Technical Field
[0001] The present invention relates to a manufacturing method and a molding method of semi-solid
metal slurry and a molding.
Background Art
[0002] It is desirable for metal slurry used in a semi-solid molding method (a rheocast
method) to have a structure in which primary crystals are maintained to be separated
by a liquid crystal matrix and primary crystal particles thereof have a very fine
and homogeneous non-dendritic form or preferably a spherical form. If such a structure
is provided, molding (casting) in a semi-solid state with a high solid-phase ratio
and a low viscosity is enabled, occurrence of a shrinkage cavity of a molded product
can be suppressed, and a mechanical strength of the molded product can be improved.
[0003] The following manufacturing technologies of metal slurry are known.
[0005] The technology described in Patent Reference 1 proposes a molding method of a mushy
metal which can simply and readily obtain a molding having a fine and spherical thixotropic
structure at a low cost irrespective of a mechanical mixing method or an electromagnetic
mixing method, and this technology crystallizes a fine primary crystal in an alloy
liquid by holding an alloy in a liquid state which has a crystal nucleus and a temperature
not lower than a liquidus temperature or an alloy in a solid-liquid coexistence state
which has a crystal nucleus and a temperature not smaller than a molding temperature
in a heat insulating container having an insulation effect for 5 seconds to 60 seconds
while cooling this alloy to a molding temperature at which a predetermined liquid-phase
ratio is shown, and then supplies the alloy into a molding die, thereby effecting
pressure forming.
[0006] However, when the technology described in Patent Reference 1 is used to actually
create slurry and then perform molding, a molding having a fine and homogeneous structure
is not necessarily obtained. In particular, this tendency is prominent in alloys other
than a JISAC4C-based alloy. That is, a molding having a fine and homogeneous structure
is not obtained unless alloys in a solid-liquid coexistence state having an extensive
temperature range are used. Further, when an alloy is directly put into a heat insulating
container, there is a restriction that a crystal grain refining element must be added.
[0007] On the other hand, the technology described in Patent Reference 2 provides a semi-solid
molding method which can readily stabilize and manufacture semi-solid metal slurry
having fine and substantially homogeneous non-dendritic (spherical) primary crystal
particles and easily fill the manufactured semi-solid metal slurry in a pressure sleeve
of a molding machine to perform pressure forming by using a simple apparatus or facility
without requiring special complicated processes, and it is configured to apply a motion
to a molten metal by pouring the molten metal into a slurry manufacture container
while maintaining at least a part of the molten metal at a temperature not greater
than a liquidus temperature and to fill the slurry manufacture container in a pressure
sleeve of a molding machine in a manufacturing method of semi-solid metal slurry which
applies a motion to a molten metal when at least a part of the molten metal has a
temperature not greater than the liquidus temperature in a process where the molten
metal is cooled, and then cools the molten metal to be semi-solidified.
[0008] In the technology described in Patent Reference 2, when slurry is actually manufactured
and then molded, a molding having a fine and homogeneous structure cannot be necessarily
obtained. In particular, this tendency is prominent in alloys other than JISAC4C-based
alloys.
[0009] Patent Reference 3 describes a manufacturing method of a metal material in a solid-liquid
coexistence state, comprising: a pouring step of pouring a molten metal into a container
simultaneously with applying to the container an electromagnetic field which does
not form an initial solid layer in the molten metal to be poured into the container,
and pouring the molten metal into this container in a state where this electromagnetic
field is applied; and a cooling step of cooling the molten metal poured in the container
to form a metal material in a solid-liquid coexistence state. In the technology described
in Patent Reference 3, however, a facility to apply an electromagnetic field is required.
Since this facility is large in size, a cost and a space for this facility are required.
Further, a time to apply an electromagnetic field is needed, thereby prolonging a
processing time.
Disclosure of the Invention
[0010] The present invention is provided to eliminate the above-described problems.
It is an object of the present invention to provide a manufacturing method of semi-solid
metal slurry which enables processing in a short time and can form a molding having
a fine and homogeneous structure without requiring a large facility.
[0011] The manufacturing method of semi-solid metal slurry according to the present invention
is characterized in that, when a metal in a molten state is poured into a container
or a sleeve (which will be referred to as a "container or the like" hereinafter),
the metal enters a supercooled state and self-mixing occurs in the container.
