U.S. patent application number 12/966456 was filed with the patent office on 2011-04-07 for manufacturing method of thin component, bearing ring, thrust needle roller bearing, manufacturing method of rolling bearing ring, rolling bearing ring, and rolling bearing.
This patent application is currently assigned to NTN CORPORATION. Invention is credited to Yuuki Kataoka, Kikuo MAEDA, Mitsuo Sasabe.
Application Number | 20110081106 12/966456 |
Document ID | / |
Family ID | 34425361 |
Filed Date | 2011-04-07 |
United States Patent
Application |
20110081106 |
Kind Code |
A1 |
MAEDA; Kikuo ; et
al. |
April 7, 2011 |
MANUFACTURING METHOD OF THIN COMPONENT, BEARING RING, THRUST NEEDLE
ROLLER BEARING, MANUFACTURING METHOD OF ROLLING BEARING RING,
ROLLING BEARING RING, AND ROLLING BEARING
Abstract
A manufacturing method of a thin component is characterized by
heating a thin component, and thereafter, while sizing with molds
and using molds as cooling media, performing one of quenching and
isothermal transformation processes on thin component. Thus, a
manufacturing method of a thin component without warping or
deformation in heat treatment with even and high hardness, a
bearing ring, a thrust needle roller bearing, a manufacturing
method of a rolling bearing ring, a rolling bearing ring, and a
rolling bearing can be obtained.
Inventors: |
MAEDA; Kikuo; (Kuwana-shi,
JP) ; Kataoka; Yuuki; (Kuwana-shi, JP) ;
Sasabe; Mitsuo; (Osaka, JP) |
Assignee: |
NTN CORPORATION
Osaka
JP
|
Family ID: |
34425361 |
Appl. No.: |
12/966456 |
Filed: |
December 13, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10574779 |
Apr 6, 2006 |
7867345 |
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PCT/JP04/14501 |
Oct 1, 2004 |
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12966456 |
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Current U.S.
Class: |
384/618 |
Current CPC
Class: |
F16C 19/48 20130101;
C21D 9/40 20130101; C21D 1/673 20130101; F16C 19/30 20130101; F16C
33/64 20130101; F16C 19/46 20130101 |
Class at
Publication: |
384/618 |
International
Class: |
F16C 19/30 20060101
F16C019/30 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 6, 2003 |
JP |
2003-347095(P) |
Dec 12, 2003 |
JP |
2003-414967(P) |
Claims
1-11. (canceled)
12. A thrust needle roller bearing including a bearing ring
manufactured by a method of a thin component, the method including
the steps of heating said thin component, and thereafter, while
sizing with molds and using said molds as cooling media of said
thin component, performing one of quenching and isothermal
transformation processes on said thin component.
13-17. (canceled)
18. A rolling bearing, comprising a rolling bearing ring and a
rolling element, wherein said rolling bearing ring is manufactured
by a manufacturing method comprising the step of after heating a
rolling bearing ring as a thin component using a manufacturing
method of said thin component by cooling said rolling bearing ring
while pressing with molds and using said molds as quenching media,
quenching said rolling bearing ring, and the manufacturing method
of the thin component including the steps of heating a thin
component, and thereafter, while sizing with molds and using said
molds as cooling media of said thin component, performing one of
quenching and isothermal transformation processes on said thin
component.
19. The rolling bearing according to claim 18, wherein said rolling
bearing is a thrust needle roller bearing.
Description
TECHNICAL FIELD
[0001] The present invention relates to a manufacturing method of a
thin component, a bearing ring, a thrust needle roller bearing, a
manufacturing method of a rolling bearing ring, a rolling bearing
ring, and a rolling bearing, and particularly, it relates to a
manufacturing method of a thin component such as a ring of a thrust
needle roller bearing and a thin bearing ring, which tend to show
great deformation in heat treatment and which are not subjected to
polishing after the heat treatment.
BACKGROUND ART
[0002] Conventionally, for a ring of a thrust needle (needle)
roller bearing or a ring of a drawn cup radial needle roller
bearing, a low-carbon SPCC (JIS: a cold rolled steel plate)
product, an SCM415 product (JIS: a steel product of chromium
molybdenum steel) and the like carburized for a short period of
time and a hardness-requiring portion of the surface layer is
hardened have been used. Also, products of mid- to high-carbon
steel have been manufactured, such as an SK5 product (JIS: a steel
product of carbon tool steel) subjected to through quenching by
whole heating. With all of these, carburizing or a batch type
furnace have been used in heat treatment.
