Training file on bucket elevator

ON

SUBMITTED BY:-

Sandeep Kumar Mechanical,7th Semster Roll no. 2108424 Doon Valley Institute of Engg. & Tech.

SANDEEP KUMAR MECH.,ROLL NO -2108424 1

DOON VALLEY INSTITUTE OF ENGG. & TECH

CONTENTS

Acknowledgement

Profile of the company

Introduction to Bucket Elevator

Working of Bucket Elevator

Parts of Bucket Elevator

Accessories

Types of Bucket Elevators

Design of Bucket Elevator

Maintenance of Bucket Elevator

Preventive Measures

Scope

Conclusion

References



COMPANY PROFILE

Infrastructure:We have sufficient area available for our manufacturing activities. All machineries required for heavy fabrication and machining are present including Bending Machines, Hydraulic Press, Plasma Welding, Argon Arc Welding, Boring Machines, Milling Machines, etc. We have Handling facilities such as Overhead Cranes of 5 and 3 Tonne capacity, Chain Pulley Block etc.

Work Force:We have experienced and skilled technicians for various activities like cutting, welding, gas cutting, fitting, machining, drawing, and designing. We nurture their skill and talent by exposing them to the latest technique.

Quality Assurance:As internal inspection, the material is inspected for inputs and out puts physically, dimensionally and visually. The critical items are subject to laboratory testing for mechanical and chemical compositions before putting to process line. Further, stage wise inspection of sub assembly and assembly is carried out. Wherever possible, No Load running is carried out before dispatch for additional satisfaction of working.

Guarantee and Assurance:All our equipments are guaranteed against manufacturing defects for 12 months. However our services are available any time as the need arises. It is our assurance that you will find us and our products most reliable.

Name of Owner : Mr. DEVI CHARAN

Establishment Year : 2009

Primary Business Type : Designers & Manufacturer Exporters

Annual Sales : 1-4Crore

Market Cover : Domestic

Product We Offer : Belt Conveyor, Chain Conveyor, Slat Conveyor, Screw Conveyor, Roller Conveyor, Bucket Elevator, Feeder, Gates & Accessories & Components



ELEVATORS

Vertical continuous bucket elevator: (1) belt, (2) bucket, (3) drive pulley, (4) backstop, (5) drive, (6) discharge spout, (7) takeup shaft, (8) loading spout

A bucket elevator consists of buckets attached to an endless chain or belt that revolves around a bottom pulley allowing buckets to fill with material and a top pulley where the bucket discharges their material. Bucket elevators are the most used systems for vertical transport of bulk, dry and liquid materials. Bucket elevator designed with various options of height, speed and constructive details depending on the type of material to be transported.



WORKING OF BUCKET ELEVATOR

A bucket elevator, also called a grain leg, is a mechanism for hauling flowable bulk materials (most often grain or fertilizer) vertically. It consists of:

1. Buckets to contain the material;2. A belt to carry the buckets and transmit the pull;3. Means to drive the belt;4. Accessories for loading the buckets or picking up the material, for receiving

the discharged material, for maintaining the belt tension and for enclosing and protecting the elevator.

A bucket elevator can elevate a variety of bulk materials from light to heavy and from fine to large lumps. A centrifugal discharge elevator may be vertical or inclined. Vertical elevators depend entirely on the action of centrifugal force to get the material into the discharge chute and must be run at speeds relatively high. Inclined elevators with buckets spaced apart or set close together may have the discharge chute set partly under the head pulley. Since they don't depend entirely on the centrifugal force to put the material into the chute, the speed may be relatively lower.

Nearly all centrifugal discharge elevators have spaced buckets with rounded bottoms. They pick up their load from a boot, a pit, or a pile of material at the foot pulley. The buckets can be also triangular in cross section and set close to on the belt with little or no clearance between them. This is a continuous bucket elevator. Its main use is to carry difficult materials at slow speed. Early bucket elevators used a flat chain with small, steel buckets attached every few inches. Current construction uses a rubber belt with plastic buckets. Pulleys several feet in diameter are used at the top and bottom. The top pulley is driven by an electric motor. The bucket elevator is the enabling technology that permitted the construction of grain elevators. A diverter at the top of the elevator allows the grain to be sent to the chosen bin.

