Plastic and nonmetallic article shaping or treating: processes – Removal of liquid component or carrier through porous mold...
Reexamination Certificate
2000-05-09
2001-12-04
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Removal of liquid component or carrier through porous mold...
C264S087000, C264S137000, C264S162000, C264S135000, C264S221000, C264S258000, C264S317000, C156S173000, C156S175000, C524S493000, C524S494000, C524S549000, C524S555000, C524S808000, C524S813000, C523S218000, C523S219000
Reexamination Certificate
active
06325958
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for manufacture of a mandrel or mold core and, more particularly, to a method for manufacture of mandrels used to fabricate rocket motors, housings and other uniquely shaped items made using a mandrel as a form or core.
BACKGROUND OF THE INVENTION
Mandrels have been used to fabricate rocket motor housings. For example, U.S. Pat. No. 5,386,777, which is incorporated by reference, describes fabrication of rocket motor housings using soluble mandrels that are composed of polyvinyl alcohol (PVA) sheets. According to U.S. Pat. No. 5,386,777, a mandrel may be formed by wrapping a core or tube with a web or sheets of highly porous polyvinyl alcohol, then coating the formed mandrel with insulation and an epoxy impregnated fiber filament that is cured, typically by heat, to form the housing over the PVA mandrel or core.
There are certain disadvantages to the fabrication methodology taught in U.S. Pat. No. 5,386,777. That is, the polyvinyl alcohol web has limited thermal stability and decomposes at elevated temperatures. More specifically, polyvinyl alcohol undergoes significant thermal decomposition in air at temperatures between about 200-220 degrees C. See D. W. Van Krevelen, Properties of Polymers 3rd Edition, Elsevier Publishers, New York, 1997, page 642; Merck Index 12th Edition, Merck & Co., Whitehouse, N.J., page 1309. Polyvinyl alcohol also has a high viscosity. A material having a lower viscosity than polyvinyl alcohol at equal solute concentrations is desirable. Polyvinyl alcohol also has a significant creep upon heating. A material having less creep is desirable.
Polyvinyl alcohol also has a tendency to be chemically reactive since it has reactive functional groups pendant to its backbone (e.g., hydroxyl groups). A material that is more chemically inert than polyvinyl alcohol is desirable. These limitations make it difficult to fabricate rocket housings and nozzles from epoxy or thermosetting resin that requires high curing temperatures. Thus, a more suitable method for manufacture of a mandrel is desired.
SUMMARY OF THE INVENTION
Briefly, the present invention comprises a method for manufacture of a mandrel or other shaped core item which may be used as a mold form and which further has utility as a carrier by virtue of the porosity of the mold form. Specifically, and by way of example, hollow ceramic microspheres are mixed together with a water soluble organic binder to form a billet. The billet is then dried by heating to form a generally solid material wherein the water is removed from the material. The binder is typically poly(-2-ethyl-2-oxazoline) and derivatives thereof. In preferred embodiments the amount of binder in the mixture is in the range of up to 50% by weight of the mixture forming the billet. The dried billet may then be machined into a mold form or core. In the event the mold form is used for manufacture of a rocket motor or casing, the mold form is then wrapped with an epoxy impregnated fiber filament known in the composites fabrication trade as a prepreg. The prepreg is then permitted to cure, often at elevated temperatures. The motor may then be transported to a launch or assembly site at which time the core which was formed from the mixture of binder and microsphere material is filled with a liquid oxidizer. Alternatively, the core (mandrel) being water soluble is washed from the housing before the housing is loaded with rocket fuel.
Thus, it is an object of the invention to provide a mandrel or mold core which may be formed as a billet, dried and machined to provide a complex core shape.
It is a further object of the invention to provide a mold core which has high thermal stability, does not decompose, and which may be manufactured inexpensively.
Yet a further object of the invention is to provide a mold core material which may be easily fabricated into a billet and then machined using existing machining technology.
These and other objects, advantages, and features of the invention will be set forth in the detailed description which follows.
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Merck Index 12th Edition, Merck & Co., Whitehouse, N.J., pp. 1308-1309.
Polymer Chemistry Innovations, Technical Information: Ceramics Applications of Aquazol (2 sheets).
D. W. Van Krevelen,Properties of Polymers 3rd Edition, Elsevier Publishers, New York 1997, pp. 642.
Material Safety Data Sheet AQUAZOL 5/50/200/500, Polymer Chemistry Innovations, Inc., Tucson, Arizona, Feb. 27, 1998.
Artz Gregory John
Lombardi John Lang
Advanced Ceramics Research, Inc.
Banner & Witcoff , Ltd.
Poe Michael I.
Silbaugh Jan H.
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