WIDTH-ALTERING SYSTEM FOR STRIP-SHAPED ROLLED MATERIAL

Abstract

A method for altering the width of a strip-shaped rolled material (5), before, during or after hot rolling the rolled material in a hot rolling mill. The problem is to specify a method for altering width so that the length of a rolled out transition piece lying outside width tolerances can be reduced. Scrap losses are to be reduced. The crown of at least one working roll and/or at least one backing roll of a stand (7) is set as a function of a width error e=B−B between a setpoint width Bsetp and the width B of the rolled material (5), wherein the crown is increased when e>0 and the crown is reduced when e<0. AA Rcrown BB Bsetp.

Description

FIELD OF TECHNOLOGY

The present invention relates to a method for altering the width of a strip-shaped rolled material, in particular before, during or after hot rolling the rolled material in a hot rolling mill.

TECHNICAL BACKGROUND

In hot rolling, a metallic rolled material, e.g. a strip-shaped rolled material made from steel or aluminum, undergoes hot forming in a roll gap of a rolling stand while the material is in a plastic state.

The invention relates to a method for altering the width of a strip-shaped rolled material, so that the rolled material passes uncut through a first unit and a second unit, the method comprises the steps:

• • producing the rolled material with a first width B₁, wherein the rolled material emerges from the first unit with a width B=B₁, and the emerging rolled material is transported in a transport direction to the second unit, while maintaining a tension σ=σ_normal on the material;
  • producing a transition piece of the rolled material, wherein the rolled material emerges from the first unit with the width B, where B₁≦B≦B₂;
  • producing the rolled material with a second width B₂, wherein the rolled material emerges from the first unit with the width B=B₂.

The invention further relates to a method for altering the width of a strip-shaped rolled material, wherein the rolled material passes uncut through a first unit and a second unit, and the rolled material is rolled in a rolling stand in the first unit and/or in the second unit, comprising the method steps:

• • producing the rolled material with a first width B₁, wherein the rolled material emerges from the first unit with a width B=B₁, and the emerging rolled material is transported to the second unit;
  • producing a transition piece of the rolled material, wherein the rolled material emerges from the first unit with the width B, where B₁≦B≦B₂;
  • producing the rolled material with a second width B₂, wherein the rolled material emerges from the first unit with the width B=B₂.

PRIOR ART

It is known from the prior art that the width of a continuously produced slab of metal can be changed in a continuous casting machine by laterally adjusting at least one narrow side wall in the mold. Also known from the prior art is the inline coupling of a continuous casting machine and a hot rolling mill, such that a cut or uncut continuous slab which is produced in the continuous casting machine can be hot rolled directly by the hot rolling mill. Such a coupling of a casting machine with a hot rolling mill is known as a combined casting and rolling plant or Thin Slab Casting and Rolling Plant (TSCR). The uncut and directly coupled operation of the thin slab casting and rolling plant is known as endless operation. The Arvedi ESP (Endless Strip Production) plant is one example of a thin slab casting and rolling plant which offers extremely effective endless operation.

Also known from the prior art is the use of a thin slab casting and rolling plant to produce a rolled material with varying width. In this case, the width of the continuous slab is typically changed in the mold, thereby producing a tapering or widening slab piece (also known as a transition piece or wedge-shaped transition piece) having a specific length (depending on the casting speed and the traverse rate of the narrow side wall). The continuous slab including the transition piece is then rolled out in the rolling mill of the combined plant, thereby producing a rolled strip which slowly tapers or widens in each case.

Since the strip which slowly changes width cannot normally satisfy width tolerances, it is disadvantageous that the strip including the rolled out transition piece cannot be sold immediately. It is therefore desirable to keep the length of the transition piece as short as possible. This can be achieved either by cutting out the transition piece from the slab or from the rolled out strip, although this inevitably results in considerable scrap losses. Otherwise, the transition piece can be trimmed or edged, thereby reducing the scrap losses to an extent. Very rapid adjustment of the narrow side walls in the mold is likewise excluded, since this can easily result in fractures in the thin strand shell of the continuous slab.

