DE102006028369A1 - Method and device for process control during rolling of metals - Google Patents

Abstract

The invention relates to a method for process control in the rolling of metals, in particular aluminum or aluminum alloys, as well as a roll stand with work rolls for rolling metals, in particular aluminum or aluminum alloys, and means for carrying out a process control of the rolling process. The object of providing a method for process control in the rolling of metals, in particular aluminum or aluminum alloys, with which process parameters of the roll gap can be determined directly during rolling, so that the influence of vibrations of the roll stand on the strip thickness is reduced and at the same time Proportion of scrap bands can be reduced is achieved by using at least one ultrasonic transceiver assembly process parameters are determined during rolling, wherein ultrasonic waves are coupled through at least one ultrasonic transmitter in the work rolls in the direction of the nip and the coupled ultrasonic waves with at least one ultrasonic receiver are received again.

Description

The The invention relates to a method for process control during rolling of metals, in particular aluminum or aluminum alloys and a rolling mill with work rolls for rolling metals, in particular aluminum or aluminum alloys and means for carrying out a process control of the rolling process.

When hot rolling and cold rolling, it is desirable to manufacture the rolled strip with a thickness as constant as possible. Unavoidable roughnesses of the rolls, particularly the back-up rolls, however, cause periodic variations in the actual run-out thickness of the strip during the rolling operation. To control the strip thickness band thickness control systems are used, which are usually based on measuring the strip thickness at the inlet of the work rolls and at the outlet of the work rolls to determine model sizes control variables and control the adjustment system of the rolling stand via appropriate control commands. There have been many different attempts to eliminate the periodic variations in strip thickness during rolling. For example, from the German patent application DE 33 31 822 A1 a method for controlling the strip thickness is known, in which on the roll adjustment, the rolling force and the spring constant of the roll stand, the size of the roll gap is determined indirectly. The determined size of the nip is corrected with directly determined and delayed tape thickness measurements. The size determined for the nip is used to control the roll adjustment of the work rolls and thus for process control of rolling. Further methods for process control during rolling of metals are known from German Offenlegungsschrift DE 103 27 663 A1 known. Since the process parameters in the nip could previously only be determined indirectly, it was not possible to eliminate fluctuations in the strip thickness since all known methods could not compensate for oscillations of the rolling stand fast enough. In addition, there was no possibility of promptly determining important parameters for process control, such as the tension profile of the work rolls, and feeding them to the process control.

Especially When rolling aluminum, additional material deposits occur and material buildup on the work rolls, which leads to errors on the rolled strip. So far, an operator of the rolling mill has a visual inspection of this Work rolls and the rolled strip performed and the rolling process in Presence of a surface defect stopped on the stripper. There are also errors in the millimeter range to scrap bands to lead, such mistakes became common too late discovered so that due to the high rolling speeds already size Lots of bad ribbons have been produced.

From This prior art is based on the present invention the object of a method for process control in rolling of Metals, in particular aluminum or aluminum alloys as well a rolling stand with work rolls for rolling metals and means for performing a To provide process control of the rolling process, with which Process parameters of the roll gap during rolling determined directly can be so that the influence of vibrations of the rolling mill on Reduces the strip thickness and at the same time reduces the proportion of reject strips can be.

According to one The first teaching of the present invention is that shown above Task for a process control process for rolling metals solved, that using at least one ultrasonic transmitter-receiver arrangement Process parameters during of rolling, wherein ultrasonic waves by at least an ultrasonic transmitter in the work rolls in the direction of the roll gap coupled with the coupled ultrasonic waves at least one ultrasonic receiver be received again.

It has surprisingly shown that over the coupling of ultrasonic waves into the work rolls important Process parameters can be obtained to control the process To improve rolling. For Ultrasonic waves are massive bodies like the work rolls though permeable. The propagation speed the ultrasonic waves and their reflection or transmission Media transitions are however, from the specific environmental conditions in the metal of the work roll or at the corresponding material transition dependent. Therefore, through a measurement of the coupled ultrasonic waves with an ultrasonic receiver immediately Conclusions about rolling conditions or rolling parameters determined and used for process control become. About that also allows the use of ultrasonic waves ensures easy and safe monitoring the rolling process.

