Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a method and apparatus for casting metals
including alloys and to a method and apparatus of manufacturing metal
materials using a casting apparatus or injection molding machine, and more
particularly, this invention relates to a metal casting method and apparatus
and
a metal material manufacturing method and apparatus, wherein semi-melted
and semi-solid metal thixotropy is effectively utilized for each method and
apparatus.
Thixo-casting (semi-melted casting) and rheocasting (semi-solid casting)
are known as casting methods utilizing thixotropy, or low viscosity and high
fluidity, of a semi-melted and semi-solid metal. These casting methods are
implemented by using a semi-melted and semi-solid metal slurry containing a
mixture of liquid-phase metal and solid-phase metal.
In thixo-casing, a solid metal is heated to form a semi-melted metal slurry
and the slurry is then supplied into a mold. In rheocasting, after a solid
metal is
perfectly melted, the molten metal is cooled to form a semi-solid slurry
containing
granular crystals and the slurry is then poured into a mold.
In the two casting methods, mold filling is improved because it is possible
to conduct casting using a metal exhibiting a high solid-phase ratio and low
viscosity. These methods further have the advantages of enabling (1) a higher
yield, (2) molding of large-sized products, (3) suppression of shrinkage
cavity
formation and improvement in mechanical strength, and (4) molding of thinner
products. In addition, the service life of a mold is prolonged owing to a
decreased
heat load on the mold.
In the above casting procedures, it is necessary that ultrafine, uniform
non-dendrite crystals (desirably spherical crystals) exist in a semi-melted
semi-
solid metal in order to effectively utilize the thixotropy of a semi-melted
metal
and the fluidity of a semi-so]id metal. However, if the solid metal is simply
heated to a semi-melted state or the melted metal is simply cooled to a semi-
solid
state, almost all metal crystals become dendrite crystals in the semi-melted
and
semi-solid metal. For this reason, it is impossible to attain sufficient
thixotropy
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of the semi-melted metal and sufficient fluidity of the semi-solid metal.
Therefore, in thixo-molding, a screw extruder is generally used in an
injection-molding machine, and a solid metal in the extruder barrel is
successively heated while applying a shearing force to the metal to obtain a
semi-
melted state metal slurry.
However, since a screw extruder is complicated in structure and expensive,
the cost to establish casting equipment having the screw extruder is very
high.
Moreover, since the metal slurry produced in the extruder barrel is supplied
directly into a mold, it is impossible to confirm whether or not the metal
crystals
have become complete non-dendrite crystals. Furthermore, it is necessary to
use
molded metal chips as a solid metal to be supplied into the barrel, making the
material cost very expensive.
In rheocasting disclosed in JP-A-HEI 10-34307, for example, a molten
metal is subjected to refrigeration in a holding furnace by contact with a
cooling
body to obtain a half-melted metal in which a solid phase and a liquid phase
coexist. The half-melted metal is further cooled in a holding vessel while
maintaining the coexisting state, thereby forming a metal slurry.
In the prior art rheocasting, the molten metal yields many crystal nuclei
when it undergoes refrigeration. The crystals become spherical in the vessel,
and a desired metal slurry can be produced without use of an expensive
extruder
generally used in thixo-casting. Moreover, the material cost increase can be
controlled, as a metal ingot can be charged into the holding furnace as it is.
In
addition, since it is easy to confirm whether or not the metal slurry has non-
dendrite crystals, a casting procedure effectively utilizing the fluidity of
semi-
solid metal can be implemented.
However, when a real mass production system is constructed by the
rheocasting, a large number of holding vessels must be installed between the
cooling body and the mold to hold the metal slurry. At the same time, the
process that refrigerates the molten metal and the process that supplies the
metal slurry into the mold need to be linked by using the large number of
holding
vessels, thus requiring extremely complicated control. Moreover, it is
necessary
to accurately control the temperature of the metal slurry in the holding
vessels
before pouring the slurry into the mold, making the control even more
complicated.
