The maximum speed for a ball bearing in operation is limited by various mechanical and kinematic criteria. Narrow tolerances of bearings and surrounding parts, special measures regarding lubrication and type of lubricant as well as special retainer materials and designs generally have a beneficial effect on the speed limit. The characteristical values for speed given in the tables only apply to specially set reference conditions. They therefore only give an indication of the relative speed suitability of the ball bearing. Please call us for more information if operating conditions are different.

The kinematically permissible speed n_zul

The ‘kinematically permissible speed n_zul’ applies to ball bearings with contact seals which do not have a thermal reference speed n_ur defined in the standard. It takes into consideration the special conditions resulting from the wiping contact between ball bearing inner ring and seals. In principle the same conditions as for the thermal reference speed n_ur otherwise apply.

The thermal reference speed n_ur

The reference conditions have been selected in DIN 732-1 so that the ‘thermal reference speed n_ur’ is identical for both types of lubrication: oil or grease. The essential operating conditions are:

• Reference temperature of the ball bearing on stationery outer ring 70^oC
• Reference temperature of the ball bearing environment 20^oC
• Reference loading P, of the ball bearing 5% of the static radial loading rating C_or
• Oil lubrication as oil bath lubrication with a conventional mineral oil without EP additives, with a kinematic viscosity of 12 mm²/s at 70^oC
• Grease lubrication with a standard lithium soap grease with a mineral base oil without EP additives. The kinematic viscosity of the base oil is 22 mm²/s at 70^oC. The grease quantity is approx. 30% of the free space in the ball bearing
• Ball bearings with standard designs, i.e. with standard accuracy, with standard radial play, with non-contact closures
• Ball bearing installed on a horizontal shaft with a stationery outer ring and installation dimensions and tolerances which do not reduce bearing radial clearance

The permissible thermal operating speed n_u 

The speed at which the average ball bearing temperature reaches the permissible value in real operating conditions is called the ‘permissible thermal operating speed n_u’. It is calculated from the thermal reference speed by multiplying it with the factor ‘speed ration f_n’ according to DIN 732-2: n_u = f_n . n_ur

Following the standard we use diagrams which make calculating this factor far easier. The different torque effects of oil and grease lubrication are taken into consideration.