gree of compaction of the zone of the steel teeming hold of the part is obtained by pressing of plates with an insert corresponding to the projecting portion.The specific wear of the hole in the experimental corundum plates in service is 2~ times less than in the plates pressed by the normal method. 1. 2.3. 4.The replacement of ladle stopper assemblies by slide valves has made it necessary to organize the production of refractory parts satisfying the requirements for teeming primarily rimmed, semikilled, and low-alloy steels.As experience has shown, teeming of electric furnace steel, including constructional, through slide valves with the use of magnesite composition refractories is accompanied by contraction of the teeming channel, narrowing of the stream, a reduction in the rate of filling of the molds, and, as the result, a breakdown in the method of teeming and poorer ingot quality [i, 2]. With two usages of a set of magnesite refractories in the gate valve a tendency is observed toward an increase in the nonmetallic inclusion content in the steel [1].It is known [3, 4] that rational selection of refractories for slide valves with a certain structure and properties promotes normalization of the process of teeming a single heat of steel and elimination of contraction of the teeming channel and skull formation in it with sufficient life in service.

A new process for production of corrosion-resistant steels provides for refining of the high-alloy semifinished product produced in electrical furnaces in a converter with bottom blowing. Before pouring into the converter, solid metal additions in a quantity of 10-12% of the weight of the heat are added to the semifinished product.The refining is done by blowing the metal bath with gaseous mixtures with different oxidation potentials, which leads to alternation of oxidation and reduction service conditions of the lining. To correct the slag conditions of the heat, lime and fluorspar are added to the converter bath.The gas--oxygen refining (GOR) process is conducted in a converter with a detachable bottom in the center portion of which are located "tube in tube" telescopic tuyeres for supplying gases to the molten metal.In oxidation periods I and II of the heat the metal bath is blown with oxygen with a protective (natural) gas and with a mixture of oxygen and a neutral gas, respectively, and in period III, the reducing period, with only neutral gas.The converter has the form and dimensions normal for similar 60 ton converters. Its walls are lined with fired periclase--chromite parts and the bottom with unfired periclase--carbon ones.Testing in the converter lining of periclase--chromite parts of sintered periclase powder and chromium ore showed their insufficient wear resistance (not more than 53 heats), which was responsible for the use of PShPKh parts made of expensive and scarce fused materials, periclase--chromite, chrome-alumina spinel, and periclase. Under similar service conditions PShPKh parts provide a converter life of up to 80 heats but their use has a significant influence on the economic indices of the process as the result of their high cost.During service of the lining the slag belt, the life of which limits the length of a campaign, is subjected to especially intense wear.The basic failure factors acting on the lining of a GOR converter are the high temperature of the process (up to 1700-1720~ the alternating oxidation--reduction character of the gaseous atmosphere and the molten slag, the aggressiveness of the slag, the unjustifiably long time of contact of the lining with the slag in period III, and the long interheat downtimes.With positive test results in the lining of a GOR converter of PShPKh parts the question of replacement of them with refracturies equivalent in wear resistance but less expensive made of not so scarce and expensive original materials remains a pressing one.

