1. Positive clutches
2. Friction clutches 1. Positive Clutches Positive clutches are use as a positive drive is necessary. The simplest kind of a positive clutch is a jaw or claw clutch. Jaw clutch allow one shaft to drive a different through a direct contact of interlock jaws. It consists of two halves, one of which is eternally fastened to driving shaft through a sunk key. The other half of the clutch is movable and it is free to slide axially on the driven shaft, but it is disallowed as of turning fairly to its shaft through means of feather key. Jaws of clutch can be of square type or of spiral type.
A square jaw type is use where engagement and detachment in motion and under load is not required. This type of clutch will convey power in also direction of rotation. Spiral jaws can be left-hand or right-hand, as power transmit with them is in one direction simply. This type of clutch is rarely use where clutch must be engage and detached as in motion. Use of jaw clutches are commonly apply to sprocket wheels, gears and pulleys. In such a case, the non-sliding part is made integral by the hub. 2. Friction Clutches Friction clutch has its main application in transmission of power of shafts and machines which have to be started and closed commonly. Its use is also found in cases in which power is to be deliver to machines partly or completely loaded. Force of friction is use to start driven shaft as of rest and slowly brings it up to correct speed with no extreme slipping of friction surfaces. In automobiles, friction clutch is use to attach engine to drive shaft. In working such a clutch, care should be taken so that friction surfaces hold simply and steadily bring driven shaft up to good speed. The proper position of bearing must be maintain and it should be placed as close to clutch as possible. It can be noted that:
1. The contact surfaces must expand a frictional force that can pick up and hold the load by sensibly low pressure among the contact surfaces.
2. Heat of friction must be quickly *dissipate and propensity to grab should be at a smallest.
3. Surfaces must be back by a material stiff sufficient to make sure a reasonably regular distribution of pressure.