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Current Location: Home >> Basic Technical Parameter >> Bearing Handing
  Basic Technical Parameter

Miniature and instrument-sized ball bearings are high precision machined parts with tolerances and raceway finishes that are measured in millionths of an inch. At the same time, their small size and often thin sections makes them vulnerable to excessive handling forces. High quality bearings cannot be expected to fulfill their performance potential if they are mistreated or contaminated and most small bearing failures can be traced to the user’s poor handling techniques. Common sense in handling a precision part goes a long way towards avoiding such problems, and the user should consider the following as “good manufacturing practices”.
Bearings are supplied in packages that are usually sealed after final inspection in class 100 clean room conditions. Even sub-micron contaminants can have a serious adverse affect on several aspects of bearing performance:
  • Torque
  • Noise
  • Bearing life
         - Ball skidding
         - Lubricant degradation
         - Heat build up

Contamination is avoided by installing bearings in a clean environment. While a clean room or laminar flow
workbench is recommended, these are not essential for normal applications as long as basic precautions are used.

  • Avoid handling bearings with bare hands. Use talc-free finger cots or surgical gloves. This is particularly important to avoid corrosion of 52100 chrome steel bearings.
  • Work areas and benches should be cleaned daily to avoid dust build up.
  • Keep bearings in original packaging until used. Never leave bearings exposed to the environment.
  • Work tools must be kept clean and burr-free
  • It is preferable that assembly workers wear clean external clothing (caps, smocks, shoe-covers) that meets clean-room specifications. No make-up or cosmetic powder.
  • Mating components should be cleaned prior to use. Be careful in the choice of cleaning materials as regular cotton swabs and cleaning cloths may add contamination from lint. Use specific lint-free clean room products.

The most common cause of small bearing failure is excessive force applied during assembly, which usually results in the following adverse effects on bearing performance:

Brinelling (raceway damage)
Higher torque
Changed mechanical characteristics
Reduced lifetime

Brinelling causes noise.

Excessive forces during assembly of small bearings are generated by poor handling techniques or incorrect/uncontrolled interference due to poor design or tolerance stack up.

NEVER press fit a bearing to a mating component by
applying force across the bearing raceways through
the balls. This will always result in brinelling damage
to the bearing. Press the inner ring for a press fit on
the shaft or the outer ring for a press fit in the housing.
Calculate the effect of worst-case tolerances on interference fits. Allow for thermal expansion and material type in calculating the maximum loss of radial play. Use a bearing with suitable radial play range. Loss of radial play will change the mechanical characteristics of the bearing (contact angle, torque, resonant frequency), and can ultimately cause bearing failure.
Excessive interference has cracked the inner race.
  • Follow all guidelines for mounting practices. Make sure that fixtures are aligned.
  • Bearings are susceptible to shock or impact loads, especially when the axial play has been removed
    through preload. Dropping a preloaded assembly, or even placing it on a hard surface, can cause
    brinelling. It is recommended that assembly work surfaces are covered with a layer of shock-absorbing material.

Bearings are susceptible to corrosion and should be kept in a dry environment. The lubricant in a bearing will provide some measure of corrosion resistance to the internal raceways, but the acid from skin can corrode the outer surfaces. 52100 chrome steel bearings will quickly corrode if the lubricant is cleaned out, so bearings made from this material should never be used “dry”.

Misalignment during assembly is a common cause of bearing noise, increased torque, and general poor performance. The free angle of misalignment that a small bearing can tolerate is typically less than 1°. (See page 13).

Bearing Misalignment
 Must be < θf (page 13)

  • Locating shoulders on mating components must be parallel to bearing raceway faces.
  • Shaft and housing bores must be concentric. This is particularly true when more than 2 bearings share a common component. For example, if a third bearing is added to the above arrangement, the resulting assembly has almost no tolerance for misalignment of the bearing outer ring.
Bearings are generally made from magnetic material. If a bearing becomes magnetized, its performance characteristics may change.

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