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.e^µα

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 T_E from a driving pulley, neglecting losses on the driving pulley due to belt stiffness is determined from the following reaction:

T_e = T₁ – T₂

T_2min > T _{E Max} (1 / (e^µα -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 T_e 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

Operating conditions	Smooth bare steel pulley	Rubber lagging with herring bone grooves	Polyurethane lagging with Herring bone grooves	Ceramic lagging with Herring bone grooves	PVC belt
Dry	0.35 to 0.4	0.4 to 0.45	0.35 to 0.4	0.4 to 0.45	0.25 to 0.35
Clean wet (Water)	0.1	0.35	0.35	0.35 to 0.4	0.15 to 0.3
Wet and dirty ( Clay or Loam)	0.05 to 0.1	0.25 to 0.3	0.2	0.35	Less than 0.25

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

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Minimum belt tension

T = 4.2 P_c ( W_b + W_m )

Where,

P_c = idler spacing on the carrying side

Types Of Belt Conveyor Drives | Belt Conveyor Drive Arrangement

Types of Belt Conveyor 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.