U.S. patent application number 11/295539 was filed with the patent office on 2006-04-27 for angular ball bearing and rolling bearing.
Invention is credited to Keiichi Ueda.
Application Number | 20060088235 11/295539 |
Document ID | / |
Family ID | 27347426 |
Filed Date | 2006-04-27 |
United States Patent
Application |
20060088235 |
Kind Code |
A1 |
Ueda; Keiichi |
April 27, 2006 |
Angular ball bearing and rolling bearing
Abstract
A rolling bearing is proposed in which even though a sealed
type, no lowering of strength of the bearing rings or lowering of
the front width will not occur for the convenience of mounting of a
seal, and design of dimensions equivalent to a non-sealed type
bearing and practicability can be achieved, and has fretting
resistance. Rolling elements 3 are disposed between an inner ring 1
and an outer ring 2 with seals 9 and 10 provided. The seal 9
arranged on a counterbore 8 of the outer ring 2 is fitted in a
pressed state on a peripheral surface portion of a cylindrical
surface 11 forming the counterbore 8. By pressing, the seal 9 is
mounted without forming a slot. The other seal 10 is fitted in a
slot 12. The inner ring and the outer ring, or rolling elements of
a bearing comprising the outer ring, inner ring, rolling elements
and a retainer are subjected to carbonitriding and a grease using a
urea compound as a thickening agent is sealed in the bearing.
Inventors: |
Ueda; Keiichi; (Mie,
JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
27347426 |
Appl. No.: |
11/295539 |
Filed: |
December 7, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10488236 |
Mar 2, 2004 |
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PCT/JP02/08899 |
Sep 2, 2002 |
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11295539 |
Dec 7, 2005 |
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Current U.S.
Class: |
384/462 |
Current CPC
Class: |
C10M 119/24 20130101;
C10M 115/08 20130101; C10M 2217/0456 20130101; F16C 33/62 20130101;
F16C 33/6633 20130101; F16C 33/64 20130101; F16C 19/163 20130101;
C10M 2215/1026 20130101; F16C 33/7853 20130101 |
Class at
Publication: |
384/462 |
International
Class: |
F16C 19/00 20060101
F16C019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 3, 2001 |
JP |
2001-265674 |
Nov 28, 2001 |
JP |
2001-361975 |
Dec 26, 2001 |
JP |
2001-394898 |
Claims
1-6. (canceled)
7. A rolling bearing comprising an outer ring, an inner ring,
rolling elements and a retainer, wherein said inner ring and said
outer ring, or said rolling elements are subjected to
carbonitriding and a grease using a urea compound as a thickening
agent is sealed in said bearing.
8. A rolling bearing as claimed in claim 7 wherein said bearing is
an angular ball bearing.
9. A rolling bearing as claimed in claim 7 wherein said bearing is
a sealed type bearing.
10. A rolling bearing as claimed in claim 7 which is used for a
support portion for a ball screw.
11. A rolling bearing as claimed in claim 10 wherein said support
portion for a ball screw is used for a machine tool.
12. A rolling bearing as claimed in claim 8 wherein said bearing is
a sealed type bearing.
13. A rolling bearing as claimed in claim 8 which is used for a
support portion for a ball screw.
14. A rolling bearing as claimed in claim 9 which is used for a
support portion for a ball screw.
Description
TECHNICAL FIELD TO WHICH THE INVENTION BELONGS
[0001] This invention relates to angular ball bearings and rolling
bearings with a seal used in general purpose industrial machinery
at a support portion for a spindle of a machine tool or a ball
screw support portion.
PRIOR ART
[0002] As shown in FIG. 8, an angular ball bearing has a large
outer diameter D3 of the inner ring 51 on its loaded (front) side,
and a small inner diameter D4 of the outer ring 52 on its loaded
(back) side so that a high axial load can be borne. The inner
diameter D2 of the inner ring 51 on its non-loaded side, and the
inner diameter D5 of the outer ring 52 on its non-loaded side are
provided with tapered portions called "counterbores" formed by
cutting off one of the shoulders of each raceway groove for
assemblability. As a result, the outer diameters D2 and D3 of the
inner ring, and the inner diameters D4 and D5 of the outer ring are
markedly different from each other.
[0003] For such an angular ball bearing, too, according to the
intended use or form of use, as with a deep groove ball bearing, it
is sometimes desired to be of a sealed type. Sealing means is
provided to prevent lubricant retained in the bearing from leaking
outside, and to prevent entry of dust and water into the bearing
from outside. In order to make an angular ball bearing into a
sealed type, as with an ordinary sealed ball bearing, as shown in
FIG. 9, seals 55, 56 are fixed to the outer ring 52 in slots 57,
58. The seals 55, 56 may be of a contact type in which lips at
their tips contact the inner ring 51 and noncontact type which do
not contact.
[0004] Among machine tools, as shown in FIG. 12, there is one in
which a ball screw 72 is rotated by a motor 71 to reciprocate a
table 73 by the rotation of the ball screw 72. Such a machine tool
is used to machine a workpiece 74 on the table 73 with a blade 75
while reciprocating the table 73.
[0005] In this arrangement, the ball screw 72 is usually supported
by a bearing 76. As the bearing 76, an angular ball bearing is
usually used. Lubrication is by grease or oil.
[0006] But in a bearing for supporting a ball screw for a machine
tool, vibrating loads are often applied due to increase in
vibrating components of machining loads produced during machining.
With increase in such vibrating loads, fretting wear damage may
develop on the rolling surfaces of such a support bearing. Such
fretting wear damage develops due to minute sliding, minute
rolling, minute vibration, etc and has a large influence on
deterioration of the bearing performance such as poor rotation
accuracy (tone).
[0007] In contrast, there is disclosed in JP patent publication
7-92104 a method in which the rolling surfaces are subjected to
carbonitriding to increase the hardness of the rolling surfaces and
improve the wear resistance.
PROBLEMS THE INVENTION INTENDS TO SOLVE
[0008] In the conventional angular ball bearing shown in FIG. 9,
since the portion 52a of the outer ring 52 where the counterbore is
formed is thin in the diametrical thickness, if the slot 57 for
fixing the seal 55 is formed, the wall thickness of the outer ring
52 becomes too thin at its portion where the slot 57 is formed.