[0003] On the other hand, in some applications quenching of a thin
product by high-frequency heating has also been performed.
Conventionally, as to quenching of a thin product or an
uneven-thickness component by high-frequency heating, there are
techniques that can be found in the following Patent Documents 1-4.
All of these, however, employ air or gas for cooling in quenching
so as to control the cooling rate for suppressing distortion, or to
eliminate difference in quenching speed between a thick portion and
a thin portion for suppressing deformation.
[0004] As to a tubular member, while there is a technique of
providing constraint in quenching can be found (for example, Patent
Document 5), it employs a solution in quenching. Hence, there has
been no technique employing a mold for constraining and also as a
quenching medium. [0005] Patent Document 1: Japanese Patent
Laying-Open No. 6-179920 [0006] Patent Document 2: Japanese Patent
Laying-Open No. 9-302416 [0007] Patent Document 3: Japanese Patent
Laying-Open No. 2001-214213 [0008] Patent Document 4: Japanese
Patent Laying-Open No. 2003-55713 [0009] Patent Document 5:
Japanese Patent Laying-Open No. 7-216456
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0010] With the conventional low-carbon SPCC or SCM415 product
carburized for a short period of time and a hardness-requiring
portion of the surface layer is hardened is excellent in material
workability. However, as carburizing is employed in the heat
treatment, the heat treatment is performed off-line, and there have
been problems that the life or strength is not stabilized due to
internal oxidation in carburizing or warping or deformation in
quenching.
[0011] The mid- to high-carbon steel such as the SK5 product is
involved with a problem that the material is high in hardness and
that it is less workable. The products subjected to whole
heating--quenching in an atmospheric furnace exhibit deformation
due to uneven cooling, as can be seen in carburizing. Though slow
and even cooling has been performed (for example, by blowing an
inert gas for cooling) to such products subjected to through
quenching, it is difficult to eliminate deformation, and tempering
for correcting warping has been required to reduce warping.
[0012] As to the products subjected to high-frequency heating also,
deformation in quenching cannot be avoided no matter how slowly the
cooling is performed, so long as air or water is used as a
quenching medium in the steps of high-frequency heating--water
quenching. Particularly when water is used, liquid replacement has
been necessary due to deterioration or consumption of the
liquid.
[0013] Quenching by a mold can attain quenching without warping or
deformation when associated with high-frequency heating. However,
in a general technique, a mold is not used as a refrigerant, and
cooling by oil or water, or drawing a product after oil quenching
at a prescribed temperature and constraining by a mold is
performed.
[0014] Accordingly, an object of the present invention is to
provide a manufacturing method of a thin component without warping
or deformation in heat treatment (in quenching) and with even and
high hardness, a bearing ring, a thrust needle roller bearing, a
manufacturing method of a rolling bearing ring, a rolling bearing
ring, and a rolling bearing.
Means for Solving the Problems
[0015] A manufacturing method of a thin component according to the
present invention is characterized by heating a thin component, and
thereafter, while sizing (correcting) with molds and using the
molds as cooling media of the thin component, performing one of
quenching and isothermal transformation processes on the thin
component.
[0016] Preferably, in the aforementioned manufacturing method of a
thin component, the step of sizing the thin component with the
molds includes the step of pressing the thin component with the
molds.
[0017] Preferably, in the aforementioned manufacturing method of a
thin component, the quenching of the thin component is performed
using the molds as quenching media.
[0018] Preferably, in the aforementioned manufacturing method of a
thin component, the mold has cooling means, and the thin component
can continuously be quenched by the molds.
[0019] Preferably, in the aforementioned manufacturing method of a
thin component, the thin component is quenched in an atmosphere in
which oxidation of the thin component is prevented.
[0020] Preferably, in the aforementioned manufacturing method of a
thin component, after the thin component is quenched, a tempering
process is performed on the thin component using the molds as
temperature controlling media.
[0021] Preferably, in the aforementioned manufacturing method of a
thin component, the molds are used in both of the steps of
quenching and tempering the thin component.
[0022] Preferably, in the aforementioned manufacturing method of a
thin component, in the step of quenching the thin component, a
molding process of the thin component using the molds is
concurrently performed.
[0023] Preferably, in the aforementioned manufacturing method of a
thin component, the heating of the thin component is performed by
induction heating.
