IT IS VERY USEFUL WHEN THE POWER UNIT HAS A LOW STARTING TORQUE WHI...
4.
It is very useful when the power unit has a low starting torque
Which of these are the advantages of centrifugal clutch?
(a) 1, 2 and 4
(b) 1, 3 and 5
(c) 2, 3 and 5
(d) 1, 3, 4 and 5
IES-19. Ans. (c)
IES-20.
Match List-I with List-II and select the correct answer using the codes
given below the lists:
[IES-1998]
List-I
List-II
Design of Friction Drives
S K Mondal’s
Chapter 2
A. Single-plate friction clutch
1. Scooters
B. Multi-plate friction clutch
2. Rolling mills
C. Centrifugal clutch
3. Trucks
D. Jaw clutch
4. Mopeds
Code: A B C D A B C D
(a)
1
3
4
2
(b)
1
3
2
4
(c)
3
1
2
4
(d)
3
1
4
2
IES-20. Ans. (d)
Belt and Chain drivesIES-21. The creep in a belt drive is due to the
[IES-2001]
(a) Material of the pulleys
(b) Material of the belt
(c) Unequal size of the pulleys
(d) Unequal tension on tight and slack sides
of
the
belt
IES-21. Ans. (d)
• 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 the
slack side. Due to these changes of length, there is a relative motion between the
belt and the pulley surfaces. This relative motion is termed as creep. The total effect
of creep is to reduce slightly the speed of the driven pulley or follower.
• Here english meaning of ‘creep’ is ‘very slow motion’ and not ‘When a part is
subjected to a constant stress at high temperature for a long period of time, it will
undergo a slow and permanent deformation called creep.’
• Therefore the belt creep is very slow motion between the belt and the pulley
surfaces due to unequal tension on tight and slack sides of the belt.
• Don’t confuse with material of the belt because the belt creep depends on both the
materials of the pulley and the materials of the belt.
IES-22.
Assertion (A): In design of arms of a pulley, in belt drive, the cross-section of the
arm is, elliptical with minor axis placed along the plane of rotation. [IES-2001]
Reason (R): Arms of a pulley in belt drive are subjected to complete reversal of
stresses and is designed for bending in the plane of rotation.
(a) Both A and R are individually true and R is the correct explanation of A
(b) Both A and R are individually true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
IES-22. Ans. (a)
IES-23.
Assertion (A): In pulley design of flat belt drive, the cross-sections of arms are
made elliptical with major axis lying in the plane of rotation.
[IES-1999]
Reason (R): Arms of a pulley in belt drive are subjected to torsional shear stresses
and are designed for torsion.
IES-23. Ans. (c)
IES-24.
Which one of the following belts should not be used above 40°C? [IES-1999]
(a) Balata belt (b) Rubber belt
(c) Fabric belt
(d) Synthetic belt
IES-24. Ans. (b)
IES-25.
In μ is the actual coefficient of friction in a belt moving in grooved pulley,
the groove angle being 2α, the virtual coefficient of friction will be
(a)
μ
/ sin
α
(b)
μ
/ cos
α
(c)
μ
sin
α
(d)
μ
cos
α
[IES-1997]
IES-25. Ans. (a)
IES-26.
In flat belt drive, if the slip between the driver and the belt is 1%, that
between belt and follower is 3% and driver and follower pulley diameters
are equal, then the velocity ratio of the drive will be
[IES-1996]
(a) 0.99
(b) 0.98
(c) 0.97
(d) 0.96.
IES-26. Ans. (d)
IES-27.
Assertion (A): Crowning is provided on the surface of a flat pulley to prevent
slipping of the belt sideways.
[IES-2006]
Reason (R): Bell creep, which is the reason for slip of the belt sideways, is fully
compensated by providing crowning on the pulley.
IES-27. Ans. (c) Belt creep has no effect on sideways.
Length of the beltIES-28.