This lowers the strength of the outer ring 52. Also, if the slot 57
is formed, since the inner peripheral portion 60 from the slot 57
to the outer ring width surface has a reduced diameter to introduce
the seal 55, the front surface width W of the outer ring 52 becomes
narrow. The width surface 61 of the outer ring 52 is a portion
which serves for axial positioning of the bearing and is also a
portion for bearing the pre-load. If a plurality of such bearings
70 are arranged as shown in FIG. 10, large loads are applied to the
width surface 61 of the outer ring 52. Such an arrangement is
usually employed for bearings for the support portion of e.g. a
ball screw. For these reasons, insufficient front surface width W
of the outer ring 58 will cause such trouble as the deformation of
the outer ring 52 and poor positioning of the bearing due to
decreased strength, and insufficient pre-load. While the front
surface width W is influenced by dimensions of various parts of the
bearing, if the slot 57 is formed at the portion of the counterbore
59, it is difficult to ensure the front surface width W.
[0009] For example, an angular ball bearing is designed so that
(ball diameter)/(outer ring outer diameter-ball pitch circle
diameter)=R will be in the range of 0.4-0.7. If the rate R is less
than 0.4, the load bearing capability would be low compared with
the size of the bearing. This is not economical. Conversely, if R
is 0.7 or over, the balls 53 occupy the bearing cavity too much to
ensure a sufficient wall thickness for the inner and outer rings
51, 52. For a bearing in which the rate R is near the lower limit
0.4 but 0.44 or over, if the slot 57 is formed as shown in FIG. 9,
it is difficult to ensure a sufficient front surface width W for
the outer ring 58.
[0010] To prevent this, one may think of reducing the ball pitch
circle diameter PCD and the ball diameter d to reduce the outer
ring inner diameter D5 on the front side (FIG. 8), thereby
increasing the wall thickness of the outer ring front side. But
with this arrangement, compared with a non-sealed type bearing
having no seals, the rigidity of the support portion, the load
bearing capacity of the bearing, and the rolling fatigue life would
lower. In particular, in an angular ball bearing used to support a
threaded shaft of a ball screw in a machine tool, such lowering of
the load bearing capacity and rolling fatigue life is problematic.
That is to say, reduced rigidity of the machine tool feed unit
leads to lowering of the machining accuracy. This is a big
disadvantage. As for the load bearing capacity and the rolling
fatigue life, too, like the rigidity, their lowering is a big
disadvantage.
[0011] On the other hand, due to the influence of internal design,
it is sometimes difficult to ensure space for the seal 55 and its
mounting portion with the same main dimensions as with a non-sealed
type bearing. In such a case, one may think of extending the width
B of the bearing. But since the main dimensions are changed,
compatibility with a non-sealed type bearing is lost. This is not
economical.
[0012] A first object of this invention is to provide an angular
ball bearing which even though it is a sealed type, does not suffer
from reduction in the strength of the bearing rings and lowering of
the front surface width for convenience of mounting of the seals,
and allows to achieve design of dimensions equivalent to those of a
non-sealed type bearing and practicality.
[0013] In recent years, for machine tools such as machines for
making molds, machining into more complicated shapes is required.
For working into such complicated shapes, microscopic feed is
needed, and the more complicated the shape is, the greater the
frequency of microscopic feed. Thus, on rolling surfaces of a
rolling bearing at a support portion for a ball screw used in a
machine tool, pivoting motion is frequently used, so that
microscopic rolling frequently occurs. Thus, only applying
carbonitriding is insufficient, and fretting wear damage often
develops.
[0014] Therefore, a second object of this invention is to provide a
rolling bearing having resistance to fretting even if used at a
support portion for a ball screw of a machine tool for machining
into complicated shapes in which the frequency of microscopic feed
has increased.
MEANS TO SOLVE THE PROBLEMS
[0015] In the angular ball bearing of this invention, rolling
elements are disposed between an inner ring and an outer ring, a
seal is provided on at least on one side thereof, the seal on at
least one side is fitted in a pressed state on a peripheral surface
of a counterbore formed by cutting off one of shoulders of a
raceway groove of the inner ring or the outer ring. That is, a seal
is fitted in a pressed state on a flat peripheral surface portion
of the counterbore.
[0016] With this arrangement, the seal provided on the peripheral
surface of the bearing ring formed with a counterbore is fitted in
a pressed state on the peripheral surface without forming a slot.
Thus the seal can be mounted without locally thinning the wall
thickness of the bearing ring at its portion where the counterbore
is formed or reducing the front surface width. Mounting of the seal
by pressing on the flat peripheral surface without forming a slot
is made possible by suitably adjusting the sectional shape of the
seal e.g. by expanding the axial width of the portion of the seal
where it is pressed, e.g. by providing a short cylindrical portion
on one side of the seal remote from the seal lip portion. Since the
seal is fitted not in a groove, it is possible to design a sealed
type angular ball bearing having main dimensions, such as ball
pitch circle diameter, ball diameter, etc. which are equivalent to
those of a non-sealed type bearing. As a result, an angular ball
bearing is provided which is high in reliability with respect to
leak of lubricant to outside, invasion of powder, dust, water, etc.
into the bearing from outside. Also, since it has parts, dimensions
of which are equivalent to those of a non-sealed type bearing, it
can be designed equivalently in rigidity of the support portion,
load bearing capacity and fatigue life. Thus, it has compatibility
with a non-sealed type bearing.
[0017] A cylindrical seal mounting surface may be formed on the
peripheral portion of the counterbore of the inner ring or the
outer ring to fit the seal in a pressed state on the seal mounting
surface.
[0018] If the seal mounting surface is a cylindrical surface,
control of interference for pressing is easy, so that stable
pressing is possible. If the peripheral surface portion is a
tapered surface, even if the cylindrical seal mounting surface is
formed, unlike a slot, influence on the wall thickness of the
bearing ring or front surface width is small. Thus it is possible
to provide a bearing ring having a wall thickness and a front
surface width that are practically equivalent to the arrangement in
which the seal mounting surface is not cylindrical.