[0024] Preferably, in the aforementioned manufacturing method of a
thin component, a material of the thin component is steel
containing carbon by at least 0.4 mass %.
[0025] A bearing ring according to the present invention is
manufactured by any of the aforementioned methods.
[0026] A thrust needle roller bearing according to the present
invention uses the aforementioned bearing ring.
[0027] A manufacturing method of a rolling bearing ring according
to the present invention is characterized by, after heating a
rolling bearing ring as the thin component using the aforementioned
manufacturing method of a thin component, by cooling the rolling
bearing ring while pressing with the molds and using the molds as
quenching media, quenching the rolling bearing ring.
[0028] Preferably, in the aforementioned manufacturing method of a
rolling bearing ring, the heating of the rolling bearing ring is
performed by induction heating.
[0029] Preferably, in the aforementioned manufacturing method of a
rolling bearing ring, the rolling bearing ring is mid-carbon steel
containing carbon by at least 0.4 mass %.
[0030] Preferably, in the aforementioned manufacturing method of a
rolling bearing ring, in the quenching, a pressing pressure by the
molds is at least 2.94 N/cm.sup.2.
[0031] A rolling bearing ring according to the present invention is
characterized in that it is manufactured by any of the
aforementioned methods.
[0032] A rolling bearing according to the present invention
includes the aforementioned rolling bearing ring and a rolling
element.
[0033] Preferably, in the aforementioned rolling bearing, the
rolling bearing is a thrust needle bearing.
EFFECTS OF THE INVENTION
[0034] The inventors of the present invention found that, in a
manufacturing method of a thin component, by performing one of
quenching and isothermal transformation processes on the thin
component while pressing the thin component with molds and using
the molds as cooling media of the thin component, a bearing ring
that does not exhibit deformation or warping, that has an even
hardness distribution, that is excellent in toughness, and that has
long life can be manufactured.
[0035] As above, according to the manufacturing method of a thin
component of the present invention, as warping and deformation are
suppressed, a thin component can be manufactured with high
precision. Further, as one of quenching and isothermal
transformation processes is performed using molds as cooling media,
a process that requires less time and that is even as compared to
quenching by air-blow or oil can be attained. By maintaining the
pressing pressure or temperature of the molds constantly, stable
quality can be assured. Additionally, as no water or oil is used,
working environment is clean and there will be no environmental
pollution because of liquid waste or the like.
[0036] Still further, as the thin component is subjected to
quenching or isothermal transformation process one by one, quality
control is facilitated.
[0037] When quenching, by using steel of a composition that can
easily be quench-hardened, not to mention S53C (JIS: steel product
of steel for machine structural use) that is the representative
mid-carbon steel, the aforementioned quality can be achieved even
when slow quench-hardening is performed in the steps.
[0038] As to isothermal transformation, since transformation is
caused by holding isothermally, the material of the thin component
becomes a bainite structure. Thus, as compared to a martensite
structure, there are advantages that less quenching distortion is
resulted, toughness is attained without performing tempering, and
secular dimensional change is suppressed. Further, as tempering is
not necessary, a rolling bearing ring can be subjected to heat
treatment peace by peace. Still further, as tempering is not
necessary, normal quenching and tempering can be finished with one
process, and thus production steps are reduced. Still further, by
generating lower bainite, hardness can also be increased.
[0039] In the aforementioned manufacturing method of a thin
component, as heating of the thin component is performed by
induction heating, an inexpensive material for high-frequency use
(steel for machine structural use) can be applied, and the life
thereof is stable. Additionally, since heating is performed by
induction heating, heating can be achieved in a short period of
time, and a surface irregular layer such as with internal oxidation
or decarburization will not be formed. Further, since heating is
performed by induction heating, a non-quenching portion or
non-isothermal transformation portion can partially be formed by
changing quenching conditions or the shape of a coil, and therefore
the method can also be applied to a product that requires a bending
process after heat treatment.
[0040] In the aforementioned manufacturing method of a thin
component, the thin component can attain enough hardness by being
mid-carbon steel containing carbon by at least 0.4 mass %.
[0041] By using the aforementioned thin component, a bearing ring
with stable life or strength and a thrust needle roller bearing
using the same can be obtained.
