U.S. patent application number 14/906209 was filed with the patent office on 2016-06-09 for sintered alloy valve guide and its production method.
This patent application is currently assigned to KABUSHIKI KAISHA RIKEN. The applicant listed for this patent is KABUSHIKI KAISHA RIKEN. Invention is credited to Rintarou TAKAHASHI.
Application Number | 20160160700 14/906209 |
Document ID | / |
Family ID | 52393284 |
Filed Date | 2016-06-09 |
United States Patent
Application |
20160160700 |
Kind Code |
A1 |
TAKAHASHI; Rintarou |
June 9, 2016 |
SINTERED ALLOY VALVE GUIDE AND ITS PRODUCTION METHOD
Abstract
To provide a sintered alloy valve guide having high thermal
conductivity and excellent wear resistance, which can be used in
engines subjected to a large thermal load due to downsizing, direct
injection and supercharging, the sintered alloy has a composition
comprising by mass 10-90% of Cu, 0-10% of Cr, 0-6% of Mo, 0-8% of
V, 0-8% of W, and 0.5-3% of C, the balance being substantially Fe
and inevitable impurities, the total amount of Cr, Mo, V and W
being 2% or more, and a structure comprising an Fe-based alloy
phase, a Cu or Cu-based alloy phase, and a graphite phase.
Inventors: |
TAKAHASHI; Rintarou;
(Kumagaya-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA RIKEN |
Tokyo |
|
JP |
|
|
Assignee: |
KABUSHIKI KAISHA RIKEN
Tokyo
JP
|
Family ID: |
52393284 |
Appl. No.: |
14/906209 |
Filed: |
July 22, 2014 |
PCT Filed: |
July 22, 2014 |
PCT NO: |
PCT/JP2014/069284 |
371 Date: |
January 19, 2016 |
Current U.S.
Class: |
419/35 ; 420/495;
420/61; 420/90 |
Current CPC
Class: |
C22C 38/24 20130101;
C22C 1/0425 20130101; C22C 38/20 20130101; B22F 1/0059 20130101;
B22F 5/008 20130101; C22C 38/22 20130101; B22F 3/16 20130101; C22C
38/12 20130101; B22F 2301/10 20130101; C22C 38/36 20130101; C22C
37/00 20130101; C22C 30/02 20130101; C22C 33/0278 20130101; F01L
3/08 20130101; C22C 37/06 20130101; C22C 38/00 20130101; B22F 1/025
20130101; C22C 9/00 20130101; B22F 2301/35 20130101 |
International
Class: |
F01L 3/08 20060101
F01L003/08; B22F 3/16 20060101 B22F003/16; B22F 5/00 20060101
B22F005/00; C22C 9/00 20060101 C22C009/00; C22C 38/12 20060101
C22C038/12; C22C 38/36 20060101 C22C038/36; C22C 38/24 20060101
C22C038/24; C22C 38/22 20060101 C22C038/22; C22C 38/20 20060101
C22C038/20; B22F 1/00 20060101 B22F001/00; C22C 30/02 20060101
C22C030/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 26, 2013 |
JP |
2013-155336 |
Claims
1. A sintered alloy valve guide having a composition comprising by
mass 10-90% of Cu, 0-10% of Cr, 0-6% of Mo, 0-8% of V, 0-8% of W,
and 0.5-3% of C, the balance being substantially Fe and inevitable
impurities, the total amount of Cr, Mo, V and W being 2% or more,
and having a structure comprising an Fe-based alloy phase, a Cu or
Cu-based alloy phase, and a graphite phase.
2. The sintered alloy valve guide according to claim 1, wherein
said Fe-based alloy phase is an Fe--Mo--C alloy, an
Fe--Cr--Mo--V--C alloy, an Fe--Cr--V--W--C alloy, or an
Fe--Cr--Mo--V--W--C alloy.
3. The sintered alloy valve guide according to claim 2, wherein
said Fe-based alloy phase has a composition comprising by mass
0-10% of Cr, 0-6% of Mo, 0-8% of V, 0-8% of W, and 0.5-1% of C, the
balance being substantially Fe and inevitable impurities, the total
amount of Cr, Mo, V and W being 2% or more.
4. The sintered alloy valve guide according to claim 1, wherein
said Cu or Cu-based alloy phase is continuous in the structure.
5. The sintered alloy valve guide according to claim 4, wherein
said Cu or Cu-based alloy phase has thermal conductivity of 200
W/mK or more.
