Basics of Conveyor

Design of belt conveyor

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1. Introduction to material handling equipments

In any industrial process, the product being manufactured passes through

various phases and it needs to be transported from place to place. This could involve

processes such as transporting of raw material to the machines and then shifting the

machines from one station to another station and finally to the store or warehouse. This

involves the use of material handling equipment. Simplest form of material handling is to

take material from one place to another place manually or with the help of worker. In large

production setups, where the production rates are high and the product to be handled is

such that manual transportation is not possible, sophisticated material handling systems

would be required.

Material handling system does not contribute directly to the product value,

but it adds to the cost of the product and is therefore sometimes is referred to as a

necessary evil. In fact, least handling is the best handling.

1.1 Basic objectives

These basic objectives that a material handling system should fulfill are:

1. Quick and precise pick-up of loads.

2. Quick and efficient transfer of load with planned time interval.

3. Transport of loads in planned quantity.

4. Safe transport without any damage.

5. Accuracy in delivering at the destination.

6. Automation with minimum human element.

7. Low initial and operational costs.

8. Simple and easy to maintain.

9. Safe operation.


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1.2 classifications

The material handling system, based on design and operational

characteristics can be broadly classified in to three groups as shown below:

Material handling equipment

I. Hoisting equipment

a) Pure hoisting equipment: jacks, winches, pulley blocks etc.

b) Cranes: EOT cranes, jib cranes etc.

c) Elevators: lift elevator, bucket elevator etc.

II. Conveying equipment: Belt conveyors, Chain conveyors, Screw conveyors, Apron

conveyors.

III. Surface and overhead equipment: Fork lifts, Trucks, Railway cars, Overhead mono-

rails.

1.3 Basic principles of selecting material handling system

1. Direction of load travel.

2. Length of load travel.

3. Properties and characteristics of the material being handled.

4. The rate of flow of material.

5. Kind of the production process.

6. Method of loading and unloading.

7. Existing layout and conditions of the work space.

8. Initial and operational costs.


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1.4 Some important material handling system

1.4.1 Conveyor • Belt Conveyor

• Apron Feeder

• Screw Conveyor

• Deep Pan Conveyor

• Drag Chain Conveyor

• Flexowell Conveyor

• Rope way Trolley

• Skip Charging System

1.4.2 Stacker Reclaimer

• Linear stacker Reclaimer

• Bridge type reclaimer

• Circular stacker cum reclaimer

• Bucket wheel stacker cum reclaimer

1.4.3 Wagon tippler

• Side discharge

• Central discharge

1.4.4 Vibro Screen

• Linear movement

• Circular movement


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2. Belt conveyors

A belt conveyor consists of an endless belt of a resilient material connected

between two pulleys and moved by rotating one of the pulleys through a drive unit

gearbox, which is connected to an electric motor. The driving pulley end is called as head

end, and the pulley is called as head pulley. Conversely, the other pulley is at the tail end

and is referred to as the tail pulley as shown in figure 2.

Material is conveyed by placing it on the belt, through a feeder. As the belt

rotates, the material is carried with it on the other end, where it is then dropped in the

discharge chute. It should be noted that discharge can be arranged at any point along the

run by means of special discharge devices.

As the belt rotates, due to the weight of the belt and the conveyed material,

the belt will sag. To support this sag, rollers called as idlers or idler pulleys are placed on

both sides (carrying side and the return side). Closely spaced idlers are placed at the

loading point, as there is some impact due to the falling material and overcrowding of the

material in this region. The belt is subjected to tension and it being from a resilient material

is prone to elongation. This reduces the tension in the belts. Reduction in tension causes

slackness of the belt on the pulleys resulting in slippage and loss in power. To

compensate for this, a tensioning device called as take-up arrangement is used.

Figure 2 Belt conveyor


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2.1 Types of belt conveyors

I. Channel Stringer Belt Conveyors

II. Truss Frame Conveyors

III. Slider Bed Belt Conveyors

IV. U-Trough Belt Conveyors

V. Flat Slide Belt Conveyors

VI. Totally Enclosed Belt Conveyors

VII. Custom engineering conveyors

2.2 Advantages of belt conveyor over other system

1. Can be operated over long distances over any kind of terrain.

2. Having high load carrying capacity and carry all kinds of loads.

3. Noiseless as compared to chain conveyors.

4. Much simpler to maintain and don’t require any major lubrication system like chain

conveyors.

5. Their reliability has been proved over a long period by its use in the industry.

6. Environmentally more acceptable.

7. Low labor and low energy requirements.

8. Unlike screw conveyors, belt conveyors can be easily used for performing

processes functions in a production line.


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2.3 Types of conveyor layout

(A) Horizontal

(B) Inclined upwards

(C) Inclined upwards – Horizontal

(D) Horizontal- Inclined upwards

(E) Horizontal Inclined Horizontal

(F) Inclined Horizontal Inclined


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2.4 Methods of loading and discharging

Consideration of assumption:

1) The material should be placed centrally on the belt.

2) The material should be fed in the direction of belt travel and at a speed as near as

possible to that of the belt.

A) Hopper based loading.

B) Processing unit based loading.

C) Loading from a preceding conveyor

i) Head and discharge

ii) Both end discharge

iii) Plow discharge

D) Tripper discharge

2.5 Major equipments of belt conveyor

i. Conveyor Belt

ii. Pulleys

iii. Idlers

iv. Coupling

v. Bearing

vi. Drive unit

vii. Electric motor

viii. Cleaning device


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2.6 Requirement of belt which is to be used in belt conveyor

2.6.1 High strength: The belt is subjected to tensile loads. It is also subjected to other

loads due to scrapers, plows. The material fed also creates an impact load on the belt. All

these conditions require the belt to have high strength.

2.6.2 Low self weight: The belt is continuously driven on the pulleys. The power

requirement to drive this belt is dependent on its weight.

2.6.3 High wear resistance: The belts are subjected to rough working conditions over a

long period of time. Besides this, scrapers, plows, and other cleaners further create wear

as they rub over the belt surface. The belt should thus have a high wear resistance to

survive in tough conditions.

2.6.4 Low elastic and permanent elongation: Any elongation in the belt reduces the

tension created in the belt. This would reduce the power transmitting capacity of the belt

should have a low elastic and permanent elongation.

2.6.5 Flexibility: They should have a good flexibility in the longitudinal and lateral planes.

In many cases, belts are made to run over many pulleys. The belt material should have the

necessary flexibility to mould over the idlers.

2.6.6 High resistance to ply separation: Belts are made from plies, which are bonded

with a rubber element. The bonding of the plies should be such that it doesn’t separate out

due to the repeated bending of the belt over the pulleys.

2.6.7 Low water absorption capability: Water if it gets absorbed by the belt increases

the weight of the belt. This would result in increased power consumption and reduced

conveying capability. It also gives more dimensional stability of the belt.


