EP0928644A1 - Control method for continuous skinpass rolling of metal strip - Google Patents

Abstract

The strip passes through an upstream reduction rolling mill cage (2) and a downstream cage (3). The tightening force of the upstream cage (2) is regulated as a function of the tension between the two cages (2, 3), the response time for this regulation being chosen to be very much greater than the response time for the speed of regulation. The strip passes through an upstream reduction rolling mill cage (2) and a downstream cage (3). The speed of the upstream cage (2) is regulated with respect to the downstream cage (3) as a function of the rate of elongation caused by the upstream cage (2). The tightening force of the upstream cage (2) is regulated as a function of the tension between the two cages (2, 3), the response time for this regulation being chosen to be very much greater than the response time for the speed of regulation.

Description

The invention relates to a method for controlling an operation. continuous hardening and reduction of a metal strip in a work hardening installation, comprising at least two successive cages of rolling.

One understands by operation of hardening and reduction in particular a operation called “skin-pass” in English or an operation of second reduction rolling (called "DR"); for this type of operation, installations with at least two cages are generally used successive of which only one, called reduction cage, realizes most of the reduction in strip thickness; in the case of a installation with two cages, the reduction cage is the upstream or first cage cage, and in the case of a three-cage installation, the reduction cage is the second cage, the one in the middle of the installation.

A rolling or work hardening cage of this type of installation has two working cylinders rotating in opposite directions in the air gap which a metal strip can be reduced and / or hardened; in terms of the clamping force of these cylinders, the thickness of the metal strip is reduced and its length, on the contrary, increased.

For a given metal strip, the elongation rate obtained is depending on the clamping force of the cage; in the case of a “skin-pass”, the elongation rate is low, whereas in the case of a “DR” operation, it can reach around 60%.

In these installations, the speed of rotation of the cylinders of two cages successive (called "cage speed" in abbreviated style) must be precisely controlled so as to maintain a level between these cages band tension high enough to prevent wrinkles but also low enough to avoid any risk of the band breaking.

Between two successive cages, the cage speed differential depends therefore the rate of elongation of the strip.

For the piloting of these installations, one therefore generally measures a firstly the rate of elongation of the strip when passing through the installation and other share the belt tension between the cages, and, depending on the values measured, we act on the following actuators: the clamping force of each cage and the cylinder speed of each cage.

To measure the rate of elongation of the strip in a cage, we generally proceeds by measuring the outgoing tape speed and the reentry belt speed, the rate of elongation deduced from the difference between these speed measurements; such a process is described in the patent British 794 290 where speed measurements are made using tachometric means mounted on upstream tape support rollers and downstream of the installation.

The invention relates to a method for adjusting these actuators according to of these measures.

• régulation selon le mode 1 : le taux d'allongement est régulé par la traction intercage.
• régulation selon le mode 2 (les références concernent la fig. 1 ci-après) :
  • régulation d'allongement par le rapport entre la vitesse du « bloc en S » 1' en amont et celle de la première cage 2 en aval ;
  • régulation (système « ATL » à bande morte) de la traction entre le « bloc en S » 1' et la première cage 2 en fonction du même rapport de vitesse et du serrage de la première cage 2.
• régulation selon le mode 3 identique à celle du mode 2, où l'on remplace les mesures de taux d'allongement par des mesures d'épaisseur (« THG »).

In the case of an installation comprising only two cages, the article by Yuli Shimoyama et al., Entitled “Kawaski continuous annealing line at Chiba” - IRON & STEEL ENGINEER, Vol. 69, No. 11, 1992, p. 35-41 - describes three control methods on page 37, left column which are illustrated in Figure 4 of this document:

• regulation according to mode 1: the rate of elongation is regulated by the interlining traction.
• regulation according to mode 2 (the references relate to fig. 1 below):
  • regulation of elongation by the ratio between the speed of the “S-block” 1 ′ upstream and that of the first cage 2 downstream;
  • regulation (dead band “ATL” system) of the traction between the “S block” 1 ′ and the first cage 2 as a function of the same speed ratio and the tightening of the first cage 2.
• regulation according to mode 3 identical to that of mode 2, where the elongation rate measurements are replaced by thickness measurements (“THG”).

