U.S. patent application number 16/359910 was filed with the patent office on 2019-07-18 for coating film and automotive part on which coating film is formed, and constant velocity universal joint.
The applicant listed for this patent is NTN CORPORATION. Invention is credited to Masato CHOKYU, Hiromi HAYASHI, Takafumi IWAMOTO, Shintaro SUZUKI, Kazuhiko YOSHIDA.
Application Number | 20190217334 16/359910 |
Document ID | / |
Family ID | 50068223 |
Filed Date | 2019-07-18 |
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United States Patent
Application |
20190217334 |
Kind Code |
A1 |
IWAMOTO; Takafumi ; et
al. |
July 18, 2019 |
COATING FILM AND AUTOMOTIVE PART ON WHICH COATING FILM IS FORMED,
AND CONSTANT VELOCITY UNIVERSAL JOINT
Abstract
The invention provides a coating film having excellent adhesion,
even without a chemical conversion film treatment being carried out
as an undercoat treatment, and a metal automotive part having the
coating film. A powder is deposited by powder-coating onto the
surface of a metal automotive part that has been quenched after
forging, and tempering of the metal automotive part and
bake-hardening of the deposited powder are carried out
simultaneously, thereby forming a skin film on the surface of the
metal automotive part. The surface of the metal automotive part
before the powder is powder-coated thereon is a work-hardened basis
material surface that has been not subjected to a chemical
conversion filming treatment.
Inventors: |
IWAMOTO; Takafumi;
(Shizuoka, JP) ; YOSHIDA; Kazuhiko; (Shizuoka,
JP) ; CHOKYU; Masato; (Shizuoka, JP) ; SUZUKI;
Shintaro; (Shizuoka, JP) ; HAYASHI; Hiromi;
(Shizuoka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NTN CORPORATION |
Osaka |
|
JP |
|
|
Family ID: |
50068223 |
Appl. No.: |
16/359910 |
Filed: |
March 20, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14420368 |
Feb 8, 2015 |
|
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|
PCT/JP2013/071592 |
Aug 9, 2013 |
|
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16359910 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F16D 3/20 20130101; C21D
2261/00 20130101; Y10T 428/31529 20150401; F16D 2250/0053 20130101;
B60B 2310/208 20130101; F16D 2250/0046 20130101; B60B 27/0036
20130101; B05D 2401/32 20130101; B60B 35/14 20130101; B60B 2310/616
20130101; F16D 2250/0023 20130101; Y10T 428/269 20150115; C21D
9/0068 20130101; B05D 2601/20 20130101; B05D 1/04 20130101; Y10T
428/31678 20150401; B05D 1/06 20130101; B05D 7/14 20130101; B60B
2900/141 20130101; B05D 3/0281 20130101; Y10T 428/294 20150115;
B05D 3/0254 20130101; B60B 2310/54 20130101; C21D 1/18 20130101;
F16D 3/223 20130101; C21D 1/42 20130101; F16D 2200/0086
20130101 |
International
Class: |
B05D 3/02 20060101
B05D003/02; F16D 3/20 20060101 F16D003/20; B05D 1/04 20060101
B05D001/04; B60B 27/00 20060101 B60B027/00; B05D 7/14 20060101
B05D007/14; B60B 35/14 20060101 B60B035/14 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 2012 |
JP |
2012-178011 |
Aug 8, 2013 |
JP |
2013-164831 |
Claims
1-12. (canceled)
13. A method of forming a coating film on a surface of a metal
automotive part, comprising: a powder-coating step in which a
powder is deposited by powder-coating on the surface of the metal
automotive part that has been quenched after forging, and a
tempering and bake-hardening step in which tempering of the metal
automotive part and bake-hardening of the deposited powder are
performed simultaneously, wherein the surface of the metal
automotive part before the powder is deposited thereon is a
work-hardened basis material surface and wherein in the
powder-coating step, the powder is deposited on a surface which is
the basis material surface, has not been subjected to a chemical
conversion film treatment and has been cleaned using an alkaline
detergent.
14. The method of forming a coating film according to claim 13,
characterized in that the basis material surface is a surface layer
that has been quenched after forging, and a turned face in which a
part of the surface layer has been turned.
15. The method of forming a coating film according to claim 13,
characterized in that the forging is cold forging, the surface
hardness after cold forging is HRB 90 to 110, and the surface
hardness after quenching is HRC 50 to 65.
16. The method of forming a coating film according to claim 13,
characterized in that the quenching is high-frequency quenching,
and tempering and powder bake-hardening are carried out by
high-frequency induction heating.
17. The method of forming a coating film according to claim 13,
characterized in that the powder is a pulverulent epoxy-based
powder coating composition.
18. The method of forming a coating film according to claim 17,
characterized in that the powder is a pulverulent coating
composition comprising a bisphenol A epoxy resin, a hydrazide
compound, and an inorganic filler.
19. The method of forming a coating film according to claim 18,
characterized in that the hydrazide compound is an organic acid
polyhydrazide.
20. The method of forming a coating film according to claim 18,
characterized in that the inorganic filler is barium sulfate.
21. The method of forming a coating film according to claim 13,
wherein the metal automotive part is an outer joint member
constituting a constant velocity universal joint, or an
intermediate shaft constituting a drive shaft.