[0012] The manufacturing method of semi-solid metal slurry according to the present invention
is characterized in that a predetermined motion energy is given to a molten metal,
the molten metal is poured into a cooling container or the like maintained at a low
temperature, nuclei are generated by a supercooling phenomenon which occurs due to
contact with a bottom portion of the container or the like at a high speed without
producing an initial solid layer, and then the molten metal itself is self-mixed to
eliminate a temperature gradient in the molten metal in the container or the like,
thereby providing a semi-solid state.
[0013] It is characteristic that an energy for the self-mixing is given by a mechanical
energy or a potential energy.
[0014] It is characteristic that the mechanical energy is a pressure energy. The pressure
energy may apply a pressure to the molten metal in a sealed container so that the
molten metal is shed to be poured into the container or the like.
[0015] It is characteristic that the motion energy is given by dropping down the molten
metal from a predetermine height.
[0016] It is characteristic that a difference (H
in) between a pouring position of the metal in the molten state and a position of the
bottom portion of the container or the like is determined to be 3.5-fold or above
of a diameter (D) of the container or the like to perform pouring.
[0017] It is preferable to set a difference between the metal in the molten state and a
height of the bottom portion of the cooling container to be fourfold or above of the
container diameter, and more preferable to set this difference to be fivefold or above.
If the difference is set to be less than 3.5-fold, a dendrite structure may be formed
depending on conditions. When the difference is set to be fourfold or above, a further
fine and homogeneous structure can be obtained.
As an upper limit, tenfold is preferable. If the difference exceeds tenfold, the molten
metal may lash, or air may be involved and the involved air may suddenly expand to
shake the molten metal depending on pouring conditions. Furthermore, it becomes difficult
to perform casting without spilling the molten metal.
[0018] It is to be noted that a shape of the container or the like is set while considering
thermal equilibrium, but 10 mm to 200 mm is preferable and 40 to 120 is more preferable
as an internal diameter. When such a dimension is adopted, a further fine and homogeneous
structure can be obtained. When the internal diameter D is increased, the poured molten
metal cannot sufficiently move in a lateral direction, and thermal mixing cannot be
satisfactorily performed. As a result, refining of a particle diameter or homogeneity
is hard to be obtained.
[0019] Incidentally, assuming that a height from the bottom portion of the container or
the like to a head portion of the same (an internal height) is h, it is possible to
design to achieve h = 3 H
in to 10 H
in, for example. In this case, pouring can be carried out from a position in the vicinity
of the head portion of the container, and spill at the time of pouring can be reduced.
On the contrary, when design to achieve h < H
in is adopted, h-D can be reduced, and hence involvement of a gas at the time of pouring
can be decreased.
[0020] It is preferable to vertically arrange the container or the like without inclination
and perform pouring from the center without being taken along a side inner wall of
the container or the like. In a prior art, the container or the like is inclined to
calmly perform pouring along the side inner wall. However, in the present invention,
it is preferable to pour quickly without being taken along the side inner wall. As
a result, self-mixing is apt to occur.
Moreover, it is preferable to directly pour the molten metal into the container or
the like without using a cooling member or the like.
[0021] A pouring time is also an important element. As a pouring time, a period of 1 to
10 seconds is preferable although it depends on a pouring amount. A period of 3 to
8 seconds is more preferable. A period of 3 to 5 seconds is further preferable. Considering
mass productivity, a shorter pouring time is preferable, but a desired structure may
not be obtained in some cases if the pouring time is less than 1 second because a
molten metal mixing time in the container is short. If a pouring time exceeds 10 seconds,
operability is deteriorated. Additionally, if a pouring time is long, the molten metal
is newly poured when the entire metal enters a semi-solid state, and hence self-mixing
is hard to occur. It is to be noted that a pouring amount is generally 200 cc to 3000
cc (e.g., 540 to 8100 kg in case of an aluminum alloy).
[0022] It is characteristic that the bottom portion of the container or the like has a concave
curved surface shape as seen from the pouring side.
