U.S. patent application number 10/569511 was filed with the patent office on 2007-01-18 for cast-iron thixocasting apparatus and method.
Invention is credited to Toshiro Maekawa, Syuichi Shikai, Masayuki Tsuchiya, Hiroaki Ueno, Chiaki Ushigome.
Application Number | 20070012415 10/569511 |
Document ID | / |
Family ID | 34213896 |
Filed Date | 2007-01-18 |
United States Patent
Application |
20070012415 |
Kind Code |
A1 |
Tsuchiya; Masayuki ; et
al. |
January 18, 2007 |
Cast-iron thixocasting apparatus and method
Abstract
Disclosed is an apparatus for and a method of thixocasting a
cast iron, that can effectively prevent the scale from mixing in
the die (cavity) thereby to obtain sound iron castings having good
mechanical properties. The apparatus includes at least a pair of
dies that can freely opened and closed to define a cavity to be
filled under a pressure, and an injector that injects the
semi-molten iron into the cavity through a hole in a gate at the
entry of the cavity so as to throttle the entry. The gate is a
separate member disposed at the entry of the cavity every time an
injection casting operation is carried out and is taken out
together with the casting after the injection casting
operation.
Inventors: |
Tsuchiya; Masayuki;
(Saitama, JP) ; Ueno; Hiroaki; (Saitama, JP)
; Ushigome; Chiaki; (Hyogo, JP) ; Maekawa;
Toshiro; (Hyogo, JP) ; Shikai; Syuichi;
(Hyogo, JP) |
Correspondence
Address: |
RONALD E. GREIGG;GREIGG & GREIGG P.L.L.C.
1423 POWHATAN STREET, UNIT ONE
ALEXANDRIA
VA
22314
US
|
Family ID: |
34213896 |
Appl. No.: |
10/569511 |
Filed: |
August 24, 2004 |
PCT Filed: |
August 24, 2004 |
PCT NO: |
PCT/JP04/12093 |
371 Date: |
February 27, 2006 |
Current U.S.
Class: |
164/113 ;
164/312; 164/900 |
Current CPC
Class: |
B22D 17/007 20130101;
B22C 9/06 20130101 |
Class at
Publication: |
164/113 ;
164/312; 164/900 |
International
Class: |
B22D 17/10 20070101
B22D017/10 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 26, 2003 |
JP |
2003-301465 |
Claims
1-3. (canceled)
4. In an apparatus for thixocasting a cast iron, comprising at
least a pair of dies that can be freely opened and closed to form a
die cavity which is to be filled with semi-molten cast iron under a
pressure, injection means operable to inject the semi-molten
injected material into the die cavity through an injection path,
and a gate located at the entry of the die cavity so as to throttle
entry from the injection means into the die cavity, the improvement
wherein the gate is constituted from a separate gate member and is
disposed at the entry of the cavity each time an injection casting
operation is carried out and is taken out together with the casting
after the injection casting operation is completed.
5. The apparatus for thixocasting a cast iron according to claim 4,
wherein the gate member has a projecting portion formed to a
certain extent around the gate hole facing the injection path.
6. In a method of thixocasting a cast iron, which comprises filling
a cavity in dies with semi-molten cast iron that is injected
through a gate that throttles the entry of the cavity under a
pressure, the improvement wherein the injected material is covered
on the circumference thereof by a steel sheet 0.2 to 0.5 mm thick
and having a melting point higher than that of the injected
material.
7. The method of thixocasting a cast iron according to claim 6,
wherein the cast iron material is injected through a gate hole
having a projecting portion formed to a certain extent around the
gate hole and facing the injection path.
8. The method of thixocasting a cast iron according to claim 6,
wherein the steel sheet is a stainless steel sheet.
9. The method of thixocasting a cast iron according to claim 7,
wherein the steel sheet is a stainless steel sheet.
Description
TECHNICAL FIELD
[0001] The present invention relates to an apparatus for and a
method of thixocasting a cast iron and, more particularly, to an
apparatus for and a method of thixocasting a cast iron, that
prevent the mixing of scale thereby to obtain sound iron castings
having good mechanical properties.
BACKGROUND ART
[0002] Thixocasting process, in which semi-molten billets, in such
a state as solid and liquid phases coexist, formed by heating cast
iron are injected into a mold constituted from dies, is capable of
manufacturing a part that has a smaller wall thickness and more
complicated shape than are possible with the conventional iron
casting processes. The thixocasting process can manufacture a part
near net shape that has substantially no casting defects such as
shrinkage cavity, and is therefore regarded as a promising new iron
casting method.