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2.6.8 Suitable working environmental conditions: Humidity, extreme heat or cold. The

belt material should be good enough to ensure that it works with optimum results under

such working environmental conditions.

2.7 Introduction to Troughed Belt Conveyor:

There are many possible variations in the design of a troughed belt conveyor

depending on the purpose and duty for which the conveyor is being designed. Similarly the

choice of individual components, features and accessories found on a conveyor should be

selected on the basis of the functions which have to be performed by the conveyor.

Troughed belt conveyors offer an efficient means of transporting materials in large

quantities (bulk), over distances ranging from a few meters to several kilometers,

continuously.

As will be seen below, troughed belt conveyors are only one of the types of

belt conveyors available in the market today however, the troughed belt conveyor takes

numerous forms and is used in many different applications with tremendous success.

It is important to draw a distinction between bulk handling of materials and

unit handling. The former refers to the transportation of particulate product(s) on a

continuous basis for example, the conveying of lumpy ore from a mine to a processing

plant or for transporting coal from a stockyard to a bunker above a crusher.

'Unit handling' on the other hand is generally described as discontinuous as

this involves the transportation of for example, packed boxes, filled bags of cement and so

forth.

A troughed belt conveyor as described in this refers to conveyors which are

used to convey product in bulk.


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2.7.1 Types of Troughed Belt Conveyors

The term 'troughed' belt conveyor originates from the form of the carrying belt within the

supporting idler sets and differentiates this conveyor from alternative bulk handling belt

conveyor types which include 'Pipe', 'Sicon', 'Sandwich', 'Pocket or Sidewall', 'Cablebelt',

'Square', 'U-con' conveyors, etc.

Examples of these different types of conveyors can be seen below.

The type of conveyor to be used in any particular application depends on a number of

factors including the conveying route, properties of the material to be transported,

environmental considerations etc.


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3. Conveyor belt

Conveyor belt is made up of compounds comprised of natural rubbers,

styrene-butadiene rubber blends of natural and other synthetics, nitriles, butyl, ethylene

propylene-based polymer, polychloroprene, polybutadiene, polyvinyl chloride, urethanes

and silicones, etc., Each of those elastomers has specific usefulness for various ranges of

properties and operating conditions from which manufacturers and end-users can choose.

Conveyor belting and its corresponding cover composition can be designated

as either

(1) General Purpose Belting, or

(2) Special Purpose Belting.

Each of these two broadly classified groups should be further defined depending upon the

specific end use.

3.1 Constructional details Conveyor belts generally are composed of three main components:

1) Carcass

2) Skims

3) Covers

Nylon or EP Belt

Steel cord


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3.1.1 Carcass: The reinforcement usually found on the inside of a conveyor belt is referred

to as the carcass. The functions of a carcass include the following:

• Provide the tensile strength necessary to move the loaded belt.

• Absorbs the impact of the impinging material being loaded on to the conveyor belt.

• Provide the bulk and lateral stiffness required for the load support.

• Belts are connected at the ends by splicing them with belt fasteners. The carcass

should provide the necessary strength to hold fasteners.

The carcass is normally rated by the manufacturer in terms of maximum

permissible operating tension. The carcass can of two major types:

1. Fabric ply type

2. Steel cord type

3.1.2 Skims:

The rubber, PVC or urethane between the plies is called as skim. Skims are

important contributors to internal belt adhesions, impact resistance and play a significant

role in determining the belt load support and trough ability. Improper skims can give

reverse effect too. It can lead to ply separation failure.


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3.1.3 Covers:

They are used in conveyor belt construction to protect the conveyor belt

carcass and also to extend its service life. Its desirable properties such as:

1) Textures.

2) Clean ability.

3) A specific co-efficient of friction.

4) A specific color.

5) Cut resistance.

6) Enhanced impact resistance.

7) Hardness.

8) Fire, oil and chemical resistance.


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4. Conveyor pulley The most commonly used conveyor pulley is the standard steel pulley. They

are manufactured in a wide range of sizes and consist of a continuous rim and two end

discs fitted with compression type hubs. In most wide faced conveyors pulleys,

intermediated stiffening discs are welded inside the rim. Outer pulleys available are self

cleaning wing types, which are used at the tail, take up or snub locations where materials

tends to built up on the pulley face, and magnetic types which are used to remove tramp

iron from the material being conveyed.

4.1 Conveyor Pulley Assemblies

Conveyor pulley construction has progressed from fabricated wood, through

cast iron, to present welded steel fabrication. Increased use of belt conveyor has led

industry away from custom-made pulleys to the development of standard steel pulleys with

universally accepted size range, construction similarities, and substantially uniform load

carrying capacity for use with belts having a carcass composed of plies or layers of fabric.

“Standard” drum and wing pulleys are suitable for these applications. The present trend,

however, is to use higher tonnage conveyor system with wider, stronger belts that

incorporate a carcass of either steel cables or high strength tensile members. In these

applications, where high tensions are encountered, the use of custom made “engineered”

welded steel pulleys is dictated.

4.2 Type of pulley based on fabrication

1. Typical welded steel pulley.

2. Fabricated curve crown pulley.

3. Spun end curve crown pulley.

4. Lagged welded steel pulley.

5. Welded steel pulley with grooved lagging.

6. Slide-lagged pulley.

7. Lagged wing pulley.

8. Fabricated wing type pulley.


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4.3 Type of pulley based on Function

1) Driving pulleys (Head and Tail pulleys)

2) Snub pulleys

3) Idlers

a) Carrying idlers.

b) Return idlers.

4.3.1 Head pulley

Normally the discharge end of the conveyor where the material is

transferred to another conveyor is called as the Head end and the pulley in this end is

called the head pulley. Most of the cases the drive is attached to the Head end of the

pulley and so head pulley will designed stronger and bigger when compared to others.

Head pulley is rubber lagged to increase the grip or friction between belt and Pulley.

Figure: Head Pulley


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4.3.2 Tail pulley

The pulley which is situated in the receiving end of the conveyor is called as tail

pulley. Some times Screw take-up will be situated in this pulley. This pulley is movable

when take up is kept in this. When belt takes a turn for take-up arrangement or for any

other drive arrangement this term comes. This acts as a support when belt takes a turn.

4.3.3 Snub pulley

Snub pulleys are incorporated into the design of a conveyor in order to increase the

angle of wrap of the belt on the drive pulley. The greater wrap angle on the pulley allows

more power to be introduced into the belt as is passes around the drive pulley without slip

occurring. In this way, fewer drives are needed on longer conveyors or conveyors with

high conveying loads.


