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SASTRA University

V - Belt DrivesWhat is a V-belt?

It is available asSingle V belt, Multiple V-belt and Ribbed belts.

A V belt is made of fabric and cord, usually cotton, rayon, or nylon, and impregnated with rubber.Therefore, these belts are manufactured only for certain standard lengths.

These belts have trapezoidal cross section and do not have any joints.. To accommodate these

belts the pulleys have V shaped grooves which makes them relatively costlier. Multiple groovepulleys are available to accommodate number of belts, when large power transmission isrequired.

It is mostly used in factories and workshops, where a great amount of power is to be transmitted,from one pulley to another, when the two pulleys are very near to each other.

What are the advantages of V belt drives? V-belt drives are most recommended for shorter center distances and give compactness.

V belt can have transmission ratio up to 1:15

The drive is positive because the belt slip is very small.

As the belts are endless type, V-belt drives do not suffer from any joint failure and are quiet inoperation.

They can be operated at any position of the drive (i.e., horizontal, vertical or inclined) and evenwith vertical shaft.

In this drive, the tight side of the belt need not compulsorily be at the bottom side of the pulley,like in flat belt drive

They can take up shocks especially at starting

High smoothness of operation is obtained owing to the absence of laced joints and other beltfasteners which may produce noise as in the case of flat belts.

During operation, the belt will not come out from pulley at any cost which may sometimeshappened in flat belt drive if the shafts parallelism is slightly changed.

The wedging action of the belt in the groove gives highest value of limiting ratio of tensions.

What are the disadvantages of V belt drives? The v-belts are not as durable as flat belts.

The v-belt drive cannot be used with large centre distances. The construction of pulleys for V-belts is more complicated than that pulleys of flat belts.

The power transmitting capacity of V-belts is in lower range than flat belt.

They cannot be used for cross-belt drive or quarter-turn drive.

What is the nomenclature of V-belt ?

A typical V-belt section is shown in Fig. The geometrical features of the belt section are indicatedin the figure. The pitch line, which is also marked as N-A, is the neutral axis of the belt section.The design calculations for V-belt drives are based on the pitch line or the neutral axis.

Fig. Cross section of a V belt Fig. Cross section of a V-grooved pulley

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SASTRA University

Derive the relations for the ratio of driving tensions of a V belt.V-belts have additional friction grip due to the presence of wedge. Therefore, modification is needed in

the equation for belt tension. The equation is modified as,

Where = Belt wedge angle and = Coefficient of friction between

the belt and sides of the groove

Why slip is less in the case of V-belts when compared with flat belts?The slip is less due to the wedge action in the grooved pulley.

What is the included angle for V-belt groove? The included angle for V-belt groove lies between 32 and 38.

What is the included angle for V-belt? The included angle for V-belt groove lies between 30 and 40.