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Metal Casting Technologies : September 2007
These electrodes have to be refined by ESR. Slag A - CaF2: Al2O3 (70:30) and Slag B - CaF2: CaO: Al2O3 (34:33:33) were prepared for the ESR process. The slags were prepared by mixing raw materials in a proper ratio and fusing in a graphite crucible in an induction furnace. The slag was held until foaming subsided. The molten slag was poured into a preheated clay graphite crucible and allowed to solidify. After cooling the solidified slag was kept in a desiccator. Before ESR melt the slag was crushed and preheated to 7000C for 3 hours in a muffle furnace to eliminate any moisture present. 900 gm slag was used for each melt giving a slag depth of about 55 - 60 mm. ESR was carried out using DC power with electrode positive. ESR melts were performed using constant voltage of25+2Vandcurrentrangeof750-775A.DCpower to the ESR unit was supplied by a generator of 60 KW rating capacity. The current was adjusted by controlling the electrode feed rate. ESR melts were carried out in a water cooled tapered steel mould. The base inner diameter of seamless mould tube is 80 mm and at top is 75 mm. This tube is placed inside a steel water jacket with inlet and outlet tubes welded to the jacket. The ESR process was started by striking an arc between electrode tip and a mild steel starting block. Once the arc was struck, preheated prefused slag was added inside the mould. The slag melted quickly and filled the space between electrode tip and the starting block, extinguishing the arc. Then onwards the heating was due to the resistance of the molten slag to the passage of current. The remaining slag was added quickly and the process stabilized quickly. Slag melting process stabilized in 5 to 6 minutes whereas the full ESR process took about 40 minutes. The slag was deoxidized by continuous addition of pure aluminium in the form of 3 mm diameter wire tied along the length of the WHO'S WHO OF METALS -- ANNUAL 2006/7 Figure 2. Melt poured into cast iron moulds 69