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5. Idlers

The needs for Idlers are to give proper support to conveyor and also to the Material

to conveyor. An endless conveyor belt in a conveyor structure is dragged from the tail

pulley where material is loaded onto the conveyor, to the head pulley or drive pulley where

the material is discharged. Between a conveyors' tail and head pulleys, whether the

distance is a number of kilometers or merely a few meters, the carrying and return strand

belting is supported on idler sets. The rolls are fitted with antifriction bearings with seals

and with adequate lubrication packed into it. The friction between the roller surface and the

belt makes the rollers to rotate and thus material is transferred from one point to another

through belt conveyor.

Figure 5 The arrangement of Idlers in a Belt Conveyor


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5.1 Idlers serve following functions

1) Support the belt and the conveyed material on the upper run and the belt in the

lower run with minimum frictional resistance.

2) Spacing of the idlers is reduced near the loading point, so as to support the belt

due to impact of material in that region. This would prevent the belt from wearing

quickly

3) Idlers help in centering the belt and guiding it to the drive and snub pulleys.

5.2 Type of Idlers

5.2.1 Carrying idler sets

These idler sets support the carrying-side (top) conveyor belt onto which the material is

loaded and transported. In the loaded zone we have Impact carrying Idler which is

covered by rubber material to absorb the loads as the loading or transferring points. Also

we have Self-aligning carrying idlers to avoid the belt off tracking.

Figure 5.2.1 carrying idlers


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Carrying or troughing idler sets usually comprise between two and five individual

idler rolls mounted into a common base, which is attached to the conveyor structure. Each

idler roll in a ‘set’ comprises its own set of bearings, seals, shaft and outer shell.

5.2.2 Return idler sets

These idler sets support the return-side (bottom) conveyor belt which returns to the tail

pulley after having discharged product over the head pulley.

The diagram shown above is flat return type of Idler where only one flat roller is

used. The return idler may also have more than one idler arrangement which is called as

Garland type idlers.

Figure 5.2.2 return idlers


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Once the material has been discharged from the carrying belt, the return belt is

guided back to the tail pulley on return idlers. The impact, carrying and return idlers are

spaced at different intervals. On the carrying-side, the mass of the belt plus the load

conveyed is greater than the mass to be supported on the return-side and thus, for the

tension in the conveyor belt (by the take-up and induced by the drive unit), the idler

spacing is selected accordingly. This 'sag' in the belt between the carrying and return idler

sets must therefore be designed on the basis of the heaviest load that the conveyor is to

transport.


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6. Coupling

6.1 Function

As the name indicates Couplings are the device used to couple or connect

two shafts, this is one of the most important component of any drive system. Since it is

impossible to maintain co linearity between two shafts couplings are designed to provide

better flexibility to allow initial or running shaft misalignment.

Following are the type of flexible couplings.

• Fluid Coupling

• Chain Coupling

• Geared Coupling

• Grid coupling

• Universal coupling

6.1.1 Fluid Coupling

There are three essential parts to a fluid coupling: the driving (input) section

known as the impeller the driven (output) section known as the runner and the casing

which bolts to the impeller enclosing the runner providing an oil tight reservoir. Both

impeller and runner each represent half of a hollow torus with flat radial vanes. At the inner

circumference a conical baffle is attached to the impeller and a flat baffle is attached to the

runner.


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These components comprise the working circuit. The operation of the fluid

coupling requires mechanical input energy, normally provided by a standard NEMA B

electric motor which is connected to the impeller and casing. The runner, which has no

mechanical connection with the impeller, is directly connected to the driven load. A variety

of mechanical connections; couplings, sheaves, and hollow shaft mountings, are available

to provide the mounting configuration best suited to the application. Finally the fluid

coupling must be initially charged by removing the fill (fusible) plug and adding the

recommended amount of oil based on the required torque.

Starting

Standard NEMA B motors are recommended when using fluid couplings and

will start virtually unloaded. Since the motor is mechanically connected to the impeller and

casing, the low inertia of these components and the oil are the only loads imposed. As the

electric motor accelerates to running speed, the impeller begins to centrifugally pump oil to

the stationary runner. Transmission of oil is diffused by the conical impeller baffle,

producing a gradual increase in torque, allowing the motor to accelerate rapidly to full

running speed. When all the oil is pumped into the working circuit, continuous circulation of

oil will occur between the impeller and runner forming a flow path like a helical spring

formed.


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As soon as the transmitted torque reaches the value of the resisting torque,

the runner starts rotating and accelerates the driven load. The time required to reach full

speed is dependent on the inertia of the driven load, the resistive torque, and the torque

being transmitted by the fluid coupling.

Running

The operation of a fluid coupling is based on the hydrokinetic principles and

requires that the output speed be less than the input. This difference in speed is called

slip. Further this principle provides that the output torque is equivalent to the input torque,

since windage and oil circulation losses are negligible. Therefore, efficiency equals 100%

minus the percent of slip. At full running speed fluid couplings will normally slip between

1% and 4%. The oil circulation between the impeller and runner has formed a vortex at the

outside circumference of the working circuit and is no longer deflected by the conical

baffle.

Overload – Stall

Should the load torque increase, the slip will increase, which causes the

runner to drop in speed. The vortex of oil circulating between the impeller and runner will

expand to provide additional torque. The extent to which this vortex can expand is limited

by the flat baffle on the runner. Consequently fluid couplings provide inherent overload

protection.

If the increase in torque causes the oil in the working circuit to expand to the point of

contacting the baffle, the coupling will stall and slip will be 100%. This continuous high slip

generates heat and the oil temperature will rise unless the overload is removed. When the

temperature rises to the temperature limit of the fusible plug, the core of the plug will melt,

release oil from the coupling and effectively disconnect power to the output shaft.


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To prevent the loss of oil the use of a proximity cutout switch or thermal trip

plug and limit switch is recommended. Coupling guards must be designed to permit air

circulation for cooling and to protect when oil is released from fusible plug due to overload.

6.1.2 Chain Couplings

Chain couplings operate similarly to gear couplings. Sprockets on each shaft

end are connected by a roller chain.

Figure 6.1.2 chain coupling

The clearance between its components as well as the clearance in mating the

chain to the sprockets compensate for the misalignment. Loading is similar to that of

geared couplings. Packed Grease Lubricants is primarily used with this types of

construction, necessitating a sealed sprocket cover. A detachable pin or master link allows

removal of the chain.


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6.1.3 Gear Coupling

Gear couplings compensate for misalignment via the clearance between gear teeth.

Figure 6.1.3 Gear Couplings

Shaft-mounted external gear teeth on both shafts mate with internal gear

teeth on a housing that contains a lubricant. Other designs mount external teeth on only

one shaft, mating with internal teeth mounted to the other shaft. Acceleration or

deceleration can result in impacts between gear teeth due to backlash from the clearance

being taken up on opposite sides of gear teeth. Misalignment will result in sliding relative

motion across mating teeth as they pass through each revolution.