[0042] The inventors of the subject invention found that, in a
manufacturing method of a rolling bearing ring, by quenching the
rolling bearing ring by cooling the rolling bearing ring while
pressing with molds and using the molds as quenching media, a
bearing ring can be manufactured, which has an even hardness
distribution, does not have defects such as oxidation or
decarburization on the surface layer face, has very few warping and
deformation, and has a long life. In this case, by using steel of a
composition that can easily be quench-hardened, not to mention S53C
(HS: steel product of steel for machine structural use) that is the
representative mid-carbon steel, the aforementioned quality was
achieved even when slow quench-hardening is performed in the
steps.
[0043] As above, according to the manufacturing method of a rolling
bearing ring of the present invention, since warping and
deformation can be suppressed, a thin bearing ring can be
manufactured with high precision. Additionally, as quenching is
performed using molds as quenching media, quenching that requires
less time and that is even as compared to quenching by air-blow or
oil can be attained. By maintaining the pressing pressure or
temperature of the molds constantly, stable quality can be assured.
Additionally, as no water or oil is used, working environment is
clean and there will be no environmental pollution because of
liquid waste or the like.
[0044] Further, as quenching is performed for one by one, quality
control is facilitated.
[0045] In the aforementioned manufacturing method of a rolling
bearing ring, as heating of the rolling bearing ring is performed
by induction heating, an inexpensive material for high-frequency
use (steel for machine structural use) can be applied, and the life
thereof is stable. Additionally, since heating is performed by
induction heating, heating can be achieved in a short period of
time, and a surface irregular layer such as with internal oxidation
or decarburization will not be formed. Further, since heating is
performed by induction heating, a non-quenching portion can
partially be formed by changing quenching conditions or the shape
of a coil, and therefore the method can also be applied to a
process that requires a bending process after heat treatment.
[0046] In the aforementioned manufacturing method of a rolling
bearing ring, the rolling bearing ring can attain enough hardness
by being mid-carbon steel containing carbon by at least 0.4 mass
%.
[0047] In the aforementioned manufacturing method of a rolling
bearing ring, by setting the pressing pressure by the molds in
quenching to at least 2.94 N/cm.sup.2, warping and distortion can
effectively be suppressed.
[0048] By using the aforementioned rolling bearing ring, a rolling
bearing with stable life or strength, for example a thrust needle
roller bearing can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] FIG. 1 is a schematic cross-sectional view showing a step of
heating a rolling bearing ring in a manufacturing method of a thin
component in one embodiment of the present invention.
[0050] FIG. 2 is a schematic cross-sectional view showing a step of
performing one of quenching and isothermal transformation processes
on the rolling bearing ring in a manufacturing method of a thin
component in one embodiment of the present invention.
[0051] FIG. 3 is a schematic cross-sectional view showing a
structure of a thrust needle roller bearing using a rolling bearing
ring in one embodiment of the present invention.
[0052] FIG. 4 is a schematic cross-sectional view showing a
structure of a drawn cup radial needle roller bearing using a
rolling bearing ring in one embodiment of the present
invention.
[0053] FIG. 5 is a schematic cross-sectional view showing a
structure of a drawn cup radial needle roller bearing in which a
plurality of roller and cage assemblies are arranged in an outer
ring.
DESCRIPTION OF THE REFERENCE SIGNS
[0054] 1 thin component (rolling bearing ring), 2 rolling element,
3 cage, 4 roller and cage assembly, 6, 7 collar portion, 10 rotary
table, 10a heat insulator, 11 heating coil, 12a, 12b mold, 13
weight.
BEST MODES FOR CARRYING OUT THE INVENTION
[0055] In the following, embodiment of the present invention will
be described based on the drawings.
[0056] FIGS. 1 and 2 are cross-sectional views showing step by step
a manufacturing method of a thin component according to one
embodiment of the present invention. First, as a material, steel
having a prescribed composition, for example mid-carbon steel
containing carbon by at least 0.4 mass % is prepared. This steel is
subjected to a process of punching or cutting of a plate-shape
product or the like, to have a shape of a rolling bearing ring as
one example of a thin component. It should be noted that, in the
present embodiment, a thin component specifically refers to a
component of at most 3 mm thickness.
[0057] Referring to FIG. 1, a bearing ring 1 is placed on a heat
insulator 10a of a rotary table 10, and induction-heated by a
heating coil 11, for example. Here, bearing ring 1 is rotated by
rotary table 10.
