U.S. patent application number 10/561536 was filed with the patent office on 2006-06-22 for magnesium-base alloy screw and method of manufacturing the same.
Invention is credited to Kenji Fukuda, Kenzaburo Hashimoto, Nozomu Kawabe, Yukihiro Oishi.
Application Number | 20060130947 10/561536 |
Document ID | / |
Family ID | 33545089 |
Filed Date | 2006-06-22 |
United States Patent
Application |
20060130947 |
Kind Code |
A1 |
Oishi; Yukihiro ; et
al. |
June 22, 2006 |
Magnesium-base alloy screw and method of manufacturing the same
Abstract
[Problems] It is an object of the invention to provide a
producing method of a magnesium-based alloy screw capable of
producing a screw made of magnesium-based alloy having excellent
strength with excellent productivity, and to provide a
magnesium-based alloy screw. [Means to Solve the Problem] The
producing method includes a head forging step in which a head
working for forming a head portion of a screw on a wire made of
magnesium-based alloy obtained by drawing is carried out by warm
working to produce a screw blank, and a thread rolling step in
which thread rolling for forming screw thread on the screw blank is
carried out by warm working to produce a screw. The head working in
the head forging step is carried out using holding die which fixes
the wire and a punch which forms a head portion of the screw. The
holding die and the punch are heated, in which at least the holding
die are heated to 140.degree. C. or higher and 250.degree. C. or
lower, thereby heating the wire to 140.degree. C. or higher and
lower than 250.degree. C.
Inventors: |
Oishi; Yukihiro; (Hyogo,
JP) ; Kawabe; Nozomu; (Hyogo, JP) ; Hashimoto;
Kenzaburo; (Osaka, JP) ; Fukuda; Kenji;
(Osaka, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Family ID: |
33545089 |
Appl. No.: |
10/561536 |
Filed: |
June 15, 2004 |
PCT Filed: |
June 15, 2004 |
PCT NO: |
PCT/JP04/08342 |
371 Date: |
December 19, 2005 |
Current U.S.
Class: |
148/667 ;
148/420 |
Current CPC
Class: |
B21K 1/46 20130101; C22F
1/06 20130101; F16B 33/00 20130101; C22C 23/06 20130101; B21H 3/06
20130101; C22C 23/02 20130101; C22C 23/04 20130101; B21J 1/06
20130101; F16B 35/00 20130101 |
Class at
Publication: |
148/667 ;
148/420 |
International
Class: |
C22F 1/06 20060101
C22F001/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 19, 2003 |
JP |
2003-175286 |
Jul 15, 2003 |
JP |
2003-275005 |
Jan 6, 2004 |
JP |
2004-001071 |
Claims
1. A magnesium-based alloy screw wherein tensile strength is 220
MPa or higher.
2. The magnesium-based alloy screw according to claim 1, wherein
the magnesium-based alloy contains Al: 0.1 to 12% by mass.
3. The magnesium-based alloy screw according to claim 2, wherein
the magnesium-based alloy contains one or more of Mn: 0.1 to 2.0%
by mass, Zn: 0.1 to 5.0% by mass and Si: 0.1 to 5.0% by mass.
4. The magnesium-based alloy screw according to claim 1, wherein
the magnesium-based alloy contains Zn: 0.1 to 10% by mass and Zr:
0.1 to 2.0% by mass.
5. The magnesium-based alloy screw according to claim 1, wherein
the magnesium-based alloy contains rare-earth element: 5.0% by mass
or less.
6. A producing method of a magnesium-based alloy screw comprising a
head forging step in which a head working for forming a head
portion of a screw on a wire made of magnesium-based alloy obtained
by drawing is carried out by warm working to produce a screw blank,
and a thread rolling step in which thread rolling for forming screw
thread on the screw blank is carried out by warm working to produce
a screw, wherein the head working in the head forging step is
carried out using holding die which fixes the wire and a punch
which forms a head portion of the screw, the holding die and the
punch are heated, in which at least the holding die is heated to
140.degree. C. or higher and 250.degree. C. or lower, thereby
heating the wire to 140.degree. C. or higher and lower than
250.degree. C.
7. The producing method of a magnesium-based alloy screw according
to claim 6, wherein the holding die and the punch are respectively
fixed to a die holder and a punch holder respectively including a
heating means, the holding die and the punch are heated by the
heating means, at least a portion of an outer periphery of the
holder is provided with a heat insulator, a heated state of the
holding die and punch is maintained by the heat insulator.
8. The producing method of a magnesium-based alloy screw according
to claim 6, wherein the following steps are continuously carried
out: a supplying step for supplying to cutting means a base wire
made of magnesium-based alloy obtained by drawing, a cutting step
for cutting the supplied base wire into pieces each having a
constant length by the cutting means, thereby obtaining a wire as a
work piece, a transferring step for transferring the cut wire to
forging means, and a head forging step for forming a head portion
of a screw on the transferred wire.
9. The producing method of a magnesium-based alloy screw according
to claim 8, wherein the cutting means includes cutting die which
hold the wire, the holding die is fixed to a die holder including a
heating means which can heat, the holding die is heated by the
heating means, the cutting die is fixed to the die holder of the
holding die, the cutting step is carried out in such a manner that
the wire is held by the cutting die, the cutting die is heated by
the heating means of the die holder, thereby heating the wire.
10. The producing method of a magnesium-based alloy screw according
to claim 9, wherein in the cutting step, the wire is heated both by
a wire heating means for directly heating the wire and by the
cutting die which is heated by the heating means of the die holder,
and the cutting die cuts the heated wire.
11. The producing method of a magnesium-based alloy screw according
to claim 6, wherein working speed of the head working is 100 mm/sec
or higher.
12. The producing method of a magnesium-based alloy screw according
to claim 6, wherein the thread rolling is carried out using thread
rolling die, the thread rolling die is heated to 100.degree. C. or
higher and lower than 250.degree. C., thereby carrying out the
thread rolling.
13. The producing method of a magnesium-based alloy screw according
to claim 12, wherein the thread rolling die include a heating means
capable of heating the thread rolling die, the thread rolling die
is heated by the heating means, a heat insulator is disposed such
as to surround an outer periphery of the thread rolling die, and a
heated state of the die is maintained by the heat insulator.
14. The producing method of a magnesium-based alloy screw according
to claim 12, further comprising a step in which moving means moves
the screw blank obtained in the head forging step to the thread
rolling die, the moving means is heated to 100.degree. C. or higher
and lower than 250.degree. C.
