Each bearing type has its own limiting speed. The theoretical speed that bearings can run at safely, even if heat generation by internal friction occurs, is called the maximum permissible speed.
The permissible speed is related to bearing type, type of cage, lubricant type, load and cooling conditions to which the bearing is subjected.
For contact rubber seals(2RS type), the permissible speeds are limited by the peripheral velocity of the seal lip. Normally, this is approximately 50 – 60% of that of non-contact rubber seals. If light contact rubber seals are required, this must be stipulated with the order.
If high loads occur, the permissible speed values must be reduced and the following supplementary factors applied, except under standard operating conditions(Cr/P<12, Fa/Fr>0.2 ).
compensation for maximum permissible speed dependent on load ratio
| Cr/P | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
|---|---|---|---|---|---|---|---|---|
| compensation factor | 0.72 | 0.79 | 0.85 | 0.90 | 0.93 | 0.96 | 0.98 | 1.00 |
compensation for maximum permissible speed under combined axial and radial load
| Fa/Fr | 0.25 | 0.50 | 0.75 | 1.00 | 1.25 | 1.50 | 1.75 | 2.00 |
|---|---|---|---|---|---|---|---|---|
| compensation factor | 1.00 | 0.95 | 0.93 | 0.91 | 0.89 | 0.88 | 0.87 | 0.86 |
If the bearing operates at over 70% of the permissible speed value, a lubricant for high speed should be selected. The values for the permissible speed are for applications with horizontal shafts and with appropriate lubrication. With vertical shafts, only 80% of the maximum speed value should be used. This is necessary due the reduced cage guidance and reduced lubricant retention in this type of application.