2. Coupling and Clutches are power
transmission elements. It is used
for transmitting power from one
shaft to the another. A Brake is a
frictional device whose primary
function is to control the motion of
the machine member.
INTRODUCTION:-
3. -:Coupling:-
A coupling is a device used to connect or couple two
shafts. Shafts are mostly available up to 7 meters length
due to transport difficulty. To get a greater length , it is
necessary to joint two or more pieces of the shaft using
coupling.
Shaft coupling are used in machinery for following
purposes:
1) To connect shafts of motor and generator which are
manufactured separately and to provide for
disconnection for repairs or alternations.
2) To reduce the transmission of shock loads from one
shaft to another.
3) To allow misalignment of the shaft or to introduce
mechanical flexibility.
4. Types of couplings
Coupling
Rigid
coupling
Sleeve or
muff coupling
Clamp or
comression
coupling
Flange coupling
Unprotected type
Protected type
Flexible
coupling
blushed pin type
flange coupling
universal
coupling
Oldham
coupling
5. Sleeve or muff coupling
•It is made from cast iron and very simple to
design and manufacture.
•It consists of a hollow cylinder whose inner
diameter is the same as diameter of the shaft.
•The hollow cylinder is fitted over the end of the
two shafts with the help of taper sunk key.
•A key and sleeve useful to transmit power from
one shaft to the other shaft.
•The main disadvantage of this coupling is that it
is difficult to assemble when there is no perfect
alignment between shafts.
7. Clamp or split muff or compression
coupling
In this coupling , the muff or sleeve is made into
two halves parts of cast iron and they are join
together by means of mild steel studs and nuts.
The advantages of this coupling is that assembling
of the coupling is possible without change the
position of shaft.
This coupling is used for heavy power transmission
at moderate speed.
9. Flange coupling
This coupling is having two separate cast iron
flanges.
Each flange is mounted on the shaft end and
keyed to it.
This coupling prevent catching clothes of
workman.
This flange couplings is most accurate and rigid.
It is used for heavy power transmission at low
speed.
11. Bush pin type flange coupling
This is modified form of protected type flange
coupling.
This type of coupling has a pins and it work as a
coupling bolts.
The rubber or leather bushes are used over the
pins.
This coupling is used to connect of shafts which
having the small parallel misalignment, angular
misalignment and axial displacement.
This type of coupling is mostly used to couple an
electric motor and machine.
13. Universal coupling
Universal coupling consists of two similar forks
keyed on the ends of the two shafts.
This coupling is used to connect two shafts whose
axis intersect.
It also used to connect two shafts, where the
angle between two shafts may be varied when
they rotate.
It is widely used in automobile and machine tools.
15. Oldham’s coupling
It consist of two flange and a central floating
disc.
This coupling is used in connecting two parallel
shafts but not in alignment, and their axis are at
small distance apart.
17. Clutches
•Clutch is a one of the form of coupling.
• Clutches is used to transmit the power from driving
shaft to driven shaft of machine which may be
required to start or stop frequently.
•It is so designed that the two members may be
engaged or disengaged whenever required either by a
hand operated device or automatically by the action
of some power driven devices.
19. Disc clutches
This type of clutch consists of two flanges, one
flange is rigidly to the driving shaft and other
flange fitted to the driven shaft.
Single disc clutches are used in automobiles.
When large torque transmission is required the
multi disc clutch are used.
Multi disc clutch has more number of contact
surfaces discs on driving and driven shaft.
21. Cone clutch
The cone clutch consists two cones , one internal
cone fixed to the driven shaft and another cone
fitted on the driven shaft.
The operating lever used only for disengagement
of the clutch.
The main advantage of cone clutch over the disc
clutch is very simple and required less axial
pressure to disengaged the clutch.
23. Centrifugal clutch
It consists of a number of shoes on the inside of a
drum or rim of the pulley.
The upper surface of the shoes are covered with a
friction material.
The spider is fitted on the driving shaft.
When centrifugal force is equal to spring force, the
shoe is just floating.
But, when centrifugal force higher than the spring
force, the shoes moves outward and comes into
contact with the driven member and pressure against
it.
The increase of speed causes the shoes to press
harder and clutch transmit more power.
25. Positive Contact Clutch
It is consists of segmental projections on one of
the flange and corresponding recesses on other
flange on the driven shaft.
Driving flange rigidly keyed to the driving shaft
while the other flange is keyed to driven shaft by
splines so that it can slide on that shaft.
The sliding flange engage with the fixed flange to
transmit the motion and power from driving shaft.
This clutch is used for the transmission of power
in agricultural equipment like tractor, thresher,
etc.
27. Brakes
•A brake is a mechanical device which
produces frictional resistance against moving
machine member, in order to slow down the
motion of machine.
• In the process of performing this function,
the brake absorbs kinetic energy of moving
member and the brake absorbs potential
energy of lowering member.
•The energy absorbed by brakes is released to
surrounding in form of heat.
29. Block brake
(1) Single block or shoe brake:
A single block is consists of a block which is
pressed against the rim of revolving brake wheel
drum.
This brake is used in railway trains and tram
cars.
The prony brake is example of block brake.
31. (2) Double block or shoe brake:
• It consists of two brake blocks at the
opposite ends of the wheel.
• These shoes apply force to both sides of
wheel and reduces the unbalanced force on
the shaft.
• The spring pulls the upper end of brake
arms together and brake is applied.
• When a force is applied to the bell crank
lever, the spring is compressed and the brake
is released.
• This brake is used on electric cranes.
• The bicycle brake is example of double block
33. Band brake
A band brake consists of a flexible steel band lined
with friction material, which wrap to the brake drum.
When an upward force is applied to the lever end, the
lever turns about the fulcrum pin and tightens the
band on the drum and hence the brakes are applied.
The friction between the band and the drum provides
the braking force.
This type of brake is used in civil construction
equipment and also in automobiles as hand brake.
The rope brake is example of band brake.
35. Internal expanding shoe brake
An internal expanding shoe brake consists of two
shoes.
The outer surface of the shoes are covered with
friction material.
Each shoe is pivoted at one end about a fixed fulcrum
and other end rests against cam.
When the cam is operated, the shoe are pushed
outwards against brake drum.
The friction between the shoes and the drum
produces the braking torque.
This type of brake is commonly used in motor cars and
light trucks.
37. Difference Between A Brake And
A Clutch
A brake is used to slow down or stop the motion of a
moving body, whereas a clutch is to transmit the
motion of a moving body to another body by means of
engagement.
In a brake , the force applied is converted into
frictional resistance , while in a clutch the force is not
converted into frictional resistance except in case of
slip.
A brake always remains disengaged and may be
engaged when required whereas a clutch always
remains engaged.
