NB_MEC503_Clutches_Questions_2020

Questions on Clutch
1) Where do we use square jaw clutches?
Answer: They have inherent limitation of sudden engagement and poor slip during
disengagement. Hence they are used for very low speed application under 10 rpm. In
current textile machines they are not used.
2) What is the main advantage of toothed clutch?
Answer: They provide positive engagement which facilitates large power transmission. For
the same reason they are smaller in size and can be accommodated in the limited space of
machine compared with friction clutches.
3) Why do we need clutch in the drive from doffer to feed roller?
Answer: During lot changes the card must be cleaned thoroughly. For this the feed roller
must be stopped while running the other elements (lickerin, cylinder and doffer).
4) What is the main advantage of friction clutches?
Answer: They are gradually engaging clutches. Initially, when the disks contact, the output
disk slips; and gradually picks up the speed. In the meantime, the motor generates enough
torque. In case of machine jamming, the output disk slip, and the torque would not be
transmitted to the motor, thus safeguarding the motor.
5) In design of friction clutch, uniform wear theory is used. Why?
Answer: In new clutch, the rigidity of disks and spring will ensure uniform pressure between
the disks. This will be for some period (months). But the clutches are used for many years.
During the major part of service life of clutches, the friction lining undergoes uniform wear.
The power transmission capacity of clutch under uniform wear is low compared with when
they undergo uniform pressure.
6) What is the advantage and disadvantage of conical clutch compared with single disk
friction clutch?
Answer: The advantage of conical clutch is very large power/torque transmission for a given
effective radius of friction lining, coefficient friction and actuating force as evidenced from
the following equations for uniform pressure criteria (same is the situation under uniform
wear criteria),For single disk friction clutch,

μFa Do − Di
T=
3 Do − Di

For conical disk friction clutch,

T=

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 NB_MEC503_Clutches_Questions_2020

Alternately, they may be made in smaller size or require less actuating force compared with
plate clutch. The disadvantage is that if the cone angle (α) is very low, it is difficult to
disengage them.

Numericals on Clutch
1. A single plate friction clutch of both sides effective has 300 mm outer diameter and 160 mm inner
diameter. The coefficient of friction o.2 and it runs at 1000 rpm. Find the power transmitted for
uniform wear and uniform pressure distributions cases if allowable maximum pressure is 0.08 Mpa.

Solution:

Given, Do = 300 mm, Di = 160mm, µ= 0.2, RPM=N=1000, p= 0.08 MPa= 0.08 N/mm2 and Number of
pairs of friction surfaces=n=2

For Constant Pressure,

Axial Force = !"#!$ − !"%

1
∴ Fa = π × 0.08 × 160#300 − 160% = 2814.87N
2
μFa Dm 1
Torque tranmitted = T = n = × 2 × 0.2 × 2814.87 × 230 = 129484 N − mm
2 2
2πNT 2π × 1000 × 129484
Power transmitted = P = kW = = 13.56 kW
60 × 10> 60 × 10>
For Uniform wear

2 #Do − Di % 2 #300 − 160 %

Mean Diameter, Dm = × = × = 237 mm
3 #Do − Di % 3 #300 − 160 %
πp πp
Axial force Fa = × #Do − Di % = × #300 − 160 % = 4046 N
4 4
μFa Dm 1
Torque tranmitted = T = n = × 2 × 0.2 × 4046 × 237 = 191880 N − mm
2 2
2πNT 2π × 1000 × 191880
Power transmitted = P = kW = = 20 kW
60 × 10> 60 × 10>

2. Inner radius of a plate type friction clutch is 50 mm. The ratio of inner to outer radii is assumed to
be 0.5. The co-efficient of friction µ= 0.25, permissible pressure is 1 N/mm2 and RPM=750. Calculate

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 NB_MEC503_Clutches_Questions_2020

power transmission capacity of clutch assuming, a) uniform wear criteria and b) uniform pressure
criteria.

3. Design a suitable clutch for a speed gear-box of lathe to transmit a power of 15 kW at 1000 RPM.
Due to space limitation the outer diameter is limited to 150mm.

Solution:

An axial friction multi disc clutch can be employed considering space limitation. Co-efficient of
friction may be assumed as µ= 0.20 and within operating temperature range of 260oC allowable
bearing pressure can be assumed between 0.3 N/mm2 and 0.7 N/mm2.