15. The producing method of a magnesium-based alloy screw according
to claim 6, further comprising a thermal treatment step in which a
screw subjected to the thread rolling is subjected to thermal
treatment at 100.degree. C. or higher and lower than 350.degree.
C.
16. The producing method of a magnesium-based alloy screw according
to any one of claims 6 to 15, wherein average crystal grain
diameter of the magnesium-based alloy is 10 .mu.m or less, and
maximum crystal grain diameter thereof is 15 .mu.m or less.
17. The producing method of a magnesium-based alloy screw according
to anyone of claims 6 to 16, wherein the magnesium-based alloy
contains Al: 0.1 to 12% by mass.
18. The producing method of a magnesium-based alloy screw according
to claim 17, wherein the magnesium-based alloy contains one or more
of Mn: 0.1 to 2.0% by mass, Zn: 0.1 to 5.0% by mass and Si: 0.1 to
5.0% by mass.
19. The producing method of a magnesium-based alloy screw according
to anyone of claims 6 to 16, wherein the magnesium-based alloy
contains Zn: 0.1 to 10% by mass and Zr: 0.1 to 2.0% by mass.
20. The producing method of a magnesium-based alloy screw according
to anyone of claims 6 to 16, wherein the magnesium-based alloy
contains rare-earth element: 5.0% by mass or less.
Description
TECHNICAL FIELD
[0001] The present invention relates to a screw made of
magnesium-based alloy and a producing method thereof.
BACKGROUND ART
[0002] The magnesium-based alloy is lighter than aluminum in
weight, and has more excellent specific strength and specific
rigidity as compared with steel or aluminum and thus, the
magnesium-based alloy is widely used for aircraft parts, automobile
parts, bodies of various electrical products and the like.
[0003] However, since Mg and its alloy have hexagonal close-packed
lattice (hcp) structure, they have poor ductility and their plastic
workability is extremely poor at room temperature. For example,
when general metal material is used, production of screw is carried
out at room temperature, but when magnesium-based alloy is used,
forging such as screw working can not be carried out at room
temperature.
[0004] The workability of the magnesium-based alloy is largely
varied depending upon the temperature. Severe plastic working such
as screw working can be carried out by increasing the temperature
of a raw material. Conventionally, when a screw is to be produced
using magnesium-based alloy, the raw material is heated to such a
temperature that the plastic working can be carried out at the time
of screw working. For example, Patent Documents 1 to 3 describe
techniques in which a screw is processed while heating a
magnesium-based alloy raw material to such a temperature that the
raw material generates superplasticity phenomenon or plastic
workability is increased.
[0005] Patent Document 1: Japanese Patent Application Laid-open No.
2000-283134
[0006] Patent Document 2: Japanese Patent Application Laid-open No.
2000-343178
[0007] Patent Document 3: Japanese Patent Application Laid-open No.
2001-269746
DISCLOSURE OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0008] The temperature at which superplasticity phenomenon is
generated or plastic workability is increased is as high as
250.degree. C. or higher. Therefore, according to the conventional
method, molds (working tools) such as a holding die and punch to be
used at the time of screw working are exposed to high temperature,
and there is a problem that the lifetimes of the working tools are
largely shortened and a screw can not be produced with excellent
productivity.
[0009] Conventionally, when severe working such as screw working is
carried out to obtain a screw made of magnesium-based alloy, it is
necessary to heat extruded material made of magnesium-based alloy
which is a work piece to be heat treated to 250.degree. C. or
higher as described in Patent Documents 1 to 3. Therefore, heat
equipment for high temperature as high as 250.degree. C. or higher
is required, working tools used for the screw working are also
exposed to high temperature and their lifetimes are shortened, and
this increases the producing cost. Thus, it is by no means
preferable for industrial production to heat the materials to
250.degree. C. or higher.
[0010] In recent years, it is required to further enhance the screw
strength. A screw obtained by heating extruded material to
250.degree. C. or higher to be screw produced has limitation for
enhancing its strength. Thus, an appropriate method for enhancing
the strength of a screw made of magnesium-based alloy is
required.
[0011] Hence, it is a main object of the present invention to
provide a producing method of a magnesium-based alloy screw capable
of producing magnesium-based alloy screw with excellent
productivity. It is another object of the invention to provide a
magnesium-based alloy screw having excellent tensile strength.
MEANS FOR SOLVING THE PROBLEMS
[0012] It is generally considered it difficult to carry out severe
working such as screw working at a temperature lower than
250.degree. C. when magnesium-based alloy is used. The present
inventors variously researched about the magnesium-based alloy and
as a result, they found out that a screw can be produced even at a
temperature lower than 250.degree. C. by using a wire which is
obtained by specific drawing previously, and they achieved this
invention. The inventors define this invention based on a point of
view that the obtained magnesium-based alloy screw has excellent
tensile characteristics.
[0013] That is, a producing method of a magnesium-based alloy screw
of the present invention includes a head forging step in which a
head working for forming a head portion of a screw on a wire made
of magnesium-based alloy obtained by drawing is carried out by warm
working to produce a screw blank, and a thread rolling step in
which thread rolling for forming screw thread on the screw blank is
carried out by warm working to produce a screw. The head working in
the head forging step is carried out using a holding die which
fixes the wire and a punch which forms a head portion of the screw.
The holding die and the punch are heated, and at least the holding
die is heated to 140.degree. C. or higher and 250.degree. C. or
lower, thereby heating the wire to 140.degree. C. or higher and
lower than 250.degree. C.
[0014] Conventionally, when a screw is obtained using
magnesium-based alloy, extruded material is used as a work piece.
If the extruded material is not heated to 250.degree. C. or higher,
the screw can not be produced. Whereas, in the present invention,
to produce a screw at heating temperature lower than 250.degree.
C., a wire obtained by a later-described specific drawing is
defined to be used.
[0015] In extruded material, the average crystal grain diameter of
alloy is 20 .mu.m or more and variation is great. In drawn material
obtained by the drawing, the average crystal grain diameter of
alloy is 10 .mu.m or less and the maximum crystal grain diameter is
15 .mu.m or less, and the drawn material has uniform and fine
structure. Further, drawn material has excellent size precision and
small deviated diameter difference as compared with extruded
material. Thus, when a wire is heated through working tools such as
the holding die which works a screw, it is possible to heat the
same stably and reliably. Further, as compared with extruded
material, drawn material can be formed into a long linear material
and thus, the linear material can be supplied to the holding die
continuously. Therefore, procedure from the cutting operation of
the linear material to the forming operation of the head portion of
a screw can continuously be carried out. According to the present
invention, the heating temperature is lowered, i.e., a screw is
produced at a temperature lower than 250.degree. C. by using the
drawn material having the above-described characteristics.
