DESIGN OF FRICTION DRIVES OBJECTIVE QUESTIONS (GATE, IES & IAS)...

2. Design of Friction Drives

Objective Questions (GATE, IES & IAS)

Previous 20-Years GATE Questions

Couplings

GATE-1. The bolts in a rigid flanged coupling connecting two shafts transmitting

power are subjected to

[GATE-1996]

(a) Shear force and bending moment (b) axial force.

(c) Torsion and bending moment

(d) torsion

GATE-1. Ans. (a) The bolts are subjected to shear and bearing stresses while transmitting

torque

.

Uniform pressure theory

GATE-2.

A clutch has outer and inner diameters 100 mm and 40 mm respectively.

Assuming a uniform pressure of 2 MPa and coefficient of friction of liner

material 0.4, the torque carrying capacity of the clutch is [GATE-2008]

(a) 148 Nm

(b) 196 Nm

(c) 372 Nm

(d) 490 Nm

GATE-2. Ans. (b) Force(P)=

^π

₄

^p

(

^D

²

⁻

^d

²

)

3

3

μ

−

D

d

P

.

T=

( )( )

3

D

d

2

2

−

=

₁₂

^μπ

^{.p. D}

(

³

⁻

^d

³

)

⁼

^0.4

^{× π × ×}

₁₂

^{2 10}

⁶

(

^0.1

³

⁻

^0.04

³

)

^=196Nm

GATE-3. A disk clutch is required to transmit 5 kW at 2000 rpm. The disk has a

friction lining with coefficient of friction equal to 0.25. Bore radius of

friction lining is equal to 25 mm. Assume uniform contact pressure of 1

MPa. The value of outside radius of the friction lining is [GATE-2006]

(a) 39.4 mm

(b) 49.5 mm

(c) 97.9 mm

(d) 142.9 mm

GATE-3. Ans.(a)

=

×

=

Torque,T

P 60

23.87N m

2

N

π ×

=

= × π

−

Axial thrust,W P

(r

r )

1

2

= μ × × π

−

−

= μ

But

T

2

P

(r

r )

wr

(r

r )

2

2

1

2

1

2

2

2

3

(r

r )

r

39.4 mm

∴

=

2

Design of Friction Drives

S K Mondal’s

Chapter 2

Belt and Chain drives

GATE-4.

Total slip will Occur in a belt drive when

[GATE-1997]

(a) Angle of rest is zero

(b) Angle of creep is zero

(c) Angle of rest is greater than angle of creep

(d) Angle of creep is greater than angle of rest

GATE-4. Ans. (a)

Belt tension

GATE-5.

The ratio of tension on the tight side to that on the slack side in a flat belt

drive

is

[GATE-2000]

(a) Proportional to the product of coefficient of friction and lap angle

(b) An exponential function of the product of coefficient of friction and lap angle.

(c) Proportional to the lap angle

(d) Proportional to the coefficient of friction

GATE-5. Ans. (b)

T

=

μ

1

0

GATE-6.

The difference between tensions on the tight and slack sides of a belt drive

is 3000 N. If the belt speed is 15 m/s, the transmitted power in k W is

(a) 45

(b) 22.5

(c) 90

(d) 100 [GATE-1998]

GATE-6. Ans. (a)

−

=

Given,

T

T

3000N

=

where

T T

tensions on tight an d slack side respectively

1 2

=

=

v belt speed 15m / sec

Power (T

T )v

=

−

3000 45000 watt 45kW

GATE-7.

The percentage improvement in power capacity of a flat belt drive, when

the wrap angle at the driving pulley is increased from 150° to 210° by an

idler arrangement for a friction coefficient of 0.3, is [GATE-1997]

(a) 25.21

(b) 33.92

(c) 40.17

(d) 67.85

GATE-7. Ans. (d) We know that Power transmitted (P) =

(

T

1

−

T .v W

2

)

0.3

5

π

⎛

⎞

T

e

T

e

or T

2.193 T

P

1.193T V W

×⎜

⎝

⎟

⎠

=

μθ

or

=

=

⇒

=

6

1

1

2

1

2

Case-I:

¹

0.3

7

T

e

or T

3.003 T

P

2.003T V W

Case-II:

¹

−

×

=

P

P

100% 67.88%

Therefore improvement in power capacity =

²

¹

P

1

Centrifugal tension

GATE-8.

With regard to belt drives with given pulley diameters, centre distance

and coefficient of friction between the pulley and the belt materials, which

of the statement below are FALSE?

[GATE-1999]

(a) A crossed flat belt configuration can transmit more power than an open flat belt

configuration

(b) A "V" belt has greater power transmission capacity than an open flat belt

(c) Power transmission is greater when belt tension is higher due to centrifugal

effects than the same belt drive when centrifugal effects are absent.

(d) Power transmission is the greatest just before the point of slipping is reached

GATE-8. Ans. (c)

Rope drive

GATE-9. In a 6

×

20 wire rope, No.6 indicates the

[GATE-2003]

(a) diameter of the wire rope in mm

(b) Number of strands in the wire rope

(c) Number of wires

(d) Gauge number of the wire

GATE-9. Ans. (b) 6

×

20 wire rope: 6 indicates number of strands in the wire rope and 20

indicates no of wire in a strand.

Self locking screw

GATE-10. What is the efficiency of a self-locking power screw?

[GATE-1994]

(a) 70%

(b) 60%

(c) 55%

(d) < 50 %

GATE-10. Ans. (d) We know that the frictional torque for square thread at mean radius while

raising load is given by

WR

_o

tan(

φ α

−

)

Where: (W = load;

R

o

= Mean Radius;

ϕ

= Angle of friction; α = Helix angle)

For self locking, angle of friction should be greater than helix angle of screw So that

tan(

φ α

−

)

WR

o

will become positive. i.e. we have to give torque to lowering the load.

GATE-11.

Self locking in power screw is better achieved by decreasing the helix

angle and increasing the coefficient of friction.

[GATE-1995]

(a) True

(b) False

(c) insufficient logic (d) none of the above

GATE-11. Ans. (a)

Efficiency of screw

GATE-12. Which one of the following is the value of helix angle for maximum

efficiency of a square threaded screw? [

φ

=

tan

⁻

¹

μ

] [GATE-1997]

(a) 45

^o

+

φ

(b)

45

^o

-

φ

(c)

45

^o

-

φ

/2

(d) 45

^o

+

φ

/2

GATE-12. Ans. (c)

Previous 20-Years IES Questions

IES-1.

Consider the following statements in respect of flexible couplings: