US20060010679A1

US20060010679A1 - Apparatus for continuously producing a rolled metal strip from a metal melt

Info

Publication number: US20060010679A1
Application number: US11/203,777
Authority: US
Inventors: Gerald Hohenbichler; Gerald Eckerstorfer
Original assignee: Voest Alpine Industrienlagenbau GmbH
Current assignee: Primetals Technologies Austria GmbH
Priority date: 2001-10-24
Filing date: 2005-08-15
Publication date: 2006-01-19
Also published as: EP1446242B1; KR100879847B1; EP1446242A1; AT410767B; CA2463962C; ES2336434T3; TWI226267B; WO2003035291A1; BR0213544B1; CN1272118C; US20050082030A1; ZA200402699B; AU2002349346B2; MXPA04003757A; DE50214057D1; KR20040045909A; US6973956B2; UA80956C2; ATE450323T1; ATA16892001A

Abstract

The invention relates to a method and to a device for producing a rolled metal strip from a molten metal by producing a cast metal strip in a strip casting device and then rolling the undivided metal strip in a roll stand to the final thickness of the strip. For controlling the course of the strip, strip guiding devices are provided upstream of the roll stand. In order to provide a stable insertion of the metal strip into the roll stand at the input side of the roll stand or at the site of rolling in accordance with the strip dimensions, the strip guidance interferes or is carried out at a distance of 1.0 to 10.0 times the strip width, preferably at a distance of 1.5 to 5.0 times the strip width, upstream of the roll stand.

