26-07-2012, 12:07 PM
COUPLING,CLUCHES&BRAKES
COUPLING,CLUCHES&BRAKES.pptx (Size: 333.02 KB / Downloads: 37)
Introduction
A coupling is a device used to connect or couple to shafts while clutch is a device which facilitate engage and disengage of driving shaft and driven shaft when ever required, even it may rotate. A clutch may be considered as one type of coupling. The brake is a frictional device whose primary function is to control the motion of machine member. It is device used to bring machine member in to rest or slow down.
Couplings
Shaft coupling are used in machinery for following purpose.
To connect shafts of motor and generate which are manufactured separately and to provided for disconnection for repairs or alternation.
To reduce the transmission of shock loads from shaft to another.
To allow misalignment of the shaft or to introduce mechanical flexibility.
To introduce protection against overloads.
Friction clutches
A friction clutch is used in the transmission of power between two machine shafts which may be required to stop or start frequently. It’s also used in cases, in which power is to be delivered to machines partially or fully leaded. The force of friction is used to start the driven shaft from rest and gradually brings it up to required speed without excessive slipping of the friction surfaces.
Disc clutch
The spring is pressed the driven flange to the driving flange. When power is not required at driven shaft, driven flange is disengaged from driving flange by operating lever. The torque is transmitted by friction between the flanges and friction disc. Multi disc clutch has more number of contact surfaces discs on driving and driven shaft.
Centrifugal clutch
It consists of a number of shoes on the inside of a drum or rims other pulley. The upper surfaces of the shoes are covered with friction material. The shoes can move radically in guides. The shoes are held in slots of the spider by help of springs. The spider is fitted on the driving shaft. The springs exert a radically inward force which is constant. Due to mass, when driving shaft revolving, the mass of shoes causes a radically outward force. This outward force increases with speed of shoes revolving with driving shaft. When centrifugal force is equal to spring force, the shoe is just floating.