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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