Mode 2 is shown schematically in the block diagram of Figure 1, where 1 ', 2 and 3 respectively designate the “S-block”, the first cage and the second cage ; 4A and 4B the elongation rate measurement device.

• régulation des tractions intercages par la vitesse,
• régulation d'allongement par le serrage de la cage 2 et par la traction entre les cages 2 et 3.

In the case of an installation comprising three cages, the article by C.SILVY-LELIGOIS entitled “Regulation of elongation in double reduction at Sollac Basse-Indre” - REVUE de MÉTALLURGIE, Vol.89, n ° 12, 1992, p.1101-1109 - describes another regulatory strategy:

• regulation of inter-traction by speed,
• elongation regulation by tightening the cage 2 and by pulling between the cages 2 and 3.

This strategy is shown below in Figure 2 which reproduces the Figure 3 of the cited article; in this figure, 1, 2 and 3 respectively denote the first, second and third cage and 4A, 4B the rate measuring device elongation.

• régulation de la traction intercage par la vitesse,
• régulation d'allongement par le serrage et, optionnellement, la traction intercage.

Finally, FIG. 3 below represents the state of the art in the case of an installation comprising only two cages 2 and 3:

• regulation of the intercage traction by the speed,
• elongation regulation by tightening and, optionally, interleaving traction.

Such a regulatory overview is also described in the document FR 2,584,631 (MITSUBISHI).

A - régulation des vitesses de deux cages successives en fonction de la valeur de tension de la bande entre ces cages, adaptée pour éviter la rupture de bande ou l'apparition de plis.

B - régulation de la force de serrage de la cage de réduction en fonction de la différence entre le taux d'allongement de bande apporté par cette cage et une consigne prédéterminée de taux d'allongement.

Thus, as illustrated in FIGS. 1 to 3, to control this type of work hardening installations, the procedure is carried out according to a double regulation:

A - regulation of the speeds of two successive cages as a function of the tension value of the strip between these cages, adapted to avoid breaking of the strip or the appearance of folds.

B - regulation of the clamping force of the reduction cage as a function of the difference between the rate of band elongation provided by this cage and a predetermined set rate of elongation.

The transfer function of regulation B is complex because the law of behavior linking force and elongation is not at all linear; this law of behavior is similar to the classical law of behavior linking the tensile and elongation, as shown in Figure 4.

According to this law, as the elongation increases from zero, traction starts to increase very strongly, then decreases slightly from irregularly, before resuming slight growth and stabilize.

As the actions on the clamping force (actuator of regulation B) affect the tension value of the belt between two stands (measurement of regulation A), regulation loop A will interact in the regulation loop B.

It is therefore important that the response time of regulation A is fast enough with regard to that of regulation B so that the changes in clamping force are unlikely to cause breakage tape or folds between two successive cages.

Thus, in this type of process, regulation B is of the “band” type dead ”.

• un temps de réponse trop long, car il doit rester supérieur à celui de la régulation A ;
• une précision insuffisante, notamment à cause de la bande morte et de la complexité (non linéarité) de la fonction de transfert.

Such a method of controlling a work hardening installation has many drawbacks in terms of regulating the rate of strip elongation (regulation B), among which:

• too long a response time, because it must remain greater than that of regulation A;
• insufficient precision, in particular because of the dead band and the complexity (non-linearity) of the transfer function.

The invention aims to remedy these drawbacks.