22. The method of forming a coating film according to claim 21,
characterized in that the coating film on the outer joint member or
the intermediate shaft has a thickness of 40 to 150 .mu.m, a pencil
hardness of H to 2H, and a corrosion resistance of 120 hr or
greater as determined by a salt water spray test.
Description
TECHNICAL FIELD
[0001] The present invention relates to a metal automotive part,
and specifically relates to a coating film that is formed on the
surface of an outer joint member that constitutes a constant
velocity universal joint and/or an intermediate shaft that
constitutes a drive shaft.
BACKGROUND ART
[0002] Drive shafts that transmit power from an automotive engine
to the drive wheels must respond to angular displacement and axial
displacement arising due to changes in the relative positional
relationship between the engine and wheels. Therefore, a
configuration is typically provided in which a sliding-type
constant velocity universal joint is provided on the engine-side
(inboard side), and a fixed constant velocity universal joint is
provided on the drive wheel-side (outboard side), with the two
constant velocity universal joints linked by a metal intermediate
shaft.
[0003] Both the sliding constant velocity universal joint and the
fixed constant velocity universal joint that are installed on the
drive shaft have a metal outer coupling member that is constituted
by a cup that houses internal parts including an inner coupling
member that is linked to the intermediate shaft and a stem part
that extends integrally from this cup part in the axial
direction.
[0004] The metal automotive parts comprising the outer coupling
member of the constant velocity universal joint that is positioned
on the inboard side, the outer coupling member of the constant
velocity universal joint that is positioned on the outboard side,
and the intermediate shaft that links the two constant velocity
universal joints, are formed by forging, and thereafter
surface-hardened by a heating treatment carried out by quenching in
order to increase their strength or other attributes. After
quenching, the parts are tempered in order to increase toughness,
release some of the stress accompanying quenching, and prevent
quench-cracking. In addition, a resin coating film is formed on the
outer surfaces of these parts in order to improve corrosion
resistance.
[0005] In order to form an anti-corrosion coat-film on an object
such as an automobile, there are known in the art electrodeposition
coating compositions which comprise (A) a cationic resin, (B) a
low-temperature-dissociating block isocyanate hardener, and (C) a
pigment paste having a pigment that is dispersed with a
pigment-dispersing resin, where the pigment-dispersing resin has a
hydrophobic resin SP value prior to cation formation of 10.0 to
11.0 and contains 1.6 to 4.0 primary amino groups per molecule, and
where the A/B/C component ratios are 10 to 88/10 to 50/2 to 50.
This electrodeposition coating composition provides stability
during coating and corrosion resistance during rapid
low-temperature baking (5 to 50 min) (patent document 1).
[0006] However, with electrodeposition, producing a thick coating
film is a problem from the standpoint of the film-forming
mechanism, and electrodeposited coating films alone produce
insufficient corrosion resistance in some cases. In addition, a
long period of time may be required for coating film formation,
including the baking time.
[0007] With the objective of reducing costs and shortening
treatment times for baking coating agents and for tempering metal
automotive parts, there have been disclosed a method in which a
metal automotive part are subjected to high-frequency quenching,
and a powder coating is then applied to the outer surfaces of the
automotive parts after quenching, whereupon tempering and baking of
the automotive parts are carried out simultaneously by
high-frequency induction heating; and a manufacturing apparatus
associated with this method (patent document 2).
[0008] Other known methods used with metal automotive parts involve
manufacturing the outer joint member that constitutes the constant
velocity universal joint by cold-forging (patent document 3)
finishing the track groove of the outer joint member, the cup-inlet
chamfer, the track chamfer, and the track-inlet chamfer by
cold-forging (patent document 4).
[0009] However, when a coating film is formed on the surfaces of
the metal automotive parts, in order to improve adhesion of the
coating film, even with the powder coating method descried above, a
chemical conversion film treatment is carried out as an undercoat
treatment. This treatment is a treatment in which the corrosion
resistance, powder coating adhesion, and durability are increased
by coating the basis material (surface to be coated) with, e.g., a
manganese phosphate coating film, a zinc phosphate coating film, or
an iron phosphate coating film. The chemical conversion film
treatment increases manufacture costs because the treatment time is
lengthened, and it is difficult to control the chemical conversion
film thickness.
PRIOR ART DOCUMENTS
Patent Documents
[0010] Patent Document 1: Japanese Laid-Open Patent Application
Publication No. Hei 7-173415
[0011] Patent Document 2: International Application No.
WO2012/039255
[0012] Patent Document 3: Japanese Laid-Open Patent Application
Publication No. 2002-346688
[0013] Patent Document 4: Japanese Laid-Open Patent Publication No.
2009-185932
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0014] The present invention was devised in order to resolve the
aforementioned problems and pertains to a coating film for a metal
automotive part which is formed by simultaneously carrying out
tempering and powder coating bake-hardening of automotive parts
that have been quenched. An object of the present invention is to
provide a coating film that has superior adhesion without carrying
out a chemical conversion filming treatment as an undercoat
treatment, a metal automotive part that has this coating film, and
a constant velocity universal joint.
Means for Solving the Problem
[0015] The coating film for a metal automotive part of the present
invention is characterized in that a powder is deposited by
powder-coating on the surface of a metal automotive part that has
been quenched after forging, and tempering of the metal automotive
part and bake-hardening of the deposited powder are performed
simultaneously to form the coating film on the surface of the metal
automotive part; the surface of the metal automotive part before
the powder is deposited thereon being a work-hardened basis
material surface that has not been subjected to a chemical
conversion film treatment.
