Types of joint (knuckle joint ,cotter joints and turnbuckle joint)

INTRODUCTION OF KNUCKLE JOINT:

. A knuckle joint is a mechanical joint used to connect two rods which are under a tensile load, when there is a requirement of small amount of flexibility, or angular moment is necessary. There is always axial or linear line of action of load. 

The knuckle joint assembly consists of the following major components:

Single eye.

Double eye or fork

Knuckle pin.

Collar

Taper pin

At one end of the rod the a single eye is formed and a double eye is formed at the other end of the rod. Both, single and double eye are connected by a pin inserted through the eye. The pin has a head at one end and at other end there is a taper pin or split pin. For gripping purpose, the ends of the rod are of octagonal forms. Now, when the two eyes are pulled apart, the pin holds them together. The solid rod portion of the joint in this case is much stronger than the portion through which the pin passes. 

The modes of failure are:

Shear failure of pin (single shear).

Crushing of pin against rod.

Tensile failure of flat end bar.

Advantages of Knuckle Joint:

Knuckle joint can withstand large tensile loads.

It has good mechanical rigidity.

It is easy to manufacture and set up.

It can be easily dismantled and assembled.

Design is simple and easy.

 

Disadvantages of Knuckle Joint:

The joint cannot withstand large compressive loads.

It permits angular movement in only one plane.

It is not as flexible as universal joint.

 

Applications of Knuckle Joint:

Knuckle joints find a wide variety of applications. They are used in:

Bicycle chains

Tractors

Trusses

Cranes

Chain straps of watches

Earth movers

Robotic joints

Structural members

INTRODUCTION ON COTTER JOINT:

This is used to connect rigidly two rods which transmit motion in the axial direction, without rotation. These joints may be subjected to tensile or compressive forces along the axes of the rods. The very famous example is the joining of piston rod's extension with the connecting rod in the cross head assembly.

   It consist of three types:

SOCKET AND SPIGOT JOINT

SLEEVE AND COTTER JOINT

GIB AND COTTER JOINT

Advantages of cotter joint :

This joint is the simplest cotter joint in existence.

It is quite rigid and can take both tensile and compressive loads.

It can be easily assembled and dismantled.

 Disadvantages of Cotter Joint:

Rectangular rods and dissimilar cylindrical rods cannot be connected using this joint.

Unlike the universal, a sleeve and cotter joint does not allow angular misalignment between its cylindrical members.

It cannot connect cylindrical members which undergo  rotation.

Applications of cotter joint :

Joint between the piston rod and and the cross head of the steam engine

Joint between the slide spindle and the fork of the valve mechanism

Joint between the piston rod and the tail

Connecting two halves of flywheel

INTRODUCTION ON TURNBUCKLE :

A turnbuckle, stretching screw or bottlescrew is a device for adjusting the tension or length of ropes, cables, tie rods, and other tensioning systems. It normally consists of two threaded eye bolts, one screwed into each end of a small metal frame, one with a left-hand thread and the other with a right-hand thread. The tension can be adjusted by rotating the frame, which causes both eye bolts to be screwed in or out simultaneously, without twisting the eye bolts or attached cables.