In view of the above problems, the present invention has been
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accomplished, and one object thereof is to provide a metal casting method and
apparatus and a metal material manufacturing method and apparatus that can
reduce their operation costs and material costs and effectively utilize
thixotropy
without need of complicated control.
To attain the above object, the present invention provides a casting
method comprising a first step of cooling a molten metal to form a metal
slurry
containing a solid phase, a second step of cooling the metal slurry to form a
solid
metal material, and a third step of heating the metal material to a semi-
melted
metal material and supplying it into a mold. In this method, the second step
preferably includes continuously forming metal materials from the metal slurry
and cutting the metal materials to a predetermined length.
This invention further provides a casting apparatus comprising first
means for cooling a molten metal to form a metal slurry containing a solid
phase
and second means for cooling the metal slurry to form a solid metal material.
The metal material is then heated to a semi-melted state and the resultant
metal
material is poured into a mold. In this apparatus, the second means preferably
forms metal materials continuously from the metal slurry and includes a
cutting
unit for cutting the metal materials to a predetermined length. Moreover, the
cutting unit can preferably move along the advancing direction of the metal
material and cut the metal material when its velocity relative to the metal
material becomes zero.
This invention further provide a metal material manufacturing method
that produces a metal material being heated to a semi-melted state and then
supplied into a mold and comprises a first step of cooling a molten metal to
form a
metal slurry containing a solid phase and a second step of cooling the metal
slurry
to form a solid metal material. In this method, the second step preferably
includes continuously solidifying the metal slurry into solid metal materials
and
cutting the metal materials to a predetermined length.
This invention further provides a metal material manufacturing
apparatus that produces a metal material being heated to a semi-melted state
and then supplied into a mold and comprises first means for cooling a molten
metal to form a metal slurry containing a solid phase and second means for
cooling the slurry to form a solid metal material. In this apparatus, the
second
means can preferably solidify the metal slurry continuously into solid metal
materials and includes a cutting unit for cutting the solid metal materials to
a
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predetermined length.
It has been found that when a metal slurry containing non-dendrite
crystals is cooled rapidly into a solid metal material, thixotropy is
potentially
maintained in the solid metal material and that when the solid material is
heated
into a metal slurry in a semi-melted state again, the metal slurry exhibits
thixotropic properties. Therefore, a metal slurry excelling in fluidity and
containing non-dendrite crystals can easily be produced, without need of
complicated control, by rapidly cooling a molten metal into a metal slurry
containing non-dendrite crystals in the first step, cooling the slurry into a
solid
metal material in the second step, and heating the metal material into a semi-
melted state. The metal slurry thus produced can be supplied into a mold.
The above and other objects, advantages and features of the invention will
become apparent from the detailed description of the invention with reference
to
the accompanying drawings, in which:-
FIG. 1 is a schematic cross section showing one embodiment of a casting
apparatus according to this invention,
FIG. 2(a) is a vertical cross section showing first means of the casting
apparatus of FIG. 1 for cooling a molten metal to form a metal slurry,
FIG. 2(b) is a lateral cross section showing the first means of FIG. 2(a),
FIG. 3(a) is a cross section showing second means of the casting apparatus
of FIG. 1 for producing a metal material from the metal slurry,
FIG. 3(b) is an enlarged cross section taken along line 3-3 of FIG. 3(a),
FIG. 4 is an enlarged cross section taken along line 4-4 in the FIG. 1,
FIG. 5 is a schematic view showing a sequence of processes for cutting a
metal material with a cutting unit of the casting apparatus of FIG. 1, and
FIG. 6 is a schematic view showing a sequence of processes for supplying
metal materials into a mold of the casting apparatus of FIG. 1.
As a result of inventors' earnest researches and studies to solve the above
problems, it has been confirmed that when a metal slurry containing non-
dendrite crystals is cooled rapidly, thixotropy is potentially maintained
after the
metal slurry is solidified into a metal material and that if the metal
material is
heated to the semi-melted state again, the semi-melted metal material exhibits
thixotropic properties for about one hour. This invention has been perfected
by
utilizing the characteristics of a metal slurry containing non-dendrite
crystals
that a solid metal material into which the metal slurry is heated and which is
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heated to a semi-melted state can show thixotropy.
