Continuous compounding of aqueous injection molding feedstocks

Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – With subsequent cutting – grooving – breaking – or comminuting

Reexamination Certificate

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C264S122000, C264S328300, C264S017000, C264S328180, C419S036000, C419S065000

Reexamination Certificate

active

06261496

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to processes for shaping metal and ceramic parts from powders, and molding compositions therefor. More particularly, the invention is directed to material compounding processes for producing molding compositions that can be shaped into complex parts which exhibit excellent green strength and which can be readily fired into high quality sintered products.
BACKGROUND OF THE INVENTION
The production of sintered parts from “green” bodies is well known in the art. Generally, the green body is formed by filling a die with a powder/binder mixture and compacting the mixture under pressure to produce the green body. The green body, a self-supporting structure, is then removed from the die and sintered. During the sintering process, the binder is volatilized and burned out.
Heretofore, aqueous compositions useful as injection molding precursors have been prepared using batch-type processes. For example, U.S. Pat. No. 4,734,237 discloses the preparation of aqueous ceramic injection molding compounds using a sigma blender for blending the precursor liquid and powder ingredients. U.S. Pat. No. 5,250,251 gives examples of aqueous compositions prepared using a batch sigma mixer for molding articles from aluminum oxide, zirconium oxide and silicon nitride. Similarly, in U.S. Pat. No. 5,087,595 a batch mixer was used to prepare yttrium oxide/zirconium oxide molding compounds for fabricating oxygen sensors. Injection molding compounds containing metal powder are disclosed in U.S. Pat. No. 5,258,155, wherein the metal powder is kneaded with binder, water and other additives in a batch mixer. Aqueous injection molding compositions containing metal powder are disclosed in U.S. Pat. No. 4,113,480, wherein the binder and metal powder are pre-blended dry and then mixed with a solution of water and additives.
It is widely recognized that the quality of the green and fired metal or ceramic body is largely dependent upon the uniformity of the precursor molding feedstock composition, and that batch-to-batch variations in the feedstock produced can have a marked effect on the properties of molded objects made from such feedstock materials.
BRIEF SUMMARY OF THE INVENTION
The invention is directed to processes for preparing metal and/or ceramic injection molding compounds in a continuous manner suitable for high volume manufacturing. The invention makes possible the preparation of homogeneous molding compounds that can be manufactured in a continuous manner in high volume, and avoids the batch-to-batch variations that are typical in batch-type processes.
The molding compositions that form the subject of this invention contain metal and/or ceramic powder, a binder, a liquid carrier that serves as the transport vehicle, and optionally, other additives.
The invention comprises the steps of continuously forming a mixture, the mixture comprising metal and/or ceramic powders, a binder and a liquid carrier. The metal and/or ceramic powder, binder and liquid carrier are supplied in a continuous manner to a twin screw extruder and compounded into a homogeneous feedstock composition. After the continuous strand of feedstock material exits the extruder through a die, it is sliced into pellets. Optionally, other additives can be added to the powder/binder mixture to produce certain desirable properties of the feedstock composition.


REFERENCES:
patent: 4113480 (1978-09-01), Rivers
patent: 4734237 (1988-03-01), Fanelli et al.
patent: 4734727 (1988-03-01), Takemae
patent: 5087595 (1992-02-01), Marsh et al.
patent: 5132255 (1992-07-01), Takeuchi et al.
patent: 5250251 (1993-10-01), Fanelli et al.
patent: 5258155 (1993-11-01), Sekido et al.

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