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Bearings

What is a Bearing ?

• A bearing is part of a machine that supports and or guides a moving part.

• The most common application for supporting a rotating shaft.

Plain Bearing (Split)

Bearing

Bearing Seat

Used in engines to support crank shaft.

Why are they used ?

• The purpose of a bearing is to reduce the friction between the moving parts.

• The reduction of friction can be accomplished by using material that will easily slide over each other or by the use of a lubricating oil.

Material Choice

• The choice of a bearing depends upon the material that the shaft is made of and the loads that the bearing/shaft combination will be subjected to.

Plain Bearings

• Bronze• White Metal• Cast Iron

• Sintered• Plastic• Composite

• These are the simplest types of bearings. They consist of a plain hole in a part in which a shaft rotates.

• This bearing is only effective with moderate speeds & loads.

Bronze

• An alloy of copper and tin.

• May also contain a small amount of phosphorus, then called a phosphor-bronze bearing.

• Fairly hard, but softer than steel.

• Good load-carrying capacity.

• Less suited for high rubbing speeds.

White Metal

• Tin alloy with small amounts of copper and antimony.

• This is a soft material that adapts to the shape of the shaft.

• Limited load carrying capacity.

Cast Iron

• Used to make flat or sliding bearings.• Two cast iron surfaces will run together,

due to similar material properties, making this an excellent bearing material.

• In terms of a bearing, no other material exhibits this same trait.

• This is probably due to the graphite found in the structure of cast iron.

Sintered

• Sintering: the fusion of powdered particles together by high temperature self-diffusion.

• These bearings are made from an oil-soaked powder of copper, tin, and graphite.

Plastic

• Nylon is a common material used for this bearing type.

• Can also be a composition material or Teflon.

• Advantages: quiet, cheap to produce, do not corrode, and do not need lubrication.

Anti-Friction

• Eliminate the problem of a shaft rubbing against the bearing.

• They do not rub, they roll between steel balls or rollers in a channel called a raceway.

Anti-Friction

Outer Race

Inner Race

Ball Bearings

Retainer (Cage)

Dust Shield (not shown)

Anti-Friction

• Used to support two types of loads.– Radial Loads: Ball Bearings– Axial Loads: Thrust Bearings

Axial Load

Radial & Axial Loads