US2771650A - Shell molding - Google Patents

Description

United States Patent SHELL MOLDING Philip R. White, Detroit, Mich, assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware No Drawing. Application February 4, 1952, Serial No. 269,909

3 Claims. (Cl. 22-193) This application has to do generally with pattern equipment as used in foundry operations for forming metal castings and is more particularly concerned with improved metal pattern equipment.

There are several processes which have been proposed for use in forming molds for foundry operations in which very accurate and smooth surface finishes are required. For example, one process sometimes called sand-resin or shell molding is in use in which a dry mixture of sand and thermosett-ing resin binder is applied to a metal pattern heated to a temperature of about 250 to 350 F. or higher. After a short time interval the resin in the sandresin mix becomes molten and serves to bind the adjacent sand grains together to form a shell mold. The excess sand-resin mixture is then removed and the heated metal pattern with an adhering layer of the sand-resin mixture is heated to a higher temperature to set or cure the thermosetting binder and form a relatively strong thin-walled mold. The shell mold then is stripped from the metal pattern. Phenolformaldehyde and melamine formaldehyde resins are typical examples of the resins employed.

In another process a mixture of a binder and silica flour is sprayed on a heated metal pattern. In this procedure the first coating of silica flour and binder is coated with a sealing coat and thereafter a second coat of a mixture similar to the first is sprayed onto the sealing coat. The metal pattern with the sprayed coatings then is heated to set the binder which may be sodium silicate. The layers on the metal pattern are then backed up with refractory sand and binder. After heating to set the binder the mold is removed from the pattern. In both of the foregoing described processes the pattern equipment must be of metal because of the temperatures which are employed which would damage patterns of non-metallic materials.

In those processes in which metal patterns are used it has been common practice to form them of various materials such as cast iron, bronze, brass, aluminum and aluminum base alloys. Aluminum and the aluminum base alloys are particularly advantageous because of their heat conducting characteristics and because of the fact that they are relatively light in weight. However, aluminum and aluminum base alloy patterns have the disadvantage that as normally used they are more susceptible to scratching, abrasion and surface wear than are ferrous metals, brass or copper, etc. Accordingly, the primary object of this invention is to improve aluminum and aluminum base alloy patterns for use in making molds for foundry operations generally and especially for use in foundry operations in which the patterns are heated during the formation of the molds.

Other objects and advantages of the present invention will become more apparent as the description proceeds.

In accordance with the present invention the objects are attained by form-ing an anodized layer on the surface of aluminum or aluminum base alloy pat-terns. By aluminum base alloys is meant those alloys of aluminum which contain about 80% or more of aluminum. Any of the known processes for anodizing aluminum may be employed to provide the anodized coating or surface on the patterns in accordance with the present invention. Preferably the anodizing treatment is carried out to the point where there is an anodized coating on 'the aluminum or aluminum base alloy pattern having a thickness of .0001 to .0002 inch. As a typical example of one anodizing solutionwhich has been found especially suitable, reference is made to an aqueous solution containing by volume 20% sulfuric acid and 5% oxalic acid. The metal pattern is made the anode in'the solution. A voltage of 12 to 20 volts D. C. is employed. A temperature of F. has been found especially suitable for this anodizing solution. An anodizing time of 30 minutes in the described solution has produced an anodized coating which has been found quite satisfactory.

Prior to anodizing the pattern it is highly desirable to thoroughly clean the same. Where the pattern may have organic material thereon it is removed from the pattern and thereafter the pattern is given a light vapor blast. After the vapor blast treatment the pattern may be dipped in a conventional alkaline cleaner for approximately 10 seconds. Thereafter the pattern is rinsed in water and is then ready for the anodizing treatment. After the anodizing treatment the pattern is rinsed with water and then dried.

