High-density kaolin refractories

Abstract

Experimental investigations and Industrial experience have shown that dense and high-density kaolin refractories produced from the pure grades of the kaolin starting material are efficient products for the lining of the stack of blast furnaces [1][2][3][4][5][6].In the USSR, the stacks of more than 40 blast furnaces including one of 5000 m 3 have been lined with dense kaolin brick of porosity below 12% [5,6]. The stacks of blast furnaces Nos. 4 and 5 of the Zaporozhstal' Plant are lined with dense kaolin refractories and their useful life is 10-11 years.A further increase in the density of the refractories by using a fine-grained composition for the semidry molding on toggle presses is difficult to achieve owing to the development of overpressure cracks even at relatively low specific molding pressures.An increase in the specific molding pressure is effective only at medium pressures. A further increase in the pressure does not result in a decrease In the porosity of the green product [7].An increase in the firing temperature does not always produce the desired effect either because the highfired coarse-grained part of the composition is compacted only slightly during sintering [8] and sometimes increases in volume by 5% [9] while the bonding part of the composition shrinks in volume by about 18%. Such a large difference in the volumetric changes of the grains and bond results in an increase in the number and size of the pores including the closed kind.In this article the results are described of development work on a new technology which permits the industrial production of refractories of a maximum porosity of 1@/o on toggle presses from relatively coarsegrained kaolin batches.The experiments were carried out with chamotte with a water absorption of 3% from Novoselitsy and Polozhsk kaolins. To begin with, an investigation was carried out of the changes in the properties of thetwo types of chamotte of fractions 1-5 mm after firing for 5 h at 1550~It was found that the apparent density of the Novoselitsy kaolin ShKN1 decreased during firing from 2.49 to 2.40 g/cm 3, while that of the Polozhsk chamotte ShKP increased from 2.44 to 2.52 g/cm 3, a finding which shows that the volumes of these chamottes change in opposite directions during firing, i.e., that of the Novoselitsy chamotte increases while that of the Polozhsk chamotte decreases. These volumetric changes of the chamottes are reflected In the physicotechnical properties of the finished products.In ideal presentation the model of a porous solid consists of eight spheres of diameter d confined in a cubic space and in direct contact with each other. The volume Vf of the free space in such a solid equals