[0003] However, the thixocasting process of the prior art has such
a problem that, when cast iron is heated so as to turn into a
semi-molten state, scale formed on the material surface may mix
into the casting, thus resulting in a defect and making it
difficult to obtain sound castings on a stable basis.
[0004] There has also been such a technical problem that the
thermal load on the die may cause melting loss and/or cracks when
casting semi-molten cast iron that is a material of high melting
point. The melting loss and/or cracks tend to occur at the end of
an injection path that runs from an injection sleeve to a mold
cavity, namely at a gate provided at the entry of the cavity. These
defects have been a factor that governs the service life of the
dies and requires much time for repairing the dies.
[0005] There is a process of thixocasting for aluminum or other
material where a gate is provided to prevent scale from mixing in
the casting.
[0006] There is also such a thixocasting system for aluminum as the
gate provided at the entry of the cavity to prevent scale from
mixing in the casting is a sliding gate. In the sliding gate
system, the gate is split into two halves, and the split gates can
slide to the right and left to open and close, so that the gate is
completed to be ready for injection casting when closed, and is in
standby when opened.
[0007] Patent Document 1: Japanese Unexamined Patent Publication
No. 8-300126
[0008] Patent Document 2: Japanese Unexamined Patent Publication
No. 9-220656
[0009] Patent Document 3: Japanese Unexamined Patent Publication
No. 2003-73768
DISCLOSURE OF THE INVENTION
[0010] Problems to be Solved by the Invention
[0011] In case a thixocasting apparatus of slide gate system is
applied to cast iron that is a material of high melting point,
however, the high temperature tends to cause melting loss and/or
cracks of the gate that may require frequent repairing of the die,
or cause such a trouble that it becomes difficult to open/close the
slide gate due to thermal strain.
[0012] Accordingly, an object of the present invention is to
provide an apparatus for and a method of thixocasting a cast iron,
that can effectively prevent the scale from mixing in the casting
(cavity) thereby to obtain sound iron castings having good
mechanical properties, by employing a system different from the
slide gate system of the prior art.
[0013] Means for Solving the Problems
[0014] After various experiments and studies conducted in order to
achieve the object described above, the present inventors have
completed the invention of an apparatus for thixocasting a cast
iron that employs a system called insert system, instead of the
slide gate system. In the insert system, a plurality of gate
members that are independent components are prepared as the gate,
and are disposed at a cavity position every time injection casting
is carried out. The gate member becomes inserted in the
casting.
[0015] A first aspect of the apparatus for thixocasting a cast iron
of the present invention is that at least a pair of dies that can
freely open and close so as to form a cavity which is to be filled
with semi-molten cast iron under a pressure, and injection means
that injects the semi-molten iron into the cavity through an
injection path are provided, while the gate is provided at the
entry of the cavity so as to throttle the entry, wherein the gate
is constituted from a separate gate member and is disposed at the
entry of the cavity every time an injection casting operation is
carried out and is taken out together with the casting after the
injection casting operation.
[0016] A second aspect of the apparatus for thixocasting a cast
iron of the present invention is that, in addition to the first
aspect described above, the gate member has a projecting portion
formed around a gate hole that faces the injection path to a
certain extent.
[0017] A third aspect of the present invention is a method of
thixocasting a cast iron, which comprises filling the cavity in the
dies with semi-molten cast iron injected under a pressure through
the gate that throttles the entry of the cavity, wherein the
injected material is covered on the circumference thereof with a
thin steel sheet 0.2 to 0.5 mm thick that has a melting point
higher than that of the injected material.
[0018] With the apparatus for thixocasting a cast iron according to
the first aspect, when the material in semi-molten state is cast by
injection by means of the injection means, one gate prepared in
advance is disposed at the entry of the cavity formed by a pair of
dies. Then the injection casting of the material is carried out by
the injection means, so that the semi-molten material passes
through the gate disposed at the entry of the cavity and fills the
cavity under pressure, thereby to make a casting. At this time, the
gate disposed at the entry of the cavity is integrated with the
casting. After the casting operation, the pair of dies is opened
and the gate is taken out together with the casting.
[0019] The gate removed with the casting can be recovered and
reused by separating the portion soldified in the gate and the
casting that has been in the cavity.
[0020] According to the apparatus for thixocasting a cast iron of
the second aspect, since the gate is formed to have a projecting
shape around the gate hole facing the injection path to a certain
extent, at least the scale on the circumference of the injected
material that is pressed against the gate is located outside the
projecting portion, and is left behind without being injected
through the gate hole into the cavity.