Description

The invention relates to a process for continuously producing a rolled metal strip from a metal melt, in particular a steel strip, in which, in a first production step, melt is introduced into a strip-casting device, and a cast metal strip with a strip thickness of less than 20 mm, preferably between 1 mm and 12 mm, and a predetermined strip width is removed from the strip-casting device, and in a second, subsequent production step, the cast, undivided metal strip is roll-deformed in at least one rolling stand until it reaches its final strip thickness, the metal strip being positioned in the roll nip by a strip diversion mounted upstream of the rolling stand. The invention also relates to an apparatus for carrying out this process, and to a method for starting up this installation.
A process of this type and a corresponding apparatus for producing a rolled steel strip from a steel melt, in which a thin cast strip is produced using the two-roller casting process using a two-roller casting device, and is hot-deformed directly from the hot casting stage in a direct further processing step carried out in a rolling stand, are already known from EP-B 540 610 and EP-A 760 397.
Furthermore, it is known from EP-B 540 610 to provide pinch roll stands at a plurality of locations in the production installation, in order to ensure reliable transportation of the cast strip from the two-roller casting machine to the strip-winding device. A diverting roll for adjusting the strip conveying after it leaves the looping pit is also provided immediately downstream of the two-roller casting installation and before the first pinch roll stand. This first pinch roll stand is intended to prevent transverse migratory movement of the strip in the installation. However, this is only possible within a limited conveying section. Furthermore, pinch roll stands are positioned upstream and downstream of trimming shears, in order to keep the steel strip under tension during longitudinal trimming.
EP-A 760 397 has likewise disclosed a two-roller casting installations with a downstream rolling stand for in-line deformation of the metal strip. According to one of the embodiments described, a pair of pinch rolls is mounted at a distance upstream of the rolling stand, in order to keep the cast strip under tension on the entry side of the rolling stand, and in addition a dancer rolls is positioned in a strip loop, between the pair of pinch rolls and the rolling stand, in order to avoid a meandering strip path when it enters the rolling stand (FIG. 3). According to a further embodiment, a plurality of diverting or pinch rolls are arranged, and required, at a successive distance from one another in a temperature-controlled region upstream of the rolling stand, in order to avoid this disruptive strip path (FIG. 7).
Therefore, it is an object of the invention to avoid these described drawbacks of the prior art and to propose a process and an apparatus which ensure for the metal strip that a stable strip entry to the rolling stand is provided on the entry side of the rolling stand or the location of rolling deformation, as a function of the strip dimensions, with little outlay on equipment.
In a process of the type described in the introduction, this object is achieved by virtue of the fact that the strip diversion takes effect or is carried out at a distance of 1.0 times to 10.0 times the strip width, preferably at a distance of 1.5 times to 5.0 times the strip width, upstream of this rolling stand. It has been possible to establish a fundamental relationship between the strip width of the metal strip which is to be rolled and the optimum location for use of the strip-diverting measures, insofar as the diversion measures can be carried out at a greater distance upstream of the rolling stand in the case of wider strips. If the strip diversion takes place too close to the rolling stand, unstable performance (e.g. overshooting characteristics, excessively extended edges, etc.) of the strip diversion must be expected. On the other hand, the strip also runs off-center if the strip-diversion measures take place at an excessively great distance upstream of the rolling stand. In this case, the diversion effects are lost again even before the rolling stand is reached.
An optimum strip path is established if the metal strip, in a region upstream of the rolling stand, between a strip-diverting device and the roll nip, is held under a strip tension of between 2.0 MPa and 15 MPa, preferably between 4.0 MPa and 8.0 MPa. If the strip tension is too low, the strip runs off-center, for example as a result of compressive stresses on one side. This manifests itself through instability, e.g. through the strip wobbling. On the other hand, the risk of the strip cracking rises as the strip tension increases. Since the strip temperature is kept high in this region, the strength of the metal strip is correspondingly lower, and therefore so is the acceptable compressive force which can be applied to the metal strip without the pinch rolls producing indentations therein.
To accurately control the center position of the strip, it is necessary for the actual lateral deviation of the metal strip from the predetermined strip-running direction to be recorded, preferably close to the location where the strip diversion acts on the metal strip, and for the position of actuators of the strip-diverting device to be controlled as a function of this parameter.
The strip path can be additionally stabilized if the metal strip is held under a strip pretension in a region upstream of the strip-diverting device. The strip tension can be kept at a lower level in this region than in the subsequent entry region to the rolling stand and serves predominantly to settle and support the metal strip emerging from the casting machine. Preferably, the strip pretension is produced or set by means of the intrinsic weight of the metal strip hanging down in a looping pit. Alternatively, the strip pretension can be produced or set by a braking force which acts in the opposite direction to the strip-running direction.
