EP0329639A1 - Process and machine for continuously casting steel - Google Patents

Abstract

In a method for continuously casting steel, molten metal is poured vertically into moulds to form a strand with an elongate cross-sectional shape and allowed to solidify during its passage through the mould. <??>In order to be able to produce a thin strand in an efficient manner, the strand (S2) is first of all cooled, the cross-section remaining the same, until a solid shell (S4), thoroughly solidified especially in the regions (S3) of the narrow sides, has formed, whereupon the strand (S5) is progressively deformed and compressed during further cooling and solidification, to form a flat preliminary strip. <IMAGE>

Description

The invention relates to a process for the continuous casting of steel, after which the melt is cast vertically in molds into a strand with an elongated cross-sectional shape and allowed to solidify during the mold passage, and to a continuous casting installation for carrying out this method.

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, and on the other hand, because of the necessary sliding movement of the strand within the mold and the strand shell, which is still not very resilient for to ensure the best possible 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-sectional reduction and, accordingly, also require expensive and complex systems. Known moving molds, which avoid a relative movement between the strand and the mold wall, are possible Ben the stationary molds compared to an increase in the casting speed and thereby allow the strand thickness to be reduced to about 100 to 150 mm thickness while the casting performance remains the same, whereby 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 allow the thin slabs to be fed directly to a rolling 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 a direct control of the slabs to a rolling mill. In addition, the difficult sealing of the Kokil lenhohlraumes, due to the wear on the sliding plate parts, 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.

The invention is therefore based on the object of eliminating these deficiencies and of specifying a method of the type described at the outset which ensures particularly economical casting of a thin strand suitable for direct further processing. In addition, a low-cost and functionally reliable continuous casting plant is to be created which is ideally suited for carrying out this process.

The invention solves this problem essentially in that the strand is first cooled with a constant cross-section until a solid shell is formed, in particular solidified in the narrow side areas, whereupon the strand is progressively deformed and pressed into a flat strip during further cooling and solidification . The strand can therefore be cast with a sufficiently large cross-section, for example with a thickness of approx. 150 mm, and remains undeformed until a suitably strong and resilient shell is properly formed, so that the casting process, the start of solidification and the initial shell formation can proceed completely without any problems. Only when a sufficient shell thickness has been achieved, which above all prevents the strand from tearing open laterally, is the strand deformed to the desired flat support strip, for which purpose lateral strand guidance is then unnecessary and a simple, opposite, equal width of the strand to the desired strip-shaped front end product leads. The strand solidifies during the deformation, and pressing together to form a flat strip guarantees that the shell halves lying on top of one another are finally welded together. Strip thicknesses of up to approx. 20 mm can be achieved without difficulty at casting speeds of 27 to 30 m / min and the pre-strip can therefore also be fed directly and with sufficient throughput to a rolling mill which only requires three stands to produce wide strip.

It is advantageous if, according to the invention, a strand is cast with a parallelogram cross section, the deformation and compression of which then takes place in the direction of the smaller cross section height. Such a parallelogram-shaped cross section results in a large central area corresponding to the use of conventional pouring tubes and also brings along narrow converging sides along the longer diagonal, which favor the formation of a rigid shell in these areas. Apart from that, this parallelogram cross section can be compressed into a plane-parallel band without too much change in shape.

According to a development of the invention, a rational continuous casting installation for carrying out this method results from the combination of a first mold with a constant cavity cross section and a second mold downstream of this with a decreasing cavity cross section. By using such a pair of molds, the two process steps of the strand formation and the strand deformation are carried out in separate devices, which enables a special approach to the respective process step and allows an optimal adaptation of each device to the process step to be carried out.

According to a particularly favorable constructive embodiment of the invention, the first mold used is a moving plate mold known per se, which consists of a pair of opposing, endlessly rotating plate chains which delimit between the mold cavity, and that the second mold, designed as a stationary mold, continues the plate chains has two wall parts delimiting between the mold cavity, which are mounted so as to be pivotable about transverse axes lying in the inlet region, the mold cavity merging from an input cross-section corresponding to the output cross-section of the first mold into a flat-plane-parallel output cross-section. Depending on the strand throughput speed and the solidification speed, the moving first mold can be of any length, for example 3000 mm long, so that a shell thickness of 10 mm can be achieved at the mold outlet at the desired high casting speed of, for example, 27 m / min. Due to the moving plate chains there is no sliding friction and the high ferrostatic pressure results in favorable heat transfer conditions between the strand and the mold, so that the required shell thickness is actually guaranteed despite the high casting speed. The strand emerging from the moving plate mold is then taken over by the reducing but stationary mold, which, with its appropriately adjusted wall parts, performs the required cross-sectional reduction. The wall parts can be swiveled so that the stationary mold can be opened at the start of casting in order to avoid faults when the first strand is passed. The wall parts are then placed on the strand and brought into the respective reducing position via the actuators, with no lateral closure in the reducing mold of the mold cavity is required and the design effort for this mold can remain relatively low. The strand then leaves the reducing mold as a flat pre-strip with a thickness of about 20 mm and with a flow rate of 27 to 30 m / min, so that this pre-strip is suitable for immediate tapping of a rolling mill, both in terms of its thickness and its outlet speed. In addition, the casting performance achievable in this way corresponds to the required performance of a broadband rolling mill and thus the supply of such a broadband rolling mill is possible by a single continuous casting installation according to the invention, for which two slab continuous casting installations were previously necessary.

