Page 81 - The Tribology Handbook

A13 Oscillatory journal bearings

SPHERICAL BEARINGS
Iwr Bearing life calculations :

EQUIVALENT BEARING
PRESSURE
W,'+ SW,'
P= L = bearing life, i.e. average number of oscillations to
W, BD
failure assuming Unidirectional loading
PROVIDED f = life-increasing factor depending on periodical re-
THAT
lubrication (ref. table below)
Wac Wr
Po = maximum bearing pressure if an average bearing-
life of IO5 number of oscillations is to be expected
(ref. table below)
L B 4 AS A RULE: OC8" p = equivalent bearing pressure (ref. formula at left)
HARDENED rBRONZE
STEEL
\\\\j_j Bearing Qpe
Remarks
Bearing HARDENED
parameters STEEL STEEL HARDENED
STEEL
PO For static load 97 MN/m' For static load
see *
see *
Maximum allowable 14000 lbf/in2
bearing pressure, 24 MN/m* 10 MN/mZ Po = -
Wmx
assuming unidirectional 3500 Ibqin2 1450 Ibf/in2 BD
dynamic loading and (bearing surfaces for nl= lo5 where
no relubrication prepared with nL is the average
molybdenum number of oscillations
disulphide) to failure
Ability to carry Good Excellent Good
unidirectional loading

Ability to carry Excellent Bad Good
alternating loading Po may be Po may have to
increased by be reduced by
a factor 1.7 a factor 0.25
5 n, < 0.3 n, Lubrication Usually Lubricant:
Recommended interval not usually n, < 0.3 n1 grease or high-viscosity oil
between relubrication, recommended containing EP or MoS, additives
in number of oscillations
Increase in bearing life f== 10-15 Practically Depends on Ref. bearing-life formula at top of
if relubricated with (difficult to none. design, and Page
interval R, exceed 10' fsl size of bearing.
oscillations with- For bearings with
out relubrication) d > 0.05 m,f* 5-10
Maximum operating - 280°C 100°C Usually, the inner sphere expands
temperature 536°F 212°F more than the outer ring. Opera-
tion at high temperature due to
high load therefore requires higher
clearances (ref. table next page)
General bearing High loads, Very high Moderate -
characteristics shock loads, average, loads, low
alternating unidirectional speeds (surface
loads loads. Moderate speed
speeds. Mainten- < 0.5 m/s)
ance-free low friction

* The table is based on dynamic load conditions. For static load conditions, where the load-carrying capauty of the bearing is based on
bearing-surface permanent deformation, not fatigue, the load capacity ofsteel bearings may reach 10 xp ., and of aluminium bronze 5 xp
AI 3.1