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Speeds
n th = Thermal reference speed [rpm]
f 0
For rough estimate calculations, the rotational speed factor can be taken from the diagram Speed coefficient calculation.
Calculation example for the thermally permissible operating speed
The single row cylinder roller bearing with cage NJ220E with the parameters
d = 100 mm
D = 180 mm
B = 34 mm
is loaded as follows
F r = 30 kN
F a = 6 kN
Constant operating speed is t n = 500 rpm.
The thermal reference speed can be taken from the bearing tables as:
n th = 3600 rpm
Factor taken from the table in the friction section
v Viscosity of lubricant under operating conditions [mm 2 /s]
d m Mean bearing diameter d m = (D+d)/2 [mm]
Q Sum of all heat removing flows [kW]
The following applies to the load paramete K P :
π f 1 · P 1 · d m
K P = 10 -6 · — · n th · ————–
30 Q
n th = Thermal reference speed [rpm]
f 1
Factor taken from the table in the friction section
v Viscosity of lubricant under operating conditions [mm 2 /s]
P 1 For dynamic equivalent radial load or [N]
load refer to the table in the friction section
D+d
d m Mean bearing diameter d m = ——– [mm]
2
The coefficients f 0 , f 1 are components of DIN 732-2 (draft )and were listed for the roller bearings from the KRW
range in Table Oil- and Grease lubricaten.
The rotational speed factor is to be determined by using an approximation equation.
The thermal reference rotational speed can be obtained from the bearing tables. The following
applies:
K · d m · B 6,5 · 140 · 34
F a admissible = ———— = —————— = 30,9 > 6 kN
1000 1000
F a admissible permissible axial force [kN]
K 6,5 for single row cage bearings
(D + d)
d m average bearing diameter ——— = 140 mm
2
B bearing width B = 34 mm
The bearing NJ220E can be axially loaded with , the additional frictional component that then results should be taken
into consideration in the thermal balance. The equivalent dynamic load becomes, since F r / F a = 0,2 > 0,11:
P = 0,93 · F r + 0,69 · F a = 0,93 · 30 + 0,69 · 6 = 32 kN
KRW 125