Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2001-04-10
2004-04-20
Elve, M. Alexandra (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S057100
Reexamination Certificate
active
06722417
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to deoxidation casting, aluminum casting and a casting machine.
Many ways of casting, e.g., gravity casting, low pressure casting, die casting, squeeze casting, thixotropic casting, are known. In many ways of casting, a molten metal is poured into a cavity of a casting die to solidify and form the metal into a prescribed shape. The ways of casting are selected on the basis of a material of the molten metal and a product to be cast.
Many kinds of products are cast. In the case of casting a product having a complex shape or high performance, the cavity must be securely filled with the molten metal so as to form no casting defects, have a prescribed strength, prevent deformation, and have a good external shape.
Aluminum and aluminum alloys have been widely used as the material of the molten metal. In the aluminum casting, aluminum is apt to make an oxide film. Due to the oxide film formed on a surface of the molten aluminum, the surface tension of the molten metal is made greater, so that fluidity and a welding property of the molten metal is made lower and casting defects are sometimes caused. To solve these disadvantages, many improvements, e.g., lubricant, pouring manners, pouring speed, pouring pressure, have been studied.
For example, in gravity casting and low pressure casting methods, the falling temperature of the molten metal is slowed by painting heat-insulating releasing agent, adjusting an arrangement of a gate, etc., so that bad molten metal running, crinkles, cold shuts, etc., which are caused by forming the oxide film on the surface of the molten metal, can be restricted. In die casting, the molten metal is filled in a short time with high pressure by adjusting the pouring speed, the pouring pressure, the arrangement of the gate, etc. In squeeze casting, the pouring pressure is highly pressurized during a step of the gravity casting so as to break and fuse the oxide film.
However, the conventional ways of casting have disadvantages, and no perfect ways are known. Especially, the oxide film, which is made or formed when the molten metal touches the inner faces of the cavity of the casting die, forms crinkles and cold shuts in a surface of a product, and the oxide film causes unsatisfactory filling of the molten metal. In the case of casting parts of airplanes and vehicles, whose surface stress and broken portions seriously influence safety, etc., all cast products are examined by means of fluorescent flaw detection. Therefore, the manufacturing cost of the products is higher. Further, the quality and reliability of the products cannot be fixed.
The problems of the oxide film are caused not only in aluminum casting but also casting with other materials.
SUMMARY OF THE INVENTION
The present invention has been invented to solve the problems caused by the oxide film formed on the surface of the molten metal.
An object of the present invention is to provide a method of deoxidation casting, which is capable of preventing the oxide film from forming on the surface of the molten metal, improving wettability to the inner faces of a cavity of a casting die, and casting high quality products with high casting efficiency.
Another object is to provide a deoxidation casting machine for executing said method.
The method of deoxidation casting of the present invention comprises the steps of:
reacting a deoxidizing compound, which is made by reacting a metallic gas on a reactive gas, on a molten metal; and
deoxidizing an oxide film on a surface of the molten metal.
A metal for the metallic gas may be selected on the basis of the molten metal. For example, magnesium nitride compound (Mg
3
N
2
) which is made by reacting a magnesium gas with a nitrogen gas, may be employed as an effective deoxidizing compound, which is capable of deoxidizing the oxide film formed on the surface of the molten metal. Magnesium is stable from room temperature to high temperature and capable of easily subliming. Therefore, magnesium can be properly used in the method. The magnesium nitride compound has a high deoxidizing property, so that the oxide film on the surface of the molten metal can be effectively deoxidized.
The deoxidation casting of the present invention relates to a method which is capable of deoxidizing the oxide film formed on the surface of the molten metal so as to make the pure molten metal. Therefore, in the case of casting with a molten metal on which the oxide film is apt to be formed, the method of the present invention is capable of effectively deoxidizing the oxide film and properly casting with the pure molten metal.
By deoxidizing the oxide film on the surface of the molten metal, the surface tension of the molten metal can be lower, fluidity of the molten metal can be higher and the wettability with respect to the inner faces of the cavity of the casting die can be higher. Since the pure molten metal touches the inner faces of the cavity, the molten metal can easily flow in the casting die, the molten metal running property can be improved and the molten metal can securely fill the cavity including minute spaces thereof.
In a conventional casting method, lubricant or heat-insulating releasing agent are used to warm a casting die and maintain the fluidity of a molten metal. In the present invention, the fluidity of the molten metal is made higher, so that no lubricant or no heat-insulating releasing agent are required. Therefore, preparation and adjustment of the casting die can be easily achieved, and casting efficiency can be made higher.
In the conventional casting method, the casting die is heated until reaching a high temperature so as to maintain the fluidity of the molten metal. The molten metal is poured into the heated casting die. The molten metal is solidified by cooling the casting die. On the other hand, in the present invention, the fluidity of the molten metal is very high, so the casting die need not be heated. Therefore, the molten metal can be solidified in a short time, the product can be quickly solidified, toughness of the product can be greater, deformation of the product, such as with sink mark, extension, can be prevented and the quality of the product can be higher. The casting die may be used at room temperature.
In conventional gravity casting, a feeding head is formed in a casting die, and the molten metal is introduced into a cavity, by its own weight, from the feeding head. In the present invention, the fluidity of the molten metal in the casting die is very high, so the capacity of the feeding head can be reduced. In a conventional die, the capacity of the feeding head is 50-60% of capacity of the die. In the present invention, since the fluidity of the molten metal can be higher, the capacity of the feeding head can be reduced to 10-20% of the capacity of the casting die. Therefore, the molten metal can be efficiently used, and the casting die can be made easily. By reducing the capacity of the feeding head, the solidification of the molten metal can be accelerated, so that a cycle time of casting can be shorter and the casting efficiency can be improved. Further, in the present invention, the product can be easily separated from the casting die, so that the product can be taken out quickly and the casting efficiency can be improved.
There are two ways of reacting the molten metal on the deoxidizing compound in the cavity of the casting die. One way comprises the steps of: making the deoxidizing compound outside of the casting die; introducing the deoxidizing compound into the cavity; and pouring the molten metal into the cavity. The other way comprises the steps of: making the deoxidizing compound in the cavity of the casting die; and pouring the molten metal into the cavity.
The deoxidizing compound is precipitated on the inner faces of the cavity so as to react the deoxidizing compound on the molten metal thereon. To effectively precipitate the deoxidizing compound on the inner faces of the cavity, a metallic gas, which is made by evaporating a metal for making the deoxidizing compound,
Ban Keisuke
Ogiwara Koichi
Elve M. Alexandra
Kerns Kevin P.
Nissin Kogyo Co. Ltd.
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