Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1994-04-08
1996-06-11
Lin, Kuang Y.
Metal founding
Process
Shaping liquid metal against a forming surface
164 61, 164 681, B22D 2713, B22D 2715
Patent
active
055247059
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method for casting oxidization-active metal under oxygen-free conditions.
BACKGROUND ART
Oxidization-active metals such as pure titanium and titanium alloy materials consisting mainly of titanium exhibit high heat resistance, excel in such mechanical properties as toughness and wear resistance, and being highly biocompatible, do not harm living organisms in which they are embedded. They therefore have the potential for extensive utility not only in industry but also in dental prosthetics, plastic surgery and other such surgical and medical fields.
However, since titanium materials are very active and are therefore exceedingly difficult to work, it has only been possible to process them in vacuo using special equipment and techniques. Because of this, it has not been possible to fabricate dentures and other complex, intricate articles from titanium.
JP-B 56-1981, for example, discloses that oxidization and other qualitative changes in a metal are prevented by maintaining an inert gas atmosphere in the melting chamber and the casting chamber from before the metal is melted until after it is cast. JP-B 56-1981 further discloses that the running of the metal is improved by causing the inert gas to pass under a differential pressure from the melting chamber through a gap passage, a passage hole, the sprue of the mold and the shaped cavity into the casting chamber so that at the time the metal is poured into the mold after being completely melted the molten metal flows smoothly into the deep regions of the shaped cavity of the mold as entrained by the inert gas flow.
The present invention proposes a method for non-oxidize casting of oxidization-active metal in which the absolute amount of oxygen is reduced to an ultra-low level by drying the mold.
DISCLOSURE OF THE INVENTION
The present invention is directed to a method for casting oxidization-active metal under oxygen-free conditions comprising a step of discharging air from a melting chamber and a casting chamber while maintaining the condition of the melting chamber pressure P.sub.R >the casting chamber pressure P.sub.C, i.e., the compressed gas pressure, and then introducing dry compressed inert gas into the melting chamber, a step of imparting directionality to the atmosphere gas of the melting chamber under the condition of P.sub.R >P.sub.C for replacing the atmosphere in a mold of the casting chamber with inert gas and establishing a non-oxidizing atmosphere in the melting chamber and the casting chamber, and a step of precision casting conducted by thereafter melting a fusible casting material and pouring it into the mold in the casting chamber, wherein the mold is dried by introducing dry compressed inert gas into the melting chamber while maintaining the condition of P.sub.1 >P.sub.2.
As the means for evapotranspiring and discharging oxygen, hydrogen and the like from the interior of the mold to the exterior so as to strongly suppress oxygen in the mold, the present invention introduces inert gas into the melting chamber 8 under high pressure after the air pressure in the casting chamber 9 has reached a prescribed degree of vacuum, thus establishing a high differential pressure (melting chamber at positive pressure higher than atmospheric pressure .fwdarw.casting chamber at pressure lower than atmospheric pressure and in a vacuum, thereby imparting the inert gas with directionality for passing, evapotranspiring and drying the mold moisture content.
Further, after evapotranspiring and drying the moisture content in the mold (the first purging), the same process is repeated multiple (two or more) times for controlling the interior of the melting chamber to an anoxic atmosphere by suppressing the absolute amount and concentration of oxygen therein to an ultra-low level, thereby establishing a state enabling selection of an appropriate pressure condition for arc discharge. This enables casting which is capable of forming ultra-fine features free of blowholes produced by reaction with oxygen.
BRI
REFERENCES:
patent: 4762165 (1988-08-01), Ogino et al.
patent: 5168917 (1992-12-01), Okuda et al.
Matsubara Norio
Miyazaki Shouichirou
Lin Kuang Y.
U-WA Tech Corporation
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