[0016] The present invention will be explained in more detail
below.
[0017] In the invention, a wire made of magnesium-based alloy is
preferably obtained by cutting a linear material having circular
cross section. The drawing for obtaining the linear material is
carried under such conditions that a temperature rising speed to
working temperature is 1.degree. C./sec to 100.degree. C./sec,
working temperature is 50.degree. C. or higher and 200.degree. C.
or lower (preferably 150.degree. C. or lower), working ratio is 10%
or more per one drawing (one pass), drawing speed is 1 m/sec or
more, and after extruded material is drawn, the obtained linear
material is heated to 100.degree. C. or higher and 400.degree. C.
or lower, more preferably 150.degree. C. or higher and 400.degree.
C. or lower. This heating annealing is effective for recovery of
strain induced by the drawing, and for grain refinement by
recrystallization. It is preferable that keeping time of this
heating temperature is about 5 to 20 minutes. By carrying out such
a specific drawing, the alloy structure can be finely divided, more
concretely, the average crystal grain diameter can be reduced to 10
.mu.m or less, and the maximum crystal grain diameter can be
reduced to 15 .mu.m or less. Plastic workability of fine-grained
material can be enhanced even if the heating temperature of the
wire is lower than 250.degree. C., and a desired screw can be
obtained.
[0018] Using the wire made of magnesium-based alloy obtained by the
drawing, first, a screw blank (intermediate product in a state in
which a head portion is formed but a shaft is not provided with
screw thread) is produced by forging. At that time, the forging,
more concretely, head working is carried out by warm working. As
concrete temperature, a wire made of magnesium-based alloy is
heated to 140.degree. C. or higher and lower than 250.degree. C. If
the heating temperature of the magnesium-based alloy wire is lower
than 140.degree. C., there is an adverse possibility that a crack
or the like is generated during forging and the head working can
not be carried out. Especially when a screw having a large diameter
like M6 is produced, it is preferable that the heating temperature
is 180.degree. C. or higher. As the heating temperature is higher,
the plastic workability is enhanced but the lifetimes of working
tools such as the holding die are shortened and thus, the upper
limit value is set to 250.degree. C. while taking productivity into
consideration. A screw can be produced at lower temperature, i.e.,
180.degree. C. or lower depending upon a shape of the head portion
to be formed (-screw, +screw, hexagonal screw, rivet and the like),
working speed, screw size and the like.
[0019] In the head forging step, the head working can be preferably
carried out using the holding die which fixes the magnesium-based
alloy wire and the punch which forms the head portion of the screw,
and working tools used for normal head working may be used. In the
present invention, the wire is heated in the head forging step by
heating both the holding die and punch. At that time, at least the
holding die is heated to 140.degree. C. or higher and 250.degree.
C. or lower. Heating both the holding die and punch to the
above-described temperature makes it possible to heat the entire
wire equally, which is preferable. If the heating temperature is
lower than 140.degree. C., the wire can not be heated to
140.degree. C. or higher, a crack or the like is generated on the
wire during forging, head working can not be carried out, and if
the heating temperature exceeds 250.degree. C., the lifetime of the
holding die or punch is shortened.
[0020] The holding die and the punch may be fixed to a die holder
and a punch holder, respectively, and these holders may include
heating means, and the holding die and the punch may be heated
using these heating means. An example of the heating means is an
electric heating type cartridge heater. It is preferable in terms
of maintenance that the heating means is mounted in such a manner
that the holder is formed with a hole and the heating means is
inserted into the hole. The holder may include a temperature sensor
so that temperature can be adjusted. Like the heating means, the
temperature sensor may be mounted in such a manner that the holder
is formed with a hole and the sensor is inserted into the hole.
[0021] When the holder is provided with the heating means, it is
preferable that a heat insulator is disposed on at least a portion
of an outer periphery of the holder, especially a portion of the
outer periphery which comes into contact with a forging apparatus
body in the holder to enhance the thermal efficiency by maintaining
the heated state and while taking into consideration the thermal
influence on the forging apparatus body on which the holder is
mounted. A heat insulator may be disposed such as to surround the
outer periphery of the holder.
[0022] When a head portion of a screw is formed in many stages
while having a plurality of punches, it is preferable that a
magnesium-based alloy wire is heated to the above temperature in
any stages to form the head. At that time, if the plurality of
punches are fixed to the same punch holder, heating means of the
punches can commonly be used.
[0023] To form a head portion more efficiently, it is preferable to
continuously carry out the following steps, i.e., a supplying step
for supplying the magnesium-based alloy base wire obtained by the
drawing to cutting means, a cutting step for cutting the supplied
base wire by cutting means into pieces having constant length to
obtain a wire as a work piece, a transferring step for transferring
the cut wire to forging means, and a head forging step for forming
a head portion of a screw using the transferred wire by the
above-described procedure. Such procedure can be carried out using
a forging apparatus capable of continuously working, and a known
forging apparatus may be used.
[0024] It is preferable that the cutting means is provided with
cutting die which holds a wire, this cutting die are fixed to the
die holder which includes the heating means, and in the cutting
step, the wire is held by the cutting die, the cutting die are
heated by the heating means of the die holder, thereby heating the
wire. Since the wire is heated in the cutting step, when the wire
is transferred to the working tools such as the holding die or
punch which form the head, the wire is heated to a certain
temperature, this facilitates the more rapid heating operation in
the head forging step, and the working speed can be increased. That
is, the productivity can further be enhanced. Especially the
holding die and the cutting die may be held by the same die holder
so that the heating means of the holding die and the heating means
of the cutting die can commonly be used. As a result, the holding
die and the cutting die can be heated at the same time, and this is
more efficient. Since the parts are commonly used, the number of
parts of the forging apparatus can be reduced.