[0023] It is preferable to form the bottom portion of the cooling container into a concave
curved surface shape as seen from a side where the molten metal is poured. When such
a curved surface shape is adopted, the molten metal which has come into contact with
the bottom portion of the cooling container to generate nuclei flows along the curved
surface. That is, when the molten metal is poured to the center of the bottom portion
of the container, the molten metal which has reached the bottom portion flows to the
outer side of the container along the curved surface of the bottom portion. When the
molten metal which has flowed to the outer side comes into contact with a wall of
the container, it again flows into the container. As a result, a convection of the
molten metal is readily produced, thereby more excellently effecting self-mixing.
Consequently, many nuclei exist on the inner side, thus obtaining a further homogeneous
and fine structure.
As a curvature of the curved surface, assuming that an internal diameter of the container
is D, 0.5 D to 3 D is preferable, and 0.6 D to 1 D is more preferable. When the curvature
is set within this range, convection is more excellently generated, self-mixing is
intensively carried out, and a temperature is better uniformed in the entire container.
[0024] It is characteristic that the metal in the molten state is pressurized and poured.
As a temperature of the molten metal on an initial pouring stage, T
C < (T
L+100) is preferable. T
L: a liquidus temperature of the metal (°C) T
C: an initial temperature of the molten metal (°C)
[0025] It is characteristic that, after the pouring, pouring is carried out to satisfy the
following expression.
Ts: a liquidus temperature of the metal
TL: a solidus temperature of the metal
Teq: a temperature when a temperature of the container or the like becomes equal to a
temperature of the metal after pouring.
[0026] It is characteristic that the container or the like is held in a heat-insulating
state.
It is characteristic that a calorific capacity of the container or the like is set
to a predetermined value in accordance with a heat quantity of the metal in the molten
state and then pouring is carried out.
It is characteristic that a wall thickness of the container or the like is set to
a predetermined value and then pouring is carried out when an internal diameter, a
height and a material of the container or the like are fixed.
It is characteristic that the container or the like is formed of a non-magnetic material
or a magnetic material. In the present invention, electromagnetic mixing is not performed.
Therefore, a degree of freedom of selecting materials of the container or the like
can be extended. There is provided a manufacturing method of semi-solid slurry according
to one of claims 1 to 20.
It is characteristic that the container or the like is formed of stainless steel or
copper. In particular, a material whose thermal conductivity is larger than that of
stainless steel is preferable.
A period of 1 to 10 seconds is preferable as a casting time even though it varies
depending on a shape of the container or the like and a casting amount. A period of
3 to 5 seconds is more preferable. When a casting time is too short, self-mixing is
hard to occur. On the other hand, when a casting time is too long, a continuous flow
cannot be formed, and homogeneity is hard to be obtained.
It is to be noted that the container or the like may be held in a heat insulating
state.
[0027] A molding method according to the present invention is characterized by molding semi-solid
metal slurry manufactured by the manufacturing method of semi-solid metal slurry according
to one of the above-described claims.
[0028] A molding according to the present invention is characterized by being molded by
the molding method.
[0029] Functions of the present invention will now be described based on knowledge obtained
when the present invention is achieved.
The present inventor has searched reasons why a fine and homogeneous structure cannot
be necessary obtained in the technologies described in Patent References 1 and 2.
[0030] In Patent References 1 and 2, generation of a crystal nucleus by a supercooling phenomenon
can be recognized. However, after pouring into the container, mixing of the molten
metal does not occur in the container, and a temperature gradient still remains. That
is, movements of the molten metal are stopped when the molten metal is poured into
the container. As a result, temperature on the container side is low, and slurry having
a high temperature and a small number of nuclei is obtained on the inner side even
if many nuclei are generated.
[0031] In Patent Reference 1 in particular, this tendency is prominent since pouring is
calmly carried out in order to prevent air to be involved (prevent generation of a
gas cavity in a molding).
[0032] On the contrary, in the present invention, a fine and homogeneous (sizes of particle
diameters are not irregular and they fall within a range of 100 to 150 µm) structure
is obtained by controlling a dropping start height.
Therefore, a predetermined motion energy is given to the molten metal to generate
nuclei without producing an initial solid layer. Many nuclei generated at the bottom
portion of the container by pouring spread in the entire container by self-mixing.
That is, the initial molten metal having many nuclei moves in the container, and hence
nuclei are uniformly distributed on the whole.
