Patent Application
20200254513
The invention relates to a continuous casting installation, which has a mold for delivering a strand and a strand guide, adjoining the mold, with rollers arranged in pairs. The invention also relates to a method for casting a strand by means of such a device.
The structure and the operating principle of the continuous casting installation of
The withdrawal and straightening unit 3 may be regarded as part of a connecting system that is provided between the strand guide 2 and a rolling mill 7 for rolling the cast strand S. The connecting system may also have a separating device 4 for dividing the strand S into slabs of a certain length, a furnace 5, to adjust the temperature of the strand S homogeneously and bring it to a temperature suitable for rolling, and a dummy bar rocker 6. If a dummy bar rocker 6 is provided, for starting the installation a dummy bar can be transported to the furnace 5 and deposited there.
A continuous casting installation of the type described above is described in DE 10 2015 210 865 A1. DE 10 2015 215 187 A1 also describes a comparable melt-metallurgical installation with a mold and a strand guide.
For low annual production or for other reasons, for instance in the case where it is used in a difficult environment or for reasons of cost or when producing special alloys, it may be advisable to design the installation more compactly and at lower cost with regard to procurement and operation. In order to make the installation of the type described above smaller, the two segments 21, 22 may possibly be replaced by a single segment, which is equipped with pairs of rollers in order to transport and bend the strand leaving the mold before it enters the withdrawal and straightening unit.
One problem that stands in the way of making the installation smaller is that the strand cannot be as thin as desired when it leaves the mold. The distance between the immersion pipe and the mold wall must not be too small, in order that the liquid metal can circulate in the mold. The immersion pipe itself must have a minimum diameter in order not to become clogged too quickly. Furthermore, the dummy bar that is transported up to the mold from the delivery side for starting the installation has a minimum thickness that generally cannot go below 40 mm. The fact that, for all these reasons, the strand cannot be cast as thin as desired has the effect that the rolling mill cannot be simply designed more compactly, since the rolling mill must be capable of rolling the slabs cast with a certain minimum thickness to the desired target thickness.
An object of the invention is to improve a continuous casting installation of the type described above, in particular to provide a continuous casting installation (by analogy a method) which, while retaining functionality, can be designed particularly compactly and/or can be operated in an energy-saving manner and/or has a high level of operational reliability and casting quality.
The object is achieved by a continuous casting installation with the features of claim 1 and a method with the features of claim 11. Advantageous developments follow from the subclaims, the following summary of the invention and the description of preferred exemplary embodiments.
The continuous casting installation according to the invention serves for casting a strand in the melt-metallurgical sector, i.e. a strand of a metal, in particular a metal alloy, preferably steel. The installation is preferably designed as a vertical bending machine, but may also be of a different form of construction. Thus, the installation may for example also be designed as a bow-type installation or vertical slab caster. The continuous casting installation has a mold, which may be configured as a funnel mold. The mold is designed to deliver the strand, preferably perpendicularly downward when seen in the direction of gravity. For this purpose, the mold is fed the molten metal to be cast and it is brought into the desired form of a strand or slab by the mold, in that the not yet solidified-through strand is discharged out of a correspondingly shaped outlet opening of the mold. The mold is adjoined by a strand guide, which has a number of rollers arranged in pairs for transporting the strand in a conveying direction. The rollers arranged in pairs respectively form a gap and altogether form a gap passageway, through which the strand passes in the conveying direction. According to the invention, one or more of the rollers of the strand guide are adjustable such that a reduction in thickness of the strand takes place in the strand guide. In other words: the rollers concerned of the strand guide are adjustable such that, during the regular casting process, the thickness of the strand leaving the mold is already reduced in the strand guide, preferably before it has solidified through completely.
The reduction in thickness of the strand in the strand guide allows a rolling mill that may be present, adjoining the strand guide or a connecting system in the conveying direction, to be designed more compactly. Typically, such a rolling mill has a number of, for example five, rolling stands (passes). Using the reduction in thickness according to the invention in the strand guide allows at least one rolling stand to be omitted. As a result, the installation as a whole, consisting of the continuous casting installation, connecting system and rolling mill, can be produced altogether more compactly, and possibly also at lower cost. Alternatively, with a conventional design of the rolling mill, a greater reduction in thickness of the strand can be achieved. It should be pointed out that less energy is required for the compressing of the strand that is still liquid in the core than would be required in the rolling mill if the reduction in thickness in the strand guide 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 in the strand guide is that the thickness of the strand does not have to be minimized at the end of the mold. It was stated in the section entitled “Background of the invention” that, for various reasons, the strand cannot be as thin as desired at the end of the mold. The further the thickness of the strand at the mold approaches this minimum limit, the greater the risk of break-outs or other production defects becomes. The reduction in thickness in the strand guide can consequently lead to an improvement in operational reliability if the strand thickness at the mold is chosen generously, without thereby lessening the overall reduction in thickness at the delivery of the rolling mill. 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.
Preferably, the rollers of the strand guide comprise first pairs of rollers, which directly adjoin the mold, and pairs of reducing rollers, which directly adjoin the first pairs of rollers in the conveying direction, the rollers of the first pairs of rollers being non-adjustable, as a result of which no reduction in thickness of the strand takes place in this region of the strand guide, i.e. a region that directly adjoins the mold. According to this preferred embodiment, the reduction in thickness consequently only commences “later”, once the strand has run through the first pairs of rollers. As a result, fluctuations in the casting level can be prevented, and it is prevented that the strand becomes detached from the mold wall, whereby the operational reliability is improved further. A good compromise between operational reliability, compactness and reduction in thickness is achieved if the strand guide has two or three first pairs of rollers and eight to fifteen pairs of reducing rollers.
