Table of contents
Speeds
The calculation of reference speeds is standardised in ISO 15312. The stated reference speeds have been calculated in accordance with this standard.
Limiting speed
The limiting speed n_{G} is based on practical experience and takes account of additional criteria such as smooth running, sealing function and centrifugal forces.
The limiting speeds indicated in the product tables must not be exceeded even under favourable operating conditions without prior consultation with Schaeffler.
Thermal speed rating
n_{ϑr} is used to calculate n_{ϑ}
The thermal speed rating n_{ϑr} is used as an ancillary value when calculating the thermally safe operating speed n_{ϑ}. This is the speed at which, under defined reference conditions, a bearing operating temperature of +70 °C is achieved.
The thermal speed rating is not a speed limit for the application of a bearing. It is primarily for the purpose of comparing the speed suitability of different bearing types under defined reference conditions.
A speed limit taking account of the thermal balance can be calculated using the thermally safe operating speed.
Reference conditions
The reference conditions are based on the usual operating conditions of the most significant bearing types and sizes.
They are defined as follows in ISO 15312:
 mean ambient temperature ϑ_{Ar} = +20 °C
 mean bearing temperature at the outer ring ϑ_{r} = +70 °C
 load on radial bearings P_{1r} = 0,05 · C_{0r}
 load on axial bearings P_{1r} = 0,02 · C_{0a}
 the operating viscosities (axial bearings in accordance with DIN 7321). These are selected for radial bearings such that similar reference speeds are achieved for both oil and grease lubrication
 radial bearings: 12 mm^{2}/s (ISO VG 32)
 axial spherical roller bearings: 24 mm^{2}/s (ISO VG 68)
 axial cylindrical roller bearings and axial needle roller bearings: 48 mm^{2}/s (ISO VG 220)
 heat dissipation via the bearing seating surfaces ➤ Equation to ➤ Equation:
for radial bearings, bearing seat A_{r} ≦ 50 000 mm^{2} ➤ Equation:
Heat flow density
for radial bearings, bearing seat A_{r} ＞ 50 000 mm^{2} ➤ Equation:
Heat flow density
for axial bearings, bearing seat A_{r} ≦ 50 000 mm^{2} ➤ Equation:
Heat flow density
for axial bearings, bearing seat A_{r} ＞ 50 000 mm^{2} ➤ Equation:
Heat flow density
Thermally safe operating speed
The thermally safe operating speed n_{ϑ} is calculated in accordance with DIN 732:2010. The basis for the calculation is the heat balance in the bearing, the equilibrium between the frictional energy as a function of speed and the heat dissipation as a function of temperature. When conditions are in equilibrium, the bearing temperature is constant.
Preconditions for calculation
The permissible operating temperature determines the thermally safe operating speed n_{ϑ} of the bearing. The preconditions for calculation are correct mounting, normal operating clearance and constant operating conditions.
Calculation not applicable
The calculation method is not valid for:
 sealed bearings with contact seals, since the maximum speed is restricted by the permissible sliding speed at the seal lip
 yoke and stud type track rollers
 aligning needle roller bearings
 axial deep groove and axial angular contact ball bearings
Limiting speed n_{G}
The limiting speed n_{G} must always be observed.
Calculate thermally safe operating speed
Calculation of frictional power
The equilibrium between the frictional power and heat dissipation is given in ➤ Equation and ➤ Equation. For an explanation of the parameters ➤ Equation.
Frictional power
Frictional power
Heat flow
The total dissipated heat flow is calculated in accordance with ➤ Equation.
Total dissipated heat flow
According to ➤ Equation, frictional power is equal to the dissipated heat flow.
Frictional power = dissipated heat flow
Lubricant film parameter K_{L}
➤ Equation can only be solved iteratively. The introduction of the lubricant film parameter K_{L}, the load parameter K_{P} and the speed ratio f_{n} has made this more manageable ➤ Equation.
Lubricant film parameter
Speed ratio f_{n}
In the normal operating range of 0,01 ≦ K_{L} ≦ 10 and 0,01 ≦ K_{P} ≦ 10, f_{n} can be calculated in accordance with ➤ Equation and ➤ Figure.
Speed ratio
Thermally safe operating speed
The thermally safe operating speed n_{ϑ} is calculated by multiplying the thermal speed rating n_{ϑr} by the factor for thermal speed ratio f_{n} ➤ Equation.
Thermally safe operating speed
Heat dissipation via the bearing seating surfaces
Heat dissipation via the bearing seating surfaces is calculated in accordance with ➤ Equation.
Heat dissipation via the bearing seating surfaces
Heat dissipation via the lubricant
Heat dissipation via the lubricant is calculated in accordance with ➤ Equation.Heat dissipation via the lubricant
Lubricant film parameter K_{L}
The lubricant film parameter K_{L} is calculated in accordance with ➤ Equation.
Lubricant film parameter
Load parameter K_{P}
The load parameter K_{P} is calculated in accordance with ➤ Equation.
Load parameter
Legend
N_{R}  W 
Frictional power 
kW 
Total dissipated heat flow 

M_{R}  Nmm 
Total frictional torque 
f_{0}   
Bearing factor for frictional torque as a function of speed 
ν  mm^{2}/s 
Kinematic viscosity of the lubricant at operating temperature 
n_{ϑ}  min^{1} 
Thermally safe operating speed 
d_{M}  mm 
Mean bearing diameter (D + d)/2 
f_{1}   
Bearing factor for frictional torque as a function of load 
P_{1}  N 
Decisive load: radial load for radial bearings, axial load for axial bearings. 
_{S}  kW 
Heat flow dissipated via the bearing seating surfaces 
_{L}  kW 
Heat flow dissipated by the lubricant 
_{E}  kW 
Heat flow. For heating by external source (+), for cooling by external source (–) 
K_{L}   
Lubricant film parameter 
f_{n}   
Speed ratio 
K_{P}   
Load parameter 
n_{ϑr}  min^{1} 
Thermal speed rating; see product tables 
k_{q}  10^{6 }kW/ (mm^{2} · K) 
Heat transfer coefficient, as a function of the bearing seating surface ➤ Figure. This is dependent on the housing design and size, the housing material and the installation position. 
Legend (continuation)
A_{S}  mm^{2} 
Heatdissipating bearing seating surface 
Δϑ_{A}  K 
Difference between mean bearing temperature and ambient temperature 
_{L}  l/min 
Oil flow 
Δϑ_{L}  K 
Difference between oil inlet temperature and oil outlet temperature 
B  mm 
Bearing width 
d  mm 
Bearing bore diameter 
D  mm 
Bearing outside diameter 
d_{1}  mm 
Outside diameter of shaft locating washer 
D_{1}  mm 
Inside diameter of housing locating washer 
T  mm 
Total width of tapered roller bearing 
Speed ratio f_{n} as a function of lubricant film f_{n} = speed ratio K_{L} = lubricant film parameter K_{P} = load parameter 
Heat transfer coefficient k_{q}as a function of the bearing seating surface k_{q} = heat transfer coefficient, as a function of the bearing seating surface A_{S} = heatdissipating bearing seating surface 