U.S. patent application number 09/829011 was filed with the patent office on 2002-01-10 for forged scroll parts and production process thereof.
Invention is credited to Ohmi, Fumihiko, Sato, Masahiro.
Application Number | 20020003012 09/829011 |
Document ID | / |
Family ID | 26589792 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020003012 |
Kind Code |
A1 |
Sato, Masahiro ; et
al. |
January 10, 2002 |
Forged scroll parts and production process thereof
Abstract
An object of the present invention is to provide an
aluminum-alloy-made forged scroll part in which harmful primary Si
crystals are not formed and variation in wrap height between the
scrolls is low. The present invention also provides a process for
producing the forged scroll part. An alloy material including Si:
8.0-12.5%; Cu: 1.0-5.0%; Mg: 0.2-1.3%; and if necessary, Ni: 2.0%
or less and/or one or more species selected from among Sr, Ca, Na,
and Sb: total 0.5% or less, is cast through continuous casting into
a round bar material having a diameter of 130 mm.phi. or less, and
subsequently, the material is subjected to upsetting and hot
forging with back pressure to produce a forged scroll part
containing substantially no Si particles having a size of 15 .mu.m
or more, the mean size of Si particles in the forged part being 3
.mu.m or less.
Inventors: |
Sato, Masahiro; (Fukushima,
JP) ; Ohmi, Fumihiko; (Ohio, OH) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
WASHINGTON
DC
20037-3213
US
|
Family ID: |
26589792 |
Appl. No.: |
09/829011 |
Filed: |
April 10, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60230807 |
Sep 7, 2000 |
|
|
|
Current U.S.
Class: |
148/551 ;
148/417; 420/534 |
Current CPC
Class: |
B21C 23/14 20130101;
F04C 18/0246 20130101; B21C 23/16 20130101; B21J 5/00 20130101;
B21K 3/00 20130101; F04C 2230/25 20130101; C22F 1/043 20130101;
B21C 23/183 20130101; F05C 2201/903 20130101; C22C 21/02 20130101;
C22C 21/04 20130101 |
Class at
Publication: |
148/551 ;
148/417; 420/534 |
International
Class: |
C22C 021/02; C22F
001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 10, 2000 |
JP |
P2000-108269 |
Claims
What is claimed is:
1. A forged scroll part comprising an aluminum alloy material,
comprising Al base material, Si in an amount of 8.0-12.5 mass %, Cu
in an amount of 1.0-5.0 mass % and Mg in an amount of 0.2-1.3 mass
%, wherein the scroll part substantially comprises no Si particles
having a size of 15 .mu.m or more, and a mean Si particle size is 3
.mu.m or less.
2. A forged scroll part comprising from an aluminum alloy material
comprising Al base material, Si in an amount of 8.0-12.5 mass %, Cu
in an amount of 1.0-5.0 mass % and Mg in an amount of 0.2-1.3 mass,
and Ni in an amount of 2.0 mass % or less; one or more species
selected from the group consisting of Sr, Ca, Na, and Sb in a total
amount of 0.5 mass % or less, or a mixture thereof; wherein the
scroll part substantially comprises no Si particles having a size
of 15 .mu.m or more, and a mean Si particle size is 3 .mu.m or
less.
3. A forged scroll part produced from an aluminum alloy material
according to claim 1 or 2, wherein the scroll part is subjected to
solution heat treatment, quenching, and aging after the scroll part
is subjected to forging.
4. A process for producing an aluminum alloy-made forged scroll
part, which comprises a step for casting an aluminum alloy material
comprising Al base material, Si in an amount of 8.0-12.5 mass %, Cu
in an amount of 1.0-5.0 mass % and Mg in an amount of 0.2-1.3 mass
into a round bar having a diameter of 130 mm.phi. or less through
continuous casting; a step for cutting the aluminum alloy round bar
into a stock material for forging; a step for subjecting the stock
material to upsetting at an upsetting ratio of 20-70% to form a
work piece; a forging step for applying pressure onto the work
piece with a punch at a temperature of 300-450.degree. C. to form a
scroll wrap in a direction of punch pressing, wherein the forging
step includes a single step in which a forged scroll part is
press-formed while a back pressure is applied to the end of the
scroll wrap part in a direction opposite to that of a punch
pressure.
5. A process for producing an aluminum alloy-made forged scroll
part, which comprises a step for casting an aluminum alloy material
Al base material, Si in an amount of 8.0-12.5 mass %, Cu in an
amount of 1.0-5.0 mass % and Mg in an amount of 0.2-1.3 mass into a
round bar having a diameter of 85 mm.phi. or less through
continuous casting; a step for cutting the aluminum alloy round bar
into a stock material for forging; a step for subjecting the stock
material to upsetting at an upsetting ratio of 20-70% to form a
work piece; a forging step for applying pressure onto the work
piece with a punch at a temperature of 300-450.degree. C. to form a
scroll wrap in a direction of punch pressing, wherein the forging
step includes a single step in which a forged scroll part is
press-formed while a back pressure is applied to the end of the
scroll wrap part in a direction opposite to that of a punch
pressure.
6. A process for producing an aluminum alloy-made forged scroll
part according to claim 4 or 5, wherein the aluminum alloy material
comprises Al base material, Si in an amount of 8.0-12.5 mass %, Cu
in an amount of 1.0-5.0 mass % and Mg in an amount of 0.2-1.3 mass,
and Ni: 2.0 mass % or less; one or more species selected from the
group consisting of Sr, Ca, Na, and Sb in a total amount of 0.5
mass % or less, or a mixture thereof.
7. A process for producing an aluminum alloy-made forged scroll
part according claim 4 or 5, further comprising subjecting the
round bar to homogenization heat treatment at 480-520.degree. C.
for 30 minutes to four hours, to surface peeling or to
homogenization heat treatment and surface peeling after the
casting.
8. A process for producing an aluminum alloy-made forged scroll
part according to claim 4 or 5, wherein work lubrication in which
the work piece is coated with graphite film in advance is carried
out in combination with die lubrication in which a
graphite-containing oily lubricant is applied to a die during
forging.
9. A process for producing an aluminum alloy-made forged scroll
part according to claim 8, further comprising heating the work
piece at 100-500.degree. C. and immersing the work piece into a
lubricant solution prepared by mixing and dispersing graphite
powder into water to subject the work piece to work lubrication
with graphite film.
10. A process for producing an aluminum alloy-made forged scroll
part according to claim 4 or 5, further comprising subjecting the
scroll part to solution heat treatment, quenching, and aging after
forging.
11. A process for producing an aluminum alloy-made forged scroll
part according to claim 10, further comprising subjecting the
surface of the scroll part to machining.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is an application filed under 35 U.S.C.
