CONTINUOUS CASTING LINE HAVING INDIVIDUAL ROLLER ENGAGEMENT

Abstract

A continuous casting line, which has a mold for the output of a strand and a strand guide connected to the mold having a plurality of rollers arranged in pairs for transporting the strand in a conveying direction. One or more of the rollers can be engaged so that a thickness reduction of the strand occurs in the strand guide.

Claims

1-13. (canceled)

14. A continuous casting installation, comprising: a mold for delivering a strand; and a strand guide adjoining the mold, the strand guide having a number of rollers arranged in pairs for transporting the strand in a conveying direction, wherein at least one of the rollers is adjustable so that a reduction in thickness of the strand takes place in the strand guide, wherein the strand guide includes at least one exchangeable segment having a number of adjustable rollers arranged in pairs.

15. The continuous casting installation according to claim 14, wherein the rollers include first pairs of rollers that directly adjoin the mold, and pairs of reducing rollers that directly adjoin the first pairs of rollers in the conveying direction, the rollers of the first pairs of rollers being non-adjustable so that no reduction in thickness of the strand takes place in this region of the strand guide, at least one of the rollers of the pairs of reducing rollers being adjustable so that a reduction in thickness of the strand takes place in this region of the strand guide.

16. The continuous casting installation according to claim 15, wherein all of the rollers of the pairs of reducing rollers are adjustable.

17. The continuous casting installation according to claim 15, wherein the strand guide has two or three of the first pairs of rollers.

18. The continuous casting installation according to claim 17, wherein the strand guide has eight to fifteen of the pairs of reducing rollers.

19. The continuous casting installation according claim to 15, wherein the rollers also comprise last pairs of rollers that adjoin the pairs of reducing rollers in the conveying direction, are preferably adjustable, but do not lead to any further reduction in thickness of the strand.

20. The continuous casting installation according to claim 19, wherein the last pairs of rollers are adjustable.

21. The continuous casting installation according to claim 19, wherein the casting installation is configured so that during a regular casting process a lowest point of a liquid pool of the strand lies in a region of the last pairs of rollers.

22. The continuous casting installation according to claim 14, wherein the strand guide has a bending region in which the strand is bent. {00409382 } 6

23. The continuous casting installation according to claim 22, wherein the continuous casting installation is constructed as a vertical bending machine, in which the strand leaves the mold vertically downward, is guided downward by the strand guide and is subsequently at least partially deflected along an arc in a direction of horizontal and transported further.

24. The continuous casting installation according to claim 14, further comprising a withdrawal and straightening unit that adjoins the strand guide in the conveying direction, the withdrawal and straightening unit having a number of driven rollers and being configured to withdraw the strand from the strand guide and bend the strand completely into a horizontal orientation.

25. The continuous casting installation according to claim 14, wherein the adjustable rollers are hydraulically, magnetically or electromotively actuable.

26. The continuous casting installation according to claim 25, wherein the strand guide has at least one hydraulic cylinder in which a piston is hydraulically displaceable for adjusting the adjustable rollers.

27. The continuous casting installation according to claim 14, wherein the adjustable rollers are adjustable into precisely two positions, the two positions being an inactive position, in which no reduction in thickness of the strand takes place at the position concerned in the strand guide, and a reducing position, in which a reduction in thickness of the strand takes place at the position concerned in the strand guide.

28. A method for casting a strand with a device according to claim 14, comprising the steps of adjusting at least one of the rollers of the strand guide so that during casting a thickness of the strand is reduced in the strand guide.

29. The method according to claim 28, including reducing the thickness of the strand in the strand guide with the core of the strand not completely solidified.

30. The method according to claim 28, including adjusting the adjustable rollers taking process parameters into account and based on a temperature calculation model, with which temperature properties of the strand are determined.

31. The method according to claim 30, including determining a position of a lowest point of a liquid pool and/or a strand shell thickness.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0023] FIG. 1 schematically shows a continuous casting installation, designed as a vertical bending machine, with two strand guiding segments and a withdrawal and straightening unit for transporting the cast strand.

[0024] FIG. 2 schematically shows a continuous casting installation with adjustable rollers.

[0025] FIGS. 3a and 3b show hydraulic activation of adjustable rollers.

[0026] Detailed description of preferred exemplary embodiments

[0027] Preferred exemplary embodiments are described below on the basis of the figures. Elements that are the same, similar or act in the same way are provided with identical reference signs, dispensing to some extent with repeated description of these elements so as to avoid redundancies.

