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Factors are considered that increase the service life of a lining for a crucible induction furnace. Results are provided for laboratory studies and industrial tests of Karelian quartzites of Jotnian age of the Shokshinsk formation and Jatulian age of the Metchang'yarvinsk formation. The effect of impurities is quartzites on crucible induction furnace lining wear resistance is studied. Brief characteristics of quartzites are provided. The possibility is established of using waste materials from quarry production of Shokshinsk quartzites for preparing quartzite mixes.Keywords: Karelian and Swedish quartzites, lining mix, induction furnace, binding and sintering addition, boric acid.Crucible melting of cast iron, steel and non-ferrous metals relates to the main requirements of casting-metallurgical technology and also exhibits economic advantages over cupola melting of cast iron, and it has a cheap and rapidly replaceable acid lining. The economics of operating melting furnaces and the quality of melted metal depend on the quality and service life of the lining. Specifications laid down for lining materials relate to refractories based on quartzite. A quartzite lining is favorably distinguished from magnesite and alumina materials by cheapness and the fact that shrinkage is balanced by growth of quartz during allotropic transformations.Domestically produced furnaces for melting cast iron, steel and alloys based on copper mainly operate on a quartz lining. This lining is also most widespread abroad. For example, in Germany about 90% of induction furnaces use it. Quartzites that during quartz inversion retain adequate strength and density are suitable for lining induction furnaces [1].In crucible induction furnaces (Fig. 1) metal has a thermal, chemical, and erosion effect on the lining. High metaland slag-resistance of the lining is provided by minimum porosity of the sintered layer of the lining, for example of the Swedish lining mix Radanit (Fig. 2). An acid lining of a quartz mix has a constant volume or little growth within the limits of 1% during service. Between the sintered part of the lining and the inductor during crucible firing and its operation a lightly-sintered (buffer) layer is created that prevents the spread of cracks deeper into the lining towards the inductor. Lining expansion gives rise to slow sintering of the rammed walls of the crucible due to which a powder buffer layer is retained for a long time. The safety of operating a furnace with an acid lining is provided by the fact that the buffer layer prevents breakthrough of molten metal to the inductor. An acid lining is quite inert with respect to molten cast iron and slag, and it exhibits the required refractoriness.

Research results are reported on the effects of components on the resistance of acid lining for the crucible induction furnace. To raise the lining resistance, one needs to eliminate components that react with the silica crucible. The extent of silicon reduction from the lining is dependent on the heating of the metal and the contents of carbon and silicon in the liquid. Increasing the carbon content and reducing the silicon concentration in the metal favor wear on the crucible. The slag components most actively influencing the resistance of the lining are magnesium and calcium oxides, which are produced on modifying cast iron, ferrous oxide, and manganese on account of reduction in the viscosity of the slag, increase in its wetting power, and penetration into the pores and unevenness in the walls of the crucible.Karelian Republic casting organizations melt cast iron in induction furnaces working at line frequency or at frequencies ³1000 Hz. The crucible material reacts with the reagents in the induction oven in a fashion dependent on various factors, mainly how the melting is conducted. In induction melting, there are marked temperature differences in the liquid, which moves under electromagnetic mixing. The slag temperature is somewhat lower than the metal temperature. The reactions may include ones either envisaged or neglected involving the additives, the slag, the atmosphere, and the crucible lining. Other effects come from the temperature in the furnace, the concentrations of harmful impurities that attack the lining, and the area of interaction, all of which influence the reaction rates.During use, the crucible lining acquires a zone structure. The internal working zone facing the liquid metal and slag tends to dissolve. Behind it lies a transitional zone, which is fairly dense, and which is subject to lower temperatures by comparison with the working contact zone. Then follows the quartzite zone, or what is called the least-altered zone, in which the grains of the quartzite lining are not connected one with another because of the inductor cooling. Chemical analysis indicates that the contact zone serves interaction between the oxides of iron, manganese, magnesium, aluminum, and other components of the metal on the one hand and the acid lining on the other. Slag is not especially added in an induction furnace with acid lining. However, the oxides formed by oxidation of the charge components constitute a form of scum or slag, which reduces the stability of the lining in the upper part of the crucible and does not favor the improvement of the metal quality. The slags with certain exceptions are formed by the oxidation of iron, silicon, and manganese in the charge, as well as from the attack on the crucible.The electromagnetic stirring causes the layer of colder oxides formed at the surface to be entrained in the recesses of the crucible, where it is heated and attacks the lining. The attack is the less the closer the composition of the slag to that of the lining. The composition of the slag on heating cast i...