[0016] The invention also is characterized in that the basis
material surface of the metal automotive part is a surface layer
that has been quenched after forging, and a turned face in which a
part of the surface layer has been turned. The invention also is
characterized in that the basis material surface has been cleaned
using an alkaline detergent.
[0017] The invention also is characterized in that the forging is
cold forging, the surface hardness after cold forging is HRB 90 to
110, and the surface hardness after quenching is HRC 50 to 65.
[0018] The invention also is characterized in that the quenching is
high-frequency quenching, and the simultaneous tempering and powder
bake-hardening are carried out by high-frequency induction
heating
[0019] The invention also is characterized in that the powder that
is deposited by powder coating to the surface of the metal
automotive part is a pulverulent epoxy-based powder coating
composition.
[0020] The invention also is characterized in that, in particular,
the epoxy-based powder coating composition powder comprises a
bisphenol A epoxy resin, a hydrazide compound, and an inorganic
filler. The invention also is characterized in that the hydrazide
compound is an organic acid polyhydrazide. The invention also is
characterized in that the inorganic filler comprises barium
sulfate.
[0021] The invention also is characterized in that the metal
automotive part on which the coating film of the present invention
is formed is an outer joint member that constitutes a constant
velocity universal joint, or an intermediate shaft that constitutes
a drive shaft.
[0022] The invention also is characterized in that the coating film
on the outer joint member or the intermediate shaft has a thickness
of 40 to 150 .mu.m, a pencil hardness of H to 2H, and a corrosion
resistance of 120 hr or greater according to salt water spray
testing.
Effect of the Invention
[0023] The coating film for a metal automotive part of the present
invention is formed by depositing a powder by a powder coating
method involving the use of a specific powder coating composition
powder (referred to below as "powder coating") and, after forging
and subsequent quenching, tempering and bake-hardening of the
powder that has been deposited are carried out simultaneously.
Therefore, a coating film having superior corrosion resistance is
obtained, even with a work-hardened basis material surface, without
the pre-powder-deposition surface being subjected to a chemical
conversion film-forming treatment. In addition, because tempering
and bake-hardening of the powder are carried out simultaneously,
the time for tempering the metal automotive part and the time for
the coating treatment are shortened.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a partial cut-away axial sectional view of an
outer joint member that constitutes a constant velocity universal
joint.
[0025] FIG. 2 shows a schematic view of a high-frequency induction
heating device.
[0026] FIG. 3 shows a diagram of a specific example of a coil
passage-type high-frequency induction heating device.
[0027] FIG. 4 shows a diagram showing a specific example of a
multi-stage high-frequency induction heating device.
[0028] FIG. 5 shows a temperature chart for a multi-stage
high-frequency induction heating device.
[0029] FIG. 6 shows an example of an intermediate shaft.
[0030] FIG. 7 shows a diagram showing baking conditions.
[0031] FIG. 8 shows a photograph of a cross-section of a coating
film.
Mode for Carrying Out the Invention
[0032] The metal automotive part is formed by a forging method
using carbon steels for machine structural use and is manufactured
by quenching and tempering. The outer surfaces of the part are also
coated for rust-proofing. Work-hardening accompanying forging,
thermal stress accompanying quenching, quench strain due to
deformation stress, and other phenomena occur at the surface of the
part. In addition, various iron oxides with different oxidation
states are generated at the surface due to heating. For this
reason, the outer surfaces of the parts, which are to be coated
faces produced by, e.g., powder coating, have faces that are not
chemically or physically uniform, and adhesion of the coating film
to these faces is difficult to improve.
[0033] The outer joint member that constitutes the constant
velocity universal joint, in particular, is constituted by a cup
portion and a shaft portion, and the boundary part thereof often
has thickened walls. In some cases, thermal strain arises due to
differences in heating/cooling rates during coating film formation
at the thickened wall part and the cup portion, and a decrease in
adhesion of the coating film tends also to occur in such cases.
[0034] Therefore, in order to increase coating film adhesion, a
chemical conversion coating is typically formed as an undercoat
treatment prior to powder coating. However, it was discovered that
the adhesion of the coating film is increased by alkali treatment
alone, without formation of a chemical conversion film. The present
invention is based on this knowledge.
[0035] An example of a metal automotive part is shown in FIG. 1.
FIG. 1 is a partial cut-away axial sectional view of the outer
joint member constituting a constant velocity universal joint.
[0036] An outer joint member 1 is constituted by a cup portion 2
and a shaft portion 3 that extends in an axial direction from a
bottom part of this cup portion 2. The cup portion 2 has an inner
circumferential face 4 formed in the shape of a sphere, and a track
groove 5 that incorporates a track transfer ball (not shown) is
formed in a plurality of locations in the circumferential direction
of the inner circumferential face 4 extending in the axial
direction. The track groove 5 has a sectional shape along the
groove bottom that is an arc-shaped curved line. The surface of the
inner circumferential face 4 is the quenched layer.
[0037] The outer joint member 1 is manufactured by a forging
process involving a plurality of steps, including cold forging, hot
forging, and warm forging, starting from cylindrical stock using
carbon steel for machine structural use such as 540C, S43C, S45C,
S48C, 550C, S53C, S55C, and S58C as stipulated in JISG4051. In
particular, the final forging process is cold forging in order to
increase the mechanical strength at the surface. The temperature
during cold forging is preferably from 0.degree. C. to 50.degree.