[0019] According to this invention, the bearing may have a seal on
the front side, fitted in a pressed state on the peripheral portion
of the counterbore on the front side of the outer ring, and a seal
on the backside fitted in a slot on the inner peripheral surface of
the outer ring on the backside. If a seal is mounted in a slot, the
axial width of the mounting portion may be narrow. Like on the
backside, at a portion where the axial width from the raceway
groove of the outer ring to the width surface is narrow but the
diametrical wall thickness is thick, there will be no shortage of
the mounting surface. Thus a seal can be mounted without causing a
problem of lowered strength due to the formation of a slot. Thus,
by pressing a seal onto the flat peripheral surface portion at a
portion where the outer ring is thin, and by mounting it in a slot
at a portion where it is axially narrow and thick in the diametric
direction, mounting of seals can be done easily and rigidly without
any influence on the bearing rings.
[0020] In this invention, the dimensions of the parts may be in the
following relations. That is, (bearing width)/(inner diameter of
inner ring)=0.2-1.0, and (bearing width)/(ball
diameter)=1.5-2.2.
[0021] Among the major dimensions of an angular ball bearing, such
as the inner ring outer diameter, outer ring outer diameter,
bearing width or height, and chamfer dimension, some are
standardized by the International Standardization Organization
(ISO), but others are not. In either case, (bearing width)/(inner
diameter of inner ring)=S is 0.2-1.0. If S is less than 0.2, it is
impossible to employ a sufficient ball size relative to the bearing
size, so that no sufficient load-bearing capacity can be obtained.
Conversely, if S exceeds 1.0, the space which the bearing occupies
increases, which increases the entire device. This is not
economical. (bearing width)/(ball diameter)=T is 1.5 to 2.2 under
the above standardization. If T is less than 1.5, the rate at which
the balls occupy in the bearing cavity increases. This will make it
difficult to ensure a sufficient wall thickness of the bearing
rings. Conversely, if T exceeds 2.2, the load-bearing capacity is
low compared to the bearing size. This is uneconomical. In a
bearing of which the rates S and T are in the above preferable
ranges, it is possible to employ a structure in which a seal is
mounted by pressing on the flat peripheral surface portion which is
the counterbore in this invention. Thus the abovesaid functions and
effects due to this mounting structure are revealed. (ball
diameter)/(outer diameter of outer ring-ball pitch circle diameter)
may be 0.44 or over.
[0022] The angular ball bearing used for a ball screw in a machine
tool is, as described in the section about problems the invention
intends to solve, designed with the value (ball diameter)/(outer
diameter of outer ring-ball pitch circle diameter)=R in the range
of 0.4 to 0.7. Even if the rate R of the balls is close to the
lower limit 0.4, for a bearing in which this value is 0.44 or over,
if a slot is formed as in the prior art, it is difficult to ensure
a sufficient front surface width on the outer ring.
[0023] Thus, in conventional bearings, in order to make it possible
to mount a seal, the ball occupying rate R had to be reduced to the
limit, thereby restricting the load bearing capacity. Since this
invention employs a structure in which the seal is pressed on the
flat peripheral surface portion, while it has seals, it can be
designed with a large ball occupying rate R to 0.44 or over, and
thus a large load bearing capacity is assured.
[0024] The angular ball bearing of this invention may be used for
supporting the threaded shaft of a ball screw.
[0025] Since high axial loads are applied to an angular ball
bearing used for supporting the threaded shaft of a ball screw, a
bearing having a large contact angle e.g. 30.degree. or over, i.e.
a bearing that is high in the axial load bearing capacity is
required. If the contact angle increases, the counterbore deepens
correspondingly, so that the front surface width of the bearing
ring decreases. Even in a bearing having such a large contact
angle, by employing the seal mounting structure according to this
invention by pressing on the peripheral surface portion, there are
no lowering of strength and lowering of the front surface width, it
can be mounted in this way.
[0026] Also, the second object of this invention is solved by using
a rolling bearing which comprises an outer ring, an inner ring,
rolling elements and retainer, and in which the inner ring and the
outer ring, or the rolling elements are subjected to
carbonitriding, and a grease using a urea compound as a thickening
agent is sealed in the bearing.
[0027] The inner ring and outer ring, or the rolling elements are
subjected to carbonitriding, and a grease using a urea compound as
a thickening agent is sealed in the bearing. As a result, a thin
oxide film of a urea compound is formed, and an oil film having a
sufficient thickness is formed on the oxide film. Since this thin
oxide film of a urea compound is high in adhesion to the
carbonitrided layer, even if micro rolling occurs frequently,
grease is retained on the rolling surfaces, so that it is possible
to effectively prevent lowering of durability by suppressing
fretting damage on the raceway surfaces. Also, even if oil film of
the grease between the rolling elements and the raceway surfaces
breaks, so that the rolling elements and raceway surfaces contact
directly, due to the function of the carbonitrided layer provided
on the rolling elements or raceway surfaces, development and
progression of fretting damage is suppressed for a while. Also,
since oil film of the grease is high in adhesion to the
carbonitrided layer, even if breakage occurs, it is repaired
quickly. Thus, even if the oil film breaks and the rolling elements
and raceway surfaces directly contact, it is possible to repair the
oil film before fretting damage develops. Thus, resistance to
fretting damage markedly improves.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a partially sectional view of the angular ball
bearing of one embodiment of this invention,
[0029] FIG. 2 is a partially sectional view of the same embodiment
in comparison with a conventional bearing of the same size,
[0030] FIGS. 3(A) and 3(B) are sectional views showing arrangements
of the angular ball bearings of the same embodiment,
[0031] FIGS. 4(A) and 4(B) are sectional views showing other
arrangements of the angular ball bearing of the same
embodiment,
[0032] FIG. 5 is a sectional view showing a feed mechanism of a
machine tool using the angular ball bearing,
[0033] FIG. 6 is a partially sectional view showing the angular
ball bearing of another embodiment of this invention,
[0034] FIG. 7 is a partially sectional view showing the angular
ball bearing of still another embodiment,
[0035] FIG. 8 is a sectional view of a conventional nonsealed type
angular ball bearing,
[0036] FIG. 9 is a sectional view of a conventional sealed type
angular ball bearing,
[0037] FIG. 10 is a sectional view of an example of parallel
arrangement of conventional angular ball bearings,
[0038] FIG. 11 is a sectional view showing an example of the
angular ball bearing according to this invention,
[0039] FIG. 12 is a schematic view showing an example of a
machining device using a bearing for supporting a ball screw,
[0040] FIG. 13 is a schematic view showing a bearing used in
Example 1 and Comparative Examples 1-3,
[0041] FIG. 14 is an assembly view for conducting Fafnir fretting
corrosion test,
[0042] FIG. 15 is a graph showing the results of a microscopic
pivoting wear test,
[0043] FIGS. 16 and 17 are graphs showing the results of a
microscopic slide wear test, and
[0044] FIGS. 18 and 19 are graphs showing the results of an
accumulated breakage probability experiment.
