Width-altering system for strip-shaped rolling rock

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 B.sub.setp 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 R.sub.crown BB B.sub.setp.

Claims

1. A method for altering the width of a strip-shaped rolled material rolling stock comprising: passing the rolling stock uncut through a first unit and then through a second unit, wherein rolling of the rolling stock 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 material rolling stock with a first width B.sub.1, wherein the rolling stock emerges from the first unit with a width B=B.sub.1, and then transporting the rolling stock downstream to the second unit; producing a transition piece in the rolling stock, wherein the transition piece is produced upstream of the portion of the rolling stock having the width B.sub.1, wherein the rolling stock emerges from the first unit including the transition piece and wherein the transition piece is a wedge-shaped piece of changing width and includes a changing width different from that of B.sub.1; producing the rolling stock with a second width B=B.sub.2, the second width being located upstream of the transition piece, wherein the rolling stock emerges from the first unit with the width B.sub.2 and wherein B.sub.2 is a width greater or lesser than B.sub.1; and setting a crown of at least one working roll and/or at least one backing roll of the rolling stand as a function of a width error e=B.sub.setp−B, that is between a setpoint width B.sub.setp and the width B of the rolling stock, wherein the crown of the at least one working roll or backing roll is increased if e>0 and wherein the crown of the at least one working roll or backing roll is reduced if e<0.

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 B.sub.actual of the rolling stock as the rolling stock 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 rolling stock from the first unit to the rolling stand.

5. The method as claimed in claim 1, wherein the setpoint width B.sub.setp is either a step function H(t) or a ramp function R(t) from B.sub.1 to B.sub.2 or from B.sub.2 to B.sub.1.

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 6, wherein the casting machine is a bow-type continuous casting machine.

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

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

10. The method as claimed in claim 9, wherein the first unit is a rolling stand of a roughing mill train.

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

12. The method as claimed in claim 1, further comprising the transporting of the rolling stock 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 rolling stock between the first unit and the second unit as a function of the width error e=B.sub.setp−B, and increasing the tension σ to σ>σnormal if e<0.

13. The method as claimed in claim 12, further comprising reducing the tension σ to σ<σnormal if e>0.

14. The method as claimed in claim 13, further comprising the setting the tension σ in a controlled manner as a function of the width error e.

15. The method as claimed in claim 13, 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 B.sub.actual of the rolling stock as it emerges from the second unit.

16. The method as claimed in claim 12, further comprising the setting of the tension σ on the basis of a mathematical necking model for the rolling stock under tension σ.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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:

(2) 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 rolling stock between a continuous casting machine and a roughing mill;

(3) FIGS. 2 and 5 each show an illustration of the width B.sub.mold of the rolling stock at the mold, the width B.sub.driveroller at the drive roller, and the setpoint width B.sub.setp at the position of the drive roller relative to time for the embodiment variant according to FIG. 1;

(4) 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;

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

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

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

DESCRIPTION OF THE EMBODIMENT VARIANTS

(8) 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=B.sub.1=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 rolling stock 5. The pair of drive rollers 10 forms the first unit 2. The rolling stock 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 rolling stock 5 which has been rolled in the rolling stand is also referred to as the rolled product 12.

(9) 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 B.sub.1=1800 mm to B.sub.2=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.sub.mold of the thin slab strand as it emerges from the mold 8 and of the rolling stock 5 as it emerges from the first unit 2 B.sub.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.

(10) 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.sub.mold and B.sub.driveroller according to this procedure are illustrated by means of dash-dot lines in FIG. 2.

(11) Also illustrated in FIG. 2 is the setpoint width B.sub.setp of the rolling stock 5, wherein the setpoint width can be expressed mathematically as B.sub.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.

(12) The principle of the invention is therefore based on changing the tension on the rolling stock 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.sub.setp−B, wherein the tension σ on the rolling stock 5 is increased in the direction of transport 6 if e is negative. This means that the tension results in necking of the rolling stock 5, thereby reducing the width of the rolling stock 5 or rolled product 12.

(13) 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.

(14) 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.sub.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.sub.setp is supplied to a tension regulator R.sub.σ for the rolling stand 7, which sets the tension σ on the rolling stock 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.sub.actual of the rolled product 12 as it emerges from the second unit 4.

(15) The essential difference between the control model in FIG. 4a and the regulating model in FIG. 4b is that the actual width B.sub.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.

(16) It is obviously also possible to select another function for the setpoint width B.sub.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 rolling stock 5 if e has a positive value. This compression causes the width of the rolling stock 5 to increase.

(17) In any case, the method according to the invention ensures that the actual width B.sub.actual of the rolled product 12 is kept closer to the setpoint width B.sub.setp and therefore the width tolerances can be better satisfied.

(18) In addition to altering the tension σ for the purpose of altering the width of the rolling stock 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.sub.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 u.sub.2. This means that the regulated section G is altered by two correcting variables u.sub.1, u.sub.2, the regulated variable being the width B.sub.actual of the rolling stock 5 after the second unit 4 (specifically the rolling stand 7). The correcting variable u.sub.1 corresponds to the correcting variable u from FIG. 4b. As is evident from FIG. 1, the actual width B.sub.actual can be measured by the width measuring device 16 at the exit of the second unit 4 and supplied to the regulating loop.

(19) 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 rolling stock 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.sub.mold, the width of the strand at the drive roller 10 B.sub.driveroller, the setpoint width B.sub.setp, and the width of the strand after it has emerged from the second unit 4, once without application B.sub.unit2 and once with application B.sub.actual of the method according to the invention. The actual width of the rolling stock 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.sub.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.

(20) 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.sub.setp B.sub.actual is used to regulate a first tension σ.sub.1 between the first unit 2 and the second unit 4 and to regulate a second tension σ.sub.2 between the second unit 4 and the third unit 17, wherein the resulting correcting variables u.sub.1, u.sub.2 act together on the regulated section G. If applicable, it is possible to select different amplification factors K.sub.1 and K.sub.2 of the amplifier elements 14, limitations of the limiter elements 15, and regulators Re in the first branch for altering the tension σ.sub.1 and in the second branch for altering the tension σ.sub.2.

(21) 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

(22) 1 Continuous casting machine 2 First unit 3 Roller table 4 Second unit 5 Rolling stock 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.sub.actual Actual width B.sub.setp Setpoint width B.sub.mold Width of the strand emerging from the mold B.sub.driveroller Width of the rolling stock emerging from the first unit B.sub.unit2 Width of the rolling stock emerging from the second unit B.sub.1 First width B.sub.2 Second width e Width error G Regulated section R Regulator R.sub.σ Tension regulator σ Tension t Time u,u.sub.1,u.sub.2 Correcting variable