6. A method for producing a sintered alloy valve guide comprising
the steps of coating prealloy powder having a composition
comprising by mass 0-10% of Cr, 0-6% of Mo, 0-8% of V, 0-8% of W,
and 0.5-1% of C, the balance being substantially Fe and inevitable
impurities, the total amount of Cr, Mo, V and W being 2% or more,
with Cu, mixing the Cu-coated prealloy powder with C powder, and
then molding and sintering.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a valve guide for guiding
the opening and closing of an engine valve, and its production
method, particularly to a high-thermal-conductivity valve guide
capable of suppressing valve temperature elevation, and its
production method.
BACKGROUND OF THE INVENTION
[0002] Though valve guides for automobile engines were
conventionally castings, they have been replaced by sintered alloy
parts produced in near-net shapes by powder metallurgy without
needing machining, and their production has been increasing at high
ratios. As an example of the sintered alloy valve guides, JP
6-306554 discloses a sintered alloy valve guide having a
pearlite-based matrix having a composition comprising by weight
1-4% of C, 1.5-6% of Cu, and 0.1-0.8% of P, the balance being Fe
and inevitable impurities, in which Fe--C--P compounds and free
graphite are dispersed.
[0003] In recent gasoline engines for automobiles, attempts have
been carried out to improve combustion efficiency by combining
various technologies of downsizing, direct injection,
supercharging, etc., for lower fuel consumption, lower emission,
and higher power. Improvement in the combustion efficiency is
achieved by reducing various losses, and attention is paid
particularly to exhaust loss, which occupies a high ratio of the
loss. To reduce the exhaust loss, compression ratios have been
increased. Higher compression ratios are inevitably accompanied by
abnormal combustion such as knocking, etc. because of higher engine
temperatures, needing the cooling of combustion chambers.
Particularly near exhaust valves exposed to high temperatures,
cooling must be improved, requiring valve guides acting to cool
valves to have high cooling capability.
[0004] Valve guides having high valve-cooling capability are made
of, for example, brass, but they suffer poor material properties
such as insufficient wear resistance, etc., and cost disadvantages
such as higher machining cost than conventional iron-based valve
guides, etc. Accordingly, sintered alloy valve guides having high
valve-cooling capability and wear resistance while meeting cost
requirements are desired.
[0005] As an iron-based sintered alloy valve guide having better
wear resistance than a conventional level for recent engines having
higher performance and higher fuel efficiency, JP 11-323512 A
discloses a sintered iron-based alloy valve guide produced by
mixing, molding and sintering Fe powder, C powder and Cu--Ni alloy
powder, which has a structure in which fine precipitates of a free
graphite phase having an average particle size of 30 .mu.m or less
are dispersed in a matrix of an Fe-based alloy phase bound by a
Cu-based alloy phase, the Fe-based alloy phase having a composition
comprising by weight 20-40% of Cu, 0.6-14% of Ni, and 1.0-3.0% of
C, the balance being Fe and inevitable impurities.
OBJECT OF THE INVENTION
[0006] In view of the above problems, an object of the present
invention is to provide a sintered alloy valve guide having high
thermal conductivity and excellent wear resistance, which can be
used in engines subjected to a large thermal load due to
downsizing, direct injection and supercharging, and a method for
producing such a sintered alloy valve guide.
DISCLOSURE OF THE INVENTION
[0007] As a result of intensive research on sintered alloy valve
guides for engines, the inventor has found that the use of an
Fe-based alloy powder containing elements selected from Cr, Mo, W
and V, which is coated with Cu, provides a sintered alloy valve
guide having high wear resistance and thermal conductivity.
[0008] Thus, the sintered alloy valve guide of the present
invention has a composition comprising by mass 10-90% of Cu, 0-10%
of Cr, 0-6% of Mo, 0-8% of V, 0-8% of W, and 0.5-3% of C, the
balance being substantially Fe and inevitable impurities, the total
amount of Cr, Mo, V and W being 2% or more, and a structure
comprising an Fe-based alloy phase, a Cu or Cu-based alloy phase,
and a graphite phase.
[0009] The Fe-based alloy phase is preferably an Fe--Mo--C alloy,
an Fe--Cr--Mo--V--C alloy, an Fe--Cr--V--W--C alloy, or an
Fe--Cr--Mo--V--W--C alloy. It preferably has a composition
comprising by mass 0-10% of Cr, 0-6% of Mo, 0-8% of V, 0-8% of W,
and 0.5-1% of C, the balance being substantially Fe and inevitable
impurities, the total amount of Cr, Mo, V and W being 2% or
more.
