The torque (T), transmitted from a middle steel bottom roller to an apron can be given by the formula:

T= (Force in pulling apron part - Force in non pulling apron part) x Middle Roll dia/2

The force ratio between the pulling part and the non pulling part of the apron is :

F (pulling) / F (non pulling) = e^(2.f.α)4

In which:

f = friction factor between steel bottom roller and apron

α = covered angle or wrap angle of apron over steel bottom roller.

The torque can now be written as:

T = F (pulling) x (1 - e^-(2.f. α)) x D/25

T = F (non pulling) x (1 + e^ (2.f. α)) x D/2..6

From this equation can be read:

1)       Torque transmitted is higher with higher pre-stress

2)       Torque transmitted is higher with higher friction values

3)       Torque transmitted is higher with larger covered angle or contact angle.

4)       Torque transmitted is higher with larger diameter of steel bottom roller