Process and device for intentionally influencing the geometry of roughed-down strips in a roughing-down stand

The invention concerns a process and a device for hot rolling in a hot strip mill or in Steckel mills, where slabs are rolled out to near-net strip in one or more roughing stands.

The near-net strip produced in this way should be straight, i.e., it should have only slight strip cambering and should have no wedging over the width of the strip. It is the task of the roughing stands not merely to maintain the geometry of the near-net strip but rather to improve it in a systematic way, since the slabs entering the stands may already be affected by wedging or cambering. A change in the geometry of the near-net strip is possible primarily in the first passes, since the slab thickness is still large relative to the width, so that transverse flow of material in the roll gap is possible.

The rolling of hot strip is sometimes attended by variably large drafts per pass over the length of the roll gap (over the width of the strip), which can be attributed to variations in the quality of the rolling stock, to variations in the roll gap itself, or to the geometry of the entering rolling stock. These variably large drafts per pass then lead to lateral deflections and shifts of the rolling stock in the stand and to lateral curvature of the exiting hot rolled strip.

Various processes and devices are known for automatically controlling the advancement of the strip and for correcting the curvature of the exiting hot rolled strip.

For example, DE 197 04 337 A1 proposes a process for automatically controlling the advancement of rolled strip as it passes through a rolling train, where the position of the rolled strip relative to the center line of the rolling train is measured in at least one rolling stand, and the measured values are used for automatically adjusting the rolling force distribution in the longitudinal direction of the rolls of this rolling stand to obtain a desired set position. This measure results in advancement of the rolled strip that is very nearly symmetrical to the center line, but it may also lead to the development of wedging of the rolled strip.

DE 43 10 547 C2 discloses another possible process for preventing lateral bending of the rolled strip, which is moved continuously through a roughing train with an edging mill for influencing the width of the strip and a horizontal rolling mill for influencing the thickness of the strip, in which hydraulically adjustable lateral guides are installed along the sides of the rolled strip. The lateral guides are arranged upstream and downstream of the edging mill and control the lateral shifting of the rolled slab, and they allow unhindered entrance and exit of the rolled strip by alternate narrowing of the distance between the lateral guides.

DE 31 16 278 C2 discloses a device for controlling the position of the strip travel, especially during finish rolling, in which guide strips arranged alongside the rolled strip have bending bars with guide rollers, which are pressed laterally against the rolled strip. The automatic position control system of these rollers has a superimposed automatic pressure control system, which, when disturbing forces arise that exceed a preset value, brings about a shift of the guide strips or guide rollers in the opening direction.

With this prior art as a point of departure, the objective of the invention is to effect systematic influencing of the geometry of the near-net strip during hot rolling in conventional hot strip mills or in Steckel mills, with the goal of producing straight near-net strips without wedging and without lateral curvature.

The objective of the invention with respect to a process is achieved such that, in at least one roughing stand, to effect systematic influencing of the geometry of the near-net strip, dynamic adjustment in the roughing stand is combined with fast and powerful lateral guides upstream and downstream of the roughing stand by means of suitable automatic controls in such a way that a slab affected with cambering or wedging is systematically shaped into a straight and wedge-free near-net strip in one or more passes in a reversing or continuous operation. Advantageous modifications are specified in the dependent claims.

In accordance with the invention, the geometry of the near-net strip is influenced by adjustment in the horizontal stand and in the two adjustable lateral guides upstream and downstream of the stand. The adjustment in the horizontal stand provides for constant strip thickness over the width of the strip (no wedging). To this end, the RAC (roll alignment control), which has not previously been used for roughing stands, is used to control the adjustment in such a way that the roll gap remains parallel even in the case of disturbances originating with the strip. Disturbance variables include above all a thickness wedge over the width of the strip on the run-in side, temperature differences over the width of the strip, eccentric position of the strip in the roll gap, and nonuniform distribution of tensile forces over the width of the strip on the run-in side as well as the runout side.

In accordance with the principle of roll alignment control, the differential force is measured, and a roll alignment value is computed by the roll alignment control system. Half of this value is then used as an additional set value for the separate automatic position control of the drive side and service side of the stand. One then proceeds accordingly for the adjustments of the contact pressures by the hydraulic cylinders. In principle, the control system compensates the stand transverse strain that arises due to the differential forces.

The purpose of the lateral guides is to prevent curvature or twisting of the strip (cambering). To this end, the lateral guides are kept parallel on each side and the same distance from the center of the stand. The synchronism of the opposite guide plates of a lateral guide is mechanically realized, and the adjustment is carried out with an electric or hydraulic drive. Hydraulically driven lateral guides are best suited for the process of the invention described here, since hydraulic drives are very dynamic and make it possible, without great expense, to achieve not only automatic position control but also automatic force control to keep the strip straight. The automatic position control keeps the lateral guides at a separation that is somewhat greater than the strip width, for example, the strip width plus 10 mm on the run-in side and the strip width plus 40 mm on the runout side.

