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Bearing speed

release time:2018-05-26
There is a limit to the running speed of rolling bearings. In general, this limit speed is set by the operating temperature of the lubricant or the material of the bearing component.
The speed at which the extreme operating temperature is reached depends on the amount of frictional heat (including any extraneous heat) generated during the operation of the bearing and the amount of heat that can be dissipated from the bearing.
Bearing type and size, internal design, load, lubrication and cooling conditions, as well as cage design, accuracy, internal clearance, etc., all affect the determination of the speed capability.
In the product table, two speeds are generally listed: the (thermal) reference speed and the (movement) limit speed, the values of these two speeds depending on the criteria considered.

Reference speed
The (thermal) reference speed listed in the product table is a speed reference used to determine the allowable operating speed of the bearing under certain load and lubricant viscosity conditions.
The listed reference speed values ​​comply with the ISO 15312 standard (this standard does not include thrust ball bearings). This ISO standard is developed for oil lubrication but is equally effective for grease lubrication.
The reference speed for a given bearing represents its speed under a particular operating condition. At this speed, the heat generated by the bearing is balanced with the heat dissipated from the bearing to the shaft, bearing housing and lubricant.
According to the ISO 15312 standard, the reference conditions for achieving this heat balance are:
– Add another 50 degrees Celsius to the ambient temperature of 20 degrees Celsius, that is, the bearing temperature is 70 degrees Celsius. The measurement point is the bearing's fixed outer ring or bearing seat washer;
– Radial bearings: a stable radial load, 5% of the basic static load rating of C0
– Thrust bearing: a stable axial load, 2% of the C0 of the basic static load rating
– Open bearing with conventional clearance
For oil-lubricated bearings:
– Lubricant: Mineral oil without EP additives, kinematic viscosity at 70°C
ν = 12mm2/s (ISO VG 32) (for radial bearings)
ν = 24mm2/s (ISO VG 68) for (for thrust roller bearings)
- Lubrication method: Oil bath, lubricated oil reaches the middle when the rolling elements are at the lowest position.
For grease-lubricated bearings:
– Lubricants: Lubricated with conventional lithium soap greases containing mineral base oils with viscosities from 100 to 200 mm2/s (eg ISO VG 150) at 40 degrees Celsius
– Grease volume: approximately 30% of the free space inside the bearing.
When the grease-lubricated bearings start, a temperature spike may occur. Therefore, the bearing may need to run for 10 to 20 hours to reach the normal operating temperature.
Under these specific conditions, the reference speeds for oil lubrication and grease lubrication are equal.
In the case of bearing outer ring rotation, it may be necessary to reduce the rating.