The friction in a rolling bearing is made up of several components, see table. Due to the large number of influencing factors, such as dynamics in speed and load, tilting and skewing resulting from installation, actual frictional torques and frictional power may deviate significantly from the calculated values. If the frictional torque is an important design criterion, please consult the Schaeffler Engineering Service.

The idling friction is dependent on the lubricant quantity, speed, operating viscosity of the lubricant, seals and the running-in condition of the bearing.

Friction is converted into heat. This must be dissipated from the bearing. The equilibrium between the frictional energy and heat dissipation allows calculation of the thermally safe operating speed n_per, see link.

Lubricating oil dissipates a portion of the heat. Recirculating oil lubrication with additional cooling is particularly effective. Grease does not give dissipation of heat.

Heat dissipation via the shaft and housing is dependent on the temperature difference between the bearing and the surrounding structure, Figure 1.

Adjacent additional sources of heat or thermal radiation must be taken into consideration.

The speed and load must also be known. The type of lubrication, lubrication method and viscosity of lubricant at operating temperature are further important factors in calculation.

Total frictional torque M_R
(calculation of axially loaded cylindrical roller bearings, see link):

Frictional energy N_R:

Frictional torque as a function of speed for ν · n ≧ 2 000:

Frictional torque as a function of speed for ν · n ＜ 2 000:

Frictional torque as a function of load for needle roller and cylindrical roller bearings:

Frictional torque as a function of load for ball bearings, tapered roller bearings and spherical roller bearings:

The bearing factors f₀ and f₁ are mean values from series of tests and appropriate data according to ISO 15 312.

They are valid for bearings after running-in and with uniform distribution of lubricant. In the freshly greased state, the bearing factor f₀ can be two to five times higher.

If oil bath lubrication is used, the oil level must reach the centre of the lowest rolling element. If the oil level is higher, f₀ may be up to three times the value given in the table, Figure 2.

If P₁ ≦ F_r, then P₁ = F_r.

In cylindrical roller bearings under axial load, sliding friction between the end faces of the rolling elements and the ribs on the rings leads to an additional frictional torque M₂.

The total frictional torque is therefore:

The bearing factors f₂ are subject to wide scatter. They are valid for recirculating oil lubrication with an adequate quantity of oil. The curves must not be extrapolated, Figure 3 and Figure 4.

In the case of bearings of TB design, the axial load carrying capacity was significantly improved through the use of new calculation and manufacturing methods.

Optimum contact conditions between the roller and rib are ensured by means of a special curvature of the roller end faces. As a result, axial surface pressures on the rib are significantly reduced and a lubricant film with improved load-carrying capabilities is achieved. Under normal operating conditions, wear and fatigue at the rib contact running and roller end faces is completely eliminated.

In addition, the axial frictional torque is reduced by up to 50%. The bearing temperature during operation is therefore significantly lower.