Bearings

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Bearings
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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.

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Plain Bearing (Split)
Used in engines to support crank shaft.
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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.

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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.

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Plain Bearings

• 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
• White Metal
• Cast Iron

• Sintered
• Plastic
• Composite

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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.

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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.

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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.

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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.

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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.

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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.

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Anti-Friction
Outer Race
Retainer (Cage)
Inner Race
Ball Bearings
Dust Shield (not shown)
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Anti-Friction

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

Radial Axial Loads
Axial Load