Reducing the carbon content in baddeleyite corundum products

Abstract

The Podolsk Refractories Factory (PZOI) produces baddeleyite--corundum refractories according to for the working zones of glass furnaces.Studies [2][3][4] showed that during the service of these refractories carbon monoxide, carbonic acid, and nitrogen separate in the glass, since the content of carbon and its oxides in the articles comes within the range 0.02-0.10%* [I].Contamination of refractories by undesirable carbon impurities is a result of the reaction of graphitic electrodes and oxides of the melt in refractory batch in the reducing conditions of electric-arc melting.In this case the carbon of the electrodes enters the melt as a result of direct transfer under the action of plasma jets, erosion, and oxidation of electrodes.Furthermore, the melt is contaminated by carbon during burning-in of the furnace with coke which occurs during single-shift working at PZOI.According to data in [3], a reducing atmosphere in the melt contributes to nitrogen absorption by bakor melt because of the formation of compounds such as nitrides and nitrocarbides of aluminum, zirconium, and silicon.In order to create oxidizing conditions and reduce the content in the articles of gasproducing impurities, experiments were done on the electric furnaces OKB 2126A in shop No. 4 of the factory using the plasma-arc method of melting.The tests were done with double-shift operation of the furnace.Before the start of the experimental meltings we created a double-shift store of sand blocks for assembling the molds, installed special electrodes with increased resistance, impregnated with borate solutions according to the technology of the Chelyabinsk Electrometallurgical Combine [5]; and furthermore the melting tank was insulated around the perimeter with shrinkage-head tiles and split blocks to avoid burnthrough in the lining.Burning-in of the furnace was done with ground coke in amounts of 40 kg. Melting was done with ordinary batch (articles grade BKCh-33).In the first shift the furnace was burnt-in, the melt was cleaned to remove coke, and the casting of ordinary articles was carried out.The experimental articles were cast in the second shift and the batch was melted with different electrical cycles.