.sctn.111(a) claiming benefit pursuant to 35 U.S.C. .sctn.119(e)(1)
of the filing date of Provisional Application 60/230,807 filed Sep.
7, 2000 pursuant to 35 U.S.C. .sctn.111(b).
FIELD OF THE INVENTION
[0002] The present invention relates to an aluminum alloy-made
forged part for an orbiting scroll and/or a fixed scroll, which is
assembled into a scroll compressor employed mainly in an air
conditioner; and to a process for producing the forged part.
BACKGROUND OF THE INVENTION
[0003] In recent years, scroll compressors have become of interest
as air conditioner compressors. One reason is that such a scroll
compressor contains a small number of parts and is driven silently.
The scroll compressor includes a fixed scroll having a spiral wrap
portion 11, as shown in FIG. 1, and an orbiting scroll having a
spiral wrap portion whose shape is similar to that of the portion
11. The spiral wrap portion of the orbiting scroll is driven for
orbital movement so that these spiral wrap portions face each
other.
[0004] In many cases a fixed or orbiting scroll (hereinafter simply
referred to as a "scroll"), which serves as a main part of a scroll
compressor, is produced from aluminum alloy in order to reduce the
weight of the compressor. The scroll is produced by, for example,
casting or forging. In order to provide a scroll with strength and
reliability, forging is advantageously carried out for producing
the scroll. Since the scroll has a complicated shape, it must be
produced through hot forging.
[0005] FIG. 2 shows a conventional production process for an
aluminum alloy scroll part by forging.
[0006] Usually, a round bar material obtained through extrusion is
employed as a stock material for forging. Firstly, an aluminum
alloy prepared by mixing alloy components and melting is cast
through continuous casting into a billet (BL) for extrusion having
a large diameter of 200 mm.phi. or more (".phi." used herein
represents "diameter".). After the inside of the BL is homogenized
through heat treatment, the BL is cut into pieces such that they
have identical volumes to provide round bars, each having
predetermined length and diameter, and each piece is subjected to
extrusion to form a round bar.
[0007] Usually, the diameter of the extruded round bar is almost
equal to the outer diameter of a forged part. The round bar is cut
into pieces, and the pieces are employed as a stock material for
forging. As described below, if necessary, the cut piece may be
previously shaped by forging or machining into a piece having a
shape similar to that of the scroll part in order to facilitate
production of a scroll part, before forging of the stock material
to employ the shaped piece as a stock material for forging.
[0008] The stock material is forged into a scroll part usually
through hot forging. In order to provide the forged part with
strength, the forged part is usually subjected to solution
(quenching) and aging heat treatment after forging.
[0009] Thereafter, if necessary, a portion of the surface of the
part is subjected to machining in order to enhance precision in the
size of the forged part.
[0010] FIG. 4 is a schematic cross-sectional view showing a
conventional forging process for a scroll. A workpiece 4 placed in
a die 2 is pressed downward with a punch 1 to form the wrap portion
11. Usually, the distance that the punch 1 moves is determined to
be consistent in order to make the thickness of a flange portion 12
of the scroll consistent.
[0011] In order to precisely forge a workpiece into a scroll wrap,
Japanese Patent Application Laid-Open (kokai) Nos. 54-159712,
59-61542, and 62-89545 disclose a process for forging an aluminum
alloy-made scroll, in which the workpiece is subjected to forging
or machining in advance to provide the piece with a previous shape,
and then the workpiece is forged into the scroll wrap. The reason
why such a process is carried out is as follows. The wrap portion
11 has a spiral shape, the height of the portion is large, and the
wrap portion is connected to the flange portion 12. Therefore, when
a workpiece is forged into a scroll as shown in FIG. 4, forming a
wrap portion having a uniform height is difficult, and thus a
workpiece having an intermediate shape is formed in advance. When
the process is carried out, the produced scroll is provided with a
shape with some degree of precision. However, the process requires
designing an intermediate shape which matches the final shape of
the scroll, and preparation of a forging die employed for
intermediate processing. Consequently, the process includes
complicated steps and involves high costs, presenting difficulty in
practice.
[0012] Japanese Patent Application Laid-Open (kokai) Nos. 60-102243
and 06-23474, among other publications, disclose a back pressure
forging process in which a workpiece prepared only by cutting a
round bar is employed without subjecting the workpiece to
pre-processing before forging, and, during forging of the
workpiece, a load is applied to the end portion of a scroll wrap 11
in a direction opposite a forging direction in order to control
material flow to realize a uniform flow into a wrap-shaped mold and
to reduce variation in the height of the scroll wrap 11. According
to the process, by using a workpiece prepared only by cutting a
round bar, a scroll in which there is a reduction in variation in
the height of a wrap portion 11 can be produced at low cost and
high productivity.
[0013] The process will be described in more detail. In the back
pressure forging process for a scroll, as shown in cross-sectional
views of FIGS. 5 and 6, a workpiece 4 is pressed with a punch 1,
and the workpiece is forged into a die space for wrap formation 2a
of a die 2 to form a wrap. During forging, a back pressure lower
than a punch pressure is applied through knock pins 7 and knockouts
6 to the end of the wrap in a direction opposite that of forging
thereby making the height L2 of the wrap uniform, as shown in a
cross sectional view of a forged part (FIG. 7).
[0014] The back pressure forging process regulates, to some extent,
the effect for making the height of a spiral wrap of a forged
scroll part uniform.
[0015] However, although variation in the height of a wrap of a
scroll is regulated to some extent through the back pressure
forging process, wrap height varies between individual scrolls
unless the thickness of individual cut materials; i.e., the weight
of individual workpieces, is strictly controlled. Therefore, a
margin for machining of the end of a wrap must be controlled in
every forged part during a post-processing step. Alternatively, in
consideration of different wrap heights among scroll products,
slightly-large-sized scrolls must be forged to provide scrolls with
a large margin for machining during a post-processing step,
resulting in low yield.
[0016] In the forging process, when a workpiece is forged into a
scroll, the thickness (L1) of a flange portion is controlled by a
stroke of the punch 1, and the remaining portion of the workpiece
is forged into a wrap portion. Therefore, the difference in the
volume of the workpiece before forging is reflected in the
difference in the height (L2) of the wrap portion.
[0017] Conventionally, in order to smoothly carry out forging of a
workpiece without production loss, the workpiece is prepared by
cutting a round bar material having a diameter nearly equal to the
maximum outer diameter of a forged scroll (i.e., the outer diameter
of a flange portion). Therefore, variation in the thickness of the
cut material is reflected in variation in volume of the workpiece;
i.e., variation in the height of a wrap portion of the scroll.
