The Belt Conveyor

A Concise Basic Course

D.V. Subba Rao

• Editorial: CRC Press
• Año: 2020
• ISBN:
  9781000177763
• Edición: 1
• Categoría: Tecnología e ingeniería
• Categoría: Ingeniería minera

This book describes all parts of belt conveyors, their functions and different types presented one after the other with necessary illustrations covering all the basic aspects so that the reader can obtain an overall understanding of their operation and implementation within the field of bulk material handling, mining and mineral processing. Dedicated study of this work will also enable engineers to carry out minor repairs on their own without having to wait for maintenance personnel.

This is an introductory preliminary book for beginners in the field of bulk material handling, mining and mineral processing, written in lucid, easy-to-understand language, well-illustrated, and with self-explanatory descriptions that do not compromise in maintaining academic standards while dealing with the subject matter. A salient feature of this book is that all the new terminology used to describe the components and their functions has been included and explained.

Much of the content of this book has been tested and evaluated positively by graduate and postgraduate students and professional engineers of several bulk material handling plants during training programs over the last twenty-five years in India.

Chapter 1
Belt conveyor components

A belt conveyor is a simple piece of equipment and the most common means of transportation of bulk materials and is capable of carrying a greater diversity of products at the rates of thousands of tons per hour in a continuous and uniform stream over long distances than any other kind of continuously operating mechanical conveyors. A typical belt conveyor consists of two drum pulleys fitted with a continuous loop of an endless belt, known as the conveyor belt, running around two pulleys and resting on troughing idlers for the carrying run and on return idlers for the return run. One of the pulleys is powered, driven by an electrical motor, which moves the belt and the material on the belt forward. The powered pulley is called the drive pulley, while the un-powered pulley at the dead end is called the tail pulley. Today’s conveyors consist of dozens of other components, each one specially designed for moving different materials.

The basic design of a belt conveyor is so robust that it will convey material under the most adverse conditions such as overloaded, flooded with water, buried in fugitive material, or abused in any number of other ways.

Any stray material that escapes from a conveyor belt at a place other than its normal discharge point is called fugitive material. It arises as spillage and leakage from transfer points, carryback or airborne dust that has been carried off the belt by air currents and the impact forces of feeding. The material, which adhered to the belt and other conveyor components, cleaned by the cleaners and sent back along with the discharge material is called carryback.

The advantages of belt conveyors are their superiority, reliability, versatility, economy and safety of operation, and practically unlimited range of capacities. Belt conveyors can receive material from one or more locations and discharge material to points anywhere along its length. Belt conveyors suit well in tunnels beneath stockpiles to reclaim and blend various materials from different stockpiles. Belt conveyors with stackers and reclaimers are found as the only practical means for large-scale operations.

A stacker is a boom-mounted belt conveyor that discharges the material at the end of the boom which can drop material onto a stockpile for storage. A rotating bucket wheel can also be equipped at the discharge end so that the belt conveyor discharges the material into the buckets of bucket wheel, and as it rotates, it will discharge or drop the material onto a stockpile. The same stacker with bucket wheel rotating in reverse direction reclaims the material from the stockpile and feeds it to the belt conveyor for transportation to another destination.

Environmental acceptability is an added advantage for the selection of belt conveyors over other means of transportation. Belt conveyors with auxiliary equipment can also perform numerous process functions during various stages of processing. Sorting and hand-picking of the material over moving belt is the best example.

Belt conveyors are suitable for transportation of material in open-cast/underground mines, steel plants, beneficiation plants, port trusts, thermal power plants, cement plants, chemical plants, fertilizer plants, etc. Thus, wherever continuous material transportation is involved, belt conveyors form the main artery of the transportation system. Belt conveyors have the adaptability to work in different types of terrain and different gradients and have flexible path of travel, and the length of the routes can be extended repeatedly as per the requirement. In the case of mining, where due to the advancement of mine, the transport system has to be relocated frequently, the conveyor system lends itself easily. In a mine, belt conveyors are used for the transportation of the mined material to a beneficiation plant, stockpiling and reclaiming of concentrated product, disposal of waste, transport of product to the point of use in a process plant or loading onto a ship for sale to an overseas user.

