Relationship of the properties of a quartz compound for lining hot tops to the addition of amorphous silica

Abstract

666.762.2:[621o746.393~66o043.! At present many steel plants of the country have developed and introduced the method of top pouring of killed electric furnace steel into big-end-down molds. In this case thermally insulated plates are placed in the upper portion of the mold [i]. The hot top lining has important value for decreasing the pipe in the metal and improving surface quality of the top, portion of ingot. In teeming of killed steel into molds with sinkheads of a molten self-hardening mixture the top cut-back of the ingot is reduced by i0-II% [2].However, to increase the effectiveness of the hot top it is necessary to improve its thermal insulation~ using for this purpose refractory materials with a reduced thermal conductivity. At the same time the mechanical properties of the thermal-insulation parts must remain high in order to resist possible mechanical loads.In the Electric Melt Shop of the Donetsk Metallurgical Plant the hot tops are lined by casting of a quartz compound of the following composition (wt.%): ground quartzite 95-97; ferrochrome slag (GOST 4757-79) 3-5; water glass with a density of 1.15 g/cm s 20 (over 100%)o Sticking of the hot top lining to the top portion of the ingot causes partial failure of the lining and after five or six pourings complete failure.To improve the quality characteristics of the hot top quartz lining an investigation was made of the influence of addition to the compound of amorphous silica in the form of dust. Amorphous silica is a waste product in the production of crystalline silicon at Zaporozhe Aluminum Plant. The chemical composition of amorphous silica is 89.88% SiO~, 0.04% Fe~Os, 0.83% AltOs, 3.15% CaO, 0.5% MgO, and 5.6% C. The choice of this addition was the result of its~high thermal insulation properties.The optimum composition of the cast compound was determined by experimental variation of the quantity of the amorphous silica from 0.5 to 3% every 0.5% in the quartz compound used in Donetsk Metallurgical Plant.Laboratory tests were conducted on cylindrical specimens with a diameter of 50 rmm and a height of 50 mm. The specimens were prepared by casting in split metal molds, dried in air and in a drying cabinet at ll0-120=C for 6 h, and then heated treated at 500=C for 4 h (according to the technical instructions of Donetsk Metallurgical Plant).The influence of the quantity of the addition on the specimen properties is shown in Tables i and 2. As may be seen from the data obtained, with the addition of up to 1.5% amorphous silica the open porosity of the specimens drops somewhat in comparison with the control ones (the.~control specimens were prepared from the quartz compound used at the Donetsk Metallurgical Plant). At the same time, the apparent density of the specimens remains almost unchanged and the strength characteristics increase.A further increase in amorphous silica content in the compound leads to an increase in porosity and a reduction in density and strength. Consequently, the optimum is an addition of 1.5%.The data of Table 2 indicates a ...