Individual adjustment of preload

In cases where universally matchable bearings or matched bearing sets are used, preload is determined at the factory during production. In some cases, however, it may be necessary to optimize the preload to accommodate the particular operating conditions. In these cases, the bearings should not be modified, as this requires special tools and knowledge, and the bearings could be damaged irreparably. Bearing modification should be entrusted exclusively to SKF Spindle Service Centres (→ Machine tool spindle service).

It is possible, however, to increase or decrease preload by using spacer rings between two bearings arranged back-to-back or face-to-face, when used in sets of two or more bearings. There is no requirement to insert spacers between bearings arranged in tandem.

By grinding the side face of the inner or outer spacer, the preload in the bearing set can be changed.

Table 1 provides information about which of the equal-width spacer ring side faces must be ground and what effect it has. The necessary dimensional deviation for the overall width of the spacer rings is listed in the following tables:

  • table 2 for bearings in the 718 .. D series
  • table 3 for bearings in the 719 .. D and 70 .. D series
  • table 4 for bearings in the 719 .. E and 70 .. E series
  • table 5 for bearings in the 719 .. B and 70 .. B series
  • table 6 for bearings in the 72 .. D series

Spacer rings

As a rule, using spacer rings with angular contact ball bearing sets is advantageous when:
  • preload in the bearing set needs to be adjusted
  • moment stiffness and moment load capacity should be increased
  • nozzles for oil lubrication must be as close as possible to the bearing raceways
  • sufficiently large space is needed for surplus grease, in order to reduce frictional heat in the bearing
  • improved heat dissipation via the housing is required at very high operating speeds

To achieve optimum bearing performance, spacer rings must not deform under load, otherwise form deviations can influence the preload in the bearing set. As a result, the guideline values for the shaft and housing tolerances should always be used.

Spacer rings should be made of high-grade steel that can be hardened to between 45 and 60 HRC, depending on the application. Plane parallelism of the face surfaces is particularly important. The permissible deviation must not exceed 1 to 2 μm.

Unless preload is to be adjusted, the overall width of the inner and outer spacer rings should be identical. The most accurate way to do this is to process the width of the concentric inner and outer spacer rings in one operation.

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