Preferably, according to a first embodiment of the method according to the invention, the pulse-echo method is used. In this method, very short ultrasonic pulses are introduced at high frequency in the work roll and received after their reflection at the nip again. From the transit time differences between transmission and reception of the ultrasound pulse as well as from the amplitude of a reflected pulse process parameters can be used for process control Rolls are won. Usually this ultrasonic pulses are at a frequency of 0.1 to 100 MHz, which are emitted at a repetition frequency of up to 50 kHz. The very high pulse frequency serves to improve the spatial resolution, since this corresponds to half the wavelength of the ultrasonic waves. By means of the repetition frequency, the measuring signal can be stabilized for better evaluation.

According to one next advantageous embodiment the method according to the invention Using at least the one ultrasonic transmitter-receiver arrangement, the band thickness of the rolled strip measured in the nip and for process control used during rolling. It has been shown that in the work roll coupled ultrasonic waves not only at the transition of the work roll to Band material are reflected, but also in the band material penetrate and on the opposite Side of the work roll to be reflected. If one measures the transit time difference between the directly at the transition the work roll to the strip material reflected ultrasonic waves and the one on the opposite Stripper reflected ultrasonic waves, can be simple Way over trigonometric considerations the thickness of the nip, which then the strip thickness in the nip corresponds to be determined. Therefore, there is a possibility a strip thickness measured directly during rolling for process control to use. The resulting short response time to the controller the adjusting elements of the rolling stand guaranteed that fluctuations in the strip thickness due to vibrations of the rolling stand clearly can be reduced.

Under Exploitation of the acoustoelastic effect can, according to a next further developed embodiment of the method according to the invention, using the at least one ultrasonic transceiver assembly the tension profile of the work roll are measured. Due to the changed acoustoelastic effect the speed of sound of ultrasonic waves in dependence from the stress state in the material linear to the yield strength of the material. In the areas of the work roll, which especially Under tension, the ultrasonic waves have particularly high Speeds up, so that proportional to the stress state in the work roll a change the duration of the ultrasonic waves takes place. This makes it possible to determine the state of stress a stripper during rolling by running time differences of the ultrasonic waves determine. This gives information about where the Working roller is particularly stressed. The data of the voltage profile can then be used for example for targeted control of the support rollers and / or the roller cooling.

Preferably, using the ultrasonic transmitter-receiver arrangement, the rolling oil film is monitored in the nip. During the transition of the ultrasonic waves from one medium to the other, for example from the work roll into the rolling oil film and the rolling stock in the nip, a reflection occurs whose reflection coefficient R is determined as follows: R = (Z 2 - Z 1 ) 2 / (Z 2 + Z 1 ) 2 the following applies to the sound wave resistance in the individual media 1 and 2: Z 1.2 = C 1.2 · ζ 1.2 ,

Where c _{1/2 is} the speed of sound in the media and ζ _1/2 the density. The sound wave resistance is proportional to the speed of sound in the medium and the reflection increases with increasing difference in the speed of sound of the media.

There the speed of sound in oil 1800 m / s and steel is about 5920 m / s, the reflection is at Exit of the ultrasonic waves in the nip at existing Rolling oil film relatively big and only a small part of the ultrasonic pulse enters the nip one. The amplitude of the reflected ultrasonic pulse at this transition is correspondingly high. For example, adheres aluminum material a location on the work roll and is a rolling oil film on In this place no longer exists, then breaks the amplitude of the reflected ultrasonic pulse, however. This is because that in aluminum the speed of sound is similar to that in steel, namely about 6300 m / s, so that only a small difference in the Sound wave resistance at the transition is present. This can be quickly and automatically detected during rolling, that adheres to the work roll material or the rolling oil film not more is available. The hitherto almost impossible monitoring of the rolling oil film in Rolling gap is made possible by the inventive method for the first time.