Means by which the scrap losses can be further reduced while maintaining a high level of operational reliability are not indicated in the prior art.

SUMMARY OF THE INVENTION

The object of the invention is to overcome the disadvantages of the prior art and to provide a method for altering the width of a strip-shaped rolled material. The method makes it possible to reduce the length of a rolled out transition piece that exceeds the width tolerances. This method is intended thereby to reduce the scrap losses.

This object may be achieved by a method for altering the width of a strip-shaped rolled material, wherein the rolled material passes uncut through a first unit and a second unit, comprising method steps:

• • producing the rolled material with a first width B₁, wherein the rolled material emerges from the first unit with a width B=B₁, and the emerging rolled material is transported in the transport direction to the second unit while maintaining a tension σ=σ_normal on the material;
  • producing a transition piece of the rolled material, wherein the rolled material emerges from the first unit with the width B, where B₁≦B≦B₂;
  • producing the rolled material with a second width B₂, wherein the rolled material emerges from the first unit with the width B=B₂.

The object is achieved by setting the tension σ on the rolled material between the first unit and the second unit as a function of a width error e=B_setp−B between a setpoint width B_setp and the width B of the rolled material, wherein the tension σ is increased to σ>σ_normal if e<0.

According to the invention, a width error e between a setpoint width B_setp and the width B of the rolled material is calculated and the tension σ on the rolled material between the first and the second unit is set as a function of the width error e. In the case of a negative width error e, the tension σ is increased to σ>σ_normal, whereby the width of the rolled material emerging from the second unit is reduced. This principle is based on the finding that not only an increase in length (elongation) but also an increase in width (lateral flow) usually occurs when a strip is rolled. If the strip is under tension, however, the width increase is less or even negative. It is noted in this context that the cited principle is by no means limited to rolling mills, but can be applied to any directly coupled units. It need merely be ensured that the tension on the rolled material between the two units can be set.

The increase of the tension σ can be effected e.g. by increasing the driving torque of the second unit which follows the first unit in the direction of transport. Alternatively or additionally, the driving torque of the first unit can be reduced. This can be effected e.g. by the drive motors in a rolling stand or in a pair of drive rollers.

For increasing the width of the rolled material, it is advantageous to reduce the tension σ to σ<σ_normal in the event of a positive width error e. In absolute terms, the tension σ can even assume negative values in this context, i.e. such that the normal stress in the direction of transport is a compressive stress.

The reduction of the tension σ can be effected e.g. by reducing the driving torque of the second unit. Alternatively or additionally, the driving torque of the first unit can be increased. This can be effected e.g. by the drive motors in a rolling stand or in a pair of drive rollers. It is therefore also possible to compensate for positive width errors at least partially, preferably completely, by means of the inventive method. It is noted in this context that although the width of a strip can be altered by the use of loopers between two rolling stands, this cannot be applied to positive width errors due to the nature of the system.

For example, the first and second units may be a casting machine and a roughing mill train, a roughing mill train and a finishing mill train, or generally the region between two drive rollers, wherein at least the driving torque of one drive roller must be independently settable in order to apply a tension to the strip between the drive rollers. It is naturally also possible for the two units to be two consecutive rolling stands of the same mill train.

The setting of the tension σ as a function of the width error e can be effected in either a controlled or regulated manner, i.e. on the basis of the measured width B_actual of the rolled material as it emerges from or after it has emerged from the second unit. The regulated setting has the advantage that the actual width of the rolled material or rolled product takes other influences into consideration after the rolling of the rolled material (e.g. the temperature of the hot strip).

According to a particularly advantageous embodiment, the setting of the tension σ (which can also have a negative operational sign and therefore be a pressure) is effected on the basis of a mathematical necking model for the rolled material. This model advantageously takes into consideration the deformation resistance, which is dependent on profiles for degree of deformation, deformation rate and temperature, the current structural state, the creep behavior, which is dependent on the current state of the rolled material, the chemical composition of the rolled material, the temperature of the rolled material, and possibly a temperature-dependent elasticity modulus of the rolled material.

