U.S. patent application number 11/882772 was filed with the patent office on 2008-02-14 for thrust bearing component.
Invention is credited to Tomoaki Kawamura, Kousuke Obayashi, Yasuyuki Watanabe.
Application Number | 20080035246 11/882772 |
Document ID | / |
Family ID | 39049436 |
Filed Date | 2008-02-14 |
United States Patent
Application |
20080035246 |
Kind Code |
A1 |
Kawamura; Tomoaki ; et
al. |
February 14, 2008 |
Thrust bearing component
Abstract
A thrust bearing component is formed of cold-reduced steel
sheets and strip having surface roughness of Rmax.ltoreq.2 .mu.m
and provided by cold rolling a high-carbon steel containing 0.9 wt
% to 1.2 wt % of carbon, 1.2 wt % to 1.7 wt % of chrome, 0.1 wt %
to 0.5 wt % of manganese, and 0.15 wt % to 0.35 wt % of
silicon.
Inventors: |
Kawamura; Tomoaki;
(Iwata-shi, JP) ; Watanabe; Yasuyuki; (Iwata-shi,
JP) ; Obayashi; Kousuke; (Fukuroi-shi, JP) |
Correspondence
Address: |
CLARK & BRODY
1090 VERMONT AVENUE, NW, SUITE 250
WASHINGTON
DC
20005
US
|
Family ID: |
39049436 |
Appl. No.: |
11/882772 |
Filed: |
August 6, 2007 |
Current U.S.
Class: |
148/318 ;
148/333 |
Current CPC
Class: |
Y10T 29/49641 20150115;
Y10T 29/49645 20150115; F16C 29/02 20130101; C22C 38/04 20130101;
F16C 17/04 20130101; F16C 33/121 20130101; F16C 33/62 20130101;
C22C 38/18 20130101; C22C 38/02 20130101; F16C 19/30 20130101 |
Class at
Publication: |
148/318 ;
148/333 |
International
Class: |
C23C 8/32 20060101
C23C008/32; C22C 38/18 20060101 C22C038/18 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 2006 |
JP |
JP2006-218342 |
Claims
1. A thrust bearing component formed of cold-reduced steel sheets
and strip having surface roughness of Rmax.ltoreq.2 .mu.m and
provided by cold rolling a high-carbon steel containing 0.9 wt % to
1.2 wt % of carbon, 1.2 wt % to 1.7 wt % of chrome, 0.1 wt % to 0.5
wt % of manganese, and 0.15 wt % to 0.35 wt % of silicon.
2. The thrust bearing component according to claim 1, wherein said
thrust bearing component is manufactured by: a step of forming said
cold-reduced steel sheets and strip into a predetermined shape by a
pressing process; a step of performing a heat treatment including a
carbonitriding process and a high-temperature tempering process;
and a step of removing a scale generated on its surface.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a thrust bearing component
such as a bearing washer of a thrust rolling bearing or a thrust
sliding bearing, and a bearing washer of a thrust receiving
mechanism.
[0003] 2. Description of the Background Art
[0004] A high mechanical property and high processing accuracy are
required for a bearing washer of a thrust rolling bearing or a
thrust sliding bearing, and a bearing washer of a thrust receiving
mechanism (referred to as the "thrust bearing component"
collectively hereinafter). Therefore, when the thrust bearing
component is manufactured, it is essential to select an appropriate
starting material and an optimal processing method appropriate for
the material.
[0005] For example, a manufacturing method of a synchronizer ring
whose structure is similar to that of the thrust bearing component
is disclosed in Japanese Unexamined Patent Publication No.
11-223225. The manufacturing method of the synchronizer ring
disclosed in the above document will be described with reference to
FIG. 6.
[0006] First, the synchronizer ring disclosed in the above document
uses a steel plate provided by hot rolling a carbon steel
containing 0.6 wt % to 1.2 wt % of carbon (C), 0.1 wt % to 0.9 wt %
of manganese (Mn), 0.3 wt % to 1.0 wt % of chrome (Cr), and 0.01 wt
% to 0.15 wt % of silicon, as a starting material.
