Keys Cotter Joints
Transcript of Keys Cotter Joints
[email protected], COTTER and JOINTS
Keys:
- These are temporary fasteners.- Used to hold pulleys, wheels, gears etc on the
rotating shafts, such that there is no relative rotary motion between the pairs.
- Functions of keys:o It is an agent in transmission of power,
motion, torque between the pairs.o It is also used as a safety feature. When
overloading occurs, the key will fail before the actual parts.
o Keys are easy to replace and costs less.
Classification of keys:
Depend chiefly upon the load to be transmitted:(1) Heavy duty keys
a. Sunk key- A key which goes in the key seat. The key seat is a
sort of groove to hold the key. Key seat is machined partly in the shaft and partly in the part supported.
- Sunk key is mostly of rectangular or square key. These two can be parallel or taper keys.
- Drawing proportions:o Rectangular key: W=0.25D and
T=0.66W.
o Square key: W=0.25D and T=W.
(b) Gib head key - Key is provided with a head at one end to facilitate withdrawal of the key.
(c) Splines- The key is actually the solid integral part of the shaft and corresponding grooves/ keyways are made on the supported parts.- There can be number of keys on the circumference of the shaft.
(2) Light duty keys:a. Flat saddle key.
- It is flat on the shaft.- As it is liable to slip on shaft, so it is used
for light duty.
b. Hollow saddle keys:
- The key is curved to fit on the shaft. - It increases friction.
c. Round or pin key - It is a circular pin. - It is fitted in a hole drilled partly in the end
of a shaft and partly in the supported part.
d. Woodruff key- It is a segmental disc with a flat or round bottom.- The keyway is also of disc type.- It is an self adjustable key.
COTTERS
- These are again the temporary fasteners.- It is a wedge shaped piece of mild steel, tapered on
one or both side (1:20-50).- It is tapered so as:
o Facilitate the positioning and withdrawing of the cotter.
o For lateral adjustment. - Used to hold two parts where the parts are
subjected to axial forces only.- Usually driven perpendicular to the axis of the
connected parts.
DIFFERENCE BETWEEN KEYS AND COTTERS
- Keys are driven parallel to the axis but cotters perpendicular to axis.
- Keys are used where parts are subjected to torque but cotters are used where parts are subjected to tensile or compressive forces.
- Keys resist shear over a longitudinal section but cotter resist shear over two transverse sections.
COTTERED JOINTS
- Joints formed by using a cotter are called cottered joints.
(1) Spigot and socket cottered joint - Used for round rods.
2. Sleeve and cotter joint.
3. Gib and cotter joint
- used for square rods. - Gib is a piece of mild steel having the same thickness as cotter and is used in combination of cotter.
- Uses of gib:
(a) When the cotter is driven in position, it has the tendency to bend the lower part of the fork end away from rod. It is prevented by using a gib.(b) To increase the bearing area of contact between the mating parts.
PIN JOINT OR KNUCKLE JOINT- Joint allows a small angular movement of the rods
relative to each other.- Joint is capable of transmitting rotary and
transverse motion.