EP1761347A1 - Method for rolling strips in a roll stand - Google Patents

Abstract

The invention relates to a method for rolling strips in the roll stand of a rolling mill, wherein said roll stand consists of two axially displaceable working rollers which are provided with a CVC-grinding or a similar contour and whose curved profile is expressed in a third or higher-order polynom and, simultaneously with simple handling of working rollers with large possibilities of adjusting the profile and flatness, the aim of said invention is to homogenize the working rollers wear. For this purpose, the increased cyclic shifting of the working rollers is induced or forced by a cyclic variation of the setting values of the curve of the working cylinders from one strip to another in a predetermined part of the adjustment range thereof, wherein the combined the action of the two adjustment systems (the curve of the working cylinders and the shift thereof) enables the parabolic effects of said two adjustment systems to supplement each other with a high approximation, thereby ensuring the flatness and, in addition, optimally homogenizing the working roller wear.

Description

 Method for rolling strips in a roll stand

The invention relates to a method for rolling strips in a rolling stand of a rolling train consisting of two axially displaceable work rolls which are provided with a CVC cut or similar contour whose curved contour can be expressed by a third or higher order polynomial is, from two back-up rolls and optionally in addition two intermediate rolls and from a work roll bending system and optionally an additional intermediate roll bending system, wherein the work roll bending or the Ar¬ beitswalzenverschiebung be used occasionally for controlling the strip flatness and the strip profile as adjusting mechanisms. Alternatively or additionally, an application of the intermediate roll bending and intermediate roll displacement can take place in the same way as the work roll bending.

The flatness of the strip is set by the use of conventional rollers by the suitable choice of a work roll crown (positive, negative or cylindrical) and the work roll bending. The disadvantage is that different work roll crowns must therefore be used with different rolling programs, which makes work roll handling difficult. Weiter¬ towards the work roll bending often reaches its limit in complicated rolling programs and thus can not always ensure the flatness.

To simplify work roll handling while positively influencing the profile and planarity, the use of work rolls with a CVC contour (CVC = Continuously Variable Crown) has also been proven in the back stands of a rolling mill.

The work roll bending rarely reaches its limits and is available for dynamic control. The disadvantage is that at one Conventional shifting practice of CVC work rolls, the Ver¬ used shift range within a rolling program is relatively low fails and the Arbeitswalzen- wear comparison only follows in a limited form er¬. As a compromise, therefore, a flat CVC grinding is used, ie a reduced CVC adjustment range with the corresponding displacement stroke.

Based on this prior art, it is an object of the invention to provide a method for rolling strips in a roll stand with axially displaceable CVC work rolls or work rolls with similar contour an¬ with the same easy handling with large profile and Flatness adjustment at the same time the work roll wear is evened out.

The stated object is achieved with the features of claim 1, characterized in that at the same time a cyclic extended displacement of the work rolls is excited or forced by a cyclical change of the work roll bending from band to band in a defined predetermined part of their control range to the band flatness or the Adjusting the body band profile, whereby the combination of the effect of the two adjusting systems (work roll bending and work roll displacement) complement each other to a good approximation parabolically acting effects of these two control systems and thus ensure the flatness and additionally cause optimal homogenization of Arbeitswal¬ zenverschleißes.

Advantageous embodiments of the invention are specified in the subclaims.

The cyclic shifting of work rolls per se is already known. However, this mode of operation has hitherto been practiced only with rolls with a conventionally cambered work roll grinding, primarily in the rear stands of a rolling train (Hitachi Review Vol. 34 (1985), No. 4, pages 153 to 167) or in exceptional cases with tapered rolls in a restricted area (EP 0153 849 A2).

The inventive cyclic change of work roll bending on CVC rolls, which have a relatively large parabolic profile range, has not yet been practiced and is new. This cyclical change in the work roll bending, which can be assisted by the rolling force or by the rolling force distribution within the rolling train, initiates an additional cyclic shift of the work rolls in the case of CVC rolls with simultaneous work roll wear uniformity. The large parabolic profile adjustment range of the CVC work rolls remains available at any time in order to be able to react to changing boundary conditions such as back-up roll wear, thermal crown, rolling force or stand load, etc. Depending on these boundary conditions, the cyclic shifting of the work rolls is then preferably carried out either in the positive, negative or in the entire displacement range.