[0058] Referring to FIG. 2, bearing ring 1 heated to a prescribed
temperature is interposed between molds 12a and 12b, and a weight
13 is placed on mold 12b. Thus, bearing ring 1 is subjected to
quenching process or isothermal transformation process, while being
pressed (sized) by molds 12a, 12b with a pressing pressure of at
least 2.94N/cm.sup.2 (0.3 kgf/cm.sup.2), for example, and using
molds 12a, 12b as cooling media. In other words, molds 12a, 12b
constrain bearing ring 1 and serve as quenching media in quenching
bearing ring 1, or as isothermal transformation media in isothermal
transformation.
[0059] After quenching bearing ring 1, bearing ring 1 may be
tempered in the state constrained by molds 12a, 12b. In this case,
molds 12a, 12b serve as tempering media in tempering bearing ring
1.
[0060] Through the aforementioned method, bearing ring 1 can be
manufactured, which has an even hardness distribution, does not
have defects such as oxidation or decarburization on the surface
layer face, has very few warping and deformation, and has a long
life.
[0061] As compared to a conventional bearing ring manufactured
using air or gas as a quenching medium, rolling bearing ring 1
manufactured as above has low and aligned flatness, and also has
stabilized hardness.
[0062] It should be noted that, when quenching bearing ring 1,
there is a method to substantially increase the heat capacity of
molds 12a, 12b as compared to that of bearing ring 1, as molds 12a,
12b are used as quenching media. For example, in order to suppress
the temperature increase of molds 12a, 12b by at most 5 C..degree.
for lowering the temperature of bearing ring 1 by 900 C..degree.,
the heat capacity of molds 12a, 12b must be at least 180 times as
great as that of bearing ring 1. As bearing ring 1 is interposed
between upper and lower molds 12a, 12b, the heat capacity of either
upper mold 12a or lower mold 12b must be at least 90 times as great
as that of bearing ring 1. Accordingly, provided that bearing ring
1 and molds 12a, 12b are formed of the same material (for example,
steel) and have the same specific heat, then the mass of either
upper mold 12a or lower mold 12b must be at least 90 times as great
as that of bearing ring 1. If a substance of great heat capacity,
for example water, is allowed to flow through the molds, the molds
themselves may be small.
[0063] If heating/quenching is performed in the air, even for a
short period of time, a thin component may be oxidized. Thus, an
oxide film may be formed, the surface hardness may be decreased due
to decarburization, or precipitation of troostite may occur. A
product such as a ring of a thrust needle roller bearing, which is
not subjected to finishing (polishing, super finishing) by a
machine process after heat treatment, requires heat treatment
(quenching) for suppressing oxidation/decarburization. Such heat
treatment can be addressed by using an inert gas in the
atmosphere.
[0064] As quenching or isothermal transformation, in which molds
are employed as cooling media as in the present embodiment, is a
heat treatment of piece-by-piece, it is not necessary to separate
the heat treatment process from a production line as in a
conventional manner, but instead it may be incorporated into the
production line of a machine process. Further, if tempering is
performed by high-frequency induction heating or high-frequency
heating while performing pressing with molds (high-frequency
press-tempering), there is an advantage of integrating the whole
processes from material input to product completion into a
line.
[0065] In light of improving a processing speed, an efficient
continuous quenching is possible by performing quenching while
constantly cooling inside of the molds or the pressing surface with
water, oil, air or the like. To this end, it is preferable to
provide cooling means for introducing medium such as water, oil,
air or the like into the molds.
[0066] It should be noted that, while tests were conducted in
examples described below with plate-like products of 1 mm
thickness, the method of the present invention is applicable to a
thick plate (a 5-6 mm thickness plate) if the pressure when
pressing is increased, though the thickness for quench-hardening at
the cooling rate by the molds may be limited.
[0067] The molding process of a flange or a collar can
simultaneously be performed when quenching, by controlling the
shape of the mold or the pressing pressure.
[0068] Using bearing ring 1 manufactured by the aforementioned
method, a thrust needle roller bearing, for example as shown in
FIG. 3, can be manufactured. This thrust needle roller bearing has
a pair of bearing rings 1, and a plurality of rolling elements 2
(needle rollers) arranged between the pair of bearing rings 1, and
a cage 3 for rollably holding the plurality of rolling elements
2.