[0018] The area of a horizontal cross section of a wrap portion is
about 1/3 to 1/5 that of a horizontal cross section of a workpiece.
Accordingly, the variation in the cut length of the workpiece is
multiplied by a factor of 3 to 5 in height of the wrap portion.
Therefore, since a margin of the end of the wrap for machining in a
post-processing step cannot be reduced, the amount of time for
machining of scrolls cannot be reduced, and material-based yield
cannot be enhanced.
[0019] In consideration of conditions under which scrolls are used,
an aluminum alloy material containing a large amount of silicon is
employed for producing a scroll to enhance strength and wear
resistance of the scroll. The material is hard, and thus a blade
for cutting the material is easily worn. Therefore, compared with a
conventionally-used alloy, variation in the thickness of the
aluminum alloy material increases during cutting, greatly affecting
variation in wrap height between individual forged scrolls.
[0020] As described above, an aluminum alloy material is employed
for producing a scroll in order to reduce the weight of the scroll.
In consideration of the balance between strength, wear resistance,
and processability, Al-Si alloy materials have mainly been
developed among a variety of aluminum alloy materials. When
characteristics of the material are regulated to impart wear
resistance to the material, fine Si particles are uniformly
dispersed in an aluminum base. Development of alloy materials other
than Al-Si alloy materials has encountered difficulty at present.
Therefore, such an alloy material is not employed in practice, and
basically modifications of Al-Si alloy materials has been carried
out.
[0021] In such an Al-Si alloy material, crystallization of Si
particles is necessary for enhancing wear resistance of the
material. However, crystallization of coarse primary Si crystals
having a size of tens of .mu.m or more causes wear of a blade
during machining, resulting in a product to having a rough machined
surface. In addition, when such coarse primary Si crystals
segregate at a portion of a scroll subjected to high stress,
fatigue breakage initiates at the portion where the scroll is
employed, greatly impairing reliability of the scroll. Furthermore,
as described above, when such an Al-Si alloy material is cut, wear
of a blade is accelerated. Thus, variation in the thickness of the
material increases during cutting. Therefore, such an Al-Si alloy
material preferably has a structure in which crystallization of
coarse primary Si crystals is suppressed and fine eutectic Si
particles having a size of several .mu.m are uniformly
dispersed.
[0022] As described above, in a conventional production process,
such an aluminum alloy material is formed through cutting into an
extrusion round bar material. In order to form the round bar
material, the alloy material is usually cast through continuous
casting into a billet (BL) having a relatively large diameter (200
mm.phi. or more). Therefore, the billet is solidified slowly during
casting, and thus crystallization of coarse primary Si crystals
having a size of 100 .mu.m or more tends to occur, and control of
the distribution of Si particles in the billet is difficult.
Furthermore, as described above, variation in the thickness of the
billet may occur during cutting. In addition, primary Si crystals
remain in a forged scroll product as a large, hard impurity, and
the crystals may cause problems in machining of the forged scroll
and reduction in strength thereof.
SUMMARY OF THE INVENTION
[0023] The present invention provides a forged scroll part employed
in a scroll compressor and a production process for the scroll
part, which is produced from an aluminum alloy material which
enables reduction in variation of wrap height within a forged part
and between forged parts, reduction in a margin for machining in
post-processing, and suppression of occurrence of coarse primary Si
crystals that would cause wear of a blade during machining and
reduction in strength of the forged scroll part.
[0024] In order to solve the aforementioned problems, the present
invention provides:
[0025] (1) a forged scroll part produced from an aluminum alloy
material comprising:
[0026] Si: 8.0-12.5 mass %;
[0027] Cu: 1.0-5.0 mass %; and
[0028] Mg: 0.2-1.3 mass %,
[0029] wherein the scroll part contains substantially no Si
particles having a size of 15 .mu.m or more, and the mean Si
particle size is 3 .mu.m or less.
[0030] If necessary, the forged part may further comprise:
[0031] Ni: 2.0 mass % or less; and/or
[0032] one or more species selected from among Sr, Ca, Na, and Sb:
total 0.5 mass % or less.
[0033] The strength of the forged part is enhanced through solution
heat treatment, quenching, and aging, and, if necessary, the forged
part is subjected to machining and is imparted with characteristics
satisfactory for a practically-used scroll part.
[0034] The present invention also provides:
[0035] (2) a process for producing the forged part, which comprises
a step for casting an aluminum alloy material into a round bar
having a diameter of 130 mm.phi. or less through continuous casting
of an aluminum alloy material comprising Si: 8.0-12.5 mass %, Cu:
1.0-5.0 mass %, and Mg: 0.2-1.3 mass %; a step for cutting the
aluminum alloy round bar into a stock material for forging; a step
for subjecting the stock material to upset at an upsetting ratio of
20-70% to form a pre-shaped product (hereinafter "a workpiece");
and a forging step for applying pressure onto the workpiece with a
punch at a temperature of 300-450.degree. C. to form a scroll wrap
in a direction of punch pressing, wherein the forging step includes
a single step in which a forged scroll part is press-formed while
back pressure is applied to the end of the wrap of scroll part in a
direction opposite that of a punch pressure.
[0036] The present invention also provides:
[0037] (3) a process for producing the forged part, which comprises
a step for casting an aluminum alloy material into a rod having a
diameter of 85 mm.phi. or less through continuous casting of an
aluminum alloy material comprising Si: 8.0-12.5 mass %, Cu: 1.0-5.0
mass %, and Mg: 0.2-1.3 mass %; a step for cutting the aluminum
alloy round bar into a stock material for forging; a step for
subjecting the stock material to upset at an upsetting ratio of
20-70% to form a workpiece; and a forging step for applying
pressure onto the workpiece by use of a punch at a temperature of
300-450.degree. C. to form a scroll wrap in a direction of punch
pressing, wherein the forging step includes a single step in which
a forged scroll part is press-formed while back pressure is applied
to the end of the wrap of scroll part in a direction opposite that
of a punch pressure.
[0038] In the aforementioned production process, the alloy material
may further comprise Ni: 2.0 mass % or less, and/or one or more
species selected from among Sr, Ca, Na, and Sb: total 0.5 mass % or
less. Preferably, after completion of forging, the forged part is
subjected to homogenization heat treatment at 480-520.degree. C.
for 30 minutes to four hours, and/or to surface peeling.
[0039] Preferably, a work lubrication process in which the
workpiece is coated with graphite film in advance is carried out in
combination with a die lubrication process in which a
graphite-containing oily lubricant is applied to a die as a
lubrication process during forging.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] FIG. 1 is a schematic representation of a forged scroll
part.
[0041] FIG. 2 is a flow chart of a process in which a conventional
material for extrusion is employed as a stock material for
forging.