[0021] The term "certain extent" means such an extent around the
gate hole as at least the scale formed on the circumference of the
injected material is located at a position sufficiently far from
the projecting portion. The projecting portion is preferably
protrude by 2 mm or more.
[0022] According to the method of thixocasting a cast iron of the
third aspect, since the injected material is covered on the
circumference thereof with a thin steel sheet that has a melting
point higher than that of the injected cast iron, the injected
material is prevented from straining when heated into semi-molten
state. There is also such an advantage that less scale is generated
when heated into semi-molten state. Thickness of the thin steel
sheet is within the range from 0.2 to 0.5 mm, because the effect of
preventing the injected material from straining when heated into
semi-molten state cannot be obtained when the thickness is less
than 0.2 mm, and the thin steel sheet cannot be folded up well
during the pressured injection operation and filling failure may
result when the thickness is more than 0.5 mm. The thickness is
preferably in a range from 0.2 to 0.3 mm.
[0023] The steel described above may be, for example, stainless
steel.
[0024] Effect of the Invention
[0025] According to the apparatus for thixocasting a cast iron of
claim 1, although the same number of the gate members are required
as the number of castings to be made, since the gate is disposed at
the entry of the cavity every time injection casting is carried
out, the gate that receives the highest thermal load is replaced
for each injection casting operation. As a result, melting loss and
cracking of the gate can be prevented unlike in the slide gate
system of the prior art.
[0026] In contrast to the slide gate system of the prior art that
requires the use of beryllium copper or other expensive material,
the gate made of a low-cost material such as spheroidal graphite
cast iron can well endure melting loss and cracking according to
the present invention.
[0027] In addition, since the die structure can be substantially
simplified, the present invention is free from such a problem of
the slide gate system that the slide gate becomes difficult to open
and close due to thermal strain.
[0028] While the gate member of the present invention is integrated
with the casting, the gate portion can be readily split from the
casting since the cast iron is white cast iron in the case of the
thixocasting, and therefore the gate can be taken away and
reused.
[0029] According to the apparatus for thixocasting a cast iron of
claim 2, in addition to the effect of the constitution of claim 1,
since the gate has a projecting portion formed to a certain extent
around the gate hole facing the injection path, most of the scale
located at the distal end of the injected material such as a billet
can be caused to stay in the space around the projecting portion.
Also the presence of the projecting portion generates a force that
presses the entire injected material against the circumference, so
that the scale can be prevented from mixing on the circumference of
the injected material. That is, the scale of the injected material
can be effectively prevented from mixing into the cavity
(casting).
[0030] According to the method of thixocasting a cast iron of claim
3, since the injected material is covered on the circumference
thereof by the thin steel sheet that has a melting point higher
than that of the injected cast iron, the injected material is
prevented from straining when heated into semi-molten state. When a
part of relatively large size is cast, in particular, it is
necessary to use the injected material such as a billet of a size
that matches the size of the part to be cast and, accordingly, the
injected material (billet) becomes more likely to strain by gravity
as the injected material becomes larger. Thus it is not preferable
to subject the semi-molten injected material that has strained to
thixocasting process, since it causes the entrapment of scales.
[0031] Also by covering the injected material on the circumference
thereof by the thin steel sheet that has a melting point higher
than that of the injected cast iron, generation of the scale can be
reduced when the injected material is heated into solid-liquid
phase.
[0032] Also because the steel sheet used for covering is a thin
sheet, the steel sheet is folded up in front of the gate when the
injected material is injected under pressure, so that the scale
formed on the injected material is captured by the folded steel
sheet, thereby to prevent it from mixing in the cavity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a longitudinal section view of an embodiment of
the present invention.
[0034] FIG. 2 is a longitudinal section view of another embodiment
of the present invention.
DESCRIPTION OF REFERENCE NUMERALS
[0035] 10: Movable die
[0036] 20: Fixed die
[0037] 21: Fitting recess
[0038] 22: Through hole
[0039] 30: Plunger
[0040] 40: Sleeve
[0041] 41: Charge port
[0042] 50: Gate member
[0043] 51: Gate hole
[0044] 52: Projecting portion
[0045] 60: Cavity
[0046] 70: Ejector pin
[0047] 80: Injection path
[0048] B: Billet
BEST MODE FOR CARRYING OUT THE INVENTION
[0049] Preferred embodiments of the present invention will now be
described in more detail with reference to the accompanying
drawings.
[0050] With reference to FIG. 1, the apparatus comprises a pair of
a movable die 10 and a fixed die 20, a plunger 30 and a sleeve 40
that constitute injection means and a gate 50.
