Influence of magnesium silicate and mullite-siliceous fibers on the efficiency of heat-insulation inserts

Abstract

For a long time to come, casting of killed steel into ingots will continue to be the principal stage in the processing of liquid steel into rolled products.It has been established [i] that about 60% of all the heat of the upper part of the ingots is lost via the top of the metal, and 40% via the side walls.This determines the compositions of the materials and the manner of their use for eliminating heat losses by the head of the ingot, the reduction of the head edge, and the increase in the yield of suitable metal from liquid steel.The materials established in the lateral part of the top of the ingot must have minimal thermal conductivity.It is known [2] that among the available industrial media, minimal thermal conductivity is exhibited by air.For lateral heating of the head part of ingots it is most expedient to use heat insulators --disperse systems --with a highly porous structure, formed by fibrous refractory materials.The thermal conductivity of the gas phase (air) of the heat insulator under comparable temperature conditions is 30-100 times less than that of its solid phase [3]. The overall effective thermal conductivity in such insulators is made up of the thermal conductivity of the solid body, Iso , and the thermal conductivity of the pores, I, filled with = + I s~ por air [4]. In this connection Iso Icond rad [4], where Icond is the conductive thermal conductivity, depending on the structure of the solid body and varying with the type of grain contact [4], ^rad~S~ is the thermal conductivity due to the capacity of the solid body to transmit thermal radiation. so With a change in the temperature T, Ira d varies far more strongly than Icond:where ~ is an empirical coefficient, and T is the temperature in ~In the pores the thermal conductivity Ipo r is ensured by the thermal conductivity of the gas (in our case mainly air or a mixture of air and carbon dioxide, I T) and by convec~por tion Ico n and radiation ^rad from one wall of the pore to the other along the temperature gradient:Ipo r = I T +Icd n + ipor rad"The convection Ico n depends on the size of the pores and the degree of their closure [2]. The values of Ico n influence IDo r when the pore size is more than i0 mm and the temperature drop of the pore walls is 3~3~K [4]. Since such conditions are seldom attained, ~por Ico n can be disregarded [2-4] and then Ipor~rad.According to [4], IP~ ~AE2dT3' where E is the degree of blackness of the pore surface, A is an empirical coefficient, and d is the pore diameter.An analysis of the above equations and data on the thermal conductivity of good heatinsulation meterials [4] shows that above 1273~ heat transfer by radiation reaches 90% of the total heat transfer.At these temperatures good heat-insulation materials are comparable with ordinary lightweight artifacts as regards apparent density, open porosity, size and degree of closure of the pores, and other indices (within known ranges).From an analysis of the theoretical equations, we concluded that heating of the side walls of the feeder head of the ingo...