Belt Conveyor | Belt Conveyor Design | Belt Conveyor Parts | Belt Conveyor Rollers

Belt Conveyor

material is fed on the belt near the other end pulley. The moving belt carrying the material towards the driver pulley is likely to sag between the two end pulleys due to its self weight and pay load. That is why the belt is supported both on the carrying side and the return side by a number of rollers, called the idlers. As the belt is always under tension, it is prone to elongation resulting in slackness over the pulleys and loss of tension and power. That is why some kind of device for tensioning the belt is incorporated in the system. This tensioning device is known as take up arrangement. The system is inherently very simple.

Belt conveyors have attained a dominant position in transporting bulk materials due to a number of inherent advantages like the economy and safety of operation, reliability and practically numerous processing functions while supporting a continuous flow of material between operations. Low labour and low energy requirements are fundamental with belt conveyors as compared with other means of transportation. The reliability of belt conveyors has been proved over decades and in every industry. Belt conveyors are environmentally more acceptable than other means of transport. They neither neither pollutes the air nor deafens the ears. Conveying of a wide variety of materials is possible with belt conveyor, and belt conveyors are capable of transporting at a hourly rate much in excess of any practical requirement. Belt conveyors can deliver materials at a great distance from the loading point covering all odd terrain.

Essential components of a belt conveyor:

Belt conveyors consists of a driving pulley at the head end, and take up pulley at the tail end, both being accommodated in a steel frame. An endless belt connects the two pulleys on both runs and supported by suitable roller type supports, called the idlers. At the upper side of the conveyor also called the carrying side, because the pay load is carried on this side, the belt is supported by idler. At the other side also called the return side because usually there is no pay load, the belt is supported by idlers. In some designs the belt is supported by a stationery runway instead of idlers. In some special installations both the upper and lower sides transport loads (usually unit load) simultaneously in opposite directions. The driving pulley receives its rotation from drive unit.

The material to be conveyed is loaded on the belt by one or more feed hoppers mounted over the conveyor belt line normally placed at the tail end side. The load conveyed by the moving belt is discharged over the driving pulley into discharge spout. However discharge can be arranged at any point along the conveying run by means of special discharge devices. At the tail end side a device called the take up arrangement is attached with the take up pulley to keep the belt under a minimum tension so that the belt does not slip over the pulleys due to extension of its length. Belt cleaner removes material adhering to the outer belt face. It is usually located near the driving pulley.

Application of belt conveyor:

Belt conveyors are employed to convey a great variety of bulk materials and also unit loads along a horizontal or gently inclined paths. Such duties can be performed within the factory shed or in outdoor work. Within the factory shed belt conveyors are also employed to carry articles of light weight in line production from one operation to another. Belt conveyors are used to mechanize material handling operations in foundries to distribute moulding sand, mould cores and cast articles. Belt conveyors are used for carrying coal, ores, and minerals in power plants, mining industries, and metallurgical process plants. For handling food grains and building materials belt conveyors are frequently employed.

Capacities of a belt conveyor system may range from 500 to 5000 m3 / Hr. and more. The distance covered for a belt conveyor system may be as small as 50m (for indoor work) to 5 Km for supplying raw material from mine area.

Belt Conveyor Belt Specification | Belt Conveyor Standards | Selection Of Belt Drive | Belt Conveyor Selection

Selection of Conveyor belt:

To select the correct conveyor belt for your application involves a large number of considerations. Final selection may very well represent a compromise between what is desired and what is available.

To assist you in obtaining the proper information required to select a proper belt construction, the following check list is provided.

