Heat-insulating inserts ("hot tops") have recently become very popular for the lateral heat insulation of metal in the riser part of ingots. Their use has reduced the level of top trimming by 3-5% [1, 2].The literature contains inadequate data on the physicoceramic and heating properties of these inserts and on the effect of these properties on the depth of penetration of shrinkage defects inside the ingot. The thermal conductivity of the lining material in the riser has a most marked effect on the shrinkage depth during crystallization of the ingots.Methods involving spheres, hollow cylinders, and ellipsoids are recommended for determining the thermal conductivity of refractories, as these are the most precise, convenient, and low-inertial methods [3][4][5]. However, the sphere and ellipsoid methods [3, 4] involve the need for precision grinding of the materials, precision preparatory work, and the preparation of specimens of complex configuration.The hollow cylinder method [5] is more acceptable. Although it involves minor errors (2-5C]o) due to the leakage of heat through the faces of the cylinder, it admits of the use of simple specimens. An analysis of the errors shows that the maximum values do not exceed 8%. Therefore, the hollow-cylinder method was used for these experiments.The specimens whose composition corresponded to hot tops (Table 1) were made in the form of cylinders. The carefully blended mixture was poured into a mold and compacted using a tamper or a vibrotable. To check that the specimens and hot tops had the same properties, measurements were made of the main characteristics affecting conductivity: density and porosity. When these factors coincided the specimens were tested for thermal conductivity.
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