[0028] FIG. 2 schematically shows a continuous casting installation, the basic construction of which is similar to FIG. 1. The mold 1 is adjoined by the strand guide 2. At the outlet of the strand guide 2, the withdrawal and straightening unit 3 is provided, for withdrawing the strand S from the strand guide 2.

[0029] As a difference from the installation of FIG. 1, the strand guide 2 of the exemplary embodiment of FIG. 2 has only a single segment 23, even if according to other exemplary embodiments a number of segments may be provided. A continuous casting installation with only one segment 23 has a greater rigidity and can absorb the bending forces produced by the withdrawal and straightening unit 3 better than a continuous casting installation of the same length with a number of segments. In the case of a continuous casting installation with two or more segments, after a fault, such as for instance a break-out, it may possibly be necessary for all of the segments to be changed one after the other. The times taken to perform these changes are generally much shorter in the case of a continuous casting installation of which the strand guide 2 has only a single segment 23, since the entire strand guide 2 can be changed without segments having to be connected to one another. When connecting segments to one another, there is the risk that two adjacent segments are not connected exactly to one another. Contaminants, wear and/or incorrect alignment of the segments may lead to stresses in the strand S, which leads to an increased risk of cracking. These sources of defects can be reduced by a strand guide 2 with a single segment 23, for which reason this exemplary embodiment is preferredin particular with regard to a compact and low-cost installation.

[0030] The segment 23 has a number of rollers 24a, 24b, 24c (referred to jointly as rollers 24), which are arranged in pairs, whereby they (two rollers 24 are always facing one another) form a gap passageway, through which the strand S leaving the mold 1 downward passes along a curved path and is guided. The not yet solidified-through strand is accordingly first guided vertically downward, then deflected by the strand guide 2 along an arc and after that transported horizontally. During transport, a cooling of the strand S takes place, which may possibly be actively assisted and/or controlled by applying a cooling fluid.

[0031] The withdrawal and straightening unit 3 is arranged as part of a connecting system downstream of the segment 23 in the conveying direction F, in order to withdraw the strand S from the strand guide 2 and bend it completely into the horizontal. For this purpose, the withdrawal and straightening unit 3 has a number of rollers 31 arranged in pairs, which are driven rollers, for instance driven by one or more electric motors (not represented).

[0032] Even if other components have not been shown in FIG. 2 for the sake of overall clarity, the continuous casting installation of the present exemplary embodiment may have, as in FIG. 1, a separating device, a furnace, a dummy bar rocker, a rolling mill and/or further components.

[0033] As a difference from the continuous casting installation of FIG. 1, according to the present exemplary embodiment one or more rollers 24 of the strand guide 23 are adjustable, comprising in particular an adjustability during the casting operation. The adjustability is provided in such a way that one or more pairs of rollers can be moved together, whereby the transporting gap can be varied, in particular reduced, along the conveying direction F.

[0034] To distinguish between different groups of rollers of the strand guide 2, one or more pairs of rollers directly underneath the mold 1 are referred to as first pairs of rollers 24a. Pairs of rollers that follow in the conveying direction F are referred to as middle pairs of rollers or pairs of reducing rollers 24b. The remaining pairs of rollers of the strand guide 2, which lie directly before the withdrawal and straightening unit 3, are referred to as the last pair of rollers 24c. Since the rollers 24 of the strand guide 2 are generally arranged in pairs, the reference signs 24a, 24b, 24c are also used to refer to the rollers themselves of the pair concerned.

[0035] According to a particularly preferred exemplary embodiment, the first rollers 24a are non-adjustable, this first group of rollers preferably having two or three pairs of rollers 24a. The fact that the first pairs of rollers 24a are non-adjustable, i.e. are mounted in a fixed manner, means that fluctuations in the casting level can be prevented, and it is prevented that the strand S becomes detached from the mold wall.

[0036] The middle pairs of rollers 24b, for example 8 to 15 pairs of rollers, preferably 11 pairs of rollers, are adjustable individually or else in groups. In particular, they can be moved together, whereby the thickness of the strand S not yet solidified in the core is reduced in the strand guide 2. Starting for example from a thickness of 52 to 45 mm at the mold outlet, the thickness is reduced for instance to 32 to 35 mm, preferably to 20 mm, at the delivery of the strand guide 2.

[0037] The last pairs of rollers 24c, preferably for instance four pairs of rollers, are preferably also adjustable. However, this adjustment serves only for following the previously set strand thickness. In this case, no further reduction in thickness of the strand S takes place in the portion comprising the last pairs of rollers 24c.

