EP0618020B1 - Method for rolling of a strip - Google Patents

Abstract

A method for rolling the strip (3;4) in a hot-strip mill (6) having at least two rolling stands (6,7) with horizontally adjustable upper and lower work rolls (10,11) each of which is supported directly or by way of an intermediate roll on a back-up roll (9), or in a reversing stand on which at least two passes are performed, in which the strip is subjected to state control, for which purpose profile-and flatness-determining final control elements act on the strip, makes it possible to meet the requirements relating to the profile accuracy and flatness of the strip despite flexible rolling programs if a target contour for the profile of the strip (3;4) is specified, for the achievement of which two groups of final control elements act successively on the strip, the final control elements (12,13) of the first group being brought into action when the thickness of the strip is above the critical thickness and primarily influencing the contour of the strip in its central area relative to the centre of the strip, while the final control elements (12,13) of the second group are brought into action when the thickness of the strip in the region of the edge is below the critical thickness. <IMAGE>

Description

The invention relates to a method for rolling a rolled strip in at least two roll stands, each with horizontally adjustable upper and lower work rolls, each of which is supported directly or via an intermediate roll on a backup roll, hot strip mill or a reversing stand on which at least two passes are rolled in which the rolling strip is subjected to a state control, for which purpose actuators which provide profile and flatness act on the rolling strip.

When hot rolling strip materials, the thermal crowning and wear of the work rolls as well as the elastic deformations are subject to relatively large changes within a rolling program. Without the correction by actuators, the crowning of the work rolls increases continuously with increasing throughput of the rolling material, and due to the changing thermal crowning, the roll contour increasingly deviates from the target contour, e.g. a parabola.

• Verdickungen im Kantenbereich (Wülste, edge built-up)
• Abfallen der Dicke im Kantenbereich.

Solche Profilanomalien schränken die walzbare Länge in einer Breite stark ein. Als Walzlänge in einer Breite wird die Summe aller Bandlängen definiert, die in einer Breite oder annähernd gleicher Breite gewalzt werden.When rolling in one width, many strips are rolled one after the other with the same width or approximately the same width. In addition to the value of the strip profile specified for a specific point (for example C ₄₀ or C ₂₅ ), rolling in one width also influences the overall strip profile shape. Here, under the description of the strip profile for a very specific point, the difference between the thickness of the strip in the middle and the mean value of the thicknesses measured at the distance - at point C ₄₀ this corresponds to 40mm - from the strip edge of each side. The increasing decline of Thermal crowning of the rollers leads to considerable profile anomalies on the belt in the area near the edge. This includes all deviations of the band from the ideal (eg parabolic) course of the band profile. The following types of profile anomalies are to be avoided in the rolling practice:

• Thickening in the edge area (beads, edge built-up)
• Decrease in thickness in the edge area.

Such profile anomalies severely restrict the rollable length in a width. The roll length in one width is defined as the sum of all strip lengths that are rolled in a width or approximately the same width.

It is known to change the thermal crown and work roll wear by suitable actuators such as sliding and / or bending members, e.g. "CVC" (Continuously Variable Crown) shift (see. DE 30 38 865 C1) or a suitable cooling, in order to compensate for the adjustment of the actual contour.

From EP 0 276 743 B1 it has become known to control the crowning and / or edge drop of the strip, the horizontal displacement of the work rolls and the bending forces acting on these work rolls of a group of roll stands of a tandem rolling mill located on the upstream side, in accordance with the rolling conditions, including the Adjust the width of the belts. In order to control the wear and the thermal crowning of the work rolls, with the aim of avoiding undesired profile shapes when rolling in a width, the work rolls are moved back and forth at predetermined intervals, regardless of the width of the strip, in a group of the roll stands located on the downstream side pushed out. Here, the rear stands are moved in opposite directions after each band by a certain amount; if the shift amount has reached a maximum value, the shift direction is reversed. This cyclical shifting evens out the wear of the work rolls over a larger area.

