At present in the USSR submersible nozzles of quartz glass are widely used in machines for continuous casting of steel. A high heat resistance is an advantage of quartz material.The wise use of continuous casting of steel in the whole World and the ever-increasing use of series casting, especially of mold steels, had led to a significant increase in the use of amorphous silica parts [i, 2].In the USSR submersible quartz nozzles to TU 14-8-231-77 are produced by the Podoisk Refractory Part Plant.The parts are made by slip casting of a suspension with a density of up to 1.80 g/cm 3 in gypsum molds.The formed green part is dried and fired in tunnel kilns at I150~The possibility of crystallization of the material in high-temperature firing is a significant disadvantage of this method.The presence of cristobalite reduces the heat resistance of the parts as the result of a sharp change in the linear dimensions in the polymorphic $ § ~-transformation of cristobalite.In connection with the above there is significant interest in the method of unfired quartz parts [3] in which the material is hardened by hydrothermal treatment.Such a treatment eliminates the formation of cristobalite and, in addition, provides a reduction in the consumption of thermal energy in production of the parts.The purpose of this work was the development and comparison of different variations of the method for submersible quartz nozzles for continuous casting machines.The work was done in collaboration with Podolsk Refractory Part Plants.In the production of unfired quartz refractories the properties of the original highly concentrated suspension have a special influence.During wet grinding of the paticles of fused quartz complex processes causing not only obtaining of the specified fineness but also mechanicochemical activation of the dispersed phase occur. The main problem consists of creation of a cast system revealing binding properties.The latter are determined by a combination of characteristics (volume share of the solid phase CV, degree of dispersion, pH, viscosity, etc.) formed directly in grinding [4].The rate of grinding, evaluated, for example, by the content in the system of fine (<5 pm) or coarse (>50 or >63 pm) fractions, is determined by many factors.The most general of them, which are the result of the type of grinder and the composition of the charge, are the effective density of the grinding bodies (APg.b is the difference in the density of the grinding bodies and the suspension), the active zone of grinding (~ is the ratio of the volume of voids between the grinding bodies to the volume of suspension being ground), and the size (diameter) of the grinder.It is known that in the highly concentrated suspension method there are two methods of wet grinding, with single-step and with portion (step-by-step) charging of the material. The first method is used in grinding comparatively coarse porosity-free materials such as quartz glass or fused quartz.In wet grinding of such a material in a ball mill the processes of crushing and fine gr...

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The processes of the formation of a solid material in VKVS (highly concentrated ceramic bonding suspensions) technology are characterized in the light of a number of changes, accompanied by alterations in the nature of the bond between the particles [1 ]. The primary structure formation of VKVS is accomplished during their partial dewatering, for example, on account of the porous mold, the filler, etc. The green article obtained from VKVS of acid or acidamphoteric composition, as a rule, is characterized by a rather high mechanical strength and elastobrittle destruction. Despite the fact that, both for the original casting in which all the pores are filled with liquid (volume proportion of kinetically bonded liquid Cws), and also for the casting after partial drying (right upto a moisture content of 0.5-I%), there is a characteristic lack of water resistance [2]. The water resistance, taken as the criterion for assessing the bonding properties of VKVS [3] is attained after drying the material to a moisture content of less than 0.1-0.2% [2]. The latter is explained mainly by the formation in the system of siloxane bonds. The probability of their formation between the microparticles of colloidal particles and the active colloidal covering of the grains of mineral constituent of VKVS in the undried material is low.Previously [2] using high-precision indicators for linear displacement it was shown for the first time that during the drying out of castings of siliceous composition, after a certain shrinkage, there is an expansion. It was postulated that it is due to polymerization of the interstitial silicic acid.Starting from the assumption about the interaction of the expansion of the casting and the water resistance and strength after drying, in the present article we deal with the problem of investigating the mechanism and features of the structure formation during drying out, bearing in mind the influence of such parameters as the type, dispersion and deduced concentration of the colloidal component cPrkk, and the critical concentration C v cr of the original VKVS.The linear changes in the castings in relation to their moisture content were studied on equipment shown in Fig. 1. The use of the induction sensor was useful for registering the change in the linear dimensions of the casting with an error of less than _+ 1 #m.The original VKVS (see Table 1) were studied in the form of suspensions of fused quartz, ordinary chamotte (27.2% A12Os), and mixed suspensions in the system ordinary ehamotte--quartz sand in the ratio 85:15 [4]. The suspensions were obtained by wet milling using the known technology, and stabilization [3]. The specimens measuring 10 • 10 • 8 mm were shaped in gypsum molds. Directly after the completion of the casting up of the specimen the casts were extracted, and then one of them was established on the equipment for measuring the linear dimensions, and using two parallel measurements we established continuous weighing in order to construct the relationship ACre 1 = f(W).Taking into account the ...

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Experience in the use of slide gates for teeming steel and the results of scientific investigations are an indication of the significant influence of the porous structure of the refractory plates on their service properties and their life in service.For example, it has been established [i] that refractory parts intended for operation in slide gates must contain primarily fine voids (finer than 30 ~m).Japanese investigators have assumed that in the periclase plates the average void size must be no greater than 2.5 ~m [2].From the results of a microscopic study of the structure of voids and the data of mercury porometry, in domestic production periclase plates about 65% of the volume of void space is due to voids with a diameter of less than 50 ~m. They are filled in impregnation of the plates with pitch [3].Using as a base periclase with a grain size of not more than 1.2 mm, plates were obtained with a fine porous structure (predominant size of the voids less than 16 Dm) which showed high wear resistance in service in steel-teeming ladle slide gates [4].The void space of the parts is formed by intragranular voids and intergranular spaces. Therefore, the distribution of voids by sizes must depend both upon the structure of the filler and the conditions of preparation of the raw material (grain and substance compositions of the charge, form and quantity of the binder, pressing pressure, etc.) and upon the character of sintering in firing.In connection with this the establishment of the interrelationship between the characteristics of part porous structure and the technical parameters of its production may be assumed to be very useful.However, information on the distribution of voids in the raw material for the periclase plates and on the change in their structure during firing is lacking.The purpose of this work was to investigate the porous structure of the periclase inserts of built-up plates after pressing and also of the changes in this structure during calcination and firing.