According to a particularly effective embodiment, the first or the second unit is a rolling stand and the rolled material is rolled in the rolling stand. In this way, the tension on the rolled material can easily be set by means of higher or lower rolling torques without any requirement for additional equipment costs.

This object of the invention is likewise achieved by a method for altering the width of a strip-shaped rolled material, wherein the rolled material passes uncut through a first unit and a second unit and the rolled material is rolled in a rolling stand in the first unit and/or in the second unit, comprising method steps:

• • producing the rolled material with a first width B₁, wherein the rolled material emerges from the first unit with a width B=B₁, and the emerging rolled material is transported to the second unit;
  • producing a transition piece of the rolled material, wherein the rolled material emerges from the first unit with the width B, where B₁≦B≦B₂;
  • producing the rolled material with a second width B₂, wherein the rolled material emerges from the first unit with the width B=B₂.

The object to be achieved is that the crown of at least one working roll and/or at least one backing roll of the rolling stand is set as a function of a width error e=B_setp−B between a setpoint width B_setp and the width B of the rolled material, wherein the crown is increased if e>0 and the crown is reduced if e<0.

If the first and/or second unit is a rolling stand, in addition to or as an alternative to altering the tension of the rolled material, the crown of a working roll or backing roll of the rolling stand can be set as a function of the width error e, wherein the crown of the roll is increased if e>0 and the crown of the roll is reduced if e<0. In this context, crown is understood to signify the central crown, wherein the thickness of the rolled material in a central region is reduced as a result of increasing the crown, such that the lateral flow of the rolled material is increased during rolling. Conversely, the central crown is reduced in the case of a negative width error e, such that the lateral flow is reduced during rolling. The setting of the crown of a roll can be effected, for example, by means of roll bending actuators and/or by means of thermal alteration (e.g. zone-specific cooling) of the roll. If it is desired to increase the crown by means of thermal alteration, the cooling in the edge regions of the roll is increased to a greater extent than in the central regions. The central region of the roll therefore expands to a greater extent than the edge regions, thereby raising the crown. Conversely, the crown is reduced if the cooling in the central region of the roll is increased to a greater extent than in the edge regions.

In order to ensure that the geometry of the rolled material is not changed excessively as a result of setting the crown for the purpose of altering the width, provision is advantageously made for both units to comprise a rolling stand, and for a modification of the crown of a roll to take place primarily in the first unit. This ensures that the rolled product has a desired geometry after rolling in the second unit.

The setting of the crown as a function of the width error e can also be effected in either a controlled or regulated manner, i.e. on the basis of the measured width B_actual of the rolled material, e.g. as it emerges from the second unit or subsequently at an additional location.

When setting the crown in particular, it is very advantageous to take into consideration the transport time of the rolled material from the first unit and/or from a measuring device for capturing the actual width B_actual to the rolling stand. It is then possible to compensate for the width of the transition piece in the rolling stand of the second unit at the correct time. However, the transport time can also be taken into consideration when setting the tension for the purpose of altering the width.

Since only strips having a specific width can usually be sold, the setpoint width B_setp is advantageously a step function H(t) from B₁ to B₂ or from B₂ to B₁. Alternatively the setpoint width B_setp can also be a ramp function R(t) from B₁ to B₂ or from B₂ to B₁. Other functions are obviously also possible.

It is generally appropriate for the first unit to be a mold of a casting machine, e.g. a bow-type continuous casting machine or two-roll casting machine, or a rolling stand, e.g. a rolling stand of a roughing mill train.

