No abstract

A technology has been developed for making carbon-ceramic composite refractories by combining carbon fibers as reinforcing component with a mixture matrix, which allows one to make refractory components of various sizes and geometry, including thin-walled large constructions. The heat resistance of these composite refractories increases with the bulk silicization during ceramic production on a carbon-carbon substrate. The degree of silicization is determined by the volume of the open microporosity of transport type, which is formed by pyrolysis of a polymer coke-forming matrix in the initial carbon plastic. The transport micropores are produced by a modification of the phenol-formaldehyde resin additive treatment, which does not give rise to coke on pyrolysis. As a result, the content of open pores in the carbon framework attains 55%, which enables one to make a silicized composite refractory of density up to 2.7 g/cm 3 with a compressive strength of 250 -300 MPa, bending strength 120 -140, and tensile strength 60 -80 MPa, elastic modulus 120 -140 GPa, linear expansion coefficient 3.5´10 -6 -4.5´10 -6 K -1 , and thermal conductivity 6 -8 W/(m × K). These refractories are widely used in various branches of industry.High-temperature plant and engines require strong heat-resisting refractory materials, which should withstand multicycle thermomechanical loading at up to 1700°C under oxidizing conditions and in the presence of ionizing radiations with minimal permissible mass loss without reduction in the strength. Stable viability under such conditions is shown by carbon-ceramic composite refractories, and aspects of the technology of making them are dealt with here.Carbon-ceramic refractories are made by the bulk mixing of carbon fibers as reinforcing component with a mixture matrix containing carbon in transitional forms dispersed in silicon carbide. The technology is based on thermochemical transformations of the polymeric coke-forming matrix of carbon-plastic material based on phenol-formaldehyde resin (PFR) in a carbon matrix for use in carbonization (firing) and graphitization with high-temperature adjustable heating and carbidization of the resulting carbon-carbon matrix. Figure 1 shows the scheme for making these refractory carbon-ceramic components.Experiment indicates that the properties of the refractory components begin to be formed in the preparation of the carbon-fiber material, which is purposively chosen as a reinforcing filler, and involves the development of a comprehensive coke-forming bonding agent. Fig. 1. Block diagram for the manufacture of components from carbon-ceramic refractory material.

Experience in the service of furnace--ladle-type unit ladles has shown that the refractory life in them is very low in comparison with other types of units for outside-the-furnace treatment of steels as the result of the more severe service conditions [1][2][3]. Therefore, to increase the ladle refractory life it is insufficient to only have refractories with higer service properties but it would also be desirable to determine the influence of the technical parameters of steel treatment on refractory wear ~for the purpose of optimization of treatment conditions.It was established that these~parameters are the chemical composition of the slag, the length of treatment, and the length of vacuum treatment [i, 3].A study of the combined influence of these parameters on refractory wear under laboratory conditions is very difficult since on a model it is practically impossible to reproduce the actual service conditions of refractories in a ladle.In ~addition, the methods of studying the influence of technical factors on refractory wear ~used until the present have made it possible to determine the action of the slag only as the combined action of its constituent oxides.It was impossible to reveal the influence of each oxide individually or of a group of oxides.It was also established that an increased manganese oxide content promotes corrosion of the refractories, but not always, and that the cor~rosiveness of the slag is determined to some degree by its basicity [4][5][6][7].Therefore, there is special interest in processing of data accumulated in normal operation of the unit.It is natural to process the data by methods of statistical analysis,* particularly with the use of step-by-step regression [8]. However, selection of the quantitative characteristic of wear is complex.According to the generally accepted method, the wear of refractories is determined as the difference between the initial and the remaining thickness of the refractories at the completion of the ladle campaign, that is, after treatment of several frequently differing heats.With this method it is impossible to determine the influence on refractory wear of the treatment technical parameters either of each heat individually or in different periods of it.Since the treatment technical parameters change from heat to heat and even in the course of a single heat, determination of the functional relationships of refractory wear to these parameters by methods of statistical analysis is possible only with a method providing measurement of refractory wear during each heat.Taking this into consideration the change in magnesium oxide content in the slag during the course of a heat was seleted as the criterion for evaluating refractory wear in the slag zone of the ladle.This choice is based on the fact that periclase--chromite refractories containing about 60% MgO are used in the lining of the ladle slag zone while, with the exception of lime with an MgO content of 1-2%, MgO is present in not one of the heat-forming and deoxidizing components added to the ladle for...