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Four-Point Contact Ball Bearings Design considerations
Used as thrust bearing
Four-point contact ball bearings are often used as entirely thrust bearings, together with a radial bearing. When used in this way, the four-point contact ball bearing should be mounted with radial clearance in the housing (fig. 1)
- in combination with a cylindrical roller bearing:
- the radial internal clearance of the cylindrical roller bearing should be smaller than the theoretical radial internal clearance of the four-point contact ball bearing after both have been mounted
- the theoretical radial clearance can be calculated from:
Cr = 0,7 Ca
where
Cr theoretical radial internal clearance
Ca axial internal clearance (table 1) - the outer ring of the four-point contact ball bearing must be able to accommodate thermal movements
Therefore, it should not be clamped axially, but a small gap should be maintained between the outer ring and the cover flange. - bearings with locating slots should be used (fig. 1) to prevent the outer ring from turning
If clamping the outer ring cannot be avoided, the outer ring must be carefully centred during mounting.
Load ratio
For proper functionality, the balls should contact only one inner ring raceway and the opposite side of the outer ring raceway. This is the case when the load ratio is:
- Fa/Fr ≥ 1,27 for bearings in the QJ 2, QJ 3 and QJ 10 series
- Fa/Fr ≥ 1,78 for bearings in the QJ 12 series
A load ratio that is smaller than recommended can reduce bearing service life.