US1893540A - Method of casting abrasive-faced articles - Google Patents

Description

Jan. 10, 1933. R s EDMONDSON METHOD OF CASTI terial, which will act as a holdin same, are distributed grains of hard wear- Patented Jan. 1 0, 1933 PATENT OFFICE MEIHOD OF CASTING ABRASIV E-FACED ARTICLES Application filed March 5, 1931, Serial No. 520,465, and in Great Britain January 26, 1931.

This invention relates to the manufacture of metal castings having protective or wearresistantsurfaces adapted to resist abrasion, such as stair treads, floor plates, ash chutes, paddle blades for mills, trench or gutter covers and the like, wherein bodies or grains of hard, wear-resistant material are embedded in a metal body or casting so as to be exposed on the surface thereof.

A well-known method of making such castings is set forth in the United States patent to Bowers No. 1,403,005; and, as there described, said method includes providing a reen sand mold and coating asurface of the mold, which is to give form to the protective surface of the casting, with a layer of finely divided or powdered material. On this mag bed for the resistant material which are to form the protective or wear-resistant face of the casting. These grains may be of emery, carborunduin, alundum. or other hard mineral substance which will not fuse at the temperature of the molten metal forming the casting.

The molten metal, generally cast iron, is poured into the mold. and the grains of wearresistant material, which are held from displacement by the bed of finely powdered material, are surrounded by and embedded in the metal of the casting and form thereon a wear-resistant surface.

The holding bed for the wear-resistant grains may be made of a material which will fuse with themolten metal and have no influence or effect upon the surface of the casting, but preferably an infusible mineral substance, as fire-clay, or a material which will be consumed or dissipated by the heat of the molten metal, as rye flour, is used. The sand of the mold is usually sprinkled with water and hence when the layer of fire-clay powder is dusted over the wet sand, it will tend to adhere thereto, and consequently the powdered material can be readily applied to vertical and irregularly shaped or overhanging mold surfaces.

When fire-clay is-employed, it is preferabl sprayed with water and thus forms a so is plastic setting thruout which the wear-resistant grains are strewn and anchored in place, the wetting of the fire-clay bed also tending to prevent shifting of the particles thereof with reference to each other and of the bed as a whole with relation to the mold.

This method of making metal castings having surfaces adapted to resist abrasion, while thoroughly practical, fails of perfection, however, in that, for example, during the pouring of the molten metal into the mold some of the grains of the Wear-resistant material will be shifted from their original positions in the holding bed and bring about an uneven distribution of the grains, thus causing unnecessary crowding of the grains in some places on the protective surface of the casting and insuificient supply of them in other places on said surfaces. Especially is this true of the grains which lie on top of other grains and form second and third layers of the grains. Also, there sometimes happens a shifting of particles of the holding bed With reference to the mold, resulting finally in an uneven distribution of the grains of hard wear-resistant material in the finished casting. This uneven distribution of the grains produces an inefficient casting.

The object of the invention, therefore, is to provide an improved method of making castings of the character described, in the exercise of which method no shifting of the wear-resistant grains will take place and likewise no shifting of the holding bed for the wear-resistant grains will occur with relation to the mold surface upon which such bed rests, nor any shifting of the particles of the bed with relation to each other.

To bring about the desired results, the holding bed and the wear-resistant grains are treated in such manner in accordance with the teachings of the invention, that the Wearresistant grains are secured firmly to the holding bed and the individual contacting grains to each other; and there is formed a thoroughly coherent holding bed, the powdered particles of which are now firmly united to each other, and the underlying particles of which are positively attached to the green sand of the mold.

In the accompanying drawing, which forms; part hereof, is illustrated a mold formed according to the invention.

Of the drawing:

Fig. l is a cross-section of a mold adapted for casting an article in accordance with the method of this invention;

Fig. 2 is a fragmentary view of the same, on an enlarged scale and showing the application of the water glass;

Fig. 3 is a similar view after the water glass has been applied; and

Fig. l is a sectional view of a part of the finished article, cast according to the method of the invention.

Referring to the drawing in detail, there is shown in Fig. l a mold l. comprising a drag 5 and cope 6 which. are formed to mold a wear-resistant article, as a stair tread 7. On a surface 8 of the green sand of the mold i: is laid the holding bed 9, preferably formed of fireclay. in which are strewn the wear-resistant grains 10.

Thefirst step in this treatment is taken preferably after the holding bed has been sprinkled with water and the wear-res1stant grains have been strewn thereover, and con- Eists in spraying the wcanresistant grains and their holding bed with a liquid 11 which has the adhesive or viscous attribute necessary to accomplish the union of the hold ng bed particles, sand mold, and the wear-resistant grains, is-described. and whichat the same time possesses the fluidity required to permit it to be ir zled or applied efficiently to the grains and their holding bed. The viscous liquid, like the material of the holding bed, must also be of such a nature that it Wlll have no influence or effect upon the surface of the casting and, therefore, it may comprise infusible matter or matter which will be fused with the molten metal poured into the mold without affecting the surface thereof or be consumed or dissipated thereby. The molten metal enters the mold through the gate 12 and flows over and about the grains 10 and thus forms the body 13 of the tread with its resistant surface 14, as shown in Fig. 4.

It will be apparent that a liquid, possessing the viscosity or adhesiveness necessary for the purpose set forth will not possess the required fluidity; and, therefore, the viscous liquid to be used should be one that can be readily diluted with some other liquid having the necessary fluidity; furthermore. the blended liquids shouldbe of such nature that the diluent can be removed from the resulting compound after the sprinkling process therewith has been completed. It is also important that these liquids should be comparatively inexpensive so as to be commercially possible.