1. Material Conveyed

a. General description

b. Density, pounds per cubic foot (pcf)

c. Lump size

d. Presence of oils or chemicals, if any

e. Maximum temperature of load, if hot

f. Requirements of fire resistance

2. Maximum loading rate or required maximum capacity, tons (2000) lbs. per hour (tph)

3. Belt

a. Belt width, inches

b. Belt speed, feet per minute ((fpm)

c. Belt Type

d. Thickness of Top and Bottom Cover (inch)

4. Drive

a. Type

b. Voltage

c. Frequency

d. Motor power

e. Motor Speed

5. Center of center distance (length) of Belt

6. Profile of Conveyor

a. Profile distance along conveyor path

b. Elevations

c. Locations of all vertical curves and angle of slope

7. Drive

a. Single-pulley or two-pulley

b. If two-pulley, geared tandem or dual-drive

c. If dual-drive, distribution of total motor horsepower at primary and secondary drive pulleys

d. Angle of belt warp on drive pulley(s)

e. Location of drive

f. Pulley surface, bare or lagged. Type of lagging

g. Type of starting to be employed

8. Pulley

a. Head Pulley Type

b. Drive Drum Diameter

c. Tail Diameter

d. Snab pulley Diameter

e. Angle of Wrap on drive Pulley

9. Take-up

a. Type

b. Location

c. Take up Pulley Diameter

d. Bend pulley Diameter

e. Take up movement

10. Idlers

a. Idler Trough Angle (30 Deg)

b. Type of Carrying Idler, Type of Return Idler, Type of Impact Idler, Type of Training Idler

c. Carrying Idler Diameter, Return Idler Diameter

d. Spacing, including transition distance at head and tail

e. Carrying Idler Pitch, Return idler pitch

11. Type of loading arrangement

a. Chutes

b. Free-fall distance, lumps to belt

c. Skirt board length

12. Lowest cold weather operating temperature anticipated, if applicable

13. Type of belt splice to be used

14. Design Conditions

a. Altitude (example.18m)

b. Material (Ex. Iron Ore Pellets)

c. Bulk Density (Ex. 2.1 t/m3)

d. Angle of Repose (Ex. 30 Degree)

e. Ambient Temperature (Ex. 38 deg. Celsius)

f. Material Characteristics (Ex. Very abrasive)

g. Rated capacity (Ex.1800 t/h)

h. Design Capacity (Ex. 2100 t/h)

i. Conveyor Slope Angle (Ex. 9.5 Degree)

j. Belt conveyor horizontal length (Ex.200 m)

k. Belt conveyor lift length (Ex. 35 m)

l. Belt conveyor length (Centers of Head & Tail) (Ex. 200 m)

Belt Conveyor Types | Troughed Belt Conveyor | Flat Belt Conveyor

Types of conveyor:

• Troughed belt conveyor
• Flat belt conveyor 

Troughed belt conveyor:

Troughed belt conveyor is that in which the belt forms a trough on the carrying side while running over idler rollers which are either in set of 5 rolls, 3 rolls or 2 rolls. The troughing angle adopted are: 15°, 20° , 25° , 30° , 35° , 40° , 45° . Return idlers are usually straight roller type.

Transverse flexibility or rigidity of the belt is another significant consideration. It is important that the belt trough properly. The empty conveyor belt must make sufficient contact with the center roll in order to track properly.

Troughed belt conveyors are used for higher capacity, higher speed requirement, and for handling bulk material of large lump size. It suitable for inclined or declined type conveyors.

Transition distance is defined as the distance from the center line of the first fully troughed idler roll to the center line of either the head or tail pulley. The distance from the pulley to the top of the wing idler is certainly greater than the distance from the pulley to the center roll of the troughing set. If the transition distance is too short, the edge of the belt can be over stretched. This will adversely affect the load support and belt life.

Flat belt conveyor:

Flat belt conveyor is that in which the belt runs flat on the carrying side over straight roller type idler or a set of idlers.

Flat belt conveyors are suitable for lower capacity, low speed requirement and for handling unit goods or bulk material of small lump size and higher angle of repose. Declination is undesirable.

