Mechanical Engineering

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°.

Minimum belt tension

T = 4.2 P_c ( W_b + W_m )

 

Where,

P_c = idler spacing on the carrying side

W_b, W_m are the weights of belt and pay load per meter length of belt respectively.