In the case of the design of friction clutches, the uniform rate of wear theory is used over uniform pressure. The reasons may be the following: 1. It gives lower frictional torque. 2. It gives higher frictional torque. 3. The intensity of pressure is maximum at the inner radius and minimum at the outer radius of the friction or contact surfaces. 4. This concept is prevalent for running and old clutches. Which of the above reasons is correct?

Option 1 : 1, 3 and 4

Explanation:

According to the uniform wear theory

Wear ∝ Pr

And Pr = constant

Where P is the pressure and r is the radius of the disc.

The pressure will be maximum where the radius is minimum i.e. at the inner radius and it will be minimum at the maximum radius i.e. at the outer radius.

It is more logical and safer to use uniform wear theory in the design of the clutches due to the following reasons:

• The uniform pressure theory is applicable only when friction lining is new.
• The uniform wear theory is applicable when the friction lining gets worn out, a major portion of the life of the friction lining comes under the uniform wear criterion.
• The torque transmitting capacity of the new clutch is slightly more than worn-out clutches because the friction radius of the new clutch is slightly more than worn-out clutches.

Note:

Generally, uniform wear theory is used to design a clutch. Since the uniform wear theory assumption gives lower torque capacity, the designing based on uniform wear theory for higher torque capacity will need bigger clutch dimensions statement 1 is correct.