EP0329639B1 - Process and machine for continuously casting steel - Google Patents

Description

The invention relates to a continuous casting plant for the continuous casting of steel, with a first mold having a cavity cross-section that remains constant in the strand direction and a deformation device downstream thereof, preferably a second mold that has a cavity cross-section that decreases in the strand direction.

In conventional continuous casting with stationary molds, on the one hand, due to the need for strong heat dissipation through the mold and the resulting intensive contact between the strand and the mold, on the other hand, because of the required sliding movement of the strand within the mold and the strand shell, which is still not very resilient for to ensure the most favorable friction conditions, only achieve low casting speeds, about 1.5 to 5 m / min and only use very short, about 900 mm long molds. In order to still be able to achieve economical casting performance despite these very restrictive requirements, strands with large thicknesses, for example strand thicknesses of 210 mm, must be selected so that the slabs or blooms resulting from this continuous casting are enormous in the subsequent further processing into broadband with a thickness of only a few millimeters Cross-section reduction and, accordingly, also require expensive and complex systems. Known moving molds, which avoid a relative movement between the strand and the mold wall, allow the stationary molds compared to an increase in the casting speed and thereby enable the strand thickness to be reduced to about 100 to 150 mm thickness, while the conventional pouring tube dimensions require a corresponding inlet cross section of the mold and make it impossible to go below these strand thicknesses without a reducing mold. The slabs that can be produced with the constant mold cross-section also remain too thick and prevent a more thorough rationalization of the further processing.

There are also stationary molds with a reducing cavity to produce thin slabs, but because of the small inlet cross-section special pouring funnels are to be used and the strand leaving the mold has only a thin shell, which requires additional support and cooling. In addition, this mold cannot be used to achieve casting speeds that would allow the thin slabs to be fed directly to a roller mill.

For the continuous casting of thin slabs with a thickness of approx. 50 mm, a reducing mold has also already been proposed, which is designed as a moving plate mold made of conically converging plate chains, whereby a large inlet cross-section adapted to the pouring tube dimensions during the mold passage is reduced to a correspondingly reduced initial cross-section. Although this reducing mold enables the production of relatively thin slabs under normal casting conditions, the achievable casting speeds remain too low for mechanical and metallurgical reasons for direct control of the slabs to a rolling mill. In addition, the difficult sealing of the mold cavity causes agitation the signs of wear on the sliding plate parts, the susceptibility to failure and the like. very high demands are placed on the mold construction and it is questionable whether the simultaneous solidification and deformation of the strand does not lead to metallurgical defects.

Continuous casting plants have also been proposed which use a combination of a first mold with a constant cavity cross section and a downstream second mold. with reducing cavity cross-section, wherein the first mold can have a rectangular cross-section (JP-A-597464, from which the preamble of claim 1 is based) or also an oval or central bulged cross-section (GB-A-1199805). The bulged cross section offers space for a pouring tube without having to make the entire cross section correspondingly thick. Relatively flat slabs can be produced at high casting speeds, but when a strand cast in this way is deformed, irregular changes in shape and different stretching and elongation occur across the cross-section, which inevitably impairs the structure and reduces the quality.

The invention is therefore based on the object of eliminating these deficiencies and improving a continuous casting installation of the type described in such a way that the economical casting of a thin strand of the best structural quality suitable for direct further processing is possible with comparatively little construction effort.

The invention solves this problem in that the cross section of the first mold has essentially the shape of a flattened parallelogram and that this cross section in the deformation device or the second The mold decreases in the direction of the smaller cross-sectional height until a plane-parallel strip cross-section is reached at the initial cross-section of the shaping device or the second mold. This cross-sectional shape offers sufficient space in the center area for the proper use of conventional pouring pipes and, thanks to the narrow converging sides, ensures the desired rapid staring of the edge shell. In addition, however, the entire cross-sectional width is recorded when the cross-section is deformed, and the prerequisites for an optimal end product are created.

A structurally advantageous embodiment results if the first mold is a moving plate mold, which consists of a pair of opposing, endlessly circulating plate chains that delimit between the mold cavity, and if the second mold, designed as a stationary mold, continues the plate chains two between has wall parts delimiting the mold cavity, which are pivotably mounted about transverse axes lying in the inlet area. According to the invention, the plates of the two plate chains of the first mold, which are assigned to one another in pairs, are bluntly angled and complement each other to form a parallelogram, the plates being supported against one another with an edge web placed on the other plate on the end face, and the wall parts of the stationary mold are divided into several Divided longitudinal beams, each with their own actuators, preferably hydraulic drives, result in particularly good conditions for the continuous casting itself. The cast strand is produced by the plate chains with a parallelogram cross section, which on the narrow sides, corresponding to the edge webs, is already one of the Desired thickness of the support strip has adapted dimensions and easily to one flat support strip can be deformed. The plates which are assigned to one another in pairs can also be adjusted transversely to the direction of passage in order to be able to change the cross-sectional dimensions. By dividing the stationary mold into individual longitudinal beams, an exact adaptation of the wall parts to the respective cross-sectional shape of the strand is also possible here. Apart from this, the strand is deformed into strips by the individual bars during the passage, which enables the desired cross-sectional reduction with minimal effort.

