Question
Bank on Friction in Bearings Unit –
III
10 ME54 Dynamics of Machines (5th semester
BE 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 friction in bearings
1. Calculate the
power lost in overcoming the friction and number of collars required for a
thrust bearing whose contact surfaces are 20 cm external radius and 15 cm in
internal radius. The coefficient of friction is 0.08. The total axial load is
30 kN. Intensity of pressure is not to exceed 3.5 x 105 N/m2.
Speed of the shaft is 420 rpm.
2. In a thrust
bearing the external and internal radii of contact surfaces are 210 mm and 160
mm respectively. The total axial load is 60 kN and coefficient of friction is
0.05. The shaft is rotating at 380 rpm. Intensity of pressure is not to exceed
0.35 N/mm2. Calculate :
i)
Number of collars
required for the thrust bearing.
ii)
Power lost due to
friction.
3.
Find the power lost in friction assuming (i)
uniform pressure and (ii) uniform wear when a vertical shaft of 100 mm diameter
rotating at 150 r.p.m. rests on a flat end foot step bearing. The coefficient
of friction is equal to 0.05 and shaft carries a vertical load of 15 kN.
4.
A conical pivot with angle of cone as 120°
supports a vertical shaft of diameter 300 mm. It is subjected to a load of 20
KN. The coefficient of friction is 0.05 and the speed of shaft is 210 rpm. Calculate
the power lost in friction assuming (i) uniform pressure and (ii) uniform wear.
5.
A load of 25 KN is supported by a conical pivot
with angle of cone as 120°. The intensity of pressure is not to exceed 350 kN/m2.
The external radius is 2 times the internal radius. The shaft is rotating at
180 rpm and coefficient of friction is 0.05. Find the power absorbed in
friction assuming uniform pressure.
6.
In a collar thrust bearing the external and
internal radii are 250 mm and 150 mm respectively. The total axial load is 50
KN and shaft is rotating at 150 rpm. The coefficient of friction is equal to
0.05. Find the power lost in friction assuming uniform pressure.
7.
A conical pivot bearing 150 mm in diameter has a
cone angle of 120º. If the shaft supports an axial load of 20 kN and the
coefficient of friction is 0.03, find the power lost in friction when the shaft
rotates at 200 rpm, assuming (i) Uniform pressure, and (ii). Uniform wear.
8.
A vertical shaft supports a load of 20 kN in a
conical pivot bearing. The external radius of the cone is 3 times the internal
radius and the cone angle is 120º. Assuming uniform intensity of pressure as
0.35 MN/m2, determine the dimensions of the bearing. If the
coefficient of friction between the shaft and bearing is 0.05 and the shaft
rotates at120 rpm., find the power absorbed in friction.
9.
A plain collar type thrust bearing having inner
and outer diameters of 200 mm and 450 mm is subjected to an axial thrust of 40
kN. Assuming coefficient of friction between the thrust surfaces as 0.025, find
the power absorbed in overcoming friction at a speed of 120 rpm. The rate of
wear is considered to be proportional to the pressure and rubbing speed.
10. The
thrust of a propeller shaft in a marine engine is taken up by a number of
collars integral with the shaft which is 300 mm in diameter. The thrust on the
shaft is 200 kN and the speed is 75 rpm. Taking μ constant and equal to 0.05
and assuming intensity of pressure as uniform and equal to 0.3 N/mm2,
find the external diameter of the collars and the number of collars required,
if the power lost in friction is not to exceed 16 kW
11. A
shaft has a number of a collars integral with it. The external diameter of the
collars is 400 mm and the shaft diameter is 250 mm. If the intensity of
pressure is 0.35 N/mm2 (uniform) and the coefficient of friction is
0.05, estimate: i). power absorbed when the shaft runs at 105 rpm carrying a
load of 150 kN and ii) number of collars required.
12. A
conical pivot bearing supports a vertical shaft of 200 mm diameter. It is subjected
to a load of 30 kN. The angle of the cone is 120º and the coefficient of
friction is 0.025. Find the power lost in friction when the speed is 140 rpm,
assuming i). Uniform pressure and ii) uniform wear.
13. A
conical pivot supports a load of 18 kN, the cone angle is 100º and the intensity
of normal pressure is not to exceed 300 kN/m2. The external radius
is 2.5 times the internal radius. Find the outer and inner radii of the bearing
surface. If the shaft rotates at 1500 rpm and the coefficient of friction is 0.05,
find the power absorbed in friction. Assume uniform pressure.
14. A
vertical shaft 150 mm in diameter rotating at 100 rpm rests on a flat end foot step
bearing. The shaft carries a vertical load of 20 kN. Assuming uniform pressure
distribution and coefficient of friction equal to 0.05. Estimate power lost in friction.
15. A
shaft has a number of a collars integral with it. The external diameter of the
collars is 400 mm and the shaft diameter is 250 mm. If the intensity of
pressure is 0.35 N/mm2 (uniform) and the coefficient of friction is
0.05, Estimate: i) Power absorbed when the shaft runs at 105 rpm carrying a
load of 150 kN and ii) Number of collars required.
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