Bearings

Bearings

• Types of bearings:• Rolling contact or anti-friction bearing

• Journal or sleeve bearings(sliding contact bearing)

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Bearings are used for carrying loads while allowing relative motion(rotation) with minimum friction

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BearingsRolling Contact Bearings – load is transferred through rolling elements such as balls, straight and tapered cylinders and spherical rollers.

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Journal (sleeve) Bearings – load is transferred through a thin film of lubricant (oil).

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BearingsJournal (Sleeve) Bearings

Load is transferred through a lubricant in sliding contact

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Design Considerations

• Bearing life and reliability• Bearing speed (rpm)• Space limitation• Accuracy

• Bearing load – radial, thrust (axial) or both

Radial loadRadial load

Thrust load

Bearings are selected from catalogs, before referring to catalogs you should know the followings:

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Rolling Contact Bearings

• Deep groove ball bearing

• Angular contact bearings (AC)

• Self alignment ball bearing

1. Ball bearings

3. Thrust bearings

• Cylindrical bearings(straight roller bearing)

• Needle bearings

• Tapered bearings

• Spherical bearings

2. Roller bearings

In general, ball bearings are capable of higher speeds and roller bearings can carry greater loads

Comparison of rolling contact and journal bearings

• Rolling contact bearings have low starting friction and are used for applications with high starting loads(coefficient of friction between 0.001 and 0.002)

• Journal bearings with hydrodynamic lubrication are suited for high rotating speeds with impact loads(the higher the rotating speed, the more effective the hydrodynamic pumping action

• Rolling contact bearings take up more radial space around the shaft, but journal bearings usually require greater axial space

• Rolling contact bearings produce more noise• Journal bearings are less expensive than ball or roller bearing for

simple applications

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Types of Ball bearings

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Ball Bearings

Deep groove (Conrad) bearing

• Primarily designed to support radial loads, the thrust capacity is about 70% of radial load capacity

• Load capacity is limited by the number of balls

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Ball BearingsAngular contact bearings (AC)The centerline of contact between the balls and the raceway is at an angle to the plane perpendicular to the axis of rotation.

• Used for high radial and thrust load applications

Extra support in the back

Direction of thrust

Self alignment bearing

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Roller BearingsRoller bearings have higher load capacity than ball bearings, load is transmitted through line contact instead of point contact.

Cylindrical bearing

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Needle bearing

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Roller BearingsTapered bearings

Designed to withstand high radial loads, high thrust loads, and combined loads at moderate to high speeds. They can also withstand repeated shock loads.

Car wheel bearings

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Tapered Bearings

Indirect and Direct mounting

Indirect mounting

Direct mounting

Indirect mounting provides greater rigidity when pair of bearings is closely spaced: front wheel of a car, drums, sheaves,..

Direct mounting provides greater rigidity when pair of bearings is not closely spaced: transmission, speed reducers, rollers,..

aa = effective bearing spread

Measure of the rigidity of the bearing mounting

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Roller BearingsBearing design uses barrel shaped rollers. Spherical roller bearings combine very high radial load capacity with modest thrust load capacity and excellent tolerance to misalignment.

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Roller Thrust BearingsSpherical Thrust Bearings

Cylindrical Thrust Bearings

Tapered Thrust Bearings

Ball thrust bearing

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Mounting Bearings

Pillow Block Flange

Common mounting, inner ring held in position by nuts threaded onto the shaft.

Alternative method, inner ring is press fitted onto the shaft.

Two-bearing mounting