C.
[0038] During cold forging, the work-hardened surface 2a of the
outer joint member 1 that has been plastically deformed as a result
of compression stress is dramatically higher in terms of tensile
strength, yield point, elastic limit, hardness, etc., but
dramatically lower in terms of elongation, contraction, etc.
[0039] In the present invention, the surface hardness of the outer
surface 2a after cold forging is preferably HRB 90 to 110. If the
surface hardness is less than HRB 90, the hardness of the basis
material will be insufficient, and when coating is carried out on
the outer surface 2a, the influence of the hardness of the basis
material will be felt, and the coating film hardness will decrease.
It is undesirable for the surface hardness to exceed 110, because
the machinability will decrease.
[0040] In addition, the surface hardness after quenching is
preferably HRC 50 to 65. If the surface hardness is less than HRC
50, the abrasion resistance will be insufficient, and the
rotational life will decrease. If the surface hardness exceeds 65,
then early failure, cracking, etc. may occur.
[0041] The surface hardness after cold forging and after quenching
is different depending on the portions of the outer surface 2a that
have different degrees of working, and therefore the surface state
will not be uniform.
[0042] In addition, there are cases in which the surface of the cup
portion 2 at the end towards the shaft portion 3 is turned after
cold forging.
[0043] The turned face may have different metal material structure
depending on the turned portion and the depth from the surface at
which the material is turned. Lubricating oil used during turning
will also remain at the surface in some cases.
[0044] For quenching, it is possible to use a device having a
heating part for heating the surface of the metal automotive part
to a high temperature at which an austenite structural state is
reached, and a cooling part for subsequently rapid-cooling the
component to achieve conversion to a martensitic structure. The
quenching method can be any one whereby the heating and cooling
described above can be carried out.
[0045] An example of the heating part is a high-frequency quenching
device employing a power source with a frequency of 1 KHz or
greater, and an example of the cooling part is a water spray
cooling device.
[0046] After quenching, a coating film 6 is formed on the outer
surface 2a of the outer joint member 1 in order to increase the
corrosion resistance. The coating film is formed by powder coating,
with tempering and baking carried out simultaneously. Tempering and
baking can be carried out using the method and the coil
passage-type or multistage-type high-frequency induction heating
device described, for example, in patent document 2.
[0047] The outer surface 2a on which the coating film 6 is formed
is a work-hardened face or a coated face on which both a
work-hardened face and turned face 2b are present together.
[0048] The coated face is not subjected to a chemical conversion
treatment such as a zinc phosphate or iron phosphate treatment and
a degreasing treatment that are typically carried out as
pretreatments for improving adhesion.
[0049] A cleaning treatment with an alkaline detergent is carried
out as a pretreatment.
[0050] The alkaline detergent may be any detergent that is composed
of an alkaline aqueous solution that can remove non-reactive soap
layers or reactive soap layers remaining on the outer surface 2a in
the cold forging and quenching step.
[0051] A preferred detergent is one that has an aqueous solution
containing, e.g., less than 5 mass % of sodium hydroxide as the
primary component. A preferred alkaline detergent is one that also
contains a surfactant that can effect, e.g., surface degreasing,
rust-proofing, and stripping of the metal automotive part.
[0052] Commercially-available alkaline detergents include ACRODINE
detergents (Kiwa Chemical), LIOMIC detergents (Lion Corp.), WA
detergents (Kaken Tech), and LIGHT-CLEAN (Kyoeisha Chemical).
[0053] Cleaning using the alkaline detergent can be carried out at
a temperature of 50 to 80.degree. C. using immersion cleaning,
spray cleaning, or ultrasonic cleaning.
[0054] The coating film 6 is formed by powder coating. The powder
that is used in powder coating is preferably an epoxy resin system,
polyester resin system, or acrylic resin system powder coating, or
a composite system powder coating which is a mixture thereof. The
powder coating method can involve producing a coating film
thickness of 50 .mu.m or greater in a single coating pass, and the
coating performance such as corrosion resistance can be
improved.
[0055] Among the powders described above, epoxy-system powder
coatings are preferred due to their excellent corrosion resistance,
acid resistance, alkali resistance, moisture resistance, and
surface hardness subsequent to coating film formation.
[0056] The epoxy-system powder coating that can be used in the
present invention is a powder coating comprising bisphenol A epoxy
resin as the epoxy resin, hydrazide compound as hardener, and an
inorganic filler.
[0057] The bisphenol A epoxy resin is an epoxy resin that is
obtained by a single-stage, or two-stage reaction method from
bisphenol A and epichlorohydrin. The bisphenol A epoxy resin has
heat-curing properties whereby bake-hardening can be carried out
simultaneously with respect to tempering of the metal automotive
part, and the material has excellent properties such as coating
film adhesion and corrosion resistance. Epoxy resins or the like
such as cyclic epoxy resins, novolak epoxy resins, and acrylic
epoxy resins may be used in conjunction with the bisphenol A epoxy
resin.