[0010] The Cu or Cu-based alloy phase is preferably continuous in
the structure. The Cu or Cu-based alloy phase preferably has
thermal conductivity of 200 W/mK or more.
[0011] The sintered alloy valve guide of the present invention is
produced by coating prealloy powder having a composition comprising
by mass 0-10% of Cr, 0-6% of Mo, 0-8% of V, 0-8% of W, and 0.5-1%
of C, the balance being substantially Fe and inevitable impurities,
the total amount of Cr, Mo, V and W being 2% or more, with Cu,
mixing the Cu-coated prealloy powder with C powder, and then
molding and sintering.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is an optical photomicrograph showing the structure
of the sintered alloy valve guide of Example 1.
[0013] FIG. 2 is a schematic view showing a wear test.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] The sintered alloy valve guide of the present invention has
a composition comprising by mass 10-90% of copper (Cu), 0-10% of
chromium (Cr), 0-6% of molybdenum (Mo), 0-8% of vanadium (V), 0-8%
of tungsten (W), and 0.5-3% of carbon (C), the balance being iron
(Fe) and inevitable impurities, the total amount of Cr, Mo, V and W
being 2% or more. The sintered alloy valve guide of the present
invention also has a structure comprising an Fe-based alloy phase,
a Cu or Cu-based alloy phase, and a graphite phase contributing to
wear resistance, thermal conductivity, and self-lubrication. The
Fe-based alloy phase comprises Fe as a main component, and the
Cu-based alloy phase comprises Cu as a main component.
[0015] In the sintered alloy valve guide of the present invention,
Cu is an indispensable alloy component to have high thermal
conductivity. The thermal conductivity of the sintered alloy valve
guide is preferably 30 W/(mK) or more, more preferably 50 W/mK or
more. Less than 10% by mass of Cu generates an insufficient liquid
phase, as well as an insufficient Cu or Cu-based alloy phase,
failing to obtain a dense sintered alloy having desired thermal
conductivity. On the other hand, more than 90% by mass of Cu forms
too small an amount of the Fe-based alloy phase, resulting in poor
wear resistance. Thus, Cu is 10-90% by mass. Cu is preferably 30%
or more by mass and 80% or less by mass, more preferably 75% or
less by mass. Because thermal conductivity is mostly governed by
the motion of free electrons in crystal grains in the metal, less
solid solution elements provide higher thermal conductivity.
Accordingly, it is important to reduce the amounts of elements
dissolved in Cu. In this sense, Mo, V, W, C, Cr and Fe do not have
adverse influence on the thermal conductivity of Cu, because Mo, V,
W and C are not substantially dissolved in Cu, and because Cr and
Fe form a mixed structure with Cu by cooling from a high
temperature at which they are slightly dissolved in Cu.
Accordingly, the Cu-based alloy phase in the present invention may
be a Cu--Cr alloy, a Cu--Fe alloy or a Cu--Cr--Fe alloy. Each of
these Cu-based alloy phases can have thermal conductivity of 200
W/mK or more. Ni is not contained in the present invention, because
Ni forms a solid solution with Cu at any ratio, undesirably
extremely reducing the thermal conductivity.
[0016] Cr, Mo, V and W are dissolved in the Fe-based alloy phase,
contributing to improvement in strength and hardness. They further
form carbides to improve wear resistance. When the total amount of
Cr, Mo, V and W is less than 2.0% by mass, good heat resistance and
wear resistance cannot be obtained. On the other hand, when Cr
exceeds 10% by mass, when Mo exceeds 6% by mass, or when each of V
and W exceeds 8% by mass, excessive or coarse precipitates are
formed, weakening the Fe-based alloy phase, increasing the
attacking of a mating member, or suffering breakage when pressed
into a cylinder head. Accordingly, the amounts of Cr, Mo, V and W
added are by mass 0-10% of Cr, 0-6% of Mo, 0-8% of V, and 0-8% of
W, the total amount of Cr, Mo, V and W being 2% or more. The upper
limit of the total amount of Cr, Mo, V and W is 32% by mass, but it
is preferably 16% or less by mass taking into consideration the
attacking of a mating member.
