The limiting speed (mechanical) is determined by criteria that include the form stability or strength of the cage, lubrication of the cage guiding surfaces, centrifugal and gyratory forces acting on the rolling elements, bearing housing precision and other speed-limiting factors, such as seals and the lubricant for sealed bearings.
Experience shows that even under the most favourable loading and frictional conditions, there are maximum speeds that should not be exceeded for technical reasons or because of the very high costs involved in keeping the running conditions stable for any length of time.
The limiting speeds listed in the product tables are valid for the basic bearing design. In cases where the limiting speed is higher than the reference speed, temperatures significantly higher than the reference value can be expected. Under these conditions, appropriate measures might be necessary (→ Speeds above the reference speed). If these measures are not adequate, the bearing internal clearance and accuracy of the housing and shaft seats should be verified and adapted to the more demanding operating conditions (→ Tolerances for total radial run-out).
The compatibility of the materials in the bearing system must also be considered relative to the bearing temperature and required service life (→ Materials for rolling bearings and Lubricating greases). When the steady state operating temperature is higher than the maximum recommended by the bearing material stabilization class, i.e. 120 °C (250 °F) for the SN class (→ Influence of the operating temperature), a bearing with a higher stabilization class might be necessary to maintain the mounting stress and bearing internal clearance.
For grease lubrication, additional factors such as lubrication of the cage guiding surfaces and grease consistency at the operating temperature should be taken into consideration (→ Grease lubrication).
Some open ball bearings have very low friction, and the reference speeds listed might be higher than the limiting speeds. Therefore, the adjusted reference speed needs to be calculated and compared to the limiting speed. The lower of the two values should be used.
To function satisfactorily, particularly at high speeds, bearings must be subjected to a given minimum load. For detailed information about the required minimum load, refer to Loads in the relevant product section.
In general, if the limiting speed is not able to meet the requirements of the application, modifications to the bearing, lubrication system or application may be required. Modifications could include improving bearing geometrical tolerances, changing cage materials, changing the lubricant or lubrication method, or improving heat dissipation.
In that case, SKF recommends contacting the SKF application engineering service for assistance.