US 2755192 A
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United States Patent Oflice Patented July 17, 1956 MOLD COAT Donald G. Mahoney, Muncie, Ind., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware N Drawing. Application December 3, 1952, Serial No. 323,939
1 Claim. (Cl. 106-3823) This invention relates to coating materials and is particularly concerned with coating materials for permanent molds and the like.
It is, therefore, the object of the present invention to provide an improved coating material for use in the coating of permanent molds in which metal castings are to be made. More specifically, the mold coating material is used in connection with permanent molds for the casting of lead and lead alloys.
Another object of the invention is to provide a mold coating for a permanent mold which comprises a mixture of cork dust, clay and sodium silicate together with suitable binders and sufficient water to make the coat flowable so that the mold may'be coated as by spraying or brushing.
Further objects and advantages of the present invention will be apparent from the following description, wherein preferred forms of'the invention are clearly disclosed.
In the manufacture of castings wherein permanent molds are utilized, mold coats are frequently employed to protect the mold surface to prevent sticking of the casting upon solidification thereof and to improve the quality of the casting.
In the casting of lead and lead alloys, for example, in the casting of storage battery grids and similar articles, the grids are cast in permanent molds which must be properly protected on the molding surface thereof by a suitable mold coat which prevents adherence of the lead after solidification and which protects the surface of the mold to some extent against erosive action and the like.
It has been found that a mold coating which is of a more or less insulating character, that is, one which has a low coefiicient of heat conductivity, also is beneficial from the casting standpoint since the coating material interposed between the molten metal and the mold slows down the cooling action of the molten metal and causes the cooling to be more uniform whereby less brittle and more uniform castings are obtained.
One other characteristic in connection with mold coats is the resistance thereof toward wearing off. It is apparent that in production applications, a mold coat which must be replenished upon each operation of the mold, would not only be costly but would retard production efforts. Therefore, it is desirable to provide a mold coat which is easy to apply as by spraying or brushing and wherein one application of the mold coat is useful over a long period of time, for example, throughout a days The mold coat to be described hereinafter meets all the requirements set forth herein. It is a coating material which has a low coefficient of heat conductivity, thereby enhancing the quality of castings made in the mold coated therewith. It is easy to apply due to its fluid nature and the finely dispersed condition of the solid ingredients. It is high in its tenacity to the mold surfaces whereby the coat is a long lasting covering and it is inexpensive to manufacture and relatively easy to maintain in satisfactory condition prior to the use thereof.
Specifically, the mold coat comprises cork in a finely ground condition together with bentonite clay, a casein glue, sodium silicate and sufficient water to produce the desired fluidity. These ingredients are properly mixed so that the solid portions thereof are in a more or less dispersed condition within the fluid ingredients, which dispersion is maintained through the use of the glue and is then stored under controlled temperature conditions. The mold coat stored under such conditions will remain in good condition for along period of time and need only be thoroughly mixed and agitated prior to use. Specifically, the mold coat has the following formula in its preferred form:
Cork dust 8 lbs., 2 oz. Casco glue (casein glue) 1 1b., 14 oz. Bentonite clay 3 lbs., 6 02. Sodium silicate 3% qts. Water 21 gallons.
In the above formula, the bentonite clay should be of such a size that will pass through a 200 mesh sieve and 96% through a 325 mesh sieve. The cork dust must be equally fine or finer. The sodium silicate used is a 40 Baum solution. All of the ingredients may be varied +10% without markedly affecting the utility of the mold coat, although the specific proportions suggested are preferred.
In the compounding of the mold coat, the dry ingredients, namely, the cork dust, glue and clay are tumbled together for about one hour. The sodium silicate is added to the water, is mixed and heated to about F. The dry mixed ingredients are then included in the wet mixed ingredients and are agitated for mixing purposes for about one-half hour whereby dispersion is complete.
The fully compounded mold coat is then stored under controlled temperature conditions for example between 45 F. and 60 F. When used, this coat in thoroughly agitated condition may be sprayed through a conventional spray gun onto the surface of a mold or it may be brushed on or otherwise suitably applied, although the spraying is the most facile method since a completely uniform dispersion of the materials is thereby applied all over the mold surface.
While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted.
What is claimed is as follows:
A mold coat for use in the coating of permanent mold surfaces, consisting essentially of the following proportions of ingredients: cork dust about 8 lbs., 2 oz.; casein glue about 1 1b., 14 oz.; finely divided bentonite clay about 3 lbs., 6 oz.; sodium silicate (40 Baum) about 3 qts.; water suflicient to make the desired fluidity.
References Cited in the file of this patent UNITED STATES PATENTS 1,720,356 Willard July 9, 1929 1,856,526 Winchester May 3, 1932 1,909,819 Emanuel May 16, 1933 2,270,770 Ray Ian, 20, 1942