Plastic and nonmetallic article shaping or treating: processes – Treatment of material by vibrating – jarring – or agitating...
Reexamination Certificate
1999-01-26
2001-12-11
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Treatment of material by vibrating, jarring, or agitating...
C264S220000, C264S225000
Reexamination Certificate
active
06328917
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns thermoset tools, such as molds for making articles by casting or forming processes, methods for manufacturing the tools, and articles made using the tools.
BACKGROUND OF THE INVENTION
The vacuum-casting industry designs tools that function as and makes molds from which additional articles are cast. Molds currently used in the vacuum-casting industry are made by serially applying plural layers of various materials to a master mold. These conventional molds generally have at least one layer, usually the first layer applied to the master mold, made from aluminized gel coats. Aluminized gel coats are relatively quite expensive, typically costing about $11-$12/pound.
After the first layer is applied to the master mold, additional “back up” layers are serially applied by hand over this layer to form a mold. Vacuum-casting methods subject these molds to significant stresses, and the molds therefore must have sufficient structural integrity so that they can withstand these stresses and be useful for their intended purposes. Molds made using conventional technology require a mold wall thickness of at least about {fraction (5/16)} inch to about ⅜ inch, which thicknesses are achieved by serially applying back up layers to the master mold until the desired mold thickness is obtained. Back up layers for vacuum-casting molds often comprise fiberglass and an aluminized tooling resin. The cost of the materials used to make the back-up layers, while significantly less than that for aluminized gel coats, still is about $5-$6/pound.
Conventional molds used by the vacuum-casting industry have a part production capacity of only about 1,000 parts. That is, the molds must be replaced after about 1,000 parts are made using such molds. Moreover, conventional molds currently used by the vacuum-casting industry have to be repaired after producing only about 75-100 parts. These two factors, the part production capacity of the mold and the need to repair the mold frequently, plus the material costs required to produce conventional vacuum-casting molds, indicate that there is a need for new materials and methods for making various molds useful for practicing vacuum-casting processes.
SUMMARY OF THE INVENTION
The present invention provides a thermosetting resin and filler composition that can be cured in a variety of shapes and dimensions to make a variety of tools. One example, without limitation, of a tool that can made according to the method of the present invention is a vacuum-casting mold. These molds can be made much less expensively, have longer useful lifetimes, such as part production capacities of about 5,000 total parts, and need repairing much less frequently, such as after producing about 1,000 parts, than conventional vacuum-casting molds.
One embodiment of the method for making tools according to the present invention first involves forming a composition useful for making tools, referred to herein as a tool composition. The tool composition comprises (a) from about 65 to about 75 weight percent filler, preferably about 70 weight percent, the filler being selected from the group consisting of Group II metal carbonates, such as calcium carbonate and magnesium carbonate, alumina, silica, ceramic materials, glass, nut shells, fiberglass, dolomite, and mixtures thereof, (b) from about 25 to about 35 weight percent, preferably about 30 weight percent, of a thermosetting resin, and (c) a catalyst for catalyzing the formation of the thermoset resin.
Particularly useful fillers are selected from the group consisting of calcium carbonates, magnesium carbonates, alumina trihydrate, silica, and mixtures thereof. Working embodiments of the tool composition have been formed comprising from about 50 to about 55 weight percent calcium carbonate, from about 35 to about 40 weight percent magnesium carbonate, and less than 2 weight percent silica.
A tool composition made according to the present invention has been found to be particularly suitable for making molds for the vacuum-casting industry. For this embodiment, from about 5 to about 10 weight percent of the filler portion of the composition comprises alumina trihydrate. The remainder of the filler portion is selected from the group consisting of Group II metal carbonates, silica, and mixtures thereof. The alumina trihydrate preferably comprises particles having an average particle size of from about 7 &mgr;m to about 10 &mgr;m, typically about 8 &mgr;m, and the remainder of the filler particles have an average particle size of from about 73 &mgr;m to about 77 &mgr;m, typically about 75 &mgr;m.
Suitable thermosetting resins for practicing the method of the present invention are selected from the group consisting of saturated polyester resins, unsaturated polyester resins, unsaturated polyester copolymer resins, styrene-unsaturated polyester copolymer resins, vinyl ester resins, vinyl ester-styrene copolymer resins, epoxy resins, epoxy-vinyl ester copolymer resins, and mixtures thereof. Preferred thermosetting resins for practicing the method of the present invention are selected from the group consisting of unsaturated polyester resins, styrene-unsaturated polyester copolymer resins, vinyl ester resins, vinyl ester-styrene copolymer resins, and mixtures thereof.
The composition typically comprises from about 1 to about 2 volume percent, based on the volume of the resin, of at least one organic peroxide catalyst. Working tool compositions have included a catalyst selected from the group consisting of methyl ethyl ketone peroxides, 2,4 pentanedione peroxides, cumyl peroxide, and mixtures thereof.
The step of forming the composition has been practiced by adding to a mixing device from about 25 to about 35 weight percent resin and from about 1 to about 2 volume percent catalyst, based on the volume of the resin. The resin and catalyst are added to the mixing device with continuous mixing and mixed for a sufficient period of time to substantially disperse the catalyst throughout the resin, thereby forming a resin-catalyst mixture. The mixing device can be a vacuum mixing device. From about 65 weight percent to about 75 weight percent filler is then added to the mixture, and the mixture and filler are blended.
Once formed, the tool composition is applied to a plug shaped so that the desired tool is formed by curing the composition on, around and/or in the plug. The composition is allowed to cure to form the tool, and the tool is then separated from the plug. The step of applying the composition to the plug has been accomplished by vibrating the plug having the tool composition applied thereto, which helps distribute the tool composition substantially uniformly on, around, about and/or inside the plug as desired.
In one embodiment, the step of allowing the resin to cure was initially practiced at ambient temperature. The method further included a heated curing step and most typically involves heating just the tool, but could involve heating the tool and plug at a temperature of from about 100° F. to about 400° F. for a period of from about 1 hour to about 12 hours after curing the resin at ambient temperature.
The present invention concerns tools that can be used for a variety of purposes, wherein at least a portion of the tool is made using the compositions described briefly above. One embodiment of the tool is useful as a mold for forming articles by vacuum-casting processes.
The present invention also is directed to a method for forming articles from tools. One embodiment of the method comprises first making (or using) a tool shaped in the form of a desired article as described above, and separating the tool from the plug. Articles are then formed, such as by vacuum-casting such articles, using the tool as a mold.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following definitions are provided solely for the convenience of the reader. These definitions should not be construed to limit the defined terms to a scope less than would be known to a person of ordinary skill in the art.
A “plug” or “maste
Klarquist & Sparkman, LLP
Kuhns Allan R.
Thermoset Molds, L.L.C.
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