Use of bank slags to form sills

Abstract

669.183.4 The processing of metallurgical wastes has received much attention in recent years [1][2][3]. One approach to solving this problem is recycling.In searching tbr optimum methods of utilizing refining products, we examined the feasibility of using bank open-hearth slag to make up the sills of open-hearth and two-bath furnaces. This material was chosen because the sills must have certain service properties: resistance to erosion and high temperatures and stability under the ferrostatic and hydrodynamic pressure exerted by the molten metal and slag. The material must also be inexpensive and readily available. Raw dolomite has traditionally been used in this capacity, but in recent years it has been replaced by crushed limestone. In connection with the continually rising cost of limestone, an attempt was made to replace it with a cheaper material -graded bank slag from open-hearth operations.When the sills are being formed, a substantial portion of the crushed limestone is usually spilled onto the working platform. It is then raked off by the charging machine and dropped into a slag ladle. The part of the sill left after a heat is also placed in the ladle.A slag sample of the 10-40 mm traction that was obtained by the inquartation method showed that 15% of it was crushed limestone. The presence of such a quantity of partially roasted limestone allowed repeat use of the slag as a material for sill construction, even though the main mineralogical components of the slag -wollastonite, fayalite, and olivine -have a melting point of 1200-1300~In addition, bank slag has a higher bulk density than crushed rock (1.8 versus 1.55 kg/m3). It is thus more resistant to the thermal and chemical action of the furnace slag and metal before the metal subsides to a level below the main sills.In trial heats, we visually evaluated the condition of the sills and studied the effect of dissolving bank slag on the process of refining the steel to rid it of harmful impurities -sulfur and phosphorus. It was established that the sills made of slag have the necessary service properties and reliably prevent "escape" of the pig iron and slag from the furnace. On the two-bath furnaces, the degree of wear of sills made of slag was the same as for sills made of crushed limestone. This can be attributed to the rapidity of the process (the time from the beginning of the hot-metal addition to the beginning of tapping averaged 2.5 h) and the fact that a source of heat energy was located inside the bath -in the region where oxygen was injected into the molten metal.In the open-hearth fnmaces, some melting of the slag sills was observed before the end of the heating period. Wear was especially noticeable in the sill of the working door, where the molten pig iron is charged. The sills had to be partially rebuilt in certain heats, as they do when cmshed limestone is used (particularly for the sill of the middle charging door).