US1951911A - Mold for castings of iron and nonferrous metals - Google Patents

Description

UNITED STATES PATENT OFFICE MOLIl FOR CASTINGS OF 'IRON AND NONFERROUS METALS Max Heusser, Winterthur, Switzerland No Drawing. .Application December 11, 1931, Serial No. 580,506. In Switzerland December 13, 1930 6 Claims. (01. 22188) It is known that the size of grain in the strucmaking molds can now. not only fill out by steps ture of a casting depends to a large degree on the interval at present existing between the therthe rate of cooling and therefore on the thermal mal conductivity of the usual material and the conductivity of the mold. When the heat is led thermal conductivity of iron, but it can also beaway slowly from the mold, and the casting is come greater than the thermal conductivity of therefore cooled slowly, the structure of the castiron.

ing is open grained, whilst when cooling or heat According to the invention, graphite is preftransmission through the material of the mold is erably used as the material, or as a constituent of more rapid, a fine-grained structure is obtained. the mixed materials, for making the molds. The

10 It is not yet known to make any use .of this coefficient of heat transmission of graphite in fact, since the known methods of improving the the solid state is 0.105 cal./cm/second/degree C. quality of castings by adopting molds made of when unheated, and 0.28 at atemperature of 555 metal, through which the thermal conductivity at C. (according to Landolt-Bornstein, Physikalischcertain parts shall be changed as compared with chemische Tabellen, 5th edition and supplemene 15 that at other parts, have the disadvantage that tary volume, 1927). in consequence of the sudden variation of the If the coefficient of heat transmission of the thermal conductivity of the material used, great usual foundry sand is taken as 1, the coefficient difierences occur in the quantities of heat transof heat transmission for cast iron is then about mitted from the casting. This leads to an all too 250, and of the new molding substance using solid 0 rapid chilling and consequently an undesirable graphite, about 180 when unheated and about 470 hardness of the material, so that not only is anat a temperature of 555 C. nealing required in order to make the structure Whilst the conductivity of the cast iron used for more uniform, but difliculties for machining are molds is 250 times greater than that of the usual also created. The known method of coating the foundry sand, and consequently also, when both 2 surface of the mold with graphite cannot reduce substances areused simultaneously beside each 89 this injurious efiect, since it solely prevents the other, the transmission of heat at a certain spot mold burning and has .no influence worth'menis 250 times greater than that at a neighboring tioning on the thermal conductivity of the matespot, 1. e. it suddenly changes; but on the other rial of the mold. hand the conductivity of the new materialfor 30 The purpose of this invention is to control the making molds changes gradually or by steps until rate of cooling of the casting and thereby the it is 470 times greater than the conductivity of formation of the structure by grading the coeifithe usual foundry sand, the figure depending on cient of heat transmission or the conductivity whether, it is unmixed, in the form of powder, in of the material used for the mold, in such a way solid form or at a high temperature; consequently 35 as to improve the quality of the casting. The inthe thermal conductivity can be changed as re- 90 vention consists in mixing into the substance quired within the limits met with in practice. used for the mold, a material the thermal con- By altering the proportions of the materials ductivity of which in the unheated state is lower used for making molds, the coefficient of heat than that of iron but greater than that of sand, transmission can be gradually, and not only sud- 40 and which is also highly refractory. Preferably denly, changed, thereby increasing the qualities the material, used by iself or as an admixture to of the casting, without any drawbacks for the maothers, will have in the unheated state a thermal chining or for any other later process having to" conductivity lower than that of iron, but increasbe put up with. ing with increasing temperatures until it is above I claim:

45 that of iron. A suitable material to use for regu- 1. A mold for casting metals comprising moldlating the thermal conductivity or heat transmising sand and a material, which in an unheated sion of the substance used for the mold is graphite. state, has a coefficient of thermal conductivity The invention is based on adopting for the mold lower than that of iron and greater than that of a material which, as compared with materials the molding sand, said material being non-uni- 50 hitherto used for this purpose, possesses a very formly distributed throughout the molding sand variable thermal conductivity. The coeflicient of and being present in greater proportion at those heat transmitted M for a certain cast iron is for places where heat is to be removed more rapidly. example 0.,15 cal/sq. cm./second/degree C., the 2. A mold for casting metals comprising moldcoefficient x2 for a typical foundry sand is 0.0006. ing sand and a material which, in an unheated 55 The thermal conductivity of the new substance for state, has a coefficient of thermal conductivity lower than that of iron and greater than that of the molding sand, andwhich, when heated to casting temperatures, has a coeflicient of thermal conductivity greater than that ofiron, said material being non-uniformly distributed throughout the molding sand and being present in greater proportion at those places where heat is to be removed more rapidly.

3. A mold for casting metals comprising molding sand, and graphite non-uniformly distributed throughout the molding sand and being present in greater proportion at those places where heat is to be removed more rapidly.

4. A mold for casting metals comprising molding sand and a material which, in an unheated state, has a coefiicient of thermal conductivity lower than that of iron and greater than that of molding sand, said material being non-uniformly distributed throughout the molding sand, the

molding sand being free from inclusion of said material at places where the cast object has the least wall thickness, and the material being present in progressively increasing amounts to places where the cast object has the greatest wall thickness, so that the conductivity and the cooling rate at difi'erent places of the cast object are in accordance with the heat to be removed at those places for the purpose of improving the structure of the casting. 1

5. A molding for east metals comprising molding sand and a materialwhich, in an unheated state, has a coeflicient of thermal conductivity lower than that of iron and greater than that of molding sand, and which, when heated to casting temperatures, has a coefficient of thermal conductivity greater than that of iron, said material being non-uniformly distributed throughout the molding sand, the molding sand being free from inclusion of said material at places where the cast object has the least wall thickness, and the material being present in progressively increasing amounts to places where the cast object has the greatest wall thickness, so that the conductivity and the cooling rate at difierent places of the cast object are in accordance with the heat to be removed at those places for the purpose of improving the structure of the casting.

6. A molding for casting metals comprising molding sand, and graphite non-uniformly distributed throughout the molding sand, the molding sand being free from inclusion of the graphite at places where the cast object has the least wall thickness, and the graphite being present in pro- 1 gressively increasing amounts to places where the cast object has the greatest wall thickness, so that the conductivity and the cooling rate at different places of the cast object are in accordance with the heat to be removed at those places for the purpose of improving the structure of the casting.

MAX HEUSSER.