EP1525061B2 - Dynamic thickness correction - Google Patents

Abstract

The invention relates to a method and a device for correcting the thickness of a metal strip during rolling comprising a roll stand with adjusting elements to regulate the thickness of the strip and at least one take-up coiler. The object to provide a method and a device to correct the thickness of a metal strip during rolling using a roll stand which ensures the production of rolled strip with a reduced thickness tolerance is solved according to method by the fact that an average strip thickness of a strip section is determined from at least one strip length measurement and the measurement of the dedicated rotation of the take-up coiler and the adjusting elements of the roll stand are controlled at least depending on the average strip thickness of the strip section. With the method according to the invention the adjusting elements can be controlled almost independently of the ambient conditions of the roll stand so that the thickness tolerances of the rolled strip can be effectively reduced.

Description

The invention relates to a method and a device for correcting the thickness of a metallic strip during rolling with a roll stand with adjusting elements for regulating the thickness of the metallic strip and at least one take-up reel, according to the preamble of the respective independent claim (see US-A-3540247).

When rolling metallic strips, such as strips of aluminum or an aluminum alloy, to reduce their thickness, the rolled metallic strips are wound after passing through a roll stand on a take-up reel as a bunch. An important quality feature of the rolled strip wound up as a bundle is, inter alia, the thickness of the strip and its fluctuations.

So far, the thickness of the metallic strip is determined by means of a radiometric measuring method and controlled the control elements of the rolling mill depending on this value. In the case of the radiometric measuring method, the radiation, transmitted through the metallic strip, of a radiator arranged on the other side of the metallic strip is measured with the aid of a detector arranged on one side of the metallic strip. The radiation measured by the detector is dependent on the absorption in the metallic band, which is determined in particular by the thickness of the metallic strip. The deviation of the radiometrically determined strip thickness from a nominal value of the thickness of the strip is used as an input variable for the control of setting elements of the roll stand for influencing the thickness of the metallic strip. However, the thickness measurement obtained by radiometry is dependent on further influencing variables, for example the alloy composition of the strip, the air density and air temperature in the measuring path, for example when blowing off or sucking off heated air, the proportion of coolant and lubricant mist in the measuring path and the temperature of the rolling stock and the System components for determining the thickness. Therefore, a determination of the influencing variables and standardization of the radiometric measuring method on the additional parameters is absolutely necessary.

A disadvantage of the hitherto known method for correcting the strip thickness of a metallic strip during rolling is that determination of the influencing variables and normalization of the radiometric measuring method to these influencing variables can not take place comprehensively under rolling conditions. Thus, in order to correct the alloy-dependent absorption behavior of the metallic strip, it is necessary to measure the alloy composition on a cast sample by means of spark spectrometry and to calculate therefrom an absorption index for the alloy, which is taken into account in the radiometric measuring method. Variations in sampling as well as measurement uncertainties in spark spectrometry mean that the radiometrically determined thickness is provided with a confidence interval, which must be taken into account depending on the product requirement.

For normalization of the radiometric measured values, on the one hand the electrical zero point of the detector signal is used with the radiator shutter closed, on the other hand at full irradiation, ie without a sample in the measuring path, a calibration factor is determined which takes into account the absorption conditions in the test section at this time. This happens automatically during the bundle change or at each opening of the spotlight cover without material to be measured. By means of the measurement of the temperature change and an empirical weighting factor determined therefrom, the temperature change in the measuring path with rolling stock is concluded. A detection of the integral temperature profile in the measuring path, which has great variations when rolling through the hot rolled strip, is not possible. The integral temperature profile can therefore not be taken into account in the radiometric thickness determination.

Furthermore, in systems known from the prior art for checking the radiometric measuring point in a hermetically sealed area in the immediate vicinity of the radiator, there are control standards, i. metallic sheets whose absorption properties do not change except by temperature changes. By checking the thickness measured values of these control standards, a correction of the absorption curve stored in the measuring system can be carried out. However, this adjustment can also be carried out only with interrupted rolling.

Due to the above-described disadvantages of the previously known methods for correcting the thickness of a metallic strip during rolling, the thickness tolerances required today can be maintained only with difficulty.

