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There
are several materials and combinations of materials that can be
used for an engine bearing, depending upon the application. Apart
from the basic function of reducing friction between a moving part
of an engine-crankshaft or camshaft and it's associated sup
-port surface - the engine bearings have to meet seven other characteristics
- fatigue strength, conformability, embedability, seizure -resistance,
corrosion resistance, temperature - strength, and thermal conductivity
- characteristics which assume criticality depen
-ding upon the bearing application.
Asiatic Bearing Co. manufactures bearings from
a variety of bearing materials described bellow. Each bearing material
has its own peculiarities which define its field of application.
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STEEL
BACKED WHITE METAL (BABBITT)
(i)
Steel Backed Tin Based Babbitt (White Metal)
This is a very popular and historical bearing material. It
contains 90% Tin as matrix with Antimony & Copper as alloying
elements. It has excellent properties of embeddability, conformability
& resistance to seizure. However, its application are
very much restricted by its low load carrying capacity. White
Metal Bearings are extensively used in Turbine, Electric Motors,
High H.P. Marine Engines, Petrol Engines and other applications
such as Camshaft Bushes, Thrust Washers auxiliary drive shaft
bushes, etc.
(ii)
Steel Backed Lead Based Babbitt (White Metal)
This is Lead based Babbitt containing 90% Lead and has similar
properties as Tin based Babbitt but is softer than it. Lead
based Babbitt have one disadvantage that they are prone to
corrosion at higher operating temperatures. Beside this limitation,
they are equally good as Tin based Babbitt and can substitute
them in most of applications. Camshaft Bushes of allmost of
all engines are of Lead based material due to their excellent
conformability. |
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STEEL
BACKED STRAIGHT COPPER-LEAD ALLOY
There
are various kinds of copper-lead alloys according to the applications
as well as load carrying capacity.
(i)
Half Bearings - 'SL' (Copper-Lead)
Half bearings made from copper-lead alloys containing a high
percentage of lead and almost no tin are comparatively softer
and therefore there is no necessity of soft, overlay plate
on there bearings. this material is built specifically for
intermediate loaded engines and offers goods embeddability
and conformability.
(ii)
Thrust Washers (Copper-Lead)
Thrust washers are manufactured from copper-lead alloys having
medium to high percentage of tin. As such these are hard and
possess high fatigue strength, high resistance to wear and
corrosion which make them very popular for thrust washers.
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(iii) Bushes (Copper-Lead)
Bushes are manufactured from various types of copper lead
alloys according to the load carrying capacity. Main bearing
bushes and camshaft bushes of stationary engines are manufactured
from copper-lead alloys having low percentage of tin. But
small end bushes, rocker arm bushes etc. are manufactured
from copper-lead alloys having high percentage of tin. These
materials posses high fatigue strength, high resistance to
wear and corrosion which make them very popular for bushes.
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(iv)
Copper-Lead Alloy with Overlay (CopperLead)
There are various kinds of copper-lead alloys according to
the different proportions of Copper : Lead : Tin. These alloys,
when plated, have higher load carrying capacity than white
metal and straight copper-lead alloys. These alloys in unplated
condition, however have poor embeddability, conformability
and resistance to corrosion.
These drawbacks are eliminated by the use for thin electro
deposited white metal overlay on intermediate copper-lead
alloy. The overlay are either lead-tin or lead-tin-copper
and having a thickness of around 0.001". These overlays
are very soft and have excellent embeddability, conformability
and corrosion resistance without impairing higher fatigue
strength of inner copper-lead-tin alloy. |
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ALUMINIUM-TIN
ALLOY
This is steel backed 20 % reticular tin-aluminium alloy bearing.
Engineers and users believe it to be the finest extra-heavy-duty
bearing made today.
Since long time, increased compression ratios of diesel engines
have brought sharp increases to journal pressures whilst the
bearing area need to support these journals has actually decreased.
Copper-lead bearings are still accepted for moderate bearings
loads but may not withstand under pounding of most of today's
engines. However, aluminium-tin bearings will withstand under
the most rigorous operating conditions because it has a combination
of properties found in no other type of bearings. |
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SOLID ALUMINIUM ALLOY
This aluminium-tin alloy usually contains 6% tin, 1% copper
and 1% nickel. This material is used to manufacture thrust
washers. This is ideal substitute for bronze items for higher
loads. |
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SOLID
BRONZE
This are various types of bronzes which are used for the manufacture
of solid bushes. This material is usually used for the manufacture
of those which are very thick and cannot be developed in steel
backed construction.
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