An automatic force control system, which protects the lateral guides from overload and presses the lateral guide against the strip with a well-defined force, is superimposed on this automatic position control system. Position monitoring increases the force set value when the lateral guides are trying to deviate.

As a result of the cooperation of these adjustment systems and control systems in accordance with the invention, it is possible to shape a slab affected with cambering or wedging into a straight and wedge-free near-net strip. If, for example, a straight slab with wedging in the thickness profile enters the roughing stand, a near-net strip that exits wedge-free is produced by the roll gap, which is forced to be kept parallel. As a result of this forced profile change, the strip exits cambered in one direction, and the strip on the run-in side tries to turn in this direction. The lateral guides prevent these movements, and reactive forces arise which act against the lateral guides. At the same time, tensile forces arise in the strip over the width of the strip, which act on the roll gap and produce material flow in the roll gap transversely to the rolling direction. This transverse flow of material, which can occur only in the case of suitably thick rolling stock, is thus the phenomenon that basically allows the geometry of the near-net strip to be influenced in accordance with the invention.

To prevent overloading of the adjustment systems in the case of extreme geometric defects and to make it possible to distribute the geometric change over several passes, in accordance with the invention, the automatic control of the adjustment of the rolls can additionally be coupled with the automatic control of the lateral guides. This coupling is achieved by the following procedure:

presetting of a reference value of the differential rolling force or of a maximum roll alignment value as a function of the current compressive forces or the current positions of the lateral guides or presetting of the position set values or of the force set values of the lateral guides as a function of the current differential rolling force or of the differential position of the roll alignment.

Further details and advantages of the invention are explained in greater detail below with reference to the specific embodiments illustrated in the schematic drawings.

FIG. 1 shows an control diagram of the roll adjustment (roll alignment control (RAC)).

FIG. 2 shows a top view of a roughing stand.

FIG. 3 shows a control diagram of the lateral guides.

FIG. 4 shows the combination of the control diagrams of FIGS. 1 and 3 .

FIG. 5 shows the coupling of roll adjustment and lateral guides.

FIG. 1 shows the part of the control system combination of the invention that relates to the roll adjustment for the horizontal rolls of the roughing stand, specifically, the control diagram of a roll alignment control (RAC) system. In the roughing stand 1 , which is shown in a front elevation with work rolls 2 , backup rolls 3 , and slab 4 , cylinder forces F CAS , F CBS are applied on the drive side (AS) and on the service side (BS) by means of hydraulic cylinders 15 mounted on the bearing of the upper backup roll 3 , and the forces resulting during the rolling operation on the lower bearing surface of the backup rolls are continuously measured. The differential rolling force ΔF LC is determined from the measured force values F LcAS and F LcBS thus obtained and, together with a reference value ΔF REF of the differential rolling force, is supplied to the roll alignment control RAC 20 , where a reference roll alignment value ΔS RAC is computed. This roll alignment value ΔS RAC is then halved and used as an additional set value together with the reference position S REF for the separate automatic position controls 25 of the drive side (AS) and the service side (BS) of the upper backup roll 3 , where the adjustment then acts laterally on the hydraulic cylinders 15 .

FIGS. 2 and 3 show the other part of the control system combination of the invention, namely, the automatic control of the lateral guides 8 , 9 , which are arranged laterally alongside the rolled strip as part of the roughing stand 1 . FIG. 2 shows a top view of a roughing stand with backup rolls 3 and work rolls 2 . Lateral guides 8 are installed opposite each other on the run-in roller table 16 upstream (with respect to rolling direction 7 ) of the rolls 2 , 3 with hydraulically driven adjustment devices 18 arranged on the drive side AS of the roughing stand 1 . As the circuitry in FIG. 3 shows, these adjustment devices 18 consist of a common hydraulic unit 11 (hydraulic pump), piston-cylinder units 12 , control valves 13 , and various hydraulic lines 10 . Furthermore, measuring instruments are present for determining the piston position 14 and the hydraulic pressure 19 . To facilitate the run-in and the centering of the slab in the center of the stand, the distance between the lateral guides 8 is conically increased at their front end.