The lowest transportation and maintenance costs, low labour and low energy requirements are the exceptional features with belt conveyors as compared to the most other means of transportation of bulk materials. The dramatic increase in the operating costs of other means of transport has placed conveyors in an extremely favourable position for applications that were not considered previously.

Materials that range from very fine, dusty chemicals to large, lumpy ore and coal are transported by belt conveyors. Closely sized or friable materials are carried with minimum degradation. Materials causing sticking or packing if transported by other means are often handled successfully on belt conveyors. Hot materials such as coke, sinter, iron ore pellets, direct reduced iron and hot briquetted iron are conveyed successfully.

Automatic sampling devices are arranged in the conveying system from where accurate samples of the material can be obtained by cutting through the stream of material flowing from one conveyor to the next or to the next operation. Materials can also be weighed accurately and continuously while the material is transported on the conveyor belt. It is one of the highlights of a belt conveyor.

Innumerable uses and applications of the belt conveyor make this device useful and reliable to carry out several major operations in industries. Today the use of belt conveyors is an important and broadly accepted means of long-distance transportation of bulk materials. They are also used economically in steel plants for transporting materials between two processing units at a wide range of rates, sometimes even at a very low rate. Belt conveyors provide a continuous flow of material while avoiding the confusion, delays and safety hazards of rail and road traffic in steel plants. Belt conveyors can be operated continuously, round the clock and 24 × 7 hours when needed without loss of time for loading and unloading or empty return trips.

The demand for ever-increasing capacities and ever-longer conveying lengths has accelerated the development of the belt conveyor systems having far greater complexity employing higher degrees of automated control. New materials are being developed, and new conveying systems are being planned and tested especially for meeting the challenges with regard to the environment control.

1.1 Components of a belt conveyor

The essential components of a typical belt conveyor are as follows:

1. The belt, which forms the moving and supporting surface on which the conveyed material is placed. The belt not only carries the material, but also transmits the pull. It is the tractive element.
2. The idlers/rollers, which form the support for the troughed carrying strand of the belt and the flat return strand.
3. The pulleys, which support and direct the belt and control its tensions.
4. The drive, which imparts power through one or more pulleys to move the belt and its load. Usually, the drive is an electric motor with reduction gears.
5. The structure, which supports and maintains the alignment of idlers, pulleys and drive.

In addition to these five components, necessary ancillary equipment is also installed in every conveyor to improve the system’s operation. The belt conveyor should be properly designed to the requirements on how the conveyor is best fed and discharged, accessibility for operation and maintenance, electrical starting and stopping needs, and many other factors must be studied and carefully coordinated. The following are the components of a belt conveyor:

1. Top strand of the belt
2. Bottom strand of the belt
3. Carrying troughing idlers/rollers
4. Transition idlers/rollers
5. Impact idlers/rollers
6. Carrying training idlers/rollers
7. Return idlers/rollers
8. Return training idlers/rollers
9. Drive or head pulley
10. Tail pulleys
11. Snub pulleys
12. Bend pulleys
13. Take-up pulleys
14. Drive motor
15. Counterweights
16. Vertical take-up arrangement
17. Feed chute
18. Skirt plates for guiding the material
19. Belt cleaners for the carrying side of the belt
20. Belt cleaner (plough type) for the bottom side of the belt
21. Pulley cleaner
22. Discharge chute
23. Dribble chute.

The components of the belt conveyor are shown in Figure 1.1 along with the notation for the different lengths as given below.

• L_P – Pulley centre distance
• L_C – Length of the conveyor
• L_RT – Idler/roller spacing top strand
• L_RB – Idler/roller spacing bottom strand
• h – Height of drop of material

Figure 1.1 Components of a belt conveyor.