According to US Pat. No. 3,540,247, an average strip thickness of a strip section is determined from at least one strip length measurement and the measurement of the associated rotation of the take-up reel and the setting elements of the rolling stand are controlled at least as a function of the determined mean strip thickness of the strip section Bandes is connected to the take-up reel with the measured tape length and Aufwickelhaspelumdrehung, from which can be determined by a fill factor, the average tape thickness. The required measured values of the strip length and of the take-up reel turn are almost independent of the influencing variables of the radiometric thickness measurement, so that a measurement value independent of the environmental conditions of the rolling stand is available for the mean strip thickness of a strip section. It has been shown that a sufficiently accurate value for the mean strip thickness can be determined even after short strip lengths. By controlling the Adjusting elements at least as a function of the determined mean strip thickness of the strip section can thus be achieved a reduction in the thickness tolerances of the rolled strip. Based on the above-described prior art, the present invention based on the object to provide a method and apparatus for correcting the thickness of a metallic strip in rolling with a roll stand, which or the production of rolled strips with a ensured reduced thickness tolerance. The problem is solved by the method by the characterizing feature combination according to claim 1.

If the strip thickness is additionally measured radiometrically and the setting elements of the rolling stand are controlled as a function of a radiometric strip thickness corrected with the mean strip thickness, it is possible according to the inventive method to dynamically correct the radiometrically determined strip thickness with the aid of the determined mean strip thickness and the setting elements of the rolling mill stand depending on the dynamically corrected band thickness value. Thus, an input variable for controlling the strip thickness when rolling a metallic strip is available which on the one hand enables an almost instantaneous influencing of the adjusting elements and on the other hand can be corrected independently of the typical influencing variables of the radiometric determination of the strip thickness during the rolling process.

A particularly high accuracy in the measurement of the strip length during rolling is, according to an advantageously further developed embodiment of the method according to the invention, achieved by measuring the strip length using the laser Doppler velocimetry method. The Laser Doppler Velocimetry (LDV) method is a standard method of measuring flow velocities. The principle is to detect and evaluate the scattered light of a particle which traverses an interference fringe system generated by a laser source. The frequency of the received signal is then proportional to the particle velocity. If the interference fringe system is imaged onto the rolled strip, then the speed of the rolled strip can be determined very precisely by scattered light evaluation. Thus, a high-precision strip length measurement is available for determining the mean strip thickness of a strip section.

If, according to a next further developed embodiment, the number of revolutions of the take-up reel is measured using high-resolution incremental encoders on the take-up reel or take-up reel motor axis, the number of revolutions of the take-up reel necessary for determining the mean strip thickness can be determined with sufficient accuracy in a simple manner.

An advantageous embodiment of the inventive method undergoes the fact that a plurality of values for the mean strip thickness of the same strip section is determined by selecting a plurality of different starting points and to be measured tape lengths for the determination of the mean strip thickness. By this measure, it is possible to perform a statistical evaluation of the values of the mean strip thickness of a strip section and to reduce the measurement error in determining the average strip thickness of a strip section, so that the strip thickness tolerances of the rolled strip can be further reduced.

The influence of the coiling process on the filling factor can, according to a further developed embodiment of the method, be taken into account by additionally smoothing the values for the mean strip thickness of the same strip section as a function of the current coil diameter of the strip on the variable-weight take-up reel. In this way it can be prevented that, especially at the beginning of the coiling process, fluctuations in the diameter of the collar have a greater effect on the determination of the mean strip thickness.

The process reliability in the determination of the mean strip thickness can be further increased by performing at least one further, redundant strip length measurement according to an advantageous embodiment of the method according to the invention.