According to the invention, the cyclic shifting of the work rolls is directly vor¬ given or forced indirectly by the cyclic changing the work roll bending, wherein the interaction of the work roll displacement and the work roll bending is controlled by a process model online.

The cyclic alteration of the work roll positions or bending is carried out only within the permissible range in which the strip quality parameters such as flatness (parabolic and higher order), strip contour quality and belt profile level can be met, whereby to ensure compliance with these criteria by the process model - monitored online - The cyclic shift stroke and / or the preset range for the work roll bending can then be limited.

Since in the case of the first break-in straps, for example after a roll change, the profile and flatness then required are automatically increased. If the shift position changes are to be expected, the cyclic change of the work rolls is activated either directly after a roll change or only shortly thereafter, for example after the first five strips.

Instead of or in addition to the cyclic change in the work roll bending, alternatively, depending on the type of scaffold, the intermediate roll bending or intermediate roll displacement or a support roll profile actuator can be used in an analogous manner in order to produce a cyclical change in the work roll positions.

Further details, features and advantages of the invention will be explained in more detail below with reference to exemplary embodiments illustrated in schematic drawing figures.

Show it:

1 strip width rolling program for 85 belts, FIG. 2 finished strip thickness rolling program for 85 belts, FIGS. 3 and 4 conventional shifting with high scaffolding load, FIGS. 5 and 6 conventional shifting with low scaffolding load, FIGS. 7 and 8 cyclic shifting with high scaffolding load, FIGS. 9 and 10 cyclic shifting with low scaffolding load, FIG. 11 work roll wear contour with cyclical shifting, FIG. 12 work roll wear contour with conventional shifting.

In the illustrated examples, the simulated two operations of work roll shifting and work roll bending for differential displacement were illustrated using an example of a rolling program of 85 coils. In the drawing figures 1 to 10, the number or the consecutive number of the bands (No. of coils) is indicated in each case as abscissa. In FIG. 1, the strip widths BB to be rolled in accordance with the rolling program and in FIG. 2 the finished strip thicknesses BD in each case are plotted as ordinate in mm. Until about Band No. 40 different strip widths BB and finished strip thicknesses BD are rolled, then bands are produced with constant Bandbrei¬ te BB of about 1200 mm and constant finished strip thickness BD of about 2.8 mm.

For the rolling program shown in FIGS. 1 and 2, the expected results for conventional displacement of the CVC work rolls with different skeleton load or different support roll wear were plotted in FIGS. 3 to 6.

In FIGS. 3 and 4, the results obtained for the required work roll displacement position VP are in mm (FIG. 3) and the applied work roll bending force BK in kN (FIG. 4) for a high support roller wear or a high framework load shown. As can be seen from FIG. 3, in this conventional mode of operation the work roll positions are set primarily in the positive range in order to produce, for B. to compensate for the burden of the scaffolding. In some cases, the maximum shift limit VP _max is reached.

FIGS. 5 and 6 show, in accordance with FIGS. 3 and 4, the results obtained for a low support roller wear or a low framework load. The curves obtained for the work roll displacement position VP (FIG. 5) and for the work roll bending force BK (FIG. 6) are similar in their characteristics to those of FIGS. 3 and 4, with the work roll displacement values VP corresponding to approximately the same bending force the changed boundary condition - be operated more in the middle shift range. What is common is that, overall, in a conventional shift of the CVC work rolls, the shift amount is relatively low and according to the rolling program, the work roll bending force BK constant from about the 40th band (BK _CO nst) - In FIGS. 7 to 10, the expected results for the cyclic shifting of the CVC work rolls or work roll bending according to the invention are plotted for different stand loadings or different support roll wear for the same rolling program.

Figures 7 and 8 show the results obtained for the work roll displacement position VP in mm (Figure 7) and the applied work roll bending force BK in kN (Figure 8) for high back-up roll wear or high stand load. Clear of the results of the conventional shifting of FIG. 3 is the large adjustment range of the CVC work rolls, the rolls being operated in the positive as well as in the negative region.

FIGS. 9 and 10 show, in accordance with FIGS. 7 and 8, the results obtained for low back-up roller wear or low back-up load. The curves obtained for the work roll displacement position VP (FIG. 9) and for the work roll bending force BK are also similar in their characteristic to those of FIGS. 7 and 8, with approximately the same bending force BK resulting in a cyclic displacement of the CVC. Rolling takes place more in the negative displacement range in accordance with the changed boundary conditions.