[0038] By varying the casting speed and/or cooling rate, for instance the amount of spray water, the position of solidification right through (lowest point of the liquid pool) in the roller way is regulated, in particular is arranged such that complete solidification right through is not within the region of the middle pairs of rollers 24b. A reduction in thickness of the solidified-through strand would require much greater adjusting forces, whereby the risk of cracking would be increased.

[0039] The adjustment profile of the middle rollers 24b can be suitably established according to the degree of reduction, distance over which the reduction takes place, material of the strand S, etc. Thus, the reducing positions of the rollers 24b may for instance be distributed linearly or parabolically. If for example a strand with a thickness of 50 mm at the mold outlet is to be reduced to 34 mm in a linear way, with 11 reducing rollers 24b the reduction at each of the reducing rollers 24b is then 16 mm/11=1.4545 mm. At the first rollers of the middle rollers 24b, the reductions may also be slightly greater, and decrease parabolically or in some other way, so that at the last reducing roller 24b only a reduction of the strand thickness of approximately 1 mm takes place.

[0040] According to a constructionally simple, low-cost exemplary embodiment, represented in FIGS. 3a and 3b, the middle rollers 24b (possibly also the last rollers 24c) are movable into precisely two positions by hydraulic cylinders. In this case, in one position, the inactive position (FIG. 3a), no reduction in thickness takes place, while the thickness of the strand S at the corresponding pair of rollers 24b in the second position, the reducing position (FIG. 3b), is reduced.

[0041] In the exemplary embodiment of FIGS. 3a and 3b, a piston 25, on which a roller 24b or 24c is attached, is provided displaceably in a cylinder 26. By hydraulic activation, for instance by means of oil, the piston 25 can be moved back and forth between the inactive position and the reducing position. Both rollers of a pair of rollers 24b or else only one roller 24b of the pair may be adjustably designed. Preferably, only the rollers 24b, 24c on the loose side are adjustable. Furthermore, the adjustment of the rollers 24b, 24c may also be technically realized in some other way, for instance magnetically or electromotively. Moreover, in certain variants of the embodiment it may be advisable that one or more or all of the middle rollers 24b and/or last rollers 24c can be brought into more than two positions, in particular are adjustable in a stepless manner. Thus, according to a variable exemplary embodiment, the thickness of the strand can be reduced to different delivery thicknesses. Alternatively or in addition, a part of the segment frame, preferably the upper frame, may also be adjustably designed, whereby a number of rollers 24b, 24c are adjustable in groups for reducing the strand thickness. It is also the case here that preferably no reduction in thickness takes place at the first rollers 24a and last rollers 24c. According to a further exemplary embodiment, two rollers or pairs of rollers 24a, 24b, 24c may also be respectively combined in a cassette; these rollers can then possibly be adjusted individually or together.

[0042] The reduction in thickness described above in the strand guide 2 allows the rolling mill 7 to be designed more compactly. Typically, the rolling mill has a number of, for example five, rolling stands (passes). In this case it is possible for at least one rolling stand to be omitted. As a result, the installation as a whole can be produced altogether more compactly, and possibly also at lower cost. Alternatively, with a conventional design of the rolling mill 7, a greater reduction in thickness of the strand S can be achieved. It should be pointed out that less energy is required for the compressing of the strand S that is still liquid in the core than would be required in the rolling mill if the reduction in thickness in the strand guide 2 were not used. This technical effect leads to an energy saving and to a further cost reduction, both in terms of the operating costs and in terms of the procurement costs. A further technical advantage of the reduction in thickness of the strand S in the strand guide 2 is that the thickness of the strand does not have to be minimized at the end of the mold. It has already been explained that, for various reasons, the strand cannot be as thin as desired at the end of the mold. Depending on the material and the process parameters, this limit typically lies at approximately 45 mm. The further the thickness of the strand at the mold approaches this limit, the greater the risk of break-outs becomes. The reduction in thickness in the strand guide 2 can consequently lead to an improvement in production reliability if the strand thickness at the mold is chosen greater, without thereby lessening the overall reduction in thickness at the delivery of the rolling mill 7. Furthermore, the internal quality of the strand can be improved, since the afterflow of liquid molten metal is reduced by the reduction in thickness in the strand guide 2, whereby undesired segregations are reduced.

