Specialized metallurgical processes – compositions for use therei – Compositions – Loose particulate mixture containing metal particles
Reexamination Certificate
1999-04-07
2001-01-09
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Loose particulate mixture containing metal particles
C524S028000, C264S122000, C536S003000, C419S036000, C419S038000
Reexamination Certificate
active
06171360
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing metal parts, ceramic parts, composite parts made of a metal with a ceramic, or the like from a metal powder, a ceramic powder, or a mixture of them with a binder by the injection molding method and a molding composition used therein.
2. Description of the Related Art
In the method for injection-molding a metal powder or a ceramic powder, the metal powder, the ceramic powder, or a mixed powder thereof is kneaded with a binder and the kneaded material is injection-molded with an injection molding machine into a green body having a desired three-dimensional shape. Then the green body is heated to be degreased by decomposing and removing part of the binder and is sintered by heating it at a high temperature to obtain a metal part, a ceramic part, or a composite part of a metal with a ceramic.
Conventionally, as a binder used in such a method for injection-molding a metal powder or a ceramic powder, an aqueous solution of a natural polysaccharide, such as agar, is known, whose sol-gel reversible reaction is utilized. Such a binder wherein a polysaccharide is used has the advantage that the removal of the binder is quite easy since water amounts to about 80% or more of the binder.
However, in the conventional art, if a molded green body cannot support the structure by itself since the subsequent handling becomes difficult an agar whose gel strength is relatively high and whose average molecular weight is as relatively high as about 200,000 to 300,000 is used as a binder.
However, a binder using an agar exhibits poor decomposability. Since the agar used in the binder has high gel strength and high molecular weight, the agar is difficult to decompose by heating and large amounts of the components of the agar residue memain after the sintering step. Therefore, the components of the agar, when sintered, are carbonized and form a graphite structure and consequently after the sintering, large amounts of carbon residue (C) and the oxygen residue (O) remain in the obtained product, thereby lowering mechanical strength of the product. Further, since the decomposability of the binder is poor, it leads to a problem that the sintered density of the obtained product cannot be increased.
Therefore, an object of the present invention is to provide a binder for injection molding of a metal powder or a ceramic powder having good thermal decomposability, thereby providing a molded product having high sintered density and excellent mechanical strength.
SUMMARY OF THE INVENTION
This invention relates to a binder for injection molding of a metal powder or a ceramic powder, comprising an agar having an average molecular weight of 30,000 to 150,000 and water.
This invention also relates to a molding composition comprising a binder comprising an agar having an average molecular weight of 30,000 to 150,000 and water, and at least one selected from the group consisting of a metal powder, a ceramic powder, and mixtures thereof
This invention further relates to a method of injection-molding a metal powder or a ceramic powder, comprising the step of mixing the binder comprising an agar having an average molecular weight of 30,000 to 150,000 and water, and at least one of a metal powder, a ceramic powder, and mixtures thereof, to prepare a molding composition; the step of injection-molding said molding composition to form a desired-shaped green body; and the step of sintering said green body.
In the present binder for injection molding of a metal powder or a ceramic powder, the present molding composition wherein said binder is used, and the present molding method wherein said binder is used, the thermal decomposability of the binder is good, since a binder comprising an agar having low gel strength and low molecular weight and water is used. Therefore, after the sintering, a molded product having less carbon residue and oxygen residue, and therefore excellent in mechanical strength, an be obtained. Further, since the decomposability of the binder is good, a high sintered density can be attained.
REFERENCES:
patent: 4734237 (1988-03-01), Fanelli et al.
patent: 5258155 (1993-11-01), Sekido et al.
patent: 5286767 (1994-02-01), Rohrbach et al.
patent: 5496936 (1996-03-01), Thami et al.
patent: 6-168810 (1994-06-01), None
patent: 6-506183 (1994-07-01), None
patent: 6287601 (1994-10-01), None
patent: 6316703 (1994-11-01), None
patent: 11-3811 (1999-01-01), None
patent: 11-36002 (1999-02-01), None
List and brief explanation o the prior art references cited in the Japanese Office Action.
Fukushima Toshiharu
Suzuki Katsunori
Mai Ngoclan
Ostrolenk Faber Gerb & Soffen, LLP
Yamaha Corporation
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