[0025] In the cutting step, since the wire is heated by heating the
cutting die, the heating operation in the head forging step is
facilitated, and the working speed is increased, and in addition to
these effects, the cutting performance can also be enhanced. If the
temperature of the wire is insufficient at the time of cutting,
there is an adverse possibility that this causes inconveniences
that the cut surface becomes rough, and cut leavings are generated
at the time of the cutting. Since the cut surface affects the shape
after the head working, it is preferable that the cut surface is
smooth. If a head portion is formed including cut leavings, the
shape after the headworking is affected as described above; thus it
is preferable that there are no cut leavings. In addition, if the
wire is cut in a state in which the temperature of the wire is
insufficient, precision of the cut wire is poor, and there is an
adverse possibility that the insertion performance of the wire into
the forging means (holding die) is deteriorated. Thus, it is
required to sufficiently heat the wire to enhance the cutting
performance. To make it possible to sufficiently heat the wire more
quickly and more stably, it is preferable that wire heating means
for directly heating the wire is provided, and the wire is heated
by both heating the cutting die and heating using the wire heating
means. The wire cutting performance is enhanced by indirect heating
of the cutting die and direct heating by the wire heating means,
the shape of the head portion is stabilized and the insertion
performance of the wire into the holding die can be enhanced. When
a screw having a large diameter is to be produced, it takes time to
rise the temperature. This method is extremely effective because it
is possible to heat the wire more quickly. An example of the wire
heating means is a dryer for blowing hot air.
[0026] In this invention, drawn material having excellent plastic
workability is used. This increases the working speed of the head
working and enhances the productivity of screws. More concretely,
the working speed of the head working can be increased to 100
mm/sec or higher. Generally, the working ratio of magnesium-based
alloy depends on the working speed, and increasing the working
speed makes it difficult to carry out the working having large
working ratio. Whereas, according to the present invention, it is
possible to form a screw with working speed of 100 mm/sec or higher
that is at industrial production level at heating temperature as
low as lower than 250.degree. C. by using the drawn material having
excellent plastic workability.
[0027] A screw blank obtained by the head forging step is subjected
to thread rolling to form a screw thread, and a screw is produced.
The thread rolling is carried out by warm working. More concretely,
it is preferable that a screw blank made of magnesium-based alloy
obtained through the head forging step is heated to 100.degree. C.
or higher and lower than 250.degree. C. If the temperature is lower
than 100.degree. C., there is an adverse possibility that a crack
or the like is generated during the thread rolling and a screw
thread can not be formed, and if the temperature exceeds
250.degree. C., the lifetimes of the working tools are
shortened.
[0028] The thread rolling may be carried out using thread rolling
die, and working tools used for normal thread rolling may be used.
In the thread rolling step, the screw blank is heated by heating
the thread rolling die to 100.degree. C. or higher and lower than
250.degree. C. If the temperature is lower than 100.degree. C., the
screw blank can not be heated to 100.degree. C. or higher, and if
the temperature exceeds 250.degree. C., the lifetime of the thread
rolling die is shortened. Especially when a screw having a large
diameter like M6 is produced, it is preferable to heat the screw
blank to 150.degree. C. or higher.
[0029] The thread rolling die is directly provided with a heating
means, and the thread rolling die is heated by the heating means.
An example of the heating means is an electric heating type
cartridge heater. It is preferable in terms of maintenance that the
heating means is mounted in such a manner that the thread rolling
die is formed with a hole and the heating means is inserted into
the hole. The thread rolling die may include a temperature sensor
so that temperature can be easily adjusted. Like the heating means,
the temperature sensor may be mounted in such a manner that a hole
is formed and the sensor is inserted into the hole.
[0030] When the thread rolling die is provided with the heating
means, it is preferable that a heat insulator is disposed such as
to surround an outer periphery of the thread rolling die,
especially a portion of the outer periphery which comes into
contact with a thread rolling apparatus body in the thread rolling
die to enhance the thermal efficiency by maintaining the heated
state and while taking into consideration the thermal influence on
the thread rolling apparatus body on which the thread rolling die
is mounted.
[0031] In the head forging step and the thread rolling step, a
screw can be produced with excellent productivity by heating the
magnesium-based alloy raw material to the specific temperature
range, but in order to further enhance the productivity, it is
preferable that the raw material is heated also when the procedure
is shifted from the head forging step to the thread rolling step.
More concretely, moving means which moves a screw blank obtained by
the head forging step to the thread rolling die is heated to
100.degree. C. or higher and lower than 250.degree. C., thereby
heating the screw blank. An example of the moving means is a shoot
rail. A shoot rail having a structure used for normal screw working
may be used. It is preferable that heating means such as an
electric heating type cartridge heater is mounted on the moving
means to heat the same. Heating the magnesium-based alloy raw
material also when the procedure is shifted from the head forging
step to the thread rolling step, i.e., heating the screw blank
previously, can shorten the heating time when the thread rolling is
carried out. Thus, the speed of the thread rolling can be increased
and the productivity of the screw can be enhanced.
[0032] The magnesium-based alloy screw obtained through the above
steps has excellent tensile strength of 220 MPa or higher. To
further enhance the tensile strength, it is preferable that head
working for forming a head portion of a screw and thread rolling
for forming a screw thread are carried out and then, the obtained
screw is subjected to thermal treatment at 100.degree. C. or higher
and lower than 350.degree. C. With this thermal treatment, the
alloy structure of the screw can be brought into structure having
finer crystal grain, and it is possible to obtain a screw having
tensile strength as high as 230 MPa or higher.
[0033] The present invention is useful for magnesium-based alloy
having hcp structure which has poor workability at room temperature
(e.g., 20.degree. C.) irrespective of alloy composition. For
example, it is possible to use casting magnesium-based alloy or
flatting magnesium-based alloy. More concretely, examples of the
magnesium-based alloy are alloy having Al: 0.1% by mass or more and
12% by mass or less, alloy having Zn: 0.1% by mass or more and 10%
by mass or less and Zr: 0.1% by mass or more and 2.0% by mass or
less, and alloy having rare-earth element having excellent heat
resistance in a range of 5.0% by mass or less. When the alloy has
Al, it has at least one or more of Mn: 0.1% by mass or more and
2.0% by mass or less, Zn: 0.1% by mass or more and 5.0% by mass or
less, and Si: 0.1% by mass or more and 5.0% by mass or less. As the
above ally compositions, it is possible to use AZ, AS, AM, ZK and
EZ based alloy and the like in typical ASTM. As the contents of Al,
Al in a range of 0.1 to less than 2.0% by mass, and Al in a range
of 2.0 or higher to 12.0% by mass may be distinguished from each
other. It is general that in addition to the above chemical
component, this is used as alloy including Mg and impurities.