A similar device with flat steps is occasionally used as an elevator for humans, e.g., for employees in parking garages. (This sort of elevator is generally considered too dangerous to allow use by the public.)



A typical bucket elevator assembly

Parts of Bucket Elevator

Elevator assembly mainly consist of head section, boot section, elevator legs, belt or chain and buckets.

Elevator Head Section



It is topmost portion of elevator. It consist of steel housing which supports the drive pulley/sprocket, throat plate, strut board and motor.

Elevator heads should be of the proper shape and size with smooth contours. The discharge side of the head should be shaped so that material thrown from the buckets will not be deflected into the downleg. The throat should be considerably below the head shaft to catch the materials that are slow leaving the buckets. Lagging on the elevator head pulley is needed in pulling heavy loads. Proper lagging increases coefficient of friction between pulley and belt. The strut board at a 45 angle under the head pulley to prevent accumulation of grain and dust. The throat plate should be easily replaceable so that it can be changed after it wear out.The head shaft must be heavy enough to resist bending and to provide the required torque carrying capacity.

Head Section of Vertical Bucket Elevator



Rubber lagged Head/Drive Pulley

CALCULATE HEAD PULLEY DIAMETER:A simplifying assumption is made that the throwcommences at the top of the head pulley. At this point thecentrifugal force and gravity force are balanced.Centrifugal force =m.v2.cosβ/r Where , m = mass in kg v = belt speed in m/s r = pulley radius in m Gravity force = m× gWhere , g = gravity constant 9.8 m/sec2.Putting both forces equal to each other :-cosβ = 1 at top dead centre.Therefore r=v2/g and diameter (d) = 2 × r

Elevator Boot SectionThe boot is the bottom portion of elevator. It receives the material to be

elevated and contain lower belt pulley or sprocket. Bucket elevator provide in a boot section a belt take up device for adjusting shaft center distances to tighten the belt as required and to provide temporary slack for installation or maintenance work.. A manual screw type takeup is most often used. On tall, heavy capacity elevator an automatic take up(gravity type) used. This provides the correct belt tension at all times.



Elevator Boot Section



Front View

Boot Pulley

Grain entry may be on either side of the boot. However, when grain enter on the downleg, additional power is required for the "dredging effect" of pulling the bucket through the grain in the boot. Cleanout included on both sides of the boot to permit fast and easy cleaning. They are usually placed at an angle and should slide easily.

Elevator Legs or Casing Elevator legs are constructed as all welded, bolted or riveted units. It forms

the structure for supporting the head, service platforms, ladder and cage, etc. while also providing a dust proof and waterproof enclosure for the elevator belt or chain and buckets. They are manufactured in standard lenght of 2.4 m, but could be manufactured in any lenght desired. Casing may be of single or dual design. The service door with removable panels is provided on upleg casing to allow access for servicing the belt or chains and bucket.



Casing with Window

Bucket

Buckets are made of different materials such as steel, plastics and come in different shapes and sizes depending on requirements. The buckets are uniform, smooth and placed with a distance that allow for efficient filling of bucket and clean discharge. Normally a Norway bolt or ovalhead type of bolt is used to attach the buckets to the belts. Also spacers are provided in between bucket and belt to prevent accumulation of material.

Plastics Bucket Metal Bucket

Belt and Belt Splicing This the component that carries the filled buckets from the boot to the head.

Belt used for bucket elevator should have high tensile strenght. Also belt should be wear resistance, low elongation, good stability, resistance of water, chemical, heat etc. and having a long service life.



Four types of belts are mainly used for bucket elevators 1) Duck, 2) Balata, 3) Stitched canvas, 4) Solid woven cotton

Any of these belts may be treated with special preparations or covered with natural or synthetic rubber. The standard cotton duck belt differs from ordinary sail duck or canvas in that the strength of the warp (lengthwise threads) is considerably greater than that of the weft

(Crosswise threads). Duck for belts is ordinarily graded as 28 oz, 32 oz, etc., according to the weight of a piece 91 cm long in the warp and 107 cm wide. Balata belts are made of waterproofed cotton duck belts held together by balata, a tree gum which is stronger than rubber at ordinary temperature but not so elastic. Stitched canvas belts are multi-ply duck belts whose plies have been stitched together and made waterproof. Solid woven belts are woven to thickness in looms and are not of multiple constructions. They are used primarily for power transmission.

