CENTRAL SPRUE FOR INVESTMENT CASTING
A sprue for use in investment casting may comprise a pin and a shell enclosing a part of the pin. A method for creating a sprue may comprise partially enclosing a pin in a shell.
The disclosed method and apparatus pertain to the manufacturing of items by investment casting.
BACKGROUNDThe lost wax investment casting process may be used to manufacture a variety of items, including jewelry, ornaments, figurines, dental components and industrial parts. In the lost wax investment casting process, a wax or plastic pattern of an item may be created by, for example, injecting wax or plastic into a rubber or metal mold, or by hand carving. These patterns 11 may then be attached to a sprue 10 to create a pattern or casting “tree” 13, such as that illustrated in
The wax or plastic patterns 11 may be affixed to the sprue 10 using a variety of methods and tools, such as with softened wax or plastic or with adhesive. The finished tree 13 may then be placed in a container called a flask (not shown). The base 12 may serve as a base or lid for the flask. Powdered investment material and water may be mixed. The investment mixture may be poured into the flask, submerging the tree 13 of patterns 11. After the investment mixture solidifies, the flask may be heated to cure the investment material to strengthen it into an investment mold into which molten metal may be poured. The base 12 may be removed after the investment mold has set and before heating. During the flask “curing” process, the patterns 11 and sprue 10 may be melted and/or burned out of the investment mold, leaving mold cavities of the pattern shape and channels into which molten metal may flow. The patterns may also be removed by chemical dissolution. Once the curing and burnout process is complete, the flask may be placed in a casting machine. Molten metal may then be poured into the investment mold. The cavity created in the investment mold by the cone 14 of the base 12 may serve to funnel the molten metal into the channels and pattern cavities formed in the investment mold by the tree. After the metal solidifies, the investment mold may be removed, and the cast objects may be cut from the tree and finished.
Using a solid wax or plastic sprue may result in increased wax or plastic material costs, in increased burnout emissions and byproducts, in trees that bend or twist as patterns are attached to the tree, in relatively large sprues that leave correspondingly large channels to be filled by molten metal, and in excessively wide channels that increase turbulence of molten metal as it flows into the flask. For example, if the sprue bends or twists in the flask, some patterns may be pushed closer to one side of the flask, resulting in an investment mold that is weaker in that area. Greater mold non-uniformity may increase the risk that the investment mold will break during curing and use. There exists a need for a method and apparatus for reducing or eliminating one or more of those disadvantages.
SUMMARYA sprue for use in investment casting may comprise a pin and a shell enclosing a part of the pin. A method for creating a sprue may comprise partially enclosing a pin in a shell.
With reference to the embodiment of
With reference to the embodiment of
The support section 30 may comprise a base end 32 having a variety of cross-sectional shapes, for example, of round, square, hexagonal, triangular or other suitable cross-sectional shape. Non-round cross-sectional shapes may allow a mold technician to more easily remove the pin 22 from the shell 24 using a turning force such as by using a wrench. Alternatively, the base end 32 may be provided with one or more slots or other apertures (not shown) configured to receive tools or keys, such as a screwdriver, socket wrench or Torx™ wrench. Preferably, little force should be required to remove the pin 22 from the shell 24. Thus, in the embodiment of
In other embodiments, the pin 22 may be of constant diameter, or may include one or more curves or taper angles. The pin 22 may be hollow, or may be perforated to better retain a shell 24. By using a relatively rigid pin 22, a sprue may be made much thinner than prior art sprues of solid wax or plastic, yet still remain sufficiently rigid for pattern attachment. A thinner sprue may result in smaller channels in the investment mold, which may correspondingly reduce the amount of molten metal that fills the channels after casting and must be recovered for reuse. This may yield a better ratio of castings to sprue weight per mold.
The shell 24 may be applied to the pin 22 in a variety of ways. As shown in the embodiment of
A pin may be enclosed by a shell in other ways, as well, such as by dipping a pin in melted wax or plastic that is then allowed to harden on the pin. Alternatively, melted wax or plastic may be applied with a brush to the pin and allowed to harden. If wax or plastic is provided in a thin sheet, the wax or plastic sheet may be wrapped around the pin and smoothed with a hot knife to create a shell.
As may be seen in
After the investment material has hardened, the base 90 and pin 65 may be removed from the flask 92, as shown in
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition, or matter, means, methods and steps described in the specification. As one will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods or steps.
Claims
1. A sprue comprising a pin and a shell, the shell at least partially enclosing the pin, and the pin comprising a smooth surface and being partially tapered so as to allow manual removal of the pin from the shell after investing while the pin and the shell are substantially at room-temperature.
2. The sprue of claim 1, the shell comprising wax or plastic.
3. The sprue of claim 1, the pin comprising a shaft and a support section, and the shell at least partially enclosing the shaft.
4. The sprue of claim 3, the pin further comprising a shoulder section, and the shell further at least partially enclosing the shoulder section.
5. (canceled)
6. (canceled)
7. The sprue of claim 4, the shoulder section comprising threading whereby the pin may be unscrewed from the shell.
8. An apparatus for investment casting comprising:
- a sprue comprising a pin and a shell, the shell at least partially enclosing the pin, and the pin comprising a smooth surface and being partially tapered so as to allow manual removal of the pin from the shell after investing while the pin and the shell are substantially at room-temperature;
- a base configured to removably support the sprue; and
- a flask sealingly mountable to the base, the flask being configured to substantially surround the sprue and contain investment material.
9. A method for creating a sprue comprising the step of at least partially enclosing a pin in a shell, and the pin comprising a smooth surface and being partially tapered so as to allow manual removal of the pin from the shell after investing while the pin and the shell are substantially at room-temperature.
10. The method of claim 9, the shell comprising wax or plastic.
11. The method of claim 9, further comprising the step of forming the pin to comprise a shaft section and a support section.
12. The method of claim 11, wherein the step of enclosing further comprises at least partially enclosing the shaft using wax or plastic.
13. A method for investment casting comprising the steps of:
- at least partially enclosing a pin in a shell, the pin comprising a smooth surface and being partially tapered;
- mounting the pin to a base;
- affixing patterns to the shell to create a tree;
- sealingly attaching the base to a flask such that the flask substantially surrounds the tree;
- pouring investment material into the flask to substantially submerge the patterns in the investment material;
- allowing the investment material to harden into an investment mold;
- manually removing the pin from the shell while the pin and the shell are substantially at room-temperature;
- removing the shell and patterns from the investment mold; and
- pouring molten metal into the investment mold.
14. (canceled)
Type: Application
Filed: Jan 3, 2011
Publication Date: Jul 5, 2012
Inventor: BILL DAVIDSON (Boerne, TX)
Application Number: 12/983,740
International Classification: B22C 9/04 (20060101); B22C 13/08 (20060101);