Types Of Mechanical Keys- Design Of Keys, Keyways
Introduction To Mechanical Key:
Functions of Key:
b)To prevent relative motion between the shaft & mating machine element
Types Of Keys:
- Sunk keys,
- Flat keys,
- Saddle keys
- Pins or round keys
(a) Rectangular sunk keys
(b) Gib head sunk keys
(c) Feather keys
(d) Woodruff keys
A woodruff key is a form of sunk key where the key shape is that of a truncated disc, as shown in the figure-. It is usually used for shafts less than about 60 mm diameter and the keyway is cut in the shaft using a milling cutter. It is widely used in machine tools and automobiles due to the extra advantage derived from the extra depth. Steel keys are widely used in securing machine parts such as gears and pulleys.
- Hollow saddle key
- Flat saddle key
- Parallel pin
- Taper pin
Lewis keys, shown in figure- are expensive but offer excellent service.
• By this means the power transmitted is equally divided amongst the number of keys giving
Design Consideration of key :
2) Tightness of fit
3) Stability of connection
5) Crushing failure of key:
6) shearing failure of key
7) The material of key, shaft should be the same but the key should be weaker than the shaft.
Application Of Mechanical Keys :
a) Rectangular sunk key: for preventing rotation of gears and pulleys on the shaft
b) Gib headed key: used where the key to be removed frequently.
c) feather key: Machine tool
2) Saddle key: for light-duty or low power transmission
3) Round key: Used for low Power drive
4) Splines: Where providing axial movement between the shaft and mounted member
Keyway Design :
- The keyway is a slot machined either on the shaft or in the hub to accommodate the key. It is cut by a vertical or horizontal milling cutter.
- A little consideration will show that the keyway cut into the shaft reduces the load-carrying capacity of the shaft.
- This is due to the stress concentration near the corners of the keyway and reduction in the cross-sectional area of the shaft. It other words, the torsional strength of the shaft is reduced.
- The following relation for the weakening effect of the keyway is based on the experimental results by
- H.F. Moore. e = 1-0.2(w/d)-1.1(h/d)
where e = Shaft strength factor.
w = Width of the keyway,
d = Diameter of shaft, and
h = Depth of keyway =Thickness of key (t )/2
It is usually assumed that the strength of the keyed shaft is 75% of the solid shaft, which is somewhat higher than the value obtained by the above relation.
- In case the keyway is too long and the key is of sliding type, then the angle of twist is increased in the ratio kθ as given by the following relation
- Kθ = 1+0.4 ( w/d ) – 0.7 ( h/d )
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