INTRODUCTION TO BEARINGS
 Bearings support moving parts, such as shafts and
spindles, of a machine or mechanism.
 Bearings may be classed as
 (i) Rolling contact (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 tough core.
 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 load.
• Possess adequate strength at high temperatures.
• 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 material.
• Be having small pieces of a comparatively hard metal
embeded in a soft metal.
• Maintain a continuous film of oil between shaft and
bearing.
TYPES OF BEARING MATERIALS
 Lead or tin based alloys (Babbitt metals)
 Cadmium-based alloys
 Aluminium based alloys
 Copper based alloys
 Silver-based alloys
 Non-metallic bearing meterials
Lead or Tin Based Alloys (Babbitt Metals)
 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 alloy
 Pb 75%
Sn 88%
 Sb 15%
Sb 8%
 Sn 10%
Cu 4%
 Lead base alloys are softer and brittle than the tin
base alloys.
 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
222°C
— Approx.
 Solidus temperature of Lead base alloys
240°C
— Approx.
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
 Chemical composition
cd
97%
Ni
2%
Ag, Cu and zn are added in small percentage.
These bearing alloys have a structure consisting of a
soft matrix containing harder crystals of intermetallic
compounds. These alloys aren't very popular because
of high price of cadmium. These bearing alloy possess
greater compressive strength than tin bearing alloys.
 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
lubricants).
• Cadmium-based alloys were tried in automobile and
aircraft industries and good results were obtained.
Aluminium based alloys
 Chemical composition
Al
Sn
Cu
Ni
91.5%
6%
1%
1%
Small amount of silicon is used along with these.
The microstructure consist of NiAl and CuAl2 in the
matrix of aluminium solid solution.
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
(J) high coefficient of expansion
 These alloys find applications as bearings in diesel
engines and tractors.
Copper based alloys
 Chemical composition
Cu 80-85%
Sn
10-15%
Pb
10%
 The term bronze covers a large number of copper
alloys with varying percentages of Sn, Zn and Pb.
 Bronze is one of the oldest known bearing materials.
 Bronze,
 (a) is easily worked
 (b) has good corrosion resistance
 (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 tubes.
 Copper-based alloys are employed for making
bearings required to resist heavier pressures such as in
railways.
Silver-based alloys
Silver bearings are produced by electro
deposition of a 0.3 to 0.5 mm layer of silver on a steel
support shell ,with an intermediate layer of Cu and Ni.
A 0.02-0.03mm of lead is then deposited on top of the
silver and the indium diffuse into the lead by heat
treatment at 180oc. This covering layer aid in
improving the running in properties and the corrosion
resistance of the silver layer.
 These are highest prized alloys
 They are employed where other materials don’t
produce satisfactory results
 These alloys are used on the connecting rod bearings
of aircraft engines
Non-metallic bearing materials
(a)Teflon (poly tetra flouro ethylene)
It has co-efficient of friction <0.004 with out
lubrication. It has good stability at high temperature. It
is chemically inert to water and many chemicals and
solvents, fillers like glass and graphite increases the
resistance to deformation.
(b)Nylon
Nylon bearings have co-efficient of friction 0.150.33 for dry friction, 0.14-0.18 with water lubrication.
0.09-0.14 for oil lubrication with load of 5-25Nand a
relative velocity of 2.5-110m/min