Draw neat labeled sketch of crank and slotted lever mechanism. Label all parts.
State any two adverse effects of imbalance.
All the rotating and reciprocating parts should be completely balanced as far as possible. If these parts are not properly balanced,
The dynamic forces are set up.
These forces increase the loads on bearings and stresses in the various members.
Also produce unpleasant and even dangerous vibrations.
Compare brakes and dynamometers (two points).
Brakes : A brake is a device by means of which artificial frictional resistance is applied to a moving machine member, in order to retard or stop the motion of a machine.
Types : Hydraulic brakes
1.Electric brakes 2.Mechanical brakes.
The brake absorbs either kinetic energy of the moving member or potential energy given up by objects being lowered by hoists, elevators etc.
The energy absorbed by brakes is dissipated in the form of heat.
Compare cross belt drive and open belt drive on the basis of: (i) Velocity ratio. (ii) Direction of driven pulley. (iii) Length of belt drives (iv) Application.
Explain: (i) Uniform pressure theory. (ii) Uniform wear theory in clutches and bearing.
(i) Uniform pressure theory:
When the mating component in clutch, bearing are new, then the contact between
surfaces may be good over the whole surface.
It means that the pressure over the rubbing surfaces is uniform distributed.
This condition is not valid for old clutches, bearings because mating surfaces may
have uneven friction.
The condition assumes that intensity of pressure is same.
P = W/A =Constant; where, W= load, A= area
(ii) Uniform wear theory in clutches and bearings:
State inversions of double slider crank chain. Explain Oldham's coupling with neat sketch
Inversions of double slider crank chain:
i.Scotch Yoke mechanism.
ii.Oldham’s coupling.
iii. Elliptical trammel.
Define stability and hunting of governor.
Stability of governor :
A governor is said to be stable when for every speed within the working range there is a definite configuration i.e. there is only one radius of rotation of the governor balls at which the governor is in equilibrium. For a stable governor, if the equilibrium speed increases, the radius of governor balls must also increase.
Hunting of governor :
State the function of flywheel in IC engine.
A flywheel controls the speed variations caused by the fluctuation of the engine turning moment during each cycle of operation.
A flywheel used in machines serves as a reservoir, which stores energy during the period when the supply of energy is more than the requirement, and releases it during the period when the requirement of energy is more than the supply.
State any two advantages of V belt drive over flat belt drive.
Advantages -1. The V-belt drive gives compactness due to the small distance between the centres of pulleys.
2. The drive is positive, because the slip between the belt and the pulley groove is negligible.
3. Since the V-belts are made endless and there is no joint trouble, therefore the drive is smooth.
4. It provides longer life of 3 to 5 years.
5. It can be easily installed and removed.
6. The operation of the belt and pulley is quiet.
7. The belts have the ability to cushion the shock when machines are started.
Define slip and creep in the belt.
Slip : When the frictional grip becomes insufficient. This may cause some forward motion of the driver without carrying the belt with it. This may also cause some forward motion of the belt without carrying the driven pulley with it. This is called slip of the belt and is generally expressed as a percentage. Creep : When the belt passes from the slack side to the tight side, a certain portion of the belt extends and it contracts again when the belt passes from the tight side to slack side.
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