Table of Contents
What is Key?
A key is a machine element which is used to connect a shaft to other machine elements like Gears, Pullies, Couplings, Sprockets or Flywheels. Its primary function is to prevent relative motion between connected parts.
Functions of the a key
It has two basic functions
- Transmit torque from the shaft to hub and from hub to the shaft
- Prevent relative motion of the shaft and the joined machine element
Types of keys
They can be classified on the basis of following factors.
- Cost
- Rigidity of connection
- Tightness of fit
- Power to be transmitted
On the basis of above factors, we have following types of keys
- Key with and without Gib head
- Parallel and taper key
- Flat and square key
- Sunk and saddle key
Types of keys
1. Saddle keys
A saddle is a key which fits in the keyway of the hub only.
Advantage of saddle key
- Since keyway is to be made only in the hub hence its cost is low.
Disadvantage of saddle key
- Power transmission capacity is low
2. Sunk key
A sunk key is a key in which half the thickness of key fits into the keyway of hub and remaining half remains in the keyway of shaft.
- A square key has square cross section.
- A rectangular key has rectangular cross section.
Advantage of sunk key
- Power transmission capacity is high compared to saddle key.
Disadvantage of sunk key
- Since keyway is to be made in both shaft and hub hence its cost is high.
3. Feather key
A feather key is a parallel key which allows relative axial movement between shaft and hub. These can be used with gears or clutches.
4. Woodruff key
Woodruff key is a sunk key in the form of almost semi circular disc of uniform thickness.
Advantage of woodruff key
- It can tilt and align itself according to the shaft
- Extra depth of key in the shaft prevents slip of shaft and hub
Disadvantage of woodruff key
- Due to extra depth of keyway, shaft has low strength
- No axial movement is permitted between shaft and hub
5. Tangent Key
A tangent key is composed of two tapered keys to ensure tight fit. They are used in heavy duty equipment.
Also read:
Good