[0069] Additionally, using bearing ring 1 manufactured by the
aforementioned method, a drawn cup radial needle roller bearing,
for example as shown in FIG. 4, can also be manufactured. This
drawn cup radial needle roller bearing has a cylindrical outer ring
1 that is bearing ring 1, and a roller and cage assembly 4 arranged
on the internal periphery side of outer ring 1. Roller and cage
assembly 4 has a plurality of rolling elements (needle rollers) 2,
and a cage 3 for rollably holding the plurality of rolling elements
2. While collar portions 6, 7 are arranged on the opposing ends of
outer ring 1, one of or both of collar portions 6, 7 may be
eliminated. Additionally, as shown in FIG. 5, a plurality of (or
two) roller and cage assemblies 4 may be arranged on the internal
periphery side of outer ring 1, as shown in FIG. 5.
[0070] As bearing ring 1 shown in FIG. 4 or 5 is cylindrical outer
ring 1, cooling molds used in quenching outer ring 1 must be in a
shape different from that of molds 12a, 12b shown in FIG. 2, i.e.,
for example a cylindrical shape.
[0071] While the case in which a thin component is a bearing ring
of a thrust needle roller bearing has been described in the
foregoing, the present invention is not limited thereto and it may
be a washer or a leaf spring that is employed in a wearing
portion.
EXAMPLE
[0072] In the following, examples of the present invention will be
described.
Example 1
[0073] Mid-carbon steel S53C was used as a material, and a thrust
needle roller bearing ring (NTN product name: AS1112) having an
outer shape of inner diameter 60 mm, outer diameter 85 mm, and
thickness 1 mm was manufactured by punching from a plate-like
product.
[0074] Using a high-frequency induction heating apparatus (80 kHz)
and rotating the ring, induction heating was performed by allowing
prescribed current to flow through an induction coil arranged
closely to one end panel (FIG. 1). In this case, heating was
conducted slowly in order for the entire ring to attain a uniform
temperature (approximately 900.degree. C.). Thereafter, the ring
was set in upper and lower press molds made of iron and having a
heat capacity substantially greater than that of the ring, the ring
was immediately pressed by pressing at a prescribed pressure and
transformation-hardened through mold cooling by pressing (FIG. 2).
Varying mold temperature at transformation-hardening and constraint
time by the molds, the relationship between hardness and
microstructure was examined.
[0075] Table 1 shows relationship among mold temperature and
constraint time (holding time) by molds, pressing pressure, warping
deformation, hardness after heat treatment, and microstructure.
[0076] Table 1 also shows relationship among warping deformation,
hardness after heat treatment, and microstructure of a sample that
was high-frequency heated and thereafter water quenched, a sample
that was wholly heated and thereafter air-blow quenched, and a
sample that was high-frequency heated and air-cooled.
TABLE-US-00001 TABLE 1 Quality of Samples After Heat Treatment
Press Cooling or Quenching Pressing Warping Steel Mold Holding
Pressure Deformation Hardness Type Temperature Time (N/cm.sup.2)
(.mu.m) (HV) Structure Example of S53C 250 1 min 2.94 16 745 TM +
LB Present 300 1 min 2.94 18 730 TM + LB Invention 320 1 min 2.94
18 685 LB 300 5 min 2.94 18 710 LB 300 30 sec 2.94 19 730 TM + LB
30 1 min 2.94 20 750 M Comparative S53C High-Frequency Heated,
Without >250 740 M Example Thereafter Water Quenched Pressing
Wholly Heated, Thereafter Without 48 710 M Air-Blow Quenched
Pressing High-Frequency Heated, Without 29 510 T Thereafter
Air-Cooled Pressing Structure: TM refers to tempered martensite, LB
refers to lower bainite, M refers to quenched martensite, T refers
to troostite
[0077] From the result shown in Table 1, it can be seen that, as in
the example of the present invention, with the pressing pressure of
2.94N/cm.sup.2 (0.3 kgf/cm.sup.2), by setting the mold temperature
to at least 250.degree. C. and at most 320.degree. C. and the
constraint time (holding time) by molds to at least 30 seconds and
at most 5 minutes, isothermal transformation occurs and a structure
having lower bainite can be obtained. It can also be seen that, in
the structure of the example of the present invention having lower
bainite, warping deformation becomes at most 19 .mu.m, and Vickers
hardness HV becomes at least 685. Further, in part of the example
of the present invention, a structure similar to tempered
martensite that appears on tempering was observed, while tempering
was not performed.
[0078] Additionally, it can be seen that, as in the example of the
present invention, when continuous cooling was performed by setting
the mold temperature to 30.degree. C. and the constraint time
(holding time) by molds to 1 minute, martensite transformation
occurs and a structure having tempered martensite can be obtained.
