Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles
Reexamination Certificate
1999-03-04
2001-12-11
Theisen, Mary Lynn (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
C264S621000, C419S036000
Reexamination Certificate
active
06328918
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for shaping metal and ceramic parts from powders and molding compositions therefor. More particularly, the invention is directed to molding processes and molding compositions for forming internally or externally threaded articles that can be readily fired to produce net-shape articles without the need for machining or other finishing operations.
BACKGROUND OF THE INVENTION
Threads are a convenient means of joining two or more components in a myriad of applications including industrial, automotive, aerospace, consumer and plumbing, among others. Machining is used to produce the vast majority of mating external and internal threads on metal and ceramic components. Machining is both a costly and time- consuming process for producing threaded components, and in many cases it may represent the costliest step in an entire manufacturing process.
Investment casting represents a net and near-net-shape method for forming threaded components. However, investment casting is generally a time-consuming, multi-step process that is inefficient for the manufacture of parts in high volume. Generally, some finishing operations are required to produce a finished article.
Injection molding is a preferred process for manufacturing complex, net-shape parts from metal and ceramic powders in high volume, and therefore offers considerable advantages over processes that require additional machining and finishing operations. The injection molding process is ideally suited for producing threaded articles that have desired properties without performing additional costly finishing operations.
The present invention provides a method for manufacturing metal and ceramic threaded parts by low pressure injection molding using aqueous feedstocks. More specifically, according to the present invention a process is provided for shaping threaded parts from metal and ceramic powders. The process generally comprises the following steps: introducing into a conventional injection molding machine aqueous feedstock consisting essentially of metal powders, ceramic powders or mixtures thereof, water, a binder from the family of polysaccharides known as agaroids, and optionally other additives to enhance the processability and/or stability of the material; molding the threaded part at low temperature (e.g, approximately 85° C.) and low pressure (e.g., between approximately 400 to 1000 psi hydraulic); cooling the molded part in the mold to a temperature below the gel point of the binder (e.g., approximately 37° C.); removing the cooled, threaded part from the mold; drying the part to remove the water; heating the part to a first elevated temperature to remove the binder, and then to a second elevated temperature to density the part to its final desired condition.
BRIEF SUMMARY OF THE INVENTION
The invention is directed to a process for forming a threaded article comprising the steps of forming a mixture comprising powder selected from the group consisting of pure stainless steel alloys, stainless steel alloying elements, intermetallic compounds, components of metal matrix composites and mixtures thereof, a gel-forming material and an aqueous gel-forming material solvent; and molding the mixture in a mold having threads formed therein under conditions of temperature and pressure sufficient to produce a self-supporting article. The threaded article may contain internal or external threads.
The invention also provides an injection molding process for forming a threaded article comprising the steps of forming a mixture comprising powder selected from the group consisting of metal powders, ceramic powders or mixtures thereof, a gel-forming material selected from the group of polysaccharides consisting of agaroids and an aqueous gel-forming material solvent; supplying the mixture to an injection molding machine having a mold with threads formed therein, the mixture being maintained during the supply step at a first temperature above the gel point of the gel-forming material; and cooling the mixture in the mold to a second temperature below the gel point of the gel-forming material to form the threaded article.
REFERENCES:
patent: 4734237 (1988-03-01), Fanelli et al.
patent: 5258155 (1993-11-01), Sekido et al.
patent: 5403373 (1995-04-01), Kitagawa et al.
patent: 5746957 (1998-05-01), Fanelli et al.
H.H. Selby et al., “Agar”, Industrial Gums, Academic Press, New York, NY, 2nd ed., 1973, Chapter, p. 29.
Schoonover James
Snow Brian
Zedalis Michael Sean
Criss Roger H.
Honeywell International , Inc.
Nerenberg Aaron
Theisen Mary Lynn
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