Development of Castables with High Thermal Shock Resistance and Volume Stability
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Development of Castables with High Thermal Shock Resistance and Volume Stability I. Roy1, M.K. Kujur1, R.K. Singh1, R.K. Pradhan2, B. Mahata2 Abstract: Vacuum Arc Degassing (VAD) ladle covers are a vital item for steel production through VAD units. Under prevailing operating conditions of VAD, ladle cover refractories need to sustain high thermal shock and a corrosive environment. Their operational conditions and lining patterns also demand a high volume stability of the refractory material. A composition of a high alumina castable suitable for the manufacture of pre-cast blocks was designed to obtain the desired properties. It was found that castables with an optimum amount of Cr2O3 in combination with the proper deflocculant and dispersing agents were the most suitable. Based on the study, pre-cast blocks were manufactured with the castable developed and tried in VAD ladle covers of ASP, SAIL. It was observed that pre-cast blocks of VAD ladle covers were highly stable under the severe VAD operating conditions and have the potential to result in a good lining life. Keywords: VAD ladle cover, high alumina castable, high thermal shock resistance, volume stability, pre-cast block
1. Introduction The alloy steels plant (ASP) is a special alloy steel producing unit of the Steel Authority of India Limited (SAIL), which has the facilities to make both stainless and non-stainless grades of steel. ASP has only one VAD unit, and the capacity of the VAD ladle is 60 T. The VAD ladle cover is a vital item for steel production through the VAD unit. The VAD ladle cover at ASP consists of a water-cooled metal ring, with the entire refractory lining inside that ring. The refractory lining pattern of the VAD ladle cover is given below: }} The first three rings (from water-cooled metal rings) are lined with high alumina bricks. }} The centre part has three pre-cast refractory blocks (these blocks are lined at the centre and around the electrode hole and the charging hole area). }} Gaps between the brick lining and the pre-cast refractory blocks are filled with high alumina castables.
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During operation it has to withstand high thermal shock and a corrosive environment. Moreover, the VAD ladle cover refractory should have high volume stability for smooth and consistent performance. In the recent past, the refractory lining life of VAD ladle covers was not satisfactory, and sometimes premature breakdown took place, which led to the plant being faced with problems in maintaining an uninterrupted and continuous operation. With this background in mind, a study was undertaken to develop improved quality refractory castables for the manufacture of
pre-cast blocks to enhance the lining performance in VAD ladle covers.
2. Experimental During the initial study it was found that three pre-cast blocks surrounding the three electrodes and also the chute are the main vulnerable areas of the VAD ladle cover. Generally, the VAD ladle cover was declared down due to damage occurring in the precast blocks of the electrode area. On judging the s
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