[0058] Examples of commercially-available bisphenol A epoxy resins
include Epo Tohto.RTM. YD-011 (epoxy equivalents 450 to 500 g/eq,
softening point 60 to 70.degree. C., Nippon Steel Chemical, Ltd.),
Epo Tohto YD-012 (epoxy equivalents 600 to 700 g/eq, softening
point 75 to 85.degree. C., Nippon Steel Chemical), Epo Tohto YD-013
(epoxy equivalents 800 to 900 g/eq, softening point 85 to
98.degree. C., Nippon Steel Chemical), Epo Tohto YD-014 (epoxy
equivalents 900 to 1000 g/eq, softening point 91 to 102.degree. C.,
Nippon Steel Chemical), Epo Tohto YD-017 (epoxy equivalents 1750 to
2100 g/eq, softening point 117-127.degree. C., Nippon Steel
Chemical), Epo Tohto YD-019 (epoxy equivalents 2400 to 3300 g/eq,
softening point 130 to 145.degree. C., Nippon Steel Chemical), Epo
Tohto YD-902 (epoxy equivalents 600 to 700 g/eq, softening point 82
to 92.degree. C., Nippon Steel Chemical), Epo Tohto YD-904 (epoxy
equivalents 900 to 1000 g/eq, softening point 96 to 107.degree. C.,
Nippon Steel Chemical), jER.RTM. Epoxy Resin 1001 (epoxy
equivalents 450 to 500 g/eq, softening point 64.degree. C.,
Mitsubishi Chemical, jER Epoxy Resin 1002 (epoxy equivalents 600 to
700 g/eq, softening point 78.degree. C., Mitsubishi Chemical), jER
Epoxy Resin 1003 (epoxy equivalents 670 to 770 g/eq, softening
point 89.degree. C., Mitsubishi Chemical), jER Epoxy Resin 1004F
(epoxy equivalents 875 to 975 g/eq, softening point 97.degree. C.,
Mitsubishi Chemical), jER Epoxy Resin 1005F (epoxy equivalents 950
to 1050 g/eq, softening point 107.degree. C., Mitsubishi Chemical),
Araldite.RTM. XAC5007 (epoxy equivalents 600 to 700 g/eq, softening
point about 90.degree. C., Ciba-Geigy Japan), Araldite GT7004
(epoxy equivalents 730 to 830 g/eq, softening point about
100.degree. C., Ciba-Geigy Japan), Araldite GT7097 (epoxy
equivalents 1650 to 2000 g/eq, softening point about 120.degree.
C., Ciba-Geigy Japan), DER-664.RTM. (epoxy equivalents 950 g/eq,
Dow Chemical), and DER-667 (Dow Chemical). These products may be
used individually, or two or more types may be used in
conjunction.
[0059] It is preferable to use a hydrazide compound as the hardener
for the bisphenol A epoxy resin. Organic acid polyhydrazides are
preferred among these hydrazide compounds. Any organic acid
polyhydrazide may be used, provided that it has two or more
hydrazide groups (--CO--NH--NH.sub.2) per molecule. Examples
include C.sub.2 to C.sub.40 aliphatic carboxylic acid dihydrazides
such as oxalic acid dihydrazide, malonic acid dihydrazide, succinic
acid dihydrazide, glutaric acid dihydrazide, adipic acid
dihydrazide, sebacic acid dihydrazide, and eicosanic diacid
dihydrazide; aromatic polyhydrazides such as phthalic dihydrazide,
terephthalic dihydrazide, isophthalic dihydrazide, pyromellitic
dihydrazide, pyromellitic trihydrazide, and pyromellitic
tetrahydrazide; monoolefinic unsaturated dihydrazides such as
maleic dihydrazide, fumaric dihydrazide, and itaconic dihydrazide;
and polyacrylic polyhydrazide.
[0060] Among them, aliphatic carboxylic dihydrazides are preferred,
and adipic acid dihydrazide is particularly preferred due to its
excellent coating film adhesion under conditions at which tempering
and baking are carried out simultaneously.
[0061] The hydrazide compound is blended in a ratio of 1 to 50
parts by mass with 100 parts by mass of epoxy resin.
[0062] A hardening accelerator can be used in the epoxy-based
powder coating along with the hardeners described above. Examples
of hardening accelerators include imidazole compounds. There are no
particular restrictions on the imidazole compound, and a compound
having imidazole groups may be used, e.g., Curazole.RTM. (Shikoku
Kasei).
[0063] It is preferable to use an inorganic filler for the
epoxy-system powder coating. Examples of inorganic fillers include
barium sulfate, talc, silica, calcium carbonate, feldspar,
wollastonite, alumina, titanium dioxide, iron oxide, and carbon
black.
[0064] Among them, barium sulfate and carbon black are essential
components.
[0065] The inorganic filler is blended in an amount of 10 to 150
parts by mass with 100 parts by mass of epoxy resin.
[0066] The epoxy-system powder coating can be manufactured using a
method that is well-known in the field of powder coatings. For
example, this coating can be manufactured by, e.g., a method
involving mixing raw materials such as a bisphenol A epoxy resin,
hydrazide compound, hardening accelerator, barium sulfate, and
carbon black with a Henschel mixer, etc., followed by melt-kneading
using a device that is well-known to persons skilled in the art,
such as an extruder or hot roller, followed by cooling, and then
milling and sizing. Melt-kneading is preferably carried out under
conditions that are at or below a temperature at which the
hardening reaction will not progress
[0067] The method for depositing the powder on the surface of the
metal automotive part by powder coating may be any method that is
well-known to persons skilled in the art, such as spray coating,
electrostatic powder coating, electric field fluidization
electrostatic coating, and fluidized coating. Electrostatic powder
coating is preferred in consideration of the surface shape of the
metal automotive part. Electrostatic powder coating can be carried
out using a gun system in which charged powder coating is sprayed
with a sprayer, or an electrostatic atomization system in which
repulsion in the charged coating itself is utilized.