If, in the event of a failure of a first strip length measurement used to determine the mean strip thickness, the strip is automatically switched to a further, redundant strip length measurement, it can be ensured that the dynamic thickness correction can be carried out continuously, even if a strip length measuring system fails. The rolling process therefore does not have to be interrupted. US-A-3540247 also discloses a device for correcting the thickness of a metallic strip during rolling with at least one rolling stand having adjusting elements for controlling the thickness of the strip, at least one take-up reel and means for measuring the strip length and the extent of the associated rotation of the take-up reel in that means for controlling the setting elements of the rolling stand are provided as a function of an average strip thickness determined from the measured strip length and the associated rotation of the take-up reel. As already described above, it is possible by means of this measure to measure and adjust the strip thickness of a metallic strip during rolling virtually independently of the environmental conditions of the rolling mill stand. The object indicated above is achieved by means of the device of the characterizing combination according to claim 8.

An input to control the actuators is, according to the device according to the invention, immediately after the rolling of the tape available, because in addition means for radiometric thickness determination of the metallic strip between Roll stand and take-up reel are provided. In addition, it is possible that by controlling the control elements of the roll stand with the aid of a dynamically corrected with the average strip thickness, radiometrically determined band thickness value, the strip thickness tolerance of the entire band can be further reduced.

An advantageous embodiment undergoes the device according to the invention in that means for redundant tape length measurement are provided. On the one hand, the process reliability during rolling in relation to the failure of a strip length measuring system can be increased thereby, on the other hand, a check of the respective strip length measurement is possible by the redundant strip length measurement, so that their accuracy can be increased.

In addition, the accuracy of the tape length measurement can be further increased in that, according to a further developed embodiment of the device according to the invention, for the tape length measurement, a laser Doppler velocimetry system is provided.

If high-resolution incremental encoders are provided on the take-up reel axle or take-up reel motor axis, it is possible according to a next further developed embodiment of the device according to the invention to determine in a simple manner the rotation of the take-up reel belonging to a specific band length in a simple manner.

There are now a variety of ways, both the method according to the first teaching of the invention, as well as to design the device according to the second teaching of the invention advantageously and further. For this purpose, for example, reference is made, on the one hand, to the patent claims 1 and 10 subordinate claims, on the other hand to the description of a preferred embodiment in conjunction with the drawings.

Fig. 1:

in einer schematischen Darstellung ein erstes Ausführungsbeispiel einer erfindungsgemäßen Vorrichtung zur Korrektur der Dicke eines metallischen Bandes beim Walzen,

Fig. 2a:

in einer schematischen Darstellung das im ersten Ausführungsbeispiel verwendete Verfahren zur Bestimmung der mittleren Banddicke aus einer Bandlängenmessung,

Fig. 2b:

in einer Schnittansicht eine Aufwickelhaspel mit mehreren aufgewickelten Lagen eines metallischen Bandes und

Fig. 3:

in einem Blockschaltbild die Steuerung eines nächsten Ausführungsbeispiels einer Vorrichtung zur Korrektur der Dicke eines metallischen Bandes beim Walzen.

In the drawing shows

Fig. 1:

a schematic representation of a first embodiment of a device according to the invention for correcting the thickness of a metallic strip during rolling,

Fig. 2a:

1 is a schematic representation of the method used in the first exemplary embodiment for determining the mean strip thickness from a strip length measurement;

Fig. 2b:

in a sectional view of a take-up reel with several wound layers of a metallic strip and

3:

in a block diagram, the control of a next embodiment of an apparatus for correcting the thickness of a metallic strip during rolling.

This in Fig. 1 illustrated embodiment of an apparatus for correcting the thickness of a metallic strip 1 during rolling has a rolling stand 2 with not shown adjusting elements for regulating the thickness of the belt 1, a deflection roller 3 and a take-up reel 4. In addition, an LDV system 5 for measuring the strip length, an incremental encoder 6 on the take-up reel axis 7 and a radiator 8 and a detector 9 for radiometric determination of the strip thickness are shown for determining the strip thickness. When rolling the metallic strip 1, after it has left the roll stand 2, deflected over a deflection roller 3 and wound on the take-up reel 4. From the number of revolutions of the take-up reel 4 and the associated strip length, an average strip thickness can be calculated.

