Bearings support moving parts, such as shafts and
spindles, of a machine or mechanism.
Bearings may be classed as
(i) Rolling contact (i.e., Ball and roller) bearings.
(ii) Plain bearings.
Rolling contact bearings are almost invariably made of
steel that can be hardened after machining.
Both plain carbon and alloy (Ni, Cr, Mo) steels are
employed for different applications.
PROPERTIES OF BEARING MATERIALS
A bearing material should:
Possess low coefficient of friction.
Provide hard, wear resistant surface with a
Have high compressive strength.
Have high fatigue strength.
Be able to bear shocks and vibrations.
Possess high thermal conductivity to dissipate
heat generated due to friction between the
bearing and the rotating shaft.
Possess adequate plasticity under bearing
Possess adequate strength at high
Be such that it can be easily fabricated.
Possess resistance to corrosion.
Be such that it does not cause excessive
wear of the shaft rotating in it, i.e., bearing
material should be softer than the shaft
Possess antiseizure characteristics.
Be having small pieces of a comparatively
hard metal embeded in a soft metal.
Maintain a continuous film of oil between
shaft and bearing in
order to avoid metal to metal contact.
Possess ability to embed in itself any dirt, etc.,
present in lubricating oil.
Should be cheap and easily available.
TYPES OF BEARING MATERIALS
Lead or tin based alloys (Babbitt metals)
Sintered bearing materials.
They may be divided as
The high tin alloys with more than 80% tin
and little or no lead.
The high lead alloys with about 80% lead
and 1—12% tin.
The alloys with intermediate percentages
of tin and lead.
Typical compositions of A lead based alloy A tin based
Pb 75% Sn 88%
Sb 15% Sb 8%
Sn 10% Cu 4%
— Lead base alloys are softer and brittle than the tin
— Lead base alloys are cheaper than tin base alloys.
— Tin base alloys have a low coefficient of friction as
compared to lead base alloys.
Lead base alloys are suitable for light and
medium loads, whereas tin base alloys are
preferred for higher loads and speeds.
Whereas tin base alloys find applications in high
speed engines, steam turbines, lead base alloys
are used in rail road freight cars.
Solidus temperature of Tin base alloys —
Solidus temperature of Lead base alloys —
Besides, both these alloys possess
Good ability to embed dirt
Good conformability to journal
Good corrosion resistance
Very good seizure resistance, etc.
Cadmium-based alloys possess
(a) low coefficient of friction,
(b) high fatigue strength,
(c) high load carrying capacity,
(d) low wear, good seizure resistance,
(e) fair ability to embed dirt, and
(f) poor corrosion resistance (using ordinary
Cadmium-based alloys were tried in
automobile and aircraft industries and good
results were obtained.
White metals are tin base or lead base bearing
alloys and are usually referred to as babbitts.
Lead or tin-based alloys.
Aluminum based alloys.
Non-metallic bearing materials.
These alloys possess
(a) excellent corrosion resistance;
(b) fair conformability to journal;
(c) good ability to embed dirt;
(d) good seizure resistance;
(e) good thermal conductivitY but
(J) high coefficient of expansion.
— These alloys find applications as bearings in
diesel engines and tractors.
Silver bearings are produced by the electro-
deposition of a 0.3— 0.5 mm layer of silver
on a steel support shell, with an inter mediate
layer of Cu or Ni.
A 0.02-0.03 mm film of lead and indium is
then deposited on top of the silver, and the
indium diffused into the lead by heart-
treatment at 180°C.
This covering layer aids in improving the
running-in properties and the corrosion-
resistance of the silver layer.
These are highest priced bearing alloys.
They are employed where other materials do
not produce satisfactory results.
These alloys are used on the connecting rod
The term bronze covers a large number of
copper alloys with varying percentages of Sn, Zn
Bronze is one of the oldest known bearing
(a) is easily worked;
(b) has good corrosion resistance; and
(c) is reasonably hard.
Tin bronze (10 to 14% tin, remainder copper) is
used in the machine and engine industry for
bearing bushes made from thin- walled drawn
Copper-based alloys are employed for making
bearings required to resist heavier pressures
such as in railways.