Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
2000-06-27
2002-09-03
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
Reexamination Certificate
active
06443625
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a roller bearing used in places where abrupt acceleration/deceleration or load fluctuations are repeated such as in mill speed reducer used for various types of iron making rolling mills or a roller bearing for use in apparatus causing large vibrations such as axles of railway vehicles or vibrating screens, that is, it relates to a roller bearing for use in places where change of rotational speed of rollers occurs repeatedly or bearing radial vibrations are exerted repeatedly and, more in particular, it relates to a cage assembled in such a roller bearing.
BACKGROUND ART
Roller bearings have been used generally for supporting rotational shafts, for example, in various industrial machines such as iron making rolling mills or vehicles. A roller bearing comprises, for example, as shown in
FIG. 1
, an outer ring
1
having an outer ring raceway
1
a
at the inner circumferential surface, an inner ring
2
having an inner ring raceway
2
a
at the outer circumferential surface, a plurality of rollers
3
assembled such that they can roll between the outer ring raceway
1
a
and the inner ring raceway
2
a,
and a cage
4
interposed rotatably between the outer ring raceway
1
a
and the inner ring raceway
2
a
in a state of holding the plurality of the rollers
3
.
The cage
4
comprises, as shown in FIG.
1
and
FIG. 2
, bar portions
7
each disposed between each of adjacent pockets
8
and opposed to the rolling surface of the roller, and a pair of circular portions
5
,
6
connecting both axial sides of the bar portions
7
and axially opposed to the end surface of the roller.
A space surrounded with the pair of the circular portions
5
,
6
and the bar portions
7
,
7
is referred to as a pocket
8
for accommodating the roller
3
, and the roller
3
is held rotatably in the cage
4
by providing a predetermined gap between the cage
4
and the roller
3
.
In the subsequent description, for a cage in which the diameter is different between the pair of the circular portions
5
,
6
as in a tapered roller bearing or a self aligning roller bearing, the circular portion of the cage having a larger diameter (larger diameter side) is referred to as a circular portion
5
, while the circular portion thereof having a smaller diameter (smaller diameter side) is referred to as a second circular portion
6
. Further, when the diameter is equal or nearly equal between the pair of the circular portions
5
and
6
as in a cylindrical roller bearing, the circular portion
5
and the second circular portion
6
are optionally specified.
Further, as shown in
FIG. 14
, roller bearings for use in various types of industrial machines described above include those having a plurality of rollers
3
arranged in two rows between the outer ring raceway
1
a
and the inner ring raceway
2
a
and having two cages
4
individually holding rollers
3
in each of the rows and disposed rotatably between the outer ring raceway
1
a
and the inner ring raceway
2
a.
The cage
4
is a comb-shaped cage, as shown in FIG.
14
and
FIG. 15
, respectively, comprising a circular portion
5
axially opposed to the end surface of the roller, and a plurality of bar portions
7
protruding from one axial side of the circular portion
5
and arranged circumferentially being opposed to the rolling surface of the roller. Also in this cage, a space surrounded by the circular portion
5
and the bar portions
7
,
7
is referred to as a pocket
8
for accommodating the roller
3
, and the roller
3
is held rotatably in the cage
4
by providing a predetermined gap between the cage
4
and the roller
3
.
In the roller bearing having the two rows of rollers
3
as described above, when individual cage
4
is assembled on every row for each of the rollers
3
as shown in
FIG. 14
, a comb-shaped cage, a configuration thereof in which the bar portions
7
protrude only from one axial side of the circular portion
5
as shown in
FIG. 15
is used. On the other hand, in a case where the rollers
3
in two rows are held by one cage, a comb-shaped cage, a configuration thereof in which bar portions
7
protrude respectively from both axial sides of the circular portion
5
as shown in
FIG. 16
is used.
In the subsequent description, a comb-shaped cage of a configuration in which bar portions
7
protrude from one axial side of the circular portion
5
as shown in
FIG. 15
is sometimes also referred to as a two component type cage, whereas a comb-shaped cage of a configuration in which bar portions
7
protrude from both axial sides of the circular portion
5
as shown in
FIG. 16
is sometimes also referred to as a one component type cage.
By the way, when the roller bearing having each of the cages
4
as described above is used in places where abrupt acceleration/deceleration or load fluctuations are repeated such as in mill speed reducer used for various types of iron making rolling mills, since rotational speed of the rollers
3
changes abruptly, the roller
3
collides against the bar portion
7
of the cage
4
again and again. A load W in the circumferential direction by the collision is applied from the roller
3
to the bar portion
7
of the cage
4
as shown in FIG.
3
and
FIG. 17
to deform the cage
4
.
As a result, since the bending stress is loaded on the circular portions
5
,
6
and the bar portion
7
repeatedly, cracks occur in the circular portions
5
,
6
or the bar portions
7
which not only fractures the cage
4
but also sometimes makes the rotation of the bearing impossible during long time use.
Since the cracks occur at a connection section between the circular portions
5
,
6
and the bar portions
7
, it is necessary for preventing fracture of the cage
4
thereby preventing deterioration for the bearing life, to moderate the bending stress caused to the connection section by the load W in the circumferential direction.
Now, in a cage of a type having a pair of circular portions
5
,
6
as shown in FIG.
1
and
FIG. 2
, the load W from the roller
3
exerts moment M
1
, M
2
to each connection section between the circular portion
5
and the second circular portion
6
, and the bar portions
7
respectively. Let the bending stress caused to an area A of the circular portion
5
in the connection section between the circular portion
5
and the bar portion
7
be denoted by &sgr;
1
, the bending stress caused to an area B of the second circular portion
6
in the connection section between the second circular portion
6
and the bar portion
7
be denoted by (&sgr;
2
, a bending stress caused to an area c of the bar portion
7
at the connection section between the circular portion
5
and the bar portion
7
be denoted by &sgr;
3
and the bending stress caused to an area D of the bar portion
7
at the connection section between the second circular portion
6
and the bar portion
7
be denoted by &sgr;
4
, bending stresses &sgr;
1
to a &sgr;
4
are expressed by the following equations based on the conditions for the balance of forces in view of the strength of materials:
&sgr;
1
=M
1
e
1
/(2
I
1
) (1)
&sgr;
2
=M
2
e
2
/(2
I
2
) (2)
&sgr;
3
=M
1
e
3
/I
3
(3)
&sgr;
4
=M
2
e
3
/I
3
(4)
I
1
, I
2
and I
3
denote, respectively, moment of inertia of area for the circular portion
5
, the second circular portion
6
and the bar portions
7
, and moment of inertia of area I
1
, I
2
and I
3
are defined by the following equations:
I
1
=∫
A1
z
1
2
dA
1
(5)
I
2
=∫
A2
z
2
2
dA
2
(6)
I
3
=∫
A3
z
3
2
dA
3
(7)
A
1
, A
2
and A
3
in the equations (5) to (7) described above denote, respectively, the cross sectional areas for the circular portion
5
, the second circular portion
6
and the bar portion
7
.
Further, e
1
to e
3
in the equations (1) to (3) described above denote the maximum distances from the center of the graph to the cross sectional circumferential edge in each of the coordinate system
Crowell & Moring LLP
Footland Lenard A.
NSK Ltd.
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