In a simple system, as shown in Figure 1.1, an endless belt, made up of carcass impregnated with rubber and covered by rubber on both sides and edges, wraps around two pulleys, a drive pulley (9) and a tail pulley (10). The top strand of the belt (1) carries the material and is usually troughed and transforms to flat shape as it reaches the drive pulley. The design of the trough depends on the quantity of the load to be carried. The bottom strand of the belt (2) is a return strand and assumes flat shape after the drive pulley, travels round the tail pulley and then slowly takes the trough shape on top run and continues to be in trough shape till it reaches the drive pulley.

The top strand of the belt is supported by a set of idlers/rollers called carrying troughing idlers/rollers (3). By the time the belt reaches the troughing idlers/rollers, the belt takes full trough shape. Between the tail pulley and the load zone, idlers/rollers with increasing trough angles are fixed in order to transform the belt into the trough shape gradually. These idlers/rollers are called transition idlers/rollers (4). Similarly, transition idlers/rollers with decreasing trough angles are fixed between the last troughing idler/roller and the drive pulley to transform the belt from trough shape to flat gradually. At the feeding section, idlers/rollers with rubber rings called impact idlers/rollers (5) are installed to absorb the shock of the falling material and also to minimize the damage to the belt. An idler/roller called carrying training idler/roller (6) works to keep the belt running in the centre of the conveyor structure. These idlers/rollers are self-aligning and react to any mistracking of the belt to move into the position that will attempt to steer the belt back into the centre. The bottom strand of the belt is supported by a set of idlers/rollers called return idlers/rollers (7). Return training idler/roller (8) works similar to the carrying training idler/roller and adjust the mistracking of the return belt. The idlers/rollers are fixed to the frames, and the frames are secured to the main steel structure called stringers. Steel trusses are employed for longer-span conveyors instead of stringers. Tubular gallery structures are also used to support the belt conveyor whenever the belt conveyor is required to be enclosed. (The structure is not shown in Figure 1.1.)

Pulley is a rotating cylinder mounted on a central shaft that is used to drive, change the direction of a conveyor belt and maintain the tension in a conveyor belt. Drive pulley, also called head pulley (9), is a pulley connected to the drive mechanism of a conveyor belt. The material is discharged over the drive pulley in many conveyor systems. The pulley near the feeding end of the conveyor system is the tail pulley (10), and it turns the return run of a conveyor belt 180° back into the carrying run.

Snub pulley (11) is a small pulley often placed immediately after the drive pulley on the return side of the belt to increase the contact of the belt with the pulley, allowing the transmission of the required tension to the belt. Snub pulley is also placed before the tail pulley on the return side of the belt for improved traction. Bend pulleys (12) are the pulleys used to change the direction of the conveyor belt as in the case of the vertical take-up arrangement (16).

As the belt is carrying the load on it while running, the belt will stretch and slack. As a result, the belt tension will decrease. A tensioning device, called take-up pulley (13), is the pulley used to remove the slack of the belt with the help of counterweights (15) attached to it by moving while the belt is running and to maintain tension. It is installed near the drive pulley on the return side of the belt. A drive, usually an electric motor (14), is attached to the drive pulley through reduction gear and is made to rotate. As the drive pulley rotates, the belt will rotate around the drive and tail pulleys and travels linearly between the two pulleys.

The material to be conveyed is fed onto the belt by a feed chute (17) or a hopper near the tail end or at the other locations as required. The vertical or inclined plates, known as skirt plates (18), extending out from a conveyor’s loading point with rubber sealing skirt material are installed closely above the belt to guide the conveyed material. This material on the carrying side is discharged in a trajectory by the head pulley.

The discharge end usually consists of discharge chute (22), belt cleaners (19), pulley cleaner (21) and a dribble chute (23). Belt cleaners remove the material which clings or adheres to the carrying or top side of the belt. Plough-type belt cleaner (20) is used to clean the bottom side of the belt on ...