US 3694264 A
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Sept. 26, 1972 5 WE|NLAND EI'AL 3,694,264
CORE"REMOVAL Filed Sept. 28, 1970 INVENTORS. STUART L. WEINLAND BY 9N .COLETTI ATTORNEY United States Patent Oflicc 3,694,264 Patented Sept. 26, 1972 3,694,264 CORE REMOVAL Stuart L. Weinland, Arlington Heights, and Donn K.
Coletti, Mundelein, Ill. (both of 250 N. 12th St., Wheeling, Ill. 60090) Filed Sept. 28, 1970, Ser. No. 56,758 Int. Cl. B08b 9/00 US. Cl. 134-22 R Claims ABSTRACT OF THE DISCLOSURE calcia-based cores in metallic objects, such as cast fiuid-coolable turbine blades, are efficiently removed by exposing the cores to the action of aqueous solutions of ammonium salts. It is particularly advantageous to use a 5 molar aqueous solution of ammonium chloride.
The present invention is concerned with core removal from metal casting and, more particularly, with core removal from investment castings of gas turbine structures such as gas turbine blades containing relatively long, narrow cooling passages.
It is known to produce fluid-coolable gas turbine blades by investment casting. In this process a wax or other fugitive model containing ceramic cores is coated with a refractory shell, the wax is removed from the refractory shell and the refractory shell plus the ceramic cores is intimated by heat. Subsequently metal is cast into the shell in place of the fugitive model.
It has been suggested (see Whittemore, Jr., US. Pat. No. 2,876,122) in a broad sense to employ calcia ceramics as cores in refractory molds. In the Whittemore patent it is disclosed that such cores can be removed merely by the use of water. Applicants have found to the contrary that when employing cores having crosssectional areas of the order of magnitude of 8 x 10" in. such as are often used in the manufacture of fluid-cooled turbine blades, it is impractical to remove such cores with water. Calcium oxide reacts with water to form calcium hydroxide which is sparsely soluble. If one attempts to remove cores in small holes with water, the resultant calcium hydroxide will gradually clog the holes and drastically reduce the rate of reaction. Of course, this effect can be minimized by forcing water into each small hole but such a scheme is impractical because of the special expensive fixtures necessary for each blade hole configuration. If one turns to strong acids, such as hydrochloric acid, one runs the serious risk of causing intergranular corrosion in the cast metal exposed to the acid. Even then such strong acids must be flushed periodically from the holes and replaced with fresh acid in order to keep a removal reaction proceeding at a satisfactory pace.
As far as applicants are aware, no one prior to the present invention has provided a means for conveniently removing cores based upon a calcia ceramic from small holes in investment-cast metallic objects. By means of the present invention, applicants can now remove such cores in a convenient and inexpensive manner which does not endanger the cast metal.
It is an object of the present invention to provide a novel process for the removal of calcia-based ceramic cores from cast metal objects.
Another object of the present invention is to provide a novel process for the removal of calcia ceramic cores from cast nickel-base or cobalt-base alloys.
Other objects and advantages will become apparent from the following description taken in conjunction with the drawing in which the figure shows, schematically, the removal of cores from turbine blade castings.
Referring now to the drawing, in accordance with the invention, castings 11 in the form of turbine blades (or any other desired shape) made of a nickel-chromium, cobalt-chromium or other corrosion-resistant alloy and containing passages or cavities 12 filled with calcia-based ceramic cores are supported in container 13 on supports 14. Container 13 is filled to liquid level 15 with an aqueous solution of an ammonium salt from the group of ammonium chloride, ammonium bromide, ammonium nitrate, ammonium fluoride and ammonium acetate. The aqueous solution is heated or maintained hot by heating unit 16 or any other conventional heating means. The calcia-based ceramic cores are completely and rapidly removed from the castings by means of the aqueous solution. Those skilled in the art will appreciate that the drawing is schematic in nature. Cavities 12 can be blind cavities and it is not necessary that supports such as supports 14 be used.
When, as is advantageous for reasons of economics and efliciency, ammonium chloride is employed in the aqueous medium, the removal proceeds overall by the reaction Of course, it may very well be that the initial step of the reaction sequence could be an hydration of the lime (CaO), followed by a reaction of the hydroxide with ammonium ion. Naturally it is necessary to employ an amount of ammonium chloride in excess of the minimum required to react with the calcia in the cores to be removed. It has been found that it is not necessary to employ solutions of ammonium chloride stronger than about 5 molar as the aqueous medium. With 5 molar aqueous ammonium chloride solution used at its boiling point the removal reaction proceeds vigorously since the escaping ammonia causes replacement of the aqueous media in even the deepest, narrowest holes likely to be encountered in commercial production. For example, it has been found that with holes 0.1 inch in diameter (7.85 x 10- in. cross-sectional area) filled with calciabased cores, removal rates in excess of one inch per hour can be attained with substantially no danger of adverse corrosion effects in the cast alloy.