The length of the belt in the case of a cross-belt drive is given in terms of
centre distance between pulleys (C), diameters of the pulleys D and d as
π
+
(a)
2C
(
D d
) (
D d
)
2
+
+
+
(b)
2C
(
D d
) (
D d
)
2
+
−
+
[IES-2002]
2
4C
π
−
(c)
2C
(
D d
) (
D d
)
2
+
−
+
+
+
+
(d)
2C
(
D d
) (
D d
)
2
IES-28. Ans. (a)
IES-29. Assertion (A): Two pulleys connected by a crossed belt rotate in opposite
directions.
Reason
(R):
The length of the crossed belt remains constant.
[IES-2008]
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
IES-29. Ans. (b) Two pulleys connected by open belt rotate in same direction whereas two
pulleys connected by crossed belt rotate in opposite direction.
The length of crossed belt is given by
⎛
+
⎞
r
r
(
)
1
2
2
= π
+
+
+ ⎜
⎝
⎟
⎠
L
r
r
2C
c
1
2
C
So length of crossed belt in constant. Both the statements are correct but Reason is
not the correct explanation of Assertion.
IES-30.
Which one of the following statements relating to belt drives is correct?
(a) The rotational speeds of the pulleys are directly proportional to their diameters
(b) The length of the crossed belt increases as the sum of the diameters of the
pulleys increases
(c) The crowning of the pulleys is done to make the drive sturdy
(d) The slip increases the velocity ratio
[IES 2007]
r
r
1
+
2
)
2
where C = centre distance of shafts.
IES-30 Ans.(b) L =
π
(
r
1
+
r
2
) + 2C +
(
C
Belt tensionIES-31. Assertion
(A): In a short centre open-belt drive, an idler pulley is used to maintain
the belt tension and to increase the angle of contact on the smaller pulley.
Reason (R): An idler pulley is free to rotate on its axis and is put on the slack side
of the belt.
[IES-1994]
IES-31Ans. (a) Both A and R are true, and R provides correct explanation for A.
IES-32. In a Belt drive, if the pulley diameter is doubled keeping the tension and
belt width constant, then it will be necessary to
[IES-1993]
(a) Increase the key length
(b) increase the key depth
(c) Increase the key width
(d) decrease the key length
IES-32Ans. (c) Due to twice increase in diameter of pulley, torque on key is double and has to
be resisted by key width. Length can't be increased as belt width is same.
IES-33. The following data refers to an open belt drive:
[IES-1993]
Pulley A
Pulley B
Purpose ……….
Driving
Driven
Diameter………
450 mm
750 mm
Angle of contact…………
θ
A
= 150
o
θ
A
= 210
o
Coefficient
of
friction
between
f
A
=
0.36
f
A
=
0.22
belt and pulley
The ratio of tensions may be calculated using the relation (T
1
/T
2
) = exp (z)
where z is
(
)(
)
(
)
( )
a f
A
θ
A
( )
b f
B
θ
B
( )
c
f
A
+
f
B
θ
A
+
θ
B
/ 4
( )
d
f
A
θ
A
+
f
B
θ
B
/ 2
T
e
=
θ
where f and θ are taken for smaller pulley.
IES-33Ans. (a)
1
f
A A
T
2
Centrifugal tensionIES-34. Centrifugal tension in belts is
[IES-1999]
(a) Useful because it maintains some tension even when no power is transmitted
(b) Not harmful because it does not take part in power transmission
(c) Harmful because it increases belt tension and rfeduces the power transmitted
(d) A hypothetical phenomenon and does not actually exist in belts
IES-34.Ans. (c)
IES-35. In the case of a vertical belt pulley drive with T
c
as centrifugal tension and
T
o
as the initial tension, the belt would tend to hang clear of the tower
pulley when
[IES-1997]
( )
a
T
c
<
T
o
b
( )
T
c
<
T
o
/ 3 c
( )
T
c
>
T
o
d
( )
T
c
<
T
o
/ 2
IES-35Ans. (c)
IES-36. Consider the following statements in case of belt drives:
[IES 2007]