In the context of hot rolling in a hot rolling mill in particular, it is appropriate to transport the rolled material from the first unit on a roller table to the second unit. However, the invention is by no means limited to this, and also functions for loops hanging freely between two units, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and features of the present invention are derived from the following description of non-restrictive exemplary embodiments, wherein reference is made to the following figures, in which:

FIGS. 1 and 8 each show a schematic illustration of part of a thin slab casting and rolling plant, wherein the purpose of the part is to effect an alteration of the width of a strip-shaped rolled material between a continuous casting machine and a roughing mill;

FIGS. 2 and 5 each show an illustration of the width B_mold of the rolled material at the mold, the width B_driveroller at the drive roller, and the setpoint width B_setp at the position of the drive roller relative to time for the embodiment variant according to FIG. 1;

FIGS. 3 and 6 each show an illustration of the width error e relative to time at the position of the drive roller for the embodiment variant according to FIG. 1;

FIG. 4 a shows a control model for performing the method according to the invention;

FIGS. 4 b, 7 and 10 each show a regulating model for performing the method according to the invention; and

FIG. 9 shows an illustration of different widths relative to time for the embodiment variant according to FIG. 8.

DESCRIPTION OF THE EMBODIMENT VARIANTS

FIG. 1 shows part of a thin slab casting and rolling plant comprising a bow-type continuous casting machine 1 for continuously casting steel melt into thin slabs, and a subsequent in-line mill train. Of the mill train, only one rolling stand 7 of the roughing mill train is illustrated; other parts of the plant are not illustrated. In the mold 8, liquid steel is continuously cast into a thin slab strand, wherein the width of the strand is initially B=B₁=1800 mm and its thickness is initially 90 mm. The casting speed 11 is 5 m/min. The metallurgical length of the continuous casting machine 1 from the mold 8 to the two drive rollers 10 is 15 m. Downstream from the mold 8, the thin slab strand is supported in the strand guide 9, guided and cooled further, wherein the strand solidifies in the final third of the curved strand guide 9. The strand guide 9 is indicated by two strand guide rollers. The solidified thin slab strand emerges from the continuous casting machine 1 via the drive rollers 10 and represents the rolled material 5. The pair of drive rollers 10 forms the first unit 2. The rolled material 5 is guided uncut in the direction of transport 6 from the first unit 2 via the roller table 3 to the second unit 4. The second unit 4 takes the form of a rolling stand 7 of the roughing mill train. The rolled material 5 which has been rolled in the rolling stand is also referred to as the rolled product 12.

If a different width of the rolled product 12 is now desired, the two narrow side plates of the mold 8 are moved transversely to the direction of casting. For example, the two narrow side plates are moved during the uninterrupted operation of the thin slab casting and rolling plant at a traverse rate of 50 mm/min from B₁=1800 mm to B₂=1850 mm. As a result of this traversing movement, a wedge-shaped thin slab strand (also known as a transition piece) of changing width forms in the strand guide 9 downstream of the mold 8. The width B_mold of the thin slab strand as it emerges from the mold 8 and of the rolled material 5 as it emerges from the first unit 2 B_driveroller are illustrated as a continuous line in FIG. 2. Depending on the length of the continuous casting machine, the head of the transition piece emerges from the first unit 2 after a delay of 3 min from leaving the mold 8.

Concerning the width adjustment in the mold, it is noted that when producing thin slabs, the narrow sides of the mold are usually slowly inclined at the beginning of the transition piece. The inclined plates are then moved, and finally the inclined plates are returned to their original gradient. This has the advantage that the strand is better supported by the mold walls. The widths B_mold and B_driveroller according to this procedure are illustrated by means of dash-dot lines in FIG. 2.

Also illustrated in FIG. 2 is the setpoint width B_setp of the rolled material 5, wherein the setpoint width can be expressed mathematically as B_setp=1800+50.H(240), wherein the Heaviside step function H(t) steps from zero to one at 240 s. For example, the step function is known from http://mathworld.wolfram.com/HeavisideStepFunction.html.

The principle of the invention is therefore based on changing the tension on the rolled material 5 between the first unit 2 (specifically the pair of drive rollers 10) and the second unit 4 (the rolling stand 7 of the roughing mill train) as a function of the width error e, where e=B_setp−B, wherein the tension σ on the rolled material 5 is increased in the direction of transport 6 if e is negative. This means that the tension results in necking of the rolled material 5, thereby reducing the width of the rolled material 5 or rolled product 12.

The width error e is illustrated in FIG. 3. The width error e for the widths as marked by dash-dot lines in FIG. 2 is not shown here.