Examples of the impurities are Fe, Si, Cu, Ni and Ca and the
like.
[0034] Examples of the AZ-based alloy having 2.0 to 12.0% by mass
Al are AZ31, AZ61, AZ91 and the like. The AZ31 is a magnesium-based
alloy, for example, containing Al: 2.5 to 3.5% by mass, Zn: 0.5 to
1.5% by mass, Mn: 0.15 to 0.5% by mass, Cu: 0.05% by mass or less,
Si: 0.1% by mass or less, and Ca: 0.04% bymassorless. The AZ61 is a
magnesium-based alloy, for example, containing Al: 5.5 to 7.2% by
mass, Zn: 0.4 to 1.5% by mass, Mn: 0.15 to 0.35% by mass, Ni: 0.05%
by mass or less, and Si: 0.1% by mass or less. The AZ91 is a
magnesium-based alloy, for example, containing Al: 8.1 to 9.7% by
mass, Zn: 0.35 to 1.0% by mass, Mn: 0.13% by mass or more, Cu: 0.1%
by mass or less, Ni: 0.03% by mass or less, and Si: 0.5% by mass or
less. Examples of the AZ-based alloy containing Al of 0.1 to less
than 2.0% by mass are AZlO, AZ21 and the like. The AZlO is a
magnesium-based alloy, for example, containing Al: 1.0 to 1.5% by
mass, Zn: 0.2 to 0.6% by mass, Mn: 0.2% by mass or more, Cu: 0.1%
by mass or less, Si: 0.1% by mass or less, and Ca: 0.4% by mass or
less. The AZ21 is a magnesium-based alloy, for example, containing
Al: 1.4 to 2.6% by mass, Zn: 0.5 to 1.5% by mass, Mn: 0.15 to 0.35%
by mass, Ni: 0.03% by mass or less, and Si: 0.1% by mass or
less.
[0035] Examples of the AS-based alloy having Al of 2.0 to 12.0% by
mass are AS41 and the like . The AS41 is a magnesium-based alloy,
for example, containing Al: 3.7 to 4.8% by mass, Zn: 0.1% by mass
or less, Cu: 0.15% by mass or less, Mn: 0.35 to 0.60% by mass, Ni:
0.001% by mass or less, and Si: 0.6 to 1.4% by mass. Examples of
the AS-based alloy having Al of 0.1 to less than 2.0% by mass are
AS21 and the like. The AS21 is a magnesium-based alloy, for
example, containing Al: 1.4 to 2.6% by mass, Zn: 0.1% by mass or
less, Cu: 0.15% by mass or less, Mn: 0.35 to 0.60% by mass, Ni:
0.001% by mass, and Si: 0.6 to 1.4% by mass.
[0036] Examples of the AM-based alloy are AM60, AM100 and the like.
The AM60 is a magnesium-based alloy, for example, containing Al:
5.5 to 6.5% by mass, Zn: 0.22% by mass or less, Cu: 0.35% by mass
or less, Mn: 0.13% by mass or more, Ni: 0.03% by mass or less, Si:
0.5% by mass or less. The AM100 is a magnesium-based alloy, for
example, containing Al: 9.3 to 10.7% by mass, Zn: 0.3% by mass or
less, Cu: 0.1% by mass or less, Mn: 0.1 to 0.35% by mass, Ni: 0.01%
by mass or less, and Si: 0.3% by mass or less.
[0037] Examples of the ZK-based alloy are ZK40, ZK60 and the like.
The ZK40 is a magnesium-based alloy, for example, containing Zn:
3.5 to 4.5% by mass, and Zr: 0.45% by mass or more. The ZK60 is a
magnesium-based alloy, for example, containing Zn: 4.8 to 6.2% by
mass, and Zr: 0.45% by mass or more.
[0038] Asrare-earthelement (RE) containedintheEZ-basedalloy,
mixture of Pr and Nd is usually used in many cases. Examples of the
EZ-based alloy are EZ33 and the like. The EZ33 is a magnesium-based
alloy, for example, containing Zn: 2.0 to 3.1% by mass, Cu: 0.1% by
mass or less, Ni: 0.01% by mass or less, RE: 2.5 to 4.0% by mass,
and Zr: 0.5 to 1% by mass.
[0039] It is difficult to obtain sufficient strength with only
magnesium, but by containing the above-described chemical
components, preferable strength can be obtained.
EFFECTS OF THE INVENTION
[0040] In the present invention, heating temperature when a screw
is produced can be reduced to lower than 250.degree. C. by using
drawn material made of magnesium-based alloy as described above.
Therefore, according to the invention, when a screw is produced, it
is unnecessary to heat the material to a high temperature of
250.degree. C. or higher unlike the conventional technique in which
extruded material is subjected to screw working as it is.
Therefore, it is possible to increase the lifetimes of working
tools such as the holding die. Further, according to the invention,
high temperature heating means is unnecessary unlike the
conventional technique. Therefore, according to the producing
method of the present invention, a magnesium-based alloy screw can
be obtained with excellent productivity.
[0041] A magnesium-based alloy screw obtained by the producing
method of the invention has excellent strength. It is possible to
obtain a screw having more excellent strength by carrying out
specific thermal treatment after the screw working.
BEST MODE FOR CARRYING OUT THE INVENTION
[0042] Embodiments of the present invention will be explained
below.
TEST EXAMPLE 1-1
[0043] Extruded materials (.phi.8.0 mm, .phi.5.25 mm) of
magnesium-based alloy (material corresponding to ASTM AZ31)
containing Al: 3.0% by mass, Zn: 1.0% bymass, Mn: 0.15% bymass,
andbalance comprising Mg and impurities were prepared. The extruded
material of .phi.8.0 mm was subjected to drawing to .phi.5.25 mm at
the temperature of about 160.degree. C. and working ratio that
cross section reduction ratio per one pass was 20% or less
(temperature rising speed to 160.degree. C. is about 10.degree.
C./sec, drawing speed is 16 m/sec). After the drawing, thermal
treatment of 350.degree. C..times.15 min was carried out. As a
result, the grains were fined by recovery and recrystallization.
