Creep

When belt passes from slack to tight side, a certain portion of belt extends and again contracts when belt passes through tight to slack side. Due to fluctuation in length of the belt, there is relative motion between belt and pulley surface. This relative motion is known as creep. Considering the creep, velocity ratio can be expressed by,

where N₁ and N₂ are the speeds of driving and driven pulleys, respectively; D₁ and D₂ are the diameters of driver and driven pulleys, respectively; σ₁ and σ₂ are the stresses developed in tight and slack side of belt, respectively; and E is the modulus of elasticity of belt materials.

Example 15.1: The speed of a driving shaft is 100 rpm and the speed of the driven shaft is 150 rpm. Diameter of the driving pulley is given as 500 mm, find the diameter of driven pulley in the following cases:

1. If the belt thickness is negligible.
2. If the belt thickness is 6 mm.
3. If total slip is 5% considering thickness of belt.
4. If a slip is 2% on each pulley considering thickness of belt.

Solution: