Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2001-05-10
2004-06-08
Lin, Kuang Y. (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S067100, C164S122100, C164S359000
Reexamination Certificate
active
06745816
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of casting and a casting machine, more precisely relates to a method of casting and a casting machine, in each of which a molten metal is poured into a cavity of a casting die so as to cast a product having a prescribed shape.
Many kinds of ways of aluminium casting. For example, gravity casting has some advantages: simple casting dies, high quality products, etc.
The casting die of the gravity casting is shown in FIG.
10
. In
FIG. 10
, the casting die
100
is made of a metal. The casting die
100
is a splittable die constituted by a lower die
102
a
and an upper die
102
b
. A cavity
104
, in which a product having a prescribed shape is cast, is formed by the lower die
102
a
and the upper die
102
b.
The upper die
102
b
includes: a metal inlet
106
, from which a molten metal, e.g., a molten aluminium, a molten aluminium alloy, is poured into the cavity
104
; a feeder head
108
provided between the metal inlet
106
and the cavity
104
; and air ventilation holes
110
, from which air in the cavity
104
is discharged when the molten metal is poured into the cavity
104
.
When the molten aluminium or aluminum alloy is solidified, its volume is reduced about 3% due to shrinkage. The shrinkage of the solidified metal in the cavity occurs a surface sink, etc. in the cast product. In the casting die
100
shown in
FIG. 10
, a gap, which is formed in the cavity
104
by the shrinkage of the solidified metal, is filled with a part of the molten metal in the feeder head
108
, so that the defect, e.g., the surface sink, can be prevented.
Surface tension of the molten aluminium or aluminium alloy is made greater by an oxide film formed on a surface of the molten aluminium or aluminium alloy. Therefore, fluidity and running property of the molten aluminium or aluminium alloy are low, and smoothness of a surface of the product is also low. To solve these disadvantages, inner faces of the feeder head
108
and the cavity
104
of the casting die
100
shown in
FIG. 10
are coated with lubricant so as to improve the fluidity and the running property of the molten metal whose surface is covered with the oxide film.
When the product is cast by the casting die
100
shown in
FIG. 10
, the molten aluminum or aluminium alloy is poured into the metal inlet
106
of the casting die
100
. The cavity
104
and the feeder head
108
are filled with the molten aluminium or aluminium alloy with discharging the air from the air ventilation holes
110
.
Next, the casting die
100
, in which the molten metal has been filled, is cooled so as to solidify the molten metal in the cavity
104
. By the solidification of the molten metal in the cavity
104
, the solidified metal is shrinked and the gap is formed in the cavity
104
, but the gap in the cavity
104
is filled with the molten metal supplied from the feeder head
108
.
However, in the conventional method of aluminium casting shown in
FIG. 10
, the inner faces of the feeder head
108
and the cavity
104
must be coated with the lubricant so as to improve the fluidity and the running property of the molten metal whose surface is covered with the oxide film. But, it is very difficult for inexperienced workers to define coating portions and to uniformly form coating layers. Therefore, surface defects of cast products, e.g., rough surfaces, cannot be avoided.
The inventors of the present invention invented and filed an improved method of aluminum casting (Japanese Patent Application No. 2000-108078), in which aluminium products having good and smooth surfaces can be cast without coating any lubricant.
The improved method will be explained with reference to FIG.
11
. Firstly, a magnesium nitride compound (Mg
3
N
2
), which is an example of deoxidizing compounds, is introduced into the cavity
104
of the casting die
100
, then the molten aluminium or aluminium alloy is poured therein.
In the improved method, the deoxidizing compound is previously existed in the cavity
104
of the casting die
100
, so that the oxide film formed on the surface of the molten aluminium or aluminium alloy can be deoxidized and the surface tension of the molten aluminium or aluminium alloy can be made lower. By deoxidizing or removing the oxide film, the fluidity and the running property of the molten metal can be improved, so that surfaces of the cast products can be smooth and can have good external surfaces.
The feeder head
108
shown in
FIG. 10
or
11
is capable of filling the gap, which is formed in the cavity
104
when the solidified metal is shrinked, with the molten metal. Therefore, at least a part of the molten metal in the feeder head
108
must have enough fluidity, even if the molten metal in the cavity
104
is solidified.
Namely, solidifying speed of the molten metal in the feeder head
108
must be lower than that of the molten metal in the cavity
104
. Thus, cooling rate of the feeder head must be lower than that of the cavity. To make the difference of the cooling rate, the feeder head
108
is formed into, for example, a pillar shape having broad traverse sectional area. By the pillar-shaped feeder head
108
, the molten metal in the feeder head
108
is not easily cooled.
However, the solidified metal in the feeder head
108
is a disused part, so it will be removed from the product. If the solidified metal in the feeder head
108
is reused, it must be molten and energy must be consumed.
Therefore, the pillar-shaped feeder head
108
, which has broad traverse sectional area, has greater volume, so yield of casting material must be lower and energy consumption for reuse must be greater.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of casting, in which volume of a feeder head can be small and cooling rate of the feeder head can be easily made lower than that of a cavity.
Another object of the present invention is to provide a casting machine, which is capable of executing the method of the present invention.
The inventors studied to achieve the objects, and they found that: in their improved method shown in
FIG. 11
, the deoxidizing compound existed in the cavity
104
of the casting die
100
deoxidizes the oxide film on the surface of the molten meal, so the molten metal has high fluidity on the inner face of the cavity
104
, which is not coated with the lubricant; and the cooling rate of the molten metal in the cavity
104
, whose inner face is coated with no lubricant, is greater than that of the molten metal in the cavity, whose inner face is coated with the lubricant.
To make a difference of heat insulating between the feeder head
108
and the cavity
104
which are made of the same material, an inner face of the feeder head
108
is coated with the lubricant, and an inner face of the cavity
104
is coated with no lubricant, so that the heat insulating of the feeder head
108
can be made greater than that of the cavity
104
.
With this structure, the cooling rate of the feeder head
108
can be lower than that of cavity
104
, so that solidification speed of the molten metal in the feeder head
108
can be slower than that of the molten metal in the cavity
104
. Then, the inventors reached the present invention.
The method of casting of the present invention is executed in a casting machine including a casting die, in which a feeder head is provided between a metal inlet and a cavity and in which heat insulating of the feeder head is greater than that of the cavity so as to make cooling rate of the feeder head lower than that of the cavity, and said method comprises the steps of:
pouring a molten metal into the cavity;
reacting the molten metal on a deoxidizing compound in the cavity so as to deoxidize an oxide film formed on a surface of the molten metal; and
supplementing the molten metal in the feeder head to the cavity when the molten metal in the cavity is solidified and shrinked.
On the other hand, the casting machine of the present invention comprises a casting die, which includes:
a metal inlet, from
Ban Keisuke
Nakatani Sakuzo
Ogiwara Koichi
Sasaki Yasuhiro
Sunohara Akira
Lin Kuang Y.
McGuireWoods LLP
Nissin Kogyo Kabushiki Kaisha
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