Siemens VAI Metals Technologies completely modernized an over 20-year-old, single-strand slab caster at the steel works of the Slovenian producer Acroni, d.o.o. The machine head and strand-guiding system were replaced and outfitted with the latest technological packages, systems and equipment to enable wider slabs be cast with a significant improvement in quality.
All onsite construction activities were completed in the Spring of 2009 within a tight timeframe of only 38 days. Plant start-up proceeded smoothly and all casting equipment and systems functioned as designed beginning with the first heat. Following fulfillment of the guaranteed performance figures for various steel grades, the Final Acceptance Certificate was received within 2 months after the plant start-up.
According to Emil Subelj, Acroni Project Manager and Deputy Steel Plant Manager, "Through the modernization of our continuous slab-casting machine we have acquired one of the most advanced machines of its kind in the world, which increases our production potential. This new acquisition enables us to cast wider slabs and increase our productivity in casting new types of steel using modern control and cooling systems."
The slab caster is capable of casting approximately 515,000 tons of steel per year comprising medium- to high-carbon, peritectic, structural, micro-alloyed, stainless steel (series 300 and 400) and Si grades. Slabs can be cast at thicknesses of 200 and 250 millimeters and in hot widths from 800 to 2,120 millimeters. (The previous maximum casting width was 1,560 mm.) The caster is equipped with a curved mold and the casting radius is 10.36 m.
Siemens VAI responsibilities for this project included the design, manufacture, delivery, supervision of installation, start-up and commissioning of the caster as well as personnel training. The project scope also involved civil and erection work, integration of new and existing equipment, the supply and installation of electrics, technological packages, Level 1 and Level 2 automation systems in addition to the media, hydraulic and lubrication systems. The existing top-feeding dummy-bar system with a chain-type dummy bar was modified for reuse. The caster workshop area was improved with new maintenance stands. Greater personnel safety is assured with the installation of safety guards which prevents operators from entering the cooling chamber during casting.
The supplied technological packages and other special features of the caster include the replacement of the previous mold with a Siemens VAI Smart Mold which, in combination with DynaWidth technology, allows the mold narrow sides to be hydraulically shifted for the flexible casting of strands of different widths. The use of so-called Smart Segments installed in the bow, straightening and horizontal zones of the caster allow the roller-gap settings to be remotely adjusted for fast slab-thickness changes. I-Star Rollers (intermediately supported trans-axle rollers) installed throughout the strand-guiding system provide ideal strand-shell support required for assuring high slab quality. Other technological packages installed in the Acroni caster are: LevCon - for the automatic and precise mold-level-control; MoldExpert for enhanced strand-break-out protection; and DynaFlex for the on-line adjustment of the mold-oscillation parameters. With the fully automatic and dynamic Level 2 Dynacs secondary-cooling model, the stand-temperature profile and the required secondary cooling-water quantities can be calculated at any position along the strand as the basis for defining the optimum secondary-cooling setpoints and final point of strand solidification. Improved internal strand homogeneity for the production of highest quality slabs is made possible with DynaGap Soft Reduction technology. This is achieved through the exact adjustment of the roller taper in the area of final strand solidification according to the Dynacs-calculated setpoints. An integrated quality management system is the basis for consistent high-slab quality.
The Slovenian steel producer Acroni d.o.o. is located in Jesenice, about 60 km northwest of the capital of Ljubljana. In 2008 the company produced a total of 375,700 tons of flat-rolled stainless, electrical, structural and special steels which were sold as hot- and cold-rolled coils, heavy plates and cold-formed profiles, primarily for special niche products.