Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR PRODUCTION OF PLATELIKE METAL MATERIAL
FIELD OF THE INVENTION
This invention relates to a method and apparatus for the production of a
platelike metal
material by effective utilization of the thixotropy inherent in a
semiliquid/semisolid metal.
BACKGROUND OF THE INVENTION
This invention relates to a method and apparatus for the production of a
platelike metal
material by effective utilization of the thixotropy inherent in a
semiliquid/semisolid metal.
The thixo-casting method (semiliquid casting method) and rheocasting method
(semisolid casting method) have been known as casting methods utilizing the
thixotropy
inherent in a semiliquid/semisolid metal, namely the property of exhibiting
small viscosity and
excelling in fluidity.
These casting methods invariably consist in casting a metal slurry in such a
semiliquid/semisolid state formed of an interfused mixture of a liquid-phase
metal and a
solid-phase metal.
The thixo-casting method is so adapted as to comprise the steps of heating a
solid metal
till formation of a metal slurry in the semiliquid state and supplying the
formed metal slurry to
a metallic mold.
The rheocasting method is so adapted as to comprise the steps of provisionally
melting
a solid metal, cooling the resultant molten metal till formation of a metal
slurry in the
semisolid state containing granular crystals, and subsequently supplying the
metal slurry to a
metallic mold.
Since these casting methods are capable of casting a metal having a high solid-
phase
ratio and exhibiting low viscosity, they are at an advantage in improving the
metallic mold in
filling capacity, thereby enhancing the yield of casting, enabling formation
of a product of a
large size, repressing occurrence of a shrinkage cavity, thereby adding to the
mechanical
strength of the product, and permitting a reduction in the wall thickness of
the product.
Further, they are capable of allaying the thermal load exerted on the metallic
mold and,
therefore, elongating the service life of the metallic mold.
With the aim of effectively utilizing the thixotropy of a semiliquid metal and
the
fluidity of a semisolid metal respectively in the casting methods described
above, it is
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necessary that the semiliquid/semisolid metal should contain non-dendritic
crystals, preferably
spherical crystals, as fine and uniform as permissible.
When the solid metal is heated till formation of a semiliquid state and the
molten metal
is simply cooled until formation of a semisolid state, these metals nearly
wholly take
part in giving rise to dendritic crystals in the semiliquid/semisolid metal
and render it
impossible to obtain the thixotropy of the semiliquid metal and the fluidity
of the semisolid
metal fully satisfactorily.
The thixo-molding method, therefore, generally resorts to a procedure of
utilizing a
screw-type extruding device popularly used in an injection molding machine and
sequentially
heating a given solid metal within the barrel of the extruding device while
exerting a shearing
force thereon till conversion of the solid metal into a metal slurry in a
semiliquid state.
Since the screw-type extruding device is complicated in structure and,
accordingly, is
expensive, the cost for application thereof to the casting equipment is very
high.
Since the metal slurry formed within the barrel of the extruding device is
fated to be
supplied in its unmodified form to the metallic mold, it cannot be confirmed
at all whether or
not the crystals formed have assumed the state of non-dendritic crystals.
Further, since the solid metal to be used for supply to the barrel must be
prepared in the
form of chips, the cost of the raw material is very high.
Meanwhile, the rheocasting method, as disclosed in JP-A HEI 10-34307, for
example,
. resorts to a procedure of exposing a metal molten in advance within a
retaining oven to a
cooling means, thereby cooling this molten metal to the solid-liquid
coexisting state formed of
a solid phase and a liquid phase, and converting this solid-liquid composite
into a metal slurry
while retaining it in the range of semiliquid temperature within a retaining
container.
The method using this procedure is enabled to obtain an expected metal slurry
without
requiring use of such an expensive extruding device as is indispensable to the
thixo-casting
method because numerous crystal nuclei are precipitated at the stage at which
the molten metal
contacts the cooling means and these crystal nuclei are destined to grow into
spheres within the
retaining container.
Moreover, since a mass of metal may be supplied in its unmodified form to the
retaining oven, the cost of the raw material can be restrained from being
increased.
This method, further, enables the casting aimed at to be fulfilled by
effective utilization
of the fluidity of the semisolid metal because it permits easy determination
of the question
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whether or not the metal slurry formed in the retaining container has assumed
the expected
state of non-dendritic crystals.