Belt Conveyor Layout | Horizontal Belt Conveyor | Inclined Belt Conveyor | Declined Belt Conveyor

Conveyor layouts:

Belt conveyors can be designed for practically any desired path of travel. It should be noted that transfer between conveyors should be avoided where possible due to additional wear on the belts at the loading points. Some of the profiles shown below:

Horizontal Conveyor

Decline Conveyor

Inclined Conveyor

Overland Conveyor

Belt Conveyor Parts | Belt Fabrics | Belt Cover Grades | Belt Splicing | Designation Of Belts

Belt Conveyor parts:

The desirable properties of an ideal belt material are:

• High Strength,
• Low self weight, 
• Small specific elongation, 
• High Flexibility, 
• High resistivity to ply separation 
• Low hygroscopic 
• Long service life

In general Reinforced Rubber Belts meet these requirements better than any other material.

In general, a conveyor belt consists of three elements:

• Top cover

• Carcass

• Bottom Cove

Carcass:

The carcass is the reinforcing element and takes up the tensile forces necessary in starting and moving the loaded belt, absorbs the impact energy of material during loading. The carcass may be of either textile reinforcement or steel cords. In case of textile reinforcement the carcass is normally built up of a number of plies of textile fabric. These plies may be made from rough woven cotton fabric and are connected by vulcanization with natural or synthetic rubber.

Sometimes the plies are made of extra strong synthetic fabrics like:

• Capron,

• Pernol

• Nylon etc

The strength of fabric and the number of plies in the carcass of the belt may be varied together to suit the strength requirement. However if the belt is too tough, troughing of the belt and bending it round the terminal pulleys will be very difficult. Therefore the belt with lesser number of plies with stronger fabric is generally preferred because it is more flexible. Steel cord belting is used when good trough ability, small specific elongation and higher operating tensile forces are required. PVC belting is generally selected for underground mining applications where fire hazard exists.

Belts cover grades:

The primary purpose of the covers is to protect the belt carcass against damage and any special deteriorating factors that may be present in the operating environment. Rubber or rubbers like compounds are used for the top and bottom covers of conveying belting. Various chemicals are mixed with these compounds to achieve the desired physical properties necessary for service conditions. The properties needed for the cover of belt include resistance to cutting, gauging, tearing, abrasion, aging, moisture absorptions and in some cases resistance to oil, chemical and heat. Different qualities of cover material are designated by different grades. The cover grade is determined by the characteristics of the material to be handled.

Some cover grades are:

Grade M24:

Natural rubber compound offering superior resistance to cutting, gauging and abrasion wear

Grade N17:

Compounded rubber with improved flex life for moderately abrasive material, high abrasion resistance, resistance to cutting and gauging is inferior to M24

Grade HR:

Suitable for handling Alumina, ash, chemical etc at temperatures over 65 deg Celsius up to 120 deg Celsius.

Grade ‘Betaplus’:

Recommended for handling materials like foundry sand, cement clinker, coke wharf, sinter ore at temperature range 65 °C to 180° C for coarse and fine materials.

Grade FR:

Suitable for underground mining and for equipment and materials requiring fire resistant and antistatic charge properties.

Grade OR:

Suitable for best possible resistance to mineral, vegetable and animal oil

Designation of Belts:

Belts are designated to denote the full thickness tensile strength per meter width and the number of reinforcing plies of synthetic textile. Examples: 500/3 belt indicates a belt having a minimum guaranteed full thickness tensile strength of 500 KN/m, incorporating 3 plies of textile reinforcement. For all synthetic fabric reinforced conveyor belting usually a factor of safety of 10 is applied to obtain the maximum working tension with vulcanized splicing.

Steel cord belting is designated by the prefix “ST” followed by the minimum full thickness tensile strength in kN/m.


Belt Splicing:

The two ends of a belt are joined directly on the conveyor either by vulcanizing or hinged metal belt fasteners of different designs. Vulcanization is the most reliable method of splicing. Vulcanization technique is a specialized job and expensive, but yields the best result. Mechanical fasteners are often used for connecting flat belting.

Belt Conveyor Idlers | Carrying Idlers | Return Idlers | Idler Spacing

Idlers:

Conveyor belts are usually supported on idler rollers. In some cases they are supported by solid wood or runway of steel sheet or a combination support comprising of the two types of supports placed alternatively.