[0068] An outer joint member constituting a constant velocity
universal joint is particularly preferably electrostatically powder
coated using a method in which coating is charged with a spray gun,
and the electrostatic force is used to coating epoxy-based powder
onto the surface of an outer joint member that has been
grounded.
[0069] Metal automotive parts having a powder coating applied to
the outer surfaces are subjected to simultaneous coating film
bake-hardening under the conditions at which the automotive part is
tempered. Tempering is carried out by high-frequency induction
heating. High-frequency induction heating can be carried out using,
e.g., the method and device described in patent document 2.
[0070] The high-frequency induction heating device is constituted
by a transport pathway such as a conveyor for conveying the outer
joint member having powder deposited to the outer surface by a
powder coating method subsequent to high-frequency quenching, and a
high-frequency induction coil that is disposed along the direction
of part transport of the transport pathway and whereby tempering
and bake-hardening of the outer joint member are carried out
simultaneously.
[0071] A schematic view of the high-frequency induction heating
device is shown in FIG. 2. FIG. 2(a) shows the schematic
configuration of the coil passage-type high-frequency induction
heating device, and FIG. 2(b) is a diagram of the schematic
configuration of the multistage-type high-frequency induction
heating device.
[0072] The coil passage-type high-frequency induction heating
device 7 shown in FIG. 2(a) is a device for continuously heating an
outer joint member 1 moving over a transport pathway 8 with a
high-frequency induction coil 9.
[0073] The multistage-type high-frequency induction heating device
7a shown in FIG. 2(b) is a device for intermittently heating the
outer joint member 1 that is moving on a conveyor pathway 8 with a
high-frequency induction coil 10.
[0074] A powder coating device (not shown) for powder coating
powder onto the outer surface of the outer joint member 1 after
high-frequency quenching is disposed at a pre-stage of the coil
passage-type or multistage-type high-frequency induction heating
device. In addition, a water-cooling and air-blowing device (not
shown) for cooling the outer joint member 1 is disposed at a
downstream stage of the high-frequency induction heating
device.
[0075] A specific example of the coil passage-type high-frequency
induction heating device is shown in FIGS. 3(a) and (b). FIGS. 3(a)
and (b) are sectional views in the direction perpendicular to the
transport direction of the outer joint member 1.
[0076] In the high-frequency induction heating device shown in FIG.
3(a), there is provided a high-frequency induction coil 9a disposed
so that a part extends in a straight line along the part conveying
direction on both sides of the transport pathway 8. The straight
parts of the high-frequency induction coil 9 of the high-frequency
induction heating device heat the outer joint member 1 on the
transport pathway 8 from both sides. The coil in the straight parts
that are disposed on one side of the transport pathway 8 and the
coil in the straight parts that are disposed on the other side,
although not shown in the drawings, form a high-frequency induction
coil by being electrically connected so as to not impede entry and
exit of the outer joint member 1 at the entrance side and exit side
of the transport pathway 8.
[0077] The high-frequency induction heating device shown in FIG.
3(b) has a high-frequency induction coil 9b that is wound in a
spiral along the part conveying direction of the transport pathway
8 so as to enclose the outer joint member 1 on the transport
pathway 8. The high-frequency induction coil 9b of this
high-frequency induction heating device is disposed so that the
entire body extends along the part conveying direction of the
transport pathway 8. This high-frequency induction coil 9b heats
the outer joint member 1 on the transport pathway 8 from the entire
circumference.
[0078] The high-frequency induction coil can be a combination of
the device shown in FIG. 3(a) and the device shown in FIG.
3(b).
[0079] A specific example of the multi-stage high-frequency
induction heating device is shown in FIG. 4. FIG. 4 is a
configuration diagram showing a specific example of the
multistage-type high-frequency induction heating device shown in
FIG. 2(b).
[0080] The high-frequency induction heating device having the
format shown in FIG. 4 has a structure in which heating positions P
at which the outer joint member 1 is heated by the high-frequency
induction coil 10 and cooling positions Q at which the outer joint
member 1 is allowed to cool are repeatingly disposed in an
alternating manner along the part conveying direction of the
transport pathway 8 that conveys the outer joint member 1. With
this device, the high-frequency induction coils 10 that are wound
as spirals are disposed above the transport pathway 8 in heating
position P. An elevation mechanism (not shown) for vertically
moving a stand 8a on which the outer joint member 1 is carried is
present at this heating position P, and the outer joint member 1 is
housed inside the high-frequency induction coil 10 by elevating the
outer joint member 1 with this mechanism. The outer joint member 1
that moves over the transport pathway 8 is elevated at the heating
position P, housed inside the high-frequency induction coil 10, and
heated under predetermined conditions described below. The member
is then allowed to cool on the transport pathway 8 in the cooling
position Q. As shown in FIG. 5, heating and cooling are repeated,
and tempering of the outer joint member and bake-hardening of the
powder coating are carried out simultaneously.
