STAR – Precision Ball Screw Assemblies
STAR – Precision Ball Screw Assemblies
STAR – Precision Ball Screw Assemblies
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Average speed and average<br />
bearing load<br />
If the bearing is subject to varying axial<br />
loads over time, the average axial bearing<br />
load can be calculated using formula 21.<br />
If<br />
the speed varies, apply formula 22. In<br />
these formulas, the qi values represent the<br />
discrete time steps in %.<br />
If the radial load Frm varies, calculate the<br />
average radial load in the same manner.<br />
Service life and load safety<br />
factor<br />
Nominal life<br />
The nominal life is calculated as follows:<br />
Static load safety factor<br />
The static load safety factor for machine<br />
tools should not be lower than 4.<br />
Friction<br />
The bearing friction torque M RL is primarily<br />
dependent on the bearing preload. The<br />
influence of the operating load F aB is<br />
insignificant as long as it does not exceed<br />
the limits at which the bearings have zero<br />
clearance. The bearing friction torque M RL<br />
gspecified in the Dimension Tables applies<br />
to the preload generated by means of the<br />
slotted nut tightening torque R aL . The<br />
bearing preload is selected so as to allow<br />
it to remain effective even at high operating<br />
loads and ensure that the bearing has<br />
zero clearance.<br />
RE 83 301/12.99 101<br />
Fam 3 3<br />
F1 n1 nm q1 100<br />
3<br />
F2 n2 nm<br />
q2 100<br />
3<br />
Fn nn nm<br />
qn 100<br />
21<br />
n m<br />
q1 100<br />
q<br />
+ 2 n1 100<br />
n2 qn nn<br />
100 22<br />
L<br />
16666<br />
Lh<br />
n<br />
N RL<br />
C F<br />
3<br />
S 0 = C 0<br />
F 0<br />
M RL n<br />
9.55<br />
23<br />
25<br />
C<br />
F<br />
26<br />
3<br />
24<br />
F am = resulting average<br />
axial load (N)<br />
q = time fraction (%)<br />
n m = average speed (min -1 )<br />
L = nominal life (10 6 revolutions)<br />
in millions of revolutions<br />
L h = nominal life<br />
in operating hours (h)<br />
C = dynamic bearing load rating (N)<br />
n = average speed (min -1 )<br />
F = equivalent bearing load (N)<br />
S 0 = static load safety factor (-)<br />
C 0 = static load rating (N)<br />
F 0 = maximum static<br />
load (N)<br />
The bearing friction torque M RL is measured<br />
at a speed of n = 5 min -1 .<br />
The friction power loss N RL of the bearing<br />
can be calculated using formula 26 .<br />
The various operating speeds n i must be<br />
incorporated in the heat balance as a<br />
function of their time fractions q i .<br />
N RL = friction power loss (W)<br />
n = speed (min -1 )<br />
M RL = bearing friction torque (Nm)
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