[0033] After all, the supercooling phenomenon is utilized to generate nuclei without producing
the initial solid layer by pouring the molten metal into the cooling container from
a fixed height and bringing this metal into contact with the bottom portion of the
cooling container. When the molten metal is dropped down from the fixed height, a
potential energy is converted into a kinetic energy. In the container, when the kinetic
energy of the molten metal is large, the molten metal lashes about in the container
until the motion energy disappears. Therefore, self-mixing is performed in the container.
When the molten metal performs self-mixing, a temperature gradient of the molten metal
in the container is eliminated, and the entire molten metal enters a semi-solid state.
As a result, slurry in which many nuclei are uniformly distributed can be obtained.
[0034] However, in order to generate self-mixing by giving the potential energy and converting
it into the kinetic energy, simply pouring the molten metal from a high position is
not necessary good. The present inventor has recognized and researched a factor other
than the height. As a result, the present inventor has discovered that a ratio of
height to diameter of the container is important. That is, the inventor has found
out that self-mixing is excellently generated by setting a ratio of height to diameter
at 3 or above.
[0035] As a temperature of the container or the like, room temperature to 100°C is generally
preferable, but it varies depending on a type of the metal, a molten metal temperature
and others. Adopting a temperature at which a cooling phenomenon occurs when pouring
is carried out can suffice. It is good enough to previously check a temperature in
accordance with each metal by an experiment or the like.
[0036] In the present invention, e.g., a BN spray may be applied on a container surface
in advance in order to generate nuclei.
The BN spray is conventionally applied to the container in order to increase mold
releasing properties, but it is applied in order to generate nuclei in the present
invention.
[0037] When the molten metal is poured into the container, nuclei are also generated on
a surface of the molten metal in the container. In such a case, when the molten metal
is newly poured to be showered down on the molten metal surface, nuclei on the molten
metal surface are mixed in the entire container by an energy (a kinetic energy of
the molten metal) of the newly poured molten metal.
[0038] In the present invention, a molten metal temperature is substantially uniformly maintained
by forced convection at the time of filling. Further, since a surface in a cup is
always washed by the molten metal, generation of many nuclei and growth of the nuclei
into a spherical shape are utilized.
In order to homogenize the above-described molten metal temperature, control over
a temperature in a thermal equilibrium state after pouring is important. This point
will now be described in detail hereinafter with reference to FIG. 1.
[0039] When a molten metal 1 is poured into a cup (a container or the like) 2 (FIG. 1(a)),
heat of the molten metal 1 starts to move to the cup 2 (FIG. 1(b)). With this movement,
a molten metal temperature is lowered, and a cup temperature is increased. It is considered
that heat no longer moves and the temperature does not vary any further when the temperature
of the molten metal becomes equal to the temperature of the cup (FIG. 1(c)).
A temperature T
eq (which will be referred to as an equilibrium temperature hereinafter) at this moment
can be given by the following expression.
![](https://data.epo.org/publication-server/image?imagePath=2007/13/DOC/EPNWA1/EP05741611NWA1/imgb0002)
[0040] In this expression, T
c is a molten metal initial temperature, T
m is a cup initial temperature, H'
f is a value obtained by dividing solidification latent heat by specific heat, and
f
s is a solid fraction. Further, γ is a value obtained by dividing a heat quantity required
to increase a cup temperature by 1 K by a heat quantity required to increase a molten
metal temperature by 1 K, and it is given by the following expression.
![](https://data.epo.org/publication-server/image?imagePath=2007/13/DOC/EPNWA1/EP05741611NWA1/imgb0003)
In this expression, ρ is a density, c is specific heat, V is a volume, a subscript
c belongs to the molten metal, and a subscript m belongs to the cup
[0041] As apparent from Expressions (1) and (2), the equilibrium temperature T
eq (or a solid fraction to be obtained) is determined by initial temperatures of the
cup and the molten metal, and the value γ which is the ratio of heat quantities of
the cup and the molten metal. However, a relationship between a solid fraction and
a temperature must be checked in advance. Furthermore, it can be understood from Expression
(2) that γ can be determined by volumes alone of the cup and the molten metal when
materials of the cup and the molten metal are specified.
Meanwhile, the molten metal in the cup is maintained in the semi-solid state when
T
eq satisfies the following expression.