The strip path can be further stabilized if a strip-running centering aid acts on the metal strip, upstream or downstream of the location of the rolling deformation, at a distance from the location of action of the strip diversion which corresponds to 1.0 times to 10.0 times the strip width, preferably 1.5 times to 5.0 times the strip width. This is important in particular in the operating phases in which the rolling stand is open, i.e. in which no rolling deformation of the metal strip is taking place, in particular in the start-up phase of the production sequence. At the same time, the strip-running centering aid serves as a fixed point for the strip center-position control, in order to be able to sufficiently center the strip despite the low strip tensions.
To produce a cast metal strip with a strip thickness of less than 20 mm, preferably between 1 mm and 12 mm, and a hot-rolled metal strip formed in a continuous production process, the invention also proposes an installation, comprising a strip-casting device, preferably a two-roll casting machine, and at least one downstream rolling stand for in-line roll forming of the cast, undivided metal strip, as well as a strip-diverting device arranged between the strip-casting device and the rolling stand. This installation is characterized in that the strip-diverting device is arranged at a distance of 1.0 times to 7.0 times the strip width, preferably at a distance of 1.5 times to 5.0 times the strip width, upstream of the rolling stand. This strip-diverting device is preferably formed by a multi-roll driver, preferably by a two-roll driver.
An advantageous refinement of this installation, with the advantages described above, results if metal-strip conveyor means, preferably the pinch rolls of a multi-roll driver, which interact with adjustment and control devices and by means of which the setting of a strip tension of between 2.0 MPa and 10 MPa, preferably between 4.0 MPa and 7.0 MPa, between the strip-diverting device and the rolling stand or the strip-running centering aid or another unit in the strip-running line can be predetermined, are arranged in the strip-diverting device.
Optimum action on the strip path is achieved if the strip-diverting device is assigned a strip-position measuring device, and metal-strip conveyor means, preferably the pinch rolls of a multi-roll driver, are arranged in the strip-diverting device, at least one of the metal-strip conveyor means being supported rotatably in a bearing device which can pivot about an axis, these means interacting with control devices for influencing the strip-running direction. The pivotable axis is preferably oriented vertically as a vertical axis or parallel to the strip-running direction.
According to an advantageous embodiment, the strip-diverting device itself forms the pivotable bearing device, and the latter is supported displaceably on guides and connected to an adjustment drive, which is preferably a coupling mechanism. Other mechanical, electromechanical, hydraulic or electrohydraulic drives are also possible. The guides may be formed by four-bar linkages or other kinematic mechanisms, rails, bars, rolls, etc.
In order to position the strip-diverting device at the appropriate distance upstream of the rolling stand, as a function of the strip width of the strip-diverting device, the strip-diverting device is supported on guides, and a displacement device for the strip-diverting device is arranged between strip-diverting device and guides. The guides are oriented parallel to the strip-running direction.
To achieve optimum strip running, it is also proposed that a device for producing a strip pretension in the metal strip is arranged between the strip-casting device and the strip-diverting device. This device may, for example, be formed by a looping pit, in which case it is substantially the length of the loop hanging down which determines the strip tension. In addition, the strip loop hanging down acts as a damping element between the two-roll casting device and the rolling stand, with the result that disruptive feedback between the successive process steps is avoided. According to another embodiment, the device for producing a strip pretension is formed by a strip-supporting device which is preferably horizontal and subject to friction, in particular a roller table with braking rolls. Simple, immobile, mechanical supporting elements which are subject to friction may be provided between the braking rolls or at the location thereof. In this case, it is the length of the strip-supporting device which determines the strip tension, the active length of the strip-supporting device amounting to at least 1.5 times the strip width, preferably at least 2.5 times the strip width. The active length is the length of the roller table fitted with braking rolls.
To maintain the diverting function in the region of the rolling stand, in particular with the roll nip open, it is proposed that a strip-running centering aid, preferably a non-divertible two-roll or three-roll driver, is arranged downstream of the rolling stand or between the strip-diverting device and the rolling stand. The strip-diverting device and the strip-running centering aid are arranged at a distance of 1.0 times to 10.0 times the strip width, preferably at a distance of from 1.5 times to 5.0 times the strip width, from one another. It follows from this that the rolling stand and the strip-diverting device are positioned very close together if the strip-running centering aid is located downstream of the rolling stand, and that the rolling stand and the strip-diverting device are further apart from one another if the strip-running centering aid is positioned upstream of the rolling stand.
To ensure that the production process or installation is run up in a stable way during the starting phase, a start-up method for the installation is proposed, this method being characterized by the following method steps:

