The actual difference between the surface speed of the belt and pulley is known as ______.

Concept:

• As the belt turns on a pulley it tends to stretch on the contact area of the driving pulley and shorten on the driven pulley.
• This localized movement of the belt is a direct result of the elastic stretch and is known as creep. The greater the load more will be the creep.
• Slip is the actual difference caused between the surface speed of the belt and pulley.
• The effect of slip may be reduced by decreasing the pulley ratio and maintaining proper alignment.

Cause of belt slip:

• Less tension
• Overload
• Oiliness in the groove of the pulley or belt

Creep

• Creep is the tendency of a solid material to move slowly or deform permanently when it is subjected to long-term exposure of high levels of stress that are still below the yield strength of the material.
• When a belt rotates through two pulleys, the upper side of this drive will be in tension i.e. tight side and the lower side will in compression i.e. slack side.
• In pulley rotation certain portion of the belt will pass through the area where it will change from tight side to slack side, then the length of that specific portion of the belt will expand and contract subsequently and a relative motion will happen between the belt and pulley surface. This phenomenon is called creep of the belt.
• This motion of belt relative to driving and driven pulley due to unequal stretching of the two sides of the drive is known as creep.

Difference between slip and creep.

• Creep is due to the elastic property of the belt whereas, the conventional slip is due to insufficient frictional grip between the belt and pulley.
• However, the effect of the creep, as well as slip, is to reduce the speed ratio, and hence power transmission.