Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2002-04-04
2004-06-08
Lin, Kuang Y. (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S067100, C164S072000, C164S122100
Reexamination Certificate
active
06745817
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a casting method and a casting apparatus, and more particularly to a casting method and a casting apparatus in which a cast product having a desired shape is cast by allowing molten metal poured into an cavity of a molding die and a reducing compound to be contacted with each other whereby an oxide film formed on a surface of the above-described molten metal is reduced.
2. Description of the Related Art
There exist various types of aluminum casting methods such as, for example, a modified aluminum casting method proposed in Japanese Patent Application No. 108078/2000 by two inventors of the present application.
A molding die to be adopted by this modified aluminum casting method is shown in FIG.
8
. The molding die
100
thus shown in
FIG. 8
is such a molding die made of metal as is used in a gravity casting method; on this occasion, the molding die is of a separate type comprising a lower die
102
a
and an upper die
102
b
. By these dies
102
a
and
102
b
, formed is a cavity
104
in which a cast product having a desired shape is cast.
Further, in the upper die
102
b
, a feeder head portion
108
is formed between a sprue
106
from which molten metal of aluminum or an alloy thereof is poured and the cavity
104
, and also air-vent holes
110
from which an air in the cavity
104
is discharged when the molten metal is poured into the cavity
104
is formed.
In the improved aluminum casting method using such molding die
100
, after a reducing compound, that is, a magnesium-nitrogen compound (Mg
3
N
2
) is introduced into the cavity
104
of the molding die
100
, the molten metal of aluminum or the alloy thereof is poured into the sprue
106
of the molding die
100
and, then, the molten metal is filled in the cavity
104
and the feeder head portion
108
while the air is discharged from the air-vent holes
110
.
Next, the molten metal in the cavity
104
is solidified by cooling the molding die
100
in which the molten metal is filled in the cavity
104
and the like as it stands still. A void which is caused by shrinkage with solidification of the molten metal is supplemented by allowing a part of the molten metal in the feeder head portion
108
to be flowed down in the cavity
104
.
The improved aluminum casting method is a reduction casting method in which an oxide film formed on a surface of the molten metal of aluminum or the alloy thereof is reduced in the presence of a reducing compound within the cavity
104
of the molding die
100
to decrease a surface tension of the molten metal and, as a result, a flowing property and a running property of the molten metal can be enhanced.
For this feature, in the improved aluminum casting method, coating of a coating agent which is to be coated on surfaces of inner walls of the feeder head portion and the cavity aiming for enhancement of a flowing property and the like of the molten metal and the like on which the oxide film is formed can be omitted thereby enabling to promote a reduction of production steps and enhance a transferring property of the molding die
100
.
Now, depending on the shapes of the cast products, there is a case in which the cavity
104
of the molding die
100
is forced to have a shape where a narrow portion having a smaller cross-sectional area than that of a terminal portion is formed halfway between the sprue and the terminal portion. For example, there is a case in which the cavity
104
is forced to have a shape where a first cavity portion
104
a
in which a molten metal inlet of the cavity
104
is arranged and a second cavity portion
104
b
, that is, the terminal portion are connected with a narrow portion
104
c
which is formed narrower than the first cavity portion
104
a
and the second cavity portion
104
b
(hereinafter, also referred to only as cavity portion
104
a
and cavity portion
104
b
respectively, or as cavity portions
104
a
and
104
b
collectively).
In the cavity
104
shown in
FIG. 9
, after the reducing compound, that is, the magnesium-nitrogen compound (Mg
3
N
2
), is introduced into the cavity
104
of the molding die
100
, the molten metal of aluminum or the alloy thereof poured into the sprue
106
is then poured into the first cavity portion
104
a
and, thereafter, poured into the second cavity portion
104
b
via the narrow portion
104
c
. Such pouring, i.e., filling of the molten metal in the cavity
104
is performed in a short period of time by allowing an oxide film formed on the surface of the molten metal to be reduced in the presence of the reducing compound.
However, since the molten metal filled in the narrow portion
104
c
of the cavity
104
is smaller in quantity than that in the cavity portions
104
a
and
104
b
and faster in cooling rate than that filled in the cavity portions
104
a
and
104
b
, the molten metal filled in the narrow portion
104
c
is solidified earlier than that filled in the second cavity portion
104
b.
For this reason, even when the void is formed while shrinkage is generated with the solidification of the molten metal filled in the second cavity portion
104
b
, the second cavity portion
104
b
is not replenished with the molten metal filled in the first cavity portion
104
a
and the feeder head portion
108
, that is, an effect of feeding the molten metal can not be expected whereupon there is a fear that a shrinkage hole or the like may be generated in an obtained cast product.
Meanwhile, though it is possible to solve the shrinkage hole or the like to be generated with the solidification of the molten metal filled in the second cavity portion
104
b
by independently arranging the feeder head portion in each of the cavity portions
104
a
and
104
b
, such an arrangement as forms feeder head portions in a plurality of different places will lead to a complexity of a constitution of the molding die.
Further, since a part of the molten metal which is solidified in the feeder head portion
108
is not a cast product, the portion is cut off to be disposed. Even when it is considered that the thus-cut off portion is reused after being melted again, a loss of energy must be expected.
Therefore, forming feeder head portions in a plurality of different places increases a capacity of a part of non-cast product, decreases a yield of the cast product of the molten metal poured into the molding die
100
and, accordingly, increases a loss in workability and energy.
SUMMARY OF THE INVENTION
Under these circumstances, an object of the present invention is to provide a casting method and a casting apparatus in which, when casting is performed using a molding die in which a number of a feeder head portion to be formed between a sprue and a cavity having a complicated shape is allowed to be as small as possible, a shrinkage hole or the like which is caused by shrinkage with solidification of the molten metal filled in the cavity and which is generated in an obtained cast product can be prevented.
As a result of an extensive study made by the present inventors to solve the above-described problems, it has been found that, in a reduction casting method which allows a reducing compound to be preliminarily present in a cavity
104
of a molding die
100
(shown in FIG.
8
), a cooling rate of molten metal filled in a feeder head portion
108
and a narrow portion
104
c
of the cavity
104
can be made slower by coating a coating agent having a heat insulating effect only on surfaces of inner walls of the feeder head portion
108
and the narrow portion
104
c
of the cavity
104
, compared with a case in which the surfaces of the inner walls of the feeder head portion
108
and the narrow portion
104
c
of the cavity
104
are not coated by the coating agent.
As described above, the present inventors have found that the shrinkage hole or the like which is caused by shrinkage with solidification of the molten metal filled in the second cavity portion
104
b
of the cavity
104
and which is generated in an obtained cast product can be pr
Ban Keisuke
Ogiwara Koichi
Sasaki Yasuhiro
Sunohara Akira
Lin Kuang Y.
McGuireWoods LLP
Nissin Kogyo Co. Ltd.
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