In the formation of molds by use of heated metal patterns it is common practice to apply a mold release agent to the metal pattern. Many materials have been proposed for this purpose. However, best results have been obtained by use of mold releasing agents which contain carnauba wax or similar natural waxes. These waxes aid greatly in releasing the mold from the heated metal pattern. Usually the Wax is applied to the heated pattern in a mixture or solution of the wax and a liquid vehicle. Any of the materials and procedures described in the copending application Serial No. 237,825, Mold Release Agents for Sand-Resin Molds, filed July 20, 1951, in the name of Donald J. Henry and assigned to the assignee of the present application, may be employed. Other mold release agents which have been employed comprise various silicone type materials. The molds formed by use of the anodizied aluminum or aluminum base alloy patterns in accordance with the present invention increase the pattern life by retaining the smooth surface finish, accurate dimensions and intricate pattern details. The anodized layer of the .0001 to .0002 inch in thickness does not impair the desirable thermal properties of the aluminum or aluminum alloy patterns. At the same time the patterns are highly scratch and wear resistant. In addition, the anodized aluminum or aluminum base alloy patterns in accordance with the present invention show easier release of the sand-resin or other molds when using carnauba wax lubricant or mold release agent than conventional aluminum patterns operating under similar conditions.

Where it may be necessary to remove periodically the carnauba wax lubricant residue resulting from continued pat-tern usage it may be removed from the metal pattern by heating the same in a circulating air-type furnace for 1 to 2 hours at 820 F. without in any way harm-ing the wear-resistant anodized layer. In the appended claims the word aluminum is intended to include not only pure or commercially pure aluminum but also the aluminum base alloys containing about 80% or more aluminum. It will be understood that the term pattern as used in the claims includes both mold patterns and core boxes and that the term mold includes both molds and cores.

Various changes and modifications may be made in the specific embodiments of my invention described herein without departing from the principles and spirit of the invention.

I claim:

1. The method of forming a mold for use in metal casting operations which comprises making an aluminum metal pattern, forming an anodized surface layer on said aluminum pattern having a thickness of .0001 to .0002 inch, applying a mold release agent consisting essentially of carnauba wax to the anodized surface of said aluminum pattern, heating said aluminum metal pattern as thus treated and applying a mold forming material comp-rising nonmetallic refractory material and a heat hardenable binder to said heated metal pattern.

2. The method of making a mold consisting essentially of nonmetallic refractory material and a heat hardenable binder which comprises applying a mixture of said nonmetallic refractory material and heat hardenable binder to a heated aluminum pattern having an anodized surface layer of about .0001 to .0002 inch in thickness and 15 carnauba wax on said anodized layer.

3. The method of making a mold consisting essentially of nonm'etallic refractory material and a heat hardenable binder which comprises applying a mixture of said nonmetallic refractory material and heat hardenable binder to an aluminum pattern heated to a temperature on the order of 250-350 F. having an anodized surface layer of about .0001 to .0002 inch in thickness and carnauba wax on said anodized layer.

References Cited in the file of this patent UNITED STATES PATENTS 840,251 Pinkus Jan. 1, 1907 1,965,682 Work July 10, 1934 2,023,645 Newton et a1 Dec. 10, 1935 2,056,048 Gregory Sept. 29, 1936 2,294,717 Carney Sept. 1, 1942 FOREIGN PATENTS 543,577 Great Britain Mar. 4, 1942 OTHER REFERENCES Anodic Coating of Aluminum, by Edwards. Pub. June 1939. Entire Booklet has 22 pages. Page 16 relied upon.

Metal Industry, Nov. 10, 1944. Pages 290-293, inclusive.

Modern Metals, October 1950, pages 22-24.

Claims (1)

1. 2. THE METHOD OF MAKING A MOLD CONSISTING ESSENTIALLY OF NONMETALLIC REFRACTORY MATERIAL AND A HEAT HARDENABLE BINDER WHICH COMPRISES APPLYING A MIXTURE OF SAID NONMETALLIC REFRACTORY MATERIAL AND HEAR HARDENABLE BINDER TO A HEATED ALUMINUM PATTERN HAVING AN ANODIZED SURFACE LAYER OF ABOUT .0001 TO .0002 INCH IN THICKNESS AND CARNAUBA WAX ON SAID ANODIZED LAYER.