This invention will be described in detail with reference to the
accompanying drawings. FIG. 1 shows one embodiment of a casting apparatus
according to the invention. This casting apparatus is for casting desired
products using magnesium alloy (AZ91D) and has a melting pot 1.
The melting pot 1 is covered at its periphery and heated by a melting
heater 2 to hold the magnesium alloy in a melted condition or liquid-phase
temperature state. The melting pot 1 has at its bottom a gate 3 for a molten
material. The gate 3 is for pouring downward molten magnesium alloy stored in
the melting pot 1. The gate 3 is bent like a crank and has a switching valve 4
in
the middle. The switching valve 4 has a slidable valve plunger 5 to open and
shut the gate 3 and a valve cylinder 6 to slide the valve plunger 5.
As first means for producing a metal slurry containing a solid phase, a
cooling unit 10 is placed near the lower area of the melting pot 1. As shown
in
FIGs. 2(a) and 2(b), the coolin.g unit 10 has a plurality of guide recesses 11
formed
on its surface and a cooling water circulating passage 12 therein. The cooling
unit 10 is inclined so the guide recesses 11 face the lower open end of the
gate 3.
Reference number 13 in FIG. 1 represents a cover block that communicates with
the lower open end of the gate 3 and has a predetermined space between it and
the surface of the cooling unit 10.
As second means for cooling the metal slurry into a solid metal material, a
reservoir 20 having a rapid cooling unit 22, a pair of feed rollers 30 and 31
and a
cutting unit 40 are set in the casting apparatus.
The reservoir 20 is open at its top and is set in position below the cooling
unit 10. A material forming passage 21 has a circular section and is attached
to
the reservoir 20. The material forming passage 21 is located at the lower part
of
the reservoir 20, extends horizontally and is open to the side wall of the
reservoir
20. The rapid cooling unit 22 is set at the end of the passage 21. As shown in
FIG. 3(a), the rapid cooli.ng unit 22 comprises a ring jacket 23 surrounding
the
passage 21 and a spouting nozzle 24 open toward the axial center of the ring
jacket 23.
The feed rollers 30 and 31 are aligned in parallel, one above the other, and
have feed recesses 30a and 31a, respectively. These feed recesses have
substantially the same radius of curvature as the inside diameter of the
material
forming passage 21. The distance between the feed recesses 30a and 31a is
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maintained equal to the inside diameter of the passage 21. Each feed roller is
coupled with a rotary actuator (not shown) so that the top feed roller 30
rotates
clockwise while the bottom feed roller 31 rotates counterclockwise, as shown
in
FIG. 3(a).
As shown in FIG. 1, the cutting unit 40 comprises a main body 41, a fixed
damper 42A, a movable damper 42B and a pair of feed-out rollers 44 and 45.
The main body 41 of the cutting unit 40 is movably held by a guide rod 46
and reciprocates horizontally along the axial direction of the material
forming
passage 21 on an extension area of the passage 21. A retraction cylinder 47 is
placed between the main body 41 and a fixed frame F. The retraction cylinder
47 serves as an actuator for allowing the main body 41 to move when an
external
force acts on the main body 41 in the direction away from the reservoir 20 and
causing the main body 41 to return back to a position near the reservoir 20
when
the retraction cylinder 47 is operated to extend.
