Chain
Drive:
Chain drives are used where positive action is required. The velocity is constant
to some extent. Power is transmitted, in this case over a shorter distance than
in the case of belt or rope drives. Chains are made up of rigid links and of various
types. They are classified as: 1.Hoisting chains 2.Conveying or elevating
chains. 3.power transmission chains. The
wheels over which chain runs are called sprocket wheels. These wheels have projecting
teeth which fit the suitable recess in the links of the chain and thus enable
a positive drive to be obtained.
The pitch of the chain is defined as the distance between a hinge center of one
link to the corresponding hinge center of the adjacent link. The pitch circle
diameter of the chain sprocket is the diameter of the circle on which the hinge
centers lie, when the chain is wrapped round the sprocket. Quality:
Sources of errors in manufacturing gears: The gears (gear
teeth) are generally made by one of the following two methods: (i) Reproducing
method , in which the cutting tool is formed involute cutter ,which forms the
gear teeth profiles by reproducing the shape of the cutter itself. In this method,
each tooth space is cut independently of the other tooth spaces. (ii) Generating
method, in which the cutting tool (hob forms) the profiles of several teeth simultaneously
during constant relative motion of the tool and bank. The
various sources of errors in the gear made by reproducing method can be due to
(i) incorrect profile on the cutting tool, (ii) incorrect positioning
of the tool in relation to the work and (iii) incorrect indexing of the blank The
sources of error when gears are made by generating method are: (i) Errors
in the manufacture of the cutting tool (ii) Errors in positioning the tool
in relation to the work and (iii) Errors in the relative motion of the tool
and the blank during the generating operation. |