KEYS

A key can be defined as a machine element which is used to

connect to the transmission shaft to rotating machine elements

like pulleys ,gears, sprockets or flywheels.

A key is a piece of mild steel inserted between the shaft and hub

of the pulley to connect these together in order to prevent relative

motion between them.

It is always inserted parallel to the axis of the shaft.

Keys are used as temporary fastenings and are subjected to

considerable crushing and shearing stresses.

A keyway is a slot or recess in a shaft and hub of the pulley to

accommodate a key.

Functions of Keys

There are two basic functions of key. They are as follows:

The primary function of the key is to transmit the torque from the

shaft to the hub of the mating element and vice versa.

The second function of the key is to prevent relative rotational

motion between the shaft and the joined machine element like

gear or pulley.

Different types of keys

Saddle or sunk key

Square of flat key

Taper or parallel key

Key with and with out gib-head

In addition there are special types of keys such as Woodruff, Kennedy or

Feather key.

The selection of the type of key for a given application depends upon the

following factors:

Power to be transmitted

Tightness of fit

Stability of connection

Cost

Design of Square and Flat Key

Square and flat keys are widely used in practice.

A square key ,is in which the height is equal to the width of cross-

section.

The design of flat key is based on two conditions:

1. Failure due to shear stress

2. Failure due to compressive stress.

Kennedy Key