Page 345 - Analysis and Design of Machine Elements

(c) Thrust ball bearings Rolling Contact Bearings 323
(d) Tapered roller bearings
3 The correct designation for the fit between the shaft and the inner ring of a rolling
contact bearing is _______.
(a) 30 H7
k6
(b) 30H7
(c) 30k6
(d) 30 k6
H7
4 A deep-groove ball bearing carries a constant load. If its rotational speed changes
−1
from 960 r min −1 to 480 r min , the life of the bearing changes from ___________.
(a) from L increases to 2L (h)
h
h
(b) from L reduces to L /2 (r)
r
r
(c) from L increases to 2L (r)
r
r
(d) from L reduce to L /2 (h)
h
h
5 An angular contact ball bearing rotates at a constant speed. If the equivalent dynamic
load reduces from 2P to P, the life of the bearing changes from L _________.
10
(a) decrease to 0.2L 10
(b) increase to 2L 10
(c) increase to 8L 10
(d) unchanged
Calculation Questions

1 A shaft is supported by a pair of angular contact ball bearings 7212 AC, as shown
in Figure P11.1. The bearings operate at a speed of n = 1200 r min −1 under constant
radial loads of R = 2500 N, R = 5000 N on bearing 1 and bearing 2, respectively.
1 2
The external axial load acting on the gears are F = 400 N, F = 2400 N. If the load
a1 a2
factor is f = 1.0, and the bearings work at room temperature. Estimate the life of
p
bearing. (e = 0.68, X = 0.41, Y = 0.87, S = 0.68R, C = 61.0 kN).
Figure P11.1 Illustration for Calculation
Question 1.

2 A bevel gear is supported by a pair of taper roller bearings 30 206 with a basic
dynamic load rating of C = 41 200 N, as shown in Figure P11.2. The radial loads act
on the bearings are R = 1200 N and R = 2000 N, respectively. The shaft rotates at
2
1