Refractory materials for purging metal with gases

Abstract

Recently, refining of steel outside the furnace, which permits a considerable reduction in the content of gases and nonmetallic inclusions in the metal and improvement of its quality, has attained wide use. Existing procedures for refining metal outside the furnace --vacuum treatment, treatment with synthetic slags, and purging with inert gases --differ from one another in complexity, cost of the equipment, and the technical efficiency.The advantages of purging metal with gases are the minimal capital costs and the possibility of using simple inexpensive equipment with the existing stock of steel-teeming ladles without significant reconstruction of the casting bays. Treatment of the metal with inert gases in the steel-teeming ladle also increases the output of the smelting units, reduces the consumption of electricity (by finishing the metal outside the furnace) and alloying additions (by transferring alloying to the steel-teeming ladle), and improves the quality of the metal by reducing its gas saturation and averaging the temperature and composition during its mixing --this is particularly important when the capacity of the units is increased.Purging of metal with inert gases in a steel-teeming ladle by means of devices with relatively large orifices (tubes, nozzles, etc. ) does not ensure preparation of a sufficiently developed gas/metal contact surface and reduces the refining efficiency; therefore, widespread use has been attained by the method of metal purging through gas-permeable refractories, laid in the bottom of the ladle [1][2][3][4][5][6][7][8][9][10][11][12]. Both outside [13][14][15][16] and in the USSR [17] the gas is fed downward to the steel-teeming ladle through a special refractory tuyere fixed into the ladle bottom (Fig. 1). The porous tuyere may be in the form of a truncated cone or pyramid with an internal porous sector, or two truncated cones with a common base.This article summarizes the experience gained in the development of refractory materials, used for metal purging, based on corundum, high-alumina chamotte, and periclase.The purging efficiency depends on the number and size of the gas bubbles and their distribution in the body of the metal, the purging time, the gas pressure, etc. Experience gained shows that with attainment of the required efficiency the gas consumption per ton of metal treated is 0.5-1 m a, corresponding, e.g., to a gas consumption of 50-100 m 3 at an excess pressure of 1 atm for 10 rain in a 100-ton ladle. An increase in the pressure of the purging gas (in comparison with the accepted excess pressure of 3-6 atm) may lead to jet effusion of the gas --this is undesirable [18]; the increase in the purging time is limited by the cooling of the metal [1].

Gas permeable forsterite refractories

“…Thus, we were faced with the task of developing gas-permeable forsterite refractories instead of periclase, designed for ensuring shortterm blowing of steel in the ladle with inert gases at 1590-1640~ [2].Experience with the development of gas-permeable refractories for the above purpose, both in our country [3] and also abroad, shows that the most stable properties are attained by forming gas-permeable structures from bodies with a granular composition close to a single fraction distribution. This principle was the basis for developing gas-permeable forsterite refractories.…”