BEARING MATERIALS

1. BEARING MATERIALS
Presented by:
GIRISH RAGHUNATHAN
Department of Mechanical and Automobile Engineering
TRIBOLOGY
1

2. OUTLINE OF THE PRESENTATION
1. Introduction
2. Characteristics of a bearing material
3. Bearing Materials
4. Conclusion
2

3. 1. INTRODUCTION
 A bearing is a machine element that constrains relative motion to only the desired
motion, and reduces friction between moving parts.
3
Fig 1. Bearings used in machines

4. 2. CHARACTERISTICS OF BEARING MATERIALS
1. Possess low coefficient of friction.
2. Provide hard, wear resistant surface with a tough core.
3. Have high compressive strength.
4. Have high fatigue strength.
5. Be able to bear shocks and vibrations.
6. Possess high thermal conductivity to dissipate heat generated due
to friction between the bearing and the rotating shaft.
4

5. 7. Possess adequate plasticity under bearing load.
8. Possess adequate strength at high temperatures.
9. Be such that it can be easily fabricated.
10. Possess resistance to corrosion.
11. Bearing material should be softer than the shaft material.
12. Maintain a continuous film of oil between shaft
and bearing.
5

6. 3. TYPES OF BEARING MATERIALS
Lead or tin based alloys (Babbitt metals)
Cadmium-based alloys
Aluminium based alloys
Copper based alloys
Silver-based alloys
Chrome Steel
Stainless Steel Alloys
Non-metallic bearing meterials
6

7. Tin based alloys with more than 80% tin and little or no
lead.
Lead based alloys with about 80% lead and 1--12% tin.
The alloys with intermediate percentages of tin and lead.
A lead based alloy (solidus
temperature 240ºC )
Pb 75%
Sb 15%
Sn 10%
A tin based alloy (solidus
temperature 222ºC )
Sn 88%
Sb 8%
Cu 4%
3.1 Lead or tin based alloys (babbittmetals)
7

8. 3.1 Lead or tin based alloys (babbittmetals)
LEAD BASED ALLOYS TIN BASED ALLOYS
 Soft  Hard
 Cheap  Expensive
 Suitable for light and
medium loads
 Suitable for heavy loads
 Have high coefficient of
friction
Have low coefficient of
friction
 Applications include rail
road freight cars
 Applications include
high speed engines and
steam turbines
8

9. 3.1 Lead or tin based alloys (babbittmetals)
Common Properties include :
Good ability to embed dirt
Good conformability to journal
Good corrosion resistance
Very good seizure resistance
9
Fig 2. Babitt metal
Fig 3. Babitt metal bearings

10. 3.2 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.
10
Fig 4. Cadmium alloy bearing

11. 3.2 Cadmium based alloys
Properties of these alloys include:
(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.
11

12. 3.3 Aluminium based alloys
Chemical composition
Al 91.5%
Sn 6%
Cu 1%
Ni 1%
 Small amount of silicon is used along with these.
The microstructure consist of NiAl and CuAl2 in the
matrix of aluminium solid solution.
12
Fig 5. Aluminium alloy bearing

13. 4/2/2018
Properties are:
(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 thermal coefficient of expansion
These alloys find applications as bearings in diesel
engines and tractors.
3.3 Aluminium based alloys
13

14. 3. 4 Copper based alloys
Chemical composition
Cu 80-85%
Sn 10-15%
Zn 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
14
Fig 6. Copper alloy

15. 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.
4/2/2018 15

16. 3.5 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.
16

17. 4/2/2018
These are expensive alloys.
They are employed where other materials don’t
produce satisfactory results.
These alloys are used on the connecting rod bearings
of aircraft engines.
17
Fig 7. Silver alloy Fig 8. Silver ball bearings

18. 3.6 Chrome Steel SAE52100
 The most common material used to produce the load
carrying components in precision ball bearings, roller bearings,
and tapered roller bearings .
These components are the inner and outer rings, balls and
rollers.
The chemical composition of this steel has high carbon and
about 1.5% chromium content.
PROPERTIES
1. Has good strength and hardness in the range Rc60-64.
2. Can perform well upto 120ºC. For withstanding higher
temperatures it is tempered which decreases load bearing
capacity.
18

19. 3.6 Chrome Steel SAE52100
3. Excellent hardness and wear resistance
4. Poor corrosion resistance due to low chromium content.
19
Fig 9. Chrome steel SAE 52100
bearing
Fig 10. Chrome steel SAE 52100
ball bearings

20. 3.7 Stainless Steel alloys
 Good corrosion resistant metal because of high percentage
of chromium.
 Commonly used stainless steel alloys are :
1) Martensitic stainless steel AISI 440C
2) Martensitic stainless steel ACD34
3) Martensitic stainless steel SV30
4) Austenitic Stainless Steel AISI316
5) Austenitic Stainless Steel AISI304
6) Medium Carbon alloy steel AISI8620 or AISI4320
7) Low Carbon Alloy steel AISI C1008 and C1010
20

21. 3.7 Stainless Steel alloys
1. Martensitic stainless steel AISI 440C
 Low Hardness but has high carbon content.
Can be hardened using heat treatment methods.
Has good corrosion resistance
More expensive when compared to chrome steel
2. Martensitic stainless steel ACD34
 Same corrosion reistance as 440C but less noisy.
Typical hardness value is Rc60
21

22. 3.7 Stainless Steel alloys
3. Martensitic stainless steel SV30
 Prepared by lowering carbon content and increasing nitrogen content.
Increases saturation of chromium that forms chromium nitrides instead of
carbides leading to high hardness, high strength and extended fatigue life
(double).
Corrosion resistance is 5 times that of ACD34 and 440C
4. Austenitic Stainless Steel AISI316
 Better corrosion resistance due to low carbon content.
However this cannot be hardened and can operate only at low speeds for
low loads.
22

23. 3.7 Stainless Steel alloys
5. Medium Carbon Alloy steel
 Bearings prepared using this material are called ‘Commercial grade’
bearings.
Low cost
Low corrosion resistance and can carry only low loads.
6. Low Carbon Alloy steel
Poor corrosion resistance hence usually coated with grease or oil.
23

24. 4/2/2018 24
Fig 15. Low and medium carbon alloy steel
Fig 11. AISI 440 C steel
Fig 13. SV30 steel
Fig 12. ACD34 steel
Fig 14. AISI316

25. 3.8 Non metallic bearing materials
(a)Teflon (PTFE)
It has co-efficient of friction <0.004 without 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.
24
Fig 16. Teflon bushings and seals Fig 17. Teflon bearing

26. (b)Nylon
 Nylon bearings have co-efficient of friction 0.15-0.33
for dry friction, 0.14-0.18 with water lubrication,0.09-
0.14 for oil lubrication.
3.8 Non metallic bearing materials
25
Fig 18. Nylon Bearings

27. 3.8 Non metallic bearing materials
(c) Ceramic
 Bearings made with ceramic materials fall into a specialty niche
in the bearing industry.
 The most common arrangement is a hybrid bearing, usually with
stainless steel rings and ceramic balls.
 The most common ceramic material used is silicon nitride. Balls
made from this material are hard, up to Rc78, and have a very
smooth surface.
 Hybrid bearings are more expensive than all stainless steel
bearings.
26

28. 4. CONCLUSION
1. Researchers are focused on developing coatings for
bearings which considerably reduce friction.
2. A study predicted that ceramic materials shall be the
commonly used bearing material in near future.
3. Incorporation of non metals for bearing materials such
as high temperature withstanding thermoplastics is
expected.
4/2/2018 27

29. 28