![](https://data.epo.org/publication-server/image?imagePath=2007/13/DOC/EPNWA1/EP05741611NWA1/imgb0004)
In reality, since heat escapes from a cup surface or a molten metal surface into atmospheric
air, a temperature lower than T
eq obtained by Expression (1) should be achieved, but a temperature reaches a value
close to T
eq given by Expression (1) by insulating a cup outer surface.
[0042] Heat insulation may be carried out by covering an outer portion of the cup with a
heat insulating material.
An actual reached temperature is represented by the following expression.
![](https://data.epo.org/publication-server/image?imagePath=2007/13/DOC/EPNWA1/EP05741611NWA1/imgb0005)
α is a correction coefficient obtained by an experiment, and it may be previously
acquired by an experiment in accordance with actual practical conditions.
For example, assuming that a cup shape is a cylindrical shape having an internal diameter
D, an internal height H and a wall thickness t (fixed), the following expressions
can be achieved.
![](https://data.epo.org/publication-server/image?imagePath=2007/13/DOC/EPNWA1/EP05741611NWA1/imgb0007)
[0043] Based on Expressions (1) and (6), assuming that the internal diameter D and the internal
height h of the cup are fixed, the equilibrium temperature T
eq is determined by the cup wall thickness t and initial temperatures of the molten
metal and the cup when considering the molten metal and the cup formed of the same
material.
As remarked above, giving initial temperatures of the molten metal and the cup, a
material, an amount, a solidus rate and a corresponding temperature T of a semi-solid
material to be manufactured can obtain a necessary wall thickness of the cup based
on Expressions (1), (2), (3), (4) and (6).
[0044] Based on this, the semi-solid material having a desired solid fraction can be manufactured,
but it is important to assure a sufficient pouring height in order to crystallize
a fine primary crystal with a uniform solid fraction in the cup.
That is, when the molten metal is sufficiently mixed in the cup, it is possible to
realize conditions under which there is no temperature difference between a part close
to a cup wall surface and a cup central part, nuclei are sufficiently generated on
the cup wall surface and the molten metal surface and growth of the nuclei is suppressed.
[0045] Incidentally, as a material of the container or the like, it is preferable to use
a material with a good thermal conductivity such as stainless steel or copper.
Moreover, although a shape of the container or the like is set while taking thermal
equilibrium and others into consideration as described above, 10 mm to 200 mm is preferable
and 40 mm to 120 mm is more preferable as an internal diameter. When such a dimension
is adopted, a further fine and homogeneous structure can be obtained.
[0046] It is to be noted that the following shows a specific example of a change in f
s when a degree of superheat of the molten metal is fixed and when a wall thickness
t of the cup is fixed. However, α in Expression (4) is 1.
(Conditions)
[0047]
Molten metal: AC4C
ρ = 2710 kg/m3
C = 963J/kg·k
TL = 612°C
Ts = 555°C
Hf = 398000 J/kg
![](https://data.epo.org/publication-server/image?imagePath=2007/13/DOC/EPNWA1/EP05741611NWA1/imgb0008)
Cup: stainless steel
wall thickness t
cylindrical shape
cup internal diameter D
cup height h
ρm = 7700 kg/m3
Cm = 500 J·kg·k
Tm = 25°C
![](https://data.epo.org/publication-server/image?imagePath=2007/13/DOC/EPNWA1/EP05741611NWA1/imgb0009)
= 7700x500/2710x963
= 1.48
![](https://data.epo.org/publication-server/image?imagePath=2007/13/DOC/EPNWA1/EP05741611NWA1/imgb0010)
Here, a relationship between a temperature and a solid fraction is evaluated by the
following expression.
![](https://data.epo.org/publication-server/image?imagePath=2007/13/DOC/EPNWA1/EP05741611NWA1/imgb0011)
[0048] When the above-described result is assigned to Expression (1), f
s is given by the following expression.
![](https://data.epo.org/publication-server/image?imagePath=2007/13/DOC/EPNWA1/EP05741611NWA1/imgb0012)
In this expression, δT = T
C-T
L, which is a degree of superheat.
[0049] A calculation example in which D, t, h and others are specific values will now be
described.