[0017] C is dissolved in the Fe-based alloy phase or forms
carbides, to improve the strength and hardness of the alloy. It is
also dispersed as graphite, imparting self-lubrication to the
alloy. When C is less than 0.5% by mass, sufficient carbides are
not precipitated, failing to obtain the above effects. On the other
hand, when C exceeds 3% by mass, excessive carbides or too coarse
carbides are precipitated, resulting in reduced toughness, and thus
lower performance. Accordingly, C is 0.5-3% by mass.
[0018] In the production method of the sintered alloy valve guide
of the present invention, Fe-based alloy powder having a
composition comprising by mass 0-10% of Cr, 0-6% of Mo, 0-8% of V,
0-8% of W, and 0.5-1% of C, the balance being substantially Fe and
inevitable impurities, the total amount of Cr, Mo, V and W being 2%
or more, is used as a starting material powder. A Cu component may
be added by mixing the Fe-based alloy powder with a Cu or Cu-based
alloy powder, or by coating the Fe-based alloy powder with Cu. A Cu
coating may be formed by plating the Fe-based alloy powder with Cu,
the mechanical alloying of the Fe-based alloy powder with Cu
powder, etc., and Cu plating is preferable. The Fe-based alloy
powder is preferably formed by water atomization, and subjected to
immersion plating in an electroless plating solution to form a
predetermined Cu component layer. The C powder is preferably
graphite powder having an average particle size of 1-20 .mu.m. The
starting material powder may contain stearate, etc. as a parting
agent.
[0019] The above starting material powders are mixed, and the
resultant mixed powder is charged into a die, compression-molded by
pressing, etc., degreased, if necessary, and then sintered at
900-1050.degree. C. in vacuum. The sintering temperature of lower
than 900.degree. C. fails to obtain a sintered body having a
desired structure because of an insufficient liquid phase formed
from Cu or its alloy, and the sintering temperature of higher than
1050.degree. C. cannot keep a predetermined shape of the sintered
body because of too much a liquid phase formed from Cu or its
alloy. The sintering temperature is 900-1050.degree. C.
EXAMPLE 1
[0020] Fe-based prealloy powder having a composition comprising by
mass 1.33% of Cr, 2.67% of Mo, 4.00% of V and 0.57% of C was
electroless-plated with Cu, to form Cu-coated powder (Cu: 45.5% by
mass per 100% by mass of the entire powder), and mixed with
graphite powder to form mixed powder (C: about 2% per 100% of the
entire mixture). 0.5% by mass of zinc stearate was added to and
blended with 100% by mass of the mixed powder to form a starting
material powder mixture. This starting material powder mixture was
charged into a die, and compression-molded by pressing at pressure
of 6.5 t/cm.sup.2 to form a green body, which was degreased, and
then sintered at 1000.degree. C. in vacuum to produce a cylindrical
sintered body of 15 mm in diameter and 50 mm in height.
[0021] FIG. 1 is an optical photomicrograph showing the structure
of the sintered body of Example 1. The sintered body had a
relatively dense structure comprising relatively coarse Fe-based
alloy phase particles 1, a Cu (or Cu-based alloy) phase 2, and
relatively fine graphite phase particles 3, with pores 4 slightly
observed. It is characterized by a continuous Cu (or Cu-based
alloy) phase 2.
[0022] [1] Wear Test
[0023] A valve guide test piece of 10 mm.times.50 mm.times.10 mm
was machined from the cylindrical sintered body, and a valve test
piece (sliding mating member) of 8 mm in diameter and 30 mm in
length, whose one end had an 8-mm-R cylindrical surface, was cut
out of an SUH alloy valve material. As shown in FIG. 2, the valve
test piece 6 was pushed to the reciprocally moving valve guide test
piece 5 under a constant load to evaluate wear resistance. The test
conditions were as follows.
[0024] Pushing load: 50 N,
[0025] Test temperature: 200.degree. C.,
[0026] Lubrication: No (dry),
[0027] Stroke: 25 mm
[0028] Sliding speed: 166 mm/second, and
[0029] Test time: 3 hours.
[0030] The receding amounts of contact surfaces of the valve guide
test piece and the valve test piece after the test were regarded as
wear. As a result, the wear in Example 1 was 2.0 .mu.m in the valve
guide test piece, and 21.5 .mu.m in the valve test piece.
