,midy+(sd+12),x+531-27,midy+(sd+15+12)); line(x+531-97,midy+(sd+12),x+531-97,midy+(sd+15+12)); rectangle(x+531-12,midy+(sd+12),x+531-112,midy+(sd+14)); rectangle(x+531-12,midy+(sd+12+15),x+531-112,midy+(sd+12+17));
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setlinestyle(2,1,1); line(x+32+17,midy-(sd+43),x+32+17,midy-(sd+29)); line(x+32+107,midy-(sd+43),x+32+107,midy-(sd+29)); line(x+32+17,midy-(sd+26),x+32+17,midy-(sd+11)); line(x+32+107,midy-(sd+26),x+32+107,midy-(sd+11));
line(x+531-17,midy+(sd+8),x+531-17,midy+(sd+20)); line(x+531-107,midy+(sd+8),x+531-107,midy+(sd+20)); line(x+531-17,midy+(sd+22),x+531-17,midy+(sd+34)); line(x+531-107,midy+(sd+22),x+531-107,midy+(sd+34)); id=(od-4*t)/4; od=od/4; rectangle(x+531,midy-id,x+506,midy+id); rectangle(x+39,midy-id,x+64,midy+id); line(x+64,midy-id,x+506,midy-id); line(x+64,midy+id,x+506,midy+id); line(x+38,midy-od,x+531,midy-od); line(x+38,midy+od,x+531,midy+od);
rectangle(x+32,midy-13,x+24,midy-5); rectangle(x+32,midy+13,x+24,midy+5); line(x+32,midy-13,x+24,midy-5); line(x+24,midy-13,x+32,midy-5); line(x+32,midy+13,x+24,midy+5); line(x+24,midy+13,x+32,midy+5);
rectangle(x+546,midy-13,x+538,midy-5); rectangle(x+546,midy+13,x+538,midy+5); line(x+546,midy-13,x+538,midy-5); line(x+538,midy-13,x+546,midy-5); line(x+546,midy+13,x+538,midy+5); line(x+538,midy+13,x+546,midy+5); line(x+532-62,midy+sd,x+532-62,midy+(sd+35)); line(x+532-62,midy-(sd+37+35),x+532-62,midy-(sd+37+20)); line (x+532-62,midy-(sd+37+20),x+532-62,midy-(sd+37+15)); line(x+532-62,midy-(sd+37+15),x+532-62,midy-(sd+37)); line(x+532-62,midy-(sd+37),x+532-62,midy-(sd+37-5)); line(x+532-62,midy-(sd+37-5),x+532-62,midy-(sd+37-20)); line(x+532-62,midy-(sd+37-20),x+532-62,midy-(sd+37-35)); line(x+32+62,midy-(sd+37+35),x+32+62,midy-sd); i=sd/3; line(x+38,midy-od,x+38+i,midy-sd); line(x+38+i,midy-sd,x+38+4*i,midy+sd); l=4; for(i=sd/3;k<=510-(4*i);k=l*i) { line(x+38+l*i,midy+sd,x+38+(l+3)*i,midy-sd); line(x+38+(l+3)*i,midy-sd,x+38+(l+6)*i,midy+sd); l=l+6; } if(sd1>5) { setcolor(0); setfillstyle(0,1); fillellipse(580,midy,4,4); fillellipse(587,midy,4,4);
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fillellipse(592,midy,4,4); fillellipse(595,midy-26,20,20); fillellipse(592,midy+25,15,19); fillellipse(595,midy+51,20,20); fillellipse(615,midy+50,35,35); } setcolor(WHITE); if(sd1==10) line(x+38+22*i,midy+sd,x+531,midy+od); if(sd1==8) line(x+38+28*i,midy+sd,x+531,midy+od); arc(x+2,midy-2,90,270,3); arc(x,midy+2,90,360,3); arc(x+568,midy-2,270,90,3); arc(x+571,midy+2,90,360,3); setlinestyle(0,1,1); rectangle(x+12,midy-21,x+32,midy-5); rectangle(x+12,midy+21,x+32,midy+5); rectangle(x+538,midy-21,x+558,midy-5); rectangle(x+538,midy+21,x+558,midy+5); setcolor(2); settextstyle(1,HORIZ_DIR,3); outtextxy(120,20,"ASSEMBLY OF SCREW CONVEYOR");