• on fait passer la dite bande dans l'entrefer des cylindres de travail d'au moins deux cages de laminage successives, une cage amont assurant l'essentiel de ladite réduction d'épaisseur et une cage aval,

   et dans lequel, afin de régler en continu la vitesse de rotation et la force de serrage des cylindres de la cage de réduction d'épaisseur,

• on mesure le taux d'allongement de la bande apporté par cette cage,
• on mesure la tension de la bande en aval de cette cage,

   caractérisé en ce qu'il comprend les étapes consistant à :

• régler la vitesse des cylindres de cette cage par rapport à celle des cylindres de la cage aval en fonction de la mesure du taux d'allongement,
• régler la force de serrage de cette cage en fonction de la mesure de tension en aval,

   le temps de réponse pour le réglage de la force de serrage étant choisi très supérieur au temps de réponse pour le réglage de la vitesse.To this end, the subject of the invention is a method for controlling a continuous work hardening and thickness reduction operation of a metal strip B in which:

• said strip is passed through the working cylinder air gap of at least two successive rolling stands, an upstream stand ensuring most of said thickness reduction and a downstream stand,

and in which, in order to continuously adjust the speed of rotation and the clamping force of the cylinders of the thickness reduction cage,

• we measure the rate of elongation of the strip brought by this cage,
• the tension of the strip downstream of this cage is measured,

characterized in that it comprises the stages consisting in:

• adjust the speed of the cylinders of this cage relative to that of the cylinders of the downstream cage as a function of the measurement of the elongation rate,
• adjust the clamping force of this cage according to the downstream tension measurement,

the response time for adjusting the clamping force being chosen to be much greater than the response time for adjusting the speed.

Preferably, the clamping force of this cage is adjusted so as to maintain said measured voltage within a predetermined range of values, the possible modification of the clamping force only intervening when said belt tension leaves said range; this type of setting is conventionally called "dead band regulation".

• les figures 1 à 3 sont des synoptiques de régulation de l'art antérieur,
• la figure 4 représente une loi de comportement typique de variation de la traction (N/mm2) de la bande en fonction de son allongement (%) dans une cage de réduction et/ou d'écrouissage,
• la figure 5 représente une vue schématique en perspective d'une installation de réduction et/ou d'écrouissage à deux cages qui peut être pilotée par le procédé selon l'invention,
• les figures 6 et 7 sont des synoptiques de régulation selon l'invention,
• les figures 8 et 9 illustrent les performances de régulation d'installation d'écrouissage, exprimées en stabilité de la valeur d'allongement (%) en fonction du temps (secondes), dans le cas d'une régulation selon l'art antérieur (figure 8) et d'une régulation selon l'invention (figure 9).

The invention will be better understood on reading the description which follows, given by way of nonlimiting example, and with reference to the appended figures in which:

• FIGS. 1 to 3 are diagrams of regulation of the prior art,
• FIG. 4 represents a typical behavior law of variation of the traction (N / mm2) of the strip as a function of its elongation (%) in a reduction and / or work hardening cage,
• FIG. 5 represents a schematic perspective view of a reduction and / or work hardening installation with two cages which can be controlled by the method according to the invention,
• FIGS. 6 and 7 are block diagrams of regulation according to the invention,
• FIGS. 8 and 9 illustrate the regulation performance of the work hardening installation, expressed in stability of the elongation value (%) as a function of time (seconds), in the case of regulation according to the prior art ( Figure 8) and a regulation according to the invention (Figure 9).

According to Figures 1 to 3, 5 to 7, by convention, the scrolling of the strip is carried out from left to right (see arrow in figure 5).

Referring to Figure 5, the strip work hardening installation continuous metal comprises, in the direction of travel of the band B, a unwinder 7, an input S block 1 ', a first cage 2 then a second cage 3, an outlet S-block 5 and a rewinder 6.

The unwinder 7 and the rewinder 6 are of a conventional type and will not be not described in detail.

The “S” blocks 1 ', 5, composed of two support rollers strip, are used in a conventional manner to vary the tension of strip B; one of the rollers of each block is provided with non-tachometric means shown 4A, 4B adapted to accurately measure the speed of passage of band B in these blocks 1 ', 5.

