Page 17 - May

METALWORKING EQUIPMENT AND TOOLS

And what dynamic characteristics should the "ideal" machine have?
Compliance, How to estimate the amount of bearing wear and the drop in bearing
conventional units stiffness due to this wear?
The answer to such questions can be obtained by modeling the
316/5,14 control box and calculating its dynamic characteristics. To do this, you can
5
use the program SpinDyna [10-13]. The program window with geometric
1 parameters and the SHU model of the TNL-120AL2 machine are shown in
Fig. 5. In the model (Fig. 5), the stiffness data from the bearing catalogs
4 were used to describe the characteristics of the bearings. Radial stiffness
of a roller double-row radial bearing: back support - 153 daN / μm, front
380/3,44
support - 173 daN / μm. For ball thrust radial bearings: radial stiffness -
3 92 daN / μm and angular stiffness 4.3E + 05 daN ∙ m / μm.
2 Calculation using the SpinDyna program with catalog data on the
stiffness of the bearings gave the frequency response of the SHU as

2 shown in Fig. 6 (curve 1). Let us consider such a machine "ideal". If,
in a double-row radial roller bearing, the stiffness is reduced to 29.5
daN / μm, that is, almost 6 times, and the stiffness of the thrust radial
bearing is not changed, then the frequency response takes a different
1
form (curve 2), which corresponds to
the experimental frequency response
of the "new" machine tool. It is unlikely
0 100 480 880 1270 1660 that in one year of operation, a radial
Frequency Hz
double-row roller bearing could wear out
Fig. 4. AFC of SHU machines TNL-120AL2 by displacement: 1 - "old" so that the stiffness dropped 6 times.
machine; 2 - "new" machine. Obviously, when assembling the ShU,
the required preload in this bearing was
not provided. No claims can be made to the supplier of this machine because the warranty
period has expired. Therefore, the management of the enterprise made a decision to repair the
machine on its own.
If the stiffness of the double-row radial roller bearing of the front support is taken as
17.3 daN / μm, that is, 10 times less than the catalog value, and the ball thrust radial bearing
is 65 daN / μm, that is, 1.4 times less than the catalog value, then we get the AFC of the SHU
(curve 3 in Fig. 4), which are close in natural frequency to the experimental AFC of the "old"
machine. In this case, with a high degree of probability, it can be assumed that the decrease in
the rigidity of the front support bearings occurred as a result of their wear. Additional studies
have shown the presence of an axial play of the spindle of the "old" machine of the order of
0.03 mm. As a measure to increase the rigidity of the front spindle bearing, it is possible to
recommend regrinding the ring with labyrinth seals in front of the radial roller bearing (Fig.
3) by an amount of the order of 0.1-0.12 mm, regrinding the lantern ring in the thrust radial
bearing by 0.03 mm.

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