Page 384 - Analysis and Design of Machine Elements

Analysis and Design of Machine Elements
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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
−1
−1
[v] = 4m s , the allowable value of pv factor is [pv] = 12 MPa m s . 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 oil (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.