EP1385656B1 - Method for continuously casting ingots, slabs or thin slabs - Google Patents

Abstract

A continuously cast strand is subjected to soft reduction between the guide rollers below the mold and between the soft reduction stretch and the mold the strand is subjected to format or thickness reduction between at least one pair of position controlled guide rollers so that independently of the quality of the steel, the casting speed and the spray cooling, the position of the type of the mold cavity and hence the molten steel therein is maintained constant along the soft reduction stretch.

Description

The invention relates to a method for the continuous casting of blocks, slabs or thin slabs in a continuous casting, the below a mold in mutually adjustable strand guide segments having acted example of weg- or position-controlled hydraulic cylinders roller pairs, wherein the casting strand by conically hiring at least one of its strand guide segments is reduced in thickness up to the sump tip soft reduction distance in the thickness and is subjected in the region of its liquid core between the mold and the soft reduction path (SR route) by at least one pair of rollers of a format thickness reduction.

In continuous casting plants for slabs, the soft reduction process (SR process) is used to reduce core porosity and core segregation.

In block systems, the soft reduction is preferably carried out in the straightener area. Prerequisite for an improvement in the internal structural quality is that the final solidification of the strand in the conically employed soft reduction (SR route) takes place. A final solidification in front of or behind the SR line not only leads to no improvement in the interior quality, but occasionally to a deterioration.

The conical roller adjustment of the strand guide segments is carried out either by a fixed setting by means of hydraulic cylinders and spacers, or by means of flexible employment, for example via position-controlled hydraulic cylinder.

The so-called operating window of the continuous casting plant, for example the adaptation of the casting speed and other casting parameters, the intensity of the spray cooling or the steel quality, is predetermined by the number of SR roller pairs and the type of employment. As the number of reels increases, the operating window can be increased. However, this increase is out of all proportion to the extra costs this entails. Furthermore, influencing the sump tip position by the spray cooling is only possible to a limited extent.

In a known method according to DE 41 38 740 A1, the strand passes through a soft-reduction route, at the entrance he is not solidified, but at the end he should be solidified, what u. a. the casting speed is an essential operating parameter. In the area of final solidification, a reduction in thickness, for example for thin slabs, between 0.5 and 3 mm per meter of casting length is carried out. For this purpose, the pairs of rolls of individual segments beyond the shrinkage behavior of the strand are set narrower in the soft reduction section, in order to achieve an improvement in the strand internal quality in the region of the solidification by structural compaction.

EP 0 834 364 A1 describes a method and an apparatus for high-speed continuous casting plants with a strand thickness reduction during solidification, wherein after the so-called casting rolling the strand cross section is reduced linearly over a minimum length of the strand guide immediately under the mold, with subsequent further strand production on the Remaining strand guide, the "soft reduction", until just before the final solidification or sump tip. By this procedural measure, the strand cross-section reduction is set so that a critical deformation of the strand shell, taking into account the high casting speed and steel grade is not exceeded.

EP 0 177 796 B1 discloses a method for guiding and straightening a cast strand in the straightening and outfeed area of a continuous sheet casting plant, wherein oppositely arranged rolls are held by a spring force against the ferrostatic pressure of the cast strand in a distance which can be adapted to the casting process. Here, a Gießstrangbereich increased strength is tracked and reduced in its passage between opposite rollers, the respective spring force by a small drag.

The slabs or blocks produced in continuous casting plants according to the aforementioned documents serve as starting material for rolling mill products for producing sheet metal or strip.

The invention has for its object to achieve an adaptation or enlargement of the operating window of a continuous casting to changing casting parameters and to obtain a comparatively constant optimal structure in the cast by influencing the silt peak location.

To solve the problem, in a method referred to in the preamble of claim 1 is proposed with the invention that by the number of pairs of rollers and their more or less close mutual employment in the liquid core of the casting a flexible adaptation of the casting process to the casting speed is made while the format thickness reduction of the casting strand with liquid core is adjusted so that regardless of steel quality, intensity of spray cooling and the casting speed, the position of the sump tip is kept approximately constant in the SR route.

In this case, for example, despite the increasing casting speed and / or changed spray cooling, the format thickness is reduced in such a way that the position of the sump tip in the SR section is kept practically constant. This is in a large casting speed range with low mechanical engineering Expense ensures a consistently good quality of the cast strand.

Thus, despite changing operating parameters during the casting process, a consistently optimal structure of the cast strand is achieved and avoided an unnecessarily increased burden of roles and their bearings within the strand guide.

