US1878870A - Method of making alpha refractory cast article - Google Patents

Description

" Sept. 20,1932. s UNDER 1,878,879

METHOD OF MAKING A REFRACTORY CAST ARTICLE Filed April 9, 1927 Patented Sept. 20, 1932 UNITED STATES PATENT; OFFICE CYBIL S. LIND'ER, OF CREIGHTON, PENNSYLVANIA, ASSIGNOR 1'0 PITTSBURGH ILATE GLASS COMPANY, A CORPORATION OF PENNSYLVANIA.

METHOD OF MAKING A REFRACTORY CAST ARTICLE Application filed April 9, 1927. Serial No. 182,329.

The invention relates to refractory articles, such as tank blocks, and the like, and the method of making them. The material employed is referably what is known asmullite, 3Al 2SiO-5, but the invention is applicable to other refractories, such as chrome ore, or compositions which consist only in extent. Hereto ore, cast mullite blocks have beenmade by fusing adjusted mixtures of alumina and silica, or diaspore and silica, etc. in an electric furnace and then casting the material into molds and annealing the castings. This process is relatively expensive,\ due to the cost of fusing, and to the requirement of slow and precise annealing. The castings are also relatively fragile and there is a tendency toward the formation of pipes or holes in the upper portions of the blocks or castings. The present invention is designed to produce blocks having the same refractory and wearing qualities of the blocks as just described, but at a lower cost, somewhat stronger and free from blow holes or pipes.

Briefly stated, the process in its preferred form consists in pouring fused mullite into a mold filled, or nearly filled, with crushed or lump mullite, so that the fused mullite acts as a binder for the lump mullite, each lump or particle being surrounded by a matrix of the fused material. The castings as thus produced are duly annealed, preferably in a tunnel vkiln,.as later described, giving a product which is strong and solid and free from voids. To assist in securing a quick flow of the fused material into all the interst1ces between the solid particles, a vibrator .may be employed upon the mold, on the order of those used in compacting molding sand about patterns In sand mold work. It is also desirable to preheat the mold and the crushed mullite contents preliminary to the casting operation, as this promotes the free flow of the fused material around the solid particles and tends to improve the bond between the fused and solid material. One apparatus for carrying out the process is shown in the accompan ing drawing, wherein:

The gure is a perspective view of a preheating kiln and leer of the tunnel type, and an electric fusing and casting furnace.

The tunnel kiln, as shown, comprises a preheating section 1, a casting section 2, and an annealing section 3. A track 4 extends through the kiln, and on this track are mounted a series of cars or trucks 5 carrying molds 6. As shown, the molds are open at the top and in four parts, so that four blocks may be made on each car. Gas burners 7 are employed for heating the kiln and any desired means may be employed for slowly moving the cars through the kiln. An

opening 8 is provided in the casting section of the kiln, and through this opening, the casting occurs from an electric furnace 9, suitably mounted for tilting movement. The opening 8 is closed by a suitable cover after the charge in the furnace is exhausted. In operation, the molds 6 are filled with crushed mullite before entering the kiln. The size of the lumps depends on the size of the block to be produced, it being possible to use larger lumps in the larger blocks. In a nine inch block, the lumps preferably run some where near the size of a hickory nut, although the size may be varied, and material may be used in which the lumps are of varying sizes. The molds and their contents are preheated during their passage through section 1, after which the fused mullite is supplied from the furnace, and the molds carried slowly through the annealing and cooling section 3. The casting may also be annealed, if desired, in the molds by covering them with an insulator to retard cooling but the method as above described is preferred.

The method, as above described, involves a considerable degree of economy over the method heretofore used, in which the entire block is formed from the fused mullite. The blocks can be satisfactorily annealed in less than one half the time required by all fused blocks, and no great care need be exercised.

Anywhere from to 50 per cent of the block consists of the crushed mullite and this crushed mullite is, pound for pound, much less costly than the material which makes up the all fused block, since it can be made in quantity with little requirement for care or precision and without annealing. It is also possible to use natural ores, preferably calcined, as the crushed material, such as kyanite, sillimanite or andalusite, although not so desirable as the artificially fused and crushed mullite, which is denser and more resistant. The process also gives an outlet for worn out or cracked, or otherwise defective mul-lite blocks without putting them through the expensive electric fusing opera tion. Further advantages over the all fused mullite block lie in the fact that the new proces can be conducted with open top molds, which makes the casting operation more rapid and convenient, and in the fact that the blocks are freer from pipes and Voids. The term refractory is used in the sense commonly accepted in the ceramic industry; namely, as descriptive of a material suitable for use in furnaces, and having a softening point upwards of 3000 degrees F.

What I claim is:

The process of making a refractory cast mullite into lump form, partially filling a mold with the crushed mullite, heating the mold and its content, and then flowing fused mullite into the mold to fill the mold, so that the fused mullite surrounds the pieces of crushed mullite.

In testimony whereof, I have hereunto subscribed my name this first day of April,

CYRE S. LINDER.

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