Question
Bank on Belt Drives Unit – III
10 ME54 Dynamics of Machines (5th semester
BE Mechanical VTU)
Usually question in
this unit consists of part a) which will be a theory or derivation and part b)
will be a numerical problem.
Some typical Questions in part a) of question paper
that appear or have appeared till now are:
1.
Define static and
dynamic friction and State Laws of dry friction.
2.
Discuss the types
of friction and laws of friction.
3. Derive the
expressions for frictional torque in a flat pivot bearing. Assume uniform
pressure conditions.
4.
Discuss briefly the various types of friction
experienced by a body.
5.
State the laws of (i) Static friction: (ii)
Dynamic friction; (iii) Solid friction; and (iv) Fluid friction.
6.
Explain the following: (i) Limiting friction,
(ii) Angle of friction, and (iii) Coefficient of friction.
7.
What is meant by the expression ‘friction
circle’?
8. Deduce an expression for the radius of friction
circle in terms of the radius of the journal and the angle of friction.
9.
From first principles, deduce an expression for
the friction moment of a collar thrust bearing, stating clearly the assumptions
made.
10.
Derive an expression for the friction moment for
a flat collar bearing in terms of the inner radius R2, outer radius
R1, axial thrust W and coefficient of friction μ. Assume uniform
intensity of pressure.
11.
Derive from first principles an expression for
the friction moment of a conical pivot bearing assuming (i) Uniform pressure,
and (ii) Uniform wear
12.
A truncated conical pivot of cone angle φ
rotating at speed N supports a load W. The smallest and largest diameter of the
pivot over the contact area are ‘d’ and ‘D’ respectively. Assuming uniform
wear, derive the expression for the frictional torque.
13.
Derive from the first principles an expression
for the friction moment of a conical pivot bearing assuming (i) Uniform
pressure and (ii) Uniform wear.
14.
Derive an
expression for ratio of tensions in flat belt drive.
15.
State the laws of
dynamic friction.
16.
Derive an
expression for frictional torque in a flat collar bearing assuming uniform
pressure.
17.
Derive an
equation to calculate the centrifugal tension in a flat belt drive.
18.
Explain: i) Slip,
ii) Creep, iii) Initial tension and, iv) Centrifugal tension in belt drive.
19.
Explain how
centrifugal tension affects the maximum tension in the flat belt drive. Also
derive the equation for centrifugal tension in a flat belt drive.
20.
Derive the
expressions for frictional torque in a flat pivot bearing for uniform pressure
and wear conditions.
21.
Derive the
expressions for frictional torque in single collar bearings for uniform
pressure conditions.
22.
Derive the
expressions for frictional torque in flat collar bearings for uniform pressure
and wear conditions
23.
Derive an
expression for the ratio of tensions in a flat belt drive.
24.
Obtain condition
for maximum power transmitted by a belt from one pulley to another.
Numerical problems on Belt Drives:
1.
A belt 100 mm wide and 10 mm thick is to
transmit power at speed of 1000 m/min. The net driving tension is 1.8 times the
tension on slack side. If the safe permissible stress is 2 MPa, calculate the
maximum power that can be transmitted at this speed. Assume the density of
leather as 1000 kg/m3. Also determine (i) the absolute maximum
power. (ii) Percentage increase in power.
2.
A leather belt is required to transmit 7.5 kW
from a pulley 1.2 m in diameter, running at 250 rpm, the angle of contact is
165° and µ = 0.3. If the safe working stress for the leather belt is 1.5 MPa
and density of leather is 1000 kg/m3 and thickness of belt is 10 mm,
determine the width of belt taking centrifugal tension into account.
3.
Determine the width of a 9.75 mm thick belt
required to transmit 15 kW from a motor running at 900 rpm. The diameter of the
driving pulley of the motor is 300 mm. The driven pulley runs at 300 rpm and
distance between centers of two pulleys is 3 m. The density of leather is 1000
kg/m3. The maximum allowable stress in leather is 2.5 MPa. The
coefficient of friction between leather and pulley is 0.3. Assume open belt
drive and neglect slip in belt drive.
4.
A flat belt is required to transmit 35 kW from a
pulley of 1.5 m effective diameter running at 300 rpm. The angle of contact is
spread over 11/24 of the circumference and the coefficient of friction between
belt and pulley surface is 0.3. Determine width of the belt required taking
centrifugal tension into account. It is given that the belt thickness is 9.5 mm,
density of its material is 1.1x103 kg/m3 and the
permissible working stress for belt is 2.5 N/mm2.