- the cast metal strip which leaves the strip-casting device is passed through the installation and threaded into the strip-coiling device substantially at a strip-running velocity, with the roll nip of the rolling stand open, which corresponds to the casting rate,
- a controlled strip tension is set between a strip-diverting device and a strip-running centering aid connected upstream of the rolling stand or a strip-running centering aid connected downstream of the rolling stand or the strip-coiling device,
- simultaneously or subsequently a controlled strip diversion is applied at a distance upstream of the rolling stand,
- the working rollers of the rolling stand are set to a roll nip which corresponds to the final strip thickness, and
- the rolling speed is matched to the casting rate.

The controlled strip diversion is in this case applied to the metal strip, which is under strip tension, at a distance, which corresponds to 1.0 times to 10.0 times the strip width, preferably 1.5 times to 5.0 times the strip width, of the cast metal strip, upstream of the rolling stand. The controlled strip tension between the strip-diverting device and the strip-coiling device or a strip-running centering aid is advantageously kept at a value of between 2.0 MPa and 15 MPa, preferably between 4.0 MPa and 8.0 MPa. This strip tension is applied even before the working rollers are moved onto the cast metal strip, i.e. before the rolling operation commences, and is maintained during the rolling operation.
Further advantages and features of the present invention will emerge from the following description of non-restrictive exemplary embodiments, in which reference is made to the appended figures, in which:
FIG. 1 diagrammatically depicts the installation according to the invention in a first embodiment,
FIG. 2 diagrammatically depicts the installation according to the invention in a second embodiment,
FIG. 3 shows a preferred embodiment of the strip-diverting device according to the invention.
In the embodiments shown in FIGS. 1 to 3, which are described below, identical components are denoted by identical reference symbols.
FIGS. 1 and 2 show an installation according to the invention for the continuous production of a rolled metal strip 1 from a metal melt 2, in which, in a first production step, a cast metal strip 3 is produced from the metal melt, and in a second production step, which directly follows the first, the cast metal strip 3 is subjected to hot deformation in a rolling process. The rolled metal strip 1 produced in this manner is then wound up into coils 4 of predetermined weight, if appropriate after having undergone a controlled cooling process, which is not described in more detail in the context of the present invention.
A strip-casting device 5 whose strand-forming core unit is formed by a single belt, running horizontally at the underside, or a plurality of revolving belts, caterpillars or mold walls, is used to produce the cast metal strip with a strip thickness of between 1.0 and 20 mm. FIG. 1 diagrammatically depicts, as one possible embodiment, a two-roller casting machine 6 which is formed by two casting rollers 8, 8′, which rotate about horizontal axes 7, 7′, and together with side walls 9 which are pressed onto the casting rollers at the end sides forms a mold cavity 10 for receiving the metal melt 2, which is supplied via a tundish 11. In a fast-moving solidification process, the cast metal strip 3 is formed in a casting nip 12 between the casting rollers 8, 8′ and is conveyed out at the bottom. The cast metal strip 3 is then diverted into the horizontal and passes through a device 15 for producing a strip pretension, which is formed by a looping pit 16. The strip loop 17 hanging down in the looping pit 16 also compensates for temporary, production-related differences in speed in the strip as it runs between the strip-casting device 5 and the rolling stand 18. The length of the strip loop 17 hanging down exerts a gentle pretension on the cast metal strip 3 and ensures stabilized, uniform strip running to the downstream strip-diverting device 19.
In a further embodiment, which is diagrammatically depicted in FIG. 2, the device 15 for producing a strip pretension and therefore the pretension acting on the metal strip is realized by a horizontally oriented strip-supporting device 20 which decelerates the cast metal strip 3 sliding over it. This braking action is produced by braking rolls 22 mounted in the roller table 21 of the strip-supporting device 20, a roller table length L which corresponds to 1.5 times to 2.5 times the strip width of the cast metal strip 3 being sufficient for this purpose.
The strip-diverting device 19 is equipped with adjustable metal-strip conveyor means 26 formed by pinch rolls 24, 25. In accordance with FIG. 1, the strip-diverting device 19 is designed as a two-roll driver 27 and is arranged at a distance A, which is partly determined by the width of the cast metal strip 3, upstream of the rolling stand 18. This distance A is in a range which amounts to 1.0 times to 10.0 times the strip width. The stand frame 28 of the strip-diverting device 19 is supported on guides 29, which may be configured as sliding guides or roller guides, and is moved into the predetermined position, which is dependent on the strip width (distance A), by a displacement device 30, which is designed as a pressure cylinder and engages on the stand frame 28 on one side and on the guides 29 on the other side. Furthermore, the pinch rolls 24, 25 of the two-roll driver 27 exert a braking force on the metal strip passing through the working rollers 32, 32′ of the rolling stand 18, this braking force corresponding to a strip tension of between 2.0 MPa and 15.0 MPa.
The strip-diverting function can be performed using various embodiments of the strip-diverting device 19 in conjunction with a strip-position center control.