In the rheocasting method, however, the actual construction of a system for
mass
production makes it necessary to interpose numerous retaining containers
between the
cooling means serving the purpose of cooling the molten metal and the metallic
mold
serving as a receptacle for storing the metal slurry being supplied thereto
and, at the same
time, synchronize the step of causing the molten metal to contact the cooling
means with the
step of supplying the metal slurry to the metallic mold through such numerous
retaining
containers. The system, therefore, necessitates extremely complicated control.
The control is all the more complicated because the metal slurry in each of
the
retaining containers requires accurate control of temperature till it is
supplied to the metallic
mold.
SUMMARY OF THE INVENTION
The present inventors, in the light of the actual state of the art mentioned
above, have
proposed a method for casting a metal, which comprises a first production step
for forming'
a metal slurry containing a solid phase by cooling a molten metal, a second
production step
for forming a solidified metal material by further cooling the metal slurry,
and a step for
heating the metal material till a semiliquid state and supplying the
semiliquid metal material
to a metallic mold.
As a result, this method is able to obtain a metal slurry abounding in
fluidity and
containing non-dendritic crystals without requiring any complicated control
and, by
supplying this metal slurry to the metallic mold, is further able to obtain a
mass of metal.
Incidentally, the press working proves advantageous in terms of cost because
the
productivity thereof is 20 - 100 times as high as that of die-casting or inj
ection-molding.
Since plates are easy of working, the desirability of materializing
manufacture of a platelike
metal material by effective utilization of thixotropy has been finding
enthusiastic recognition.
This invention, conceived and perfected with a view to attaining the desire
mentioned
above, aims to provide a method for the production of a platelike metal
material by such
effective utilization of thixotropy as to permit manufacture of a product by
press working and
an apparatus for the production thereof.
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According to an aspect of the present invention, there is provided a method
for the
production of a platelike metal material comprises a first production step for
cooling a
molten metal to form a metal slurry containing a solid phase and a second
production step
for cooling the metal slurry and rolling it at the same time to form a
continuous, solidified,
platelike metal material.
According to another aspect of the present invention, there is provided a
method for
the production of a platelike metal material, comprising a first production
step for cooling
a molten metal (M 1) to form a metal slurry (M2) containing a solid phase by
allowing the
molten metal (M 1) to flow down along an inclined surface of a cooling unit
furnished in an
interior thereof with a circulating path for cooling water and a second
production step for
cooling and, at the same time, rolling said metal slurry to form a continuous,
solidified,
platelike metal material (M3).
The second production step preferably embraces a cutting work for cutting a
continuous, solidified, platelike metal material into pieces of a stated
length or a winding
work for winding a continuous, solidified, platelike metal material into rolls
of a stated
diameter.
According to yet another aspect of the present invention, there is provided an
apparatus for the production of a platelike metal material which comprises a
first production
means for cooling a molten metal to form a metal slurry containing a solid
phase and a
second production means for cooling the metal slurry and rolling it at the
same time to form
a continuous, solidified, platelike metal material.
According to a further aspect of the present invention, there is provided an
apparatus
for the production of a platelike metal material, comprising a first
production means for
cooling a molten metal (M1) to form a metal slurry (M2) containing a solid
phase by
allowing the molten metal (Ml) to flow down along an inclined surface of a
cooling unit
furnished in an interior thereof with a circulating path for cooling water and
a second
production means for cooling and, at the same time, rolling said metal slurry
to form a
continuous, solidified, platelike metal material (M3).
The second production means is preferably furnished with a cutting mechanism
for
cutting a continuous, solidified, platelike metal material into pieces of a
stated length or a
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winding mechanism for winding the continuous, solidified, platelike material
formed into
rolls of a stated diameter.
This invention, by dividing the process of operation into two production steps
as
described above, enables the numerous crystal nuclei precipitated in the metal
slurry to attain
further growth into spheres and, by subjecting the metal slurry in the ensuing
state
simultaneously to the treatments of cooling and rolling, makes it possible to
render the
product fit for press working and to exalt the productivity of the operation
itself markedly.