[0042] FIG. 3 is a flow chart of the process of the present
invention.
[0043] FIG. 4 is a schematic cross-sectional view showing a
conventional forging process for a scroll.
[0044] FIG. 5 is a cross-sectional view of a material, a punch, and
a die before the forging step of the present invention.
[0045] FIG. 6 is a cross-sectional view of a material, a punch, and
a die during the forging step of the present invention.
[0046] FIG. 7 is a schematic representation showing a
cross-sectional view of a forged scroll part.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0047] The present invention will be described in more detail.
[0048] The aluminum alloy scroll is usually produced from an
Si-containing aluminum alloy in order to impart wear resistance to
the scroll. Crystallization of fine particles of added Si enhances
wear resistance of the scroll against another scroll.
[0049] When the content of Si contained in the alloy is about 11
mass % or less, fine eutectic Si particles having a size of several
.mu.m dispersedly crystallize in an Al base in proportion to the
content of Si, and the Si particles enhance wear resistance of the
alloy scroll. Therefore, the content of Si is preferably high. When
the content of Si contained in the alloy is less than 8.0 mass %, a
sliding part, such as a scroll formed from the alloy, exhibits
unsatisfactory wear resistance.
[0050] In contrast, when the content of Si contained in the alloy
is in excess of 12.5 mass %, crystallization of primary Si crystals
occurs. The primary Si crystals tend to become large to have a size
as large as tens of .mu.m. The large Si crystals cause wear of a
blade during cutting, and cause loss of the edge of a cutting tool
during machining in post-processing, resulting in a problem in
finishing. In addition, when the crystals segregate at a portion in
the vicinity of the outer surface of a forged part, which is
susceptible to stress concentration, breakage of the forged part
initiates at the portion, resulting in lowering of mechanical
strength. Therefore, the upper limit of Si content is 12.5 mass
%.
[0051] When Cu is added to the aluminum alloy in an amount of
several %, strength of the Al base is enhanced through post heat
treatment. Addition of Cu also contributes to enhancement of wear
resistance of the alloy. However, when the content of Cu contained
in the alloy is less than 1.0 mass %, Cu does not contribute to
enhancement of strength of the alloy. When the content of Cu is in
excess of 5.0 mass %, Cu does not contribute to enhancement of
strength of the alloy commensurate with the content of Cu.
Therefore, the content of Cu is preferably 1.0-5.0 mass %.
[0052] Mg combines with Si, precipitating in the form of Mg.sub.2Si
in the alloy after heat treatment, and this precipitation
contributes to hardening of the alloy. Mg also forms MgSiCu through
precipitation after heat treatment, and the compound contributes to
hardening of the alloy. Such Mg compounds enhance the strength of
the alloy. When the content of Mg is less than 0.2 mass %, Mg fails
to exert such a effect. When the content of Mg is in excess of 1.3
mass %, the effect of Mg does not increase commensurate with the
content of Mg. In addition, an oxide generates and invades the
alloy during casting, resulting in defects of the alloy. Therefore,
the content of Mg is preferably 0.2-1.3 mass %.
[0053] If necessary, the alloy of the present invention may further
contain Ni in an amount of 2.0 mass % or less. Addition of a small
amount of Ni exerts an effect of enhancing heat resistance of the
alloy. When the content of Ni is 0.1 mass % or less, Ni fails to
exert the above effect. When the content of Ni is in excess of 2.0
mass %, large crystals generate, resulting in lowering of toughness
of the alloy. Therefore, the content of Ni is preferably 0.1-2.0
mass %.
[0054] In the alloy of the present invention, eutectic Si particles
contribute to enhancement of wear resistance of the alloy. In order
to uniformly disperse the Si particles in the alloy and to suppress
generation of coarse primary Si crystals, the alloy may contain one
or more species selected from among Sr, Ca, Na, and Sb in a total
amount of 0.5 mass % or less. Preferably, Sb is contained in an
amount of 0.05-0.5 mass %, and Sr is contained in an amount of
0.005-0.05 mass %. Sr is particularly preferable, since addition of
a trace amount of Sr exerts the above effect, and weight loss of
the alloy during melting is small.
[0055] A characteristic feature of the present invention resides in
the alloy composition or in the process including a melting step of
the alloy and a forging step, particularly in the steps of the
process. With reference to FIG. 2, there will be described a
conventional production process for a forged part by use of a
material for extrusion as a stock material for forging. In the
conventional process, an aluminum alloy round bar for extrusion is
cut into pieces and the piece is employed as a stock material for
forging, since a flange portion of a scroll has a round shape and
has an outer diameter of about 80-130 mm.phi.. Firstly, the
aluminum alloy is melted, and cast through continuous casting into
billets for extrusion. Each billet is subjected to homogenization
heat treatment, and cut into pieces having a length of tens of cm,
and each piece is extruded through an extrusion machine into a
round bar having a diameter nearly equal to that of a scroll.
Subsequently, the round bar is cut in a direction perpendicular to
the longitudinal direction of the bar to obtain a stock material
for forging. The material is heated, a lubricant is applied to the
material, and then the material is subjected to hot forging.
[0056] When the alloy is cast into a usual billet for extrusion,
the billet usually has a diameter as large as 200 mm.phi. or more.
Therefore, since the billet is cooled slowly and solidified
gradually, crystallization of coarse primary Si crystals having a
size of about 100 .mu.m easily occurs when the content of Si in the
alloy is in excess of 10%. Consequently, the crystals may remain in
the extruded round bar of small diameter. The primary Si crystals
tend to segregate at the center portion of the billet, at which the
cooling rate of the billet is particularly low. When the content of
Si is nearly equal to 12%, the primary Si crystals generate
randomly in the entirety of the cross section of the billet.
[0057] FIG. 3 shows an example of the process of the present
invention. In the present invention, in order to avoid generation
of coarse primary Si crystals, an aluminum alloy is cast through
continuous casting into a round bar material having a diameter of
130 mm.phi. or less. In contrast to a conventional billet for
extrusion, a round bar material having diameter of 130 mm.phi. or
less, which is obtained through continuous casting, is cooled very
rapidly and thus solidified rapidly. Therefore, eutectic Si
particles become fine in the round bar material, and even when the
content of Si is in excess of 10 mass %, coarse primary Si
crystals, which generate in the conventional billet, do not
generate in the round bar material. Particularly, in the case in
which the aforementioned modification elements, such as Sr, Ca, Na,
and Sb, are added to the alloy in an amount up to the Si content of
12.5 mass %, generation of primary Si crystals is substantially not
observed in the round bar material; i.e., the aforementioned
problem is avoided. The round bar material substantially comprises
no Si particles when Si particles having a size of 15 .mu.m or more
are substantially not observed in the following process.
