Metallurgist, Vol. 44, Nos. 1-2, 2000

N E W SOLUTIONS I N C O N T I N U O U S CASTING*

A. L. Liberman

Resonance Mold. The main shortcomings of all lever-operated and four-cam oscillators are the imprecise movement of the mold and the deviations from the prescribed oscillation parameters. The tirm Mannesman Demag Metallurgy (MDM) has developed a new type of mold oscillation system that is free of these problems and can be used for vertical and radial molds. The mold is supported and directed by springs. The outside ends of the springs are secured to a stationary frame, while their inside ends are affixed to the oscillating parts of the mold. This design eliminates air gaps and ensures precise movement of the mold. The hydraulic cylinders of the system are mounted directly on the oscillating parts of the mold, which obviates the need tor reduction gears and bearings - the possible reason for the different types of deviations in mold movement seen in other systems. The use of a resonance mold significantly reduces the weight of the moving equipment: the only parts that vibrate are the water-cooled jacket, the copper walls, the equipment of the narrow walls, and the rollers. The hydraulic drive makes it possible to control the oscillation parameters and the amplitude, frequency, and mode of vibration during casting. The company M D M has modified the resonance mold to allow its use on existing continuous casters. The new mold makes it possible to improve the quality of the surface of cast slabs.

In comparison tests performed at the Zalgitter plant

(Austria) of the firm Preussag Stahl, a visual evaluation of the surface of cast slabs of different grades of steel confirmed the advantages of the resonance mold: the number of nondefective ingots cast through the new mold and a conventional mold was 72 and 49%, respectively; when austenitic corrosion-resistant steel AISI 304 was cast through the resonance mold, there was an 18-53% reduction in the depth of the vibration tracks. The number of heats that were able to be cast before the narrow walls of the mold had to be reconditioned increased from 450 to 1100. Optimization of F l o w s of the Melt in the Mold. The velocity and configuration of the flows of metal in the mold and in the liquid pool of a continuous-cast ingot have a significant effect on the quality of the surface and the intemal structure of semifinished products. To optimize these flows, mathematical and hydraulic modeling was used to develop a special design of submersible nozzle. The design was developed on the basis of three conditions: 9 the formation of a smooth metal surface free of waves and disturbances in the mold during casting; 9 maintenance of a unilorm and constant configuration of the flows in the liquid pool; 9 minimization of the depth of penetration of the stream of molten metal into the liquid pool. A nozzle of the new design (Fig. 1) was tested on continuous caster No. 1 at the factory of Zalgitter AG in the casting of 100 series of heats (an average of five steel-pouring ladles were used in each series). In contrast to conventional submersible nozzles - which have two lateral discharge holes - the new nozzle ensures very low flow velocities in the meniscus region, with no waves being tbrmed on the surface of the metal inside the mold. The depth of penetration of the stream was decreased by shortening the displacement zone from 6.5 to 2.5 m when changing over from one heat to the next. The same could be achieved with a conventional submersible nozzle only by resorting to electromagnetic deceleration of the flow. The new nozzle also improves the structure of the axial region and reduces the incidence of surface cracks on the cast slabs. Sections with Spatially Linked F r a m e s (SLF-Seetion). In the sections of the new design (Fig. 2), the top frame is secured to the bottom frame by special rods. This obviates the need for side frames and gaskets. The use of a hydraulic drive %

From materials prepared by Edmund Becker, Rfidiger Heine, and Pr. Marc Walter (Mannesmann Demag, Germany): Materials of the 3rd European Conference on Continuous Casting. October 20-23, 1998. pp. 901-922. Translated from Metallurg, No. 1, pp. 42-43, January, 2000.

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0026-0894/00/0102-0030525.00 02000 Kluwer Academic/Plenum Publishers

Fig. 1. Submersible nozzle designed by the company MDM.

Fig. 2. Section with spatially linked frames (SLF-section).

Fig. 3. Diagram of dynamic light reduction with the use of SLF-sections (v 1, v2 - casting speeds).

makes it possible to regulate the distance between the rollers to maintain the required conicity, which in turn makes it possible to subject the metal to light dynamic reduction during the casting of different grades of steel with the use of different speeds and secondary cooling (Fig. 3). H i g h - S p e e d Casting of Semifinished Sections.

Tests on the high-speed casting of steel were conducted on the

six-strand continuous caster at the Nova Huta plant (in the Czech Republic) in the casting of semifinished products with a cross section of 130 • 130 mm. Casting speed was increased from 2.5 to 5.0 m/min when an open stream was used, while it was increased to 4.8 m/rain when the molten metal was introduced under the surface of the bath. Thus, the throughput of the unit was increased by nearly 100%. To achieve this result on the sixth strand, the following measures were implemented: 9 the length of the mold was increased from 700 to 1000 ram, and the working space was given the form of a parabolic cone;

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9 the flow velocity of the coolant water for the mold was increased from 9 to more than 14 m/sec by increasing the size of the gap between the sleeve and the jacket and increasing water pressure and discharge; 9 the sensitivity of the transducer that senses the level of the metal in the mold was increased by increasing the power of the radioactive emitter; 9 the rate of secondary cooling was increased by increasing the number of nozzles, the length of the torced-cooling zone, and water pressure and discharge; 9 the velocity of the mold was increased. Continuous Casting of Blooms with the Use of Light Reduction. The quality of the finished product is improved and one costly operation - the annealing of blooms - is eliminated by subjecting the steel to light reduction in the semi-solid state while constantly monitoring its temperature and mixing it in the mold. Porosity and macroscopic segregation in blooms are reduced as a result of compensation for the difference in the volumes of the liquid and solid phases during compression of the continuous-cast ingot at the final stage of its solidification. The company MDM has developed equipment for such light reduction and installed it on a six-strand caster at the Ruhrort plant in Duisburg. The caster was designed to cast blooms with a cross section of 265 • 385 mm. The new unit consists of five stands, each of which can reduce the ingot by 3 mm. Trial use over two years has shown the technology to be efficient: the number of breaks of cord wire occurring in the course of its production from the continuous-cast metal decreased by 60%, and a sharp reduction in axial segregation was seen in the casting of bearing steel 100Cr6. Continuous Casting of Semifinished Products That Are Close in Form to the Final Product. On the three-strand unit ProfilABED at Differdange (in Luxembourg), MDM has developed a technology for the continuous casting of I-beams with dimensions of 500 • 400 x 100, 690 x 450 x 130, and 1119 • 500 • 132 mm. Here, the maximum casting speeds have been 1.3, 1.0, and 0.8 m/min, respectively. The quality required of the semifinished products was obtained by implementing the following measures: limitation of the temperature of the metal being cast; the use of a slag of moderate viscosity in the mold; treatment of the melt with calcium-silicon on a ladle-furnace unit; proper positioning of the submersible nozzles in the mold. The production of I-beams from continuous-cast semifinished I-beams might increase useable output by 20% compared to the output attained by using conventional ingots cast in ingot molds.

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