line(x+39,midy+(sd+22+35),x+531,midy+(sd+22+35)); line(x+39,midy+(sd+22+30),x+39,midy+(sd+22+40)); line(x+531,midy+(sd+22+30),x+531,midy+(sd+22+38)); settextstyle(2,HORIZ_DIR,4); outtextxy(x+40,midy+(sd+22+29),"<"); outtextxy(x+527,midy+(sd+22+29),">"); line(x-25,midy-sd,x+38+i,midy-sd); line(x-25,midy+sd,x+38+4*i,midy+sd); line(x-15,midy-sd,x-15,midy+sd); line(x+32+62,midy-(sd+37+15),x+531-62,midy-(sd+37+15)); settextstyle(2,HORIZ_DIR,5); outtextxy(x+230,midy+(sd+60),"OVERALL LENGTH"); outtextxy(x+250,midy+(sd+40),"1000 mm"); outtextxy(x+200,midy-(sd+70),"CENTRE TO CENTRE LENGTH"); outtextxy(x+250,midy-(sd+50),"750 mm"); outtextxy(x+32+68,midy-(sd+37+23),"<"); outtextxy(x+531-65,midy-(sd+37+23),">"); settextstyle(2,VERT_DIR,4); outtextxy(x-35,midy-30,"SCREW DIA."); sprintf(sdc," %3.2f mm ",4*sd); outtextxy(x-15,midy-30,sdc); getch(); closegraph(); }
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OUTPUT FOR THE PROGRAM
TRIAL 1ENTER THE CAPACITY DESIRED IN TPH:2.654ASSUMING CENTER TO CENTER DISTANCE =1000 MM:SELECT THE SCREW DIA FROM FOLLOWING STD SIZES6,9,10,12,14,15,16,20:6YOU HAVE SELECTED A 6 INCH CONVEYOR FOR WHICH FROM GRAPH, FORTHE GIVEN CAPACITY,THE VALUE OF RPM IS: 59.938156
MATERIAL CLASS MEANS FOLLOWING:A-VERY FINE, 100MESH2-FREE FLOWING ANGLE7-MILD ABRASIVEY- AERATES AND BECOMES FLUIDSCREW DIAMETER = 153MODIFY THE SCREW DIAMETER TO THE STANDARD VALUE, WHICH ARE GIVEN BELOW.100125160200250315355400450500560630SO, GIVE THE STANDARD VALUE WHICH YOU HAVE SELECTED NOW:160CALCULATING THE DIA. OF HOLLOW SHAFT WHICH IS LOCATED AT THE CENTRE:*************************************************************************c=3.142/4*(d2*d2-dl*dl)*p*k*BD*RPM*60ENTER THE PITCHNORMALLY FOR DIA < 400 MM DIA = PITCH125HOLLOW SHAFT O.D.=38.97863'k' IS 0.3 FOR 30 % LOADING'dl' IS SHAFT DIA.'BD'IS THE BULK DENSITY
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WE SELECT AN ELECTRIC RESISTANCE WELDED (E.R.W.) PIPETYPE. 'C'CLASS BECAUSE IT HAS MORE THICKNESS, WHICH WILL AVOIDBENDINGSELECT STD VALUE OF THE PIPE O.D. WITH THE HELP OF FOLLOWINGTABLE:PIPE O.D. * THICKNESS#############################################33.7 * 2.542.4 * 2.548.3 * 3.560.3 * 476.1 * 588.9 * 5114.3 * 5.5139.7 * 6152.4 * 7############################################
NOW, GIVE THE VALUE OF STANDARD PIPE O.D. FROM ABOVE TABLE:
NOW, GIVE THE VALUE OF STANDARD PIPE O.D. FROM ABOVE TABLE:42.4
SELECT STANDARD WALL THICKNESS FROM THE TABLE:2.5
PIPE INSIDE DIAMETER IS37.400002CONVEYOR OVERALL LENGTH WOULD BE = 1250ESTIMATING THE HORSE POWER REQUIRED:************************************IN ORDER TO CALCULATE THE POWER REQUIRED WE SHALL ASSUME 100% LOADINGCAPACITY AT 100% LOADING = 8.404825e+09CONVERTING INTO LBS/HOUR SO,THE VALUE OF CAPACITY IN LBS/HOUR IS = 1.853264e+13H.P.=l*(cl*F)/l00000‘1’IS THE LENGTH OF CONVEYOR IN FEET‘f’ IS THE H.P FACTOR =l FOR PORTLAND CEMENT