The Advantages of the method according to the invention arise not only in hot, but also in cold rolling of metals, since the inventive method a direct determination of Rolling parameters enabled and thus a particularly fast control of the roll gap can be achieved is, which can also consider vibrations of the rolling stand.

Does the ultrasonic transmitter-receiver assembly on a plurality of ultrasonic transmitters and receivers, which in the axial direction along the work rolls are arranged, the nip, the tension profile and the rolling oil film of the work roll over the entire width of the work roll can be determined or monitored and fed to a corresponding process control. However, it is also conceivable that a single combination of ultrasonic transmitter and receiver is used, which is arranged, for example, movable on the work roll and monitors it periodically.

Preferably the ultrasound transmitters and receivers are via a liquid medium, in particular via a Rolled emulsion, coupled to the work rolls, so that the losses at the exit or when entering the ultrasonic waves in the work rolls as possible can be kept low. The use of rolling emulsion is particularly advantageous because it is ubiquitous in the rolling process and for example, a simple stripping of the rolling emulsion of the work roll is sufficient for disposal.

are the ultrasonic transmitters and receivers of Ultrasonic transmitter-receiver arrangement Seen in the axial direction of the work roll V-shaped, can by a simple arrangement of the ultrasonic transmitter and receiver the Rolling gap of the work rolls are measured. In this arrangement The ultrasound from the ultrasonic transmitter can be directly into the work roll be coupled. However, it is also possible to have a combined one Transmitter and receiver head to use as an ultrasonic transmitter-receiver arrangement.

According to one second teaching of the present invention is derived above Task for one rolling mill solved by that an ultrasonic transmitter-receiver arrangement is provided, which has at least one ultrasound transmitter and receiver, wherein the ultrasonic transmitter ultrasonic waves by at least a work roll in the direction of the roll gap emits and with the ultrasonic receiver emitted by the ultrasonic transmitter and at the nip and / or Received by the material in the nip reflected ultrasonic waves are.

As already to the inventive method described, allows the rolling mill according to the invention, on the Ultrasonic transmitter-receiver arrangement the roll gap and parameters required for process control of rolling, such as the presence of a rolling oil film, to measure directly. Equipped accordingly rolling mills enable thus a particularly good process control, since so far essentially only indirect measurements, for example with regard to the size of the nip, used for process control.

includes the ultrasonic transmitter-receiver arrangement a plurality of ultrasonic transmitters and receivers which are in the axial direction the work rolls are arranged, the work roll in the roll stand on their entire working length monitored and the nip above the entire working length be set.

A seen in the axial direction of the work rolls V-shaped arrangement the ultrasound transmitter and receiver guaranteed a minimum number of media transitions the Ultrasonic waves or ultrasonic pulses from the transmitter to the receiver. by virtue of the resulting maximum signal strength in the ultrasonic receiver is improves the measuring accuracy.

To the The same purpose is also served by the means preferably provided for for the acoustic coupling of the ultrasonic transmitter-receiver arrangement to the stripper. For example, the ultrasonic transmitter and receiver the ultrasonic transmitter-receiver arrangement be arranged in a roller emulsion beam, which the ultrasonic transmitter or receiver Completely surrounds and is directed continuously against the work roll. Furthermore An arrangement is also conceivable in which the work roll immersed in a pan with rolling emulsion, in which an ultrasonic transmitter or receiver is arranged.

Finally, point the ultrasonic transmitter and / or receiver acoustic lenses for On or to decouple the ultrasonic waves. ultrasonic waves can be bundled by simple geometric bodies, often made of plastic focus. By bundling and focusing can be under consideration the refraction of the ultrasonic waves in the media transition targeted a radiation field be adjusted in the roller, which leads to particularly good results leads. For example, the coupling of the ultrasonic waves should do so to lead, that the entering into the work roll beam as possible little divergent, so that at the nip reflects the highest possible intensity becomes.

