Paper Pulleys
Paper pulleys are made from compressed paper fibre and are formed with a metal in the centre. These pulleys are usually used for belt transmission from electric motors, when the centre to centre shaft distance is small.
Fast and Loose Pulleys
A fast and loose pulley, as shown in Fig. 1, used on shafts enables machine to be started or stopped at will. A fast pulley is keyed to the machine shaft while the loose pulley runs freely. The belt runs over the fast pulley to transmit power by the machine and it is shifted to the loose pulley when the machine is not required to transmit power. By this way, stopping of one machine does not interfere with the other machines which run by the same line shaft.Paper Pulleys, Fast and Loose Pulleys.
The loose pulley is provided with a cast iron or gun-metal bush with a collar at one end to prevent axial movement.
The rim of the fast pulley is made larger than the loose pulley so that the belt may run slackly on the loose pulley. The loose pulley usually have longer hub in order to reduce wear and friction and it requires proper lubrication.
Fast and loose pulley drive, is used when the driven or machine shaft is to be started or stopped when ever desired without interfering with the driving shaft. A pulley which is keyed to the machine shaft is called fast pulley and runs at the same speed as that of machine shaft. A loose pulley runs freely over the machine shaft and is incapable of transmitting any power.
Reference A Textbook of Machine Design by R.S. Khurmi and J.K.Gupta