(a) When superheat is fixed
D = 60 mm
h = 150 mm
δT = 50 (K)
t (mm) |
fs (%) |
1 |
3 |
2 |
17 |
3 |
31 |
4 |
45 |
5 |
60 |
6 |
74 |
[0050] (b) When a wall thickness is fixed
D = 60 mm
t = 4 mm
δT (k) |
fs (%) |
0 |
56 |
10 |
54 |
20 |
52 |
50 |
45 |
100 |
35 |
[0051] According to the present invention, the following many effects are achieved.
A large facility is not required.
Semi-solid slurry can be manufactured in a short time.
A molding having a fine and homogenous structure can be formed.
Semi-solid metal slurry can be manufactured without being restricted to a type/composition
of a target metal.
That is, material selectivity can be expanded. It is possible to apply an iron alloy,
an aluminum alloy, a magnesium alloy and other alloys. As for an aluminum alloy, an
AC4C-based alloy alone can be subjected to semi-solid molding in the prior art, but
an ADC10-based alloy which cannot be practically applied in the prior art can be applied
in the present invention. For example, even an alloy having a composition in the vicinity
of an eutectic point can be applied to semi-solid molding.
[0052] Semi-solid molding is possible without being restricted to a temperature of a molten
metal. An accurate temperature is conventionally required, and hence a complicated
control system is needed, but such a complicated control system does not have to be
provided in the present invention, thereby simplifying a system.
[0053] Moreover, a refining material (e.g., Ti or B) is conventionally added in order to
achieve refining of crystals, but refining of crystals can be attained without using
such a refining material. Of course, a refining material may be added in the present
invention, and further refining can be achieved in such a case. Additionally, effecting
heat balance can readily control a solid fraction.
Brief Description of the Drawings
[0054]
FIG. 1 is a conceptual view showing a thermal equilibrium state.
FIG. 2 is a perspective view of a container used in Embodiment 1.
FIG. 3 is a graph showing a temperature measurement result in Embodiment 1.
FIG. 4 is a micrograph of a molding using a semi-solid material manufactured in Embodiment
1.
FIG. 5 is a side view showing a pouring method according to Embodiment 2.
FIG. 6 is a graph showing a relationship between a particle diameter of a crystal
and Hin/D in Embodiment 3.
FIG. 7 is a micrograph of a test No. 3 in Embodiment 3.
FIG. 8 is a micrograph of a test No. 4 in Embodiment 4.
Description of Reference Numerals
[0055]
- 1
- molten metal
- 2
- container (cup)
- 10
- plunger
Best Mode for Carrying out the Invention
[0056] In an embodiment according to the present invention, mixing which does not form an
initial solid layer in a molten metal poured into a container or the like is produced
without supplying an electromagnetic field from the outside, and the molten metal
is poured into this container or the like. The molten metal which has been poured
into the container is cooled to form a metal material in a solid-liquid coexistence
state, thereby manufacturing semi-solid metal slurry.
An embodiment according to the present invention will now be described hereinafter
with reference to the accompanying drawings.
Embodiment 1
[0057] Pouring was carried out by using a container shown in FIG. 2 under the following
conditions.
Molten metal material: AC4CH
Ts = 610 to 612°C
TL = 555°C
Molten metal initial temperature: 670°C
Cup wall thickness t: 3 mm
Cup material: SUS304
Cup internal diameter: 60 mm
Cup height h: 150 mm
Cup initial temperature: 5°C
Pouring height Hin: 550 mm (pouring from a position 400 mm above a cup upper portion)
Hin/D = 9.1
Casting time: 8 seconds
Heat insulation of the cup: provided (not shown) Pouring time: 5 seconds
[0058] A change in temperature at each portion was measured immediately after pouring the
molten metal. FIG. 3 shows its result. As apparent from FIG. 3, an equilibrium attained
temperature is approximately 590°C and held between T
s and T
L. FIG. 4 shows a micrograph of a molding molded by using a semi-solid material obtained
in this example. It can be understood from FIG. 4 that small primary crystals uniformly
exist in an entire structure of the molding obtained in this example.
Embodiment 2
[0059] In FIG. 5, a bottom plunger tip 10 of a container 2 is arranged to provide a curved
surface having a curvature at an end of the plunger tip. The curved surface forms
a concave shape as seen from a pouring side. The curved surface has a curvature of
R = 70 mm.
A molten metal was poured into this container.
