Page 93 - The Tribology Handbook

A16 Profiled pad thrust bearings

GUIDE TO BEARING DESIGN Power loss
Bearing inner diameter should be chosen to provide adequate For a bearing designed in accordance with the recom-
clearance at the shaft for oil feeding and to be clear of any mendations given, the power loss may be estimated by:
fillet radius at junction of shaft and runner. H = Kl IC, K3 d3 n1.66
Bearing outer diameter will be determined, according to
the load to be supported, as subsequently described. where the symbols have the meanings given in the following
Bearing power loss is very sensitive to outer diameter, and table.
conservative design with an unnecessarily large outside
diameter should therefore be avoided.
Oil-ways should occupy about 1520% of bearing cir- Symbol Meaning SI units Imperial
cumference. The remaining bearing area should be divided units
up by the oil-ways to form pads which are approximately d Inner mm in
‘square’. The resulting number of pads depends upon the diameter
outerlinner diameter ratio-guidance on number of pads
is given in Fig. 16.4 n Speed revls r.p.s.
H Power loss W h.p.
Safe working load capacity K, 5.5~ 10-6 0.12~ 10-3
Bearing load capacity is limited at low speed by allow- K2 Table 16.2
able film thickness and at high speed by permissible operat-
ing temperature. K3 Table 16.3
Guidance on safe working load capacity is given for
the following typical operating conditions :
Lubricant (oil) feed temperature, 50°C
Lubricant temperature rise through bearing housing, Table 76.2 Viscosity grade factor for
20°C
power loss
in terms of a basic load capacity W, for an arbitrary
diameter ratio and lubricant viscosity (Fig. 16.2), a viscos- Vkcosity grade
ity factor (Fig. 16.3) and a diameter ratio factor (Fig. IS0 3448
16.4). That is:
32 0.64
Safe working load capacity = W, x (Viscosity factor)
x (Diameter ratio factor) 46 0.78
68 1 .o
Example
100 1.24
To find the necessary outer diameter D for a bearing of
inner diameter d = 100 mm to provide load capacity of
lo4 N when running at 40 revls with oil of viscosity grade
46 (IS0 3448):
From Fig. 16.2, W, = 3.8 X lo4 N. Table 16.3 Diameter ratio factor for
From Fig. 16.3, viscosity factor 0.75. power loss
Necessary diameter ratio factor
1 n4
1v
- = 0.35
-
3.8 x lo4 x 0.75 1.5 0.42
From Fig. 16.4, D/d required is 1.57. 1.6 0.54
Therefore, outer diameter D required is 157 mm.
1.7 0.66
1.8 0.80
1.9 0.95

2.0 1.1
2.2 1.5
2.4 1.9
2.6 2.4

AI 6.2