Sliding gates are becoming more and more widely used in steel casting in Soviet steelworks. Experience of the use of these gates is constantly being analyzed. On the basis of these analyses, the specifications for the refractory materials are refined and the operational conditions during casting improved.The main factor determining the reliable operation of the gates is their metal resistance, i.e., the ability of the material of the refractory tiles to withstand the aggressive action of liquid steel. From 30 to 5(f/o of unsatisfactory castings arise from factors associated with the development of excessive interaction between the tile material and the components of the liquid steel [1].

The failure of parts of refractory materials used in the slide valves of steel teeming ladles is a complex physicochemical process occurring in the contact of the refractory with the metal being teemed.For several years intense searches have been made for criteria of strength most fully corresponding to the failure mechanism of a refractory, easily reproducible under laboratory conditions, and not complex to determine by calculation [1][2][3]o As a criterion of the strength of refractories this article proposes the use of the failure gradient of the temperature field, which in this case is considered as a characteristic of the material.The basis of this selection of a criterion is the following physical concepts: uniform heating of a homogeneous and isotropic solid, i.e., heating in which the gradient of the temperature field at any point of the solid is equal to zero and which with the absence of limitation of thermal deformations may not cause failures; the vector field of the temperature gradient characterizing the nonuniformity of temperature distribution in the volume of the solid clearly corresponds to the temperature field; + under the action, on a homogeneous isotropic solid, of the mass forces F(x, y, z) and the temperature field T(x, y, z), the thermal stresses satisfy the vector equation of § equilibrium in the displacements W(x, y, z): in contact with a metal, the maximum temperature gradients develop on the surface of contact and the greatest values of ~T/$n (n is the normal to the surface) occur in the first minutes after contact. Under these conditions and because of the comparatively low thermal conductivity of a refractory, the temperature boundary conditions on the other (other than the contact) surfaces of the solid are not significant and the solid may be c~nsidered as semibounded;an analysis of experience in the use of the refractory plates of slide valves in steel plants shows that a frequent reason for the failure of these parts is failure of the contact surfaces caused by the development of a multitude of surface cracks and "loosening" of the contact surface of the refractory, which opens the way for interaction of the refractory with the metal, not only on the surface, but in a surface layer with a thickness of several millimeters.All-Union Institute of Refractories.

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.046.518 and V. P. Karasev An analysis of the operation of steel-teeming slide gate plates showed that to a large degree their life is determined by the operating reliability of the gate and depends upon the service conditions. The difference in properties of refractories used for production of the plates and the variety of operating conditions make pressing the rational selection of the form of refractories in relation to the conditions of their use.The thermal action of the molten steel causes the occurrence in a 10-20-mm-deep surface layer of very high gradients in the temperature field. Even 5-15 sec after contact with the molten metal the temperature gradient reaches the maximum value, which at a depth of 1-3 mm is 250-350~ 5-10 times greater than the failure gradient of periclase and corundum refractories [I].During teeming in operation of the gate the temperature field changes, but for a long time the temperature gradient changes but exceeds the limiting value. The greatest variations in temperature occur in the supporting portion in relation to the metal of the lower movable plate, which is responsible for reliable shutting off of the stream. The more shut-offs during teeming, the more intense the thermal action of the molten metal on the contact layer of the refractory. Corundum refractories are 1.5-2 times more heat resistant than periclase. Therefore, for gates for teeming on a continuous billet casting machine it is desirable to use periclase refractories, and in top teeming into molds corundum refractories.The essence of the corrosive action of molten steel on the gate plate material consists of spontaneous liberation on the contact surface of endogenic oxides of the primary oxide phase of the molten metal and subsequent development of the chemisorption process. The composition of the primary oxide phase is determined by the type of steel melted and the method of deoxidation of it. Depending upon the composition of the primary oxide phase the oxides precipitated may be in the liquid or solid state [2]. Steels containing flowable components of the primary oxide phase of the FeO-MnO-Si02 system, which are characteristic of rimmed and semikilled steels, are the most aggressive toward the refractory. Corundum refractories possess a lower resistance toward the corrosive action of such steels than periclase. Therefore, for teeming of them it is desirable to use periclase refractories. Since with an increase in temperature and contact time the corrosive action increases, for teeming on a continuous billet casting machine and teeming of large heats it is also desirable to use periclase refractories.Killed carbon steels are deoxidized with a somewhat larger quantity of silicon and sometimes aluminum is used. The oxide components of such molten steels are most frequently solid phases. In these cases there is not capillary penetration causing significant development of the depth of the reaction layer, and corrosion of the refractory is practically absent. In teeming of such steels the selection of the refractor...

As the result of design features of the reforming furnace replacement of the parts by earlier approved or standard ones is impossible.