Each cage 2, 3 has two supported working rolls each by a support cylinder; means not shown allow to varying the clamping force of the working rolls towards each other; others means not shown allow the speed of rotation to be varied working cylinders of each cage.

Finally, the work hardening installation also includes means (not shown) to measure the belt tension between stands 2 and 3.

We will now describe the operation of the work hardening installation according to the invention.

While the tape B is scrolling through the installation (in the direction of the arrow affixed on strip B between cages 2 and 3 - cf. figure 5), at the level from the last cage, i.e. from cage 3, no lubricant is sprayed onto band B in the air gap of this cage so as to obtain no elongation or very reduced elongation of the band B at this level; strength clamping of this cage 3 is adapted to adjust, in a manner known in itself, the flatness of the strip B at the exit of the cage; the very elongation reduced may be of the order of 0.1 to 0.5% and remains sufficiently stable to not not disturb the regulation.

A' - régulation des vitesses des cages successives amont 2 et aval 3 en fonction de la différence entre le taux d'allongement de bande apporté par la cage amont 2 et une consigne prédéterminée de taux d'allongement.

B' - régulation de la force de serrage de la cage amont 2 en fonction de la différence entre ladite tension mesurée entre la cage amont 2 et la cage aval 3 et une consigne prédéterminée de tension.

While the strip B is scrolling through the installation, according to the invention, the following double regulation is then carried out:

A '- regulation of the speeds of the successive upstream 2 and downstream 3 cages as a function of the difference between the rate of band elongation provided by the upstream cage 2 and a predetermined set rate ratio.

B '- regulation of the clamping force of the upstream cage 2 as a function of the difference between said voltage measured between the upstream cage 2 and the downstream cage 3 and a predetermined voltage setpoint.

• régulation de la traction intercage par le serrage de la cage amont 2,
• régulation d'allongement par la vitesse.

FIG. 6 then represents the corresponding regulatory diagram:

• regulation of the intercage traction by tightening the upstream cage 2,
• elongation regulation by speed.

For regulation A ', the measurement of the elongation rate of the upstream cage 2 conventionally follows from the tachometric measurements practiced in 4A, 4B at level of block in S input 1 'and output 5, after deduction of the rate reduced elongation of the cage 3.

The regulation B ′ is preferably of the “dead band” type, that is to say that the clamping force is only acted on if the tension of the strip comes out of a predetermined range of values (the maximum corresponding for example to a risk of rupture, the minimum, for example, a risk of creases).

According to the invention, the gain of regulation B 'must be adapted so that the response time of this regulation is much greater than the response time responds to regulation A '.

As a variant, the regulation operation B ′ can even be carried out "Manually" by the installation operator.

• une très grande précision du taux d'allongement de la bande : pour des taux d'allongement correspondant à une opération de « skin-pass » et généralement compris entre 0,4% et 4%, on atteint une précision de ± 0,05 %.
• une très grande « robustesse » de régulation, car la fonction de transfert de la régulation A' est linéaire puisque ce sont des mesures de vitesse de bande qui agissent sur un actionneur de vitesse.
• une très grande régularité dans la précision et un temps de réponse très court, ce qui permet de diminuer sensiblement le chutage de bande ; l'actionneur de vitesse étant beaucoup plus rapide que l'actionneur de serrage, pour la régulation A', on atteint un temps de réponse de 200 ms.

This new configuration of the regulation of the work hardening installation brings the following advantages:

• very high accuracy in the elongation rate of the strip: for elongation rates corresponding to a “skin-pass” operation and generally between 0.4% and 4%, an accuracy of ± 0.05 is reached %.
• a very high “robustness” of regulation, because the transfer function of regulation A 'is linear since these are belt speed measurements which act on a speed actuator.
• very regularity in precision and a very short response time, which makes it possible to significantly reduce tape drop; the speed actuator being much faster than the clamping actuator, for regulation A ', a response time of 200 ms is reached.