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6.1.4 Grid couplings

External grid couplings use a corrugated steel grid that bends to compensate

for loading induced by misalignment.

Figure 6.1.4 Grid Coupling

Grooved discs attached to the ends of each shaft house the grid, which

transmits torque between them. Low amplitude sliding motion develops between the grid

and grooves as the grid deforms under load, widening in some locations and narrowing in

others over each revolution.


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6.1.5 Universal Coupling

Universal joints are used for maximum allowable misalignment up to 20 to 30

degrees, depending upon the specific design. They are used extensively for the drive

shafts of vehicles to allow the wheels to move with the suspension system. Universal joints

use a four-spindled component called the spider to connect two shafts terminating in

yokes or knuckles at right angles.

Figure 6.1.5 Universal Joint

Each of the four spider journals is supported by a bearing or bushing contained in one of

the knuckles, which allow articulation. In some cases, greater articulation can decrease

wear rates by allowing more complete development of a lubricating film.


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7. Bearing

As we all know, Bearings are used to give support the shaft of the roller or

idle pulley at both ends. They give also rotational motion of shaft by giving it support with

very less friction. Though some friction is taken place due to the metal to metal contact

inside the bearing between metal balls and metal casings, it is very negligible as compare

with the direct contact of rotating shaft and main frame of the conveyor.

Types of Bearings:

There are many types of bearings, each used for different purposes. These include

ball bearings, roller bearings, ball thrust bearings, roller thrust bearings and tapered roller

thrust bearings.

7.1 Ball Bearings

Ball bearings, as shown below, are probably the most common type of bearing. They are

found in everything from inline skates to hard drives. These bearings can handle both

radial and thrust loads, and are usually found in applications where the load is relatively

small.

Figure 7.1 Exploded view


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In a ball bearing, the load is transmitted from the outer race to the ball, and from the ball to

the inner race. Since the ball is a sphere, it only contacts the inner and outer race at a very

small point, which helps it spin very smoothly. But it also means that there is not very

much contact area holding that load, so if the bearing is overloaded, the balls can deform

or squish, ruining the bearing.

7.2 Roller Bearings

Roller bearings like the one illustrated below are used in applications like conveyer belt

rollers, where they must hold heavy radial loads. In these bearings, the roller is a cylinder,

so the contact between the inner and outer race is not a point but a line. This spreads the

load out over a larger area, allowing the bearing to handle much greater loads than a ball

bearing. However, this type of bearing is not designed to handle much thrust loading. A

variation of this type of bearing, called a needle bearing, uses cylinders with a very small

diameter. This allows the bearing to fit into tight places.

Figure 7.2 Cutaway view of a roller bearing


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7.3 Ball Thrust Bearing

Ball thrust bearings like the one shown below are mostly used for low-speed

applications and cannot handle much radial load. Barstools and Lazy Susan turntables

use this type of bearing.

8. Drive unit for belt conveyor

A) Direct gear motor drive

B) Drive through parallel shaft gear box

C) Drive through primary reduction by v belt and secondary by gear box

D) Drive through spiral bevel or worm gear box

9. Motor

Motor is a prime source of the energy to run the whole belt conveyor system.

By taking current, it produces the mechanical work and this mechanical work is given to

head pulley or tail pulley of the conveyor by means of gear box drive as discussed above.

We can also use an induction motor with variable speed drive by changing its frequency.

10. Cleaning device

An important property of the rubber covered conveyor belts is the high

coefficient of friction of rubber. This reduces the tendency of material to slip on inclines.

However it also increases the difficulty of cleaning the belt.

Some of the devices for belt cleaning are discussed below:

a) Belt scraper

b) Rotating belt cleaners

c) Water spray and wiper


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11. Problem

Design a belt conveyor to transfer 200 t/hour of foundry sand through a horizontal

distance of 20 meter. Foundry sand has density of 1.25-1.3 t/hour. Assume all the

related data for belt speed and angles.

Co-efficient of friction between belt drive roller and belt is 0.3.

What happens when the transfer of same material at some angle for the same condition?

Conclude from results.

Given data

Material is to be conveyed = foundry sand

Length of the conveyor = 20 m

Capacity of the conveyor = 200 tonnes

Type of the conveyor = horizontal


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Solution:

11.1 Design of belt

Important factors are to be considered:

a) Angle of repose and angle of surcharge b) Flow ability c) Effective belt width for material d) Volume capacity of belt, Q e) Mass capacity of belt f) Belt speed

11.1.1 Selection of belt width

• angle of repose of the material to be conveyed = 45 degree

• therefore surcharge angle = 30 degree


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11.1.2 Density of the material which is to be conveyed

• density = 1.25 – 1.3 tonnes/m3 (from following table)

Density and angle of repose of commonly conveyed materials

Material

Recommended max. angle of

belt to horizontal, deg

Density tones/m3

Angle of

repose,

deg

Anthracite, fine, dry 0.8-0.95 45

Gypsum, small lump 1.2-1.4 40

Clay, dry, lump 1.0-1.5 50

Gravel 12 1.5-1.9 45

Earth, dry 1.2 45

Foundry sand 24-26 1.25-1.3 45

Ash, dry 23 0.4-0.6 50

Lime stone, Lump 20 1.2-1.5 45

Coke 17 0.36-0.53 50

Wheat flour 23 0.45-0.66 55

Oat 18 0.4-0.5 35

Saw dust 27 0.16-0.32 39

Dry sand 18 1.4-1.65 45

Wheat 18 0.65-0.83 35

Iron ore 18-25 2.1-2.5 50

Peat 18 0.33-0.41 45

Coal(from mine) 18 0.65-0.78 50

Dry cement 20 1.0-1.3 50

Slag, anthracite 22 0.6-0.9 45


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11.1.3 Angle of throughing belt

Angle of throughing, β = 36 degree

The cross section of the lump on throughed belt of width ‘w’ is shown in figure

Area of c/s of lump,

A = 1 /2 ( .6 W + .6 W + 2 2 W c o s ) .2 W s in 1 / 2 ( .6 . .4 c o s )1 / 2 ( .6 .4 c o s )W W W W c o t

θ θ

θ θ φ

× ×

+ + +

Where,

= th ro u g h ed an g le = an g le o f rep o se

θ

φ


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Volume/meter length of the belt = A x l

This must be equal to volume of material to be conveyed/meter length of belt,

Mass/meter length of the belt L = ___________________________

density of the material A×

= mc/l

c/ = 1/2(.6w +.6w+2 .2w cos ) .2w sin

+1/2(.6w+.4w cos )1/2(.6w+.4w cos )cot

m ρ θ θ

θ θ φ

× ×∴------ 1

Where, mc = mass/meter length of belt

Ρ = density of material

If we know the values of mc, Ρ, θ and Ø then we can find width of the belt from standard

belt size data.