>J×K LMN# OP% >J× S× J

Average Torque=Taverage = = = 143.24 N-m
QR Q× JJJ
Assuming 25% overload capacity, Design Torque = Td= 1.25 x 143.24 = 179 N-m
TUV#WXYWZ%
From formula, Torque transmission capacity = Td = n
[
(where, n= number of pairs of friction surfaces, Fa = (1/2)x πpDi(Do-Di), Do = 150mm

and Di= 0.6x Do=90mm)

Therefore, 179x 103 = (n/4) x 2π x 0.35 x (90/2) x (150 - 90) x (150 + 90)

From the above equation, n = 5.02

Let us select n = 6, a multi disc friction clutch is with n1 = 4 and n2 =3 (n = n1+ n2 -1)
[ \] [ × ^_ × J
For checking, Fa =
× ×# Y %
= > ×J. = 2486.1 N
×# SJ _J%

[`>.
Operating pressure,
# %
= = 0.293 N/mm (checked, within limit)
×Q× Q×_J# SJ _J%

3. A cone clutch with leather friction lining transmits power at 500 rpm. Semi-cone angle is 12.5o.
The mean diameter of the clutch is 300 mm, the face width of the contacting surface of the friction
lining is 100 mm. Take µ=0.2 and pmax = 0.07 N/ mm2. Calculate axial force and torque capacity.

Solution: From the given condition,

#Do + Di%⁄2 = 300 mm , b = 100 mm, from the figure b = #Do − Di%⁄2 sin α

Therefore, Do-Di= 2x100xsin12.5o = 43.287 mm

From the above we can have Do= 321.64 mm and Di= 278.356 mm
Qf Q×J.J^
Now from operating equation, Fa = Do − Di = #322 − 278 % = 1450.68 N
[ [

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 NB_MEC503_Clutches_Questions_2020

TUV#WXYWZ% J. ×# Y ^`%
Torque capacity, g = [ h
= [× .Si
= 201074.0974 N-mm=201.074 N-m

3. Design a single plate clutch consist of two pairs of contacting surfaces for a torque capacity of 200
N-m. Due to space limitation the outside diameter of the clutch is to be 250mm. Assume suitable
friction material (say leather of µ = 0.3 to 0.5), pressure, p = varies from 0.07 to 0.29 Mpa.

Select µ = 0.4, P = 0.135 N /mm2.

4. A multi plate clutch having effective diameter 250mm and 150mm has to transmit 60 kW at 1200
rpm. The end thrust is 4.5 kN and coefficient of friction is 0.08 calculate the number of plates assuming
(i) Uniform wear and (ii) uniform pressure distribution on the plates.

5. A multi plate clutch of alternate bronze and steel plates is to transmit 6 kW power at 800 rpm.
The inner radius is 38 mm and outer radius is 70 mm. The coefficient of friction is 0.1 and maximum
allowable pressure is 350 kN /m2. Determine,
(i) Axial force required
(ii) Total number of discs
(iii) Average pressure and
(iv) Actual maximum pressure

6. In a multi plate clutch radial width of the friction material is to be 0.2 of maximum radius. The
coefficient of friction is 0.25. The clutch is 60KW at 3000 rpm. Its maximum diameter is 250mm and
the axial force is limited is to 600N. Determine (i) Number of driving and driven plates (ii) mean unit
pressure on each contact surface assume uniform wear.

7. A Multiple plate clutch has steel on bronze is to transmit 8 KW at 1440 rpm. The inner diameter of
the contact is 80mm and outer diameter of contact is140 mm. The clutch operates in oil with
coefficient of friction of 0.1. The overage allowable pressure is 0.35Mpa. Assume uniform wear
theory and determine the following.
a) Number of steel and bronze plates
b) Axial force required
c) Actual maximum pressure

8. A cone clutch is to transmit 7.5 KW at 600 rpm. The face width is 50mm, mean diameter is
300mm and the face angle 15°. Assuming co efficient of friction as 0.2, determine the axial force
necessary to hold the clutch parts together and the normal pressure on the cone surface.

9. A friction cone clutch has to transmit a torque of 200 N-m at 1440 rpm. The longer diameter of
the cone is 350mm. The cone pitch angle is 6.25°the force width is 65mm. the coefficient of friction
is 0.2. Determine i) the axial force required to transmit the torque. ii) The average normal pressure
on the contact surface when maximum torque is transmitted.

10. An engine developing 30 KW at 1250 rpm is fitted with a cone clutch. The cone face angle of
12.5°. The mean diameter is 400 rpm µ = 0.3 and the normal pressure is not to exceed 0.08 N / mm2.
Design the clutch.

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