Calcia-base cores which can be removed by the presently disclosed techniques include not only the types of cores disclosed by Whittemore, Jr. in US. Pat. No. 2,876,122 but also any core which has a continuous network of calcia or calcia-rich ceramic material. Thus calcia cores disclosed by Whittemore, Jr. in US. Pat. No. can include amounts of magnesia, silica, iron, cobalt and nickel oxides, alumina and like materials either per se or chemically bound to the calcia which do not either reduce the refractoriness of the cores to undesirably low levels or shield the calcia of the cores from the action of the removal agents disclosed hereinbefore. The cores can be made by the techniques disclosed by Whittemore, Jr. or by other ceramic techniques. When producing holes of small diameter, it is advantageous to use cores produced by techniques which use fine mesh calcia particles rather than the relatively course particles used by Whittemore, J r.
Metal castings made using calcia-based cores and the removal techniques of the present invention advantageously are made from nickel-chromium, cobalt-chromium or iron-chromium alloys which tend to resist overall corrosion. Many prior art core removal techniques employed with such corrosion-resistant alloys tend to cause localized intergranular corrosion especially if used for excessive periods of time. With the presently disclosed technique, no adverse intergranular corrosion has been noted It should be cautioned, however, that with some alloys, mixtures of ammonium chloride and ammonium nitrate in aqueous solution may give some difliculty in this regard.
As indicated hereinbefore, it is advantageous to remove calcia-based cores from small diameter, deep holes using aqueous ammonium chloride solution at its boiling point. The high temperature tends to reduce the solubility of ammonia and thus promote solution agitation and replacement of solution at the face of the core being removed. The invention, of course, is not limited to use of the solutions at or near their boiling points but for reasons of speed it is advantageous to do so. Likewise, while no particular concentrations of the ammonium salts in water are essential to the operability of the removal technique of the present invention, it is advantageous to employ at least about by Weight of the ammonium salt in water. As will be recognized by those skilled in the art, the aqueous core removal media used in the process of the present invention can advantageously contain additives such as wetting agents, foam depressants and the like. Also, the apparatus shown in the drawing can include a conventional stirring means. Further, it is advantageous to carry out the core removal under a hood or in an enclosed volume wherein the released ammonia can be recovered before any venting to the atmosphere.
While the present invention is applicable to the removal of cores of any size from any size holes in castings, it is particularly applicable to the removal of cores from holes having major cross-sectional dimensions of about 0.01 to about 0.3 inch and which are deep in comparison to their diameter. It is also to be observed that such fine holes can also be produced in wrought metallic structures particularly by extruding billets having holes drilled therein and filled with a filler or core. Such fine holes can be produced as disclosed in Peyches U.S. Pat. 2,628,417, Graham U.S. Pat. No. 2,914,841, Horne U.S. Pat. No. 2,970,368 and the Hignett et al. U.S. Pat. No. 2,972,805.
While the present invention has been described in conjunction with advantageous embodiments, those skilled in 4 the art will recognize that modificatiorg and variations may be resorted to without departing from the spirit and scope of the invention. Such modifications and variations are considered to be within the purview and scope of the invention.
1. A process for removing calcia-base cores from holes located in a casting comprising exposing said calcia-base cores to the action of an aqueous solution of a salt selected from the group consisting of ammonium chloride, ammonium bromide, ammonium nitrate, ammonium fluoride and ammonium acetate.
2. A process of claim 1 wherein the cores are located in metal alloy castings.
3. A process as in claim 1 wherein the aqueous solution is maintained at its boiling point.
4. A process as in claim 1 wherein the aqueous solution contains at least about 5% by weight of ammonium chloride.
5. A process as in claim 4 wherein the aqueous solution is maintained at its boiling point.
References Cited UNITED STATES PATENTS 2,502,337 3/1950 Moir 134-3 2,666,001 1/ 1954 Marshall.
2,876,122 3/1959 Whittemore 106-63 2,914,841 12/1959 Graham 29-1568 H 3,026,605 3/1962 Turner 29-156.8 H 3,039,178 6/1962 Kent et a1. 29-1568 H 3,045,328 7/1962 Turner et a1 29-1568 H 3,196,046 7/1965 Brite 134-22 R 3,576,065 4/1971 Frazier 29-1568 H BARRY S. RICHMAN, Primary Examiner U.S. Cl. X.R.
Patent No. Dated Sept. 26, 1972 Inventor) Stuart L. Weinland et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Column 1, line 5, Assignee: Martin Marietta Corporation should be added;
same column, line 27, after "Wax" insert model Column 2, line 49, delete "disclosed by Whittemore, Jr. in U. S. Pat. No.
and insert removable by the process of the present invention 1 I Signed and. sealed this 26th day of Februery 19714..
EDWARD M.FLETCHER JR C MARSHALL DANN' Attesting Office? Commissioner of Patents FORM PC4050 I uscoMM-Dc scan-Pea