Keys in machine design

Keys :

What is the key ?

• A key can be defined as a machine element which is used to connect the transmission shaft to rotating machine elements like pulleys, gears, sprockets or flywheels.

Key joints consisting of shaft, hub and key.

Keys may be made of plain carbon steels like 45C8 or 50C8.

Functions of key :

• To transmit the torque from the shaft to the hub of the mating element and vice versa.
• To prevent relative motion between the shaft and the joined machine element like gear or pulley.
• In some cases, it is also used to prevent axial motion between two elements in case of father key or splined connection.

A drawback of the key joint :

• The main drawback of a key joint is due to keyway stress concentration in the shaft and the part becomes weak.

There are different types of keys are available and there is a number of standards.