The Fig. 2a shows the basic sequence of the method for determining the mean strip thickness of a metallic strip 1 using an LDV system 5 and a take-up reel 4. The LDV system 5 measures the tape length during winding of the tape 1 on the take-up reel 4, wherein the first layer of the tape 1 when winding a fixed by the take-up reel 4 radius r occupies.

wobei L_n die ab einem willkürlichen Startpunkt laufende Länge ist, n die zugehörigen Anzahl der Umdrehung der Aufwickelhaspel 4, L_m eine Festlänge ab dem gleichen Startpunkt und m die zugehörige Anzahl an Umdrehungen der Aufwickelhaspel 4 zur Festlänge L_m ist. Fig. 2b shows now in a sectional view a take-up reel 4 with several wound layers of a metallic strip 1. The average layer spacing h of the wound strip 1 results from the difference in radius of the radii r _m and r _n and the number of layers wound between the radii, ie the associated Number of revolutions of the take-up reel 4. For the mean ply spacing h between any two take-up radii r _m and r _{n, the} following therefore applies: $$H=\frac{\frac{L_n}{n\pi }-\frac{L_m}{m\pi }}{n-m}.$$

where L _{n is} the length running from an arbitrary starting point, n is the associated number of revolutions of the take-up reel 4, L _{m is} a fixed length from the same starting point and m is the associated number of revolutions of the take-up reel 4 to the fixed length L _m .

As Fig. 1 In turn, in order to measure the tape lengths L _n or L _m , in principle also the deflection roller 3 can be used, however, a non-contact and slip-free measurement with the LDV system 5 is preferable, since thus a much more accurate tape length measurement is made possible. High-resolution incremental encoders 6, which are arranged on the winding hull 7, provide the associated number n or m of revolutions of the take-up reel. With these measured values, a mean layer distance h is first calculated according to the above formula, so that h is the mean strip thickness of a strip section can be calculated using a fill factor. The calculation of the mean strip thickness takes place after an adjustable strip length with the aid of the computer 10, which on the one hand displays the measured mean strip thickness via the display 11 and on the other hand forwards the value for the dynamic thickness correction to a first comparison device 12. In the comparison device 12, the value of the mean strip thickness is compared with the desired thickness 13 of the strip 1 and the difference is forwarded as a dynamic thickness deviation to a next comparison device 14. The radiometric strip thickness 15 determined with the aid of the radiator 8 and the detector 9 is used to add the value of the dynamic thickness deviation to the comparison device 14 and fed to a further comparison device 17 as a dynamically corrected actual thickness 16. This now determines the controlled variable for the control of the adjusting elements 18 from the deviation of the dynamically corrected actual thickness 16 of the target thickness 13. The value of the dynamic thickness correction, during the rolling process already after short tape lengths, for example, after a wound tape length of about 50m, sufficient be accurately determined. Although this does not apply to the beginning of the rolling process, since in that case the fluctuations due to the winding process are still too great, a correction possibility of the radiometrically determined strip thickness 15 is available in the course of the rolling process, which is independent of the influencing variables of the radiometric strip thickness measurements , By excluding these influencing factors, the control of the adjusting elements of the roll stand 18 can be carried out much more accurately, which leads to a significant reduction in the strip thickness tolerances.

In addition, it is possible to release the correction calculation only under certain parameterizable conditions. The block diagram of the control of a corresponding embodiment of a device for correcting the thickness of a metallic strip during rolling shows the Fig. 3 , The parameters, quantities and conditions mentioned below are only to be regarded as an example configuration of the control, which may vary depending on the rolling stock to be produced.

This in Fig. 3 Block diagram shown initially has a logical AND gate 19 with 6 inputs 20, 21, 22, 23, 24, 25 and an output 26. By means of the inputs 20 to 24, for example, the conditions as to whether the laser is functional, whether the target thickness is more than 0.8 mm, for example, whether data on the alloy of the alloy are stored in a table, whether manual or automatic mode is selected, and whether the belt speed is greater than, for example, 100 m / min, queried and used to unlock the thickness correction. Other conditions can be considered via additional inputs on the AND gate 19.

