US2532155A

US2532155A - Thixotropic investment material

Info

Publication number: US2532155A
Application number: US778469A
Authority: US
Inventors: Elbert E Ensign
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1947-10-07
Filing date: 1947-10-07
Publication date: 1950-11-28
Anticipated expiration: 1967-11-28

Description

Patented Nov. 28, 1950 THIXOTROPIC INVESTMENT MATERIAL Elbert E. Ensign, Ypsilanti, Mich., assignor to Ford Motor Company, Dearborn, Mich., a corporation of Delaware No Drawing. Application October 7, 1947, Serial No. 778,469

4 Claims. 1

This application is concerned with the foundry molding art and more particularly with a process for the precision casting of metals by the investment or lost wax process. Basically this process depends upon the use of a destructible pattern constructed of wax, low melting point metal, combustible or soluble material. Such a pattern is surrounded or invested in a hardenable mixture which is then permitted to set or harden. The mold so prepared and containing the pattern is then treated to remove the pattern. If wax is chosen as the pattern material it can be removed by gentle heating to melt the wax. A similar treatment can be applied to low melting metal patterns. The combustible or soluble patterns can be removed by heating or dissolving. The choice of pattern material for any particular use is dictated by considerations well known to those skilled in the art and need not be elaborated upon here.

There are many satisfactory investment materials for the lower melting alloys and metals such as pewter, aluminum, bronze, brass, etc. However, attempts to extend the use of investment casting to steel have met with only limited success because of the lack of a really satisfactory investment material. Such a material must be strong and thermally stable to give a faithful reproduction of the original pattern. In addition, it must be sufliciently refractory to remain in contact with molten steel at temperatures circa 3000 F. without fusing or gassing and must under these high temperatures impart to the metal a smooth surface. In addition to the above, a commercially successful investment material must be fairly cheap if precision casting is to be competitive with other methods of fabrication.

To date the most widely used investment molds for use with steel have contained silica obtained from the hydrolysis of ethyl silicate or other organic ester of silicic acid; While such organosilica compounds did yield satisfactory castings,

they are objectionable commercially because of To provide such an investment material for use in ferrous casting, applicant has taken advantage of the thixotropic properties of zeolitic materials, either natural or synthetic. When properly prepared these zeolitic investment materials have the property of remaining plastic indefinitely as long as they are kept agitated and the loss of moisture is prevented. Thus large batches of investment material may be prepared in advance and used as required.

While natural zeolitic materials may be used in the manufacture of applicant's investment material, considerations of economy, convenience and reproductibility of results dictate the use of the synthetic materials. Silica flour which is a form of very finely divided silica is the base material employed in the manufacture of the synthetic zeolite. To such silica flour is added water, an acid, a source of aluminum ions and a source of sodium and/or potassium ions. The following is a specific example of a method for preparing a successful investment material. A solution was prepared comprising:

Per cent Water 83.5 Sodium Phosphate 6.6 Potassium alum 3.4 Hydrochloric Acid 22 B 6.5

One part of this solution was mixed with three parts of fine silica flour and intensively agitated at room temperature. Under these conditions a reaction took place to yield a plastic, synthetic zeolite. The proportions given are by way of i1- lustration only and represent only one of an endless series of mixtures which can be employed for the same purpose. For example, ordinary sodium chloride can be employed instead of the sodium phosphate. Apparently it is only essential that a source of acid, aluminum ions and sodium and/ or potassium ions be added. However, the anions used should be selected with regard to their behavior during the firing and subsequent pouring of the mold.

The use of applicants thixotropic zeolitic investment materials requires no variation from previously developed techniques based upon the use of organic silicates. The only precaution to be observed is the constant agitation of the zeolitic material to prevent setting. The unused zeolite should, of course, be protected from loss of moisture.

What is claimed is:

l. The process of preparing a thixotropic investment material comprising mixing by weight 83.5 parts of water, 6.6 parts of sodium phosphate, 3.4 parts of potassium alum, 6.5 parts of 22 B. hydrochloric acid, adding to the solution so formed three times its weight of fine silica flour, and intensively agitating the mix at room temperature.

2. The process of preparing thixotropic investment molding material comprising mixing an aqueous solution containing a soluble acid and a soluble aluminum compound and a soluble compound chosen from the group consisting of sodium and potassium compounds with sufficient silica flour to give a molding material of the desired consistency and intensively agitating the mix.

3. The process of preparing a thixotropic investment molding material comprising mixing an aqueous solution containing a soluble acid, a soluble aluminum compound and a soluble sodium compound with sufficient silica flour to give a molding material of the desired consistency.

4. The process of preparing a thixotropic investment molding material comprising mixing an aqueous solution containing a soluble acid,

4 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,052,514 Poulson Feb. 11, 1913 1,756,623 Behrman Aug. 29, 1930 1,872,183 Porter Aug. 16. 1932 1,889,007 Wallace Nov. 29, 1932 2,193,346 Ruddle Mar. 12, 1940 2,213,530 Montero Sept. 3, 1940 2,233,701 Grossman Mar. 4, 1941 2,237,592 Dunbeck Apr. 8, 1941 2,237,593 Dunbeck Apr. 8, 1941 2,256,456 Dietert Sept. 16, 1941 OTHER REFERENCES American Foundryman, April 1947, page 36.

20 (Copy in Division 3.)

and soluble aluminum compound and a soluble 25 and their Physical Properties. by C. S. Ross and potassium compound with sufficient silica flour to give a molding material of the desired consistency.

ELBERT E. ENSIGN.

Earl V. shamon, pages 88-90.

Claims

2. THE PROCESS OF PREPARING THIXOTROPHIC INVESTMENT MOLDING MATERIAL COMPRISING MIXING AN AQUEOUS SOLUTION CONTAINING A SOLUBLE ACID AND A SOLUBLE ALUMINUM COMPOUND AND A SOLUBLE COMPOUND CHOSEN FROM THE GROUP CONSISTING OF SODIUM AND POTASSIUM COMPOUNDS WITH SUFFICIENT SILICA FLOUR TO GIVE A MOLDING MATERIAL OF THE DESIRED CONSISTENCY AND INTENSIVELY AGITATING THE MIX.