[0007] Thus, it is disclosed that the synchronizer ring is
manufactured through a step of forming the above starting material
into a predetermined shape by a pressing process, a step of
providing a predetermined dimension by a machining process such as
a turning process, a step of providing predetermined hardness by a
heat treatment including quenching and tempering, and a step of
smoothing the surface by a grinding process as a finishing
process.
[0008] Recently, the environment in which the thrust bearing is
used has become increasingly harsh, and accordingly it is required
that the mechanical property of the thrust bearing washer is to be
further improved. Meanwhile, as price reduction of the thrust
bearing is required, the manufacturing process needs to be
simplified without changing its quality.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide a thrust
bearing component whose manufacturing cost is lowered by
simplifying a manufacturing process and mechanical property is
further improved.
[0010] A thrust bearing component according to the present
invention is formed of a cold-reduced steel sheets and strip having
surface roughness of Rmax.ltoreq.2 .mu.m and provided by cold
rolling a high-carbon steel containing 0.9 wt % to 1.2 wt % of
carbon (C), 1.2 wt % to 1.7 wt % of chrome (Cr), 0.1 wt % to 0.5 wt
% of manganese (Mn), and 0.15 wt % to 0.35 wt % of silicon
(Si).
[0011] Preferably, the thrust bearing component is manufactured by
a step of forming the cold-reduced steel sheets and strip into a
predetermined shape by a pressing process, a step of performing a
heat treatment including a carbonitriding process and a
high-temperature tempering process, and a step of removing a scale
generated on its surface.
[0012] When the carbon steel having the above chemical components
is used, the mechanical property of the thrust bearing component is
improved. More specifically, a quenching property is improved, a
rolling fatigue life and a load bearing property are improved,
friction and wear are reduced, hardness is improved, and damage of
the thrust bearing component due to the pressing process and the
like can be prevented.
[0013] In addition, since the steel plate manufactured through the
cold rolling process can provide desired dimension, surface
smoothness, and hardness, a turning process for adjusting the
dimension and a grinding process for smoothing the surface and the
like can be omitted in the manufacturing process of the thrust
bearing component. Thus, since the manufacturing process of the
thrust bearing component can be simplified, the manufacturing cost
of the thrust bearing component can be lowered.
[0014] According to the present invention, since the steel plate
for the thrust bearing component provided by cold rolling the
carbon steel having the predetermined chemical components is used
as a starting material, the thrust bearing component can be low in
cost and superior in mechanical property.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a view showing a thrust needle roller bearing
according to one embodiment of the present invention;
[0016] FIG. 2 is a flowchart showing main steps of the
manufacturing process of a steel plate for a thrust bearing
component;
[0017] FIG. 3 is a flowchart showing main steps of the
manufacturing process of a thrust bearing component from the steel
plate for the thrust bearing component;
[0018] FIG. 4 is a view showing a thrust sliding bearing according
to another embodiment of the present invention;
[0019] FIG. 5 is a view showing a thrust sliding bearing according
to still another embodiment of the present invention: and
[0020] FIG. 6 is a flowchart showing main steps of the
manufacturing process of a synchronizer ring.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] A thrust needle roller bearing 11 and a manufacturing method
of bearing washers 12 and 13 of the thrust needle roller bearing 11
according to one embodiment of the present invention will be
described with reference to FIGS. 1 to 3. In addition, FIG. 1 is a
view showing the thrust needle roller bearing 11, FIG. 2 is a
flowchart showing main manufacturing steps of a cold-reduced steel
sheets and strip that is a starting material of a thrust bearing
component, and FIG. 3 is a flowchart showing main manufacturing
steps of the thrust bearing component.
[0022] First, referring to FIG. 1, the thrust needle roller bearing
11 comprises a pair of upper and lower bearing washers 12 and 13, a
plurality of needle rollers 14 arranged between the pair of bearing
washers 12 and 13 radially, and a retainer 15 retaining the
interval of the adjacent needle rollers 14.
