BELT CONVEYORS

A belt conveyor is rubber or textile structure with a belt shape closed ring, with a vulcanized or metallic joint, used for material transportation.

Belt conveyors are the most used for transport of solid objects and bulk materials at great speed, covering great distances (up to 10 km)

INTRODUCTION

BELT MATERIAL

IDLERS(ROLLERS)

DRIVING ARRANGEMENT

TENSIONING ARRANGEMENT

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Components of belt conveyor

Conveyor belts generally are composed of three main components:1. Carcass2. Skims3. Covers

There are two types of belt available:Rubber beltSteel Cord

BELT CONSTRUCTION

The reinforcement usually found on the inside of a conveyor belt is normally referred to as the “carcass”. The carcass is used for following reasons:-

Absorb the impact of the impinging material being loaded onto the conveyor belt. Provide the bulk and lateral stiffness required for the load support.

CARCASS

The most common carcass design is made up of layers or “plies” of woven fabrics bonded together. This “conventional plied” belt construction, generally employs a plain weave or twill weave carcass which is built up into as many layers as is required to provide the necessary belt strength…usually bound together with rubber.

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.

PVC belting is generally selected for underground mining applications where fire hazard exists.

The rubber, PVC or urethane between plies is called a “skim.” Skims are important contributors to internal belt adhesions, impact resistance, and play a significant role in determining belt “load support”.

Improper or marginal “skims” can adversely affect belt performance in general and can lead to ply separation and/or idler junction failure.

2. Skims

Covers are used in conveyor belt constructions in order to protect the base conveyor belt carcass and, if possible, to extend its service life. In addition, covers do provide the finished belt with a wide variety of desirable properties, including the following:

A. Textures To increase friction To increase inclination

B. CleanabilityC. A specific coefficient of frictionD. A specific colorE. Cut resistanceF. Enhanced impact resistance, etc.G. HardnessH. Fire Resistance, Oil & Chemical Resistance

3. COVERS

In addition to selecting proper compounds for cover material, it is also necessary to determine the proper cover thickness.

The thickness of a cover is influenced by the amount of abuse and wear the belt will receive. The cover is usually the lowest cost component of the belt. The severity of the wear depends on the nature of the material and on the size, weight, shape and trip rate of the Material conveyed.

Sharp edges, particularly on large pieces, can quickly cut a cover badly. On the other hand, if loading conditions are ideal, with the material being loaded in the direction of travel of the belt, and with only a slight impact onto the belt, even very sharp material may not seriously cut or wear the belt surface.

IDLERS (ROLLERS)

TYPES OF CARRYING IDLERS

TYPES OF IDLERS

TYPES OF RETURN IDLERS

DRIVING ARRANGEMENT

All belt conveyors require the use of some form of take up device (Tensioning Arrangement) 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.

1.Fixed take up device that may be adjusted periodically by manual operation2.Automatic take up devices for constant load type

TENSIONING ARRANGEMENT

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.

DISADVANTAGEThe 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.

Manual Screw 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:

Inclined conveyors require an anti-runback device to prevent reverse movement of the belts. Such a device is referred to as a backstop, or holdback.

Though backstops are most likely to be found on inclined conveyors, they are also employed on flat, overland conveyors to avoid the unusually severe shock loading on start-up where the loaded belt sags between idlers. This paper will direct its attention to backstops installed on inclined conveyors.

Without a backstop, a reversing conveyor can rapidly accelerate to a runaway condition, which can kill or injure personnel, damage or destroy drive train components, tear or rip expensive belting, or cause considerable other damage.

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