According to the embodiment illustrated in FIG. 1, the adjustable pinch roll 24 is supported rotatably in a pivotable bearing device 33 and is coupled to a corresponding adjustment and control device 34 and to a strip-position measuring device 35 in order for it to be positioned. The strip-position measuring device 35 is arranged close to and downstream of the strip-diverting device 19. It is also possible for the strip-position measuring device to be positioned upstream of the strip-diverting device. This strip-position measuring device is used to record the deviation of the metal strip from the predetermined strip-running center and to transmit a corresponding signal to the adjustment and control device 34. The pivoting movement of the bearing device 33, which results in an inclined position of the axis 36 of a pinch roll 24 in relation to the axis 37 of the further pinch roll 25 (rotary adjustment in the direction indicated by the arrow) or of both pinch rolls (24, 25) supported in a common bearing device in relation to the instantaneous strip-running direction, this inclined position amounting to at most a few degrees, allows the cast metal strip 3 to be oriented to the predetermined strip-running direction R and thereby ensures that the metal strip passes centrally through the downstream rolling stand 18.
FIG. 2 diagrammatically depicts an embodiment in which controllable compressive forces are applied to the pivotable bearing device 33 of the pinch roll 24 in the direction indicated by the arrow, preferably in the region of the opposite bearing locations of the pinch roll in the pivotable bearing device 33. The transverse forces which in this case flow into the cast metal strip 3 transversely to the strip-running direction R displace the strip-running in the direction of these transverse forces.
FIG. 3 diagrammatically depicts a preferred embodiment of the strip-diverting device 19. the stand frame 28 which accommodates the pinch rolls 24, 25 is supported, in such a manner that it can pivot about a vertical axis 50, by means of curved, in particular arcuate, guides 49, and the orientation of the stand frame 28 with respect to the strip-running direction R can be set by means of a pivoting device 51, which is formed, for example, by hydraulic or electromechanical actuating devices, in particular also having a coupling mechanism. The vertical axis 50 represents the instantaneous center of rotation of the pivoting movement. The transverse forces or differential strip tensions which thereby act on the metal strip displace the strip-running direction in the direction of these transverse forces.
The strip-diverting device 19 is assigned a strip-position measuring device 35, e.g. an optical, capacitive or inductive measurement system, which determines the actual position of the strip edges and/or of the strip center of the metal strip. The measurement results determined are fed to a control device, from which control signals are emitted to the respective actuators of the strip-diverting device.
To allow sufficient strip centering to be realized despite the low strip tension, a strip-running centering aid 46 is positioned downstream of the strip-diverting device 19, either upstream or downstream of the rolling stand 18. This strip-running centering aid forms a fixed point for the strip diversion and, when the rolling stand 18 is closed, has an additional stabilizing action on the strip running. In FIG. 1, the strip-running centering aid 46 is diagrammatically depicted as a three-roll driver and is illustrated on the outlet side of the rolling stand 18, while in FIG. 2 the strip-running centering aid 46 is illustrated as a two-roll driver on the inlet side of the rolling stand 18.
In a hot-deformation process, which takes place in the rolling stand 18 (two-high, four-high or six-high rolling mill), the cast metal strip 3 is rolled, with a degree of reduction of up to 50%, in an in-line rolling operation to form a hot-rolled metal strip 1 with a predetermined final strip thickness. If multi-stand rolling trains are used, it is possible to achieve higher degrees of reduction and therefore lower final strip thicknesses. To set a predetermined, uniform rolling temperature, it is possible for a temperature-compensation zone 39, which is formed by a temperature-compensation tunnel furnace or a strip edge heater, to be connected upstream of the rolling stand 18. After it has left the rolling stand 18, the metal strip 1 is subjected to controlled cooling in a cooling section 40, is divided up using transverse cutting flying shears 41 at locations corresponding to the desired coil weight, and is wound up into coils 4 in a strip-coiling installation 42.
During the start-up operation, in which the first piece of a cast metal strip is threaded through the installation at casting speed using, for example, a start-up strand, the roll nip 44 of the rolling stand 18 is open. The start-up strand is separated from the cast metal strip using the transverse cutting flying shears and the metal strip is fed to the coiling installation, where it starts to be wound up. Even before it starts to be wound up, a strip tension is built up, in particular between the strip-diverting device 19 and the strip-running centering aid 46, and at the same time or subsequently a predetermined strip tension is set. Subsequently, the working rollers 32, 32′ of the rolling stand are moved together so as to move to the desired roll nip 44, and the coiling speed is matched to the degree of deformation which is set in the rolling stand. In this way, steady-state operation of the installation is achieved. As an alternative to the strip-running centering aid 46, it is also possible for the strip-coiling installation 42 or the entry driver 48 connected upstream of it to be used to build up the strip tension. Each driver arrangement positioned between the strip-diverting device 19 and the strip-coiling installation can perform this function and is therefore covered by the scope of protection of the present invention.