[0058] According to the process using the alloy composition,
eutectic Si particles having a size of 15 .mu.m or more are
substantially not observed and the particle size is usually about
10 .mu.m at most. The mean particle size is 3 .mu.m or less. As
used herein, the phrase "substantially not observed" refers to "the
percentage of non-observation in a field of view under a microscope
is 99% or more." In the present invention, the round bar material
substantially comprises no Si particles having a size of 15 .mu.m
or more since Si particles are not substantially observed in the
foregoing process.
[0059] The particle size of Si may be directly determined from a
photomicrograph of the round bar material. Preferably, the particle
size is obtained through image processing by use of a microscope
image analyzer (e.g., Luzex), since a correct value is obtained
through this technique. As used herein, the term "particle size"
refers to the diameter of a circle having the same area as that of
the particle.
[0060] The diameter of a cast round bar material is preferably
small, since the material having a small diameter is solidified
rapidly. When the diameter of the material is small, eutectic Si
particles in the material easily become fine, and generation of
primary Si crystals is greatly suppressed. Therefore, a round bar
material having a diameter of 85 mm.phi. or less is more preferable
as a cast material from the viewpoint that such a material exhibits
excellent upsetting effect as described below.
[0061] The material of the present invention may be cast to have a
diameter that matches the outer diameter of a scroll product, and
cut into a stock material for forging. A characteristic feature of
the present invention is that the cast material has a diameter
smaller than that of the outer diameter of a scroll product; the
cast material is cut to have a length corresponding to the weight
of a forged scroll part; and the cut material is subjected to
upsetting to attain a desired diameter. The diameter of the
material after upsetting is determined to match the outer diameter
of a flange portion of the scroll product. Through cutting of the
continuously cast bar material having a small diameter and
upsetting of the cut material, the material exhibits improved
ductility and fatigue characteristics, due to uniform dispersion of
Si particles.
[0062] Upsetting of the cut round bar material may be carried out
through free-forging; i.e., through application, under two punches,
of pressure onto the material in a vertical direction to
sufficiently enlarge the diameter of the material. However,
upsetting of the material is preferably carried out through
die-forging, in which the outer diameter of the material is
determined by a die, in order to enhance precision in the diameter
and the thickness of the material and to carry out scroll forging,
which is the next step, at high productivity.
[0063] During upsetting, the upsetting ratio of the material is
appropriately 20-70%.
[0064] The upsetting ratio is obtained by the following
formula:
[0065] Upsetting ratio (%)
[0066] =100.times.(cross-sectional area of material after
processing--cross-sectional area of material before
processing)/cross-sectional area of material after processing
[0067] =100.times.(height of material before processing--height of
material after processing)/height of material before processing
[0068] Usually, upsetting may be carried out at room temperature
when the upsetting ratio is low. Preferably, upsetting is carried
out after the material is heated, since the upsetting ratio can be
increased. However, even in the case in which upsetting is carried
out at elevated temperature, when the upsetting ratio is very high,
cracking occurs on the circumferential surface of the material
beyond material ductility. In addition, since the ratio of the
height of the material to the outer diameter thereof becomes high,
buckling of the material occurs during upsetting, and thus a
high-quality upset material cannot be obtained. Therefore, in the
case of the material of the present invention, the upsetting ratio
is appropriately 70% or less, preferably 60% or less. When the
upsetting ratio is less than 20%, the material may fail to exhibit
improved ductility and fatigue characteristics. In addition,
variation in characteristics of the below-described material for
forging is not reduced satisfactorily.
[0069] When upsetting is carried out, the material is usually
heated. The material may be heated before upsetting, and then
subjected to upsetting. However, in order to improve the surface
condition of the material during peeling and facing as described
below and to enhance the shapability of the material during
upsetting, the material is preferably subjected to homogenization
heat treatment before upsetting. The homogenization heat treatment
is appropriately carried out at 480-520.degree. C. for 30 minutes
to four hours. When the temperature is lower than 480.degree. C.,
the material is not satisfactorily homogenized. When the
temperature is higher than 520.degree. C., eutectic fusion occurs
at boundaries between crystal particles. The temperature is
preferably 495-510.degree. C. When the treatment time is less than
30 minutes, the material is not satisfactorily homogenized. When
the time is in excess of four hours, eutectic Si particles tend to
become large.
[0070] If necessary, the surface of the material may be subjected
to peeling and facing in advance. Through peeling and facing,
precision in the diameter of the material is enhanced, and the
condition of the circumferential surface of a workpiece after
upsetting is improved.
[0071] The process for casting an aluminum alloy into a round bar
material having a small diameter, which includes cutting the cast
material into a stock material for forging; and subjecting the
stock material to upsetting to form a workpiece, has the following
three advantages.
[0072] A first advantage is that generation of primary Si crystals
is suppressed and eutectic Si particles become fine in the cast
material, since the material is cooled rapidly as described above.
When the cast material is subjected to plastic working to some
extent, the material exhibits improved ductility and fatigue
characteristics.
[0073] A second advantage will be described in relation to the
following reason. Variation in the length of the cut cast round bar
material leads to variation in the volume (weight) of the stock
material for forging, which results in variation in the height of a
wrap portion of a forged scroll part. The cast round bar material
is usually cut by use of a round sawing machine. When the cast
round bar has a small diameter, the material is accurately fed into
the sawing machine to determine the length of the material, and
thus variation in the length (thickness) of the cut material tends
to be low. In addition, when the diameter of the cast round bar
material is small, the area of the cross section of the material is
small. Therefore, even if variation in the length (thickness) of
the material occurs, the variation in the volume (weight) of the
material is low compared with that in a material having a larger
diameter. More specifically, when the diameter of the cast round
bar material is small, variation in the volume (weight) of the
stock material for forging becomes low, resulting in low variation
in the height of a wrap portion of a forged scroll part.
[0074] A third advantage is enhancement of material-based yield.
When the round bar material is cut into the stock material for
forging having a predetermined length, unwanted pieces are obtained
from both ends of the bar material, and powdery chips are
generated. The amount of loss of the material attributed to the
powdery chips is determined by the thickness of a cutting blade and
the diameter of the round bar material. Specifically, when
different stock materials having the same volume are cut from round
bar materials having different diameters, the amount of powdery
chips which are formed when a stock material is cut from a round
bar material having a large diameter is larger than that of powdery
chips which are formed when a stock material is cut from a round
bar material having a small diameter. Therefore, when a stock
material for forging is cut from a round bar material having a
small diameter, loss of the material is reduced. As a result, the
stock material for forging can be obtained at high yield, which
leads to an economical benefit.