Finally, it is known from EP 0 219 844 B1 to determine the profile of each work roll in the axial direction, which changes during the time interval between changing the work rolls. Then, on the basis of the determined roll profile, the configuration of the gap between the upper and lower work rolls in the axial direction is determined as a function of the size of a relative adjustment of the roll layers in order to determine the size of the adjustment of the roll layers that has the smoothest possible configuration in the axial direction for the gap within the contact area between the rolled strip and the work rolls. It is therefore a matter of smoothing the roll gap.

However, the known measures are not sufficient to be able to meet the increased requirements with regard to profile accuracy and flatness even under extreme boundary conditions. Nowadays, when it comes to the production of hot strip, these consist of being able to put together the rolling programs flexibly. In addition to larger thicknesses and material changes, width changes in the direction of narrow and wide are desired (mixed rolling). In addition, the number of strips of the same width should be increased within a rolling program.

The invention has for its object to provide a method with which the requirements for profile accuracy and flatness of the rolled strip can be met despite flexible rolling programs.

This object is solved by the features of claim 1. Thus, it is no longer a target profile for a very specific point, but rather a very specific, predetermined strip profile shape that is adapted to the intended use of the rolled strip. For a hot strip that is to be further processed, for example, a more parabolic target contour of the rolled strip profile and for the entrance profile of a cold mill a profile that is adapted to the conditions there (diameter, rolling force, etc.) aimed at with a flat body crown and a little more waste at the band edges. The invention is based on the knowledge found and exploited by extensive investigations that cross-material flow also takes place in the middle rolled strip area in the case of thick strip, whereas cross-material flow is only possible in the edge region in the case of thin strip. So if the strip profile shape is to be changed in the middle rolled strip area, this can only be achieved with thick strip. On the other hand, a change in the shape of the strip can also be achieved in the case of thinner strip, without impermissibly high unevenness, but this can only be carried out in the closer strip edge area. With decreasing strip thickness, the relevant strip profile influenceability gradually moves outwards, ie towards the strip edge.

This finding has, according to the invention, had a direct influence on the appropriate use of the actuators, that is to say that the first group of actuators primarily affects the middle band contour, while the actuators of the second group act in the band edge area. With the help of a calculation model (calculation method), the actuators can be used in such a way that, taking into account the technological limits (e.g. rolling force, temperature, etc.), the flatness limits (these result from the respective material cross flow of the strip and thus represent physical limits), If necessary, also higher order, actuator limits and, in particular, taking into account the material cross-flow behavior, an optimal belt shape is created that comes as close as possible to the specified target contour.

beschrieben wird, wobei Y die Banddickenkoordinate und X die Bandbreitenkoordinate darstellt. Durch das Weglassen der ungeraden Glieder wird Symmetrie erzeugt. Da A₀ = 0 ist, geht die Funktion durch X=0, Y=0 (entspricht der Bandmitte). Das Verwenden von Gliedern höherer Ordnung ermöglicht es, einen steileren Übergang an der Bandkante zu beschreiben.It is particularly advantageous if the predetermined target contour of the strip profile for a specific material quality is based on a calculation model and is dependent on the bandwidth coordinate and the strip thickness by means of a polynomial function $${\text{Y = A}}_{\text{2nd}}{\text{X}}^{\text{2nd}}{\text{+ A}}_{\text{4th}}{\text{X}}^{\text{4th}}{\text{+ A}}_{\text{6}}{\text{<figure-callout id="6" label="X" filenames="imgf0003.png,imgf0005.png" state="{{state}}">X</figure-callout>}}^{\text{6}}{\text{+ A}}_{\text{n}}{\text{X}}^{\text{n}}$$

is described, where Y is the strip thickness coordinate and X is the Represents bandwidth coordinate. By omitting the odd links, symmetry is created. Since A ₀ = 0, the function goes through X = 0, Y = 0 (corresponds to the middle of the band). The use of higher order terms enables a steeper transition at the band edge to be described.