The process ausgestaltend is provided that arrangement and / or employment of the roller pairs for the format thickness reduction in the region of the liquid core of the cast strand are determined in accordance with the Gießquerschnitt or format cross section of the cast strand.

Finally, the method according to the invention provides that the thickness reduction is carried out immediately before the SR section.

Thus, an adaptation or enlargement of the operating window of the continuous casting to changing casting parameters is achieved cost-effectively, and in particular an influence of the silt peak position largely independent of the Gießparametern guaranteed in such a way that the sump tip is always in a section of the SR route, the the required improvement in the internal quality of the cast strand leads. This ensures a consistently good cast strand structure in a large casting speed range with low mechanical complexity.

Details, features and advantages of the invention will become apparent from the following explanation of an embodiment schematically illustrated in the drawing.

1 shows a purely schematic representation of a strand guide below a mold with a configuration according to the invention and with a soft reduction path SR.

In the plant part of the strand guide according to Figure 1 is located below the mold, a first strand guide segment 2.1 for parallel strand guide.

The sketch-like representation of the strand 5 below the melt inlet 6 in the mold 1 shows a first approach of a forming strand shell. 8

According to the invention, the strand 5 is subjected to a size reduction in the region of its liquid core 7 between the mold 1 and the soft reduction section SR by at least one pair of rollers 4, 4 '. The reduction in size by the pairs of rollers 4, 4 'is followed by a strand guide segment 2.2 for parallel strand guidance of the cast strand 5. The pairs of rollers 4, 4' are each acted upon by displacement or position-controlled, not shown in detail hydraulic cylinders, so that they the hydrostatic pressures of the melt. 8 overcome and thereby a local format reduction or thickness reduction in the strand 5 z. B. 10 mm / m in the casting direction before the soft reduction path SR with a thickness reduction of, for example, 1 mm / m cause. In the casting direction below the soft reduction section another strand guide segment 2.3 for parallel strand guidance is arranged.

Number and employment of the roller pairs 4, 4 'in the region of the liquid core 7 of the cast strand 5 allow a flexible adaptation of the casting process to the casting speed or a change thereof.

Due to the thickness reduction of the strand 5 with liquid core depending on the casting parameters such as casting speed, steel quality, casting temperature, the format dimension is always adjusted so that the sump tip 9 largely independent of the aforementioned Gießparametern in a section of the SR track is, to the required Improvements in the internal quality of the cast strand leads. For example, with increasing casting speed or reduced spray cooling, the format thickness is reduced so that the position of the sump tip 9 is kept practically constant in the SR route. This ensures a consistently good internal quality of the cast product in a large casting speed range with low mechanical complexity.

Claims (5)

1. Method for the continuous casting of ingots, slabs or thin slabs in a continuous casting plant which comprises, below a mould (1), strip guide segments (2.1 to 2.n), which are settable at a mutual spacing, with roller pairs (4, 4') able to be acted upon by, for example, hydraulic cylinders regulable in travel or position, wherein the cast strip (5) in the case of a forming strip skin (8) is reduced in thickness by conical adjustment of at least one of its strip guide segments (2.1 to 2.n) in a soft reduction path (SR path) reaching up to the liquid phase end and is subjected to a format thickness reduction in the region of its liquid core (7) between mould (1) and the soft reduction path (SR path) by at least one roller pair (4, 4'), characterised in that a flexible adaptation of the casting process to the casting speed is undertaken through the number of roller pairs (4, 4') and the mutual adjustment thereof with greater or lesser tightness in the region of the liquid core (7) and in that case the format thickness reduction of the cast strip (5) with liquid core (7) is so set that the position of the liquid phase end (9) in the SR path is kept approximately constant independently of steel quality, intensity of spray cooling and the casting speed.
2. Method according to claim 1, characterised in that the arrangement and/or adjustment of the roller pairs (4, 4') for the format thickness reduction in the region of the liquid core (7) of the cast strip (5) is or are determined in accordance with the casting cross-section or format cross-section of the cast strip.
3. Method according to claim 1 or 2, characterised in that the format thickness reduction is undertaken directly ahead of the SR path.
4. Method according to one or more of claims 1 to 3, characterised in that the rollers (4) for the format thickness reduction of the cast strip (5) in the SR path are adjusted in position-regulated manner.
5. Method according to one or more of claims 1 to 4, characterised in that the rollers (4) for format thickness reduction of the cast strip (5) in the region of the liquid core (7) thereof are adjusted in position-regulated manner.