The process of obtaining fused periclase in the block in the OKB-955N furnace involves a high outlay of energy and raw materials. Thus, during the melting of brucite raw materials in an ordinary round bath of diameter 2800 mm the consumption of electric power over a period of about 50 h is approximately 5100 kW-h per ton of finished product, and the consumption of batch amounts to 3.9-4.0 ton per ton of finished product.The raw materials delivered for melting, depending on the heat assimilation of the energy from the electric arcs, undergo a series of sequential changes. A typical feature is that only part of the batch fed into the furnace is subjected to melting, while the remainder plays the role of heat-insulating layers between the melt and the furnace housing, passing through the stages of only heating, dehydration, and slntering. The formation of the insulating layers commences under the action of the energy of the electric arcs and continues on account of the extraction of heat from the melt, in which is separated part of the applied electrical power P , and also on account of the transmission of heat to the material within the deep layers of Pmelt in a horizontal direction [1], During the processes of sintering and dehydration the boundaries of the insulating layers (skin, dust, brucite) are displaced in the direction from the melt to the housing. After a certain time the accumulation of heat by the batch is discontinued, the temperature of the external surface reaches a maximum, and the transfer of heat from the melt becomes stationary; and under these conditions the process of forming the insulating layers is completed, and the following equality is justified:where ~., ~_, and ~b are the thermal conductivity values of the layers of skin, dust, and brua cite, k~/(m.K); Sk, Sd, and Sb, thicknesses of the respective layers, m; tm, temperature of the melt, ~ and tsi, temperature of the start of sintering, ~ tde, temperature of dehydration of the brucite, ~ th, temperature of the external surface of the housing, =C; t u , temperature of the surroundings, eC; a~ coefficient of heat transfer from the housing s rr 2 into the surroundings, kW/(m .K).The equation shows that a reduction in the overall thickness of the insulating layer of batch causes an increase in the capacity for heat transfer from the external surface, and conversely an increase in the heat transfer from the surface of the housing displaces the corresponding layers towards the melt. Moreover, the higher the heat transfer from the external surface, the lower the consumption of heat by the layers of batch between the melt and the housing. Therefore, the main factors influencing the formation of the insulating layers are the total thickness of the layers of batch between the melt and the housing, and the capacity for heat transfer, which in the final account determines the thickness of the sintering part of the batch (skin). In the cross section of the block of the fusing part of the periclase there forms a triangle, and therefore in the ordinary ...

At the Magnesite Combine a method has been developed and introduced forelectromelting of brucite into a block [1][2][3][4] and of fired magnesite powder [5,6] and of periclase-spinellides [7][8][9] with obtaining of fused materials for new effective refractories [I, 6, 9, 10-15] in OKB-955N furnaces with a 1200 kVA ETMN 1600/10 transformer.During introduction of the method work was done in the direction both of improving the quality of the fused periclase and increasing furnace productivity.The quality of the periclase was improved by a periodic change in power delivered to the furnace during melting [2], a rational ratio of the powers on the higher and lower voltage steps of the transformer [16], an increase in purity of the original material [17,18], increasing the melting time [18], providing the conditions Pd > Psh reached at Zf < 5"10 .3 [19], changing the form of the bath shell, and increasing the intensity of heat dissipation from its surface [3,4].The productivity of the furnace was increased by supplying an oxygen enriched blast to the furnace [20], melting in a furnace with a current-and heat-conducting hearth [21,22], increasing the diameter of decomposition of the electrodes [7,18], increasing the current by 10-20% above the nominal, and the introduction of rational electrical conditions of melting [4, 5].As the result of work done on an OKB-955N furnace with a 1200-kVA transformer with a diameter of decomposition of the electrodes of 1050 mm a maximum productivity in melting of magnesite, brucite, and fired magnesite powder of 258 [20], 260 [4], and 236 kg/h [6], respectively, was obtained.