The speed of rolling bearings is subject to certain limits. When bearings are operating, the higher the speed, the higher the bearing temperature due to friction. The limiting speed is the empirically obtained value for the maximum speed at which bearings can be continuously operated without failing from seizure or generation of excessive heat. Consequently, the limiting speed of bearings varies depending on such factors as bearing type and size, cage form and material, load, lubricating method, and heat dissipating method including the design of the bearing's surroundings.
The limiting speeds for bearings lubricated by grease and oil are listed in the bearing tables. The limiting speeds in the tables are applicable to bearings of standard design and subjected to normal loads, i. e. C/P≥ 12 and Fa /Fr≤ 0.2 approximately. The limiting speeds for oil lubrication listed in the bearing tables are for conventional oil bath lubrication.
● Correction of Limiting Speed
When the bearing load P exceeds 8% of the basic load rating C, or when the axial load Fa exceeds 20% of the radial load Fr, the limiting speed must be corrected by multiplying the limiting speed found in the bearing tables by the correction factor shown as below.
When the required speed exceeds the limiting speed of the desired bearing, then the accuracy grade, internal clearance, cage type and material, lubrication, etc., must be carefully studied in order to select a bearing capable of the required speed. In such a case, forcedcirculation oil lubrication, jet lubrication, oil mist lubrication, or oil-air lubrication must be used. Some types of lubricants are not suitable for high speed, even though they may be markedly superior in other respects. When speeds are more than 70 percent of the listed limiting speed, it is necessary to select an oil or grease which has good high speed characteristics.
If all these conditions are considered. The maximum permissible speed may be corrected by multiplying the limiting speed found in the bearing tables by the correction factor shown on the right side. It is recommended that Copland be consulted regarding high speed applications.
● Limiting Speed Correction Factor for
High- Speed Applicationss
|Bearing Types||Correction Factor|
|Deep Grooove Ball Brgs.
Tapered Roller Brgs.
● Limiting Speed for Rubber Contact Seals for Ball Bearings
The maximum permissible speed for contact rubber sealed bearings (DDU type) is determined mainly by the sliding surface speed of the inner circumference of the seal. Values for the limiting speed are listed in the bearing tables.