It There are a lot of possibilities now inventive method to develop the process control during rolling and the rolling mill according to the invention and to design. Reference is made on the one hand to the claims 1 and 10 subordinate claims, on the other hand to the description of exemplary embodiments in conjunction with the drawing. The drawing shows in

1a) in a schematic, radial sectional view of the work rolls according to a first embodiment of the rolling mill according to the invention,

1b) in a schematic, radial sectional view of the work rolls according to a second embodiment of the rolling mill according to the invention,

2 in a radial sectional view of the beam path of the ultrasonic pulses in the region of the nip in the embodiment 1a) .

3 in a schematic, radial sectional view of the beam path of the ultrasonic waves in the voltage profile measurement of the embodiment 1a) .

4 in a time-amplitude diagram of a typical waveform in the measurement of the voltage profile 3 .

5a) , b) coupling means of the ultrasonic transmitter and receiver according to a second embodiment of the rolling stand according to the invention and

6a , b) different lens geometries of ultrasound transmitters and receivers.

A schematic, radial sectional view of the work rolls 1 . 2 a first embodiment of a rolling mill according to the invention 3 shows 1a) , The rolling stand according to the invention 3 has an ultrasonic transmitter-receiver arrangement 4 . 5 and not shown means for process control. The ultrasound transmitter 4 joins the stripper 1 ultrasonic waves 6 , for example in the form of pulses. The ultrasonic pulses have frequencies in the range of 0.1 to 100 MHz, for example.

Usually, the ultrasonic pulses are emitted at a repetition frequency of up to 50 kHz to stabilize the measurement of the reflected signal. The ultrasonic pulse 6 is from the ultrasonic transmitter 4 into the stripper 1 coupled, leaves the stripper 1 in the area of the nip and is on the opposite work roll 2 reflected again, then into the work roll 1 and from the ultrasonic receiver 5 as an ultrasonic pulse 7 to be measured. In the 1a) is also a back-up roll 9 represented, over which the load distribution of the work rolls 1 can be adjusted.

A comparison with the embodiment 1a) simplified, second embodiment of the device according to the invention for process control during rolling shows 1b) , The rolling mill in 1b) does not include back-up rollers, so the ultrasonic transmitter-receiver assembly 4a the ultrasonic waves perpendicular to the nip in the work roll 1a can couple. The duration of the coupled and the material transition from the rolling stock in the second work roll 2a reflected ultrasonic pulse 6a is thus directly proportional to the thickness of the rolled strip 8a , In this embodiment, the ultrasonic transmitter-receiver arrangement 4a consist of a single transmitter-receiver probe.

In 2 is the area of the nip 10 out 1a) shown enlarged again. The ultrasonic pulse 6 coupled in the rolling gap in the rolling stock 8th and is at the stripper 2 reflected back. The reflected back ultrasonic pulse 7 will then be from the receiver 5 which is in 2 not shown, received again. From the running time, which is the ultrasonic pulse 6 . 7 Required in the range of rolling stock, the thickness of the rolling stock h and thus the nip itself can be calculated by simple trigonometric calculations. However, the reflected ultrasonic pulse 7 only be measured when the rolling stock 8th via a, not shown rolling oil film to the work roll 1 is connected, ie no air gap between the work roll and rolling stock 8th consists. An air gap would be due to the large difference in acoustic wave resistance to a complete reflection of the ultrasonic pulse 6 lead at the nip.

in the In contrast to the previously known methods for determining the roll gap, can measure the size of the nip using ultrasonic metrology directly from runtime differences using simple geometric considerations be determined. It stands with this measured value an actual value of Roll nip size available, which ideal as a manipulated variable for process control can be used.