EMBODIMENTS OF THE INVENTION
[0045] The first embodiment of this invention will be described
with reference to the drawings. In this angular ball bearing, a
plurality of rolling elements 3 are disposed between raceway
grooves 5 and 6 of an inner ring 1 and an outer ring 2 as bearing
rings. These rolling elements 3 are retained in pockets 4a of a
retainer 4. Compared with deep groove ball bearings, the inner ring
1 has a larger outer diameter on the loaded side (front side F),
while the outer ring 2 has a smaller inner diameter on the loaded
side (backside B) to create a contact angle .theta. between the
raceway grooves 5 and 6. For the sake of assembling the bearing, a
counterbore 7 where one of the shoulders of the raceway groove 5 is
cut off is formed on the non-loaded side of the inner ring 1. A
counterbore 8 where one of the shoulders of the raceway groove 6 is
cut off is formed on the non-loaded side of the outer ring 2,
too.
[0046] In the bearing cavity between the inner and outer rings 1
and 2, seals 9 and 10 are arranged. The seal 9 on the front side F
is pressed into the inner peripheral surface 11 of the outer ring 2
which forms the counterbore 8. The seal 10 on the backside B is
fitted in a slot 12 formed in the inner-diameter surface of the
outer ring 2. These seals 9 and 10 may be contact seals or
non-contact seals, but are contact seals in this embodiment.
[0047] The inner peripheral surface 11 forming the counterbore 8 of
the outer ring 2 is a conical surface, and a portion outside of the
bearing is a cylindrical seal mounting surface 11a. The seal 9 on
the front side has a short cylindrical fitting portion 9a at its
proximal end, i.e. opposite a seal lip portion. The fitting portion
9a is pressed into the seal mounting surface 11a. Since the seal 9
on the front side is pressed with interference, it will not fall
after press-fitting. The fitting force between the seal 9 and the
outer ring 2 is freely selectable by adjusting the interference.
The short cylindrical fitting portion 9a is cylindrical with its
outer-diameter surface parallel to the axial direction. The seal 9
has a core metal 14 to which is fixed an elastic member 15. The
seal lip portion 9b formed by an elastic member 15 is in contact
with the outer peripheral surface of the inner ring 1. The core
metal 14 has an L-shaped section with one edge forming the fitting
portion 9a. Part of the elastic member 15 covers the outer
periphery of the short cylindrical portion at the proximal end of
the core metal 14 in contact with the seal mounting surface 11a.
But the core metal 14 may be directly fitted on the seal mounting
surface 11a. Also, the outer-diameter surface of the fitting
portion 9a may not be a cylindrical surface but be tapered. Even if
it is tapered, the seal 9 can be fixed. If it is tapered, the seal
mounting surface 11a of the outer ring 2, too, is a tapered
surface. For example, it is a surface contiguous with the other
portion of the inner peripheral surface 11.
[0048] The seal mounting surface 11a may be finished by lath
turning or grinding. At the edge of the seal mounting surface 11a
opposite the press-fitting side, a recess 13 is formed to allow a
lathing tool and a grinder to be removed. While the recess 13 is a
kind of groove, since it is not used to fix the seal 9 on the front
side, it is shallow in groove depth and will not result in
insufficient wall thickness of the outer ring 2. The shape of the
seal lip portion 9b can be arbitrarily determined, and either of
the contact type and noncontact type may be used.
[0049] The seal 10 on the backside has an elastic member integrally
fixed to a core metal and fitted in the slot 12 of the outer ring
2. The portion 16 of the outer ring 2 from the slot 12 to its inner
edge has an increased inner diameter to introduce the seal 10 on
the backside. The shape of the seal lip portion 10b of the seal 10
on the backside may also be either the contact type or noncontact
type.
[0050] The peripheral surfaces of the inner ring 1 and outer ring 2
opposing the seal lip portions 9b and 10b of the seals 9 and 10 are
flat in this embodiment. But they may be formed with oil grooves in
which the seal lip portions 9b and 10b of the seals 9 and 10 may
contact or be loosely fitted. The lubrication of the bearing may be
by grease or oil.
[0051] With this arrangement, since the seals 9 and 10 are provided
on the front side and backside, respectively, it can be a sealed
type. Thus it can be an angular ball bearing which is high in the
reliability and prevents leak of the lubricant and entering of the
dust and water into the bearing from outside. Since the seal 9 on
the front side provided at the peripheral surface portion 11 formed
with the counterbore 8 of the outer ring 2 is fitted in the inner
peripheral portion 11 by pressing. Thus it can be fitted without
the need of forming a slot. The shape of the seal 9 on the front
side can be of any shape so long as the fixed portion can be
mounted on the flat seal mounting surface 11a. The shape of the
seal lip portion 9b can be arbitrarily determined, and may be
either contact type or noncontact type. Since the shape of the seal
lip portion 9b of the seal 9 on the front side is no different from
that of a conventional groove-fitted type seal, the function of
preventing leak of lubricant and the function of preventing dust,
debris or water from entering into the bearing from outside will
not lower. Although the seal 10 on the backside is fitted in the
slot 12, since the outer ring 2 is thick in the wall thickness on
the backside, there will be no problem of lowering the strength due
to the provision of slot 12. Since the backside is narrow in the
axial width from the raceway groove 6 of the outer ring 2 to the
end face, by providing the slot 12, it can be easily mounted in a
narrow space.
[0052] Since the seal 9 on the front side can be fixed at the
portion of the outer ring 2 where the counterbore 8 is formed,
without forming a groove, it is possible to prevent local reduction
in the wall thickness at the abovesaid portion of the outer ring 2.
It is also possible to ensure the front surface width W. Also, both
the seals 9 and 10 on the front side and backside can be fixed in
the bearing internal space in the case of a non-sealed type
bearing. Thus, there will be no change in width even if it is of
the sealed type.
