The Cherepovetsk Metallurgical Factory is mastering the production of heat-insulating inserts (hot tops). The refractory filler consisted originally of quartz sand which is a "silicodangerous" material. To replace the sand the factory tried chamotte, raw and fired dunite, raw and fired dolomite, Khabozersk and Kytlymsk olivines. The trial inserts were made according to the specifications, and the properties are shown in Table 1.The best results for casting steel were obtained with the inserts based on Kytlymsk olivines, fired dunites, and chamotte; using these inserts for trial meltings there was no boiling of the metal in the head section, and no burning of the inserts on to the ingot. A satisfactory ingot macrostructure commenced at a level of 4-10% from the top. Since the Khabozersk olivines contained a large amount of iron oxides (up to 15%) the tests of the inserts were unsatisfactory and the ingots developed a lot of crust, and a satisfactory macrostructure in the rolled blanks was obtained starting only from a level of 10-14% from the top of the ingot.Cbend, kgf/cm z P,%
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