Are the longitudinal beams equipped with lined up, staggered from bar to bar rollers, which are preferably stored in adjustable pedestals, and are nozzles or the like between the bars and the rollers. provided for introducing a coolant, there is an improvement in the friction in the reducing mold and the staggered and therefore overlapping rollers ensure proper strand deformation. The adjustable bearing blocks make it possible to adapt the rollers to different strand cross-sections and, above all, to the respective course, whereby the height and inclination of the axis of rotation of the rollers can be changed by means of intermediate blocks or the like. A use of coolant in turn makes it possible to influence the cooling and solidification process during the passage of the strand through the second mold and, if necessary, to adapt it to the deformation process.

Since, due to the space requirement of the molds, a certain free space remains between the first and second molds, according to a development of the invention, a strand guide bridging this free space can be provided, which preferably consists of two shell parts and rollers and cooling slots or the like. The strand leaving the moving mold is safely supported by this strand guide and transferred to the stationary mold so that there are none There are faults and there can be no cracking of the strand shell. The strand guide has a constant cross section, is preferably in two parts for assembly and maintenance and can be equipped with rollers and cooling slots or the like to improve the friction and cooling conditions.

In order to ensure that a solidified pre-strip with a uniform thickness and good structure leaves the continuous casting plant, a pair of transverse press rolls is arranged downstream of the second mold, which, through pressure welding, ensure a unification of the core parts that have solidified during the deformation and the compressed shell parts.

• Fig. 1 eine erfindungsgemäße Stranggießanlage in einem Anlagenschema, die
• Fig. 2 und 3 Schnitte nach den Linien II-II bzw. III-III der Fig.1 durch die erste Kokille bzw. die Strangführung dieser Anlage in größerem Maßstab, die
• Fig. 4 und 5 die zweite Kokille der Stranggießanlage im Längsschnitt und in Draufsicht ebenfalls größeren Maßstabes sowie die
• Fig. 6 und 7 Querschnitte nach den Linien VI-VI und VII-VII der Fig.4.

In the drawing, the subject matter of the invention is illustrated purely schematically using an exemplary embodiment, namely show

• Fig. 1 shows a continuous caster according to the invention in a system diagram, the
• 2 and 3 sections along the lines II-II and III-III of Figure 1 by the first mold or the strand management of this system on a larger scale, the
• 4 and 5, the second mold of the continuous caster in longitudinal section and in plan view also on a larger scale and the
• 6 and 7 cross sections along the lines VI-VI and VII-VII of Fig.4.

The continuous casting installation shown for the rational production of a flat strip is composed of a casting device 1, a first mold 2 and a downstream second mold 3, a strand guide 4 inserted between the molds, and a pair of press rolls 5 adjoining the second mold 3 together. The casting device 1 consists of a reservoir 11 for receiving the steel melt S₁ and a pouring tube 12, through which the melt S₁ enters the mold cavity 21 of the first mold 2. This first mold 2 is a moving plate mold made of a pair of opposing endlessly circulating plate chains 22 which delimit the mold cavity 21 which has a constant cross section. The plate mold 2 is manufactured per se in a conventional design, the plates 23 of the two plate chains 22, which are assigned to one another in pairs, being angled and complementing one another in cross section to form a parallelogram. The plates 23 are each in one piece and support one another with an edge web 24, which edge webs 24 abut against the plate inner walls delimiting the mold cavity 21 (FIG. 2). The result is a simple, stable, functionally reliable and failure-prone plate mold which can be adjusted in width to different cross-sectional sizes by mutually transverse displacement of the plate chains 22.

The melt S₁ is now cast in the first mold 2 to a strand S₂ constant, approximately parallelogram-shaped cross section, which cools during its passage through this moving plate mold 2 until a solid shell S₄, especially in the narrow side areas S₃, has already solidified . The mold cavity 21 is large enough to be able to penetrate with the pouring tube 12 to below the melt level in the mold cavity 21, and the moving mold 2 allows intensive contact between the strand and the mold for rapid heat dissipation, with the best possible friction conditions, so that high temperatures under proper casting conditions Casting speeds and by appropriate selection of the mold length at the given solidification speeds, the desired shell thicknesses can also be achieved without difficulty.

The strand S 2 leaving the first mold 2 now enters the second mold 3, the strand guide 4 ensuring a functionally reliable and trouble-free transition of the strand from the first to the second mold. To simplify assembly and maintenance, the strand guide 4 is composed of two half-shells 41 which limit a constant guide cross section corresponding to the outlet cross section of the mold 2. To improve the frictional conditions 41 rollers 42 can be inserted into the half-shells 41 and suitably distributed cooling slots 43 allow a corresponding heat dissipation and strand cooling.