[0053] Thus, with the angular ball bearing of this embodiment, it
is possible to design a sealed type bearing having the same main
dimensions, ball pitch circle diameter PCD, and ball diameter d as
a non-sealed type bearing. Thus, the reliability improves in
preventing leak of the lubricant to outside and preventing dust,
debris and water from entering the bearing. Also, it is possible to
achieve the rigidity of support portions, load bearing capacity and
rolling fatigue life, that are equivalent to those of a non-sealed
type bearing. Thus, the angular ball bearing of this embodiment is
compatible with a non-sealed type bearing.
[0054] FIG. 2A is a view showing an angular ball bearing in which
the bearing of this embodiment is applied to an angular ball
bearing for supporting a ball screw, and FIG. 2B shows a
conventional angular ball bearing in which seals are fixed in
slots, by arranging them side by side with the same dimensions for
comparison sake. As for the bearing size, the inner ring inner
diameter is 75 mm, the bearing width is 20 mm, and the contact
angle is 60.degree. for both. R=((ball diameter)/(outer diameter of
outer ring-ball pitch circle diameter)=0.549
[0055] If a sealed type angular ball bearing (FIG. 2(B)) is
designed with a conventional arrangement in which a slot 57 is
formed, as described in the section describing problems the
invention intends to solve, the front surface width W of the outer
ring 52 on the front side, and the wall thickness of the outer ring
52 at the portion of the counterbore would be too small at the
portion of the slot 51, trouble such as deformation of the outer
ring 52 and poor bearing positioning, and insufficient pre-load
will be caused.
[0056] On the other hand, in the embodiment of this invention (FIG.
2(A)), the seals 9 and 10 are both fixed to the outer ring 2 with
the seal 10 on the backside fixed in the slot 12 similar to a
conventional one and the seal 9 on the front side fixed by pressing
to form a sealed type bearing.
[0057] In this case, there is no reduction in the front surface
width W of the outer ring on the front side and the wall thickness
of the outer ring at the counterbore portion 8 as in the
conventional arrangement. Thus it will be a practicable design.
[0058] In this embodiment (FIG. 1, FIG. 2(A)), axial positioning of
the seal 9 on the front side is controlled by the difference
between the width surface 17 of the outer ring on the front side
and the width surface of the seal 9. But positioning may be done by
pushing the seal 9 into the boundary between the recess 3 and the
counterbore portion 11.
[0059] Angular ball bearings for supporting a ball screw often form
a support portion by combining a plurality of rows, for example, by
using in two or three rows as shown in FIGS. 3(A), 3(B), or in four
rows as shown in FIGS. 4(A) or 4(B). In the example of FIG. 3(A),
two rows of angular ball bearings 20 are arranged with their fronts
facing each other to bear axial loads in one row. In the example of
FIG. 3(B), two (two right rows in the figure) of the three rows
have their fronts facing each other, and the remaining row arranged
facing the same direction as the adjacent one to bear axial loads
in two rows. In the example of FIG. 4(A), the central two rows have
their front facing each other with the rows on both sides thereof
in the same direction as the adjacent one (so-called DFTT
combination) to bear axial loads in three rows. In the example of
FIG. 4(B), two at one end (right in the figure) of the four rows
have their fronts facing each other and the remaining two rows in
the same direction as the adjacent one (DTFT combination) to bear
axial loads in three rows.
[0060] When angular ball bearings 20 are arranged in a plurality of
rows in this manner, large loads are applied to the width surface W
of the outer ring 2 on the front side (ditto for the width surface
of the inner ring 1 on the backside). But with the angular ball
bearings 20 of this embodiment, since the front width W of the
outer ring 2 is sufficiently ensured, they can be used even for
applications in which they are combined in a plurality of rows as
described above. Besides, since they have main dimensions, rigidity
of support portions, load bearing capacity and rolling fatigue life
which are equivalent to those of a non-sealed type bearing,
replacement of a non-sealed type bearing with the sealed type
bearing of this embodiment will result in no functional
trouble.
[0061] FIG. 5 shows a feed mechanism of a machine tool using this
angular ball bearing. A table 31 is reciprocably mounted on a base
32 through a guide (not shown), and is reciprocated by driving a
motor 33 through a ball screw 34. The ball screw 34 has a nut 35
mounted to the table 31 and a threaded shaft 36 rotatably supported
on the base 32 at support portions 37 and 38 at both ends thereof.
The threaded shaft 36 is coupled to the motor shaft 33a of the
driving motor 33 through a coupling 39. The support portions 37, 38
support the threaded shaft 36 through rolling bearings 20, 41
provided in housings 37a and 38a. For the rolling bearing 40 of the
support portion 37 on the side of the driving motor 33, the angular
ball bearings 30 of the above embodiment are used. For the support
portion 37, angular ball bearings 20 are arranged in a plurality of
rows as shown in FIGS. 3(A), (B), FIGS. 4(A), (B).
[0062] Next, the dimensional relation of parts of the angular ball
bearing 20 of the first embodiment shown in FIG. 1 will be
described. This dimensional relation is an example when e.g. it is
applied to a bearing for supporting a ball screw used in a feed
line of a machine tool.
[0063] In this angular ball bearing, S=(bearing width)/(inner
diameter of inner ring)=0.2 to 1.0 T=(bearing width)/(ball
diameter)=1.5 to 2.2 Also, R=(ball diameter)/(outer diameter of
outer ring-ball pitch circle diameter).gtoreq.0.44 Also,
R.ltoreq.0.7
[0064] The contact angle .theta. is 30.degree. or over.
[0065] The main dimensions of rolling bearings refer to dimensions
that show the contour of bearings. For international compatibility
and economical production, they are standardized by International
Standards Organization (ISO). In Japan, they are stipulated under
JIS B 1512. The main dimensions are the inner diameter, outer
diameter, width or height of a bearing and chamfering dimensions.
These dimensions are important when the bearing is mounted on a
shaft and a housing. In principle, dimensions concerning the
internal structure are not stipulated. While many dimensions of
rolling bearings are stipulated, they are for preparation of the
future standardization, and those actually used now are not all of
these dimension groups.
[0066] As described above, while there are standardized ones and
non-standardized ones among the main dimensions for rolling
bearings, in either case, (bearing width)/(inner ring inner
diameter)=S is 0.2 to 1.0. If S is less than 0.2, it is impossible
to employ a sufficient ball size relative to the bearing size. Thus
a sufficient load bearing capacity is not obtainable. Conversely,
if S exceeds 1.0, the bearing occupying space increases, so that
the entire device becomes bulky. This is uneconomical.