Preferably, the rollers of the strand guide also comprise last pairs of rollers, which 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. According to this embodiment, no further reduction of the strand thickness takes place in the last portion of the strand guide, for example before the strand is taken up by the rollers of a withdrawal and straightening unit. Preferably, the installation is controlled such that, during regular casting, the lowest point of the liquid pool of the strand lies in the region of the last pairs of rollers. The lowest point of the liquid pool refers here to the position of the strand in the conveying direction at which the still liquid core goes over into the solidified-through region. Since the strand 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.
If the strand guide is adjoined in the conveying direction by a withdrawal and straightening unit, which has a number of driven rollers and is designed to withdraw the strand actively from the strand guide, the strand is preferably solidified through when it reaches the withdrawal and straightening unit.
Preferably, the strand guide has a bending region, in which the strand is bent. If the continuous casting installation is constructed as a vertical bending machine, the strand leaves the mold vertically downward, is guided downward by the strand guide and is subsequently deflected along an arc. In this case, the strand does not have to be bent completely into the horizontal within the strand guide. The remaining bending into the horizontal takes place in the withdrawal and straightening unit. After that, the strand may be further transported horizontally, in order to run through further stations, such as for instance a withdrawal and straightening unit, a separating device for dividing up the strand into slabs of a certain length, a furnace and a rolling mill.
Preferably, the strand guide has one or more exchangeable segments, each with a number of rollers arranged in pairs. In this way, a conventional continuous casting installation without a reduction in thickness can be retrofitted in an easy way with a strand guide of the type described. Exchanging one or more segments of a conventional strand guide for one or more segments with adjustable rollers allows the retrofitting to be performed in a modular manner. Thus, smaller delivery thicknesses from the strand guide, and as a result thinner final dimensions at the delivery of a rolling mill that may be present, 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 and only to install an adjustable segment (by analogy a number of adjustable segments) in the case of production of the particularly thin dimensions. Alternatively, the adjustable segment (by analogy a number of adjustable segments) may be permanently installed, the adjustable rollers only being moved into a reducing position in the case of the production of the particularly thin dimensions and otherwise being in an inactive position without a reduction in thickness.
Preferably, the adjustable rollers are hydraulically, magnetically or electromotively actuable. According to a particularly preferred embodiment, the strand guide has one or more hydraulic cylinders, in each of which a piston is hydraulically displaceable for adjusting an adjustable roller attached thereto. By hydraulic activation, for instance by means of oil, the piston can be moved back and forth between the inactive position and the reducing position. Both rollers of a pair of rollers or else only one roller of the pair may be adjustably provided. Moreover, in certain variants of the embodiment it may be advisable that adjustable rollers 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 frame part of the aforementioned segment (by analogy a number of segments) of the strand guide may also be adjustably designed, whereby a number of rollers are adjustable in groups for reducing the strand thickness.
The method according to the invention concerns the casting of a strand by means of a device of the type described above, one or more rollers of the strand guide being adjusted such that, during the regular casting process, the thickness of the strand is reduced in the strand guide. The technical effects, preferred embodiments and contributions to the prior art that have been described with respect to the device apply analogously to the method.
The adjustment profile of the rollers can be suitably established according to the degree of reduction, distance over which the reduction takes place, material of the strand, etc. Thus, the reducing positions of the rollers may for instance be distributed linearly or parabolically, so that the reduction in thickness takes place linearly or parabolically along the strand guide.
According to a particularly preferred embodiment, the reduction in thickness of the strand takes place with the core not solidified through, which makes energy-saving operation of the installation possible and also contributes to an improvement of the casting quality.
Preferably, the adjustable rollers are adjusted with process parameters taken into account and on the basis of a temperature calculation model, with which temperature properties of the strand, for instance the position of the lowest point of the liquid pool and/or the strand shell thickness, can be determined.
Further advantages and features of the present invention can be derived from the following description of preferred exemplary embodiments. The features described therein can be implemented individually or in combination with one or more of the features set forth above, in as far as the features are not mutually exclusive. The following description of the preferred exemplary embodiments is performed with reference to the appended drawings.
Detailed description of preferred exemplary embodiments
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.
As a difference from the installation of
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.
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).
Even if other components have not been shown in
As a difference from the continuous casting installation of
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.
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.
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.
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.
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.
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.
According to a constructionally simple, low-cost exemplary embodiment, represented in
In the exemplary embodiment of
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.
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.
A method for reducing the thickness of the strand in the strand guide 2 according to an exemplary embodiment is described below:
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.
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.
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.
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.
1 Mold
2 Strand guide
3 Withdrawal and straightening unit
4 Separating device
5 Furnace
6 Dummy bar rocker
7 Rolling mill
21,22,23 Segments of the strand guide
Rollers of the strand guide
24
a First rollers/pairs of rollers
24
b Reducing rollers/pairs of reducing rollers
24
c Last rollers/pairs of rollers
25 Piston
26 Hydraulic cylinder
31 Rollers of the withdrawal and straightening unit
S Strand/slab
F Conveying direction
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2017 219 464.2 | Oct 2017 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/076879 | 10/2/2018 | WO | 00 |