The 3 shows in an axial, schematic sectional view of the course of the ultrasonic waves 6 . 7 which is at the transition between stripper 1 and rolling stock 8th be reflected. The duration of the emitted ultrasonic pulse 6 and the reflected ultrasonic pulse 7 due to the acousto-elastic effect and the elastic roll deformation depends in particular on the stress state of the work roll. By an axially continuous arrangement of ultrasonic transmitters and receivers 4 . 5 is made possible to determine a tension profile of the entire work roll over the entire working width of the rolls. The acoustoelastic effect states that in the area of the elastic deformation of a material, the speed of sound increases in proportion to the increase in stress. Due to the high forces, which over the work rolls 1 be applied to the rolling stock, the speed of sound in the areas which are subject to special stresses, increases significantly. Different stress states of the work rolls are there due to different transit times for the ultrasonic pulse 6 . 7 noticeable.

Though is the speed of sound in solids, such as steel, about that beyond dependent from the temperature of the material. However, here too rises Sound velocity with increasing temperature linear, wherein the temperature increase per temperature increase by two orders of magnitude less than the acoustoelastic effect. This ensures that even when correcting the speed of sound due to a Temperature compensation of the work rolls the state of tension of Work rolls can be reliably measured.

Parameters for the process control of the rolling process, in particular for the roll cooling but also for the control of the working and / or support rolls, can easily be determined from the stress profile 1 . 2 and 9 are obtained, which should ensure a uniform load distribution on the work rolls and thus over the width of the work rolls uniform formation of the roll gap.

As already described above, at media transitions, analogous to the refractive laws of optics, a reflection takes place at the interfaces. This results from the ultrasound transmitter 4 emitted ultrasonic pulse 6 . 7 one at the ultrasonic receiver 5 measurable amplitude, which depends on the reflection of the ultrasonic pulse at the transition between the work roll 1 and the rolling stock 8th is dependent. Is at one point the work roll 1 no sufficient rolling oil film is present and adheres material, such as aluminum, at this location on the work roll 1 On, there is almost no reflection at the transition between work roll and material adhesion, since aluminum and steel have similar sound wave resistance. The amplitude of the reflected ultrasonic pulse 7 decreases significantly. With the method according to the invention it is therefore possible to detect the adhesion of material to the work roll immediately, as soon as the roll gap only a small reflection of the ultrasonic pulse 6 takes place. The amplitude of the reflected ultrasonic pulse 7 Thus, it can be used to monitor the presence of a sufficient rolling oil film or to detect material buildup. The characteristic amplitude of existing rolling oil film results from the clear difference between the acoustic wave resistance of both materials. So far, such material buildup could only be detected by defects in the rolled strip, so that large amounts of scrap material were often made before the errors were detected.

Both the data obtained on the tension profile of the work roll 1 As well as the data on the monitoring of the rolling oil film can be forwarded to the means for process control of the rolling, not shown, for example, to achieve automatic monitoring of material adhesions or to control the size of the roll gap directly.

An exemplary waveform in the evaluation of the received ultrasonic pulses 6 . 7 shows the diagram 4 , On the x-axis is in 4 the time plotted and on the y-axis the measured amplitudes. The diagram in 4 shows two amplitude values a0 and a1 at the times t0 and t1. The time axis t is with the ultrasonic transmitter 4 synchronized, so that the ultrasonic pulses t0 of the amplitude a0 the ultrasonic pulse reflected at the nip 6 . 7 equivalent. The amplitude a0 can therefore be used as a measure of the presence of a rolling oil film. The time t0, however, can be used as the transit time for determining the voltage profile. The time difference between t0 and t1 then gives a measure of the size of the roll gap h.

For the acoustic coupling of the ultrasonic receiver and transmitter 4 . 5 to the stripper 1 are in 5a) and b) two different principal embodiments shown in a sectional view. The sectional views show the work roll 1 and the ultrasonic transmitter exemplified here 4 , In 5a) is the ultrasound transmitter 4 in a container 11 including a coupling medium, for example a rolling emulsion, arranged. The container 11 is arranged so that the work roll 1 into the overflowing coupling medium 12 dips and so an acoustic coupling of the ultrasonic transmitter 4 to the stripper 1 guaranteed. In 5b) points the container 11 a nozzle from which the coupling medium 12 exits in a jet. The use of a nozzle, as in 5b) shown, allows the coupling to the work rolls 1 from any point.

