Timken Super Precision Bearings for Machine Tool Applications

A
ENGINEERING
During the starting period, care must be taken because the radial
thermal expansion is not immediately compensated by the axial
expansion of the spindle. That occurs later. During this “transient
period,” a decrease of the axial end play or an increase of preload
is generally recorded (Figure 95). The loss of end play can be
calculated by using the same formula, but ignoring the parameter
“L.” For this reason, it is generally recommended to initially set the
bearings with a light, cold end play to avoid any bearing burn-up, due
to excessive preload during the transient temperature rise. During
the testing phase, it will be possible to modify this initial end play
to obtain the optimum setting for the application.
Figure 95 shows also that a three-support layout is more sensitive
to thermal effects, leading to a higher temperature rise and loss of
end play, than a simple arrangement because of the short bearing
geometric spread at the fixed position.
Bearing geometric spread
a
Bearing geometric spread
b
a
Axial endplay
b
b
Fig. 95. Evolution of the spindle system
setting and temperature during the
transient period:
a) Simple mounting
b) Three-support mounting.
Temperature
0
Time
b
a
0
Time
102 TIMKEN MACHINE TOOL CATALOG