Pouring conditions are the same as those in Embodiment 1.
When the semi-solid slurry obtained in this example was used to perform molding and
a structure of a molding was observed, a finer and more homogeneous structure than
that in Embodiment 1 was obtained.
[0060] Although the above has described the example of the aluminum alloy in the foregoing
embodiment, other molten metals may be used, and they demonstrated the same effects
as those in the foregoing embodiment.
Embodiment 3
[0061] In this example, H
in/D was changed and then pouring was carried out.
Hin: pouring height
D: internal diameter of a container
Other points are the same as those in Embodiment 1.
Test No. |
Hin/D |
Particle diameter of a crystal* |
1 |
1 |
3 |
2 |
2 |
2.8 |
3 |
3 |
2.7 |
4 |
3.5 |
2.3 |
5 |
4 |
1.5 |
6 |
5 |
1.2 |
7 |
7 |
1.1 |
8 |
8 |
1 |
9 |
9 |
1 |
10 |
10 |
0.9 |
11 |
11 |
** |
*: A particle diameter of a crystal (a size of a spherical primary crystal) indicates
a relative value of a particle diameter of a crystal with the test No. 9 being determined
as a reference (1)
*: Involvement of air occurred. |
FIG. 6 shows a relationship between a particle diameter of the crystal and H
in/D. Further, FIGS. 7 and 8 respectively show micrographs of the test No. 4 and the
test No. 5.
It can be understood from each drawing that a very excellent structure can be observed
when H
in/D is not smaller than 4.
Embodiment 4
[0062] In this example, an influence of an initial temperature of a molten metal was examined.
AC4CH was likewise used in this example. However, a liquid-phase temperature of a
material in this example is 617°C.
An experiment was conducted while changing a casting temperature to 610 (-7), 620
(+3), 640 (+23), 655 (+38), 670 (+53), 680 (+63), 700 (+83), 720 (+103) and 730 (+113)°C.
A difference from a liquid-phase temperature is in parentheses.
Other conditions are the same as those in Embodiment 1.
A particle diameter of the crystal was decreased as a temperature is increased.
However, a peak temperature was 700°C, and a saturation or slight declining tendency
was demonstrated at temperatures above the peak temperature.
Embodiment 5
[0063] In this example, a pouring time was changed.
Other points are the same as those in Embodiment 1.
No. |
Pouring time (sec) |
Particle diameter of a crystal* |
Homogeneity of a structure** |
4-1 |
0.5 |
2.0 |
C |
4-1 |
1 |
1.3 |
B |
4-3 |
2 |
1 |
B |
4-4 |
3 |
1 |
A |
4-5 |
4 |
1 |
A |
4-6 |
5 |
1 |
A |
4-7 |
6 |
1 |
A |
4-8 |
7 |
1 |
B |
4-9 |
8 |
1 |
B |
4-10 |
9 |
1 |
B |
4-11 |
10 |
1.4 |
B |
4-12 |
11 |
1.5 |
C |
4-13 |
12 |
1.6 |
C |
*: A particle diameter of a crystal (a size of a spherical primary crystal) indicates
a relative value of a particle diameter of a crystal with samples Nos. 4-6 being determined
as a reference (1).
**: In regard to homogeneity of a structure, with the samples Nos. 4-6 being determined
as a reference (A), B indicates a case where inhomogeneity including segregation is
large and C indicates a case where the same is considerably large. |
Embodiment 6
[0064] In this example, a ratio of a wall thickness and an internal diameter D of a container
(t/D) was changed in Embodiment 1.
A fine and homogeneous crystal structure was obtained when t/D is 0.01 to 0.08 as
compared with other cases.
In particular, when the diameter D of the container falls within a range of 40 to
120 mm, this tendency was prominent.
1. A manufacturing method of semi-solid metal slurry characterized in that, when a metal in a molten state is poured into a container or a sleeve (which will
be referred to as a "container or the like" hereinafter), the metal is poured in such
a manner that self-mixing occurs in the container or the like.
2. A manufacturing method of semi-solid metal slurry characterized in that nuclei are generated without producing an initial solid layer by a supercooling phenomenon
which occurs by giving a predetermined kinetic energy to a molten metal, pouring the
molten metal into a container or the like and bringing the molten metal into contact
with an inner wall of the container or the like at a high speed, and then the molten
metal itself is self-mixed to eliminate a temperature gradient in the molten metal
in the container or the like, thereby providing a semi-solid state.