Claims

1-21. (canceled)

22. Apparatus for continuous production of a rolled metal strip comprising:

a strip-casting device for producing a cast metal strip having an initial strip thickness when produced of less than 20 mm, and the strip passing from the strip casting device along a path;

at least one rolling stand downstream of the strip-casting device along the path and the rolling stand is adapted for in-line roll deforming of the cast, undivided metal strip;

a strip-diverting device along the path of the metal strip between the strip-casting device and the rolling stand, wherein the strip-diverting device is spaced at a distance of 1.0 times to 10.0 times the width of the strip upstream of the rolling stand.

23. The apparatus of claim 22, wherein the strip-casting device comprises a two-roll casting machine for producing a cast metal strip.

24. The apparatus of claim 22, wherein the strip casting device produces a cast metal strip having an initial thickness in the range between 1 mm and 12 mm.

25. The apparatus of claim 22, wherein the strip diverting device is at a distance upstream of the roll stand along the path of the metal strip of between 1.5 times to 5.0 times the width of the strip.

26. The apparatus of claim 23, wherein the strip diverting device comprises a multi-roller driver for the strip.

27. The apparatus of claim 22, further comprising a metal strip conveyor for conveying the strip along the path;

adjustment and control devices at the strip diverting device and connected with the conveyor for setting the strip tension of the metal strip conveyed by the conveyor at between 2.0 MPa and 15 MPa between the strip diverting device on the one hand and one of the rolling stand, a strip running centering aid or another element on the path of the strip.

28. The apparatus of claim 27, wherein the conveyor comprises cooperating pinch rolls of a multi-roll driver for the strip.

29. The apparatus of claim 27, wherein the strip tension set by the adjustment and control devices is between 4.0 MPa and 8.0 MPa.

30. The apparatus of claim 27, further comprising a strip position measuring device connected with the strip diverting device;

the metal strip conveyor is at the strip diverting device;

the metal strip conveyor having at least one element that is rotatably supported in a pivotable bearing device and the bearing device is pivotable to adjust the direction of the at least one element to affect the strip running direction, and the conveyor and the at least one element supported on the conveyor are controllable and positionable for influencing the strip running direction on the path, and control elements for influencing the strip running direction.

31. The apparatus of claim 30, wherein the conveyor comprises a multi-roll driver on the path of the strip for acting on the strip, the conveyor element that is rotatably supported in the pivotable bearing device comprises one roll of the multi-roll driver, the pivotable bearing device supporting the one roll for allowing adjustment of the orientation of the one roll for redirecting the strip direction along the path.

32. The apparatus of claim 31, wherein the strip diverting device includes the pivotable bearing device which is pivotable about an axis transverse to the axis of the one roll supported at the pivotable bearing device;

curved guides displaceably supporting the pivotable bearing device and an adjustment device for adjusting the position of the pivotable bearing device along the curved guides.

33. The apparatus of claim 22, further comprising guides on which the strip diverting device is supported; a displacement device for displacing the strip diverting device for setting the distance of the diverting device from the rolling stand, and the displacement device is between the strip diverting device and the guides.

34. The apparatus of claim 27, further comprising a device for producing strip pretension in the metal strip and being located along the path of the strip between the strip casting device and the strip diverting device.

35. The apparatus of claim 34, wherein the device for producing strip pretension comprises a looping pit into which a loop of the strip may hang.

36. The apparatus of claim 34, wherein the device for producing strip pretension comprises a strip supporting device which is horizontal and subject to friction.

37. The apparatus of claim 36, wherein the device for producing strip pretension comprises a roller table having braking rolls acting thereon.

38. The apparatus of claim 35, wherein the strip supporting device has an active length along the path of the strip that is at least 1.5 times the strip width.

39. The apparatus of claim 36, wherein the strip supporting device has an active length along the path of the strip that is at least 2.5 times the strip width.

40. The apparatus of claim 22, further comprising a strip running centering aid arranged downstream of the rolling stand or between the strip diverting device and the rolling stand along the path of the strip.

41. The apparatus of claim 40, wherein the strip running centering aid comprises a non-divertible two roll or three roll driver.

42. The apparatus of claim 41, wherein the strip diverting device and the strip running centering aid are at a distance from each other of 1.0 times to 10.0 times the strip width.

43. The apparatus of claim 40, wherein the strip diverting device and the strip running centering aid are at a distance from each other of 1.5 times to 5.0 times the strip width.