These advantages make it possible to limit the falling of tape in production.

• la première cage 1 joue le rôle du « bloc en S » 1' de l'installation précédemment décrite , sa vitesse servant à régler la traction devant la deuxième cage 2 (voir figure 7) ; cette première cage ne réalise quasiment aucun allongement comme la dernière cage 3 de l'exemple précédent ; cette première cage a donc une fonction de « pinceur » de bande.
• les deux autres cages fonctionnent comme les cages 2 et 3 de l'exemple précédent.

In the case of a rolling and / or work hardening installation comprising three successive cages 1, 2 and 3, and where the cage 2 is the reduction cage, the invention can be implemented as follows:

• the first cage 1 plays the role of the “S block” 1 ′ of the installation described above, its speed being used to adjust the traction in front of the second cage 2 (see FIG. 7); this first cage achieves almost no elongation like the last cage 3 of the previous example; this first cage therefore has a strip "pinch" function.
• the other two cages work like cages 2 and 3 in the previous example.

• régulation de la première traction intercage par la vitesse, comme dans l'art antérieur (figure 2),
• régulation de la deuxième traction intercage, en aval de la cage 2, par le serrage de la cage 2, qui est la cage qui applique la réduction d'épaisseur principale,
• régulation d'allongement par la vitesse relative des cages 2 et 3.

The regulation strategy according to the invention is illustrated in this case in FIG. 7:

• regulation of the first intercage traction by speed, as in the prior art (FIG. 2),
• regulation of the second intercage traction, downstream of the cage 2, by tightening the cage 2, which is the cage which applies the main thickness reduction,
• regulation of elongation by the relative speed of the cages 2 and 3.

The following example illustrates the advantages provided by the invention.

Example :

The purpose of this example is to compare the performance of the regulation according to the invention compared to those of a conventional art regulation previous in the case of a steel strip rolling operation carried out after annealing (called "double reduction").

To assess performance, we measure the rate of elongation of the band (%) as a function of time (seconds) in the face of a voluntary disturbance caused on the reduction cage, and we evaluate the fluctuations of this rate elongation; the performance of regulation is all the better as these fluctuations are small or the rate of elongation is stable.

Figure 8 illustrates these fluctuations in the classic case where pull-ups are regulated by speed and where the band elongation (or thickness) is regulated either directly by tightening the reduction cage or indirectly by traction interlining with recentering by tightening the reduction cage; there are significant fluctuations in the elongation: ± 3% around the average value of 37.5%.

Figure 9 illustrates, facing the same disturbance, these fluctuations in the case, according to the invention, the intercage traction is regulated by the tightening of the reduction cage and where the elongation is directly regulated by the speed of the last cage; we note that the elongation remains almost constant, the fluctuations being reduced by a factor of at least 5 compared to the case previous.

Claims (2)

Method for controlling a continuous work hardening and thickness reduction operation of a metal strip B in which: said strip is passed through the working cylinder air gap of at least two successive rolling stands, an upstream cage (2) providing most of said thickness reduction and a downstream cage (3), and in which, in order to continuously adjust the speed of rotation and the clamping force of the cylinders of the thickness reduction cage (2), the rate of elongation of the strip provided by this cage (2) is measured, the tension of the strip downstream of this cage (2) is measured, characterized in that it comprises the stages consisting in: adjust the speed of the cylinders of this cage (2) relative to that of the cylinders of the downstream cage (3) as a function of the measurement of the rate of elongation, adjust the clamping force of this cage (2) according to the downstream tension measurement, the response time for adjusting the clamping force being chosen to be much greater than the response time for adjusting the speed. Method according to claim 1 characterized in that the clamping force of this cage (2) so as to maintain said tension measured within a predetermined range of values, the change possible clamping force occurring only when said tension of strip comes out of said fork.

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