In the same way, lateral guides 9 are installed opposite each other on the runout roller table 17 downstream of the rolls 2 , 3 . The distance separating the lateral guides 9 has been adjusted to the now changed strip width (this change in strip width is not shown in the drawing). The control diagram used in accordance with the invention is explained with reference to FIG. 3 for the lateral guide 9 shown in FIG. 2 . The current piston positions determined by the measuring instruments 14 are fed to a position computer 30 , and the current compressive forces determined by the measuring instruments 19 are fed to a force computer 40 . The current values obtained there for the positions S SACT are fed to the position control unit 35 , and the current values for the compressive forces F SACT are fed to the force control unit 45 . The preassigned reference values for the positions S SREF and for the hydraulic pressures F SREF are used to determine the positions and forces that are to be automatically set, and these positions and forces are transmitted to the piston-cylinder units 12 via the control valves 13 .

The effect of the two simultaneously performed automatic controls of the invention are shown schematically in FIG. 4 . The slab 4 , which enters the rolling stand in rolling direction 7 (the rolling stand is symbolized only by the work roll 2 ), contains a tapered thickness profile (denoted h 0 ) over the width of the slab, with the thickness increasing towards the drive side (AS). The rolling operation eliminated the tapered thickness profile and produced a near-net strip with the thickness profile h 1 . During the rolling operation, the rolling force F WAS to be applied by the work rolls 2 on the drive side (AS) was greater than the rolling force F WBS to be applied on the service side (BS), so that a transverse flow of material occurred from the drive side to the service side in arrow direction 6 .

To prevent lateral twisting of the entering slab 4 and cambering of the near-net strip 5 during the elimination of the tapered thickness profile, the entering slab 4 is laterally supported by the lateral guides 8 , and the exiting near-net strip 5 is laterally supported by the lateral guides 9 .

The supporting forces F 1 and F 2 upstream and downstream of the rolling stand produce as a reaction the tension profile σ 0 in the entering slab 4 and the tension profile σ 1 in the exiting near-net strip 5 . These tension profiles σ 0 , σ 1 act on the roll gap and allow the transverse flow of material 6 , which in turn makes it possible to correct the geometric defect of the slab.

FIG. 5 is a schematic representation of the above-described possibilities of the coupling, in accordance with the invention, of the adjustment of the rolls and the lateral guides with the goal of limiting the load of the adjustment system and of distributing the correction of the slab geometry over several passes.

The drawing shows a coupling control unit 50 . The current values of a rolling stand for

the differential rolling force ΔF LC the differential position of the differential roll alignment value ΔS RAC the positions of the lateral guides S SACT the compressive forces of the lateral guides F SACT

flow into the coupling control unit 50 , as indicated by corresponding directional arrows, and set points are taken from the coupling control unit 50 for use in the downstream rolling stand, again, as indicated by corresponding directional arrows:

a reference value of the differential rolling force ΔF REF a maximum roll alignment value ΔS RACMAX the position reference values of the lateral guides S SREF the force reference values of the lateral guides F SREF .

The invention is not limited to the illustrated embodiments but rather can be varied, for example, according to the design of the roughing stand that is used or according to the design of the lateral guide drives that are used, as long as the given embodiment is still based on the measure of the invention of combining roll alignment control (RAC) of the rolls with mechanical adjustment of the lateral guides for the rolling stock.

AS roll drive side

BS roll service side

1 roughing stand

2 work roll

3 backup roll

4 slab

5 near-net strip

7 rolling direction

8 lateral guide, run-in side

9 lateral guide, runout side

10 hydraulic lines

11 hydraulic unit

12 piston-cylinder unit for lateral guides

13 control valve

14 measuring instrument for piston position

15 hydraulic cylinder for roll alignment control

16 run-in roller table

17 runout roller table

18 adjustment device for lateral guides

19 measuring instrument for hydraulic pressure

20 roll alignment control (RAC)

25 automatic position control for roll alignment control

30 position computer for lateral guides

35 automatic position control for lateral guides

40 force computer for lateral guides

45 automatic force control for lateral guides

50 coupling control unit

Rolled Strip Characteristics

6 direction of transverse flow h 0 thickness profile on the run-in side h 1 thickness profile on the runout side σ 0 tension profile on the run-in side σ 1 tension profile on the runout side

Positions

S REF reference position S SREF position reference values S SACT current positions of the lateral guides ΔS RAC reference roll alignment value ΔS RACMAX maximum roll alignment value

Forces

F LcAS measured force, drive side F LcBS measured force, service side F CAS cylinder force, drive side F CBS cylinder force, service side ΔF LC differential rolling force ΔF REF reference value of the differential rolling force F SREF force reference value of the lateral guides F SACT current compressive forces of the lateral guides F WAS rolling forces on the drive side F WBS rolling forces on the service side F 1 , F 2 forces on the lateral guides