Belt SplicingType of belt splice depends on the thickness of the belt and the severity of

service. There are three types of splices normally used with elevator belts. Each is described below.1) Lap Joint Splice

This is the easiest splicing method. On a lap joint splice, the lap extends a distance of three to five buckets and is sucured by same bolts that hold the buckets.



This splice is not suitable for belts more than seven plies thick because it is too stiff to pass tightly over the pulleys.

2) Butt-strap Joint SpliceThe butt-strap joint splice may be used on belts of eight or more plies.

3) Clamp Joint Splice/Mechanical SpliceThis is superior splice. For the clamp joint, belt ends must be bend outwards

at right angles to form a ridge that is then bolted between a bar clamp.



Drive Unit

Drive Assembly Sprocket

Taper Bush

Accessories

Service Platform For Head and Ladder

Service platform provide work area for performing routine inspection and maintenance on the elevator head section, particularly the drive mechanism. Ladder provide access to the service platforms.



Discharge Transition and Y Section

A transition is used to adapt a square outlet to round spouting or a distributor. Y section divide the flow of material from one way into two way and vice versa.

One Way Transition Two Way Transition



Types of Bucket Elevator

According To Type of Discharge Used

A. Centrifugal Discharge B. Positive discharge

C. Continuous Discharge

1. Centrifugal Discharge Elevator

It is most common type of discharge elevator. It is having great travelling speeds in the range of 1 m/s to 2 m/s. Speeds can be relatively high for fairly dense materials, but must be lowered considerably for low bulk density materials to prevent fanning action.This type of elevator will handle almost any free flowing small lump material. This type of discharge is most commonly used for grains.

2. Positive(gravity) Discharge Elevator

It is having lower travelling speeds in the range of 0.5 to 1 m/s. Positive discharge elevator essentially same as centrifugal discharge units, except that the bucket are mounted on two strands of chain and are snubbed back under the head sprocket to invert them to allow positive discharge. This type of discharge especially used for material that are sticky or tend to pack.



3. Continuous(Direct Gravity) Discharge Elevator

This type of discharge elevator are generally used for larger lump materials or for materials too difficult to handle with centrifugal discharge elevator. In this type buckets are closely spaced and the back of the preceding one serves as discharge chute for the bucket that is dumping as it rounds the head pulley. Close bucket spacing reduces the speed at which the elevator operates.



Sr.No. BUCKET ELEVATOR CAPACITY (TPH)

3 5 7.5 10 20

1Head Pulley

L(mm)*D(mm) 140*152 180*202 215*280 215*280

270*420

2Head Pulley Shaft

L(mm)*D(mm) 360*25 410*40 475*40 475*40 560*45

3 UCP(Pillow Block Bearing) UCP 205 UCP 208 UCP 208 UCP

208 UCP 209

4Boot Pulley

L(mm)*D(mm) 150*150 150*200 215*270 215*270

270*400

5Boot Pulley Shaft

L(mm)*D(mm) 305*25 375*40 405*40 405*40 475*456 UCF(Flanged type

bearing) UCF 205 UCF 208 UCF 208 UCF 208

UCF 209

8 Gear Motor1 HP,

100 RPM

1.5 HP,

92 RPM

2 HP,

82 RPM

2 HP,

82 RPM

3 HP,

58 RPM

9 Bucket Size(Inch)

4” * 3.5” 4.5” * 4” 6” * 5” 6” * 5” 8” *5.25”

10Belt Size

W(mm)*T(mm) 130*10 178*10 195*10 195*10 230*10

11Bucket Spacing

(In mm) 180 125 210 160 180

12 Belt Speed(In m/s)

0.79 0.97 1.20 1.20 1.27

13 Casing Size(In mm)

180*180 210*180 260*210 260*21 315*225

Specification of Bucket Elevator



Where, L= Width of Pulley(mm)D= Diameter of Pulley(mm)W=Width of Belt(mm)T=Thickness of Belt(mm)

Sr.No.