It can also be seen that, in this sample, warping deformation
becomes 20 .mu.m, and Vickers hardness HV becomes 750.
[0079] As above, it has been shown that, with all samples of the
present invention, warping deformation becomes at most 20 .mu.m,
and Vickers hardness HV becomes at least 685.
[0080] On the other hand, samples of the comparative example were
in a quality in which warping deformation was more than 20 .mu.m
and which cannot attain Vickers hardness of at least HV 685.
[0081] As to the representative of these bearing rings, result of
performing life estimation with the condition shown in Table 2 is
shown in Table 3.
TABLE-US-00002 TABLE 2 Thrust Bearing Life Test Condition Bearing
Ring NTN Product Name AS1112(.phi.60 .times. .phi.85 .times. t1)
Cage, Roller Half (twenty-four) of Rollers of NTN Product Name
AXK1112 Number of 5000 rpm Revolutions Bearing Load 9.8 kN
Lubricating Oil VG10 Oil Film Parameter 0.101 Calculated Life 11.3
h (Considering Oil Film Parameter) Number of Test 6 pieces
Specimens
TABLE-US-00003 TABLE 3 Life Test Result of Samples Press Cooling or
Quenching Steel Heat Mold Holding Life Test Result Type Treatment
Temperature Time L10(h) L10 ratio Example of S53C High- 250 1 min
19.3 1.2 Present Frequency 300 1 min 16.5 1.0 Invention Heating 320
1 min 15.2 1.0 300 5 min 16.9 1.1 300 30 sec 17.2 1.1 30 1 min 15.8
1.0 Comparative S53C High-Frequency Heated, Without Test Impossible
Due to Example Thereafter Water Quenched Pressing Great Deformation
Wholly Heated, Thereafter Without L10 = 11.9 h Air-Blow Quenched
Pressing High-Frequency Heated, Without Test Impossible Due to
Thereafter Air-Cooled Pressing Low Hardness
[0082] Here, since the ring of the example of the present invention
subjected to isothermal transformation is partially or wholly
subjected to isothermal transformation, tempering was not
performed.
[0083] The rings of the example of the present invention subjected
to martensite transformation by continuous cooling quenching were
subjected to tempering of 150.degree. C..times.120 minutes. The
test was conducted under a scarce lubrication condition.
[0084] From the result of Table 3, it can be seen that L10 life of
the samples of the example of the present invention was at least
15.2 hours, which was increased. The sample of the comparative
example, which was high-frequency heated normally and thereafter
water quenched, was so deformed that it could not be tested. The
sample of the comparative example, which was wholly heated and
thereafter air-blow quenched, exhibited 11.9 hours of L10 life,
which was reduced. Despite being a thin component, the sample of
the comparative example, which was high-frequency heated and
thereafter air-cooled, was not quench-hardened.
[0085] From the result above, with the ring obtained by the present
method (the example of the present invention), warping deformation
can be suppressed, and hardness and life can be increased as
compared to the comparative example.
Example 2
[0086] As materials, mid-carbon steel S53C and steel of a
composition that is improved in quenching property and that can
attain sufficient hardness with slow cooling (0.7 mass % C--1.0
mass % Si--0.6 mass % Mn--1.5 mass % Cr--0.3 mass % Mo) were
used.
[0087] From these materials, thrusts needle bearing ring (NTN
product name: AS1112) having an outer shape of inner diameter 60
mm, outer diameter 85 mm, and thickness 1 mm was manufactured by
cutting.
[0088] Using a high-frequency induction heating apparatus (80 kHz)
and rotating the ring, induction heating was performed by allowing
prescribed current to flow through an induction coil arranged
closely to one end panel (FIG. 1). In this case, heating was
conducted slowly in order for the entire ring to attain a uniform
temperature (approximately 900.degree. C.). Thereafter, the ring
was set in upper and lower press molds made of iron and having a
heat capacity substantially greater than that of the ring, the ring
was immediately pressed by pressing at a prescribed pressure and
quench-hardened through mold cooling by pressing (FIG. 2). In this
case, by setting the pressing-pressure to at least approximately
2.94N/cm.sup.2, deformation/warping in quenching-hardening was
prevented. The time required for quench-hardening (the cooling time
until normal temperature was attained) was approximately two
second. The mass of one of upper and lower press molds used this
time was 3.4 kg at the lightest. As the mass of the ring was 22 g,
the heat capacity of one of the press molds was approximately 150
times as great as that of the ring.