BRIEF DESCRIPTION OF THE DRAWINGS
The other objects and characteristic features of this invention will become
apparent
from the detailed description to be given herein below with reference to the
annexed
drawings, in which:-
Figure 1 is an explanatory diagram schematically depicting the construction of
an
apparatus for the production of a platelike metal material as one embodiment
of this
invention,
Figure 2(a) is a schematic longitudinal cross section of a cooling unit for
forming a
metal slurry in the apparatus of Figure 1,
Figure 2(b) is a section of the cooling unit of Figure 2(a),
Figure 3 is a partially omitted cutaway plan view of the leading end portion
of a
nozzle in the apparatus of Figure 1,
Figure 4(a) is an explanatory diagram depicting the state in which the metal
slurry
flows in the direction of the opening at the leading end of the nozzle in the
apparatus of
Figure 1,
Figure 4(b) is an explanatory diagram depicting the state in which the metal
slurry
shown in Figure 4(a) is on the verge of emanating from the opening of the
nozzle,
Figure 4(c) is an explanatory diagram depicting the operation of cooling and
rolling
the metal slurry shown in Figure 4(b).
Figure 5 is an explanatory diagram schematically depicting the configuration
of a
winding mechanism used in the apparatus of Figure 1,
Figure 6(a) is a photomicrograph showing the platelike metal material produced
according to the method of the present invention,
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Figure 6(b) is a photomicrograph showing the platelike metal material of
Figure 6(a)
that has been heated again at a solid-liquid coexisting temperature and then
quenched in
water,
Figure 6(c) is a photomicrograph showing a casting ingot produced by a
conventional
method.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 schematically illustrates the construction of the apparatus for the
production
of a platelike metal material according to one embodiment of this invention.
In this diagram,
reference numeral 1.1 denotes a melting tank for retaining a magnesium alloy
represented by
the AZ type or the AM type, for example, in a molten state or in a state of
liquid phase
temperature. This melting tank 11 is furnished around the periphery thereof
with a heater
12.
The melting tank 11 is provided in the lowermost part thereof with a tapping
path 11 a
bent roughly in the shape of a crank and used for discharging the stored
molten magnesium
alloy M1 downward.
At the halfway point of the tapping path 11 a, there is provided a switch
valve 13 that
is composed of a valve plunger 13p so disposed as to produce a forward or
backward motion
to open or close the tapping path 11 a and a valve cylinder 13c serving the
purpose of moving
the valve plunger 13p forward or backward.
Below the melting tank 11, a cooling unit 21 is disposed as a first production
means.
This cooling unit 21, as illustrated in detail in Figures 2(a) and 2(b), is so
constructed as to
be furnished on the surface thereof with a guide groove 22 and in the interior
thereof with
a circulating path 23 for cooling water. Though the example of Figure 2 is
depicted as using
one guide groove 22, it is permissible to use a plurality of such guide
grooves.
This cooling unit 21 is disposed as being slanted in such a state that the
guide groove
22 is opposed to the lower end of the tapping path 11 a.
The cooling unit 21 is so disposed in a cover block 24 that this cover block
24 covers
the cooling unit 12 while securing a stated intervening space between the
opposed surfaces.
The empty space on the upper surface of the cooling unit 21 communicates with
the lower
end of the tapping path 11 a.
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The cover block 24 and a storing tank 32 that will be specifically described
herein
below are jointly provided with a, guide block 25 through which they are
interconnected.
A second production means which is denoted by reference numeral 31 comprises
the
storing tank 32 furnished in the lowermost part thereof with a material path
32a for discharging
a stored metal slurry M2 downward, a nozzle 33 disposed on the lower side of
the storing tank
32 and furnished with a supply path 33p formed roughly in the shape of the
letter L so as to
communicate at the upper end thereof with the lower end of the material path
32a, a switch
valve 34 for controlling the flow of the metal slurry M2 from the material
path 32a to the
supply path 33p, an auxiliary heater 35 disposed in the nozzle 33 and adapted
to retain the
metal slurry in the nozzle 33 at a stated temperature, width regulating guides
36L and 36R
disposed on the left and right sides of the leading end of the nozzle 33 as
illustrated in Figure 3
and adapted to regulate the width of a continuous, platelike metal material
M3, a pair of coarse
roller 37D and 37U adapted to cool and roll simultaneously the metal slurry M2
discharged
from the nozzle 33, a pair of finishing rollers 38D and 38U for performing a
finishing roll on
the continuous, platelike metal material M3 which has been rolled by the
coarse rollers 37D
and 37U, and a cutting mechanism 39 for cutting the continuous, platelike
metal material M3
discharged through the gap between the finishing rollers 3 8D and 3 8U.
