The use of sliding gates in steel--teeming ladles ensures reliable pouring of metal ~ad improves the working conditions [1,2]. Mullite-corundum, corundum, and zircon plates, magnesian plates with a periclase working layer [2][3][4][5][6][7][8][9][10], and magnesite plates with a periclase insert are used in sliding gates.The muIlite-corundum plates in use at the Donetsk Metallurgical Works (DMW) for pouring steel into molds from 170-140 ton ladles, and the magnesite plates with a periclase working layer on MNLZ, permit pouring of only one melt [5]. Although steel pouring through a sliding gate is definitely advantagenous from the aspect of organization and improvement of working conditions, it is only economically advantageous when not less than 60% of the refractories of the sliding gate are used twice [4].
The production of baddeleyite by concentration of the residues of the nonmagnetic fraction of Kovdor deposit iron ore fraction has broadened the raw-material base for production of zirconium dioxide refractories. Investigations of Kovdor deposit baddeleyite [1][2][3][4] have shown that this raw material is among the purest varieties and is no less pure than the baddeleyite of Brazilian and Ceylonese deposits. The impurities found in nature are not chemically related to baddeleyite and with removal of them 98-99%* pure zirconium dioxide is obtained.After concentration, the grains of baddeleyite powder with a size primarily of less than 0.5 mm (major portion 0.2-0.09 mm) are single crystals of monoclinic ZrO2 of isometric irregular shape. The difficulty in grinding haddeleyite single crystals to obtain finely dispersed powders is responsible for the method of producing parts of it: stabilization of baddeleyite single crystals by electric melting with the obtaining of granular powders, or the use of natural grain-size baddeleyite (less than 0.5 mm) in combining stabilization with firing of the material.The method of production of parts from natural grain-size baddeleyite is far simpler than the method from baddeleyite stabilized with CaO by electric melting. Investigations of combining stabilization with firing of finely dispersed baddeleyite powders (less than 0.02 ~m) with the use of a stabilizing addition in the form of chalk or calcium zirconate (less than 0.02 ~m) showed (Fig. i) that with the addition of calcium zirconate, volume changes in powders in firing are not observed. This must increase the probability of obtaining goodquality parts, which agrees with published datat [5][6][7].With the use of natural grain-size baddeleyite the process of binding and redistribution of the calcium oxide cannot occur in the material in sufficient volume up to the temperature of polymorphic transformation of the zirconium dioxide. The degree of stabilization at I000-1200~ is only 30-40% with the addition of about 3.5% CaO (10% CaZrOs), and 35-45% with the addition of 4-4.3% CaO (12.5% CaZr03), despite slowing of the rate of temperature increase (to 10~ Therefore, in this range, significant volume changes are preserved in the material.The greater the CaZrO3 content added to the binder and the lower the quantity of finely dispersed component in the material, the greater the volume changes of samples (Fig. 2). With an increase in finely dispersed component content from 40 to 50% the change in volume of samples at 1200~ decreases by 0.6% (Fig. 2b) and instead of growth of the sample after firing, there is a small amount of shrinkage (0.3%).The stabilizing addition content and also the ratio of finely dispersed and granular components of the material determine the properties of samples pressed under a pressure of 50 MPa and fired at 1580 and 1750~The porosity of the samples increases and the density drops with an increase in CaZrOs content (Fig. 3). The strength of samples fired at 1580~ *Here and subsequently weight percentage...
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