[0067] Also, (bearing width)/(ball diameter)=T is preferably 1.5 to
2.2 for the above standardization and the like. If T is less than
1.5, the rate at which the balls occupy in the bearing cavity
increases, so that it becomes difficult to ensure a sufficient wall
thickness of the raceway ring. Conversely, if T exceeds 2.2, the
load bearing capacity will be low compared with the bearing size.
This is uneconomical. With a bearing of which the rates S and T are
in preferable ranges, a structure can be employed in which the seal
9 is mounted by pressing into the flat peripheral surface portion
which forms the counterbore 8 in this embodiment. In such a case,
the above functions and effects are revealed.
[0068] For an angular ball bearing used e.g. for a ball screw of of
a machine tool, the value of (ball diameter)/(outer ring outer
diameter-ball pitch circle diameter)=R is, as described in the
section of problems the invention intends to solve, usually set in
a range of 0.4 to 0.7. If the rate R is 0.4 or less, the load
bearing capacity would be low for the bearing size. This is
uneconomical. Conversely, if R is 0.7 or over, the rate at which
the balls occupy in the bearing cavity would increase. This makes
it difficult to ensure sufficient wall thicknesses of the inner and
outer rings. In a bearing in which even though the ball occupying
rate R is close to the lower limit 0.4, if it is 0.44 or over, a
slot 57 is formed as in the conventional example of FIG. 9, it
becomes difficult to ensure a sufficient front surface width W of
the outer ring 58.
[0069] Thus, in a conventional bearing, in order to make it
possible to mount seals, it was necessary to decrease the ball
occupying rate R as much as possible, thereby restricting the load
bearing capacity. In this invention, since a seal is pressed into
the flat peripheral surface portion, it is possible to increase the
ball occupying rate R to 0.44 or over. Thus, design which permits a
larger load bearing capacity is possible.
[0070] As for the contact angle .theta., to a bearing for
supporting a ball screw of a machine tool, since high axial loads
are applied, the bearing should have a contact angle .theta. of
30.degree. or over. Namely, the angular ball bearing 30 has a high
axial load bearing capacity.
[0071] In the above embodiment, the seal 10 on the backside is
fitted on the outer ring 2 using the slot 12. But as shown in FIG.
6, like the seal 9 on the front side, the seal 10A on the backside,
too, may be pressed into the inner peripheral surface of the outer
ring 2. In this case, the seal 10A on the backside is, like the
seal 9 on the front side, formed into a shape having a tubular
fitting portion 10Aa at the proximal end. In the embodiment of FIG.
6, the seal 10A on the backside has the same sectional shape except
that it is different in diameter from the seal 9 on the front
side.
[0072] In the above embodiments, the seals 9, 10, 10A are mounted
on the outer ring 2. But this invention is also applicable to the
arrangement in which seals 9B and 10B are fitted on the inner ring
1 as shown in FIG. 7. In this case, the seal 9B is pressed on the
portion of the inner ring 1 where a counterbore 7 is formed.
[0073] In the above embodiments, the seals 9, 10, 10A, 9B, 10B have
an elastic member such as rubber fixed to a core metal. But these
seals may be metallic shield plates or of an oil seal type. In any
of the above embodiments, seals 9, 10, 10A are provided on both
sides. But according to the intended use, this invention is
applicable to an arrangement in which a seal is provided only on
one side if the seal is fitted on the counterbore side.
[0074] Next, the rolling bearing according to this invention is, as
shown in FIG. 11, a bearing comprising an outer ring 83, an inner
ring 81, rolling elements 87 and a retainer 88, and in which
cabonitrided layers 85 are provided by subjecting the inner ring 81
and the outer ring 83 to carbonitriding, and grease 86 using a urea
compound as a thickening agent is sealed in the bearing. Also,
while not shown in FIG. 11, a rolling bearing in which
carbonitrided layers 85 are formed on the rolling elements 87
instead of on the inner ring 81 and the outer ring 83 is included
in the rolling bearing of this invention.
[0075] As material for the outer ring 83, inner ring 81 and rolling
elements 87, SUJ2, SUJ3 or steel containing C: 0.1-1.0 wt %, Mn
0.1-1.0 wt %, Cr 0.1-20 wt %, the balance being Fe and unavoidable
impurities, etc. can be cited.
[0076] The carbonitriding is one of the means for hardening a
metallic surface. The carbonitriding is applied because with
ordinary carburization it is possible to obtain a tough material,
but it is unstable to heat. In contrast, by nitriding, the material
surface is hardened and the residual austenite becomes stable to
heat, so that the material becomes resistant to impact. Further, a
suitable amount of carbide deposits, so that it is possible to
increase the fatigue strength without lowering the resistance to
cracking. Such a carbonitrided layer 85 may be formed on the inner
ring 81 and outer ring 83, or on the rolling elements 87.
[0077] As the carbonitriding method, after carbonitriding in a
high-temperature gas in which ammonium gas is added to a
carburizing atmosphere, the material may be hardened and
tempered.
[0078] The amount of the residual austenite is preferably 20-40%.
If less than 20%, improvement in the rolling fatigue life may not
be sufficient. On the other hand, if over 40%, the hardness of the
carbonitrided layer may decrease, so that the wear resistance
properties lower.
[0079] The grease 86 contains a urea compound as a thickening
agent, and a base oil added thereto. By using a grease of which the
thickening agent is a urea compound, a thin oxide film of urea
compound is formed on the raceways of the inner and outer rings. On
the film, an oil film-having a sufficient thickness is formed.
[0080] In particular, by applying carbonitriding to the inner and
outer raceways, even if oil film of grease between the rolling
elements and the raceways disappears and the rolling elements and
the raceways directly contact, due to the function of the
carbonitrided layer formed on the raceways or rolling elements,
progression of fretting wear damage is suppressed. Also, oil film
of grease is high in adhesion to the carbonitrided layers, even if
breakage of oil film occurs, it is quickly repaired. Thus, due to
the synergistic effects of the grease and the carbonitrided layer,
it is possible to suppress fretting wear and effectively prevent
lowering of the durability.