[0051] The movable die 10 has a recess in the surface thereof that
makes contact with the fixed die 20, the recess making a cavity 60.
The movable die 10 has ejector pins 70 inserted therein for
ejecting the casting the casting out of the die after casting.
[0052] The fixed die 20 has an injection path 80 formed therein
that communicates with the sleeve 40. The fixed die 20 also has a
fitting recess 21 where the gate 50 is fitted so as to be held on
the surface in contact with the movable die 10. In communication
with the fitting recess 21, a through hole 22 is provided as a part
of the injection path 80.
[0053] The plunger 30 moves back and forth in the injection path
80, so as to push the semi-molten billet B that is the injected
material forward as it advances, so as to fill in the cavity 60
with a pressure via the gate 50.
[0054] The sleeve 40 has a charge port 41 through which the billet
B is fed into the injection path 80.
[0055] The injected material in the form of the billet B is cast
iron, that is charged into the injection path 80 in semi-molten
state through the charge port 41.
[0056] The gate may be made of, for example, spheroidal graphite
cast iron, but may also be made of various low-cost metallic
materials as long as the material would not be melted by the heat
of the injection casting process. Ceramics may also be used. Since
the gate 50 is used each every time injection casting is carried
out, the material is required to be of low cost. In addition, such
a material that is not susceptible to melting loss and cracking,
and is suitable for separation from the casting when recovered and
reused, so as to be favorably reused, may be used.
[0057] The gate member 50 has a through gate hole 51. Diameter of
the gate hole 51 is made smaller than the diameter of the injection
path 80, as a matter of course, and is smaller than the diameter of
the billet B. The gate member 50 is fitted in the fitting recess 21
of the die so that the center of the gate hole 51 is located near
the center of the cross section of the billet B to be injected.
[0058] The gate member 50 is fitted in the fitting recess 21 of the
fixed die 20 before the pair of dies 10 and 20 are closed. The
fitting action is carried out so that the gate 50 is reliably
fastened in the state of the fixed die 20 and the movable die 10
being mated with each other, without mechanically connecting the
gate member 50 and the fixed die 20.
[0059] The gate member 50 is disposed at the entry of the cavity 60
when the pair of dies 10 and 20 are closed (the state shown in FIG.
1), and the gate hole 51 of the gate member 50 serves as a
throttled entry to the cavity 60. The billet B is injected through
the gate hole 51 into the cavity 60.
[0060] Upon completion of the injection casting, the dies 10, 20
are opened and the casting is ejected from the cavity 60 by the
ejector pins 70, so as to be taken out together with the gate
50.
[0061] The casting that has been taken out is integrated with the
gate 50 by the material that is solidified in the gate hole 51. In
the case of the thixocasting process cast iron, since the cast iron
is white cast iron, the solidified portion of the gate member 50
can be readily split from the casting and therefore the gate 50 can
be taken away and reused.
[0062] An embodiment shown in FIG. 2 is a variation of that shown
in FIG. 1 with a different configuration of the gate member 50.
With other regards, the two embodiments are the same and therefore
description will be given with identical reference numerals shown
in FIG. 2.
[0063] In the embodiment shown in FIG. 2, the gate 50 has a
projecting portion 52 formed to a certain extent around the gate
hole 51 of the gate member 50. The term "certain extent" means such
an extent around the gate hole 51 as the scale formed on the
circumference of the billet B is located at a position sufficiently
far from the projecting portion 52. In order to cause most of the
scale located at the distal end of the billet B to stay in the
space around the projection 52, the certain extent described above
is set to such a small distance around the gate hole 51 as the
effect described above can be achieved.
[0064] The projecting portion is sized to about 2 mm to 10 mm.
[0065] By forming the projecting portion 52 around the gate hole 51
of the gate member 50, the scale formed on the billet B can be
prevented from mixing (being entrapped) in the cavity 60.
[0066] In order to prevent the scale formed on the billet B from
mixing in the cavity 60 during the thixocasting process of the cast
iron, it is preferable to cover the circumference of the billet B
with a thin sheet of steel that has a melting point higher than
that of the billet B. Thickness of the thin steel sheet made be in
a range from 0.2 to 0.5 mm, and preferably from 0.2 to 0.3 mm. The
reason for setting this thickness has been described
previously.
[0067] Functions of the thin steel sheet are to prevent the billet
B from straining when heated, to reduce the scale generated on the
surface of the billet B, and to become folded up in front of the
gate member 50 when the injected material is injected, so as to
capture the scale formed on the billet B by means of the folded
thin sheet, thereby to prevent the scale from entering the gate
hole 51.