[0023] According to the above thrust needle roller bearing 11,
although there are various advantages such that load capacity and
rigidity can be high with a simple form, differential sliding is
generated between the bearing washers 12 and 13 and the needle
roller 14. According to the needle roller 14, pure rolling is
provided in the center in its longitudinal direction and relative
sliding is linearly increased toward both ends thereof. Especially,
since the needle roller bearing 14 is long, the difference in
peripheral speed at both ends of the needle roller 14 is large and
a sliding amount is large as compared with other bearings.
[0024] Thus, since an wear amount of the bearing washers 12 and 13
is large at a part in which the differential sliding is largely
generated, surface origin type peeling is generated at an rolling
track edge. Especially, since the thrust needle roller bearing 11
have many rollers and narrow in internal space, lubricant oil is
not likely to be spread on the track surface. As a result, the
surface origin type peeling is easily generated as compared with
the other bearings.
[0025] In addition, a high thrust load is applied to the bearing
washers 12 and 13 in the thrust needle roller bearing 11 having the
above constitution. Furthermore, predetermined hardness and surface
smoothness are required for the track surface on which the needle
roller 14 rolls.
[0026] Thus, a description will be made of a manufacturing method
of the steel plate for the thrust bearing component that will be
the starting material of the thrust bearing component to be used in
the above environments with reference to FIG. 2. First, a billet
containing 0.9 wt % to 1.2 wt % of carbon (C), 1.2 wt % to 1.7 wt %
of chrome (Cr), 0.1 wt % to 0.5 wt % of manganese (Mn), 0.15 wt %
to 0.35 wt % of silicon (Si), the remainder of inevitable
impurities, and iron (Fe) is prepared as the starting material
(S11). In addition, it is to be noted that the oxygen concentration
in steel is not more than 0.0010%.
[0027] Carbon (C) is an essential element to ensure the strength
required for the thrust bearing component. In addition, 0.9 wt % of
carbon is needed to ensure the hardness of HRC58 or more on the
surface and core part of the thrust bearing component. Meanwhile,
when the carbon content exceeds 1.2 wt %, a large carbide is
generated on the surface of the thrust bearing component, which
lowers the rolling fatigue life and load bearing property and
increases friction and wear. Thus, it is desirable the carbon
content is within a range of 0.9 wt % to 1.2 wt %. In addition, the
"HRC" designates Rockwell hardness.
[0028] In addition, chrome (Cr) is an essential element to improve
the quenching property and rolling fatigue life of the thrust
bearing component, ensure the hardness by the carbide, prevent the
friction and wear, and improve the load bearing property. In
addition, 1.2 wt % or more of chrome is needed to obtain the
predetermined carbide. Meanwhile, even when an amount exceeding 1.7
wt % is added, its added effect is not provided so much. When it
exceeds 5.0 wt %, a large carbide is generated, which lowers the
rolling fatigue life and load bearing property and increases the
friction and wear. Thus, it is desirable the chrome content is
within a range of 1.2 wt % to 1.7 wt %.
[0029] In addition, manganese (Mn) is an element used for
deoxidation when the steel is manufactured and it is an essential
element as the starting material of the thrust bearing component.
In addition, 0.1 wt % of manganese is needed to remove oxygen from
the steel satisfactorily. Meanwhile, when more than 0.5 wt % of
manganese is added, the material becomes fragile and the thrust
bearing component could be damaged at the time of pressing. Thus,
it is desirable that the manganese content is within a range of 0.1
wt % to 0.5 wt %.
[0030] In addition, silicon (Si) is an essential element in the
steel material and the lower limit value of its content is 0.15%.
Meanwhile, when it exceeds 0.35 wt %, the thrust bearing component
could be damaged at the time of pressing. Thus, it is desirable
that the silicon content is within a range of 0.15 wt % to 0.35 wt
%.
[0031] In addition, since oxygen forms an oxide in steel, that
becomes an origin of fatigue destruction as a nonmetal inclusion,
it reduces the rolling fatigue life and load bearing property and
increases the friction and wear. Thus, it is desirable that the
oxygen concentration in steel is not more than 0.0010%.
[0032] Then, the steel plate is formed of the above material by hot
rolling (S12). A large cast structure becomes a fine and preferable
rolling texture through the hot rolling. In addition, since the
work hardening of the material can be prevented by rolling at a
temperature more than a recrystallization temperature, the
thickness can be immediately reduced.