As shown in Fig. 3(b), the fixed clamper 42A and movable damper 42B are
block members having clamp through-holes 49A and 49B that are made open by
slits 48A and 48B. The clamp through-holes 49A and 49B are formed to have a
slightly larger inside diameter than the material forming passage 21. The
slits
48A and 48B are formed along a plane containing the axis of the clamp through-
holes 49A and 49B and adapted to increase or decrease the diameters of the
clamp
through-holes 49A and 49B by changing the widths of the slits. Tapered
surfaces
50A and 50B are located at the open ends of the slits 48A and 48B, and rod
through-holes 5 1A and 51B intersect the slits 48A and 48B at positions midway
of
the slits. The tapered surfaces 50A and 50B are inclined so that their widths
increase gradually toward the outside. The rod through-holes 51A and 51B are
parallel to each other and have hemispheric dent portions 52A and 52B at their
respective open ends.
Clamping hydraulic cylinders 53A and 53B and unclamping hydraulic
cylinders 54A and 54B are set on the dampers 42A and 42B.
The damping hydraulic cylinders 53A and 53B have piston rods 53aA and
53aB inserted via clamp pieces 55 into the rod through-holes 51A and 51B and
held by the dampers 42A and 42B because clamp pieces 56 are attached to the
dent portions 52A and 52B at the ends of the piston rods 53aA and 53aB. The
damp pieces 55 and 56 have spherical parts facing and conforming in radius to
the dent portions 52A and 52B of the rod through-holes 51A and 51B. These
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clamp pieces can reduce the widths of the slits 48A and 48B of the dampers 42A
and 42B via the dent portions 52A and 52B when hydraulic pressure is applied
to
the hydraulic cylinders 53A and 53B. As a result, the diameters of the clamp
through-holes 49A and 49B can be made smaller.
The unclamping cylinders 54A and 54B, with the pointed ends of piston
rods 54aA and 54aB opposing the open ends of the slits 48A and 48B, are held
by
the dampers 42A and 42B via a holding bracket 57. An expansion rod 58 is
located between the piston rods 54aA and 54aB of the unclamping hydraulic
cylinders 54A and 54B and the tapered surfaces 50A and 50B of the slits 48A
and
48B. The expansion rod 58 is a columnar part attached to the tapered surfaces
50A ad 50B. When the unclamping hydraulic cylinders 54A and 54B receive
unclamping hydraulic pressure, the expansion rod 58 spreads the slits 48A and
48B of the dampers 42A and 42B via the tapered surfaces 50A and 50B, or
increases the diameter of the clamp through-holes 49A and 49B.
The fixed damper 42A adjusts the axis of the clamp through-hole 49A to
coincide with the axis of the material forming passage 21 and is fixed onto
the
main body 41 of the cutting unit 40 along the vertical above part of the slit
48A.
On the other hand, the movable clamper 42B is set on a cutting cylinder
59 along the vertical below part of the slit 48B so that its end facing the
reservoir
20 abuts on the fixed damper 42A.
The cutting cylinder 59 and its cylinder body 59b are set on the main body
41 of the cutting unit 40 so that its piston rod 59a is directed vertically
downward,
and moves the movable clamper 42B in a vertical direction relative to the
fixed
damper 42A. When the cutting cylinder 59 retracts to its maximum position,
the movable clamper 42B stops at its uppermost position so that the axis of
the
clamp through-hole 49B coincides with the axis of the material forming passage
21 or so that the clamp through-hole 49B coincides with the damp through-hole
49A of the fixed damper 42A. Conversely, when the cutting cylinder 59 extends
to its maximum position, the movable clamper 42B descends to its extreme
position and stops at a position where the clamp through-hole 49B deviates
completely from the clamp through-hole 49A of the fixed clamper 42A.
The feed-out rollers 44 and 45 are set parallel to each other, one above the
other, on a roller bracket 60 extending from the movable damper 42B. The
feed-out rollers 44 and 45 have feed-out recesses 44a and 45a on their
circumferences, and the radius of curvature of each feed-out recess is
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substantially the same as the inside diameter of the material forming passage
21.
The interval between the feed-out recesses 44a and 45a is secured to coincide
with
the inside diameter of the material forming passage 21. The feed-out rollers
44
and 45 are lin.ked to rotary actuators (not shown). As shown in FIG. 5(c), the
upper fed-out roller 44 rotates clockwise, while the lower feed-out roller 45
rotates
counterclockwise.