[0081] Any high-frequency power source can be used for the
high-frequency induction heating device, provided that it supplies
high-frequency current to the heating coil. Examples include an
electric generator oscillator, an electron tube oscillator, a
thyristor inverter oscillator, and a transistor inverter
oscillator. A current transformer (output transformer) may also be
provided in order to supply high current at low-voltage to the
heating coil side.
[0082] There are no particular restrictions on the frequency of the
high-frequency current, but the current is typically of a frequency
of 1 kHz or above. If the frequency is increased, only the vicinity
of the surface of the part will be heated due to an eddy current
surface skin effect, whereas if the frequency is decreased, heating
will extend into the interior.
[0083] The outer joint member onto which powder has been deposited
at the outer surface by powder coating using the high-frequency
induction heating device described above is heated from room
temperature to the maximum attained temperature of 200 to
240.degree. C. over a period of about 3 to 5 min. Tempering of the
outer joint member 1 and bake-hardening of the powder coating are
then carried out simultaneously under these heating conditions.
Subsequently, the outer joint member 1 is transported to the
cooling position and is cooled while being transported, then cooled
with a water-cooling and an air-blowing device for a period of
about 1 to 3 min.
[0084] An example of the metal automotive part on whose surface a
coating film has been powder coated is an outer joint member that
constitutes a constant velocity universal joint, or an intermediate
shaft that constitutes a drive shaft. An example of an intermediate
shaft that links a pair of constant velocity universal joints and
constitutes a drive shaft is shown in FIG. 6.
[0085] With the intermediate shaft 11, the two shaft end parts 12
are linked to the inner joint member of the constant velocity
universal joint, and therefore a coating film is formed on the
outer circumferential face (cross-hatched part 14) of the shaft
center part 13, excluding at least the two shaft end parts 12. The
metal automotive part of the present invention can be utilized in a
hub constituting a wheel bearing device, and, in such a case, the
region in which the coating film is formed is the hub pilot
part.
[0086] The coating film that is formed on the surface of the
intermediate shaft or the outer joint member preferably has a
thickness of 40 to 150 .mu.m. Corrosion resistance will be inferior
if the thickness is less than 40 .mu.m, whereas the powder coating
will not sufficiently adhere to the face to be coated if the
thickness exceeds 150 .mu.m, the bake-hardening time will increase,
and running will tend to occur in the coating film after
bake-hardening.
[0087] The coating film preferably has a coating film hardness of H
to 2H in terms of pencil hardness, and the corrosion resistance as
determined by a salt water spray test is preferably 120 hr or
greater. If the pencil hardness is less than H, then the coating
may separate by external contact (stepping stones, etc.), whereas
flexibility will decrease if the hardness exceeds 2H.
[0088] Regarding corrosion resistance as determined by the salt
water spray test, the corrosion resistance is improved to 120 hr or
greater over conventional coating films such as water-soluble baked
coatings, because a thick coating film can be formed.
[0089] The constant velocity universal joint of the present
invention has an outer joint member with a powder coated surface
coating film as described above, an inner joint member, a drive
shaft that is linked to the inner joint member, and boots that are
installed on the outer joint member and drive shaft, directly or
with another member interposed. The coating film is formed on the
intermediate shaft surface of the drive shaft.
[0090] The following examples are presented in regard to the
structure of the constant velocity universal joint. The outer joint
member and drive shaft described above can be utilized in all of
the structures.
[0091] By forming the coating film of the present invention, the
treatment time required for coating film formation is decreased,
the characteristics of the resulting coating film are exceptional,
and a constant velocity universal joint with excellent durability
can be manufactured with excellent productivity.
[0092] (A) A structure which has an outer universal joint on which
three straight track grooves are formed in the inner
circumferential face, extending in the axial direction, a tripod
member serving as the inner joint member having three trunnion
shafts that are provided so as to protrude in the radial direction,
and rollers serving as rotating bodies that are rotatably supported
on the trunnion shafts of the tripod member, with the rollers
disposed so as to rotate freely along the track grooves of the
outer joint member.
[0093] (B) A structure which has an outer joint member in which a
plurality of straight track grooves are formed in the cylindrical
inner circumferential face extending in the axial direction, an
inner joint member in which a plurality of straight track grooves
forming pairs with the track grooves of the outer joint member are
formed in the spherical outer circumferential face, balls (3 to 8)
provided as rotating bodies that are disposed between the track
grooves of the outer joint member and the track grooves of the
inner joint member, and a cage that retains the balls that are
provided between the outer joint member and inner joint member.
[0094] (C) A structure which has an outer joint member in which a
plurality of straight track grooves are formed in the inner
circumferential face, an inner joint member having a structure in
which a plurality of straight track grooves that form pairs with
the track grooves of the outer joint member are formed in the outer
circumferential face, with these track grooves and the track
grooves of the outer joint member being inclined with respect to
each other at a predetermined angle in the reverse direction with
respect to the axis, balls (4, 6, 8, 10) that are interposed at the
intersections of the outer joint member track grooves and inner
joint member track grooves, and a cage that retains the balls
between the outer joint member and inner joint member.
[0095] The constant velocity universal joint having the coating
film of the present invention can have any configuration and is not
limited to sliding constant velocity universal joints provided with
a mechanism that slides in the axial direction of the outer joint
member such as the tripod-type, double offset-type, or
crossed-groove type described above. The joint therefore can be
used as a fixed constant velocity universal joint of the type that
employs balls, such as a Zeppa type (Birfield type). The
tripod-type constant velocity universal joint also may be a double
roller-type or single roller-type.