Component Material Used

1 Bucket HDPE(High density polyethylene)

2 Belt Polyester or Nylon or both

3 Head MS Sheet of 3 mm

4 Boot MS Sheet of 3 mm

5 Casing MS Sheet of 1.6 mm

6 Casing Angle MS Sheet of 4 mm

7 Take up unit plate MS Sheet of 4 mm

8 Take up unit angle MS Sheet of 3 mm

9 Platform sheet MS Sheet of 5 mm

10 Platform angle MS Sheet of 3 mm

Design of Bucket Elevator

STEPS:

1. Overview of belt bucket elevators and their use.2. Determine throughput capacity.3. Determine belt speed and throw.4. Calculate motor power.5. Calculate top and bottom pulley shaft sizing.6. Drive arrangement and design.7. Shaft bearing and seal arrangement.8. Selecting elevator frame structural members.



9. Inlet and outlet chute design.10. Considerations in choosing panel materials.11. Selecting belts and buckets.12. Methods to take-up belt tension.13. Protection against bogging the buckets.14. Clean-out considerations.15. Dust extraction requirements.16. Installing the bucket elevator in place.17. Correct operation of belt bucket elevators.18. Maintenance of belt bucket elevators.

Necessary Product Parameters:.

1. Service Use.2. Material Name.3. Bulk Density in (Kg/m3)4. Maximum Duty (Kg/hr) or (m3/hr)5. Maximum Lump Size - Dimensions6. Average Size7. Percentage Of Lumps In Total8. Height of Product is to be raised (meters) and Angle Of Incline If Any. 9. Product Characteristics.

Abrasiveness Flowability (Free/Cohesive/Slug) Dampness. % Moisture Friability (Firm/Breaks/Powders) Particle Shape. Length/Size/Volume Temperature Of Product Which Is To Be Handle Angle Of Repose Corrosiveness

10. Operating Environment, Location and Conditions.11. Corrosive/Damp12. Service Required (Continuous/Intermittent).

SELECT BUCKET SIZE AND SPACING

The size and number of buckets is determined from the required throughput using an iteration process.Select the bucket from the range in the bucket supplier’s catalogue. Only 2/3 (67%) of the bucket.s design capacity is used in calculations.Centrifugal discharge conveys usually have a spacing between buckets that is 2 to 3 times the bucket projection, though the spacing can be greater for free-flowing products.

DETERMINE BELT SPEED



The bucket spacing times the number of buckets per second determines the required belt speed. The speed for centrifugal bucket elevators is usually in the range of 1 m/sto 2 m/s to insure the product throws into the chute at the head pulley.

SHAFT BEARING AND SEAL ARRANGEMENT

Once the shaft size is determined the bearing size can be selected. Follow the bearing manufacturer’s selection process for calculating the required bearing type and configuration for the equipment design life and service factors. Provide shaft seals for the bearing at the bearing housing and at the penetration into the elevator frame. The bearing must never be exposed to dust or dirt or moisture while in the production environment. Do everything necessary to protect the bearing.The bearing and seal suppliers can advise other ways of mounting and protecting the bearing. The best bearing arrangement design is to stand the bearing off the elevator frame with a clearance of around 25 mm.

ELEVATOR FRAME MEMBERS

The frame can either be made of an angle iron skeleton to which sheets of steel are attached or from sheets of steel pressed to the required rectangular shape that are flanged and bolted together. The thickness and lengths of section used in the frame must be sufficient to prevent buckling under load.

INLET AND DISCHARGE CHUTE DESIGN

The inlet chute should be designed to promote product flow and to minimise the amount of bucket drag. Preferably the product feed falls into the buckets as they come around the tail pulley without being dragged through a fully plugged boot.The feed chute should be made with a slightly smaller width than the buckets. It should be sufficiently steep to insure product always flows and does not build back. Test the product’s flow ability if possible by putting some on a bent sheet of the elevator chute material shaped into a .U. the same width as the chute. Tilt it to find the angle that produces flow. Insure there are no restrictions or protrusions into the chute that will cause the product to build back. The discharge chute size is known from the initial design. The angle at which it is set must meet the same criteria as the inlet.