[0043] A conventional continuous casting installation without a reduction in thickness in the strand guide 2 can be retrofitted with adjustable rollers 24b, 24c. Exchanging one or more segments of a conventional strand guide for one segment 23 that contains the adjustable rollers 24b, 24c allows the retrofitting to be performed in a modular manner. Thus, smaller delivery thicknesses from the strand guide 2, and as a result thinner final dimensions at the delivery of the hot rolling mill 7, can be obtained at a subsequent time by procuring segments with individual roller adjustment. If thinner final dimensions are only to be produced occasionally, it is possible to work with a number of non-adjustable segments 21, 22 and only to install the adjustable segment 23 (by analogy a number of adjustable segments) in the case of production of the particularly thin dimensions. Alternatively, the adjustable segment 23 (by analogy a number of adjustable segments) may be permanently installed, the adjustable rollers 24b, 24c only being moved into the reducing position in the case of the production of the particularly thin dimensions and otherwise being in the inactive position.

[0044] A method for reducing the thickness of the strand in the strand guide 2 according to an exemplary embodiment is described below:

[0045] The continuous casting installation is started in a conventional way with the aid of a dummy bar. As soon as the dummy bar is uncoupled and possibly stowed away by the dummy bar rocker 6, the thickness of the strand can be reduced. If the bar head (for example of 52 to 45 mm) is too thick for the rolling mill 7, the non-reduced bar head (for example of 4 m in length, which corresponds to the length of the casting machine, i.e. the distance between the mold 1 and the delivery of the strand guide 2) can be broken down into scrap in the separating device 4. The adjustable reducing rollers 24b of the strand guide 2 subsequently reduce the strand S not yet solidified through in the core. If required, the position of the lowest point of the liquid pool and the strand shell thickness at all of the positions of the rollers may be calculated by a temperature calculation model. The lowest point of the liquid pool refers here to the position of the strand S in the transporting direction at which the still liquid core goes over into the solidified-through region. Since the strand S solidifies at the surface first and the temperature increases from the outside inward, the liquid core has approximately the form of a cone in the conveying direction, with the tip of the cone being referred to as the lowest point of the liquid pool. The casting speed and cooling rate, preferably the amount of spray water, are then regulated such that the lowest point of the liquid pool is displaced forward into the region of the last pairs of rollers 24c. There, the thickness of the strand is not reduced any further. If the already solidified-through strand S were compressed, the adjusting forces required would increase greatly and there would be the risk of internal cracks. The average temperature at the entrance of the furnace 5 is all the greater the closer the lowest point of the liquid pool gets to the end of the casting machine, i.e. to the delivery of the strand guide 2. When the withdrawal and straightening unit 3 is reached, the strand S is preferably completely solidified through.

[0046] The fact that the continuous casting installation is regulated such that the lowest point of the liquid pool is in the region of the last rollers 24c means that an optimum reduction in thickness can be achieved in the strand guide 2, since all of the reducing rollers 24b are active, which would not be the case with a strand S that has solidified through too early.

[0047] Variable activation of the reducing rollers 24b allows different strand thicknesses to be cast, and the distribution of the reduction can be adapted to the process values at the particular time. This is useful since the distribution of the reduction is preferably chosen such that greater reductions take place in the region with a still completely liquid core (Liquid Core Reduction LCR) than in the region with the first dendritic growth in the core (soft reduction). In this way, the risk of internal cracks can be reduced. Since the positions of the liquid boundary and the lowest point of the liquid pool change dynamically with the process values (casting speed, analysis, overheating, casting level, amounts of water, water temperature, etc.), a dynamic temperature calculation model is preferably used for the calculation thereof. With the reduction in the strand guide 2, the last reduction is preferably not so far away from the mold 1 that there can no longer be any afterflow of molten metal.

[0048] To the extent that they are applicable, all of the individual features that are represented in the exemplary embodiments can be combined with one another and/or exchanged with one another without departing from the scope of the invention.

LIST OF REFERENCE SIGNS

[0049] 1 Mold

[0050] 2 Strand guide

[0051] 3 Withdrawal and straightening unit

[0052] 4 Separating device

[0053] 5 Furnace

[0054] 6 Dummy bar rocker

[0055] 7 Rolling mill

[0056] 21,22,23 Segments of the strand guide

[0057] Rollers of the strand guide

[0058] 24a First rollers/pairs of rollers

[0059] 24b Reducing rollers/pairs of reducing rollers

[0060] 24c Last rollers/pairs of rollers

[0061] 25 Piston

[0062] 26 Hydraulic cylinder

[0063] 31 Rollers of the withdrawal and straightening unit

[0064] S Strand/slab

[0065] F Conveying direction