Finding belt size width,

Assume, travel speed initially = 2.5 meter/s,

Mass rate = 200 tonnes/hour

Ø = 36 degree

Θ = 45 degree


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Therefore,

mc = mass rate to be conveyed / speed of travel ----------------------- 2

= (200 x 1000) / (3600 x 2.5)

= 22.22 kg

And the density of the foundry sand = 1.3 tonnes/m3 = 1300 kg/m3

Now putting this value in equation 1,

Therefore 22.22/1300 = 1/2 (.6w+.6w+2 x.2w cos36) x .2w sin36

+1/2(.6w+.4w cos36)1/2(.6w+.4w cos36) cot45

= (.7618w)(.1175w) + (.4618w)(.4618w)

= .3027w2

Therefore, 22.22 / 1300 = 0.3027w2

W min = 0.2376 m or 237.6 mm

This is minimum width required of belt, to avoid spillover select 400 mm width of belt which

is a standard one.

Now, let recalculate the equation 1, because according to belt width in mm belt speed may

vary.

So, for 400 mm belt width, maximum recommended speed, v = 2 m/s (from the table)


37

Now put this value in the equation 2,

mc = (200 x 1000) / (3600 x 2) = 27.8 kg

Now put this value of mc in equation 1,

27.8/1300 = 1/2 (.6w+.6w+2 x.2w cos36) x .2w sin36

+1/2(.6w+.4w cos36)1/2(.6w+.4w cos36) cot45

Therefore,

27.8/1300 = 0.3027w2

And so, w min = 0.265 m = 265 mm

Allowable belt conveyor speed in m/s

Belt width, mm Type of material conveyed

400 500 650 800 1000

Gravel, stone, coal, ash, ores 1.5 1.75 2 2.75 2.75

Coke, friable materials 1.25 1.5 1.5 1.75 2.0

Dry and wet sand, grains and

light materials

2 3 3.5 4 4

Abrasive materials, fine coke,

slag, crushed ore

1.25 2 2 2.5 2.5

Abrasive materials:

In large lumps, slaggy rock,

ores

- - 1.75 1.75 2


38

Here, we conclude that belt must require minimum 0.265 m width to avoid spill over select

400 mm belt width. 11.1.4 Mass of the belt/meter length of the belt mb = 5 kgf /meter (from table)

11.1.5 Length of belt for one passes,

Here conveyor is having horizontal layout and so the angle of elevation = 0 degree

Angle of elevation ά = tan -1 0/20 = 0

So, length of belt l = 20/cos 0 = 20 m

Weight of conveyor belts, kgf/meter

Belt width, mm 400 500 650 800 1000

Average weight

per meter run, kgf

5 6.5 9 12 16


39

11.1.6 Total length of belt passes,

(We can calculate this after the calculation of pulley diameter and the thickness of belt,)

We are getting,

Diameter of the pulley D = 500 mm =0.5 m

Thickness of the belt t = 8 mm = 0.008 m

So, Total length of the belt = D + 2 (t/2) + 20(2)

= 0.500 + 2(0.008/2) + 40

= 0.504 + 40

= 40.504 m


40

11.1.7 To check the no. of plies of belt,

Here, our belt width = 400 mm

And the density of conveyed material = 1300 kg/m3

So, from table

Table to check the number of plies of belt

Density of material conveyed, t/m3

over 0.4 0.85 1.25 1.75

Up to 0.85 1.25 1.75 2.5

Designation of belt fabric, oz

Belt

width,

mm

No. of

plies, i

28 32 28 32 36 42 32 36 42 48 32 36 42 48

Min 3 3 3 3 - - 4 - - - - - - - 400

Max 5 4 5 4 - - 4 - - - - - -

-

Min 3 3 4 4 3 - 4 4 - - - - - -

500

Max 6 5 6 5 5 - 5 5 - - - - - -

Min 4 4 5 4 4 3 5 5 4 - 5 5 4 - 650

Max 7 6 7 6 5 5 6 5 5 - 6 5 5 -

Min 4 4 5 5 4 4 5 5 4 3 6 6 4 4 800

Max 8 7 8 7 6 6 7 6 6 5 7 6 6 5


41

Min 4 4 6 5 5 5 7 6 5 4 8 7 6 5

1000

Max 10 9 10 9 8 8 9 8 8 7 9 8 8 7

Designation of belt fabric, oz 32

No. of plies i min = 4 i max = 4


42

11.1.8 Working tension in conveyor belt,

For oz 32, belt & mechanical joint and gravity take up joint belt,

Working tension per mm width of ply is taken from the table

Working tension in conveyor belts

Designation

28 oz

32 oz

36 oz 42 oz

48 oz

Vulcanized

joint &

gravity take

up

0.54

0.62

0.71

0.82

1.07

Working

tension,

kgf/mm

width per

ply

Mechanical

joint and

gravity take

up

0.48

0.57

0.66

0.77

0.98

Working tension is 0.57 kgf/mm width per ply.


43

11.2 Design of end pulleys

11.2.1 Diameter of pulley

The pulley dimension can be decided on the basis of the number of plies in the belt, the

minimum pulley diameter ‘D min’ can be roughly approximated by this formula:

D min = k x i where, k = multiplying factor which depends on the number of plies

= 125 (for 2 to 6 plies)

= 150 (for 6 to 12 plies)

i = number of plies

So, our calculation k = 125, because belt plies in our case are 4,

i = 4.

Now put these values in the main formula:

D min = 4 x 125 = 500 mm. 11.2.2 Width of the pulley

The pulley width can be taken as ‘W’

Formula: W = b + 2 x s where, b = belt width in mm

S = side margin (taken as 60 to 75 mm)

Assume, side margin s = 65 mm &

Calculated belt width b = 400 mm

So, W = 400 + 2 x 65

= 400 +130

W = 530 mm.


44

The calculated value should then be rounded off to the nearest standard size.

Some of the standard sized pulleys are listed in table, most of the preferred sizes are

based on the R 10 series of preferred numbers.

So, pulley width = 600 mm.

belt type/width/pulley diameter(mm)/piy 3 4 5 6 7 8 9 10 11 12

CC belt BE/BR 400 500 600 800 1000 1250 1250 1400 1600 1600NN100

250 315 400 500 630 800 1000 1250

NN150 250 315 400 500 630 800 1000 1250 NN200 315 400 500 630 800 1000 1250 1400 NN250 400 500 630 800 1000 1250 1250 1400 NN300 500 630 800 1000 1250 1400 1400 1600

NN belt

NN400 630 800 1000 1250 1400 1600 1600 1800 EP100

250 315 400 500 630 800 800 1000

EP150 250 315 400 500 630 800 800 1000 EP200 500 630 800 1000 1250 1400 1400 1600 EP250 630 800 1000 1250 1400 1600 1600 1800 EP300 630 800 1000 1250 1400 1600 1600 1800

EP belt

EP400 800 1000 1250 1400 1600 1800 We are selecting here NN type of belt for 500 mm diameter pulley and width of pulley is

600 mm.

