Manufacture of improved fused cast refractory

The process of manufacturing basic fused cast refractory having principal crystal phases of periclase and magnesium-spinel and analytically consisting essentially of (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, 0-10% TiO.sub.2 and 0-3% fluorine,

• which comprises forming a molten mass of the refractory, pouring a stream of the molten mass into a mold cavity and thereby filling the cavity with the molten mass cast there-into, adding particles of grog to the molten mass before, during and/or after pouring of it into the mold cavity, and at least partially solidifying the cast molten mass in the mold cavity to a state of self-sustaining cast shape substantially complementary to the interior surface configuration of the mold cavity,
• wherein the improvement comprises substantially increasing the modulus of rupture at least within the temperature range of about 1340.degree. to 1500.degree. C. and inhibiting formation of shell in the refractory by providing at least half of the added grog as particles of nonfused oxidic inorganic material having 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, the aggregate added grog particles being of a size and in an amount to about 70% by weight of the cast refractory sufficient to effect at least partial melting of and penetration into the particles by and resolidification with the cast molten mass so as to form a continuous coherent crystal structure throughout the solidified cast mass wherein discrete grog particles and remnants thereof are not optically identifiable, and at least that portion (if any) of the grog in excess of about 35% by weight of the cast refractory being SiO.sub.2.