5.
An open belt drive is used to connect two
parallel shafts, 4 m apart. The diameter of the larger pulley is 1.5 m and that
of smaller pulley is 0.5 m. The mass of the belt is 1 kg/m length. The maximum
tension is not to exceed 1500 N. The coefficient of friction is 0.25. The
bigger pulley which is the driver runs at 250 rpm. Due to slip, the speed of
driven pulley is 725 rpm. Calculate the power transmitted, power lost in
frictions, and the efficiency of the drive.
6.
2.5 kW of power is transmitted by an open belt
drive. The linear velocity of the belt is 2.5 m/s. The angle of lap on the
smaller pulley is 165°. The coefficient of friction is 0.3. Determine the
effect on power transmission in the following cases:
i)
Initial
tension in the belt is increased by 8%.
ii)
Initial
tension in the belt is decreased by 8%.
iii)
Angle of lap is increased by 8% by the use of an
idler pulley, for the same speed and tension on the tight side.
iv)
Coefficient of friction is increased by 8% by
suitable dressing to the friction surface of the belt.
7.
A shaft rotating at 200 rpm drives another shaft
at 300 rpm and transmits 6 kW through a belt. The belt is 100 mm wide and 10 mm
thick. The distance between the shafts is 4 m. The smaller pulley is 0.5 m in
diameter. Calculate the stress in the belt, if it is :
i)
An open belt drive, and ii)
A cross belt drive. Take μ= 0.3
8.
An op en belt drive is required to transmit 10
kW of power from a motor running at 600 rpm. Diameter of the driving pulley is
250 mm. The speed of the driven pulley is 220 rpm. The belt is 12 mm thick and
has a mass density of 0.001 g/mm3. Safe stress in the belt is not to
exceed 2.5 N/mm2. The two shafts are 1.25 m apart. The coefficient
of friction is 0.25. Determine the width of the belt.
9. Two
parallel shafts that are 3.5 m apart are connected by two pulleys of 1 m and
400 mm diameters, the larger pulley being the driver runs at 220 rpm. The belt
weighs 1.2 kg per meter length. The maximum tension in the belt is not to
exceed 1.8 kN. The coefficient of friction is 0.28. Owing to slip on one of the
pulleys, the velocity of the driven shaft is 520 rpm only. Determine the:
i)
Torque on each shaft
ii)
Power transmitted
iii)
Power lost in friction
iv)
Efficiency of the drive.
10. The
maximum power transmitted by a belt is 60 kW. The belt is 250 mm wide and 10 mm
thick and weighs 9.81 kN/m3. If the ratio of tensions on the tight
and slack sides is 2, determine the maximum stress induced in the belt.
11. In a
belt drive, the mass of the belt is 1 kg/m length and its speed is 6 m/s. The
drive transmits 9.6 kW of power. Determine the initial tension in the belt and
the strength of the belt. The coefficient of friction is 0.25 and the angle of
lap is 220°
12. In
an open belt drive the diameters of the larger and smaller pulleys are 1.2 m
and 0.8 m respectively. The smaller pulley rotates at 320 rpm. The center
distance between the shafts is 4 m. When stationary, the initial tension in the
belt is 2.8 kN. The mass of the belt is 1.8 kg/m and the coefficient of
friction between the belt and the pulley is 0.25. determine the power
transmitted.
13. The
initial tension in a belt drive is found to be 600 N and the ratio of friction
tensions is 1.8. The mass of the belt is 0.8 kg/m length. Determine:
i)
Velocity of the belt for maximum power
transmission
ii)
Tension in the tight side of the belt when it is
started, and
iii)
Tension in the tight side of the belt when the
running at maximum speed.
14. An
open belt drive transmits 4 kW of power. The smaller pulley is the driver and
rotates at 300 rpm. The diameters of the two pulleys are 280 mm and 640 mm and
center distance is 3 m. The coefficient of friction between the belt and the
pulley is 0.3. If the safe working stress is 8 N/mm widths, determine the
minimum width of the belt. Also calculate the initial tension in the belt and
the length of the belt required. The initial tension in a belt drive is found
to be 600 N and the ratio of friction tensions is 1.8. The mass of the belt is
0.8 kg/m length. Determine:
Compiled
by
N. S. SRIRAM, VVIET, Mysore
·
I acknowledge with thanks the contributions made by various
teachers, students in the different websites, from which the above question
bank materials have been compiled.
·
I thank all of them who made this compilation possible.
No comments:
Post a Comment