Reference numeral 61 in FIG. 1 denotes a guide block that connects
between the cover block 13 and the reservoir 20.
As shown in FIG. 1, an injection apparatus 70 is set in the casting
apparatus. The injection apparatus 70 supplies heated semi-melted metal into a
mold 90 and has a heating chamber 71. The heating chamber 71 has a
substantially sealed space covered by a heater 72. An outlet nozzle 73
provided
on the upper end of the heating chamber 71 is connected to a sprue 91 of the
mold
90 through an auxiliary nozzle 74.
A suction rod 75 and a pre-heating barrel 76 are set on the heating
chamber 71.
The suction rod 75 is a movable columnar part in the upper end wall of the
heating chamber 71. It is connected to a suction cylinder 77 and moved into or
out of the heating chamber 71 by the suction cylinder 77.
The pre-heating barrel 76 is a cylindrical part extending horizontally from
the side wall of the heating chamber 71. The distal end of the pre-heating
barrel
76 has substantially the same inside diameter as the material forming passage
21
of the reservoir 20. The inside diameter of the proximal end of the barrel 76
adjacent to the heating chamber 71 is slightly larger than the distal end
inside
diameter, and these ends are connected by a part with a tapered inside
diameter.
As shown in FIG. 4, a material intake hole 78 is set at the distal end of the
pre-
heating barrel 76, and a shoot board 79 is connected to the material intake
hole
78.
A pre-heater 80 is set around the proximal end of the pre-heating barrel
76, and a plunger 81 is set at the distal end of the pre-heating barrel 76.
The pre-heater 80 surrounds the pre-heating barrel 76 and heats the pre-
heating barrel 76, and is set to have a slightly lower temperature than the
heater 72 of the heating chamber 71.
The plunger 81 is a cylindrical part having a size fitted into the distal end
of the pre-heating barrel 76. A push-out cylinder 82 is connected to the
plunger
....... ... ....,:.. :,.,.. . . .:... .., . ..w..w.:u: . k+ ,.. . . . ..... ,
.... .
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81 in order to move the plunger 81 forward and backward inside of the pre-
heating barrel 76.
In the casting apparatus, magnesium alloy ingots are flrst introduced into
the melting pot 1, and the melting heater 2 is turned on. With the melted
magnesium alloy held in the melting pot 1, cooling water is circulated in the
cooling unit 10 and then supplied into the rapid cooling unit 22 to establish
a
standby state. In this operation, the retraction cylinder 47 in the cutting
unit 40
is operated to extend and the main body 41 of the cutting unit 40 is located
near
the reservoir 20. Simultaneously, the cutting cylinder 59 is operated to
retract,
and the movable clamper 42B is stopped at the highest location. Unclamping oil
pressure is then applied to the unclamping hydraulic cylinders 54A and 54B so
that the clamping hydraulic cylinders 53A and 53B are held at tank pressure
and
the fixed damper 42A and movable damper 42B spread the inside diameters of
the clamp through-holes 49A and 49B. Moreover, the feed rollers 30 and 31 are
rotated at a fixed speed, while the feed-out rollers 44 and 45 are held
stopped.
If the valve cylinder 6 retracts and the valve plunger 5 is moved backward
in the standby state, the gate 3 for the molten material is opened and a
molten
magnesium alloy M1 stored in the melting pot 1 is poured onto the cooling unit
10
through the gate 3 (Arrow A in FIG. 1).
The magnesium alloy Ml poured onto the inclined cooling unit 10 flows
along the guide recess 11 of the cooling unit 10 downward (Arrow B in FIG. 1)
and
is then held in the reservoir 20. During the above operation, the molten
magnesium alloy Ml flowing onto the cooling unit 10 is suitably cooled by the
cooling unit 10 and becomes a metal slurry M2 with many nuclei crystallized
out
therein. These crystal nuclei then grow to become finely grained and uniformly
spherical crystals. The metal slurry M2 may thus be sufficiently fluid without
use of an expensive extruder, thereby greatly decreasing the equipment cost.
