Bearing Alloys

8/13/2019 Bearing Alloys

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Bearing Alloys


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Need for bearings?

The concept behind abearing is very simple:Things roll better than theyslide. The wheels on your

car are like big bearings. Ifyou had something like skisinstead of wheels, your carwould be a lot more difficultto push down the road.

Bearing are the devicesused to support movingparts.


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Loads acting on bearing


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Giant ball bearings

The new San

Francisco

International

Airport uses many

advanced buildingtechnologies to

help it withstand

earthquakes.


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Requirements of bearing material


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Bearing Materials


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Bearing Materials

TinLead based alloys ( Babbitts)

Copper based alloys ( Brasses and Bronzes)

Aluminium based alloys Cast iron


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White Bearing Materials

Either tin-base or lead-base.

The former represents the better-quality high-duty white metals, are known as Babbitt

metals, named after Isaac Babbitt theiroriginator.

All white bearing metals contain between 3.5

and 15 % antimony, and much of thiscombines chemically with some of the tin,giving rise to an intermediate compound SbSn.


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This forms cubic crystals (cuboids), which areeasily identified in the microstructure.

These cuboids are hard, and have low-frictionproperties, consequently, they contribute thenecessary bearing surface in white metals.

In the interest of economy, some of the tin is

generally replaced by lead. The lead-rich white metals are intended for lower

duty, since they can withstand only limitedpressure.


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White Bearing Metals


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Microstructure of White Bearing

Material


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Aluminium-tin alloys

Aluminium-tin alloys containing 20% tin are now usedas main and big-end bearings in automobile design.

Aluminium and tin form a eutectic containing 0.5 %aluminium so that the final structure of these bearings

consists of an aluminium network containing smallareas of soft eutectic tin which wears and so assistslubricant flow.

Because of the long freezing range of this alloy,segregation is a danger so that the cast material is

usually cold rolled and annealed to break up theeutectic leaving small islands of tin in aluminiummatrix.


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Copperbase bearing metals

Include plain tin bronzes (10-15% tin) andphosphor bronzes (10-13% tin, 0.3-10%phosphorus).

Some of the tin and copper combine to formparticles of a very hard intermetallic compoundCU31Sn7 , whilst the remainder of the tin dissolvesin the copper to form a tough solid solution

matrix. These alloys are widely used for bearings when

heavy loads are to be carried.


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Documents

Bearing Alloys