[0081] The urea compound may be aliphatic, cycloaliphatic or
aromatic, and can be used by mixing them at an arbitrary rate.
Among them, a diurea or polyurea expressed by the following formula
1 is preferable. Among them, diurea is preferable.
(Formula 1)
[0082] (wherein R2 is an aromatic hydrocarbon, aliphatic
hydrocarbon or cycloaliphatic hydrocarbon group having a carbon
number of 6-15, R1 and R3 are aromatic hydrocarbon groups having a
carbon number of 6-12, cyclohexyl groups, cyclohexyl derivatives
having a carbon number of 7-12 or alkyl groups having a carbon
number of 6-20.
[0083] As the base oil, one or more lubricating oils selected from
mineral oil, synthetic hydrocarbon oil and ether oil, or a mixed
oil mixed at an arbitrary rate may be used. Among them, a mineral
oil is preferable. Since a mineral oil has a good compatibility
with the urea thickening agent, good lubricity and suitable
consistency, there will be no leak of grease, and repairability of
the grease film will not be impaired.
[0084] The mixing rate of the thickening agent in the urea grease
is preferably 1-40 wt %, more preferably 5-20 wt %. If less than 1
wt %, gel hardening of the thickening agent would be insufficient,
and the consistency increase, so that grease tends to leak. On the
other hand, if over 40 wt %, the consistency would lower, worsening
the flowability.
[0085] To the urea grease, within such a range that the function of
the urea grease will not be impaired, known rust preventives,
antioxidants, extreme pressure additives, wear suppressants,
oiliness improvers, corrosion inhibitors, pour point depressants,
viscosity index improvers, structure stabilizers, thickeners,
antistatic agents, emulsifiers and colorants may be added.
[0086] The grease 86 is filled into the bearing, specifically
between the inner ring 81 and the outer ring 83 as shown in FIG. 11
so as to cover the rolling elements 87 and the retainer 88. If a
sealed type bearing is used as the rolling bearing, it is sealed by
seals 89 and 90 at the front side and the backside of the bearing.
If the sealed type rolling bearing is used, it is possible to
prevent the grease 86 from leaking out. Instead of the seals,
shield plates may be used.
[0087] The two seals 89 and 90 have different shapes. With this
arrangement, it is easy to confirm the bearing mounting direction.
Thus it is possible to prevent assembling error.
[0088] As the kind of rolling bearing according to this invention,
it is not specifically limited, but is preferably an angular ball
bearing.
[0089] The rolling bearing according to this invention can be used
at a support portion of a ball screw, particularly a support
portion of a ball screw used in a machine tool. Among support
portions of ball screws of the machine tool, if it is used at a
support portion of a ball screw of a machining center for machining
of complicated shapes in which the frequency of microfeed is high,
it can effectively reveal the fretting resistance. This is more
preferable.
EXAMPLES
[0090] Hereinbelow, more detailed description is made with
reference to Examples. First in Examples 1 and 2, as judgment about
resistance to fretting wear damage, tests were conducted for micro
sliding wear and micro pivoting wear.
[Carbonitriding Treatment]
[0091] Using inner ring and outer ring plates made of SUJ2, their
rolling surfaces were subjected to carbonitriding. For
carbonitriding, they were held for 40 minutes at 880.degree. C. in
a continuous furnace in which 10% ammonium gas in volumetric ratio
was added to NX gas. Next, they were subjected to tempering at
180.degree. C. for two hours to obtain carbonitrided plates.
[0092] The surface hardness (HRC) of the plates obtained was 63.2.
The HRC before treatment was 61.9.
Example 1
Micro Pivoting Wear Test
[0093] The outer ring 90a and inner ring 90b that have been
subjected to the abovesaid carbonitriding, and rolling elements 90C
(made of SUJ2) were assembled to manufacture a bearing 91 (inner
ring inner diameter.times.outer ring outer diameter.times.width=20
mm.times.40 mm.times.14 mm). At this time, 1 g of urea grease
described in Table 1 was sealed (grease is not shown in FIG. 13).
Using this bearing 91, Fafnir fretting corrosion test was conducted
under ASTM D 4170. Specifically, as shown in FIG. 14, the outer
ring 90a and the inner ring 90b were fixed to two bearing retaining
portions 96, and a shaft 93 was passed to a bolt 92 in the order
shown. And by adjusting the tightening of the bolt 92, a load was
applied by a spring 94 (load=2.45 kN). With a chuck portion set in
a tester, a pivoting portion 95 and a motor were coupled together
by a crank rod, and the motor was rotated in the atmosphere at room
temperature. With the pivoting angle set to 12 deg (critical
pivoting angle: 30 deg) and the pivoting cycle set to 30 Hz, the
test was conducted for eight hours. In terms of weight reduction of
the inner and outer rings after the test, the wear property of the
plates was evaluated. The results are shown in FIG. 15.
Comparative Example 1
[0094] Except that an inner ring and an outer ring made of SUJ2 and
not subjected to carbonitriding, and a lithium-family grease shown
in Table 1 was used, a microscopic pivoting wear test was conducted
in the same manner as in Example 1. The results are shown in FIG.
15.
Comparative Example 2
[0095] Except that as a grease, a lithium grease shown in Table 1
was used, a microscopic pivoting wear test was conducted in the
same manner as in Example 1. The results are shown in FIG. 15.
Comparative Example 3
[0096] Except that as a grease, a urea grease shown in Table 1 was
used, a microscopic pivoting wear test was conducted in the same
manner as in Example 1. The results are shown in FIG. 15.
(Results)
[0097] From Example 1 and Comparative Examples 1-3, it became
apparent that by subjecting the rolling surfaces to carbonitriding
and using a urea compound as a grease, microscopic pivoting wear,
namely, wear produced due to microscopic rolling markedly
decreases. Thus, it became apparent that it had resistance to
fretting wear resulting from it.
Example 2
Microscopic Slide Wear Test
[0098] With rolling elements (made of SUJ2) placed on a plate
subjected to the carbonitriding, and using the urea grease
described in Table 1 as a grease, micro slide wear tests were
conducted by the following method. As for the test conditions at
this time, the load applied to the rolling elements was 98 N,
amplitude of the rolling elements on the plate was 0.47 mm, the
frequency was 30 Hz, the number of loadings was 8.6.times.10.sup.5
cycles, and the test time was eight hours.
