Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2001-04-05
2002-10-08
Elve, M. Alexandra (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S072000
Reexamination Certificate
active
06460602
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for metallic mold-casting of a magnesium alloy and more specifically to a method for metallic mold-casting of a magnesium alloy, which is a method for casting and molding a magnesium alloy using a metallic mold, such as a die casting method, a thixo-molding method, a squeeze casting method, a low pressure die casting method and a gravity casting method, and which permits the casting of a magnesium alloy while ensuring good resistance to penetration.
2. Description of the Prior Art
There have increasingly been required for the development of light weight materials from the viewpoint of making motorcars lighter (this results in the reduction of the rate of fuel consumption), in the motorcar industry, and of making portable household appliances lighter (this permits the improvement of the portability of the appliances), in the fields of the portable household appliance. Accordingly, there have widely been used resin materials and light weight metallic materials. However, it is generally difficult to recycle these resin materials and therefore, a problem arises as to how to post-treat the same or a problem of environmental pollution arises. Contrary to this, it is in general easy to recycle metallic materials. For this reason, aluminum alloys have widely been used and more lighter magnesium alloys have recently been used for the production of, for instance, the bodies of equipment for portable household appliances and a variety of casing parts for motorcars.
As methods for processing a magnesium alloy, there have in general been known, for instance, casting and molding methods using a metallic mold (hereunder referred to as “metallic mold-casting method”) such as a die casting method, a thixo-molding method, a squeeze casting method, a low pressure die casting method and a gravity casting method. In these casting methods using metallic molds, a variety of releasing agents are used for controlling any penetration to thus ensure release characteristics of such a metallic mold.
However, the metallic mold-casting of a magnesium alloy inevitably suffers from such a problem that the penetration of the alloy to the metallic mold is easily caused and further it is generally difficult to eliminate the problem of such penetration through the use of the usual releasing agent. This correspondingly leads to substantial reduction in the productivity of the metallic mold-casting method and the quality of the resulting products of the method, under the present conditions. In particular, in the casting methods such as die-casting and thixo-molding methods, in which molten metal is brought into contact with a metallic mold at a high speed and a high pressure, the problem of this penetration becomes more conspicuous. In addition, the problem of the penetration likewise becomes conspicuous when,metallic mold-casting magnesium alloys containing calcium and/or rare earth metals having high reactivity with iron, which are incorporated into the alloys to improve the creep characteristics thereof at a high temperature and room temperature, among other magnesium alloys.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method for metallic mold-casting a magnesium alloy, which can ensure good resistance to penetration. Another object of the present invention is to provide cheap and high quality magnesium alloy cast products.
The inventors of this invention have conducted various studies to solve the foregoing problems associated with the conventional techniques, have found that the penetration of a casting material to the metallic mold would be ascribed to the chemical affinity of the iron, as a material for the mold, for the molten magnesium alloy and have thus come to such a conclusion that it would, in fact, be effective. for inhibiting such penetration to prevent any direct contact between the molten magnesium alloy and the metallic mold per se and, in particular, to prevent such direct contact in regions in which the molten magnesium alloy is quite susceptible to the penetration to the metallic mold, such as the region immediately after gate portions.
As measures to prevent any direct contact between the molten magnesium alloy and the metallic mold per se, a releasing agent has conventionally been used and there has likewise been proposed the use of a variety of methods for treating the inner surface of the metallic mold. In the practical metallic mold casting, however, certain sites become susceptible to the penetration depending on the flowing conditions of the molten metal. Therefore, the conventionally used releasing agent and surface treatments are insufficient in the effect of preventing the penetration at the foregoing sites quite susceptible to the penetration or the penetration-inhibitory effect thereof becomes insufficient after only a few casting operations although they would permit the inhibition of the penetration at the majority of sites. Accordingly, such sites quite susceptible to the penetration should be subjected to any particular treatment for the inhibition of the penetration.
The casting operations may certainly be repeated using the same metallic mold over many times without encountering any penetration, if a substance having low chemical affinity for the molten magnesium alloy can easily be adhered to the entire surface (inner wall) of the metallic mold on the cavity side thereof or the surface of the mold, on the cavity side, at sites susceptible to penetration during casting, at an instance slightly before the casting cycle in which the penetration may take place after a large number of casting cycles.
Under such circumstances, the inventors of this invention have intensively investigated the foregoing substances and methods for adhesion, have found that it is effective for the achievement of the foregoing object of the present invention to form a coating layer by applying a mixture comprising at least one member selected from the group consisting of high melting metals, ceramic materials and graphite, and an aqueous surfactant solution or low boiling liquid oils and fats to at least part of the surface of the metallic mold on the cavity side, then applying heat to the coated portion to thus adhere the mixture to the inner surface of the metallic mold and thus have completed the present invention on the basis of the foregoing findings.
According to an aspect of the present invention, there is provided a metallic mold-casting method excellent in the resistance to penetration, which comprises the steps of forming a coating layer by applying a mixture comprising at least one member selected from the group consisting of high melting metals, ceramic materials and graphite, and an aqueous surfactant solution or low boiling liquid oils and fats to at least part of the surface of a metallic mold on its cavity side, then applying heat to the coated portion to thus adhere the mixture to the inner surface of the mold, and thereafter repeatedly casting a magnesium alloy in the metallic mold provided with the coating layer.
According to another aspect of the present invention, there is provided a metallic mold-casting method excellent in the resistance to penetration, which comprises the steps of forming a coating layer by applying a mixture comprising at least one member selected from the group consisting of high melting metals, ceramic materials and graphite, and an aqueous surfactant solution or low boiling liquid oils and fats to at least part of the surface of a metallic mold on its cavity side, then applying heat to the coated portion to thus adhere the mixture to the inner surface of the mold; thereafter repeatedly casting a magnesium alloy in the metallic mold provided with the coating layer; again forming a coating layer, after repeating the casting operations over a number of cycles and before the generation of any penetration, by applying a mixture comprising at least one member selected from the group consisting of high melting metals, cera
Kikawa Kazuo
Koike Seiichi
Kubota Kohei
Nosaka Yoichi
Washizu Kazuhiro
Elve M. Alexandra
Kerns Kevin P.
Mitsui Mining and Smelting Co. Ltd.
Young & Thompson
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