Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
2001-10-26
2004-06-01
Hannon, Thomas R. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
C384S576000
Reexamination Certificate
active
06742934
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rolling bearing for supporting a spindle shaft of a machine tool that rotates at a high speed, and a spindle apparatus for machine tool using the rolling bearing.
2. Description of the Related Art
The conventional art will be described with a cylindrical roller bearing as an example. A bearing for supporting a spindle shaft of a machine tool requires high rotational accuracy and rigidity in order to keep the machining accuracy high. The cylindrical roller bearing used for this purpose is usually used with an inner clearance of the bearing adjusted to a small clearance of about 5 &mgr;m after the roller bearing was incorporated into the spindle shaft and a housing.
On the other hand, there is a recent tendency to use the spindle apparatus at a high speed in order to improve the machining efficiency, and it is necessary for the bearing to correspond to the speed-up. As a bearing capable of corresponding to this request, a cylindrical roller bearing having an inner ring with ribs and an outer ring without ribs (N type) is used more widely, which can more readily exhaust the supplied lubricating oil to the outside of the bearing than a cylindrical roller bearing having an outer ring with ribs and an inner ring without ribs (NU type). Further, as a retainer guide type (retainer positioning type) that is widely used at the present time, there are an inner ring guide type in which the retainer is made of a copper alloy and guided by the outer surface of the ribs of the inner ring, and a roller guide type in which the retainer is made of synthetic resin and guided by the rollers.
Further, in the conventional rolling bearing, rolling elements such as balls, rollers, or the like are interposed between raceway surfaces formed on the outer surface of the inner ring and the inner surface of the outer ring. In this rolling bearing, in order to retain the rolling elements on the raceway surface at equal intervals in the bearing circumferential direction, an annular retainer is interposed between the outer ring the inner ring.
A bearing for spindle apparatus of the machine tool that is an example of the rolling bearing requires low vibration and low noise in order to improve machining accuracy. Further, the bearing recently requires high-speed rotary performance (that it can be stably used at a high rotational speed for a long time) with grease lubrication that is effective from viewpoints of easiness of handling, environment and cost. In order to satisfy this characteristic, conventionally, there has been used a retainer which is light, superior in softness, and made of synthetic resin to which reinforced fibers are added for improvement of the strength.
FIGS. 34 and 35
shows a conventional roller bearing using a retainer of an outer ring guide type and both-side guide.
FIG. 35
is a sectional view taken along a line of XXXIV—XXXIV in
FIG. 34. A
roller bearing
200
is schematically composed of an outer ring
201
, an inner ring
202
, rolling elements
203
, and a retainer
204
.
As shown in
FIG. 35
, the axial both ends of the inner ring
202
has ribs
202
a
that protrude toward the outer ring side in the radial direction.
The retainer
204
is made of synthetic resin, and has pocket portions
205
for retaining the rolling elements
203
in its circumferential direction at intervals. Further, the retainer
204
has sidewalls
204
b
,
204
b
that are erectly provided on the axial both sides toward the outer ring side in the radial direction. The leading end surface of the sidewall
204
b
, which is opposed to the outer ring
201
, i.e. a guided surface
204
a
in this example, comes into sliding contact with the outer ring
201
or comes into close contact with it. Since the retainer
204
is guided (slide-guided) by the slide-contact of the guided surface
204
a
with the inner surface (guide surface) of the outer ring
201
, the retainer
204
rotates relatively with respect to the outer ring
201
.
Further, the retainer made of synthetic resin described the above is formed by injection-molding, and has been applied to a bearing for machine tool that frequently runs with the very small amount of grease or lubricant oil to be used in order to minimize heat-generation at the operating time. Hereby, in the bearing for machine tool, the essentially minimum amount of lubricant is used, to thereby suppress agitation resistance of softener such as the grease or the lubricant oil, and heat generation due to the agitation resistance. As a method for manufacturing such the synthetic resin-made retainer, there is a radial draw type of an injection-molding method.
FIG. 36
shows a partially sectional view of a forming mold
210
used in the radial draw type of injection molding method. A part of the forming mold
210
is schematically composed of a movable mold
211
, a first slide core
212
, and a second slide core
213
.
The movable mold
211
has an outer surface with a cylindrical shape that forms an inner surface of the retainer. At the outer periphery of the movable mold
211
, plural slide cores (not shown) are arranged, which form an outer surface of the retainer and pocket portions for retaining rolling elements at the mold tightening time. The first slide core
212
and the second slide core
213
of the plural slide cores are formed in a convex shape in section, and they are composed of circular-arc shaped base portions
212
a
,
213
a
located along with the outer surface of the movable mold
211
and columnar protrusions
212
b
,
213
b
that are erectly provided substantially perpendicularly toward the surfaces on the movable mold
211
side of the base portions and form the pocket portions of the retainer.
When the forming mold
210
is tightened, the protrusions
212
b
,
213
b
of the slide cores
212
,
213
come into contact with the predetermined positions on the outer surface of the movable mold
211
, and the adjacent side surfaces
212
c
,
213
c
of the base portions
212
a
,
213
a
of the slide cores comes into contact with each other, whereby a cavity space of the retainer is formed. Then, by injecting the synthetic resin in the cavity space, an annular retainer
220
made of the synthetic resin is formed, which has the pocket portions arranged in the circumferential direction at intervals.
FIG. 37
shows a side view of the retainer
220
formed by the forming mold
210
. A parting line PL, which has been formed by bringing the side surfaces
212
c
,
213
c
of the slide cores
212
,
213
into contact with each other at the injection-molding time, is formed between the adjacent pocket portions of the plural pocket portions
221
to each other on the outer surface of the retainer
220
.
FIG. 38
is a plan view of the retainer
220
viewed from a direction XXXVII in FIG.
37
.
Moreover, in the rolling bearing in which the guide type of the retainer is an inner ring guide type or an outer ring guide type, a appropriate clearance (guide clearance) is provided between the inner diameter surface of the retainer (or outer diameter surface) that comes into contact with a raceway ring (the inner ring and outer ring) and a contact surface of the raceway ring. The guide clearance is set to be a difference between a diameter of a retainer guide surface of the raceway ring and a diameter of the guided surface of the retainer. Further, in order to guide and retain the rolling element, a clearance (pocket clearance) is provided between the rolling element in the pocket of the retainer and the pocket.
Conventionally, in this type of rolling bearing used for high-speed rotation, a guide clearance
5
of the retainer
4
is 0.4 to 1.0%of a guide diameter d
1
(a retainer inner diameter
4
a
), and a pocket clearance
6
is 2 to 4% of the ball diameter, which is 0.5 to 2 times the above guide clearance
5
(FIG.
39
).
In case that the bearing rotates at a high speed at the operating time of the machine tool, grease filled inside the bearing or lubricating oil supplied by oil-air lubrication
Anzai Takaaki
Koiwa Yu
Matsuyama Naoki
Misawa Tamotsu
Sugita Sumio
Hannon Thomas R.
NSK Ltd.
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