BELT DRIVES

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.

CONVEYOR

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.