HEAD AND TAIL PULLEY DESIGN

The head pulley dimensions have been determined. For simplicity the tail pulley should be to the same dimensions as the head pulley.

This will keep the buckets a constant distance off the elevator wall and product pick-up and simplify chute design and fabrication. Both head and tail pulleys



need to be crowned to centralise the belt and permit the belt to be tracked if it wanders. The crowning should be 2 degrees both left and right from the center of the drum. The head pulley could be rubber lagged if desired to increase the coefficient of friction and lower the belt tension. This will allow use of a lighter duty belt. But there is always the possibility the lagging will be stripped off during operation. It is best to design for a metal drum and use lagged pulleys only when detection of bogged conditions is installed. Ribbing can also be mounted on the top pulley to increase friction and act by .digging. into the rubber belt and producing a grabbing effect. The ribs are placed across the full axial length of the drum and positioned so that at least two ribs are always in contact with the belt. The rigs should be 3 mm to 4 mm high and contoured into the drum so as not to rip the belt. The tail pulley should be a self-cleaning design. This can be achieved in two ways. Constructing the pulley drum of 20 mm or 25 mm round bars of length wider than the belt. The bars are spaced around the end plates with gaps for product to fall through. Size the spacing between ribs with sufficient clearance for small product to fall through. Larger product will not fit through the gaps.- provide a twin opposed-cone hub with the cone.s base starting at the center and tapering to the shaft at the ends of the pulley. 20 mm or 25 mm round bars are welded to the outer rim of the cones and gussetted back to the cone wall forstiffness.

Maintenance of Bucket Elevator

A good maintenance program involves through general housekeeping, periodic inspection, adequate lubrication, and timely adjustment.

At frequent and regular intervals, perform these inspections:

A. Remove accumulated dirt from the motor, reducer housings and bearings:- 1. Motors depend upon unobstructed airflow over their housings for effective cooling. 2. Reducer gear cases must also be free of dirt for effective heat radiation. 3. While cleaning the reducer, check the reducer's lubricant level and condition. If the level is low, find and correct the leak. If the lubricant is dirty or shows signs of overheating, schedule a change of lubricant as soon as possible. 4. Listen carefully for a noisy motor, reducer, or bearings, or a rubbing belt. Any of these sounds can be a forewarning of overheating and fire or explosion.

B. Periodically remove the drop-down clean out door from each end of the boot:-



Cleanse the boot of all accumulated dirt and material to prevent vermin infestation and corrosion.

1. If the boot has a screw takeup, clean the acme takeup screws and nuts. Apply a protective coating of rust-inhibiting lubricant.

2. If the boot has a Posi-Guide gravity takeup, cleanse the polyethylene guide sleeves and the stainless steel guide shafts of accumulated dirt to insure that the pulley and weight box assembly move up and down freely.

C. Examine the head lining:- Extreme wear patterns can sometimes distort the discharge and if not corrected,wear completely through the head. Spouting may also wear through.

D. Check to make sure the pressure relief vents, if installed, on the head and/or legging are unobstructed. In order to provide relief, they must be free to blow out.

E. Inspect all ladders and platforms. Tighten any loose fasteners. Note any defective field welds and schedule immediate repair. Also schedule replacement for any damaged ladder sections, platform structural members, or floor grates. While inspecting platforms and ladders, be sure to examine guying cable brackets and /or bracing. Note any defects and schedule immediate repair.

F. Examine guying. Tighten any clamp fasteners, which are loose. If a cable is excessively slack, adjust turnbuckles to restore tension.

DANGER

Excessive guy cable tension will twist,bend and/or collapse the Elevator structure,causing severe injury or death.Maintain proper gu cable tension at all times.