Finally shows 6 in a sectional view of various embodiments of an ultrasonic transmitter 4 for coupling ultrasonic waves or ultrasonic pulses into the work roll 1 , As from the comparison of 6a) and 6b) becomes clear, by choosing the acoustic lens 13 the coupling and the divergence of the beam 14 be set. Usually, the narrowest possible beam is set, so that despite the long beam path within the work roll 1 a sufficient signal strength from the ultrasound receiver 5 can be received.

Claims (14)

Process control process for rolling metals, in particular aluminum or aluminum Umlegierungen, characterized in that using at least one ultrasonic transmitter-receiver arrangement process parameters are determined during rolling, wherein ultrasonic waves are coupled by at least one ultrasonic transmitter in the work rolls in the direction of the nip and the coupled ultrasonic waves are received again with at least one ultrasonic receiver , Method according to claim 1, characterized in that that the pulse-echo method is used. Method according to claim 1 or 2, characterized that using the at least one ultrasonic transmitter-receiver arrangement the strip thickness measured in the nip and for process control during Rolling is used. Method according to one of claims 1 to 3, characterized that using the at least one ultrasonic transmitter-receiver arrangement the tension profile of the work roll is measured. Method according to one of claims 1 to 4, characterized that using the at least one ultrasonic transmitter-receiver arrangement the rolling oil film monitored in the nip becomes. Method according to one of claims 1 to 5, characterized that the metal is hot or cold rolled. Method according to one of claims 1 to 6, characterized that the ultrasonic transmitter-receiver arrangement a plurality of ultrasonic transmitters and receivers, which in axial Direction along the work rolls are arranged. Method according to one of claims 1 to 7, characterized that the ultrasonic transmitter and receiver via a liquid medium, in particular via a Rolling emulsion to which work rolls are coupled. Method according to one of claims 1 to 8, characterized that the ultrasonic transmitter and receiver in the axial direction of Stripper seen V-shaped are arranged. Roll stand with work rolls ( 1 . 2 ) for rolling metals, in particular aluminum or an aluminum alloy, and means for carrying out a process control of the rolling process, in particular for carrying out a method according to claims 1 to 9, characterized in that an ultrasonic transmitter-receiver arrangement ( 4 . 5 ) is provided, which at least one ultrasonic transmitter ( 4 ) and receiver ( 5 ), wherein with the ultrasonic transmitter ( 4 ) Ultrasonic waves or ultrasonic pulses ( 6 . 7 ) by at least one work roll ( 1 ) in the direction of the roll gap and with the ultrasonic receiver ( 5 ) from the ultrasonic transmitter ( 4 ) and reflected at the nip and / or the material in the nip ultrasonic waves or ultrasonic pulses ( 4 . 5 ) are receivable. Roll stand according to claim 10, characterized in that the ultrasonic transmitter-receiver arrangement ( 4 . 5 ) comprises a plurality of ultrasonic transmitters and receivers, which in the axial direction of the work rolls ( 1 . 2 ) are arranged. Roll stand according to claim 10 or 11, characterized in that the ultrasonic transmitter ( 4 ) and receiver ( 5 ) in the axial direction of the work rolls ( 1 . 2 ) are arranged V-shaped seen. Roll stand according to one of claims 10 to 12, characterized in that means ( 11 . 12 ) for the acoustic coupling of the ultrasonic transmitter-receiver arrangement ( 4 . 5 ) to the work roll ( 1 . 2 ) are provided. Roll stand according to one of claims 10 to 13, characterized in that the / the ultrasonic transmitter and / or receiver ( 4 . 5 ) acoustic lenses ( 13 ) for bundling the ultrasonic waves ( 6 . 7 ) or have ultrasonic pulses.