MOTOR SELECTION***************FOLLOWING TABLE SHOWS STANDARD HP,FRAME SIZE & RATED RPM OFMOTORSFRAME HP RATED RPM#############################56 0.125 132056 0.16 1340
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63 0.25 135071 0.33 137071 0.5 138080 0.75 140080 1 140090S 1.5 1410112M 5 1440132S 7.5 1440132M 10 1450160M 15 1450160M 20 1455##################################SELECT STANDARD FRAME SIZE FROM ABOVE TABLE:
56FRAME SIZE SELECTED = 56ENTER THE SELECTED RPM:1340REDUCTION RATIO IS = 22WE USE THE GEAR BOX TO REDUCE THE SPEED FROM 1340 RPM TO59.938156 RPM
FLIGHT SELECTION******************FLIGHT IS MADE FROM A HOLLOW DISC WHICH IS RADIALLY CUT ANDPULLED TO FORM A FLIGHTSEVERAL SUCH FLIGHTS ARE BUTT WELDED TO FORM THE COMPLETESCREW.THE PROPORTIONS FOR THIS HOLLOW DISC ARE AS FOLLOWS:DISC I.D. = 103CONSTANT-SCREW DIA+PIPE O.D.CONSTANT = 202.399994DISC O.D. = 305.399994NUMBER OF FLIGHTS = 8WE TAKE ONE HANDED FLIGHTTHEREFORE NUMBER OF RIGHT HANDED FLIGHTS = 7THICKNESS OFFLIGHTS: 2 TO 5 MMMATERIAL OF FLIGHT IS M.S.
TROUGH SELECTION:*******************WE SELECT A FLANGED TROUGH.THE TOP FLANGES ARE FORMED INTEGRALLY FROM A SINGLE STEEL SHEET.WE SELECT SQUARE INLET & OUTLET POINTS ON THE TROUGH.BEARING SELECTION:*****************
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DEPENDING UPON THE END SHAFT DIAMETER 'SKF' BEARINGS MAY BE SELECTED.UNTILL THIS WE HAVE BEEN DISCUSSING THE DESIGN.NOW WE SWITCH ON TO THE GRAPHICS FUNCTION WHICH WILL GIVE US THE VIEW OF THE CONVEYOR.ENTER THE SCREW DIA SELECTED IN INCHES:6ENTER THE STANDARD SHAFT DIA SELECTED IN MM:42.4ENTER THE STANDARD THICKNES IN MM:2.5
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TABLE NO. 1
MATERIAL CLASS DESCRIPTION
Size Material characteristics ClassVery fine – 100 mesh and under
Fine – ½ inch mesh and under
Granular – ½ inch and under
Lumpy – containing lumps over ½ inch
Irregular – being fibrous, stringy, or the like
A
B
C
D
HFlowability Very free flowing – angle of repose up to 30º
Free flowing – angle of repose 30º to 45º
Sluggish – angle of repose 45º and up
1
2
3Abrasiveness Nonabrasive
Mildly abrasive
Very abrasive
6
7
8Other
characteristics
Contaminable, affecting use or saleability
Hygroscopic
Highly corrosive
Mildly corrosive
Gives off dust or flames harmful to life
Contains explosive dust
Degradable, affecting use or saleability
Very light and fluffy
Interlocks or mols to resist digging
Aerates and becomes fluid
Packs under pressure
K
L
N
P
R
S
T
W
X
Y
Z
TABLE 2
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