Characteristic for the operation according to the invention of the cyclic sliding is the opposite interaction between the work roll displacement position VP and the work roll bending force BK, which becomes clear in the drawing figures. When the CVC work rolls are displaced in the negative direction VP _n , a bend in the positive direction BK _{P can be seen} and vice versa.

The Arbeitswalzen Verschleissvergleichmässigung achieved by the inventive cyclic shifting of the CVC work rolls is in Figures 11 and 12 clearly. Plotted here are the work roll wear AV in mm over the work roll bale length BL in mm, which arises at the end of the rolling program. With approximately the same amount of wear in the center of the roller, the roller contour WK in the cyclic mode of operation (FIG. 11) is more harmonious in the edge region compared to the conventional mode of operation (FIG. 12), while due to the smaller displacement in the conventional mode of operation a steeper wear flank recognizable with a more angular Ll- transition.

A haromonish work roll wear contour has a positive effect on the quality of the strip contour. The formation of band bulges or an increased band edge drop (edge drop) can thus be compensated more efficiently. LIST OF REFERENCE NUMBERS

AV Work roll wear BB Belt width BD Finished belt thickness BK Work roll bending force BKconst Constant bending force BK _max Maximum bending force BK _p Bending in positive direction BL Work roll bale length no. Coil number VP Work roll shift position VPmax Maximum shift limit VPmin Minimum shift limit VP _n Shift in negative direction VP _p Shift in positive direction WK Work roll contour

Claims

claims 1. A method for rolling strips in a roll stand of a Walzstra¬ SSE consisting of two axially displaceable work rolls, which are provided with a CVC cut or similar contour whose curved contour can be expressed by a polynomial of third or higher order, from two Support rollers and optionally additionally two Zwischenwal¬ zen and from a work roll bending system and optionally an additional intermediate roll bending system, the Arbeitswal¬ zenbiegung or the work roll displacement are occasionally applied to control the band flatness and the strip profile as adjusting mechanisms, characterized in that by a cyclical change of the work roll bending of Band to band in a defined predetermined part of their control range at the same time a cyclic extended displacement of the work rolls an¬ excited or enforced to adjust the band flatness or the body band profile, which is due to the combination of Effect of bei¬ the positioning systems (work roll bending and work roll displacement) complement each other parabolically acting effects of these two Stell¬ systems to a good approximation and thus ensure the flatness and zu¬ additionally make an optimal equalization of Arbeitswalzenverschleißes. 2. The method according to claim 1, characterized in that depending on the boundary conditions such as Stützwalzenverschleiß, thermal crown, rolling force, etc., the cyclic displacement of the work rolls is preferably carried out either in the positive, negative or in the entire Verschiebestellbereich. 3. The method according to claim 1 or 2, characterized in that the cyclic displacement of the work rolls is directly specified or enforced indirectly by the cyclic changing of the work roll bend gene. 4. The method of claim 1, 2 or 3, characterized in that the interaction of the work roll displacement and the Ar¬ beitswalzenbiegung is controlled by a process model online. 5. The method according to claim 4, characterized in that the cyclic changing of the work roll positions or bending is performed only in the permissible range in which the Bandquali- tätsparameter such as flatness (parabolic and higher order), Bandkon¬ turgüte and band profile level are met, wherein the cyclical shift stroke and / or the preset range for the work roll bending can be restricted by the process model online in order to comply with these criteria. 6. The method according to one or more of claims 1 to 5, characterized in that the work roll bending is supported by a cyclic change in the rolling force or the rolling force distribution within the rolling mill. 7. The method according to one or more of claims 1 to 5, characterized in that instead of or in addition to the cyclical change of the work roll bending alternatively depending on the scaffolding type the intermediate roll bending or intermediate roll displacement or a back-up roll actuator in ana be used loger type to produce a cyclic change of Arbeits¬ roller positions. 8. The method according to one or more of claims 1 to 7, characterized in that the cyclic changing of the work rolls directly after the Wal¬ zenwechsel or shortly thereafter, for example, after the first five Bän¬ countries, activated, as at the first Einfahrbändern at Adjustment of profile and flatness automatically larger sliding position changes are to be expected.