[0033] In addition, a step of annealing the rolled steel plate may
be added after the hot pressing step. Since a crystal grain becomes
fine and the direction of the crystal is adjusted by annealing, the
accuracy and operability of the surface can be improved.
[0034] Then, acid pickling is performed in order to prevent rust
and remove oxide layer (scale) attached on the surface of the steel
plate (S13). The oxide layer shortens the life of a tool in a
machining process and lowers production efficiency, and causes
physical and chemical changes on the surface of the steel plate to
lower the effect of the surface processing. Thus, as the oxide
layer is removed through the acid pickling, production efficiency
in the following steps and product quality can be improved. In
addition, a pickling solution includes hydrochloric acid, sulfuric
acid, nitric acid and the like, and 5% to 15% of dilute
hydrochloric acid solution is used at 40.degree. C. to 50.degree.
C. in many cases.
[0035] Then, the steel plate reaches a predetermined size and
machinery properties such as hardness and surface smoothness and
the like required for the thrust bearing component are provided by
cool rolling (S14). A predetermined plate thickness can be
accurately provided and uniform smoothness can be provided by
rolling at a room temperature. In addition, since the steel plate
is work-hardened by rolling at a temperature below the
recrystallization temperature, the hardness of the steel plate is
improved.
[0036] In addition, the surface roughness of the wall surface to
become the track surface of the thrust bearing component is
required to be Rmax.ltoreq.1.6 .mu.m in view of the smooth rolling
of the needle roller 14. As will be described below, since
barreling can be only preformed as far as a head of the surface
roughness is removed after the shape of the thrust bearing
component has been processed, it is desirable that the surface
roughness after the cold rolling process is such that Rmax.ltoreq.2
.mu.m. Furthermore, in view of preventing the damage at the time of
press forming, the hardness after the cold rolling process is
preferably Hv220 or less. Here, the "Rmax" designates a maximum
height and "Hv" designates Vickers hardness.
[0037] Here, the surface roughness, hardness and thickness of the
steel plate provided by the cold rolling process are affected by
the surface roughness of the rolling roll, the flexibility of the
rolling roll, a rolling ratio (ratio of the thickness between after
and before the rolling), the gap between the rolling rolls, a
rotation speed and the like. Therefore, in order to provide the
desirable surface roughness, hardness and plate thickness, it is
necessary to set the above elements appropriately.
[0038] In addition, although the predetermined thicknesses may be
provided by the above hot rolling process and the cold rolling
process respectively, the predetermined thickness may be provided
through a plurality of processes such as rough rolling, middle
rolling and finish rolling.
[0039] When the billet comprising the above chemical components is
processed by the above processes, the steel plate for the thrust
bearing component (cold-reduced special steel sheets and strip) can
provide very high mechanical property. Thus, in order to confirm
the effect of the present invention, tensile strength, 0.2% proof
stress, total elongation at rupture, work hardening coefficient (n
value) and plastic strain ratio (r value) of the above steel plate
for the thrust bearing component were measured. The measured result
is shown in Table 1. In addition, in Table 1, a minimum value, a
maximum value and average value are shown with respect to each lot
(No. 1 to No. 3).
TABLE-US-00001 TABLE 1 Total elongation at Work hardening Tensile
strength 0.2% proof stress rupture coefficient Plastic strain ratio
Mini- Mini- Mini- Mini- Aver- Mini- Aver- mum Maximum Average mum
Maximum Average mum Maximum Average mum Maximum age mum Maximum age
value value value value value value value value value value value
value value value value 560 622 589 388 458 428 28 32 30 0.15 0.16
0.16 0.96 1.48 1.26 572 628 596 364 452 406 27 31 29 0.15 0.16 0.16
0.94 1.46 1.22 586 638 607 394 462 434 26 30 28 0.15 0.16 0.15 0.92
1.52 1.21
[0040] Referring to Table 1, the tensile strength of the above
steel plate was 550N/mm.sup.2 or more. In addition, as the tensile
strength and the 0.2% proof stress become high, the total
elongation at rupture and the work hardening coefficient and the
plastic strain ratio become low as will be described below. Since
these values largely affect the workability of the steel plate, the
material showing high values of those is not preferable for the
material for manufacturing the thrust bearing component. Thus,
although the maximum value of the tensile strength is 638/mm.sup.2,
and the maximum value of the 0.2% proof stress is 462N/mm.sup.2 in
Table 1, it is preferable the tensile strength is preferably
approximately 550N/mm.sup.2 and the 0.2% proof stress is preferably
approximately 350N/mm.sup.2.
