US1770684A - Mold and facing therefor - Google Patents

Description

Patented July 15, 1930 UNITED" STATES CLYDE C. DE ml, BOUGHT-ON, MICHIGAN MOLD m racme 'rnnnnron Ho Drawing.

This invention relates to molds such as are employed in the casting of metals, the principal object bein the provision of a mold with a facing designed to effect a more perfeet casting than is possible in the conventional constructions, together with a facmg for molds.

In conventional sand molding pract1ce, it is a common occurrence for the sand employed for making-the mold to. stlck to the surface of the casting, thereby makmg 1t rough, and entailing a cleaning operation that is both diflicult and relatively costly in many cases. Furthermore, in view of the roughened condition in which the surface of the casting is left, the surface must often be subjected to a smoothing operation, that 1s also expensive, in order to make the casting suitable for use.

It is the primary purpose of the present invention to provide means in connection with such molds whereby the sand will be prevented from adhering to the surface of the casting when poured therein, and which will result in a casting having a smooth and unblemished surface.

The facing which I employ for this purpose is composed of relatively finely divided slag, such as is obtained from blast or other furnaces in the fused condition. This slag is first crushed or powedered, and where necessary, suitably graded as to size. That portion thereof of the desired size may then be applied to the face of the mold in which the castingis to be made in any desired manner, so as to form a coating for the same. In some cases this material may be dusted on to the mold surface, or may be mixed into a paste or fluid-like form with or without a binder, and painted or daubed on the surface of the mold in a thin coat. This coating is, of course, allowed to dry before the metal is cast in the mold. .While any suitable binding agent may be used for such purpose, it is preferable to employ one that will not generate a gas upon heating by the molten metal, in order that no defects in the casting will arise due to the presence of such gas. A binder which I prefer to employ is finely divided hydrated iron oxide such as hematite Application at; April s,"1929."sria1 no. 353,892.

or limonite, suitably mixed with the crushed slag, and to which water has been added until the whole is formed into a mass of gruellike consistency which is readily painted or daubed on the surface of the mold. The

thickness of the coating of this facing material will ordinarily vary in accordance with the thickness of the casting itself; that is, a relatively thin castin will require a relatively thin coating of this material on the mold, and a heavier casting will require a heavier coating on the mold. On the heavier castings the mold may be treated with two or more coats of this material where found necessary for optimum results.

A number of different fusible slags may be employed for the purpose of making this coating. Synthetic slags of very low fusing points are ordinarily not as satisfactory as slags having a higher fusing point, particularly where the casting is of a ferrous nature. Such slags melt too easily and are liable to run into the intersticesof the main molding material so as to leave a bare sand surface to be presented to the hot metal. In general, a slag having a fusing point of from 800 degrees centigrade to 1000 degrees centigrade will give the best results with iron and steel castings. Whatever the fusing point or the composition of the slag material, it is preferable that the fused slag shall not react with the iron or steel or other metal, and that in the semi-molten condition of the metal the fused slag will wet the hot metal surface and cling thereto until the forces set up by the inequalities in rates of cooling and thermal contraction of the metal casting and of the fusible slag mold facing cause the slag to crack off the casting when it has solidified on the surface of the cooling casting.

A fused slag composed of silicates of calcium and iron, such as is formed in the ordinary open hearth furnace,has been found to work very Well when used as a mold facing for iron and steel castings. Those slags which form dark semitranslucent masses of glasslike material when cooled, work satisfactorily when powdered and used as mold facing in the manner described heretofore.

It will, of course, be apparent that in order to wet the'surface of the castin durin pouring, the facing must melt an there ore, in

urin metals having a relatively low melting point the facing used should be capable of melting at that temperature.

The action of this mold facing is as fol- Iowa: The material forming a coating for the mold surfaces melts upon the introduction of the molten metal into the mold,-and wettin the surface of the molten metal, acts to maintain the metal out of contact with the sand, and further, forms a smooth surface against which the molten metal bears. Consequently, as the metal is kept out of contact with the sand, there is no possibility of sand inclusions in the surface of the casting, and a smooth surface is imparted to such casting. Due to the different coefficients of expansion of the facing material and the casting when the casting cools and solidifies, the facing material also cools and solidifies, and during such cooling the different rates of contraction causes the facing material, which has now fused together, to pull itself off of the surface of the casting so that when the casting is shaken out of the mold, the surfacing material is removed with the molding material, thus leaving a casting with a smooth surface, and substantially ellminating any cleaning operation whatsoever.

While I have herein specified the material from which the mold itself is made as being sand, it is of course apparent that this facing ma equally well be employed in connection wit molds formed from materials other than sand, and even in molds of the so-called permanent type, and it is to be understood in interpreting the appended claims that the term sand, where used, includes any material which may be employed in its stead.

Formal changes may be made in the specific embodiment of the invention described without de arting from the spirit or substance of the broad invention, the scope of which is commensurate with the appended claims.

What I claim is:

1. A facing for molds comprising a mix ture of slag and iron oxide.

binder agent comprising finely divided iron ore.

7. The method of forming a metallic casting com rising, in combination first forming a mo d, applying to the mold depressions a coatin of a mixture of fused metallic silicate an iron ore, and then filling said depressions with molten metal.

8. The method of forming a metallic casting comprising, in combination, forming a mold for said casting, coating the surface of the mold de ressions with a mixture of a fused slag an iron ore having a fusing point lower than the melt-ing point of the metal to be poured, and then pouring the molten metal into said mold.

CLYDE C. DE WITT.

2. A facing for molds comprising a mixture of sla and hydrated iron oxide.

3. A facing for molds comprising a mixture of finely divided furnace slag and iron ore havin a fusing point above 600 degrees centrigra e.

4. A facing for molds comprising a mixture of crushed fused slag containing as principal ingredients silicates of calcium and iron, and iron ore.

5. A mold in which the molding depressions are coated with a layer of a mixture of furnace slag and iron ore.

6. A mo d in which the molding de ressions are provided with a coatin of ely divided slag maintained in posltion by a y