PROBLEMS DURING BUCKET ELEVATOR WORKING

1) Dust Explosion(Deflagration)

Dust is generated at explosive concentrations during product feed and discharge due to the conveyance mechanics and material characteristics. As the buckets are loaded, move through the elevator, and unload, they disperse dust throughout the elevator. All that is needed for an explosion to occur is an ignition source. Ignition sources may include heat generated fire, welding, and sparks. Upon ignition, it can propagate throughout the elevator and to any areas connected to the elevator, causing secondary explosions.

A dust explosion results when finely divided combustible matter is dispersed in an atmosphere containing sufficient oxygen to permit combustion and a source of ignition of appropriate energy is present. Dust explosions have certain similarities to gas explosions, especially with regard to the chemical processes involved and in



cases where the particle size of the dust is less than 5 pm. However, there are significant differences which make the study of dust explosions extremely difficult. For a dust explosion to occur there must be a degree of turbulence, if only to disperse the dust into a suspension. Gas explosions can occur when the gas is in a quiescent state, the mixture being homogeneous and consisting of molecular size particles.

The suspensions of dusts encountered in dust explosions are, however, unlikely to be homogeneous, and would normally contain a range of concentrations of particles which are many orders of magnitude larger and heavier than gas molecules and which settle out of suspension due to gravity. A dust explosion involves such a high rate of combustion that individual particles and agglomerates are either consumed or oxidized. The combustion of carbon in organic material produces gaseous products which in themselves take up more space than the solids of the parent material. An expanding flame front will also result from the ignition of flammable gases produced by the decomposition of the dust. A dust explosion therefore requires more space because of the expansion of the hot gaseous products. In industrial plant, the heat released during a dust explosion is likely to exceed the natural rate of cooling and consequently an explosion would be accompanied by significant, and, in some cases, uncontrolled expansion effects. In an unconfined situation, there would be mainly localized flames and pressure effects. However, in the confined situations commonly found in plant handling particulate matter, the expansion effects are likely to be sufficient to burst through the confines of the plant equipment and/or piping.

Principle Factors Responsible for Dust Explosion:

1) The mixture of dust and air in the form of dust cloud, and mixture must be combustible.

2) The dust must be in suspension in the atmosphere which must contain sufficient oxygen to support combustion.

3) A source of ignition, such as hot surfaces, sparks and flames.4) Chemical reaction in a confined volume.

Explosive Limits:

Although a mixture of dust and air may burn with explosive violence, not all mixtures will do so. There is certain range of concentration of dust and air within which the mixture can explode, but mixture above and below this range cannot. The lowest concentration or lower explosive limit of grain and flour dusts may be assumed at (20 g/m3). Below this concentration dust do not explode because of the greater distance between the dust particles.

Heat is consumed by the air before it reaches the next particles. Only if the particles are close enough to each other is the combustion released in a chain reaction resulting in a dust explosion. The upper explosive limits not well defined,



but for flour dust 1000 g/m3 of air, and the other grain dusts 2000 g/m3 of air have been suggested. For still higher dust concentrations, the incomplete combustion of the dust particles retards the ignition and prevents the explosion. Particle size exerts a considerable influence on the explosiveness of the dust clouds. A reduction in size of particles means an increase in chance of ignition.

The moisture content of dust also influences the explosive limit. Dry dust tends to increase the flammability of dust particle and increase in chances of dust explosion.

Effects of a Dust Explosion

Bucket elevators are often subject to explosions and fires, and numerous examples have occurred in the past, particularly with vegetable dusts, for which these elevators have customarily been used. The design of these elevators leads to dust clouds being continuouslypresent during working, particularly at the head and the boot of the elevator. The buckets are also regularly subject to impact and the belt supporting the buckets can slip on the pulleys and generate frictional heat. As a result, a source of ignition and a dust suspension can be present simultaneously, causing explosion or fire. Modern high capacity elevators, with separate delivery and return legs, have a reduced risk because of the reduced volume per unit weight of dust conveyed. Grain and flour dusts can form explosive clouds and because explosions from such cloud some of the worst industrial accidents, it is necessary to draw public attention to this problem. Statistics of United States show that more than 50% of all explosions of combustible dusts have occurred in grain elevator and flour mills. Dust from wheat and other grains, as well as from flour, ignite and propagates flames readily because the source of heat required is relatively small. A dust explosion is accompanied by an extremely rapid rise of pressure. This is due to partly sudden evoluation of large volumes of gases produced by the chemical reaction, partly also to the local pressure rise caused by large amount of heat liberated.