The structure of the obtained drawn material of .phi.5.25 mm was
checked, the average crystal grain diameter was 7.5 .mu.m, and the
maximum crystal grain diameter was 10.2 .mu.m. A drawn material of
.phi.1.66 mm was also prepared under the same conditions (the
average crystal grain diameter was 6.8 .mu.m, and the maximum
crystal grain diameter was 9.8 .mu.m).
[0044] The long drawn materials (base wires) of .phi.5.25 mm and
.phi.1.66 mm obtained through the above procedure, and the long
extruded material of .phi.5.25 mm (the average crystal grain
diameter was 28 .mu.m and the maximum crystal grain diameter was 75
.mu.m) which was not subjected to drawing were supplied to the
forging apparatus as they are, and a head portion of a screw was
formed.
[0045] In this example, the head working was carried out using the
forging apparatus having the holding die which fixes the wire at
the time of the head working and a plurality of punches which form
the head portion of the screw. This forging apparatus includes
cutting means capable of cutting the supplied long linear material
into constant length, and transferring means for transferring the
cut wire to the holding die, and the forging apparatus can
continuously carrying out the procedure from the cutting operation
of the long materials to the forming operation of the head
portion.
[0046] In this example, the holding die and the punches
respectively have heating means for heating them. The cut wire can
be heated by the heating means through the holding die and the
punches. FIG. 1 is a schematic diagram showing structures of the
holding die and the cutting die portions in the forging apparatus
used for this example. A holding die 10 is fixed to a die holder
11, the die holder 11 is provided with a heater hole 11a, an
electric heating type cartridge heater 12 is inserted into the
heater hole 11a, and a temperature sensor 13 is also inserted in
the same manner in a hole which is separately formed such that the
temperature of the die holder 11 can be adjusted. The die holder 11
is fixed to a forging apparatus body (not shown). Therefore, in the
die holder 11, heat insulators 14 are disposed on contact surfaces
with respect to the forging apparatus body (left, right and rear
three surfaces in FIG. 1), thereby enhancing the thermal efficiency
by maintaining the heating temperature of the die holder 11 and
protecting the apparatus body. In this example, in addition to the
holding die 10, the die holder 11 includes cutting die 15 for
holding the wire in the cutting step. Thus, the heater 12 can heat
both the holding die 10 and the cutting die 15. By heating the
cutting die 15 in the cutting step, when the long materials are cut
into wires having constant length, the wire can be heated by
heating the cutting die 15. At the same time, the holding die 10
can also be heated.
[0047] FIG. 2 is a schematic diagram showing a structure of punch
portion in the forging apparatus used in this example. This example
includes two punches 20A and 20B. The punch 20A carries out
preliminary forming of the screw blank, and the punch 20B can
obtain a screw blank having a completed head portion. The punch 20B
has a plus head. The punches 20A and 20B are held by a punch holder
21, the punch holder 21 is provided with a heater hole 21a, an
electric heating type cartridge heater 22 is inserted into the
heater hole 21a, and a temperature sensor 23 is also inserted in
the same manner in a hole which is separately formed such that the
temperature of the punch holder 21 can be adjusted. This punch
holder 21 is also fixed to the forging apparatus body (not shown),
a heat insulator 24 is disposed on a contact surface of the punch
holder 21 with respect to the forging apparatus body (one rear
surface in FIG. 2) to enhance the thermal efficiency and prevent
heat emission to the apparatus body.
[0048] The procedure from the cutting operation of the long
materials to the forming operation of the head portion was
continuously carried out in the following manner using the forging
apparatus having the above-described structure. First, a long
materials are inserted into a cutting blade hole 15a of the cutting
die 15 heated by the heater 12 and then, they are cut by a cutter
(not shown), the cut wire is transferred to a position of the
center hole 10a of the holding die 10 heated by the heater 12 by
transferring means (not shown), it is inserted into the center hole
10a by the punch 20A and at the same time, the head working is
carried out. With this operation preliminary forming of the screw
blank is carried out and then, the head working is carried out by
the punch 20B, and a screw blank having a completed head portion is
obtained.
[0049] By changing the outputs of the heaters 12 and 22 by above
procedure using the above forging apparatus, the heating
temperatures of the heaters 12 and 22 were changed to change the
temperature of the wire, the head working was carried out under
various temperature conditions, and it was checked whether the head
working could be carried out. In this example, screw blanks for M6
and screw blanks for M2 were produced. A result thereof is shown in
Table 1. In Table 1, .largecircle. shows that headworking could be
carried out in two stages, x shows that a crack and the like were
generated and head working could not be carried out, and
.tangle-solidup. shows that head working could be carried out in
two stages but heating temperature was high and there was a problem
in terms of the lifetimes of working tools such as the holding die
and punches. The forging speed of the drawn material and the
extruded material was about 120 mm/sec. The wire temperature when
the head working was carried out was measured by a contact
thermometer. TABLE-US-00001 TABLE 1 Average crystal grain M6 M2
diameter, maximum crystal Temperature working can be Temperature
working can be Work piece grain diameter (for M6) of wire (.degree.
C.) carried out or not of wire (.degree. C.) carried out or not
Drawn 7.5 .mu.m RT x RT x material 10.2 .mu.m 105 x 107 x 152 x 154
.smallcircle. 182 .smallcircle. 180 .smallcircle. 243 .smallcircle.
240 .smallcircle. 266 .tangle-solidup. 265 .tangle-solidup. 298
.tangle-solidup. 301 .tangle-solidup. Extruded 28.0 .mu.m RT x
material 75.0 .mu.m 108 x 151 x 199 x 241 x 270 .tangle-solidup.
299 .tangle-solidup.
[0050] It can be found that when drawn material is used as shown in
Table 1, screw blank for M2 can be subjected to head working when
the wire temperature is 140.degree. C. or higher. It can be found
that when the wire temperature is 180.degree. C. or higher, even
screw blank for large diameter M6 can be subjected to head working.
It can be found from Table 1 that when drawn material is used, head
forgoing can sufficiently be carried out even if the wire
temperature is lower than 250.degree. C. Especially in this
example, the working was carried out at the forging speed of 120
mm/sec that is at industrial production level, and the head working
could be carried out without any problem. In this example, working
having large working ratio, i.e., plus head was carried out, but in
this case also, the head working could sufficiently be carried out
even if the wire temperature was lower than 250.degree. C. Even
when the wire was heated to higher than 250.degree. C., head
working could be carried out. However, in consideration of the
lifetimes of working tools such as the holding die and punches, it
is preferable to work while heating the wire to lower than
250.degree. C.