[0041] In addition, the total elongation at rupture of the above
steel plate was 25% to 35%. In addition, the work hardening
coefficient was 0.12 to 0.18. Furthermore, the plastic strain ratio
was 1.20 to 1.30. In addition, as the values of the total
elongation at rupture, the work hardening coefficient and the
plastic strain ratio are increased, the forming limit is improved,
which is advantageous in manufacturing the thrust bearing
component. However, according to the present invention, the values
are set within the range described above in view of the relation
with the tensile strength and the 0.2% proof stress.
[0042] In addition, the tensile strength, the 0.2% proof stress,
and the total elongation at rupture were measured based on JIS
(Japanese Industrial Standards) Z 2241. Similarly, the work
hardening coefficient (n value) and the plastic strain ratio (r
value) were measured based on JIS Z 2253 and JIS Z 2254,
respectively.
[0043] Next, a description will be made of the manufacturing method
of the thrust bearing component according to one embodiment of the
present invention with reference to FIG. 3. In addition, FIG. 3 is
a flowchart showing main manufacturing steps of the thrust bearing
component. First, the steel plate (cold-reduced steel sheets and
strip) for the thrust bearing component described with reference to
FIG. 2 is employed as the starting material (S21).
[0044] Then, the steel plate is formed into the thrust bearing
component by pressing (S22). According to the above starting
material, since its thickness, surface roughness and the like are
already in preferable conditions by the cold rolling process, the
process such as a turning process may be omitted. As a result,
since the manufacturing process can be simplified, the
manufacturing cost of the thrust bearing component can be low. In
addition, although the preferable configuration may be provided by
the one pressing process, the preferable configuration may be
provided through the plurality of pressing processes. In addition,
a burring process may be performed after the pressing process.
[0045] Then, in order to provide the mechanical property required
for the thrust bearing component, a heat treatment including a
carbonitriding process and high-temperature tempering is performed
(S23). In addition, a nitrogen enrichment layer is formed on the
surface of the thrust bearing component by the carbonitriding
process. This nitrogen enrichment layer is effective in improving
the rolling fatigue life and load bearing property and in reducing
the friction and wear.
[0046] In addition, not only the high temperature resistance
characteristics are improved but also the residual austenite is
split into tempered martensite and fine carbide by the high
temperature tempering, which is effective in improving the rolling
fatigue life and the load bearing property and in reducing the
friction and wear under a high load condition, especially.
[0047] In addition, a tempering temperature needs to be 230.degree.
C. or more to keep the residual austenite below 5%. Meanwhile, when
the tempering temperature is 280.degree. C. or more, the hardness
becomes HRC60 or less, which could not maintain the hardness
required for the thrust bearing component. Thus, it is preferable
that the tempering temperature is within a range of 230.degree. C.
to 280.degree. C.
[0048] Finally, the oxide layer (scale) generated on the surface of
the thrust bearing component during the heat treatment is removed
(S24). The scale removing process includes a mechanical method such
as a barreling process and blast cleaning or a chemical method such
as acid pickling as described above.
[0049] Here, the "barreling process" is a process in which the
thrust bearing component, a compound and a medium are put into a
barrel and the barrel is rotated or vibrated. By this method, the
scale can be removed and the thrust bearing component can be burred
and the surface roughness can be improved. Since the surface
roughness of the starting material of the thrust bearing component
is already such that Rmax.ltoreq.2 .mu.m at the stage after the
cold rolling process as described above, the surface roughness such
that Rmax.ltoreq.1.6 .mu.m required for the thrust bearing
component can be provided without an independent grinding
process.