It is recommended that, in the case of a strip profile shape deviating from the target contour, the mechanical actuators are used in such a way that there is a minimal deviation between the calculated strip shape and the target strip shape or target contour. If the strip profile shape cannot be produced in the stand i, the mechanical actuators must be adjusted in order to minimize the deviation. Deviations of the calculated strip shape from the target strip shape can be weighted differently over the bandwidth.

One embodiment of the invention provides that the mechanical actuators are supported by non-mechanical actuators, for which purpose - depending on the contour of the strip, in particular in the edge region - work rolls advantageously used as mechanical actuators can be locally heated or cooled in a targeted manner.

According to a proposal of the invention, work rolls used as mechanical actuators can be ground during the rolling operation. This can be achieved, for example, with oscillating grinding plates and allows the rolls to be smoothed or polished or their contours changed for the purpose of specifically influencing the strip contours. Such an "on-line" grinding is recommended, in particular when changing the program to wider rolled strips, because grinding the work roll ends while the narrow roll strips are still rolling has no influence on the quality of these narrow strips, since the preparatively ground work roll ends are outside the roll width lie.

It is proposed that the mechanical actuators be used as early as possible. Under Taking into account the limits to be complied with, for example the flatness and the setting range, the aim is to achieve the target contour of the profile of the rolled strip as early as possible. If this is not yet possible in the first scaffolding, the task is automatically passed on to the subsequent scaffolding. Should the strip shape change from roll stand to roll stand or from constant to constant from stitch to stitch, a deviation can be tolerated in accordance with the law of material cross-flow with thicker strip in the edge area, ie the achievement of the strip shape or target contour in the middle rolled strip area has priority. If it is possible to create the strip profile shape on a roll stand, eg stand k, the ultimate goal is to keep this strip shape constant in the subsequent stands.

Figur 1

eine erste vorgegebene Zielkontur des Profils eines Walzbandes;

Figur 2

eine zweite vorgegebene Zielkontur des Profils eines Walzbandes;

Figur 3

ein den Materialquerfluß in Abhängigkeit von der Dicke des Walzbandes darstellendes Diagramm;

Figur 4

ein den Materialquerfluß über die Bandbreite darstellendes Diagramm;

Figur 5

ein den Materialquerfluß in Abhängigkeit der Bandbreitenkoordinate und der Materialdicke für eine Materialqualität Q darstellendes Diagramm;

Figur 6

ein die Wirkung des thermischen crowns mit zunehmender Anzahl von Walzbändern bei bekannten Walzverfahren darstellendes Schaubild;

Figur 7

ein bei gleicher Anzahl von Bändern wie in Figur 6 mit den erfindungsgemäßen Maßnahmen zu erreichendes Bandprofil;

Figur 8

in schematischer Darstellung den Aufbau einer Kontur-und Planheitsregelung für Warmbandwalzwerke.

Further features and advantages of the invention result from the claims and the following description, in which some exemplary embodiments of the subject matter of the invention are explained in more detail. Show it:

Figure 1

a first predetermined target contour of the profile of a rolled strip;

Figure 2

a second predetermined target contour of the profile of a rolled strip;

Figure 3

a diagram showing the material cross-flow as a function of the thickness of the rolled strip;

Figure 4

a diagram showing the material cross flow over the bandwidth;

Figure 5

a diagram representing the material cross flow as a function of the bandwidth coordinate and the material thickness for a material quality Q;

Figure 6

a diagram illustrating the effect of the thermal crown with increasing number of rolled strips in known rolling processes;

Figure 7

a band profile to be achieved with the measures according to the invention with the same number of bands as in FIG. 6;

Figure 8

a schematic representation of the structure of a contour and flatness control for hot strip rolling mills.

