US 3407864 A
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3,407,864 Patented Oct. 29, 1968 ice United States Patent 3 407 864 by enabling the gas to escape into the sintered salt core. Furthermore the r u tr tru tur lfects a essen- FORMING HOLLOW CAST ARTICLES 0 S Sm e S c e e 11 Kurt Anderko, Heflbrmm (Neckar), Rudolf Heme, tial decrease of time necessary for removing the core Neckarsulm, Wurttemberg, and Manfred Stark, from the castlng- ()dh im, Ge assignors t K -l S h idt 5 More particularly, sodium or potassium chloride mixed G.m.b.H., Neckarsulm, Wurttemberg, Germany, a with up to about of a sintering aid (the above re- P f Germany ferred to second constituent) is placed in an appropriately Flled J e 1966! 554,331 shaped mold and pressed into the shape of the mold for Claims priority,applgaltiog ygigamany,June 12,1965, about 1.5 to 2.5 minutes. The molded shape is then 4 Claimcs 1O dried, e.g. for about an hour at 200 C., and then sintered, e.g. for about /2 to 1 hour at about 700 C. The sintered This invention relates to the production of hollow core shap s are then cooled to about pffifel'ably castings. It more particularly refers to improvements in Without removing them from the sintering heating means. the production of cast metal articles having void spaces The thus produced sintered cores are available for use therein 15 in preparing hollow castings by suitably placing them in It is known to produce cast articles having voids therein the casting die and casting an appropriate material about by forming soluble cores and casting the desired article hem- It may in some cases be desirable to smooth out about the core or cores. After the article has been cast, the surfaces and particularly the edges of the sintered core. the cores are dissolved out thereby leaving the desirable This may be accomplished by sanding or grinding as the voids in the casting. One particularly desirable applica- 04186 y tion of this practice is in the manufacture of cylinder It has been found to be desirable in making use of the blocks for internal combustion engines. Channels for thus prepared sintered cores, to preheat them prior to cooling Water are suitably cast into the block by the insertion in the casting mold. Alternatively, it may be referred to technique of fugitive cores. practical to transfer the cores hot from the sintering step It has been the practice in the past to utilize water soluescribed directly to the casting mold. It has been found ble ma erials as the fugitive cores since they can be advisable to provide the sintered core at a temperature of dissolved and washed out most easily and economically. b ut 5-0 to 300 C. Where such core is to be used in Exemplary of the water soluble core materials which the production of hollow metal castings. Where the casthave been used are metal halide salts particularly sodium ings are to be made of materials having a lower melting and potassium chloride. These materials are quite inex- 3 Point, it y be desirable to Provide the sintered Cores at pensive as Well as easy to Work with and readily somewhat lower temperatures. recoverable. One specific example of a core made according to this It has been found that simple moldings and castings invention contained 95 weight percent: sodium chloride, produced in the prior art manner are excellent. However, 3 Weight percent borax, 1 weight percent magnesium oxide it has been found that in producing intricately shaped and 1 weight percent talc. Amixture of these materials in articles such as those containing sudden changes in crosshe r cit d proportions was made into a sintered core and section, the stresses on the core materials, both mechanillsfid to Produce a hollow cast metal PieCe. After the cal stresses and those induced by heating, are greatly casting had been cooled, the core was removed by simple increased. The soluble core materials of the prior art dissolution in Water. have been found to be somewhat lacking in these situa- The time required for the removal of the sintered salt tions. core was only /10 of that necessary for the removal of It is therefore an object of this invention to provide the salt cores of the known art. an improved core material for use in producing castings What is claimed is: containing voids. 1. In the method of forming a solid casting having at It is another object of thi invention t id an i nleast one predetermined void space therein which comproved process for the production of hollow cast articles. prises casting molten metal around at least one soluble Other and additional objects of this invention will be- Salt Core and then dissolving the Core material; the come apparent from a consideration of this entire specifi- P Ovetnent which comprises Providing as Said Core mate cation including the claims appended hereto, rial sintered salt comprising at least one soluble metal In accord with and f lfillin th j hi i halide salt and up to about 10 weight percent at least one tion includes the production of a hollow cast article by material Selected from the g p Consisting of bOIaX, casting such article about a fugitive core comprising at magnesium Oxide, and talcleast one soluble metal halide salt and up to about 10% The improved Process Claimed in Claim 1 wherein by weight of at least one second constituent selected from Said metal halide i8 Sodium Chloridethe group consisting of borax, magnesium oxide and talc. The improved Precess claimed in claim 1 wherein It is preferred to use water soluble cores. It is preferred, Said metal halide is Potassium Chlorideprincipally for economic reasons, to use sodium or potas- The improved Process Claimed in Claim 1 wherein i hl id as h metal h lid l said core contains borax, magnesium oxide, and talc.
Cores for use in this invention are suitably prepared by molding an appropriate mixture of metal halide and the References Cited second constituent into the shape of the void desired in UNITED STATES PATENTS the final casting. The shaped core is then dried and heated 1 523 5 9 25 Gibbons 0 3 9 to a sintering temperature by which treatment the core 554 97 9 1925 Alden 254-317 shape becomes dimensionally stable and strong enough 1,603,262 10/1926 Ald 106 .38,9 to withstand greater thermal and mechanical stresses than 2,420,851 5/ 1947 Zahn et a1. 164---35 was possible with prior art cores. 2,736,077 2/ 1956 Bartlett l64-36 The sintered salt cores according to the invention have 3,131,999 5/1964 Suzuki et a1. 164-16 also further advantageous properties. Owing to their 3,218,684 11/1965 Spink 164--79 porous sinter structure they are able e.g. to eliminate the V detrimental effect of the gas formation inevitably occur- SPENCER OVERHQLSEK p'lmary Emwnerring during the solidification of technical aluminum melts E, MAR, Assistant Examiner.