Moreover, as a metal ingot can be supplied into the melting pot 1 without
conducting any pre-treatment, the material cost can be reduced.
The metal slurry M2 stored in the reservoir 20 is continuously discharged
through the material forming passage 21. At the same time, the metal slurry
M2 passing through the passage 21 is cooled by the cooling water flowing in
the
ring jacket 23 in the rapid cooling unit 22 and rapidly cooled by the cooling
water
supplied from the spouting nozzle 24, and perfectly solidified as a columnar-
rod
metal material M3. In this operation, perfectly solidified metal material M3
is
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produced by rapidly cooling a metal slurry with perfect thixotropy, and
therefore
potentially retains the thixotropy itself. This can easily be confirmed by
observing the crystal structure in the metal material M3.
The metal material M3 discharged from the reservoir 20 is supplied to the
cutting unit 40 by the feed rollers 30 and 31, and passes through the clamp
through-holes 49A and 49B of the fixed and movable dampers 42A and 42B, and
is then supplied to between the feed-out rollers 44 and 45.
During the above operation, the rotation of the feed rollers 30 and 31 is
always observed in the casting apparatus. When the number of rotations
reaches a pre-fixed value, the metal material M3 is cut in accordance with the
following procedure.
When the number of rotations of the feed rollers 30 and 31 reaches the
pre-fixed value, the oil pressure applied to the clamping hydraulic cylinders
53A
and 53B and undamping hydraulic cylinders 54A and 54B is adjusted so that the
diameters of the clamp through-holes 49A and 49B are decreased by the fixed
and
movable dampers 42A and 42B. As a result, as shown in FIG. 5(a), the metal
material M3 is clamped by the two dampers 42A and 42B. Because the main
body 41 of the cutting unit 40 moves together with the metal material M3 along
the guide rod 46 while the retraction cylinder 47 retracts, the relative
velocity
between the clampers 42A and 42B and the metal material M3 becomes zero.
The cutting cylinder 59 is then operated to extend, and the movable
damper 42B is gradually moved downward relative to the fixed damper 42A. As
result, as shown in FIG. 5(b), a shearing stress acts between part of the
metal
material M3 that has passed through the fixed clamper 42A and part of the
metal
material M3 before passing through the fixed damper 42A. The metal material
M3 is then sheared, with the parts as the boundary.
As shown in FIG. 5(c), when the cutting cylinder 59 extends to its
maximum position and the metal material M3 has been sheared, the oil pressure
that acts upon the claniping and unclamping hydraulic cylinders 53B and 54B in
the movable damper 42B is suitably switched. The movable damper 42B
increases the diameter of the clamp through-hole 49B. At the same time, the
feed-out rollers 44 and 45 are rotated to move the sheared metal material M3
out
of the movable damper 42B and discharge it onto a carrying conveyor 100 (FIG.
1).
When the sheared metal material M3 has been discharged onto the
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carrying conveyor, as shown in FIG. 5(d), the feed-out rollers 44 and 45 are
stopped
and simultaneously the cutting cylinder 59 and fixed clamper 42A are returned
to
their respective standby positions. The retraction cylinder 47 is then
operated to
extend, and the unit body 41 is also returned to its standby position.
By repeating the above operation, the metal materials M3 of the pre-fixed
length are continuously discharged onto the carrying conveyor 100.
In the above cutting process, since the cutting unit 40 cuts a metal material
M3 when the relative velocity thereof to the metal material M3 becomes zero,
continuous cutting is possible without interrupting the formation of metal
material
M3.
As shown in FIG. 4, the metal materials M3 thus produced are successively
passed through the shoot board 79 and dropped into the pre-heating barre176
from
the material intake hole 78. As shown in FIG. 6(a), both the pre-heater 80 and
the
heater 72 of the heating chamber 71 are operated in order just when one piece
of the
metal material M3 has been dropped into the pre-heating barrel 76.