So, belt type is NN 200.

Rubber cover property Code Tensile strength(Mpa) Elongation rate(%) Abrasion(mm3)

Scratch� split H ≥24 ≥450 ≤120 Abrasion D ≥18 ≥400 ≤100 Common L ≥15 ≥350 ≤200


45

11.3 Design of idlers: 11.3.1 Weight of revolving parts of idlers in kgf/ idler assembly, Our belt width = 400 mm so, assume that tube diameter of idlers = 125 mm and diameter

of antifriction bearing = 25 mm.

From table,

Weight of revolving parts of idlers in kgf/idler assembly

Tube diameter, mm

100

125

140

150

Belt

width,

mm

Bearing

diameter(antifriction),

mm

20 25

20

25

20

25

20

25

Troughing idles

400

500

13.6 14.1 16.4 20 - - - -

650 - - 17.9 21.6 24.4 24.6 - -

800 - - 19.4 23.1 26.2 27.4 - 34.7

1000 - - - - 29.9 30.2 - 37.8

Straight idlers

400

500

7.6 7.8 16.4 20 - - - -

650 - - 11 12.2 15.8 15.9 - -

800 - - 12.65 13.7 18.2 18.8 - 22.5

1000 - - - - 21.3 21.4 - 25.1

Then, the weight of throughing idler = 20 kgf/idler assembly, and The weight of the straight idler = 10.7 kgf/idler assembly


46

11.3.2 Maximum spacing for idlers in meter,

Belt width = 400 mm and

Density of conveyed material = 1300 kg/m3

From table,

Maximum spacing between idlers, m

Density of material conveyed,tonne/m3

Over 0.4 1.2 2.0

Belt

width,

mm

Up to 1.2 2 2.8

Return

idler

400 1.6 1.5 1.4 3.0

500 1.6 1.5 1.4 3.0

650 1.6 1.5 1.4 3.0

800 1.5 1.3 1.2 3.0

1000 1.5 1.3 1.2 3.0

So, max. Spacing for carrying idlers = 1.5 m And for return idlers max. Spacing = 3 m


47

11.3.3 For finding no. of both idler

a. carrying

b. return

Here, we have found max. Spacing between two idler assemblies for both carrying and

return idlers are a.5 m and 3 m respectively.

Our total length of conveyor is equal to 20 meters.

So, we can find out the total no. of carrying idlers and return idlers.

For carrying idlers = 20/1.5 = 13.33 =14 idlers assemblies.

For return idlers = 20/3 = 6.66 = 6 idlers assemblies.


48

11.4 Selecting the drive (head or both):

In this case, we have to select that drive which consists maximum intensity of

pressure. Higher the intensity of pressure more friction between the belt and the pulley can

be achieved. Because of that, better gripping of belt with the drive pulley can be achieved

and negligible chance of slipping of belt. Better power transmission by belt can be

achieved.

Pushing is better phenomenon than the pulling one and by calculations we

could find that the intensity of pressure per square mm of belt is higher on head pulley so

that we select head drive.


49

11.5 Estimation of power:

Work is required to raise the material against the gravity and to overcome the

rolling resistance between idler rollers and belt. It is very easy to estimate the work to raise

the material against the gravity. To estimate the rolling resistance, we have to calculate the

normal reaction between rollers of top run and bottom run. Normal reaction between top

run and idlers depends upon total mass of the material and belt on top run. While, for

bottom run it will depend upon mass of belt on roller. The co-efficient of rolling resistance

kr for such application lies between 0.15 and 0.30.

Normal reaction for top run Rt = g x m1x l x cos ά

Normal reaction for bottom run Rb = g x m2 x l x cos ά

Where m1 = mb + mc

m2 = mb

mb = mass of belt/unit length of belt

mc = mass of material conveyed/unit length of belt

l = length of belt

11.5.1 Mass of material conveyed /unit length of belt mc = mass rate to be conveyed /

speed of belt travel

= 200 x 1000 / (3600 x 2.0)

mc = 27.8 kg / meter and mb = 5 kg / meter

Therefore,

m1 = 27.8 + 5 = 32.8 kg / meter


50

Resistance to motion of top run Ft = Kr x Rt

= Kr x g x m1x l x cos ά

= 0.2 x 9.81 x 32.8 x 20 x cos 0

= 1287.07 N

Resistance to motion of bottom run Fb = Kr x Rb

= Kr x g x m2 x l x cos ά

= 0.2 x 9.81 x 5 x 20 x cos 0

= 196.2 N

Force to raise the material Fr = g x mc x l x sin ά

= 9.81 x 27.8 x 20 x sin 0

= 0 N

Therefore,

Power required = total force x speed

= (Ft + Fb + Fr) x v

= (1287.07+196.2+0) x 2

= 2996.54 W

Power of motor = power required / transmission efficiency

= 2996.54 / .75

= 3955.386 W

= 3.955 KW

Power of motor = 4 KW


51

Case 2: when the transfer of the given material is at 20 degree from the

horizontal surface,

Resistance to motion of top run Ft = Kr x Rt

= Kr x g x m1x l x cos ά

= 0.2 x 9.81 x 32.8 x 20 x cos 20

= 1209.45 N

Resistance to motion of bottom run Fb = Kr x Rb

= Kr x g x m2 x l x cos ά

= 0.2 x 9.81 x 5 x 20 x cos 20

= 184.36 N

Force to raise the material Fr = g x mc x l x sin ά

= 9.81 x 27.8 x 20 x sin 20

= 1865.50 N

Therefore,

Power required = total force x speed

= (Ft + Fb + Fr) x v

= (1209.45+184.36+1865.50) x 2 = 6518.62 W

Power of motor = power required / transmission efficiency

= 6518.62 / .75

= 8691.49 W

= 8.61 KW

Power of motor = 9 KW


52

12. Problem Conclusion

From this example of designing belt conveyor, we can conclude that at

transportation of material at some angle through belt conveyor system, consumes more

power than the transportation with zero angle to the horizontal plane.

Having some angle of inclination, increases the gravitational force with each

instance and thus the force to transfer the material from lower side to upper side is quite

power consuming.


53

13. Software for analysis

13.1 Introduction of pro-belt

Pro-belt computer software has been proven in the field to be highly accurate

for the design of all belt conveyors of any size or configuration. We can our pro-belt

calculations for a very long overland conveyor with a length of 12,345 meters. The

conveyor had a very small decline of 41 meters. This was an excellent example to use to

certify the accuracy of pro-belt because most of the belt tension and power requirement

came from friction calculations and very little came from lift requirements. High incline

conveyors are not a good example to use because lift power is a scientific absolute. The

calculations were made with our metric version, but the English version gives identical

results after units conversion.