If, according to the invention, the plates of the two plate chains which are assigned to one another in pairs are angled and complement one another in cross section to form a parallelogram, the plates being supported against one another with an edge web butting against the other plate, and the wall parts of the stationary mold are divided into several individual longitudinal beams, which each have their own actuators, preferably hydraulic drives, result in particularly good conditions for carrying out the continuous casting process. The cast strand is produced by the plate chains with a parallelogram-shaped cross section, which on the narrow sides, corresponding to the edge webs, already has a dimensioning adapted to the desired thickness of the preliminary strip and can be easily deformed into a flat preliminary strip. The plates 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, the wall parts can also be adjusted exactly here to the respective cross-sectional shape of the strand possible. 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.

If the bars are equipped with rows of rollers arranged one behind the other, offset from one bar to the next, there is an improvement in the friction in the reducing mold, and the offset rollers, which therefore have an overlapping effect, ensure proper strand deformation.

In order to be able to adapt the rollers to different strand cross-sections and, above all, to the respective deformation profile, they are mounted in adjustable bearing blocks on the beams, whereby the height and inclination of the roller axes of rotation can be changed using these bearing blocks with the aid of spacers or the like .

If nozzles or the like are provided between the bars and the rollers for introducing a coolant, the cooling and solidification process can be influenced during the passage of the strand through the second mold and, if necessary, matched to the deformation process.

Since, due to the space requirement of the molds, a certain free space remains between the first and second molds, a strand guide bridging this free space can be provided according to a further development of the invention, which preferably consists of two shell parts and has rollers and cooling slots or the like. The strand leaving the moving mold is transferred safely and supported to the stationary mold by this strand guide, 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, by pressure welding, ensure a unification of the core parts which 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 a variety of cross-sectional sizes by a mutual 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 Pouring speed and the desired shell thicknesses can be achieved without difficulty by appropriate selection of the mold length at the given solidification speeds.

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 beams 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 adjust 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 a smooth transition from parallelogram to flat cross-section can be achieved. 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 start-up scrap from the preliminary strip S₆ by means of appropriate cutting devices 8 before the preliminary strip is then or the like with a straightening punch 9. is fed to the deflection and support rollers 6 for proper withdrawal, so that the lack of cross-sectional reduction at the start of the casting is irrelevant.

Claims (10)

1. A process for the continuous casting of steel, after the melt is cast vertically in molds into a strand with an elongated cross-sectional shape and is allowed to solidify during the mold passage, characterized in that the strand is first cooled with a constant cross-section until a solid, especially in the narrow side areas through solidified shell is formed, whereupon the strand is progressively deformed and pressed together during the further cooling and solidification to a flat preliminary strip. 2. The method according to claim 1, characterized in that a strand is cast with a parallelogram cross-section, the deformation and compression then takes place in the direction of the smaller cross-sectional height. 3. Continuous casting plant for carrying out the method according to claim 1 or 2, characterized by the combination of a first mold (2) with a constant cavity cross section and a second mold downstream of this (3) with a decreasing cavity cross section. 4. Plant according to claim 3, characterized in that the first mold (2) is a known moving plate mold, which consists of a pair of opposing, between the mold cavity (21) delimiting, endless plate chains (22), and that the second mold (3) designed as a stationary mold has, in continuation of the plate chains, two wall parts (32) delimiting the mold cavity (31) between them, which are pivotably mounted about transverse axes (34) lying in the inlet area, the mold cavity (31) from a the initial cross section the first mold (2) corresponding input cross section merges into a flat-plane-parallel output cross section. 5. Plant according to claim 4, characterized in that the pairs of plates (23) of the two plate chains (22) are angled and complement each other in cross section to form a parallelogram, the plates (23) each having one on the other plate Support butt-fitting edge web (24) against one another, and that the wall parts (32) of the stationary mold (3) are divided into several individual longitudinal beams (33), each of which has its own actuating drives (35), preferably hydraulic drives. 6. Plant according to claim 5, characterized in that the bars (33) with lined up, from bar to bar staggered rollers (36) are equipped. 7. Plant according to claim 6, characterized in that the rollers (36) are mounted in adjustable bearing blocks (37) on the beams (33). 8. Installation according to one of claims 5 to 7, characterized in that between the bars (33) and the rollers (36) nozzles (38) or the like. Are provided for introducing a coolant. 9. Installation according to one of claims 3 to 8, characterized in that a free space between the first and second mold (2, 3) bridging strand guide (4) is provided, which preferably consists of two shell parts (41) and rollers (42) and cooling slots (43) or the like. 10. Plant according to one of claims 3 to 9, characterized in that the second mold (3) is arranged downstream of a pair of transverse press rolls (5).

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