A control model for implementing the method according to the invention is illustrated in FIG. 4a. Specifically, the width error e is determined by the difference between the setpoint value for the width B_setp and the width B, where B is determined from the width of the thin slab strand at the exit of the mold 8 by the dead time element, taking into consideration a dead time of 3 min. The width error is then amplified by an amplifier element 14 and held within permitted minimal and maximal limit values by the limiter element 15. The result σ_setp is supplied to a tension regulator R_σ for the rolling stand 7, which sets the tension σ on the rolled material 5 accordingly. The correcting variable u is applied to the regulated section G, wherein the regulated section G delivers output in the form of an actual width B_actual of the rolled product 12 as it emerges from the second unit 4.

The essential difference between the control model in FIG. 4a and the regulating model in FIG. 4b is that the actual width B_actual of the rolled product 12 is measured by the width measuring device 16 immediately after it emerges from the second unit 4 (see FIG. 1), and is fed back to the regulating circuit such that the accuracy of the width alteration can be significantly increased.

It is obviously also possible to select another function for the setpoint width B_setp, e.g. as per FIG. 5. However, using identical width values B, such a selection results in positive and negative values for the width error e, and therefore the control process as per FIG. 4a or the regulating process as per FIG. 4b compresses the rolled material 5 if e has a positive value. This compression causes the width of the rolled material 5 to increase.

In any case, the method according to the invention ensures that the actual width B_actual of the rolled product 12 is kept closer to the setpoint width B_setp and therefore the width tolerances can be better satisfied.

In addition to altering the tension σ for the purpose of altering the width of the rolled material 5, it is also possible to set the crown of a working and/or a backing roll of the rolling stand 7 as a function of the width error e. In order to achieve this, use is made of e.g. the regulating model according to FIG. 7. This differs from the model according to FIG. 4b in that the width error e is also supplied to a regulator R_crown for altering the crown of a working and/or backing roll of the rolling stand 7, the crown of the roll being altered by means of the correcting variable u₂. This means that the regulated section G is altered by two correcting variables u₁, u₂, the regulated variable being the width B_actual of the rolled material 5 after the second unit 4 (specifically the rolling stand 7). The correcting variable u₁ corresponds to the correcting variable u from FIG. 4b. As is evident from FIG. 1, the actual width B_actual can be measured by the width measuring device 16 at the exit of the second unit 4 and supplied to the regulating loop.

Like FIG. 1, FIG. 8 shows a part of a thin slab casting and rolling plant comprising a continuous casting machine 1, a first unit 2 in the form of a pair of drive rollers 10, a second unit 4 in the form of a rolling stand 7, and additionally a third unit 17 in the form of a further rolling stand 7. In order to achieve greater drawing and/or retaining forces, the first unit 2 could obviously also comprise a plurality of drive rollers 10. The second unit 4 and the third unit 17 together form the roughing mill train of the thin slab casting and rolling plant. In FIG. 8, the rolled material 5 is extracted from the continuous casting machine 1 with a thickness of 90 mm by the drive rollers 10, then rolled to a thickness of 50 mm in the second unit 4, and finally reduced to a thickness of 30 mm in the third unit 17. FIG. 9 shows the width of the strand after the mold 8 B_mold, the width of the strand at the drive roller 10 B_driveroller, the setpoint width B_setp, and the width of the strand after it has emerged from the second unit 4, once without application B_unit2 and once with application B_actual of the method according to the invention. The actual width of the rolled material 5 or rolled product 12 is again measured by the width measuring device 16 immediately after the second unit 4. It is evident from FIG. 9 that the actual width B_actual of the rolled product 12 remains within the width tolerance for a considerably longer time when the method is applied, thereby reducing the scrap losses.