The metal material M3 that has been dropped into the pre-heating barre176
is supplied into the heating chamber 71 by the reciprocating movement of the
plunger
81 and held therein in a semi-melted condition as shown in FIG. 6(b).
According to the casting apparatus, the metal material M3 in the pre-heating
barrel 76 is heated by the pre-heater 80, so it is possible to obtain a semi-
melted
magnesium alloy M4 immediately when the metal material M3 reaches the heating
chamber 71. Since the inside diameter of the distal end of the pre-heating
barre176
is the same as the outside diameter of the metal material M3, the distal end
is closed
by the metal material M3 not semi-melted to prevent the semi-melted magnesium
alloy M4 in the heating chamber 71 from flowing backward.
As shown in FIG. 6(c), when a necessary volume of semi-melted magnesium
alloy M4 is stored in the heating chamber 71, the extending action of the feed-
out
cylinder 82 allows the plunger 81 to advance. At the same time, the suction
rod 75
is moved into the heating chamber 71 by the extending action of the suction
cylinder
77. As a result, the semi-melted magnesium alloy M4 stored in the heating
chamber
71 is supplied into the mold 90 through the outlet nozzle 73 and auxiliary
nozzle 74
and molded into a desired shape.
The semi-melted alloy M4 supplied into the mold 90 is obtained by
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heating the metal material M3 that potentially has thixotropy, and is able to
exhibit thixotropy again when molded into a desired shape. Therefore, the
casting successfully utilizing thixotropy can be ensured. In other words, the
casting using magnesium alloy having low viscosity and a high solid-phase
ratio
can be conducted. The filling ability of the mold 90 and the yield are
therefore
improved and the casting rate is increased. Therefore, it is possible to
manufacture large-sized products, suppress the shrinkage cavity formation,
improve the mechanical strength and manufacture thin products, thus creating
many new advantages. Furthermore, the thermal load on the mold 90 can be
reduced to prolong the service life of the mold.
Moreover, the casting apparatus is designed so that the metal slurry M2 is
solidified to form a metal material M3 that is then heated to form a semi-
melted
metal material that is then supplied into the mold 90. It is therefore
unnecessary to couple the cooling unit 10 which cools the molten metal Ml and
the injection apparatus 70 together or to accurately control the temperature
of
the metal material M3. This eliminates the need for complicated control, and
it
is possible to easily carry out casting that effectively utilizes thixotropy.
Moreover, it is possible to handle the solidified metal material M3 as a small
billet,
which may lead to more convenient handling procedures.
After the termination of supplying the semi-melted magnesium alloy M4
into the mold 90, the push-out cylinder 82 retracts, the suction cyli.nder 77
retracts and the level of the molten metal in the heating chamber 71 decreases
as
shown in FIG. 6(d). This prevents the semi-melted magnesium alloy M4 from
being solidified in the outlet nozzle 73 and auxiliary nozzle 74.
The above actions are then repeated to mass-produce desired products
using the mold 90.
Moreover, in the above embodiment, the casting apparatus manufactures
products from magnesium alloy, but it can also manufacture products from
aluminum, aluminum alloy and other metals and alloys.
Furthermore, in the above embodiment, the cutting unit is used to cut the
metal material for easier handling, but this is not always necessary. In the
absence of the cutting unit, it may be adopted to heat the produced metal
material to a semi-melted state and supply the semi-melted metal material into
the mold. Furthermore, the cross section of the produced metal material need
not be circular.
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As has been described in the foregoing, this invention helps reduction of
the operation and material costs, because it does not require use of an
expensive
extruder normally used in thixo-casting and because metal blocks can be used
without any pretreatment. Moreover, the formed metal slurry is solidified, so
it
is not necessary to couple the metal slurry forming process and its supply to
the
mold, eliminating the need to accurately control the temperature of the
solidified
metal slurry. It is also possible to perform casting that effectively utilizes
thixotropy.