[0031] [2] Measurement of Thermal Conductivity
[0032] A disc-shaped test piece of 5.0 mm in diameter and 1.0 mm in
thickness was cut out of the cylindrical sintered body,
mirror-polished on bottom surfaces, and its thermal conductivity
was measured by a laser flash method. The thermal conductivity in
Example 1 was 50 W/mK.
[0033] Examples 2-8, and Comparative Examples 1-5
[0034] Sintered bodies were produced in the same manner as in
Example 1, except for changing the Fe-based prealloy composition,
the amount of electroless Cu plating, and the amount of C powder
added as shown in the column of "Chemical Components" in Table 1. A
valve guide test piece for the wear test and a disc-shaped test
piece for the thermal conductivity measurement were formed from
each sintered body, and subjected to the same wear test and thermal
conductivity measurement as in Example 1. The results are shown in
Table 1 together with those of Example 1.
TABLE-US-00001 TABLE 1 Wear (.mu.m) Thermal Chemical Components (%
by mass) Valve Conductivity No. Cr Mo V W C Cu Fe Guide Valve
(W/mK) Example 1 0.7 1.4 2.1 -- 2.3 45.5 Bal. 2.0 21.5 50 Example 2
0.5 1.1 0.8 1.7 2.1 65.6 Bal. 6.0 12.5 84 Example 3 0.6 0.8 0.5 1.2
0.9 85.2 Bal. 11.0 12.0 123 Example 4 3.6 4.5 1.8 5.4 2.0 10 Bal.
1.8 22.8 32 Example 5 0.7 1.5 2.2 0.6 3.0 46.7 Bal. 2.2 18.5 45
Example 6 9.6 0.8 1.6 -- 2.5 20.0 Bal. 3.1 21.2 38 Example 7 -- 5.0
-- -- 0.5 30.5 Bal. 8.5 14.7 62 Example 8 2.0 -- 6.2 5.6 1.6 50.2
Bal. 3.2 24.3 55 Com. Ex. 1 0.4 0.2 0.1 0.05 0.4 4.8 Bal. 290.5 0.5
28 Com. Ex. 2 0.2 0.05 -- -- 0.3 95.2 Bal. 495.6 1.0 355 Com. Ex. 3
12.0 6.8 8.3 9.8 0.2 8.0 Bal. 1.1 86.5 18 Com. Ex. 4 3.4 0.1 5.2
12.0 3.5 10 Bal. 1.3 100.3 16 Com. Ex. 5 17.8 0.4 0.1 0.3 2.0 3.2
Bal. 5.3 59.1 17
[0035] It is clear from Examples that when the total amount of
alloy elements of Cr, Mo, V and W is 2% or more by mass, the valve
guide undergoes less wear. On the other hand, when the total amount
of the alloy elements exceeds 16% by mass, the valve suffers
drastically increased wear. The thermal conductivity gets higher by
increasing the amount of Cu, but it is also influenced by the alloy
phase composition, low in Examples 4 and 6 containing large amounts
of alloy elements. Because Example 7 contains a small amount of C,
the valve guide has small self-lubrication by graphite, suffering
more wear, though it has higher thermal conductivity than that of
Example 5 containing more Cu. The reason therefor appears to be
that C contained in a continuous Cu structure has little influence
on decreasing thermal conductivity. In Comparative Examples 1 and
2, in which the total amount of alloy elements is less than 2% by
mass, the valves (sliding mates) suffer little wear, but the valve
guides per se suffer increased wear. Particularly in Comparative
Example 2 containing a small total amount of the alloy elements and
more than 90% by mass of the Cu component, the valve guide per se
suffers drastically increased wear because of insufficient strength
and hardness. Because in Comparative Examples 3-5, any of the alloy
elements (all of Cr, Mo, V and W in Comparative Example 3, W in
Comparative Example 4, and Cr in Comparative Example 5) is more
than the required amount, the valves (mating members) suffer large
wear, though the valve guides undergo little wear. Further, they
have as insufficiently low thermal conductivity as 20 W/mK or
less.
EFFECTS OF THE INVENTION
[0036] Because the sintered alloy valve guide of the present
invention comprises a wear-resistant Fe-based alloy phase, a Cu or
Cu-based alloy phase having excellent thermal conductivity, and a
graphite phase having excellent self-lubrication, it has excellent
wear resistance and high valve-cooling capability, thereby avoiding
abnormal combustion such as knocking, etc. in high-performance,
high-load engines, and contributing to improving engine
performance.
* * * * *