An evaluation of the effectiveness of use of hot tops

Abstract

The solution of the problem of resource economy in the country is directly related to a reduction in the consumption of metal in processing of it. With the existing level of technology of metallurgical production the most effective method of economy of metal in teeming is the use of hot tops with heating of the pool of metal with lunkerite, making it possible to significantly reduce the top cut-back and improve the quality of the finished rolled metal without an increase in steel melted.At present in teeming of carbon and alloy types of steel the top portion of the ingot is heated primarily with hot tops of relatively ineffective type KRTV-I compositions or with chamotte brick, which do not provide a significant saving in metal.For the purpose of improving the methods of heating of the sinkhead and a further increase in the output of finished metal the Eastern Refractory Institute together with the Scientific-Research Institute for Metallurgy and Chelyabinsk Metallurgical Combine has done work on evaluation of the effectiveness in teeming of high-quality alloy steels of other hot tops produced by industry, particularly those based on mullite-silica fiber [i] and two-layer ones, the working layer of which is made of mullite-silica fiber and the outer of a sand-cellulose material. The effectiveness of use of the exothermal hot tops developed by the Scientific-Research Institute for Metallurgy and tested earlier at Zlatoust Metallurgical Plant was evaluated simultaneously [2, 3].To conduct comparative service tests an experimental lot of hot tops of the two types according to the drawings of Chelyabinsk Metallurgical Combine for SS-6 molds was prepared at Pervouralsk Dinas Plant.The hot tops of the first type MKV-I were prepared from a slip with a composition of 77.6%* mullite-silica fiber, 22.4% PVAD binder (with a 50% dry residue cont~mt), and 90% (above 100%) water.The hot tops of the second type MKV-2 were two layer ones. The sand-cellulose slip of the first layer corresponded to the slip for KRTV-I hot tops and its composition was 76.5% sand, 3.5% refractory clay, 10.0% waste paper, 10.0% commercial lignosulfonate, and 65.0% (above 100%) water. The composition of the slip of the second fibrous layer was 77.6% mullite-silica fiber, 22.4% commercial lignosulfonate, and 90% (above 100%) water.The plates were prepared using the normal shop method. The technical parameters and properties of the hot tops are given in Table i. The hot tops prepared were tested in No. 2 Open Hearth Shop of Chelyabinsk Metallurgical Combine on seven heats of steel of types 40KhN, 45Kh, 40KhFA, 38KhS, 36SGNA, 35, and 18KhGT.The metal was teemed into molds using the existing method for 6.0 ton ingots. On one four-position stool there were placed two molds with MKV-I and MKV-2 hot tops. The steel was teemed~under an ash-graphite mixture, the consumption of which was 2.5 kg/ton, and the upper portion of the sinkhead of the ingots was additionally heated with 2.5 kg/ton of 28Sh lunkerite.From the results of stripping of ingots of experiment...