Page 58 - The Tribology Handbook

Steadv load Dressure fed iournal bearinas A9

BEARING LOAD CAPACITY
Operating load Guide to start-up load limit

The bearing lload capacity is often quoted in terms o For whitemetal bearings the start-up .,ad shol be
specific load (load divided.by proiected area of the bear- limited to the following values:
._ I
ing, W/bd) and it is common practice to keep the specific v
load below 4 h4N/rn2. This is consistent with the practical S'tcifzc load limit* at start-up MN/mz
guide shown in Fig. 9.6 which also shows that loads may Frequent stops/starts Several a day
have to be much lower than this in order to work within an 1.4
appropriate speed range. Infrequent stopdstarts One a day or less 2.5

* Other limits at operating speeds must still be allowed for as
shown in Fig. 9.6

BEARING PERFORMANCE

Figures 9.7 to '3.9 give the predicted minimum film thickness, power loss and oil flow requirements for a 2-axial grooved
bearing with the groove geometry and feed conditions shown in Fig. 9.7, Any diametral clearance ratio Cd/d can be
considered; however, the maximum should be used when estimating flow requirements. In some cases it may be necessary
to judge the influence of different load line positions (at thick film conditions) or misalignment; both are considered in Figs.
9.10 to 9.12. A design guide 'check list' is given below.

DESIGN GlllDE CHECK LIST

(i) Using mintimum clearance

Infomation
-~ ~~
~
See recommended minimum clearance Fig. 9.5
Check that the bearing is within a safe region of operation Fig. 9.6
adjust (or choose) geometry and/or oil as found necessary
Predict oil film thickness ratio (minimum film thickneddiametral clearance) Fig 9.7
Predict power loss Flg 9.8
Allow for non-symmetric load angle (relative to grooves), if necessary Figs 9.10 and 9.1 1
Allow [or the influence of misalignment on film thickness, if necessary Fig 9.12
Check that modified minimum film thickness is acceptable Fig 9.4

(ii) Using maximum clearance
Information

Calculate maximum clearance Fig. 9.5 and tolerance equation
Predict film thickness and check that it is acceptable Figs 9.7 and 9.4
Predict oil flow requirements Fig. 9.9
Allow for non-symmetric load line and/or misalignment if necessary Figs 9.10, 9.11 and 9.12
Check that modified minimum film thickness is acceptable Fig. 9.4

A9.5