3. The manufacturing method of semi-solid metal slurry according to claim 1 or 2, wherein
an energy for the self-mixing is given by a mechanical energy or a potential energy.
4. The manufacturing method of semi-solid metal slurry according to claim 3, wherein
the mechanical energy is a pressure energy.
5. The manufacturing method of semi-solid metal slurry according to claim 3, wherein
the potential energy is given by dropping down the molten metal from a predetermined
height.
6. The manufacturing method of semi-solid metal slurry according to claim 5, wherein
a difference in height (Hin) between the metal in the molten state and a bottom portion of the container or the
like is determined to be 3.5-fold or above of a diameter (D) of the container or the
like to perform pouring.
7. The manufacturing method of semi-solid metal slurry according to claim 6, wherein
Hin/D is set to 4 to 11.
8. The manufacturing method of semi-solid metal slurry according to claim 6, wherein
Hin/D is set to 5 to 10.
9. The manufacturing method of semi-solid slurry according to one of claims 1 to 8, wherein
the diameter of the container or the like is 10 to 200 mm.
10. The manufacturing method of semi-solid slurry according to claim 9, wherein the diameter
of the container or the like is 40 to 120 mm.
11. The manufacturing method of semi-solid slurry according to one of claims 1 to 10,
wherein the molten metal is directly poured into the container or the like.
12. The manufacturing method of semi-solid slurry according to one of claims 1 to 11,
wherein a casting time is 1 to 10 seconds.
13. The manufacturing method of semi-solid slurry according to claim 12, wherein the casting
time is 3 to 5 seconds.
14. The manufacturing method of semi-solid metal slurry according to one of claims 1 to
13, wherein the bottom portion of the container or the like has a concave curved surface
shape as seen from a pouring side.
15. The manufacturing method of semi-solid slurry according to claim 14, wherein a curvature
radius of the concave curved surface shape is 0.5 D to 3 D, where D is an internal
diameter of the container or the like.
16. The manufacturing method of semi-solid slurry according to claim 15, wherein the curvature
radius of the concave curved surface shape is 0.6 D to 1 D.
17. The manufacturing method of semi-solid metal slurry according to one of claims 1 to
16, wherein the metal in the molten state is pressurized to be poured.
18. The manufacturing method of semi-solid slurry according to one of claims 1 to 17,
wherein Tc < (TL+100) is achieved,
where TL: a liquidus temperature of the metal (°C)
TC: an initial temperature of the molten metal (°C).
19. The manufacturing method of semi-solid slurry according to one of claims 1 to 18,
wherein, after the pouring, pouring is carried out to satisfy the following expression:
TL: a liquidus temperature of the metal
Ts: a solidus temperature of the metal
Teq : a temperature when a temperature of the container or the like becomes substantially
equal to a temperature of the metal after pouring.
20. The manufacturing method of semi-solid slurry according to claim 17 or 18, wherein
a calorific capacity of the container or the like is set to a predetermined value
in accordance with a heat quantity of the metal in the molten state to perform pouring.
21. The manufacturing method of semi-solid slurry according to claim 20, wherein, when
an internal diameter, a height and an initial temperature of the container or the
like are fixed, a wall thickness of the same is set to a predetermined value to perform
pouring in such a manner that a thermal equilibrium state is maintained.
22. The manufacturing method of semi-solid slurry according to claim 21, wherein t/D =
0.01 to 0.08 is achieved, where t is the wall thickness of the container or the like.
23. The manufacturing method of semi-solid slurry according to one of claims 1 to 22,
wherein the container or the like is formed of a non-magnetic material or a magnetic
material.
24. The manufacturing method of semi-solid slurry according to one of claims 1 to 23,
wherein the container or the like is formed of stainless steel or copper.
25. The manufacturing method of semi-solid slurry according to one of claims 18 to 24,
wherein the container or the like is heat-insulated from the outside.
26. A molding method characterized by molding semi-solid metal slurry manufactured by the manufacturing method of semi-solid
metal slurry defined in one of claims 1 to 26.
27. A molding characterized by being molded by the molding method defined in claim 26.