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10. Limiting Speed of Bearings

Each bearing has its own rotational speed limit. The empirical speed limit up to which the bearing can continue to operate stably without causing any problems, even when the bearing’s internal friction generates heat, is called the “limiting speed.” The limiting speed varies according to the conditions such as the types of bearings and cages, lubrication method, bearing load, and cooling conditions around the bearing.

The limiting speed of bearings that use the contact rubber seals (2RS) is limited by the circumferential velocity at the seal contact part, so can be lower than that of the non-contact-type bearing.

When the bearing is operated under a large load, the limiting speed must be made smaller. When the bearing is not used under normal load conditions, the limiting speed must be multiplied by the correction factor shown in the table below (C_r/P<12 and F_a/F_r>0.2).

The limiting speed of duplex bearings is about 20% of the limiting speed of a single bearing. When a nylon cage is used, the limiting speed may be 1.5 times faster, compared to when a steel cage is used for the bearing.

Correction of limiting speed according to the bearing’s load

Correction of limiting speed under combined load

In addition, the limiting speed must be multiplied by the correction factor in the table below to obtain the final limiting speed, depending on whether the bearing uses outer ring rotation or inner ring rotation, and whether the lubricant is grease or oil.

Correction of limiting speed depending on the rotating ring and lubricant

You may want to refer to the usage conditions below when the sealing device is embedded in the shaft or the housing (not in the bearing itself), and when nitrile rubber seal is used.

Usage conditions of nitrile rubber seals