There are two basic types of idlers:

• Carrying idlers

• Return idlers 

Carrying Idlers:

The most commonly used type of carrying idlers used for handling bulk load consist of three in line idler rolls of equal length. The three equal length roll troughing idlers form the belt into the best troughed shape to carry a maximum load cross section.

For handling unit load or for handling nominal bulk load, or for supporting belt in return side, straight idlers are used, positioned between brackets attached directly to the conveyor frame. Another type of carrying idlers is used at the loading points where the lump size and the weight of the material ma seriously damage the belt if the belt were rigidly supported. Such idlers are called impact idlers. The most frequently used type of impact idlers consist of a three roll assembly, each roll being made of spaced resilient discs. These idlers are also known as cushion idlers.

Return idlers:

The return idlers which carry the weight of the empty belt in the return side or the lower side of the conveyor are mostly single roller straight idler. The main dimensions of the idler are the diameter and length. The diameters in millimeters of carrying and return idlers shall be selected from the following:

63.5, 76.1, 88.9, 101.6, 108, 114.3, 127, 133, 139.7, 152.4, 168.3, 193.7.

Idler spacing:

The spacing of idlers on the loaded run of the conveyor, carrying bulk material, depends on the belt width, the specific weight of the bulk material, the type of the idler. The spacing of the idlers in the loading zone of the belt is about half the normal spacing of idlers in the carrying side.

A set of self aligning idler or training idler should be provided at the carrying side and return side at an interval of 15m on the carrying run and 30m at the return run. It consists of an ordinary troughed three roller idler mounted on swivel frame which is free to swivel within a limit about a vertical pivot. When the belt shifts off the crane the edge contacts on actuating roller with a slight pressure and this makes the idler take a skewed position when a force acts which tends to steer the belt back to its central position. As the belt returns to its central position, it automatically returns the idler to its initial position.

The idlers along the carrying and return side offer rolling resistance to the motion of the belt. It is taken into account by an artificial coefficient of friction, dimensionless, comprising of rolling resistance of the idlers along the carrying and return sides of belt and the belt advancement resistance. This coefficient of friction has a basic value of 0.02 for normally aligned belt conveyors and the same has a basic value of 0.012 for downhill conveyor requiring a brake motor.

The basic value of 0.02 of the coefficient of friction is only applicable to installations used at 70% to 110% of their nominal capacity, equipped with three roll carrying idlers for the upper side of the belt, a 30° side troughing angle, belt speed of about 5 m/s, surrounding temperature of about 20°C, and 108 to 159 mm diameter carrying idlers with ball bearing and labyrinth grease seals, together with idler spacing of 1.0 to 1.5m for the carrying side and 3 m for the return side of the belt.

Under favourable conditions, such as properly aligned installations with properly lubricated ball bearings, the value of the coefficient of friction may be as low as 0.016. For unfavourable conditions, such as poorly aligned belt conveyors with old bearings ‘f’ may be as high as 0.03.

Belt Conveyor Drive Arrangement | Belt Conveyor Design Calculation

Drive arrangement:

In belt conveyors the driving power is transmitted to the belt by the driving pulley which is rotated by an electric motor. The basic mechanism of transmission of power from the pulley to the belt is based on the theory of friction drive.

The fundamental equation for a belt conveyor drive is given by: (The Euler’s equation)
T1 ≤ T2.eµα



Where,

T1 and T2 are the tight side and slack side tensions of the belt at the driving pulley

α = wrap angle of the belt in radiation

e = Naperian base

µ = Friction factor

The peripheral effective pull TE from a driving pulley, neglecting losses on the driving pulley due to belt stiffness is determined from the following reaction:
Te = T1 – T2

T2min > T E Max (1 / (eµα -1))



Where,

T E Max is the maximum effective peripheral pull in N, which often occurs when starting up or when braking the completely loaded conveyor.