As a prerequisite for achieving desired flat and profile-accurate rolled strips, target contours 1 and 2 of the profile of a rolled strip 3 and 4, not shown, are given in accordance with the intended use in FIGS. 1 and 2. According to the requirements, a target contour 1 according to FIG. 1, for example, and a target contour 2 according to FIG. 2, for example, are desired for a rolling strip 3 to be processed directly. FIG. 1 is an almost parabolic target contour, while target contour 2 according to FIG. 2 has a flat body crown and a somewhat greater drop on the band edges. The C ₄₀ point entered for both target contours 1, 2 results from the difference between the thickness of the rolled strip 3 or 4 in the middle H _M and the mean value of the thicknesses measured at a distance of ₄₀ mm from the strip edge 5 at each Side or strip edge 5 of the rolled strip 3 or 4.

The creation of the target contours 1 and 2 presupposes the knowledge resulting from FIGS. 3 to 5, namely that a strip contour influence can only be achieved where a material cross flow is possible. As has been found out by intensive investigations, in the case of rolled strips with a strip thickness above the critical thickness H _crit (see FIG. 3), a material cross-flow also takes place in the middle, ie the area adjacent to the middle of the strip (see FIG. 5), while on the other hand in the case of rolled strips with a smaller thickness below H _crit , a material cross flow only takes place in the strip edge area. The limit value of the thickness, ie, the critical thickness H _crit can be for any hot strip tandem mill as a function of roll material, experimentally determined temperature, roll diameter as well as decrease or stitch distribution, it is generally known that an effect on the profile of the rolled strip, with simultaneous avoidance of planar defects achieved only can be as long as the Flow resistance of the material transverse to the rolling direction is still so low that in addition to the strip elongation there is a minimum amount of strip spreading in the roll gap. As can be seen from FIG. 4, a material cross flow below the critical thickness (for example 10 or 12 mm) over the bandwidth is only possible to a very small extent. This relationship is also clear from FIG. 5, in which, in addition to the coordinates for the material cross flow and the bandwidth, the material thickness is also entered.

FIGS. 6 and 7 show the strip profiles to be achieved using the known rolling processes (see FIG. 6) and the profile and flatness control according to the invention (see FIG. 7) within a rolling program comprising fifty strips or coils; the numbers circled at the bottom left indicate the number of coils. While in both cases the shape of the profile is still almost unchanged for the first strip or coil to be rolled, the effect of the thermal crown on the work rolls with the disadvantageous anomalies for the profile increases with the number of strips in the known rolling methods. flat strip profiles and edge beads are produced (see FIG. 6 the strip profiles after the rolling of 10, 20 or 50 strips). In contrast, according to FIG. 7, the band profile can be kept largely constant, and edge beads are avoided. The target tape contour is also almost reached.

A hot strip tandem mill 6 which enables the desired strip profiles (see FIG. 7) to be reached is shown in FIG. 8, in some cases very schematically and with only symbolic identifications for the mechanical actuators including the elements supporting them, and in the form of black boxes for computers and measuring devices . It consists of several roll stands, of which the first and last roll stands 7 and 8 are shown. However, it can also be a rolling mill with a reversing stand on which several passes are rolled. Each of the roll stands 7, 8 has horizontally adjustable upper and lower work rolls 10, 11 supported by support rolls 9. The latter can be moved axially, preferably with a CVC shift 12, as well as with work roll bending devices 13; the work rolls to be axially displaced (provided with a ground, thermal and wear contour) or the CVC shift 12 and the work roll bend 13 are used as mechanical actuators which act either in the strip center region or in the strip edge region.

