The invention concerns a method and apparatus for rapidly solidifying and cooling molten metal oxides and metal oxide-base compositions by continuous casting.
In many industrial processes an attempt is made to obtain rapid solidification and cooling of melted products based on metal oxides, for reasons either of safety or of convenience: for example, when exhausted drosses or slags from electro-metallurgical operations have to be taken rapidly to the tip without the risk of transporting them in the liquid or partially solidified state, or for structural reasons, when rapid cooling is necessary to give the product certain physical properties. For example, abrasives based on corundum and on corundum and zirconia are known to have mechanical properties which improve commensurately with the rapidity with which the molten product, manufactured by fusion in an electric furnace, is cooled. This fact has been pointed out particularly in French Pat. No. 1 332 975 in the name of CARBORUNDUM Company, which recommends casting in a graphite mold, in French Pat. No. 2 127 231 in the name of PECHINEY directed to casting the melted product onto steel balls, in French Pat. No. 2 133 595 in the name of TREIBACHER CHEMISCHE WERKE AG directed to casting onto iron spheres, and in French Pat. No. 2 166 082 in the name of NORTON directed to casting between solid metal plates 1.6 to 12.7 mm apart.
For obvious reasons it would be desirable for the rapid cooling to take place continuously. In the case of drosses and slags, as a matter of fact, cooling in ingot molds, which is the usual practice, is very slow and necessitates a large number of molds, which take up space in the workshop. In the case of abrasives with fine crystallization, casting between closely spaced metal plates or onto steel balls leads to very low productivity.
A certain number of processes for cooling rapidly by continuous casting have previously been described.
French Pat. No. 1 319 102 to NORTON describes the casting of electro-melted alumina, in a thin layer, onto a hollow cylinder which is cooled by sprinkling water onto its internal surface.
U.S. Pat. No. 3,993,119, and French Pat. No. 2 290 266 to NORTON, describe an arrangement for casting between stationary, thick metal plates, through their base onto an endless conveyor. The conveyor passes over rollers which causes the plates to move apart and the blocks of cooled abrasive to be separated and drop into a receiving means.
French Pat. No. 2 422 462 to NORTON describes another arrangement for continuous casting between cooled metal belts which are kept in contact with the solidifying abrasive by a series of guiding rollers.
These various pieces of apparatus are mechanically complex and ill adapted to cheap, continuous mass production of electro-melted abrasives with fine crystallization.