Mullite corundum articles for electric furnace roofs

Abstract

The development of electrometallurgical processes, the construction and introduction into service of large tonnage arc electric furnaces, the hardening of service conditions for the refractories in these units, especially with the introduction of furnaces of superhigh capacity, require use to be made of high-grade refractory materials. Besides the increased resistance of the walls, one of the most urgent problems is to get an increase in the life of the roof linings in electric furnaces.Foreign practice and Soviet experience show that in the linings of the roofs of steelsmelting furnaces it is possible successfully to use high-alumina refractories with a mass percentage of 75-85% A1203. The essential property of such articles in addition to spalling resistance should be the high deformation resistance during high service temperatures [1][2][3].The essential condition in making such products is the use of high-purity raw materials. The traditional methods of making mullite and mullite-corundum articles in our country are usually based on using mixtures of natural aluminosilicate raw materials (clays, kaolins, bauxites) with alumina.Abroad, as a rule, high alumina refractories are made on the basis of high purity bauxites, for example, Guyana, containing 60% A1203, 1.4% Fe203, 2.8% Ti02, 4-6% Si02, 31% Amcalc [4].The impurity oxides contained in the natural raw materials contribute to the formation of glass phase which, in the refractory, has a continuous distribution nature, and in most cases fills the role of bond (intercrystalline layer) betweenthe aggregates of grains of corundum and mullite [5, 6]. The presence of such a bond reduces the refractoriness, and the resistance to deformation at elevated temperatures, and limits the possibility of high-temperature use of the refractories, despite their adequately high concentration of A1203.The production technology for articles based on aluminosilicate raw materials or mixtures with alumina is complicated by the need to carry out double firing (pellets and articles) and double milling (alumina and chamotte).The East Institute of Refractories has developed a method for producing synthetic mullite--corundum articles intended, among others, for lining the roofs of electric steel-smelting furnaces. The technological developments for roof refractories involved the use of the results of previous work [7][8][9][10][11]. The production of such goods is based on the use of granular electrofused corundum and a combination of polydispersed mixtures of alumina (corundum) and silica (coarse crystalline quartzite). The granular electrocorundum acts as an inert filler, and the dispersed corundum and the coarsely crystalline quartzite are synthesized into mullite.The firing cycle of the products, isothermal soaking in the region of the chemical reaction of mullite formation, and polymorphic inversions of the silica, accelerating the solid phase mullitization, enabled us to obtain up to 35-45% mullite phase in the products. The starting components during sintering of the articles a...

A test of synthetic mullite-corundum parts in the roof of an arc furnace

“…In addi~ tion to high temperatures (up to 1800~ and higher) and thermal shocks, the roof refractories experience local thermal stresses and mechanical loads and are also subject to the action of melting dust having variations in chemical and mineral compositions [I, 2].Investigations conducted earlier showed that the use of mullite-corundum refractories in electric furnace roofs [3,4] is most effective with the use of them in combination with PKhS periclase-chromite parts (COST 10888-76) using specially developed methods of lining [5,6].This article presents the results of investigations of two lots of synthetic mullitecorundum refractories produced by direct synthesis with a single firing in the Experimental Plant of Eastern Refractory Institute [7] after service in the lO0-ton arc steel melting furnaces (DSP-I00) of Chelyabinsk Metallurgical Combine. In the first lot of parts the weight % of AI203 varied from 58 to 72%.…”