The regulating model relating to FIGS. 8 and 9 is shown in FIG. 10. Unlike the regulating model according to FIG. 4b, the width error e=B_setp−B_actual is used to regulate a first tension σ₁ between the first unit 2 and the second unit 4 and to regulate a second tension σ₂ between the second unit 4 and the third unit 17, wherein the resulting correcting variables u₁, u₂ act together on the regulated section G. If applicable, it is possible to select different amplification factors K₁ and K₂ of the amplifier elements 14, limitations of the limiter elements 15, and regulators Ro in the first branch for altering the tension σ₁ and in the second branch for altering the tension σ₂.

Although the invention has been illustrated and described in detail by the preferred exemplary embodiments, it is not restricted by the examples disclosed therein, and other variations can be derived therefrom by the person skilled in the art, without departing from the scope of the invention.

LIST OF REFERENCE CHARACTERS

• 1 Continuous casting machine
• 2 First unit
• 3 Roller table
• 4 Second unit
• 5 Rolled material
• 6 Transport direction
• 7 Rolling stand
• 8 Mold
• 9 Strand guide
• 10 Drive roller
• 11 Casting speed
• 12 Rolled product
• 13 Dead time element
• 14 Amplifier element
• 15 Limiter element
• 16 Width measuring device
• 17 Third unit
• B Width
• B_actual Actual width
• B_setp Setpoint width
• B_mold Width of the strand emerging from the mold
• B_driveroller Width of the rolled material emerging from the first
• B_unit2 unit
• B₁ First width
• B₂ Second width
• e Width error
• G Regulated section
• R Regulator
• R_σ Tension regulator
• σ Tension
• t Time
• u, u₁, u₂ Correcting variable

Claims

1. A method for altering the width of a strip-shaped rolled material comprising: passing the rolled material uncut through a first unit and then through a second unit, wherein rolling of the rolled material is performed in a rolling stand in at least one of the first unit and the second unit, and further comprising method steps of:producing the rolled material with a first width B1, wherein the rolled material emerges from the first unit with a width B=B1, and then transporting the emerging rolled material to the second unit;producing a transition piece of the rolled material, wherein the rolled material emerges from the first unit with the width B, where B1≦B≦B2;producing the rolled material with a second width B2, wherein the rolled material emerges from the first unit with the width B=B2; and

2. The method as claimed in claim 1, further comprising the setting of the crown is in a controlled manner as a function of the width error e.

3. The method as claimed in claim 1, further comprising the setting of the crown in a regulated manner as a function of the width error e, wherein the width B is the measured width Bactual of the rolled material as the rolled material emerges from the second unit or after the material emerges.

4. The method as claimed in claim 1, further comprising the setting of the crown takes into consideration the transport time of the rolled material from the first unit to the rolling stand.

5. The method as claimed in claim 1, wherein the setpoint width Bsetp is either a step function H(t) or a ramp function R(t) from B1 to B2 or from B2 to B1.

6. The method as claimed in claim 1, wherein the first unit is a mold of a casting machine.

7. The method as claimed in claim 1, wherein the first unit is a rolling stand.

8. The method as claimed in claim 1, further comprising the transporting of the rolled material from the first unit to the second unit is on a roller table.

9. The method as claimed in claim 1, further comprising the transporting of the rolled material emerging from the first unit is in the direction of transport to the second unit while maintaining a tension σ=σnormal; and setting the tension σ on the rolled material between the first unit and the second unit as a function of the width error e=Bsetp−B, and increasing the tension σ to σ>σnormal if e<0.

10. The method as claimed in claim 9, further comprising reducing the tension σ to σ<σnormal if e>0.

11. The method as claimed in claim 10, further comprising the setting the tension σ in a controlled manner as a function of the width error e.

12. The method as claimed in claim 10, further comprising the setting of the tension σ in a regulated manner as a function of the width error e, wherein the width B is a measured width Bactual of the rolled material as it emerges from the second unit.

13. The method as claimed in claim 9, further comprising the setting of the tension σ on the basis of a mathematical necking model for the rolled material under tension σ.

14. The method as claimed in claim 6, wherein the casting machine is a bow-type continuous casting machine.

15. The method as claimed in claim 6, wherein the casting machine is a rolling stand of the roughing mill train.

16. The method as claimed in claim 7, wherein the first unit is a rolling stand of a roughing mill train.