In contrast to the first mold 2, the second mold 3 adjoining the strand guide 4 is a stationary mold and has a narrowing mold cavity 31. To limit this mold cavity 31, there are two wall parts 32, each of which is divided into a plurality of longitudinal beams 33, each of which Longitudinal beam 33 is pivotally mounted about a transverse axis 34 located in the entry area and is pivotally supported by an actuator 35. By appropriately positioning the bars 33, a mold cavity 31 is created, which changes from a parallelogram-shaped input cross-section (FIG. 6) corresponding to the guide cross-section of the strand guide 4 into a flat, plane-parallel output cross-section (FIG. 7), so that the strand S₅ during its passage through the stationary one Mold 2, proceeding from a parallelogram cross section striding into a flat supporting strip S Vor is deformed and compressed.

To reduce friction, the beams 33 are equipped with rollers 36 arranged in series, an offset of the rollers 36 from beam to beam having an overlapping mode of operation. In order to be able to adapt the position of the rollers to the course of the deformation and to the respective strand cross-sections, there are adjustable bearing blocks 37, so that the transition from parallelogram-shaped to flat cross-section can be achieved as evenly as possible. In order to influence the heat dissipation and the rate of solidification during the passage of the strand through the mold 3, nozzles 38 for applying a coolant are provided between the bars 33 and the rollers 36.

Since the strand S₅ entering the second mold 3 already has a solid shell S₄ solidified on the narrow side regions S₃, the reducing mold 3 need no longer have side boundary walls and it suffices for the limitation of the reducing mold cavity 31 by the opposite wall parts 32.

The flat compressed pre-strip S₆ is then passed to the second mold 3 between press rolls 5, which ensure a compact structure of the pre-strip and ensure a secure connection of the pressed shell parts due to the press weld 5 achievable with these press rolls.

The preliminary strip S₆, which leaves the continuous casting plant with a correspondingly thin cross section and sufficient speed, is deflected via guide and support rollers 6 and can be fed directly to a rolling mill 7, of course for the necessary control and straightening devices, control device or the like, not shown. to be worried.

To start up the continuous casting plant, the reducing mold 3 is opened in order to avoid faults due to the first passage of the strand through the narrowing mold cavity 31. Only after the end of the strand has passed through the mold 3 is this activated by acting on the actuators 35 for the beams 33 until the desired cross-sectional reduction is achieved. The beginning of the strand S₇ is separated as starting scrap from the preliminary strip S₆ by means of appropriate cutting devices 8 before the preliminary strip or the like with a straightening punch 9. is fed to the deflection and support rollers 6 for a proper take-off, so that the lack of cross-sectional reduction at the start of casting is irrelevant.

Claims (5)

1. A continuous casting plant for the continuous casting of steel, comprising a first chill mould having a cavity cross-section which remains constant in the direction of casting, followed by a shaping means, more particularly a second chill mould (3) having a cavity cross-section which decreases in the direction of casting, characterised in that for strip casting the cross-section of the first chill mould (2) basically has the shape of a parallelogram and in that this cross-section decreases in the shaping means or second chill mould (3) in the direction of the smaller cross-sectlonal height until a plane-parallel strip cross-sectlon is obtained at the outlet cross-section of the shaping means or second chill mould (3).

2. A continuous casting plant according to claim 1, characterised in that the first chill mould (2) is a co-moving plate mould consisting of a pair of opposite endlessly revolving plate chains (22) defining the mould cavity (21) between them, the plates (23) associated with one another in pairs in the two plate chains (22) being bent at an obtuse angle, complementing one another to form a parallelogram, and bearing on one another in each case by an edge web (24) bearing on the end of the other plate, and in that the second chill mould (3), which is constructed to be stationary, comprises two wall parts (32) defining the mould cavity (31) between them, the wall parts (32) being divided up into a number of pivotally mounted longitudinal bars (33), each engaged by its own adjustment drive (35), preferably a hydraulic drive.

3. A continuous casting plant according to claim 2, characterised in that the longitudinal bars (33) are equipped in known manner with rollers (36) disposed consecutively and in a staggered arrangement from one bar to the next, said rollers being mounted preferably in adjustable bearing brackets (37), and in that nozzles (38) or the like for introducing a coolant are provided between the bars (33) and the rollers (36).

4. A continuous casting plant according to any one of claims 1 to 3, characterised in that a continuous casting guide (4) which bridges the free space between the first and second chill moulds (2, 3) is provided and preferably consists of two halves (41) and comprises rollers (42) and cooling slots (43) or the like.

5. A continuous casting plant according to any one of claims 1 to 4, characterised in that the second chill mould (3) is followed by a pair of transverse press rolls.

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