EXAMPLES
Example 1
[0096] The outer joint member shown in FIG. 1 was cold forged from
cylindrical stock using carbon steel for machine structural use
(S53C). The axial length of the cup portion was 88.4 mm, the outer
profile was 84.8 mm, the shaft portion length was 81.9 mm, and the
diameter was 34.9 mm. The surface hardness of the outer surface 2c
after cold forging was HRB 99.
[0097] After cold forging, the surface portion was subjected to
high-frequency quenching. After quenching and before tempering,
cleaning was carried out by immersion in alkaline detergent
(ACRODINE, Kiwa Chemical Industry) having a pH of 12 and a
surfactant as the primary component, whereupon the material was
rinsed with water and dried.
[0098] Epoxy-based powder coating (POWDAX.RTM. E70, Nippon Paint)
was applied onto the surface of the cup portion using a corona
discharge-type electrostatic powder coater.
[0099] After powder coating, the high-frequency induction heating
device shown in FIG. 2(a) and FIG. 3(a) was used, and annealing of
the outer joint member and bake-hardening of the powder were
carried out simultaneously. A coating film was formed on the
surface of the outer joint member. The baking conditions are shown
in FIG. 7, and a cross-sectional photograph of the coating film is
shown in FIG. 8. FIG. 8(a) is a sectional view of the coating film
that was formed on a turned face, and FIG. 8(b) is a sectional view
of the coating film that was formed on a forged face. An oxide
coating film was confirmed at the boundary between the basis
material and the coating film in the cross-section of the coating
film that was formed on the forged face.
[0100] The characteristics of the coating film of the outer joint
member obtained by the method described above, i.e., coating film
hardness, corrosion resistance determined by a salt water spray
testing, and water resistance and oil resistance determined by
immersion methods were evaluated by the evaluation methods
described below. Water resistance was also measured for the
examples in which a chemical conversion treatment was carried out
as a pretreatment and in which alkali cleaning was similarly
carried out. The results are shown in Table 1.
(1) Coating Film Hardness
[0101] The pencil hardness was measured according to "Scratch
Hardness (Pencil Hardness Method)" as described in JIS K 5600
paragraph 5.4.
(2) Corrosion Resistance (Salt Water Spray Test)
[0102] The outer joint member on which the coating film had been
formed was evaluated by a salt water spray testing as described in
JIS Z 2371. The salt water spray conditions involved continuous
spraying of the coating film face for 120 hr with a 5-mass % NaCl
aqueous solution having a pH of 6.5 to 7.2 during the salt water
spray test maintaining 35.degree. C. The presence of rust was then
evaluated visually.
(3) Water Resistance
[0103] The outer joint member on which the coating film had been
formed was then immersed for 48 hr in 40.degree. C. purified water,
then dried. The adhesive performance was then measured as described
in JIS K 5600 paragraph 5.6.
(4) Oil Resistance
[0104] After the outer joint member on which a thin film had been
formed for 96 hr was immersed in engine oil at room temperature,
the liquid resistance was measured as described in JIS K 5600,
paragraph 6.1.
Example 2
[0105] With the exception that the alkali detergent was changed to
an all-purpose detergent (WA-2061.RTM., Kaken Tech), a coating film
was formed on the cup part surface of an outer joint member in the
same manner as in Example 1. The coating film characteristics were
measured in the same manner as in Example 1, and the results are
presented in Table 1.
Comparative Example 1
[0106] With the exception that alkali cleaning was not carried out,
and a cleaning method involving cleaning with 60.degree. C.
purified water was utilized, a coating film was formed on the cup
part surface of an outer joint member in the same manner as in
Example 1. The coating film characteristics were measured in the
same manner as in Example 1, and the results are presented in Table
1.
Comparative Example 2
[0107] With the exception that alkali cleaning was not carried out,
but a chemical conversion treatment was carried out with iron
phosphate, a coating film was formed on the cup part surface of an
outer joint member in the same manner as in Example 1. The coating
film characteristics were measured in the same manner as in Example
1, and the results are presented in Table 1.
TABLE-US-00001 TABLE 1 Coating film Corrosion Water Oil hardness
resistance resistance resistance Example 1 H No rust Good coating
Good coating film film Example 2 H No rust Good coating Good
coating film film Comparative H Coating film Coating film Good
coating Example 1 separation separation film Comparative H Coating
film Coating film Good coating Example 2 separation separation
film
INDUSTRIAL APPLICABILITY
[0108] The coating film of the present invention has superior
corrosion resistance and therefore is suitable for use on metal
automotive parts such as constant velocity universal joints.
EXPLANATION OF REFERENCE NUMERALS AND SYMBOLS
[0109] 1 Outer joint member [0110] 2 Cup portion [0111] 3 Shaft
portion [0112] 4 Inner circumferential face [0113] 5 Track groove
[0114] 6 Coating film [0115] 7 Coil passage-type high-frequency
induction heating device [0116] 7a Multistage-type high-frequency
induction heating device [0117] 8 Transport pathway [0118] 8a Stand
[0119] 9, 9a, 9b, 10 High-frequency induction coil [0120] 11
Intermediate shaft [0121] 12 Shaft end part [0122] 13 Shaft middle
part [0123] 14 Cross-hatched part
* * * * *