Page 198 - Improving Machinery Reliability

Machinery Reliability Audits and Reviews 169

180
170
160
1 SO
140
TOII,'F 130
(stabilized) ,20
110
100
90

9,000
70,000
11,000
12,000
13,000
14,000
Be 16,000
Ilf 16,000
.M
17,000
18,000
79,000
20,000
21,OM)

Figure 3-60. Comparison between bearing submergence in oil, operating temperature,
and bearing life for the old and new designs. (Courtesy of Goulds Pump, Seneca Falls,
New York.)

However, while roller and tapered roller bearings may present a viable alternative
in selected instances, they do have potential drawbacks when used in centrifugal
pumps: First, proper alignment of the shaft is much more critical to ensure proper
roller-to-race contact and minimize stresses. Spacing or shimming between housing
end plate and housing must be quite accurate. This assembly method is used to
ascertain proper roller-to-race contact (i.e., not too much end-play in the shaft) with-
out preload. Tapered roller bearings also have much higher internal friction and thus
will not run as fast and as cool as comparable ball bearings. Therefore, proper lubri-
cation, i.e., proper type of lubricant, proper amount, and proper application method
will be even more important with roller and tapered roller bearings than with ball
bearings.