[0051] Whereas, when extruded material which was not subjected to
drawing is used as shown in Table 1, head working could not be
carried out without heating the wire to 250.degree. C. or higher.
The working speed of the head working is lower as compared with a
case in which drawn material is used, and it is considered that the
productivity is poor.
[0052] In this example, the cutting die 15 is heated by the heater
12 of the die holder 11 shown in FIG. 1, and the long materials are
indirectly heated by this heating and, then, are cut.
Alternatively, a structure for directly heating the long materials
may further be provided. For example, a dryer may be provided for
directly blowing hot air against the long materials. At that time,
the long materials can be heated faster, more stably and
sufficiently by the heating operation of the cutting die 15 and the
heating operation by the hot air, and the cutting performance can
further be enhanced. This is effective especially when a screw
having a large diameter exceeding M4 is to be formed.
TEXT EXAMPLE 1-2
[0053] Similar tests were carried out using magnesium-based alloys
having different compositions. That is, after extruded materials
were subjected to drawing, drawn materials subjected to thermal
treatment were subjected to head working at various temperatures
using the same forging apparatus (screw blank for M2 and screw
blank for M6 were produced). Compositions of magnesium-based alloys
used for the test will be shown below.
[0054] A magnesium-based alloy containing Al: 1.2% by mass, Zn:
0.4% by mass, Mn: 0.3% by mass, and balance comprising Mg and
impurities (material corresponding to ASTM AZ10)
[0055] A magnesium-based alloy containing Al: 6.4% by mass, Zn:
1.0% by mass, Mn: 0.28% by mass, and balance comprising Mg and
impurities (material corresponding to ASTM AZ61)
[0056] A magnesium-based alloy containing Al: 9.0% by mass, Zn:
0.7% by mass, Mn: 0.1% by mass, and balance comprising Mg and
impurities (material corresponding to ASTM AZ91)
[0057] A magnesium-based alloy containing Al: 1.9% by mass, Mn:
0.45% by mass, Si: 1.0% by mass, and balance comprising Mg and
impurities (material corresponding to ASTM AS21)
[0058] A magnesium-based alloy containing Al: 4.2% by mass, Mn:
0.50% by mass, Si: 1.1% by mass, and balance comprising Mg and
impurities (material corresponding to ASTM AS41)
[0059] A magnesium-based alloy containing Al: 6.1% by mass, Mn:
0.44% by mass, and balance comprising Mg and impurities (material
corresponding to ASTM AM60)
[0060] A magnesium-based alloy containing Zn: 5.5% by mass, Zr:
0.45% by mass, and balance comprising Mg and impurities (material
corresponding to ASTM ZK60)
[0061] With any of the samples, in screw blanks for M2, head
working could be carried out by heating the wire to 140.degree. C.
or higher and lower than 250.degree. C. Even when the wire has
large diameter as large as M6, the head working could be carried
out by heating the wire to 180.degree. C. or higher.
TEST EXAMPLE 2-1
[0062] Screw blanks for M2 and Screw blanks for M6 having head
portions prepared through the procedure of the test example 1 were
subjected to thread rolling.
[0063] In this example, thread rolling was carried out using a
thread rolling apparatus having thread rolling die. Further, in
this example, apparatus has heating means capable of heating the
thread rolling die so that the screw blank can be heated through
the thread rolling die. FIG. 3 is a schematic diagram of a
structure of a thread rolling die portion of the thread rolling
apparatus used in this example. In the thread rolling die used in
this example, a movable die 30A which can slide and a stationary
die 30B are opposed to each other, the die 30A and 30B respectively
have heater holes 31, and electric heating type cartridge heaters
32 are inserted into the heater holes 31, respectively. The
stationary die 30B is separately provided with a hole so that the
temperature thereof can be adjusted, and a temperature sensor 33 is
inserted into this hole. The movable die 30A and the stationary die
30B are fixed to a thread rolling apparatus body (not shown). To
enhance the thermal efficiency and to protect the apparatus body,
in the moving die 30A and the stationary die 30B, heat insulators
34 are disposed on contact surfaces with respect to the thread
rolling apparatus body (in FIG. 3, left, front and rear three
surfaces in the case of the moving die 30A, and right, front and
rear three surfaces in the case of the stationary die 30B). Grooves
(not shown) are formed in opposed surfaces of the die 30A and 30B
for forming a screw thread on a shaft portion of the screw blank,
the shaft portion of the screw blank is disposed between the
opposed surfaces, the moving die 30A is slid, thereby carrying out
the thread rolling.
[0064] Further, a thread rolling apparatus has a shoot rail which
moves the screw blank to the thread rolling die. In this example, a
thread rolling apparatus which has a shoot rail including heating
means is utilized. The screw blank is preliminarily heated by the
heating means. FIG. 4 is a schematic diagram showing structures of
the shoot rail portion and the thread rolling die portion of the
thread rolling apparatus used in this example. The shoot rail 40
arranges screw blanks 100 obtained in the head forging step, and
moves the screw blanks 100 toward the thread rolling die. The shoot
rail 40 sandwiches a shaft portion 101 of the screw blank 100. The
shoot rail 40 is fixed by a support member 41. A rod 42 which moves
the screw blank 100 is provided between the moving die 30A and the
stationary die 30B. In this example, an electric heating type
cartridge heater 43 is disposed outside of the shoot rail 40, and a
temperature sensor 44 is disposed to adjust the temperature.
[0065] Using the thread rolling apparatus, output of the heater 32
was changed to change the heating temperature of the thread rolling
die, the temperature of the screw blank was changed, screw blank
for M2 and screw blank for M6 obtained in the test example 1 were
subjected to thread rolling at various temperatures, and it was
checked whether thread rolling could be carried out. A result
thereof is shown in Table 2. In Table 2, .largecircle. shows that
thread rolling could be carried out, .DELTA. shows that thread
rolling could be carried out but fine cracks were generated, x
shows that cracks and the like were generated and thread rolling
could not be carried out, and .tangle-solidup.0 shows that thread
rolling could be carried out but heating temperature was high and
there was a problem in terms of the lifetimes of working tools such
as the thread rolling die. TABLE-US-00002 TABLE 2 Heating working
can be temperature (.degree. C.) of carried out or not Work piece
thread rolling die M6 M2 Drawn RT x x material 100 .DELTA.
.smallcircle. 150 .smallcircle. .smallcircle. 200 .smallcircle.