In other conditions Te is the average effective pull. Maximum effective pull is usually 20% to 50% more than the average effective pull, depending on the type of motor starter and coupling.

Table: Coefficient of friction between driving pulley and rubber belting type of pulley lag

he value of α depends on the particular drive system selected and may range from 180° to maximum 440°.

Minimum belt tension
T = 4.2 Pc ( Wb + Wm )



Where,

Pc = idler spacing on the carrying side

Wb, Wm are the weights of belt and pay load per meter length of belt respectively.

Types Of Belt Conveyor Drives | Belt Conveyor Drive Arrangement

Types and Selection of Drives:

Single Unsnubbed Bare / Lagged pulley Drive

Snubbed Bare / Lagged Pulley Drive

Tandem Drive

Special Drives

Single Unsnubbed Bare / Lagged Pulley Drive:

This is the simplest drive arrangement consisting of a steel pulley connected to a motor and the belt wrapped round it on an arc of 180°. This can be used for low capacity short center conveyors handling non-abrasive material. The pulley may be lagged to increase the coefficient of friction.

Snubbed Bare / Lagged Pulley Drive:

Here the angle of wrap is increased from 180° to 210° or even up to 230°, by providing a snub pulley to the driving pulley. In majority of medium to large capacity belt conveyors, handling mild abrasive to fairly abrasive materials, 210° snub pulley drive with load pulley lagged with hard rubber is adopted.

Tandem drive:

Here belt tension estimated to be high; the angle of wrap is increased by adopting tandem drives. Both of tandem pulleys are driven. The tandem drive with arc of contact from 300° to 480° or more can operate with one or two motors. The location of such drive is usually determined by the physical requirements of the plant and structural constraints.

Special Drive:

Special drives with snub pulleys and pressure belts used in heavy and long conveyors.

Pulley | Belt Conveyor Pulley | Belt Conveyor Pulley Types | Belt Conveyor Power Calculation

Pulley:

The diameters of standard pulleys are: 200, 250, 315, 400, 500, 630, 800, 1000, 1250, 1400 and 1600 mm. pulley may be straight faced or crowned. The crown serves to keep the belt centered. The height of the crown is usually 0.5% of the pulley width, but not less than 4 mm. The pulley diameter Dp depends on the number of plies of belt and may be also be determined from the formula:

Dp > K.i (mm)

Where

K = a factor depending on the number of plies (125 to 150)

i = no of plies

The compound value should be rounded off to the nearest standard size. While selecting the pulley diameter it should be ascertained that the diameter selected is larger than the minimum diameter of pulley for the particular belt selected.

The drive pulley may be lagged by rubber coating whenever necessary, to increase the coefficient of friction. The lagging thickness shall vary between 6 to 12 mm. The hardness of rubber lagging of the pulley shall be less than that of the cover rubber of the running belt.

Pulley types:

Pulleys are manufactured in a wide range of sizes, consisting of a continuous rim and two end discs fitted with hubs. In most of the conveyor pulleys intermediate stiffening discs are welded inside the rim. Other pulleys are self cleaning wing types which are used as the tail, take-up, or snub pulley where material tends to build up on the pulley face. Magnetic types of pulleys are used to remove tramp iron from the material being conveyed.

Typical welded steel pulley-Drum conveyor pulley

Spun end curve crown pulley

Spiral drum conveyor pulley

Welded steel pulley with diamond grooved lagging

Welded steel pulley with grooved Lagging

Spiral Wing Conveyor pulley

Power calculation for the drive unit:

The horse power required at the drive of a belt conveyor is derived from the following formula:

H.P = Te . V

Where

Te is the effective tension in the belt in N

V = velocity of the belt in m/s

The required effective tension Te on the driving pulley of a belt conveyor is obtained by adding up all the resistances.

