A coupling is termed as a device used to make permanent or semi-permanent
connection where as a clutch permits rapid
connection or disconnection at the will of the operator.
Shaft couplings are used in machinery for several
purposes the most common of which are following:-
1. To provide for the connection of shafts of units that are manufactured
separately such as a motor and a generator, and to
for repairs or alterations.
2. To provide for misalignment of the shafts or to introduce mechanical
3. To reduce transmission shock loads from one shaft to another.
4. To introduce protection against overloads.
5. To alter the vibration characteristics of rotating units.
Shaft couplings will be used under the following conditions:-
1. With shafts having collinear axes, that is, axes in the same straight line. Rigid or flexible
couplings of various form used here.
2. With shafts having intersecting axes. Universal Coupling is employed.
3. With shafts whose axes are parallel and at a relatively small distance apart. Here the
double slider crank principle of
mechanism is used.
A shaft coupling should have the following requirements:-
1. It should be easy to connect or disconnect.
2. It should transmit the full power of the shaft.
3. it should hold the shafts in perfect alignment.
4. It should have no projecting parts.