[0075] In view of the foregoing, when the upsetting ratio is low
during upsetting of the stock material for forging, the
aforementioned advantages are obtained to an unsatisfactory degree.
Therefore, the upsetting ratio is 20% or more, preferably 40% or
more.
[0076] A pre-shaped material which has undergone the aforementioned
upsetting, i.e., a workpiece, is subjected to hot forging. The
diameter of the workpiece is determined to match the outer diameter
of a flange portion of a scroll part.
[0077] An aluminum alloy material is subjected to hot forging at
300-450.degree. C., preferably at 350-450.degree. C. When the hot
forging temperature is very low, the material fails to be formed
into a predetermined shape or cracking occurs in the material,
whereas when the temperature is very high, swelling or buckling of
the material may occur.
[0078] When a workpiece is subjected to hot forging, in order to
prevent seizing of a workpiece into a forging die, a lubricant is
usually applied to the workpiece and the die. In general, when an
aluminum alloy material is subjected to hot forging, a liquid
lubricant containing a mixture of graphite and water or mineral oil
is widely employed. Usually, when a workpiece is forged into a
product having a simple shape, satisfactory lubrication and release
effects are obtained through mere spraying of a lubricant directly
onto a forging die. However, in the case in which a workpiece is
forged into a product having a complicated shape, when lubrication
is not carried out thoroughly, a lubricant becomes short, and thus
the workpiece is forged into a poorly-shaped product, or the
workpiece is seized into a die and cannot be forged into the
product. In order to solve such problems, a workpiece is immersed
into a liquid lubricant in advance to coat the piece with a
lubrication film. When a workpiece is forged into a scroll having a
complicated shape, the workpiece is forged in a die having a
wrap-shaped deep groove to form a wrap portion having a large
height. Therefore, since a lubricant fails to cover the entirety of
the wrap-contoured inner walls of the die when only spraying is
carried out, shaping and release of the workpiece is not
satisfactorily carried out; i.e., forging of the workpiece is
difficult. In order to solve such a problem, preliminary immersion
of the workpiece into the lubricant is carried out in combination
with spraying of the lubricant onto the die. As a result, improved
lubrication and release effects are obtained, and forging at high
productivity is realized.
[0079] In order to coat a workpiece having lubrication film
thereon, a solution prepared by mixing a solvent with a graphite
lubricant is applied to the workpiece. In order to increase
productivity, a lubricant prepared by diluting the solution with a
rapid-drying solvent is applied or sprayed to the workpiece.
[0080] In a most economical process, a lubricant is prepared by
mixing and dispersing graphite powder into water serving as a
solvent, a workpiece is heated and then immersed into the
lubricant, and the resultant workpiece is dried. In this case, the
workpiece must be heated at a temperature at which water serving as
a solvent is evaporated or dried within a very short time. When the
heating temperature of the workpiece is lower than the boiling
point of water, the lubricant fails to dry and remains on the
workpiece after immersion of the workpiece; i.e., the lubricant is
not rapidly dried. Therefore, the heating temperature of the
workpiece must be 100.degree. C. or higher. In consideration of
productivity, the heating temperature is preferably 130.degree. C.
or higher. The upper limit of the heating temperature may be a
temperature at which deterioration of the workpiece, such as
melting, does not occur. Briefly, the heating temperature is
500.degree. C. or lower, preferably 450.degree. C. or lower. The
workpiece is usually heated in a heating furnace. Alternatively,
the residual heat of the workpiece after hot upsetting may be
utilized; i.e., the workpiece is immersed into a lubricant
immediately after upsetting. In this case, the lubricant is baked
onto the workpiece which has undergone upsetting, and the workpiece
is removed from the lubricant and then dried.
[0081] Through this procedure, cutting, heating, upsetting,
lubrication, and forging may be carried out successively, resulting
in high productivity.
[0082] Upsetting and forging may be carried out simultaneously in a
single pressing apparatus. In this case, continuous production of a
scroll part is possible through carrying out cutting, heating,
lubrication, upsetting, and forging successively.
[0083] A workpiece that has undergone upsetting and lubrication is
forged into a scroll as follows. If necessary, the workpiece is
additionally heated, and the workpiece is pressed downward with a
punch 1 into a die space 2a to form a wrap portion downward in the
die space 2a. Before the workpiece is pressed with the punch 1,
knockouts 6 connected through knock pins 7 to a back pressure
apparatus are inserted, in advance, in the die space 2a for forming
a wrap, such that the knockouts 6 reach the vicinity of the upper
end of the die space 2a. When the workpiece is pressed into the die
space 2a to form a wrap, pressure is applied to the end of the wrap
in a direction opposite the pressing direction from the back
pressure apparatus through a back pressure plate 3, the knock pins
7, and the knockouts 6 to form the wrap having a uniform
height.
[0084] When the back pressure is not applied to the workpiece
during forging, the amount of the metal that flows into the
wrap-forming portions in the die can become nonuniform. Therefore,
the object of applying the back pressure is to obtain a uniform
amount of metal flow into the wrap-forming portions in the die. The
amount of the back pressure can regulate the uniformity of the
amount of the metal flow into the wrap-forming portions in the die.
Accordingly, by applying the appropriate back pressure to the
workpiece, the amount of metal flow into the wrap-forming portions
in the die can be uniform, and thus the height of the wrap portions
of the product can be uniform. When the back pressure is very high,
buckling of the wrap occurs during wrap formation, and a good
product is not obtained. Therefore, when a forged part such as a
scroll, in which the ratio of the area of a horizontal
cross-section of a wrap portion to that of a horizontal
cross-section of a flange portion is about 1/3 to 1/5, and the
height of the wrap portion is 4 to 10 times the thickness of the
wrap portion, is formed at the aforementioned heating temperature,
the surface pressure applied to the end of the wrap is
appropriately 40-120 N/mm.sup.2, preferably 60-100 N/mm.sup.2.
[0085] In order to impart strength and wear resistance to the
forged scroll part, the scroll part must be subjected to solution
(quenching) and aging treatment. The solution temperature is
preferably 490-500.degree. C. After the scroll part is subjected to
quenching in water, the scroll is subjected to aging for hardening
under appropriate conditions; i.e., temperature: 160-210.degree.
C., time: 1-8 hours. Through this procedure, the scroll part is
imparted with a satisfactory hardness of about HRB 70-85.
[0086] If necessary, the heat-treated forged scroll part is further
subjected to machining to precisely regulate the height and the
shape of the wrap portion. The thus-produced scroll part can be
provided in a compressor or the like.
EXAMPLES
[0087] The present invention will next be described by way of
Examples. Unless indicated otherwise herein, all parts, percents,
ratios and the like are by weight.