To support these mechanical actuators 12, 13, a strip edge heater 14 is arranged in front of and behind the first stands of the finishing train to change the edge heating of the rolled strip 3 or 4. To thermally influence the strip shape, namely via the changes in the thermal crown of the work rolls 10, 11 caused thereby, the hot strip tandem mill 6 has a work roll zone cooling 15 in the area of the front or rear roll stands, e.g. in the form of spray nozzles directed in the corresponding zones onto the work rolls 10, 11, as indicated behind the first roll stand 7. A band edge cooling 16 with e.g. spray nozzles and work roll cover shells 18 arranged in the side guides, as shown for the last roll stand 8. The lubrication of the work rolls 17 in the strip edge area influences the load distribution in the roll gap and thus the strip contour. Thickness, flatness and temperature measuring devices 19, 20, 21 are also arranged behind the last rolling stand 8.

The measuring devices 19 to 21 as well as the mechanical actuators 12, 13 and the thermal and other influencing elements 14 to 18 are connected to a strip contour and flatness computer 22. The measured data determined, in particular for the profile and the flatness of the finished rolled strip 3, 4, can therefore be used directly to correct the upstream control systems or actuators, with the aim of achieving the predetermined target contour of the profile of the rolled strip for all strips. A pass schedule calculator 23 supplies the strip contour and flatness calculator 22 with input data. A data feedback 24 is intended for the purpose of redistributing the rolling force.

The procedure described for achieving a predetermined target contour of the profile of the rolled strip is used in online operation. Nevertheless, when creating the rolling program (planning the rolling programs), the processes can be simulated offline in advance and the strip shape in particular can be determined in this way. If it turns out that the optimization process carried out beforehand with regard to a strip shape for certain strips is not successful, the rolling programs can be changed over or the strips can be used in another rolling program. Also included can be a cyclical displacement of the rear work rolls or roll stands adapted to the rolling program and / or an optimized positioning, for example, of the cover shells 18 for the thermal crown influencing of the work rolls 10, 11. After the strip has been selected or the rolling program changed, the target contour begins optimizing process from scratch until offline, ie can achieve an acceptable band shape in advance.

Claims (7)

1. Method of rolling a roll strip in a hot strip rolling train, which comprises at least two roll stands with horizontally adjustable upper and lower working rolls, each of which is supported at a backing roll either directly or by way of an intermediate roll, or in a reversing stand at which at least two passes are rolled, in which the roll strip is subjected to a condition regulation, characterised thereby that a target contour of the profile of the roll strip is preset, for the attainment of which successively two groups of setting elements act on the roll strip, of which the setting elements of the first group are brought into use in the case of roll strip thicknesses lying above the critical thickness and predominantly influence the contour of the roll strip in the middle region thereof referred to the strip centre, whilst the setting elements of the second group are brought into use in the case of roll strip thicknesses, which lie below the critical thickness, in the strip edge region.
2. Method according to claim 1, characterised thereby that the preset target thickness of the strip profile is described by a polynominal function $${\text{Y = A}}_{\text{2}}{\text{X}}^{\text{2}}{\text{+ A}}_{\text{4}}{\text{X}}^{\text{4}}{\text{+ A}}_{\text{6}}{\text{X}}^{\text{6}}{\text{+ A}}_{\text{n}}{\text{X}}^{\text{n}}\text{,}$$

   

   wherein Y represents the strip thickness co-ordinate and X the strip width co-ordinate.
3. Method according to claim 1 or 2, characterised thereby that in the case of a strip profile shape departing from the target contour the mechanical setting elements are so brought into use that a minimum deviation between the achieved Strip shape and the desired strip shape or target contour results.
4. Method according to one or more of claims 1 to 3, characterised thereby that the mechanical setting elements are brought into use as early as possible.
5. Method according to one of claims 1 to 4, characterised thereby that the mechanical setting elements are assisted by non-mechanical setting elements.
6. Method according to one of claims 1 to 5, characterised thereby that working rolls used as mechanical setting elements are locally heated in targeted manner.
7. Method according to one of claims 1 to 6, characterised thereby that working rolls used as mechanical setting elements are ground during the rolling operation.

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