Preventive Measures



1) Use of elevators should also be avoided for dusts known to be readily ignited by friction, e.g., sulphur.

2) Where the use of bucket elevators is unavoidable, their positioning should be carefully considered and regular maintenance is essential.

3) The elevators should be mounted outside the building, e.g., supported by an outside wall, and the intake and delivery points should preferably be isolated from the rest of the dust handling plant by means of chokes.

4) The elevator casing should be a fire resistant construction, sufficient to retain a fire, dust-tight and of sufficient strength not to rupture in the event of an explosion.

5) To meet the strength requirements, the casing should be provided either with automatic suppression or with explosion relief at the head and the boot, with vent areas calculated per NFPA 68. Long elevators, say more than 6 m (20 ft), may require additional relief at intervals along the casing to ensure that no point is too remote from a vent.

6) Particular care should be taken to ensure that flame burning dust, etc., discharged from the vents during an explosion cannot injure operators or damage nearby plant. Provision of ducting or deflectors over the vents may be required.

7) Where it is unavoidable to site a bucket elevator inside a building it is desirable for the internal pressure to be slightly below atmospheric to minimize leakage of dust.

Steps should be taken during designing of bucket elevators to minimize Dust Explosion

1) The provision of strong fixing for the buckets and strong bearings for all shafts, external to the casing, provided with detectors for overheating.

2) The main drive to the elevator should be external to the casing. 3) Belt slip within the casing can be detected by belt speed meters, and anit-

runback devices can also be installed. Development of friction within the casing can thereby be reduced.

4) Exhaust ventilation can be applied to the casing of bucket elevators which assists the removal of suspension of dust in air. These suspensions contain the dust fractions of smaller particle size, and ventilation would also give a slight negative pressure relative to atmosphere, within the casing. The ventilation system should be conducted to a dust collection unit in a safe area, and should be provided with explosion protection on a similar basis to that in the elevator casing itself.

5) Automatic explosion suppression can be used to protect bucket elevators when explosion relief is not practicable, often because of the situation of the elevator being located within a building.

6)Preventative strategies such as bearing temperature and belt alignment monitoring, metal detectors, or spark extinguishing systems are often employed. However, these methods only reduce the frequency of explosion.



7) The correct explosion protection strategy for any application depends on the explosion protection objectives of the responsible engineer, as well as regulatory, system and economic considerations. For simplicity, the most commonly applied protection strategies in three levels, from minimum to maximum protection are

1) Explosion Venting 2) Isolation 3) Suppression

1) Explosion Venting

Explosion venting is the most widely accepted and utilized explosion protection strategy. The most comprehensive guidance for venting of bucket elevators is outlined in the1999 edition of NFPA (National Fire Protection Association) 61, Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Products Facilities. This recently revised standard specifies vents to be located at intervals no greater than 20 ft. along the casing. Vents are to be installed on each side of the casing with a minimum area per vent equal to 2/3 the casing cross section. The head must also be vented with an area of 5 ft2 for every 100 ft3 of head volume.

Features and Benefits1) No moving parts so eliminate routine maintenance.2) Low cost and long service life.



Bucket Elevator with Explosion Venting

Explosion Venting with Explosion Isolation

The addition of Explosion Isolation will prevent flame propagation from the bucket elevator head or boot sections through the feed and discharge spout. NFPA 654, states that isolation devices shall be provided to prevent deflagration propagation between pieces of equipment connected by ductwork.

Features & Benefits:1) Prevents pressure piling and secondary explosions with interconnected

equipment.

Integrates with the process controls to enable remote and automated operation, process shut down and annunciation devices



Bucket Elevator with Explosion Venting and Chemical Isolation

2) Explosion Suppression

Explosion suppression is most widely used for bucket elevators located indoors. It provides additional protection benefits when compared to venting, or venting with isolation.

Features & Benefits:1) Extinguishes the flame within the bucket elevator, preventing fire damage.2) Compliance with NFPA regulation barring the venting of explosions indoors.