[0088] Production of a workpiece for forging of the present
invention
[0089] Alloy materials A through F shown in Table 1 were employed
in Examples 1 through 8, and alloy materials G and H shown in Table
1 were employed in Comparative Examples 5 and 6. Each alloy
material was cast into a bar having a diameter of 82 mm.phi. and a
length of 5,000 mm through continuous casting at a casting rate of
about 300 mm/minute. The bar was subjected to homogenization heat
treatment at 500.degree. C. for one hour, and then subjected to
facing by use of a peeling machine to attain a diameter of 78
mm.phi..
[0090] Subsequently, the bar was cut into workpieces having a
thickness of 65 mm by use of a round saw having a thickness of 2.5
mm.
[0091] Each workpiece was heated at about 400.degree. C. in a
heating furnace, and the disk-shaped workpiece was pressed with a
punch into a die by use of a 630-ton press machine to attain a
diameter of 114 mm.phi. to upset the workpiece through die-forging.
The upsetting ratio is obtained from the following calculation:
[0092] upsetting ratio={1-(78/114).sup.2}.times.100=53%.
[0093] When the bar was cut into workpieces, chips (45 g per
workpiece) were formed.
[0094] Production of a workpiece for forging through a conventional
process
[0095] Alloy materials B and C shown in Table 1; i.e., alloy
materials of Examples 4 and 5, were employed in Comparative
Examples 3 and 4. Each alloy material was cast into a billet for
extrusion having a diameter of 200 mm.phi. through continuous
casting at a casting rate of about 150 mm/minute. The billet was
subjected to homogenization heat treatment at 500.degree. C. for
one hour, and then extruded into a stock material having an outer
diameter of 114 mm.phi., which is equal to that of the above upset
workpiece. The stock material was cut into workpieces having a
thickness of 30.4 mm, so that that the volume of each workpiece was
the same as that of the above upset workpiece, by use of a round
saw having a thickness of 2.5 mm.
[0096] When the stock material was cut into workpieces, chips (80 g
per work piece) were formed. The amount of loss of the material was
about twice the loss of the material in the cases of Examples 1
through 8 in which the round bar obtained through continuous
casting was cut into workpieces.
[0097] Observation of internal metallographical structure of a
workpiece for forging
[0098] Subsequently, in order to observe the internal
metallographical structure of each of the above-prepared
workpieces, or to measure the size and the weight of the workpiece,
10 upset workpieces or 10 cut workpieces were collected as
samples.
[0099] After the sizes and the weights of these 10 workpieces were
measured, a 20 mm-square sample was cut out of the center portion
of each workpiece having a diameter of 114 mm.phi., and the
internal microstructure of the sample was observed.
[0100] Through this observation, the existence of primary Si
crystals, the size of the crystals, the number of the crystals, and
the size of eutectic Si particles were measured. The weight of each
sample was measured by use of an even balance. The thickness of
each sample was measured at two points per sample by using of a
micrometer. The results are shown in Table 2. The weight and the
thickness are shown by a range of 10 samples.
[0101] The results reveal that, when a workpiece is subjected to
upsetting, coarse primary Si crystals are not formed in the
workpiece, variation in the size and the weight of the workpiece is
reduced, and production yield is improved; i.e., a highly-reliable
workpiece exhibiting high precision in size can be produced
economically.
[0102] Scroll forging
[0103] Subsequently, the above upset workpiece and the above
extruded-and-cut workpiece were heated at 200.degree. C. in a
heating furnace, and then each workpiece was immersed into a
water-containing graphite lubricant for several seconds, then
removed therefrom to coat the workpiece with a lubrication
film.
[0104] While the workpiece was heated at 400.degree. C., the
workpiece was subjected to forging at a punch pressure of 450 tons
and at a back surface pressure of 40-120 N/mm.sup.2 to produce a
scroll having a flange diameter of about 115 mm.phi., a flange
thickness of about 23.0 mm, a wrap height of 39.6 mm, and a wrap
thickness of 5.7 mm. The ratio of the area of a horizontal cross
section of the flange to that of a horizontal cross section of the
wrap was about 4.0.
[0105] In Comparative Examples 1 and 2, upset workpieces obtained
from alloy material A were subjected to forging at back pressures
of 30 and 130 N/mm.sup.2, respectively.
[0106] Under the aforementioned conditions, 50 workpieces of each
Example or each Comparative Example were successively subjected to
forging to produce 50 scroll parts. Difference in the height (the
maximum height--the minimum height) of the scroll wrap of each
forged part was measured to obtain variation in wrap height
difference between the 50 forged parts. In addition, the mean
height of the wrap of each forged part (the mean value of the
heights of the wrap measured at three points 11a, 11b, and 11c
shown in FIG. 1, wherein 11a represents a spiral initiation point;
11c represents a spiral termination point; and 11b represents a
point on a line joining the points 11a and 11c, the point 11b being
adjacent to the point 11c) was measured to obtain variation in mean
wrap height between the 50 forged parts. Furthermore, the shape of
the wrap of each forged port was observed.
[0107] The results are shown in Table 3. The results reveal that,
when the back pressure is 30 N/mm.sup.2, difference in wrap height
of one forged part is in excess of 1 mm; i.e., the height of the
wrap becomes non-uniform when the back pressure is low. In
contrast, when the back pressure is 130 N/mm.sup.2, buckling of the
wrap occurs, and a good forged part is not produced.
[0108] The results reveal that variation in mean wrap height
between forged parts produced from workpieces obtained through the
conventional process including extrusion and cutting is 1.0 mm or
more. That is, as shown in Table 2, variation in volume between the
workpieces causes variation in wrap height between the forged
parts.
[0109] According to the present invention, variation in height of
the wrap of one forged part falls within 0.5 mm, and variation in
mean wrap height between forged parts also falls within 0.5 mm.
That is, a forged part having a good shape can be produced.
[0110] Subsequently, 10 forged parts of each of Examples 4 and 5
and Comparative Examples 3 through 6 were heated at 500.degree. C.,
and then subjected to quenching in water. Subsequently, the parts
were subjected to aging treatment at 180.degree. C. for six hours.
Thereafter, a tensile test piece was obtained from each forged
part, and tensile characteristics of the forged part were
evaluated. In addition, the side wall of the wrap of each forged
part was machined about 0.5 mm by use of an end mill, and then the
machined surface was observed. Furthermore, the workpiece for
forging was subjected to heat treatment in a manner similar to that
of the above procedure, and a fatigue test piece was obtained from
the workpiece. The fatigue test piece was subjected to a test by
use of an Ono-type rotating bending fatigue test apparatus, and
fatigue characteristics of the workpiece were evaluated on the
basis of breakage stress at 10.sup.7 cycles. The results are shown
in Table 4.