[0099] And at 5 or more points and in a direction perpendicular to
the wear direction, measurement was made on a Talysurf surface
profiler and the deepest value was used as the plate wear depth.
Also, the wear amount (.gamma.) of the rolling elements was
calculated by measuring the wear diameter with a microscope and
using the following formula. The results of plate wear depth are
shown in FIG. 16, and the results of wear amount of the rolling
elements are shown in FIG. 17. .nu.=(.pi.h.sup.2.times.(3r-h))/3
h=r-(4r.sup.2-c.sup.2).sup.1/2/2 wherein .gamma.: radius of the
ball, h: wear depth of the ball, c: diameter of wear marks
Comparative Example 4
[0100] Except that an inner ring and an outer ring made of SUJ2 and
not subjected to carbonitriding, and a lithium grease shown in
Table 1 were used, a microscopic slide wear test was conducted in
the same manner as in Example 2. The results of plate wear depth
are shown in FIG. 16, and the results of wear amount of the rolling
elements are shown in FIG. 17.
Comparative Example 5
[0101] Except that as a grease, a lithium grease shown in Table 1
was used, a microscopic slide wear test was conducted in the same
manner as in Example 2. The results of plate wear depth are shown
in FIG. 16, and the results of wear amount of the rolling elements
are shown in FIG. 17.
Comparative Example 6
[0102] Except that as a grease, a urea grease shown in Table 1 was
used, a microscopic slide wear test was conducted in the same
manner as in Comparative Example 4. The results of plate wear depth
are shown in FIG. 16, and the results of wear amount of the rolling
elements are shown in FIG. 17. TABLE-US-00001 TABLE 1 grease
viscosity of base oil thickening (mm.sup.2/s) brand maker agent
consistency base oil 40.degree. C. 100.degree. C. urea Pyronic
Nisseki urea 289 mineral 108.5 11.9 grease Universal Mitsubishi oil
N6C lithium Alvania SHOWA lithium 277 mineral 131.5 9.9 grease No.
2 Shell oil
(Results)
[0103] From Example 2 and Comparative Examples 4-5, it became
apparent that by subjecting the rolling surfaces to carbonitriding
and using a urea compound as a grease, microscopic slide wear,
namely, wear produced due to microscopic sliding markedly
decreases. From Example 2 and Comparative Example 6, it became
apparent that Example 2 had a sufficient micro slide wear
resistance.
Example 3
[0104] An inner ring 81 and an outer ring 83 made of SUJ2 were
subjected to the carbonitriding and assembled with rolling elements
made of SUJ2 to manufacture the angular ball bearing shown in FIG.
11. And as a grease, urea grease shown in Table 1 was sealed. A
load of 6.9 kN (radial load) was applied to the bearing and it was
rotated at 2000 rpm. The accumulated breakage probability 10% life
at this time was measured. The results are shown in FIG. 18.
[0105] The "Accumulated breakage probability 10% life" refers to
the substantially total number of revolutions or operating hours
during which 90% (reliability 90%) of identical bearings in a group
can be rotated without producing flaking due to rolling fatigue
when they are individually rotated under the same conditions.
Comparative Example 7
[0106] Except that an inner ring 81 and an outer ring 83 made of
SUJ2 were subjected to the through hardening, the accumulated
breakage probability 10% life was measured in the same manner as in
Example 3. The results are shown in FIG. 18.
[0107] Through hardening is a treatment in which after a bearing
steel has been heated to and held at 800-850.degree. C., it is
cooled rapidly. This forms a martensitic composition in the steel,
so that the material is hardened.
Example 4
[0108] Except that foreign matter was mixed in the urea grease
described in Table 1 used as a grease, the accumulated breakage
probability 10% life was measured in the same manner as in Example
3. The results are shown in FIG. 19.
Comparative Example 8
[0109] Except that an inner ring 81 and an outer ring 83 made of
SUJ2 were subjected to the through hardening, the accumulated
breakage probability 10% life was measured in the same manner as in
Example 4. The results are shown in FIG. 19.
(Results)
[0110] From Examples 3 and 4 and Comparative Examples 7 and 8, it
became apparent that the angular ball bearing obtained by
subjecting the rolling surfaces to carbonitriding and using a urea
compound as a grease had a sufficient durability.
EFFECT OF THE INVENTION
[0111] With the angular ball bearing of this invention, since
rolling elements are disposed between the inner ring and the outer
ring, a seal is provided at least on one side, and the seal is
fitted on the peripheral surface portion of the counterbore in a
pressed state, even though it is of a sealed type, lowering of the
strength of the bearing rings or reduction of the front width for
the convenience of mounting of the seal will not occur. Thus design
is possible for dimensions and practicability equivalent to a
non-sealed type bearing.
[0112] Also, with the bearing according to this invention, since
the inner ring and the outer ring or the rolling elements are
subjected to carbonitriding and the grease using a urea compound as
a thickening agent is sealed in the bearing, a thin oxide film of a
urea compound is formed and a sufficiently thick oil film is formed
on the oxide film. Because the thin oxide film of urea compound is
high in adhesion to the carbonitrided layer, even if microscopic
rolling occurs frequently, grease is held on the rolling surfaces,
so that it is possible to suppress fretting damage on the rolling
surfaces, thus preventing lowering of the durability
effectively.
[0113] Further, even if oil film of the grease between the rolling
elements and the rolling surfaces should break, so that the rolling
elements and rolling surfaces contact directly, due to the function
of the carbonitrided layers provided on the rolling elements or the
rolling surfaces, production and progression of fretting damage are
suppressed for a while. Also, since oil film of grease is high in
adhesion to the carbonitrided layers; even if breakage of film
occurs, it is quickly repaired. Thus, even if oil film breaks and
the rolling elements and rolling surfaces directly contact, oil
film can be repaired before fretting damage occurs. Thus,
resistance to fretting damage improves greatly.
[0114] Also, since this bearing for supporting a ball screw has a
seal, the bearing interior is sealed. Thus, scattering of grease,
which was observed in a conventional open type bearing, is
suppressed.
[0115] Further, it is possible to prevent entering of foreign
matter such as coolants into the grease from the atmosphere.
[0116] Still further, since two kinds of seals are of different
shapes, it is easy to confirm mounting directions when assembling
the bearing. Thus it is possible to prevent mis-assembling.
* * * * *