It is well known that dense taphole clay is very effective for elongation of tapping time. As methods of making dense taphole clay, we have studied following two measures. 1) Reduction of low temperature volatile matter in tar binder. 2) Reduction of binder by application of ultra-fine powder. As an evaluation of dense structure, taphole clay is pushed in a hot condition and proved its dense structure under hot condition. Furthermore, we have adjusted linear expansion characteristic in accordance with estimated internal taphole structure and studying stress caused by thermal expansion. Then , as aresult of application of developed taphole clay at large scale blast furnace, it become possible to achieve long tapping time and stable drilling performance.

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