[0089] Table 4 shows deformation state of conventional various
products and deformation state in the experiment conducted this
time.
TABLE-US-00004 TABLE 4 Quality of Samples After Heat Treatment
Pressing Warping Steel Heat Pressure Distortion Hardness Type
Treatment Quenching (N/cm.sup.2) (.mu.m) (HV) Example of S53C High-
Press- 0.98 47 730 Present Frequency Quenching Invention Heating
High- Press- 2.94 20 760 Frequency Quenching Heating High- Press-
9.80 19 770 Frequency Quenching Heating 0.7% C High- Press- 0.98 75
750 Steel Frequency Quenching Heating High- Press- 2.94 52 780
Frequency Quenching Heating High- Press- 9.80 48 775 Frequency
Quenching Heating Comparative S53C High- Water Without 690 740
Example Frequency Quenching Pressing Heating SCr 415 Carburizing
Oil 830 730 Quenching SPCC Carburizing Oil 715 730 Quenching SK5
Whole Oil 650 760 Heating Quenching SCr 415 Carburizing Air-Blow 99
730 Quenching SK5 Whole Air-Blow 78 750 Heating Quenching
[0090] From the result of Table 4, while conventional air-blow
quenching products show few warping, deformation or warping of the
products according to the present method still show smaller degree
than the air-blow quenching products, irrespective of the steel
types. Accordingly, distortion correction or warping correction
after heat treatment is not necessary. By setting pressing-pressure
to at least a prescribed value, deformation was suppressed to at
most a certain value. It should be noted that, as actual quenching
is not quenching using water soluble cooling agent or oil, the
periphery of the quenching mechanism can be maintained clean,
eliminating waste liquid processes.
[0091] After performing the aforementioned quenching to the test
rings, tempering at 150.degree. C. for two hours was performed, and
finishing process was performed on the surface thereof. Thus, the
rings were subjected to life estimation. The test was conducted
under a scarce lubrication condition. The rolling life test
condition was the same as the condition shown in Table 2. The test
result is shown in Table 5.
TABLE-US-00005 TABLE 5 Life Test Result of Samples Pressing Steel
Heat Pressure L10 life Life Type Treatment Quenching (N/cm.sup.2)
(h: hour) Ratio Example of S53C High- Press- 2.94 15.8 1.0 Present
Frequency Quenching Invention Heating High- Press- 9.80 17.7 1.1
Frequency Quenching Heating 0.7% C High- Press- 2.94 25.6 1.6 Steel
Frequency Quenching Heating High- Press- 9.80 27.9 1.8 Frequency
Quenching Heating Comparative S53C High- Water Without Test Example
Frequency Quenching Pressing Impossible Heating Due to SCr 415
Carburizing Oil Great Quenching Warping SPCC Carburizing Oil
Quenching SK5 Whole Oil Heating Quenching SCr 415 Carburizing
Air-Blow Without 15.9 1.0 Quenching Pressing SK5 Whole Air-Blow
13.8 0.9 Heating Quenching
[0092] From the result of Table 5, in the rings according to the
present method that provides less warping deformation, even S53C
attained the life of the conventional carburized product level. 0.7
mass % C steel attained longer life than the carburized steel. This
may be attributed to its higher content of C as compared to S53C,
which facilitates attaining high hardness. Additionally, it is
considered that much Si, Mo, and Cr content contributed to the long
life. The thin races in the shape of the present case exhibited
great warping deformation with free quenching by oil or water, and
therefore life test could not be conducted.
[0093] From the result above, with the rings (example of the
present invention) obtained through the present method, warping
deformation was suppressed as compared to the comparative example,
and the life thereof can be increased.
[0094] It should be understood that the embodiment and examples
disclosed herein are illustrative and non-restrictive in every
respect. The scope of the present invention is defined by the terms
of the claims, rather than the description above, and is intended
to include any modifications within the meaning and scope
equivalent to the terms of the claims.
INDUSTRIAL APPLICABILITY
[0095] The manufacturing method of the present invention is
advantageously applied to a manufacturing method of a thin
component, such as a ring of a thrust needle roller bearing or a
thin bearing ring, which tends to show great deformation in heat
treatment and to which a polishing process after the heat treatment
is not performed.
* * * * *