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Manufacture of massive castings in the Metallurgy Division


Early in June 2018, electric steelworks staff succeeded in casting the first of three massive castings of cross girders for the BONATRANS modernization project. The whole story, however, began much earlier. Thanks to long-term and successful negotiations of the representatives of the sales department and the management of the company, we managed to get a prestigious contract for the modernization of the BONATRANS wheel rolling mill. The contract includes, among others, a press for which the manufacture of very massive semi-products is required, in this case the cross girder castings. The original structure and technology of pouring the cross girders was so massive that there was a need to outsource the castings. Consequently, the designers and developers of the Engineering Division have designed and verified a new, lighter design of the cross girder itself (see the picture) and the technologists of the Metallurgy Division have optimized the technology of pouring to minimize the casting risering. The result of this close cooperation between the two divisions was the reduction of the gross weight of the castings including all technological allowances to 83 tons (upper girder), 88 tons (movable girder) and 90 tons (lower girder). So, these weights are not record-breaking for the Metallurgy Division. For the most massive lower girder, the “2015” record was only repeated, when a middle girder having gross weight of 90 tons was poured for the Engineering Division. Unique, however, is that the pouring of all three massive castings took place over a short period of time – over five weeks. Each of the cast pieces had to cool down in the sand mould to which it was poured for two weeks from a casting temperature approaching 1600° C down to a temperature of 500° C. Then the castings were pulled out of the moulds and transferred to air cool. Then the finishers removed the gating and dressed the casting to be able to heat-treat it at a temperature of about 900° C. After partial cooling from this annealing temperature, so called risers and pockets were flame-cut off the casting, and now, at the ambient temperature, both the grinding of the surfaces and the dressing are done. From this stage of production, there is a photo of the upper girder casting you see in the picture. In order for the casting material to achieve the required mechanical properties, the heat treatment is another important manufacturing step that for this type of steel consists of normalization and tempering to the required strength. In the following period, the girder castings will be gradually roughed in the Engineering Division, returned to the Metallurgy Division to repair any defects detected by non-destructive testing. Before Christmas 2018, all the pieces should be back at the Engineering Division ready for final machining. Appreciation and thanks for well-done and professional work go to all technicians and workers involved in this prestigious engagement.