The owner field tested this conveyor in 1995. The testing was extensive and

was considered to be highly accurate. Pro-belt gave a "Recommended Minimum Motor

Power" of 1746 kW versus the field test result of 1720 kW. The pro-belt analysis was

101.5% of the actual power requirement. This accuracy within 1.5% is considered to be

outstanding because this very long overland conveyor did not have much lift. The most

important calculation in belt conveyor design is to estimate the idler friction and belt flexure

friction accurately, since the lift calculation is a scientific absolute.

Pro-belt goes beyond CEMA to provide extremely accuracy results. It allows

belt conveyors to be divided into multiple sections with different loading conditions in each

section. The software gives identical accuracy whether the conveyor is divided into a few

sections or many sections. The designs are accurate for conveyors of any length including

extremely long overland belt conveyors.


54

The pro-belt pulley shaft design program was certified accurate by one of the

largest independent engineering firms in the world. The program calculates the deflection

at the pulley hub based on a free shaft analysis. The bending moment between the shaft

and hub is neglected. This gives a conservative design that eliminated many of the

common pulley failures. The program also performs a combined bending and torsional

fatigue analysis throughout the shaft in accordance with ANSI / ASME Standard B106.M.

The drive pulley extension is also analyzed for either directly connected drives or shaft

mounted drives. A warning message is displayed when the deflection or stress is outside

of allowable limits.

The pro-belt feeder program was tested by a world renowned bulk materials

handling equipment manufacturing company. They tested a very large belt feeder at

Kennecott Copper in Magna, Utah. The results were highly accurate and slightly on the

conservative side. They proceeded to use the pro-belt feeder program to design fifteen

(15) very large belt feeders for a large ore processing project in South America. Our feeder

program formulas are proprietary. Highly accurate results are produced for belt feeders of

any size operating with any bulk material. We will not publish the formula used to obtaining

this high degree of accuracy. The feeder program can also be used to model apron

feeders and drag chain conveyors. Belt feeders can be designed with either slider bed or

idler supported belts. The feeder and have a conveyor section as well as a feed hopper

section. The three page report gives the detailed results for all friction loads within the

feeder.

13.2 working

Pro-belt can be used to design horizontal curves in any troughing belt

conveyor of any length and belt sizes in either English or Metric units. The troughing belt

system and the return belt system are both included in the design. The troughing idlers

must be the 3-roller design of equal troughing angle on each lateral roll. The lateral rolls

can be longer than the middle roll to allow more drift, if desired. The idler troughing angle

is generally between 30 and 45 degrees. The return idlers must be a 2-roller "V" design.


55

Return idlers generally have a troughing angle between 10 and 30 degrees but more

commonly in the 15 to 20 degree range. Flat idlers cannot be used in horizontal curve

conveyors neither on the troughing belt nor on the return belt.

Pro-belt calculates the drift to the inner curve and drift to the outer curve

under any belt tension or loading condition. Maximum drift to the inner curve occurs at

maximum belt tension when the belt in the curve area is empty. The conveyor requires a

load case analysis with the conveyor loaded to the curve but empty thereafter. The

acceleration belt tensions should be used to check the curve design for maximum drift to

the inner circle. Tail drive regenerative conveyors would normally have a maximum inner

circle drift with the opposite conditions; i.e., stopping with the belt empty in the curve and

full thereafter. This program will design the curve for both loaded and empty conditions on

the same report. The return belt can also be checked for drift to the inner circle and the

outer circle.

Maximum drift to the outer curve occurs at minimum belt tension when the

belt in the curve area is loaded. The conveyor requires a load case analysis with the

conveyor loaded in the curve or throughout. The stopping belt tensions should be used to

check the curve design for maximum drift to the outer curve. Tail drive regenerative

conveyors would normally have maximum outer curve drift with the opposite conditions;

i.e., accelerating with the belt full throughout. Many other load case possibilities should be

considered.

Pro-belt allows faultless belt tracking of the conveyor belt by setting idler banking, tilt and

tracking.

13.3 nomenclatures

The Idler banking angle or super-elevation is the primary conveyor design

parameter used to provide a faultless tracking of the conveyor belt. The idlers are raised

on the inner side of the curve to provide a slope to the idler base. Banking angles of 8

degrees are common. A high banking angle will succeed in reducing the empty belt drift to

the inner curve but will also cause an increase in drift of the full belt to the outer curve.


56

Banking with an idler tilt up to 2 degrees has been a successful approach to curve design.

Provisions in the design should allow an adjustment of the idler banking, tilt and tracking in

the field, if necessary.

The Idler tilt angle is the secondary conveyor design parameter used to

provide a faultless tracking of the conveyor belt. The idlers are tilted forward at the top in

the direction of belt travel to provide up to 3 degrees of tilt to the idler base. The belt

tracking will probably not be as effective as indicated by the program when set above 3

degrees. A tilt angle of 2 degrees has been shown to be a successful approach to curve

design.

The Idler tracking angle is a tertiary conveyor design parameter used to

provide a faultless tracking of the conveyor belt. The idlers are moved forward in the

direction of belt travel on the inner side of the curve to provide up to 2 degrees of tracking

to the idler base. Tracking utilizes belt friction on the idlers to effect a movement in the belt

and is not the most reliable method for belt guidance. However, tracking can be used in

the field to make minor adjustments in the belt drift. A small tracking angle can make a

large change in the drift. The sum of tracking plus tilt should not exceed 3 degrees.

The Throughout belt factors are used to analyzes the effect in belt drift as a

result of belt trough ability. A belt which is stiff transversely has a reduced trough ability

and applies a greater force on the lateral idler rolls and a lower force on the central idler

roll. A belt with greater stiffness and lower trough ability actually improves belt tracking.

The Material follow factors represent the ability of the material to follow the

drift of the belt without moving toward the lower edge. A value of 1.0 represents a material

that has no movement when the belt drifts on the idlers. The value will be zero for very free

flowing materials that flow like water.

The Belt friction adjustment uses a friction multiplier to adjust the friction

between the belt and the idlers. This friction is very important in layouts which include tilt

and/or tracking of the idlers. The belt will not track as intended when the actual friction is


57

less that assumed. The friction multiplier can be changed to see the sensitivity of the final

horizontal curve design to friction.

The Allowable belt friction is calculated based on the input parameters.

The allowable belt drift is dependent on the unused space on the lateral idlers, belt edge

distance with the given material loading and material follow factors. The belt is allowed to

drift slightly beyond the edge of the lateral rollers by an amount of 1 inch or 25 mm. The

actual drift results is compared to the allowable belt drift and an "OK" or "FAIL" indicator is

given for each section point on the curve. These results are given for all three conditions:

1) troughing belt empty, 2) troughing belt loaded and 3) return belt.

