What Is Cotter Joint And Knuckle Joint? Difference Between Cotter & Knuckle Joint - SKengineers

 

WHAT IS A COTTER JOINT AND KNUCKLE JOINT?

Ø  COTTER JOINT –

Ø  Introduction –

1.      A cotter joint is used to connect two co-axials rods or bars, which are subjected to axial tensile and compressive forces. It is temporary joint.

2.      A cotter is a flat wedge shaped piece having rectangular cross-section.

3.      Width of cotter is tapered (either on one side or both sides) from top to bottom for easy adjustments such as in and out of a rectangular slot made in spigot as well socket.

4.      Value of taper: taper in cotter varies from 1 in 48 to 1 in 24.

5.      Material for cotter: mild steel and wrought iron.

Ø  APPLICATIONS OF COTTER JOINT –

·        Connection of piston rod to cross-head of a reciprocating steam engine.

·        Valve rod and its stem.

·        Strap end of connecting rod.

·        Lewis foundation bolt and other cottered foundation bolts.

·        Piston rod to the tall end (rod) in an air pump.

Ø  TYPES OF COTTER JOINT –

1.      Socket and spigot cotter joint.

2.      Sleeve and cotter joint.

3.      Gib and cotter joint.

Ø  ADVANTAGES OF COTTER JOINT –

                           i.          Quick to assemble and dismantle parts.

                          ii.          Very high tightening force due to the wedge action developed. Which prevents loosening of parts in service.

                         iii.          Simple to design.

                         iv.          Easy to manufacture.

Ø  KNUCKLE JOINT –

Ø  Introduction –

1.      A knuckle joint is used to connect two circular rods, which are subjected to tensile loads. A knuckle joint may be easily disconnected for adjustment or repairs.

2.      In knuckle joint, the end of one rod is made into shape of an eye.

3.      Similarly, one end of other rod is formed into shape of a fork with an eye in each of the two fork legs.

4.      The knuckle pin passes through both, eye hole and fork holes.

5.      Knuckle pin can be secured by means of collar and taper pin as split pin.

6.      Knuckle joint allows relative angular movement of rod in the plane about axis of pin.

Ø  APPLICATIONS OF KNUCKLE JOIINT –

·        Used to connect links and structural members.

·        Air brake arrangement on locomotive.

·        Connections of valve rods and eccentric rods.

·        Reversing gear mechanism in case of steam locomotive.

·        Remote controls of steam valves.

Ø  ADVANTAGES OF KNUCKLE JOINT –

                           i.          Simple to design.

                          ii.          Easy to manufacture.

                         iii.          Due to less number of parts , cost of knuckle joint is less.

                         iv.          Highly reliable.

                          v.          Quick assembly as well as quick dismantling, whenever required.

Ø  DIFFERENCE BETWEEN COTTER JOINT AND KNUCKLE JOINT –

Sr. No.	COTTER JOINT	KNUCKLE JOINT
1.	Capable of taking both tensile as well as compressive load.	Can take only tensile load.
2.	Cannot permit angular movement between rods.	Permits limited angular movement between rods.
3.	Cotter is not subjected to bearing failure.	Knuckle pin is subjected to bearing failure.
4.	It is known as single cotter joint.	It is known as forked pin joint.
5.	Taper and clearance is provided in the cotter.	Theoretically, no taper or clearance is provided. But, in actual practice, to permit angular movement between rods, a very small clearance exists.
6.	Cotter is rectangular in cross-section.	Knuckle pin is circular in cross-section.
7.	APPLICATIONS – Cotter foundation bolt, Joining piston rod with cross-head. Joining two rods with a pipe, Big end of connecting rod of a steam engine.	APPLICATIONS – Tie bar and roof truss, Links of suspension bridge, Valve mechanism, Fulcrum of the lever, Links of bicycle chain, Joint for rail shifting mechanism.