For procedures, see your mechanical laboratory manual.

Title: Slip And Creep Measurement in a Belt Drive

Aim

1. To measure the coefficient of friction between pulley material and different belt material.
2. To measure power transmitted with varied belt tension and plotting a graph of power output Vs (T1-T2)/2 ie tension characteristics
3. To measure percentage slip and fixed belt tension by varying load on the brake drum and input graph of (T1-T2) Vs percentage slip or slip characteristics fixing a creep zone from the graph.
4. To measure belt slip speed and observe the limited value of load constant speed when the slip just starts.

Theory

Slip in a belt drive

Slip in a belt drive is a phenomenon of the relative motion between the belt and pulley. The slip is mainly due to reduced frictional grip between the belt and the pulley and by increasing the angle of contact between the pulley and the belt. Ideally, it should be zero. The difference between the linear speed of the pulley rim and the belt is called the measure of slip. This slip is expressed in percentage; Slip reduces the driven pulley and power transmission efficiency. In other words, when the belt gets mounted on the slip arch of the pulley; At that time due to inappropriate friction between the two, the pulley travels with relatively greater velocity, leaving the belt behind.

Creep in a belt drive

When the belt moves over the pulley to transmit power, the tension on the right side is more than the tension on the slack side. As the belt material is elastic, it elongates more on the right side than on the slack side, resulting in unequal stretching on two sides of the drive.
Therefore, the length of the belt received by the driving pulley is more than the length that moves of the driving pulley. Hence, the belt must creep back slightly relative to driving pulley rim. On the other hand, the length of the belt received by the driven pulley is less than the length that moves of the driven pulley. Hence, the belt must creep forward slightly relative to the driven pulley rim.

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. The effect of creep back on the driving pulley is to slow down the speed of the belt with respect to the driving pulley and the effect of creep forward on the driven pulley is to slow down the speed of the driven pulley. Thus the net effect of creep is to reduce the speed ratio than the theoretical expected.

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.

Applications

1. Drives to beaters on conventional blow rooms. crossed flat-belt transmits drives from cylinder to flat on old cards.
2. Drives in high production cards such as the drive from motor to lickerin and cylinder; drive to cleaner roller at the delivery side; drive from motor to flat- stripper roller and crossed-flat-belt drive from cylinder to a pulley from where further drive proceeds through double stage speed reduction using worm and worm gears and a mechanical clutch to the driving-shaft of flat.
3. Drive to drafting rollers and other rolling elements on a single delivery drawing machine.
4. Drives to opening rollers, friction drums, and take-off rollers on friction spinning machine
5. Drive to the rotor on rotor-spinning machine
6. Main drive on the draw-texturing machine.
7. Drive to creel-rollers of a high-speed drawing machine.

References

1. Basics of Belt Drives, planetengineering.com
2. Belt, wikipedia.org