Abstract: A novel method of making a refractory material is disclosed comprising the steps of providing an electrical arc metal furnace, charging that furnace with a charge of refractory oxide, and selecting voltage, amperage and electrode spacings to create novel "hum and scum" melt conditions. This hum and scum condition is maintained until said charge is substantially melted. The described technique is particularly useful for melting magnesia chrome materials to produce fusion cast refractory products which are highly reduced and quite dense. The elaboration of this product requires higher energy input per pound concurrent with an increased consumption of reducing materials compared with standard preparation conditions. The resulting product exhibits higher oxidation weight gains, higher densities, lower porosities, high cold crush strengths, more thermal shock resistance, and better corrosion-erosion resistance than similar magnesia chrome refractory products fused using prior "arc and bark" processes.

Abstract: In an extrusion die, restricted flow of material from large to small feed holes is relieved by the formation of a transition zone within the die. The transition zone is formed by extending either or both of the large and small feed holes so that they axially overlap.

Abstract: Thermally collapsible core of three to five solid carbonaceous segments of generally equal volume and of wedge-like shape arranged around a collapse axis of the core in narrowly spaced apart relation to each other. Core includes spacers occupying a minor portion of the narrow spacing nearest the external periphery of the core and which are made of metal, glass, ceramic or mixtures thereof having a melting point below the highest temperature to which the core is subjected by molten material solidifying therearound, e.g. fusion-cast refractory. The segments are the larger parts of the core. Heat transferred from solidified molten material to core causes spacers to melt and allow segments to collapse inwardly toward collapse axis to accommodate cooling shrinkage of casting without cracking. Melted spacers can drain downwardly out of core. Design yields highly quenched microstructure in fusion-cast refractory, which is especially beneficial in tap hole blocks for steelmaking furnaces and vessels.

Abstract: Basic fused cast refractory with principal crystal phases of periclase and magnesium-spinel is made by adding nonfused oxidic inorganic grog particles to molten mass of the refractory as it is cast into a mold cavity, thereby resulting in increased modulus of rupture at temperature in the range of about 1340.degree.-1500.degree. C. and avoidance of shell formation. Molten mass has a composition consisting essentially (by weight) of 45-78% MgO, 0-30% Cr.sub.2 O.sub.3, 0-35% Al.sub.2 O.sub.3, 0-17% FeO + Fe.sub.2 O.sub.3, at least 82% MgO + Cr.sub.2 O.sub.3 + Al.sub.2 O.sub.3 + FeO + Fe.sub.2 O.sub.3, 1-8% SiO.sub.2, 0-2% CaO + BaO + SrO.sub.2, 0-10% TiO.sub.2 and 0-3% fluorine. Nonfused particles have a loss on ignition at 1000.degree. C. of less than about 0.5% by weight and an aggregate SiO.sub.2 content at least about equal to the SiO.sub.2 content of the molten mass forming the cast refractory. Grog particles are of a size (e.g., within the range of particles passing about 25 mm.