Specifically, according to the invention, there is employed silicate of soda, commonly known as water glass, and which is prepared by melting together silicon dioxide and caustic soda and dissolving in water the resulting mass obtained from the fusion. The ordinary grades of water glass contain a ratio of silica to alkali of about 3 to 1; and, while such ordinary grades might be made use of, it is proposed to employ a special grade of water glass containing a higher ratio of silica to alkali, as will later be described. lVater glass, while itself economical, has the further advantage that it is miscible with water, a quality lacking from some other substances which might otherwise be used. YVater, furthermore, is the cheapest and most common diluent.

After the wear-resistant grains have been distributed on the holding bed, therefore, as heretofore noted, the bed and grains are sprayed with water glass which has been di-- luted with water to the extent necessary to permit such spraying. The diluted water glass will. penetrate between the particles of the holding bed and cause them to adhere to the face of the mold and to each other, and, more important still, will likewise cause the wear-resistant grains to adhere firmly to the holding bed. and, when contacting, to each other.

After the application of the water glass compound to the grains and their holding bed, the next step in the process is to remore the diluent or water content from the compound before the molten metal comes into direct contact therewith, as otherwise the water, under the influence of the heat, might cause blowing of the mold. -When ordinary grades of water glass are used, the water can only be removed from the compound by applying heat thereto, as by means of a blow torch, but this is not true of the special grade of water glass, as will presently be seen.

It may be noted at this point that when fire-clay, which is preferably used for the holding bed in the present process, is dried or baked by the application of heat thereto without the use in connection therewith of a suitable viscous binder, such as water glass, it will lose its holding power and will not retain the wear-resistant grains in place. By the use of water glass, however, in the man ner indicated, the heat of the torch can be applied and not only will the water he evaporated from the water glass compound, but the lire-clay and water glass will be baked or dried to form a composite mass in which the wear-resistant grains are firmly held, and which will be firmly secured to the face of the mold.

Referring now to the special grade of silicate of soda to which reference has been made and which constitutes a very important feature of the invention, it is one which contains silica to alkali in the ratio of at least 8.2 to 1 and may be produced in the ordinary way by increasing the proportion of silica to the caustic used, when melting the two together. Good results have been obtained with water glass containing silica to alkali in a ratio as high as 4.05 to 1. A ratio of 6 to 1 is even possible. In this connection, it may be stated that by silica is meant SiO and by alkali N a O as determined by chemical analyses.

One important advantage of using such a special grade of water glass arises from the fact that it is capable of quick air-drying and 'does not require the use of the blow torch or other application of heat, and furthermore, the viscous or adhesive nature of the cement is greater than in the case of water glass of the or inary grades. An even greater advantage is that the use of this special grade of water glass does not result in blowing of the molds when the molten metal is poured into them, as is sometimes the case when the ordinary grades of water glass are employed. Moreover, dueto the lower percentage of alkali in the special grade of water glass, it has less tendency to fuse the metal with the sand of the mold surface.

After removing the water or other diluent from the water glass compound in the manner above described, the molten metal is poured into the mold and the casting operation completed.

It may be added that water glass, whether of ordinary grades or of the special grade last described, Wlll be dissipated by the heat of the molten metal when the latter is poured into the mold so as not to interfere with the proper union of the metal with the wear-resistant grains during the casting operation.

A brief summary of the process may be helpful. After the mold has been prepared, the sand surface is moistened or sprinkled with water and the fire-clay in powdered form is then dusted onto the wet sand surface. The fire-clay is next s rinkled or sprayed with water to insure the ormation of a soft plastic holding bed for the grains of wear-resistant material which are then strewn upon it. the diluted water glass is now sprayed upon the holding bed and then dried to remove the water from the water glass compound. As before noted, in the case of the special grade of water glass, no application of heat is necessary, since it is capable of quick air-drying. As the final step in the rocess, molten metal is poured into the mol to form the casting.

The invention is not limited to the precise member or sequenceof steps or to the use of the particular materials described, as changes may be made therein without departing from the spirit of the invention or sacrificing any of its chief advantages. For example, a variation from the particular method hereinbefore described consists in sprinkling a layer of coarser grains of the hard wear-resistant materials over the first layer of grains With the grains in place,

already secured in the holding bed and then spraying again with the water glass after which the diluent is removed as heretofore described. These and other variations will readily suggest themselves to those skilled in the art now that the present process has been disclosed.

Having thus described our invention, what we claim is:

1. A method of forming a metal casting having a wear-resistant surface, which method comprises providing a mold, applying to a mold surface thereof, which is to give form to the wear-resistant surface of the casting, a layer composed of particles of holding material to form a holding bed for the wear-resistant material distributing grains of a wearresistant material over said bed, applying to said bed and grains a solution of silicate of soda, drying said solution, and introducing molten metal into the mold.

2. A method according to claim 1, characterized-by the fact that the silicate of soda solution contains a ratio of silica to alkali of at least 3.2 to 1.

3. A method according to claim 1, characterized by the fact that the silicate of soda solution contains a ratio of silica to alkali of 4.05 or above to 1.

4. A method according to claim 1, characterized by the fact that the silicate of soda solution therein referred to contains silica and alkali, the silica content predominating and in such proportion that the blowing of the mold will be prevented when the molten metal is poured into the same.

5. A method according to claim 1, characterized by the fact that the silicate of soda solution therein referred to contains silica to alkali, the silica content predpminating and in such proportion that the water may be evaporated from the solution without the ap-

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