.smallcircle. 240 .smallcircle. .smallcircle. 260 .tangle-solidup.
.tangle-solidup. 290 .tangle-solidup. .tangle-solidup. Extruded RT
x material 100 x 150 x 200 x 240 x 260 .tangle-solidup. 290
.tangle-solidup.
[0066] It can be found from Table 2 that when screw blank made of
drawn material is used, the screw blank is heated by heating the
thread rolling die to 100.degree. C. or higher, and the thread
rolling can be carried out. It can be found from Table 2 that even
if the heating temperature of the thread rolling die is lower than
250.degree. C. the thread rolling can sufficiently be carried out.
Especially when the screw had a large diameter as large as M6, the
thread rolling could sufficiently be carried out with heating
temperature of the thread rolling die of 150.degree. C. or higher.
Even if the thread rolling die is heated to higher than 250.degree.
C., thread rolling could be carried out. However, in consideration
of the lifetimes of working tools such as the thread rolling die,
it is desired to work by heating the thread rolling die lower than
250.degree. C.
[0067] The strength of the obtained M6 screws were checked, and it
was found that a torsion fracture torque was 3.5 to 4.5 Nm, and the
screws have excellent strength.
[0068] Whereas, when screw blanks made of extruded material which
is not subjected to drawing as shown in Table 2 are used, when the
thread rolling die is not heated to 250.degree. C. or higher,
thread rolling can not be carried out.
TEST EXAMPLE 2-2
[0069] Similar tests were carried out using magnesium-based alloys
having different compositions. That is, screw blanks (for M2 and
M6) produced in the test example 1-2 were subjected to thread
rolling using thread rolling die which were heated at various
temperatures. As the magnesium-based alloys, the following
materials having the same compositions as those shown above were
used, i.e., a material corresponding to AZ10, a material
corresponding to AZ61, a material corresponding to AZ91, a material
corresponding to AS21, a material corresponding to AS41, a material
corresponding to AM60 and a material corresponding to ZK60.
[0070] As a result of the test, with any of the samples, thread
rolling could be carried out sufficiently by heating the thread
rolling die to 100.degree. C. or higher and lower than 250.degree.
C. like the test example 2-1. Even if the diameter of the sample
was as large as M6, thread rolling could sufficiently be carried
out by heating the same to 150.degree. C. or higher like the test
example 2-1.
TEST EXAMPLE 3
[0071] In the same manner as those of the test examples 1 and 2,
drawn material was subjected to head working for forming head
portion and thread rolling for forming screw thread to obtain
screws, and the obtained screws were subjected to thermal treatment
at various temperatures, and tensile characteristics and toughness
of the obtained screws were evaluated. In this test, tensile
strength was measured as the tensile characteristics. As the
toughness, head striking test described in JIS B1051 was carried
out, and it was checked whether there existed a crack.
[0072] Drawn material having the same composition as that of the
test example 1-1 was produced under the same condition, and such
drawn materials were used in this example (.phi.5.25 mm, average
crystal grain diameter is 7.5 .mu.m, maximum crystal grain diameter
is 10.2 .mu.m).
[0073] The drawn material was subjected to the head working under
the same condition as that of the test example 1-1. Screw blank
subjected to the head working was subjected to thread rolling under
the same condition as that of the test example 2-1 (heating
temperature was 150.degree. C.).
[0074] A result of the test is shown in Table 3. In Table 3, the
term "forging temperature" means temperature directly measured from
a wire using a contact thermometer. The term "thread rolling
temperature" means temperature measured from thread rolling die by
a temperature sensor of the thread rolling die. Thermal treatment
was carried out for 15 minutes at each annealing temperature.
TABLE-US-00003 TABLE 3 Forging Thread rolling Annealing Tensile
temperature temperature temperature strength Result of head
striking Work piece (.degree. C.) (.degree. C.) (.degree. C.) MPa
test Drawn 182 150 Not heated 227 Satisfactory (no crack) material
100 235 Satisfactory (no crack) 150 248 Satisfactory (no crack) 200
240 Satisfactory (no crack) 250 236 Satisfactory (no crack) 300 230
Satisfactory (no crack) 350 233 Satisfactory (no crack) 400 227
Satisfactory (no crack)
[0075] As shown in Table 3, it can be found that when screw working
is carried out using drawn material, the screw can be produced
sufficiently even it is heated lower than 250.degree. C., and a
screw having tensile strength as high as 220 MPa or higher and
excellent toughness can be obtained. Especially, it can be found
that subjecting the screw to thermal treatment after the screw
working further enhances tensile strength. It can be found from
Table 3 that the temperature of the thermal treatment is preferably
in a range of 100 to 350.degree. C.
INDUSTRIAL APPLICABILITY
[0076] The producing method of magnesium-based alloy screw of the
present invention is optimal for obtaining a magnesium-based alloy
screw having excellent tensile characteristics. Especially, the
producing method of the invention has lower working temperature
when screw working is carried out and has excellent productivity.
Therefore, the producing method of the invention can be applied
when a magnesium-based alloy screw having excellent strength is to
be obtained with excellent productivity. The obtained
magnesium-based alloy screw can be utilized in a field where high
strength is required.
BRIEF DESCRIPTION OF THE DRAWINGS
[0077] FIG. 1 is a schematic diagram of structures of holding die
and cutting die portions in a forging apparatus used in a test
example 1.
[0078] FIG. 2 is a schematic diagram of a structure of a punch
portion in the forging apparatus used in the test example 1.
[0079] FIG. 3 is a schematic diagram of a structure of thread
rolling die portion in a thread rolling apparatus used in a test
example 2.
[0080] FIG. 4 is a schematic diagram of structures of shoot rail
and thread rolling die portions in the thread rolling apparatus
used in the test example 2.
EXPLANATION OF LETTERS OF NUMERALS
[0081] 10 holding die, 10a center hole, 11 die holder, 11a heater
hole, 12 heater, 13 temperature sensor, 14 heat insulator, 15
cutting die, 15a cutting blade hole, 20A, 20B punch, 21 punch
holder, 21a heater hole, 22 heater, 23 temperature sensor, 24 heat
insulator, 30A movable die, 30B stationary die, 31 heater hole, 32
heater, 33 temperature sensor, 34 heat insulator, 40 shoot rail, 41
support member, 42 rod, 43 heater, 44 temperature sensor, 100 screw
blank, 101 shaft portion
* * * * *