[0050] According to the present invention, when the carbon steel
having the above chemical components is used, the various
mechanical properties of the thrust bearing component are improved.
As a result, the rolling fatigue life and load bearing property are
improved and the friction and wear are reduced in the thrust
bearing component.
[0051] In addition, when the cold rolling process is contained in
the manufacturing process of the starting material (shown in FIG.
2), the thickness, hardness, surface roughness and the like
required for the thrust bearing component can be provided. Thus,
the turning process and the grinding process can be omitted in the
manufacturing steps of the thrust bearing component (shown in FIG.
3). As a result, the manufacturing process of the thrust bearing
component is simplified and the manufacturing cost of the thrust
bearing component can be lowered.
[0052] In addition, although the description has been made of the
manufacturing method of the bearing washers 12 and 13 of the thrust
needle roller bearing 11 in the above embodiment, the present
invention is not limited to this and the present invention can be
applied to a manufacturing method of another thrust bearing
component. For example, the present invention may be applied to a
thrust rolling bearing in which a rolling element is a cylindrical
roller or a ball, or a thrust sliding bearing having no rolling
element. Thrust bearings according to other embodiments of the
present invention will be described with reference to FIGS. 4 and
5. In each of FIGS. 4 and 5, an upper part is a perspective view
and a lower part is a side sectional view.
[0053] First, referring to FIG. 4, a thrust sliding bearing 21
according to another embodiment of the present invention comprises
two bearing washers 22 and 23. The bearing washers 22 and 23 are
disk-shaped members having holes 22a and 23a in the center,
respectively and they overlap with each other so that their track
surfaces 22b and 23b abut on each other.
[0054] According to the thrust sliding bearing 21, the bearing
washer 22 is fixed to a rotation shaft (not shown) and the bearing
washer 23 is fixed to a housing (not shown), for example. Since the
bearing washer 22 rotates while slides on the bearing washer 23,
the rotation shaft can be rotatably supported. In addition, it is
to be noted that the above rotation shaft includes not only the one
rotating in a certain direction but also the one that oscillates.
In addition, it is to be noted that the bearing washer 23 includes
the one that is fixed to another rotation shaft relatively rotating
with the above rotation shaft.
[0055] Next, referring to FIG. 5, a thrust bearing component 31
according to still another embodiment of the present invention
comprises two bearing washers 32 and 33. The bearing washers 32 and
33 are rectangular members and overlap with each other so that
their track surfaces 32a and 33a abut on each other.
[0056] According to this thrust sliding bearing 31, the bearing
washer 32 is fixed to a reciprocating member (not shown) and the
bearing washer 33 is fixed to a housing (not shown), for example.
Since the bearing washer 32 reciprocates (shown by an arrow in FIG.
5) while slides on the bearing washer 33, it can support the
reciprocating member moving linearly within a certain range. In
addition, it is to be noted that the bearing washer 33 includes the
one that is fixed to another reciprocating member moving relatively
with the above reciprocating member.
[0057] Large thrust load is applied to the bearing washers 22, 23,
32 and 33 in the thrust sliding bearing 21 and 31, and certain
hardness and surface smoothness are required for the track surfaces
22b, 23b, 32b and 33a. Thus, when at least one of the bearing
washers 22 and 23 of the thrust sliding bearing 21 and at least one
of the bearing washers 32 and 33 of the thrust sliding bearing 31
are manufactured by the method shown in FIGS. 2 and 3, the effect
of the present invention can be provided.
[0058] In addition, it is to be noted that the "thrust bearing
component" in this specification includes not only the disk-shaped
bearing washers 12, 13, 22, and 23 as shown in FIGS. 1 and 4 but
also the rectangle-shaped bearing washers 32 and 33 as shown in
FIG. 5.
[0059] Although the embodiments of the present invention have been
described with reference to the drawings in the above, the present
invention is not limited to the above-illustrated embodiments.
Various kinds of modifications and variations may be added to the
illustrated embodiments within the same or equal scope of the
present invention.
[0060] The present invention can be advantageously applied to
manufacturing of the bearing washer and the like of the thrust
rolling bearing or the thrust sliding bearing.
* * * * *