Starting in the 1960s as a result of continuous improvements in electric arc furnaces and the melting technology for electric steels, there have been increases in outputs, and the grades of steels have been altered, all of which demanded basic changes in the electrical equipment, the energy and technological melting schedules and management procedures in the electric steel-melting shops.In these conditions, periclase--chromite refractories, having found extensive use in the roofs of steel-melting furnaces, are now proving to have inadequate roof resistance. Thus, the life of roofs in the arch-suspension design of powerful 100-ton furnaces with a roof rise of from 0.13 to 0.14 of its diameter (to provide adequate constructionstrength) is on average 80-90 heats [i]; and in this case the chief causes of destruction of the refractories in the peripheral zones are cracking and spalling under the action of stresses developing during regeneration and volume changes in the refractory, saturated with slag, and also the influence of thermal impacts, gravity forces, etc; and in the central part --spalling and melting as a result of the formation of relatively low-melting compounds due to the saturation of the working zone of the refractory with iron oxides, silica and other elements from the furnace dust and the action of high temperatures.Investigations show that the life of the roofs made from periclase--chromite refractories can be increased by 15-20% as a result of design changes in the structure (for example, annular construction instead of sector-arch, etc.) [2,3]. In foreign plants, for electric furnace roofs extensive use is being made of high-alumina refractories and materials containing from 65 to 97% A1203. However, working experience shows that only refractories containing 85% or more A1203 will provide adequate roof life. It is noted that the successful use in these roofs of refractories made of alumina materials should possess, in addition to good slag resistance, an enhanced mechanical strength at elevated temperatures, and also significant spalling resistance [4].In this article we shall present results from the use of mullite corundum refractories in the roofs of electric furnaces of average specific capacity (250 kVA/ton), melting stainless and ball-bearing steels.The Institute together with the Semiluksk refractories factory has developed grade MK-80 refractories of mullite corundum composition with structural reinforcement using nonisometric grains of fused mullite [5]; the production of these refractories was mastered at the Semiluksk plant. Testing of the mullite corundum articles MK-80 possessing high spalling resistance (Table i) was done in stages in the roofs of 50-ton (actual capacity 65 tons) electric furnaces at the Dneprospetsstal' factory; in the first stage for melting stainless, and in the second ballbearing steels.The roofs had a sector-arch structure with a rise of from 0.08 to 0.09 of their diameters. In the first stage the roof was laid dry; one roof was almost completely made up of exp...

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The Ukrainian Scientific-Research Institute for Refractories together with the Dnepr Special Steel Electrometallurgica! Plant has conducted investigations [1][2][3][4] on the development and selection of refractory materials for slide valve parts in teeming of bearing and stainless steels, which are prone to clogging of the steel-teeming channel, for the purpose of providing stability in operation of the valve, a reduction in crust formation, and an increase in the times of use of the plates, nozzles, and well blocks.The service tests of mu!lite--corundum, mullite, and kaolin refractories showed that they answer these requirements since in use of them because of the reduced thermal conductivity in comparison with periclase parts there is a reduction in crust formation and clogging of the steel teeming channel and the teeming process is more regular without a reduction in steel quality [2,4].This article presents experience in the production of chamotte nozzles and nozzle collectors and service of them in the slide gates of steel-teeming ladles of stainless steel at the Dnepr Special Steel Plant.The parts of the experimental lot were produced at the Zaporozhe Refractory plant from the raw material used in the production of chamotte refractory parts, ShKGP chamotte, PLK-0 kaolin, and DN2 clay.The charge for the molding mixture consisted of granular chamotte with a water absorption of 3% containing about 39% A1203 and a mixture of ground kaolin and clay. The mixture, with a moisture content of about 6%, was prepared in mixing mills using the normal plant method for 4 min. The nozzles (No. 13) and the nozzle collectors (No. 23) with a height of 250 and 300 mm and a channel diameter of 80 and 60 mm, respectively, were formed on a 6.3MN hydraulic press under a pressure of about i00 MPa in two stages with premolding from below in view of the significant height of the part.The apparent density of the freshly formed raw material varied within limits of 2.20-2.25 and 2.13-2.16 g/cm 3 for the nozzles and the nozzle collectors, respectively.The parts were dried and fired in a 120 m long tunnel kiln with a maximum temperature of 1400~ The nozzles were placed on the kiln cars in the vertical position on a base of chamotte brick in two rows with one part of the upper row on four of the lower with the large diameter downward. The properties of the chamotte SHS-32 nozzles and the nozzle collectors met the requirements of Technical Specification 14-8-385--81 (Table I).For the more complete characteristics of the chamotte parts the heat resistance, thermal conductivity according to the method of [5], and boundary angle of wetting by the metal in relation to heating temperature [6] in comparison with high-alumina and periclase parts were also determined.The thermal conductivity of the slide gate parts is an important property in teeming of stainless steel.It is known [i, 2] that the intensity of formation of the crust on the walls of the teeming channel is in relation to the thermal conductivity of the refractory material.It has be...