With the introduction of new capacity for the production of fused materials at the Magnesite Combine, a production process has been developed and mastered for producing powders made from fused periclase; tamping masses and articles based on them have been produced for lining the electric smelting furnace aggregates, including induction furnaces for smelting pig iron and steel. The fused periclase powders are made from the highest quality magnesite, e.g., the PPM-96 ) must contain at least 96.5% of MgO,* ~ 1.5% SiO=, and ~ 1.6% Fe203. The choice of batch and the development of the technology for the production of periclase was done after taking into account the requirements laid down in . Normally, for making periclase in accordance with the above specifications, the batch is a sintered powder of fractions 3-0.5 mm, obtained by firing Satkinsk magnesite in shaft furnaces and containing 93-95% MgO, 0.8-1.5% SiO=, 0.i-0.5% AI2Os, 1.5-2.2% Fe203, 1.4-2.1% CaO, and O.i-0.3~ loss on ignition. The batch is fused into a block in OKB-955N ore-smelting furnaces. The smelting process can be divided into three characteristic periods.The first period lasts for 30-120 min and begins as soon as the furnace is switched on and continues until the predetermined current (6.6 kA) is reached when intensive melting of the block begins. The form of the volt--ampere characteristics (Fig. i) indicates that during the first period the furnace operates in a nonarc regime.The second firing period generally lasts for 15-24 h and includes the portional charging of batch and melting of the portions of the powder. In this period the electrodes are raised up, alternating with a short periodic descent in the interval between the charges at moments when the batch under them is effectively melted (Fig. 2). The furnace operates in the arc regime (Fig. la). During this period the main, dense zone of the block is melted; the block cross section is in the shape of a trefoil (Fig. 3) and consists of highest-quality periclase.The third and final firing period is limited to the moment when the tank is completely filled with batch (end of charging) and the furnace is switched off. The furnace is mainly operated with open arcing which is accompanied by significant heat loss and the formation of a conchoidal zone (Fig. 3) in the upper part of the block.Judging from the character of the path of the electrodes (Fig. 2), the rate of melting of the block in the vertical direction when firing in the fifth voltage setting of the transformer (84V) is higher than when firing is carried out in the ninthvoltage setting (70.8 V). The block melted at the ninth voltage setting is found to be slightly more evolved in the horizontal section than the block melted at the fifth setting.The overwhelming majority of firings were carried out at the fifth, ninth, and partly at the seventh (77 V) voltage setting (Table i). With a change from the ninth to the fifth voltage setting, the duration of firing is shortened and furnace productivity is increased. The melting at the first t...
One of the basic conditions for high wear resistance of slide gate periciase plates is a low content of silicon, calcium, iron, and aluminum oxide impurities. Therefore, a study of the influence of the brucite melting cycle and solidification of the molten compound on periclase quality is a pressing one.The transformers of OKB-955 furnaces have nine voltage steps from 105 to 70 V, the current may be varied from 0.6 to 6.6 kA, and the total power from 1050 to 160 kW. The recorded form of the voltage--current characteristic is experimental confirmation of the arc character of electric power liberation in the working volume of the furnace. One portion of the introduced electric power is liberated in the arc (Pa) and the other in the melt (Pm) in passage of the electrical current in it. The arc intensely transmits heat to the charge being loaded and, with melting, the electrodes are lowered to the position providing the specified current. Therefore, movement of the block in the vertical direction, which is determined by the power Pb, occurs.With movement of the block upward the deep-seated molten material releases heat to the material primarily in the horizontal direction. The energy is used for additional melting of the periclase, firing of the crust, and heating and dehydration of the screes. Therefore~ it may be assumed that the power Pm liberated in the melt determines the development of the block in the horizontal direction and an important role in this process is played by circulation flows in the melt and the melting time.In melting with the first step of transformer voltage and a current of 6~ kA, there is a high vertical rate of fusion of the block (time of the process 20-22 h) in which three limited columns of fused material, only directly under the electrodes for the whole height of the furnace and fused to each other only at the level of charging of the bottom, are obtained. In melting with the ninth voltage step and a current of 6.6 kA (time of the process 60-65 h) a block of periclase well developed in the horizontal plane is obtained.The maximum furnace productivity (140-150 kg/h) with the minimum power consumption is obtained in melting with transformer step five and a current of 6.6 kA, when the power introduced into the furnace is divided between Pa and Pm approximately equally. Therefore, the maximum furnace productivity is provided with obtaining of a block with the correct ratio of volumes of fused material in the vertical and horizontal directions. However, with the high rates of fusion of the block using the fifth voltage step, and with the maximum furnace productivity, the impurity oxides are not able to migrate into the center and peripheral portions of the block but solidify in the volume of the periclase in the intergranular areas, thereby having a detrimental effect on its quality. Fusion of the block Magnesite Combine. "Tsentroenergochermet" PTP.
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