Explosion vents must be discharged to a safe location. Indoor applications are difficult to vent even with discharge ducts.



Bucket Elevator with Explosion Suppression and Chemical Isolation



3) Grain/Seed Damage In Vertical Bucket Elevator

New technologies have been introduced to increase crop productivity, but little work has been done to ensure quality control. Grain/seed damage is major cocern for producers. Grain/seed often is broken or otherwise physically damaged during postharvest handling operations. Much of this breakage is attributed to the equipment and methods used in the handling of grain. There is also evidence that grain characteristics, such as dryness and brittleness may affect the amount of breakage occuring during handling operation.

Generally, grain/seed mainly damage in bucket elevator during loading and unloading. During loading grain/seed from upleg side, grain/seed damage due to the impact between grains and bucket. when grain feed from downleg side then there is possibility of grain damage due to abrasion caused by dragging the grain from boot. During discharge of grain/seed in the head section, grain/seed undergo numerous impacts against the steel element of head units. The consequence of those impacts is broken grain/seed and cracks, as well as invisible internal damages. The mechanical damage decreases the commercial values of grain/seed.It also decreases the biological values of grain/seeds. The principle effect of the negative influence of the mechanical damage is the reduction of germination and yields. This is a serious problem for seed production.

Grain/seed damage in vertical bucket elevator mostly depend on operating parameter such as elevator speed. A properly designed bucket elevator driven at the correct speed will make a clean discharge directly into the discharge chute ensuring slight damage and little or no backlegging or downlegging.

If the head pully speed is too slow as shown in fig.A, the buckets spill the grain/seed into the legs. Grain/seed damage occurs when the grain/seed tumbled within the pulley and re-elevated.

Fig. A, Too Slow Speed Fig. B, Optimum Speed



Fig. C, Too Fast Speed

The optimum speed is shown in fig. B. At this speed the buckets fill and carry optimally and discharge the paddy directly into discharge chute. So there is no grain/seed spillage , no breakage. Theoretically, optimum speed of head pully is calculated by,

Where, RPM = Revolution per minute of head pulley R = Radius of the head pulley plus one-half the projection of the

bucket(m).If the head pulley speed is too fast as shown in fig. C, grain/seed is damaged

by rough and fast handling and the bucket will not fill properly. The bucket lose all their holding and discharge control. The result is inefficient operation as well as excessive breakage.

Grain/seed damage depends not only on the design characteristics of the elevator unit and it's operating parameters, but also on properies of grain/seed. Moisture content and Temperature are two important grain/seed properties that mostly influenced on grain/seed damage.

Previous reserch showed that moisture content and temperature of grain/seed significantly influenced the physical damages of grains/seeds. Physical damages increased with decreases in moisture content and temperature. The value of this basic information is important to engineers, food scientists and processors who may exploit these properties and find new uses.

Public attention has been attracted to the grain damage problem because damaged grain/seed lead to a lower price in the export market and is vulnerable to attack by insects and mold. But the literature indicates, there is little published work on studying the grain/seed damage in vertical bucket elevator.



If grain Industry is to reduce the amount of breakage caused by vertical bucket elevator, it needs reliable information on the causes and extent of grain breakage in vertical bucket elevator grain handling method now in use.

SCOPE

Bucket Elevators as name suggests lifts the material using bucket like containers. The Bucket Elevator is one more equipment that is most preferred when it comes to large capacity, more height and space restrictions.

The Bucket Elevators can handle variety of materials from powders, granules and lumps very effectively with small handling cost.

To suit various types of materials, various capacities and heights, there are different type of Bucket Elevators designed by engineers to increase ease, cost and effectiveness.

Mainly, There are Following Types Popularly Available :-

Belt Bucket Elevators using Belt as lifting element. Chain Bucket Elevators using Chain as lifting element.

Above Types are Further Divided in sub Types Such As :-

Centrifugal Discharge or Spaced Bucket Elevators. Continuous Discharge or Closed Spaced Bucket Elevators. Chain Bucket Elevator may be Single Strand or Double Strands Chain

Elevators.



Training file on bucket elevator

Documents