Sliding Bearings 361

3 What should one pay attention to while designing grooves on a bushing?

4 In the hydrodynamic sliding bearing design process, if the calculated minimum oil
film thickness hmin is too small or the temperature rise Δt is too high, what measures
could be taken to increase hmin or to reduce Δt?

5 What are the specific requirements for the liner materials of sliding bearings?

Objective Questions
1 A journal operates in a steady hydrodynamic lubrication state in a sliding bearing.
Which part of Figure P12.1 shows the right position of the journal?

F F F F

ω ω ω
O O O O
Oʹ Oʹ Oʹ Oʹ
ω

(a) (b) (c) (d)

Figure P12.1 Illustration for Objective question 1.

2 To form hydrodynamic oil film, the inlet and outlet velocity profiles in a wedged
lubricated gap should be ___________.

(a) (b) (c) (d)

Figure P12.2 Illustration for Objective question 2.

3 At _______, the viscosity of lubricant in a sliding bearing should not be chosen as

high.
(a) overload
(b) high operating temperature
(c) high speed
(d) variable loads

4 While designing hydrodynamically lubricated bearings, we usually ________ to

reduce the working temperature of sliding bearings.
(a) increase the relative clearance 𝜓 and reduce the ratio of B/d
(b) increase the relative clearance 𝜓 and increase the ratio of B/d
(c) reduce the relative clearance 𝜓 and reduce the ratio of B/d
(d) reduce the relative clearance 𝜓 and increase the ratio of B/d
362 Analysis and Design of Machine Elements

5 Which of the following is most likely to form hydrodynamic lubrication ________?

(a) (b) (c) (d)

Figure P12.3 Illustration for Objective question 5.

Calculation Questions
1 A boundary-lubricated sliding bearing has a width of B = 200 mm and a diame-
ter of d = 200 mm. The shaft rotates at n = 300 rpm. The material of the bearing
is ZCuAl10Fe3. The allowable pressure is [p] = 15 MPa, the allowable velocity is
[v] = 4 m s−1 , the allowable value of pv factor is [pv] = 12 MPa m s−1 . Determine
the maximum radial load the bearing can carry.

2 A sliding bearing carries a load of 200 kN, supporting a shaft rotating at a speed
of 500 rpm. The ratio of bearing width to diameter is 1.0, where the shaft diame-
ter is 200 mm. The surface roughness of the journal and bearing are 0.0032 mm and
0.0063 mm, respectively. If the diametral clearance is 0.250 mm. The dynamic vis-
cosity is 0.045 Pa s at operating temperature of 50∘ C. Select the factor of safety as 2.
Determine whether the bearing can form fluid hydrodynamic lubrication. If oper-
ating temperature is increased to 60∘ C, the load carrying capacity will increase or
decrease? Why?

3 A hydrodynamic sliding bearing, whose journal diameter is 200 mm, rotates at a

rotational speed of 750 rpm. The allowable oil film thickness is [h] = 0.02 mm. The
ratio of the bearing width to diameter is B/d = 1.0. Three pairs of variables can be
chosen from:

Relative bearing Viscosity of

No clearance 𝝍 oil 𝜼 (Pa s)

1 0.0015 0.027
2 0.002 0.027
3 0.002 0.018

Please decide:
(1) By selecting which combination of variables, the sliding bearing can have the
largest load carrying capacity?
(2) Calculate the maximum load the sliding bearing can carry according to your
selection.
 Sliding Bearings 363

4 A sliding bearing with a journal diameter of 200 mm carries a radial load of 100 kN
at 500 r min−1 . The B/d ratio is unity. The relative bearing clearance is 0.00125. The
average temperature is t m = 50∘ C, with dynamic viscosity of 0.045 Pa s. Decide:
(1) the minimum film thickness of the bearing;
(2) the eccentricity;
(3) the coefficient of friction of the bearing;
(4) friction power loss;
(5) the total oil flow rate through the bearing Q;
(6) oil temperature rise through the bearing.

5 A sliding bearing has a journal diameter of 50−0.05/−0.075 mm, and a bushing bore
diameter of 50 mm, with a unilateral tolerance of +0.025 mm. The ratio of the bearing
width to diameter is B/d = 1.0. The journal rotates at 1200 r min−1 under a radial
steady load of 2000 N. The bearing is lubricated with SAE grade 20 oil (equivalent to
ISO viscosity grade 68) at 50∘ C. If the heat transfer coefficient 𝛼 s = 80 W (m2 ∘ C)−1 ,
decide the inlet and outlet temperature at the maximum and minimum clearance. At
both the minimum and maximum clearance assembly estimate the minimum film
thickness and coefficient of friction.

Design Problems
1 A journal bearing operates under a steady radial load of 60 kN at a speed of 960 rpm.
The journal diameter has been determined as 160 mm from shaft rigidity analysis.
Design a suitable hydrodynamic bearing.

2 In an automotive crankshaft application, a hydrodynamic bearing has a diameter of

100 mm with a unit B/d ratio. The bearing must support a radial load of 1000 N, and
the journal rotates at 3000 rpm. The lubricant is to be SAE grade 20 oil. Determine a
suitable combination of bearing width, radial clearance and lubricant variables suit-
able for the proposed application.

3 A hydrodynamically lubricated bearing is required for a machine tool. The journal

nominal diameter is 25 mm, rotates at 2500 rpm, carrying a radial load of 2250 N.
The desired ratio of width to diameter is 1.0. Design the sliding bearing.

4 A partial journal bearing with 127 mm diameter, 63.5 mm width and 0.0635 mm
radial clearance supports a radial load of 18 570 N. The shaft rotates 1800 rpm. The
lubricant has viscosity of 0.0073 Pa s, supplied at atmospheric pressure. Estimate the
minimum oil film thickness, friction power loss and required oil flow rate.

Structure Design Problems

1 Design the structure of a solid radial sliding bearing.

2 Design a typical solid liner and split liner for a radial sliding bearing.
364 Analysis and Design of Machine Elements

CAD Problems
1 Write a flow chart for bearing design process to complete the Example Problem 12.2.

2 Develop a program to implement a user interface similar to Figure P12.4 and com-
plete the Example Problem 12.2.

Figure P12.4 Illustration for CAD problem 2.