[0068] Therefore, there is no limitation to the thickness of the
thin sheet which may be such as can be folded up well at the time
of injection casting, and that can sufficiently prevent the
generation of the scale that would be formed on the surface of the
billet B.
EXAMPLES
[0069] Table 1 shows chemical components of hypo-eutectic cast iron
material used in the thixocasting process of an example. Both
Examples and Comparative Examples used billets that were sampled
from a continuously cast rod of the same batch, that can be
regarded as the same material without any substantial variation in
the chemical composition. TABLE-US-00001 TABLE 1 Composition (% by
weight) C Si Mn P S Ni Cr Fe Billet 2.35 2.00 0.60 <0.04
<0.04 1.00 <0.04 balance
[0070] The billet measures 75 mm in diameter, 150 mm in length and
5 kg in weight. The same casting conditions for the thixocasting
operation were set for Examples and Comparative Examples, except
for the injection rate, injection pressure and the billet heating
temperature.
[0071] 20 test pieces were cast in each of Examples 1 to 6 and
Comparative Examples 1 to 4.
[0072] In Examples 1 and 2, thixocasting process was carried out by
using a flat gate member without projecting portion. In Examples 3
and 4, thixocasting process was carried out by using a gate member
having a projecting portion. Examples 5 and 6 are Examples 1 and 2
plus a thin sheet of stainless steel having a thickness of 0.3 mm
provided to cover the billet. In Comparative Examples 1 and 2,
thixocasting process was carried out without using a gate member.
In Comparative Examples 3 and 4, a flat gate member without
projecting portion is used and a thin sheet of stainless steel
having a thickness of 0.6 mm provided to cover the billet.
[0073] Visual inspection and ultrasonic flaw detection test were
employed to see whether the billet was strained when heated or not,
whether the scale was entrapped after casting or not, and whether
there were other defects.
[0074] Table 2 shows the conditions of injection casting, the
number of castings that included scale entrapped therein, and the
presence of other defects.
[0075] In the column "Scale entrapment defect" in Table 2, entry of
"2P/20" indicates that defect was found in two out of the 20 test
pieces. TABLE-US-00002 TABLE 2 Billet heating Stainless Strain
Scale temperature steel film of entrapment (.degree. C.) Gate
member (mm) billet defect Other defects Examples 1 1205 Flat None
None Present 2P/20 None 2 1220 Flat None Present Present 3P/20 None
3 1205 Projecting None None Present 1P/20 None shape 4 1220
Projecting None Present Present 2P/20 None shape 5 1205 Flat 0.3
None None None 6 1220 Flat 0.3 None None None Comparative 1 1205 No
gate None None Present 20P/20 Air entrapped Examples 2 1220 No gate
None Present Present 20P/20 Air entrapped 3 1205 Flat 0.6 None None
Gate hole clogged filling defect 4 1220 Flat 0.6 None None Filling
defect
[0076] With reference to Table 2, Comparative Examples 1 and 2 are
cases where injection casting was carried out without providing a
gate member, and scale entrapment defect and air entrapment defect
were found in all test pieces.
[0077] In Examples 1 and 2, a flat gate member without projecting
portion was used without covering the billet, where entrapment of
the scale was significantly reduced and other defects did not
occur, although the billet strained when heated to 1220.degree.
C.
[0078] In Examples 3 and 4, a gate member having a projecting
portion was used without covering the billet, where entrapment of
the scale hardly occurred and other defects did not occur, although
the billet strained when heated to 1220.degree. C.
[0079] In Examples 5 and 6, a flat gate member without projecting
portion was used while covering the billet with stainless steel
sheet 0.3 mm thick, where entrapment of the scale and other defects
did not occur, and the billet did not strain when heated to
1220.degree. C.
[0080] Comparative Examples 3 and 4 are the same as Examples 5 and
6, except for covering the billet with the stainless steel sheet
having a thickness of 0.6 mm. In case the billet was heated to
1205.degree. C., the covering sheet blocked the gate hole resulting
in filling defect. In case the billet was heated to 1220.degree.
C., there was a large resistance that strained the covering sheet,
thus resulting in filling defect. Sheet thickness of 0.6 mm was too
large.
INDUSTRIAL APPLICABILITY
[0081] The thixocasting process is capable of manufacturing a part
that has a smaller wall thickness and more complicated shape than
are possible with the conventional iron casting processes. The
thixocasting process can manufacture a part near net shape that has
substantially no casting defects such as shrinkage cavity, and is
therefore regarded as a promising new iron casting method.
* * * * *