Conveyor Take Up Arrangement | Take Up Pulley | Screw Take Up Conveyor | Quick Take Up Master Cylinder

Conveyor Take-up Arrangement:

All belt conveyors require the use of some form of take-up device for the following reasons:

To ensure adequate tension of the belt leaving the drive pulley so as to avoid any slippage of the belt

To ensure proper belt tension at the loading and other points along the conveyor

To compensate for changes in belt length due to elongation

To provide extra length of belt when necessary for splicing purpose.

Usually there are two types of take up arrangements.

Fixed take up device that may be adjusted periodically by manual operation

Automatic take up devices for constant load type

In a screw take up system the take up pulley rotates in two bearing blocks which may slide on stationery guide ways with the help of two screws. The tension is created by the two screws which are tightened and periodically adjusted with a spanner. It is preferable to use screws with trapezoidal thread t decrease the effort required to tighten the belt.

The main problem with the use of manual take-up is that it requires a vigilant and careful operator to observe when take up adjustment is required. Perfect tension adjustment with this system is also not possible. For this reason these devices are used only in case of short conveyors of up 60 m length and light duty.

In automatic take up arrangement the take up pulley is mounted on slides or on a trolley which is pulled backwards by means of a steel rope and deflecting pulleys. The carriage travels on guide ways mounted parallel to the longitudinal axis of the conveyor, i.e., horizontally in horizontal conveyors and at an incline in inclined conveyors. Hydraulic, pneumatic and electrical take up devices are also used.

Automatic take-up has the following features:

• It is self adjusting and automatic
• Greater take-up movement is possible.

Belt Conveyor Take Up Design | Conveyor Belt Take Up System | Horizontal Take Up In Belt Conveyor

Belt Conveyors for bulk materials:

Take up Arrangement:

All belt conveyors require the use of some form of take up device for the following reasons:

1. To ensure adequate tension of the belt leaving the drive pulley so us to avoid any slippage of the belt.

2. To ensure proper belt tension at the loading and other points along the conveyor.

3. To compensate for changes in belt length due to elongation.

4. To provide extra length of belt when necessary for splicing purpose.

Usually there are two types of take up arrangements.

These are:

1. Fixed take up device that may be adjusted periodically by manual operation

2. Automatic take up device (constant load type)


Manual Screw Take Up:

The most commonly used manual take up is the screw take up. In a screw take up system the take up pulley rotates in two bearing blocks which may slide on stationery guide ways with the help of two screws. The tension is created by the two screws which are tightened and periodically adjusted with a spanner. It is preferable to use screws with trapezoidal thread to decrease the effort required to tighten the belt.

The main problem with the use of manual take up is that it requires a vigilant and careful operator to observe when take up adjustment is required. Perfect tension adjustment with this system is also not possible. For these reason these devices are used only in case of short conveyors of up 60m length and light duty.


Automatic Take Up:

In automatic take up arrangement the take up pulley is mounted on slides or on a trolley which is pulled backwards by means of a steel rope and deflecting pulleys. The carriage travels on guide ways mounted parallel to the longitudinal axis of the conveyor, i.e., horizontally in horizontal conveyors (Ex.: Gravity type automatic take up arrangement) and at an incline in inclined conveyors. Hydraulic, Pneumatic and electrical take up devices are also used.

Automatic take up has the following features:

1. It is self adjusting and automatic

2. Greater take up movement is possible

For the perfect conveying of materials, adding a resistance with the peripheral forces on the driving pulley of a belt conveyor is important. Some of the resistances are:

1. The inertial and frictional resistance due to acceleration of the material at the loading area

2. Resistance due to friction on the side walls of the skirt board at the loading area.

3. Pulley bearing resistance applicable for other than the driving pulley

4. Resistance due to the wrapping of the belt on pulleys

5. Special resistances include

a. Resistance due to idler tilting

b. Resistance due to friction between material and skirt plate

c. Frictional resistance due to belt cleaners

d. Resistance due to friction at the discharge plough

Special resistances are usually small. Here the resistance due to idler tilting and skirt resistance is ignored. There being no discharge plough the resistance due to plough is ignored. For belt speeds greater than 3 m/s, the edge clearances are applicable.