The switch valve 34 comprises a valve plunger 34p adapted to producing a
forward or
backward motion to open or close the material path 32a and a valve cylinder
34c adapted to
move the valve plunger 34p forward or backward.
The cutting mechanism 39 comprises a cutter 39c disposed on the downstream
side of
the finishing rollers 38D and 38U and an end-detecting sensor 39s disposed on
the downstream
side of the cutter 39c as being separated by a stated length (the length of
pieces obtained by
cutting) from the cutter 39c and adapted to detect the end (leading end) of
the continuous,
platelike metal material M3.
The coarse rollers 37D and 37U are so constructed as to directly contact and
suddenly
cool the metal slurry M2 by means of a built-in water-cooled cooling unit, for
example.
Incidentally, the leading end of the supply path 33p is diverged in the
vertical direction
as illustrated in Figure 4 so as to facilitate the emission of the metal
slurry M2.
The pair of coarse rollers 37D and 37U are adapted so as to be synchronously
rotated
by a drive mechanism omitted from illustration here, with the result that the
coarse roller 37D
will be rotated counterclockwise and the coarse roller 37U clockwise.
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Then, the pair of finishing rollers 38D and 38U are adapted so as to be
synchronously
rotated by a drive mechanism omitted from illustration here, with the result
that the finishing
roller 38D will be rotated counterclockwise and the finishing roller 38U
clockwise.
Now, the operation of the apparatus will be explained. First, by introducing a
mass of
a magnesium alloy into the melting tank 11 and actuating the heater 12, the
melting tank 11 is
enabled to retain the molten magnesium alloy Ml and, at the same time, the
cooling unit 21 is
enabled to admit the flow of the cooling water. Then, the apparatus is readied
for operation
by setting the coarse rollers 37D and 37U rotating at a stated speed and also
setting the
finishing roller 38D and 38U rotating at a stated speed.
In this case, the cooling units in the coarse rollers 37D and 37U are made to
allow flow
of cooling water therethrough and the auxiliary heater 3 5 is connected to a
power source.
When the valve cylinder 13c is actuated from the reset state to impart a
backward
motion to the valve plunger 13p, the tapping path 11 a is opened and the
molten magnesium
alloy Ml stored in the melting tank 11 is supplied via the tapping path l la
to the cooling unit
21.
The molten magnesium alloy Ml that has been supplied to the cooling unit 21
flows
down the guide groove 22 along the inclination of the cooling unit 31 and is
then put to
temporary storage in the storing tank 32.
The molten magnesium alloy M1 that flows down the cooling unit 21 is properly
cooled by the cooling unit 21 and consequently transformed into the metal
slurry M2 having
numerous crystal nuclei precipitated therein. In the storing tank 32, the
crystal nuclei further
gain in growth into spheres and eventually give rise to fine and uniform
spherical crystals.
Then, by actuating the valve cylinder 34 so as to impart a backward motion to
the valve
plunger 34p and consequently opening the material path 32a, the metal slurry
M2 which has
been stored temporarily in the storing tank 32 is enabled to be continuously
discharged through
the supply path 33p of the nozzle 33 to the ambience as illustrated in Figure
4(a).
The metal slurry M2, while passing through the supply path 33p, is retained at
a stated
temperature by the auxiliary heater 3 5.
Then, the metal slurry M.2 containing the spherical crystal nuclei and
discharged
through the supply path 33p as illustrated in Figure 4(b) is cooled by
contacting the coarse
rollers 37D and 37U currently in rotation, with the result that it will be
continuously discharged
in the form of a perfectly solidified plate and eventually enabled to form a
continuous, platelike
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metal material M3 as illustrated in Figure 4(c).
Thus, the continuous, platelike metal material M3 discharged through the
supply path
33p is conveyed as being compressed by the width regulating guides 36L and 36R
to a stated
width and rolled by the coarse rollers 37D and 37U and subsequently given a
finish rolling
treatment by the finishing rollers 38D and 38U and advanced through the gap
between the
cutters 39c.