13.3 advantages of analysis software (pro-belt)

a) It is used worldwide.

b) It is easy to use.

c) Will design any belt conveyor.

d) Allows any length without limit.

e) It is flexible.

f) Designs belt feeders, apron feeders & chain drag conveyors.

g) Designs pulley shafts.

h) Provides unlimited technical assistance.

i) It is very easily justified.

j) It is DOS based but easier and faster than Windows programs.

k) It is unquestioned in accuracy.


58

14. Dynamic analysis

For simple conventional belt conveying systems there are many well

documented procedures to calculate required powers, tensions and other factors. With the

assistance of computers, this rigid body analysis has been successfully streamlined,

allowing the designer to concentrate on the problems of chute design, drive house layouts

and components of manufacture.

However, with the growing need for larger, longer conveying systems, there is a need to

refine the analysis procedures. Generally, when conveying systems are analysed as rigid

bodies in a stationary state, the effects of boundary conditions - starting and stopping - are

ignored.

Dynamic Analysis is a computer simulation of the properties and

performance of the system in motion - an analysis of the starting and stopping

characteristics of a belt conveyor.

Explaining dynamic analysis

During steady state running..

Figure 1 shows a simple conveyor system during steady state running,

modeled as a series of masses and springs. In a steady state condition, the spring

extension before the drive (L1) and after the drive (L2) remains constant. In the steady

state condition, the torque due to the effective belt tension on the pulley is matched by the

torque produced by the drive.


59

FIG. 1 Mass-spring representation of

steady state running

The tension in the springs between the masses is determined by their stiffness and

extension. Since during steady state running, the distance between the masses (and the

spring extension) remains constant, the tension in the springs also remains constant.

After a coasting stop...

Figure 2 shows the same system, after the drive has been turned off.

1. The removal of the drive torque from the pulley leaves the torque unbalanced. This

results in a rapid deceleration of the drive pulley from v to (v._v), so that the rim of

the pulley moves a shorter distance than do the masses adjacent to it.

FIG. 2 Mass-spring representation of Coasting stops


60

2. This results in the shortening of the spring upstream of the pulley (with a resulting

decrease in tension) and a lengthening of the spring downstream and an increasing

in tension.

3. The change in tension on only one side of the masses adjacent to the pulley,

subsequently produces a force imbalance on these masses which causes them to

decelerate.

4. The deceleration causes changes in the extension and hence tension of the springs

on the other side of the masses. The resulting force imbalance causes the

disturbance to propagate further along the conveyor.

The resulting wave of decreased tension propagates down the carry side of

the conveyor and a wave of increased tensions propagates down the return side. For

simplicity, the variations in tension will be referred to as "compression" and "tension"

waves. These labels are not entirely accurate, since it is not possible to get true

compression on a conveyor belt, but the terms are widely accepted.

If the magnitude of the "compression" wave is greater than the actual steady-

state tension of a region of the conveyor through which the wave passes, highly non-linear

behavior will result. The belt tension in the region will not become negative but extremely

low tensions and large belt sag between idlers will occur. Destructive dynamic effects

frequently result from this type of occurrence.


61

FIG. 3 Mass-spring representation of coasting stop

with gravity take-up

Coasting stop with gravity take up

Figure 3 is the same as Figure 2, except that a take-up is located immediately

downstream of the drive. The increase in tension downstream of the pulley, instead of

inducing a tension wave, produces a force imbalance on the take-up, causing it to

accelerate upwards. This upward movement of the take up, absorbs the "tension" wave.

As a result, the return side of the belt is unaffected by the drive stopping until the

"compression" wave from the carry side has traveled completely around the conveyor.

The speed with which the initial waves propagate is a function of the system

mass and the belt axial stiffness. The loaded side of the belt will be heavier and

consequently waves on the carry side will propagate more slowly than waves on the return

side. Other important factors are the drive inertia and the belt stiffness. The steady state

velocity of the belt does not influence the magnitude of the stress wave.


62

14.2 When we can use it?

There are no cut off points to dynamically analyzing a conveying system. At

present it is usual to analyze large systems with complex profiles. Dynamic analysis tends

to be introduced for conveyors in excess of 1000m with capacities about 100 tph. This may

be the norm, however any conveying system experiencing large take-up movements or

adverse shock wave propagation resulting in premature pulley or drive failure, should fall

into the spectrum.

It is often possible to identify dynamic problems in a conveyor when large movements of

the take-up occur. These movements are related either to elastic stretch in the belt, thus

certain sections of the belt moving at different speeds to other sections, or large quantities

of belt being dumped between the idlers causing a loss of tension, or a combination of

these symptoms.

It has unfortunately become common practice to eliminate the symptom of

take-up movement by "fixing it" with a winch. This has the effect of making the design

perform as a rigid body, and it must therefore be over-designed to cater for the effects of

wave propagation. Failure to over-design, results in the shock wave destroying pulley or

drive components. Since this normally occurs in a progressive way (fatigue), it does not

always show itself as a dynamic problem.


63

benefiting from dynamic analysis

The advantages are generally seen in reduced costs and downtime. A

dynamic analysis can give the designer the confidence to reduce safety factors,

thereby lower the specifications for belting and allowing an increase in idlers spacing,

thus reducing power use and component spares holding. It should be noted that

conveyors set up with dynamic analysis techniques are operating with a safety factor

for the belt of less than five.

FIG. 4 A typical examples of theoretical and actual readings. The take-up

movement is an ideal test for model accuracy as it can be measured

in the field, giving substantial justification for confidence

in the modeling.


64

14.3 Conclusion

Setting up a basic model although very time consuming and highly complex,

allows the designer greater freedom in designing the system. A full analysis needs upward

of 100 runs to satisfy all the possible combinations of events. Today's computers require

two hours to complete a single analysis, and a full analysis would therefore take in the

region of 200 working hours.

When the basic analysis has been concluded, and problems like shock wave

propagation, excessive take up or negative belt tensions have been identified, it is then

possible to test various solutions. What if a brake were installed. Where is the best position

for a brake? Should we increase system inertia? All these questions can be investigated.

Once this exercise has been completed, it is then possible to show the results

of the full analysis using computer simulated models which, through a time base, can

display the operating parameters allowing for the correct formulation of the control

philosophy.

By using the simulation approach right from the design stage, the designer

can advance the roll of the conveyer to greater heights and lengths. Eliminating transfer

points and pushing the conveyor to higher speeds, knowing that he is not sacrificing

safety, will ensure that the final system will provide cost-effective bulk transportation for

many years to come.


65

15. Bibliography:

www.nbelts.com

www.conveyorkit.com

www.pro-belt.com

Material handling systems

Design data book

Basics of Conveyor

Documents

steady state

steady state

long overland

idler sets

conveyed speed

troughed belt

allowable

troughed belt