[0111] The results reveal that, when an upset stock material is
employed as a workpiece, the fracture elongation of the workpiece
was improved, and thus a forged part exhibiting high fatigue
strength and having an excellent machined surface was produced.
That is, when formation of coarse primary Si crystals was
suppressed, the above effects are obtained.
[0112] In order to observe the internal metallographical structure
of the forged part, a test piece was cut out from the central
portion of the forged part of each of Examples 1 through 8 after
aging treatment, and the test piece was subjected to observation of
microstructure. Consequently, primary Si crystals were not observed
in each test piece, and change in the size of eutectic Si particles
attributed to forging and heat treatment was not confirmed.
[0113] In Comparative Examples 5 and 6, in which the Si content of
the alloy material falls outside the range of the present
invention, scratches were formed on the machined surface of a
forged part, the scratches were attributed to formation of primary
Si crystals, and the strength of the forged part was lowered. Such
a forged part is not suitable for a scroll.
1TABLE 1 Alloy material (unit: wt %) subjected to test and
production process for forged part Stock material Forging for
forging back Chemical analysis value (mass %) Diameter pressure
Alloy Test No. Si Cu Mg Ni Sb Sr Others (mm.phi.) Working
N/mm.sup.2 A Example. 1 10.2 2.9 0.5 -- -- -- Bal. 82 Upsetting 80
Example. 2 10.2 2.9 0.5 -- -- -- Bal. 82 Upsetting 40 Example. 3
10.2 2.9 0.5 -- -- -- Bal. 82 Upsetting 120 Comp. Ex. 1 10.2 2.9
0.5 -- -- -- Bal. 82 Upsetting 30 Comp. Ex. 2 10.2 2.9 0.5 -- -- --
Bal 82 Upsetting 130 B Example. 4 11.5 4.5 0.6 -- -- -- Bal 82
Upsetting 80 Comp. Ex. 3 11.5 4.5 0.6 -- -- -- -- 200 Extrusion 80
C Example. 5 10.4 2.6 0.3 -- -- -- Bal 82 Upsetting 80 Comp. Ex. 4
10.4 2.6 0.3 -- -- -- Bal. 200 Extrusion 80 D Example. 6 8.9 2.1
0.4 -- 0.22 -- Bal 82 Upsetting 80 E Example. 7 12.0 1.2 1.1 1.2
0.25 -- Bal 82 Upsetting 80 F Example. 8 11.2 4.6 0.7 -- -- 0.01
Bal 82 Upsetting 80 H Comp. Ex. 5 13.1 4.8 0.5 -- -- -- Bal. 82
Upsetting 80 G Comp. Ex. 6 7.0 0.3 0.2 -- -- -- Bal. 82 Upsetting
80
[0114]
2TABLE 2 Metallographical observation and size measurement of
workpiece for forging Internal microstructure Primary Si crystal
Eutectic Si particle Maximum Mean Maximum Size Note size size size
Diameter Thickness Weight Alloy Test No. Number (.mu.m) (.mu.m)
(.mu.m) (mm.phi.) (mm) (g) Examples A Ex. 1 None -- 2.0 4.8 114.0
30.40-30.49 841-843 B Ex. 4 None -- 2.1 6.7 114.0 30.35-30.51
845-848 C Ex. 5 None -- 2.0 4.4 114.0 30.38-30.52 840-842 D Ex. 6
None -- 1.9 4.4 114.0 30.37-30.50 839-842 E Ex. 7 None -- 2.1 7.2
114.0 30.42-30.52 841-843 F Ex. 8 None -- 2.1 5.3 114.0 30.44-30.51
845-847 Comparative B Comp. Ex. 3 5 100 2.5 10.3 114.0 30.20-30.58
844-850 Examples C Comp. Ex. 4 2 52 3.0 15.5 114.0 30.33-30.63
840-845 H Comp. Ex. 5 5 110 2.0 8.4 114.0 30.37-30.46 845-848 G
Comp. Ex. 6 None -- 1.8 4.8 114.0 30.41-30.49 840-842
[0115]
3TABLE 3 Size measurement and observation of forged part in each
test Difference in wrap height 50 Forged parts Back in one forged
Mean wrap pressure part/mm height/mm Alloy Test Work piece
N/mm.sup.2 (Max.-Min.) Minimum Maximum Note Example A Ex. 1 Upset
piece 80 0.3 to 0.4 39.4 39.7 Ex. 2 Upset piece 40 0.3 to 0.5 39.0
39.4 Ex. 3 Upset piece 120 0.2 to 0.4 39.2 39.5 B Ex. 4 Upset piece
80 0.3 to 0.4 39.2 39.6 C Ex. 5 Upset piece 80 0.3 to 0.4 39.4 39.7
D Ex. 6 Upset piece 80 0.3 to 0.4 39.2 39.7 Comparative A Comp.
Upset piece 30 1.3 to 2.0 -- -- Variation in Example Ex. 1 wrap
height Comp. Upset piece 130 0.2 to 0.4 39.0 39.3 Buckling of Ex. 2
wrap B Comp. Extruded piece 80 0.3 to 0.5 38.2 39.8 Ex. 3 C Comp.
Upset piece 80 0.3 to 0.5 38.4 39.7 Ex. 4
[0116]
4TABLE 4 Mechanical characteristics and machining test of forged
part Fatigue Tensile characteristics characteristics 0.2% proof
Tensile Fracture (room temperature) Observation of stress strength
elongation 10.sup.7 cycle machined Alloy Test (MPa) (MPa) (%) (MPa)
surface Example B Ex. 4 401 456 6.3 210 No tool scratch C Ex. 5 322
403 13.8 190 No tool scratch Comparative B Comp. 408 448 3.2 180
Tool scratch Example Ex. 3 C Comp. 330 415 10.8 165 Tool scratch
Ex. 4 H Comp. 410 458 3.8 170 Tool scratch Ex. 5 G Comp. 200 301
15.1 130 No tool scratch Ex. 6
[0117] According to the alloy material and the forging process of
the present invention, mass-production of an aluminum alloy-made
forged scroll, in which formation of primary Si crystals which
cause lowering of strength of the scroll and adversely affecting
machining of the scroll, is suppressed can be achieved. According
to the present invention, variation in wrap height of one forged
scroll can be reduced and variation in mean wrap height between
forged scrolls can also be reduced.
[0118] While the invention has been described in detail and with
reference to specific embodiments thereof, it will be apparent to
one skilled in the art that various changes and modifications can
be made therein without departing from the spirit and scope
thereof.
* * * * *