Incidentally, the perfectly solidified continuous, platelike metal material M3
is formed
by suddenly cooling the metal slurry M2 which still, retains thixotropy
sufficiently. The latent
retention of this thixotropy can be easily confirmed by visual observation of
the crystal
structure contained in the continuous, platelike metal material M3.
When the end-detecting sensor 39s detects the leading end of the advancing
continuous,
platelike metal material M3, the cutter 39c is actuated to cut the continuous,
platelike metal
material M3 into pieces of a stated length. The cut pieces are conveyed as
platelike metal
materials M4 by means of a conveyor, for example.
While the continuous, platelike metal material M3 is being cut into platelike
metal
materials M4, this continuous, platelike metal material M3 droops and absorbs
excess length.
When the cutter 39c is opened, the continuous, platelike metal material M3
advances with the
elasticity of its own.
Thereafter, the continuous, platelike metal material M3 is successively cut
likewise to
give rise to platelike metal materials M4.
Since this invention is capable of producing platelike metal materials M4 by
effectively
utilizing thixotropy as described above, the platelike metal materials M4 are
enabled by press
working to give rise to required products with high productivity as compared
with the
die-casting or the injection-molding.
Figure 6(a) is a photomicrograph of the platelike metal material produced by
cooling
the melt of magnesium alloy (AZ91D magnesium alloy) in the melting tank with
the cooling
unit into a metal slurry in the storing tank and bringing the metal slurry
discharged from the
nozzle into contact with the guide rollers.
It is found from the photomicrograph that numerous crystal nuclei grown to a
large size
are crystallized in the platelike metal material thus produced.
Figure 6(b) is a photomicrograph, for comparison with that of Figure 6(a), of
the
platelike metal material that has been heated again at 570 C, from which it is
found that
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thixotropy emerges because liquid metal exists around the crystals.
Figure 6(c) is a photomicrograph of a conventional metal material obtained by
casting a
melt of metal without use of the cooling unit of the present invention, from
which it is found
that emergence of thixotropy cannot be expected because the crystals have a
non-dendritic
structure.
Though the embodiment described above has illustrated the production of
platelike
metal materials from a magnesium alloy as the raw material, this invention is
capable of
producing platelike metal materials using aluminum, aluminum alloys, other
metals and alloys
thereof as the raw materials.
In Figure 1, the example of furnishing the apparatus with the cutting
mechanism
(cutting step) for successively cutting the continuous, platelike metal
material to produce
platelike metal materials has been cited by way of illustration. Since the
products of spherical
crystals show an increase in strength by about 15% over the products of
dendritic crystals, the
necessity for furnishing the apparatus with the cutting mechanism may be
obviated by
providing a winding mechanism (winding step) for winding the continuous,
platelike metal
material directly around itself or indirectly around a core of a stated
diameter. Figure 5 shows
the apparatus equipped with the winding mechanism in place of the cutting
mechanism, in
which the metal slurry M2 containing spherical crystal nuclei that is
discharged from the
nozzle 33 is brought into contact with the coarse rollers 37D and 37U for
cooling, then rolled
by the finishing rollers 38D and 38U and wound on a winding drum 40 in the
form of the
continuous, platelike metal material.
Incidentally, when the apparatus is furnished with the winding mechanism
(winding
step), the length of the continuous, platelike metal material which permits
the formed roll on
the winding drum 40 to acquire a stated diameter may be calculated with a
calculating
mechanism prior to the cutting work with the cutter 39c.
When the continuous, platelike metal material that has been finish-rolled by
the
finishing rollers 38D and 38U is subjected directly to the press working,
neither the cutting
mechanism nor winding mechanism is required.
When the continuous, platelike metal material is wound in rolls, the raw
material (plate
material) for the manufacture of finished products allows easy handling and
also allows easy
supply of the raw material to the site of manufacture. Thus, the raw material
suitable for
mass production can be handled and supplied.
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Since this invention is capable of producing platelike metal materials by
effectively
utilizing thioxtropy as described above, it is enabled by subjecting these
platelike metal
materials to the operation of press working to give rise to required products
with high
productivity as compared with die-casting or injection-molding.
