Properties of graphite-containing crucibles

Abstract

The crucibles containing a significant amount of crystalline graphite as one of the refractory components are used in a number of induction crucible furnaces [I]. The produc tion technology of the crucibles involves maxing of the initial (raw) components, shaping the body using one technique or other, and firing [2].The composition and the dispersion of the original body, its moisture content, and the production technology of the crucibles (the mode of compaction and the firing conditions) determine the structure of the material of the crucibles and the degree of uniformity (homogeneity) throughout the volume which, in turn, determine the properties.In order to calculate the thermal and electrical parameters, to determine the main parameters of the induction crucible furnaces, and to evaluate the structuraluniformity of the crucibles, it is necessary to study the properties of the material (such as density, thermal conductivity, and electrical resistance) in different parts (zones).In view of this, we studied the properties of three types of graphite-containing crucibles. Table i gives the basic information regarding these crucibles.According to the data of x-ray structural analysis* of the specimens subjected to technological heat treatment and subsequently used for determining the property indices, the material of the TKG crucible contains graphite and silicon carbide B-SiC as the main components, the material of the TGG crucible contains graphite, ~-cristobalite, and mullite, and the material of the TGN crucible contains graphite and silicon.In order to evalaute the effect of structural nonuniformity of the material of the crucible on its properties, specimens were taken from different parts (zones) of the crucibles (Fig. i) and their thermal conductivity and electrical resistance were measured.For carrying out thermal conductivity measurements, 10-mm-thick plate-specimens in the form of squeres having a side of 85 mm were cut out parallel to the working surfaces of the crucible: from the side walls, specimens were taken in the immediate vicinity of the external surface after removing the glaze layer and from the base, specimens were taken in the regions close to the internal surface.In order to conduct the measurements of electrical resistance, specimens were cut out in the form of prisms having a cross section of I0 • i0 mm and a height of 25-30 mm in the directions perpendicular to the side wall and the base of the crucible.

Carbon Based Refractories

“…124) Isostatic pressed carbonbonded crucibles with resin bonded and clay bonded one has proved positively great influence on the property value in particular bulk density and the thermal conductivity of crucibles compared by the plastic pressing. 124) The life of the refractory lining of a blast furnace is one of the principal factors determining the length of a campaign. One approach to the extension of the life is to minimize the ex tent of chemical attack through the use of cooling.…”

Porous structure of graphitic crucibles

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In recent years graphite-containing refractories have been used, together with other types: they are superior to many refractories in terms of thermal-shock resistance, thermal conductivity, slag-and metal-resistance [i, 2].Of the range of graphitic products the most widespread are crucibles used for melting and casting nonferrous metals [3,4]. They are used when a high-quality metal is required in small amounts, and so the condition of the crucibles, their composition and the resistance to a large degree, influence the economics of the process, the quality of the final metal or alloy, and the safety of the melting procedures.

The resistance of such crucibles is determined by many factors, among which the most crucial is the resistance of the graphite to oxidation.

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