The input 25 of the AND gate 19 is connected to the output of a logic OR gate 27, which in turn has two inputs 28 and 29, which are connected to the output of the comparison elements 30 and 31, respectively. In the comparison element 30, the actual value of the strip length 32 is compared with a calculated from the target thickness 33 via a function member 34 start value of the tape length 35 and an output signal to the OR gate 27 switched as soon as the actual value of the tape length 32 above a certain starting value of the tape length 35th lies. By contrast, the comparison element 31 compares, with the aid of the absolute element 38, the absolute value of the difference 39 determined between the target thickness 33 and the average strip thickness 37 determined by the differential element 36 with a value dependent on the target thickness 33. If the absolute deviation is less than, for example, 1% of the nominal thickness, the output of the comparison element 31 is switched on and a signal is applied to the input 29 of the OR element 27.

Thus, if the deviation of the mean strip thickness 37 from the set thickness 33 is less than 1% of the set thickness or the actual value of the strip length 32 is greater than a starting value of the strip length 35, a signal is applied to the input 25 of the AND element 19. If the inputs 20 to 25 of the AND element 19 are connected, the output 41 of the logic circuit is set to "auto-correction switched on" via the output 26 of the AND element 19 with the aid of the set element 40. At the same time a signal is applied to the input 42 of the PID gate 43. The PID element 43 then determines the dynamic thickness correction 44 of the radiometrically measured actual thickness 46 of the strip from the control deviation applied in the form of the difference 39 between the desired thickness 33 and the average strip thickness 37 determined by the LDV method. By means of a comparator 46 connected to the PID element 43, however, the regulation of the PID element 43 can be prevented, provided that the deviation 39 is, for example, less than 1% of the nominal thickness 33.

In the adding element 47, the dynamic thickness correction 44 is then added to the measured actual thickness 45 and applied to the input 49 of a switch 50 as a corrected actual thickness 48. The output 51 of the switch 50 is in turn connected directly to an input, not shown, the control of the control elements of the rolling stand.

If the output 41 of the logic circuit is switched to "auto-correction on", ie if a signal is applied to the PID element 43, the switch 50 connects the input 49 to the output 51 and the position elements of the rolling stands are controlled with the corrected actual thickness 48. In the unillustrated control of the control elements, the value output via the output 51 is again compared with the setpoint thickness 33 and the control elements of the roll stand 2 are correspondingly controlled.

Moreover, it is possible with the aid of the switch 50 to manually switch the control of the control elements to the actual thickness 46, in that the output 51 of the switch 50 is connected to the input 52 of the switch 50 is connected. Under certain circumstances, an automatic switching to the controller with the actual thickness 46 can take place, namely, when the reset element 54, the output 41 is reset via the OR gate 53. This is the case when the input 55 of the OR gate 53, which checks the operating state radiator in the outlet, or the input 56 of the OR gate 53, which monitors the falling below a minimum value for the belt speed, a signal. As a result, it can be prevented, for example, that in spite of the emitter 8 being switched off, an automatic thickness correction is made in the outlet of the strip 1.

Claims (9)

1. A method for correcting the thickness of a metal strip during rolling by a roll stand with adjusting elements to regulate the thickness of the strip and at least one take-up coiler, whereas an average strip thickness of a strip section is determined from at least one strip length measurement and the measurement of the dedicated rotation of the take-up coiler and the adjusting elements of the roll stand are controlled at least depending on the average strip thickness of the strip section,
   characterised in
   that the strip thickness is additionally measured radiometrically, the adjusting elements of the roll stand are controlled depending on a radiometric strip thickness corrected using the average strip thickness and the strip length is measured using the laser Doppler velocimetry method.
2. The method according to claim 1,
   characterised in
   that the rotation speed of the takeup coiler is measured using thigh-resolution incremental sensors on the axis of the take-up coiler or the axis of the take-up coiler motor.
3. The method according to any one of claims 1 to 2,
   characterised in
   that a plurality of values for the average strip thickness of the same strip section is measured by selecting a plurality of different starting points and strip lengths to be measured to determine the average strip thickness.
4. The method according to claim 3,
   characterised in
   that the values for the average strip thickness of the same strip section are additionally smoothed with variable weighting depending on the actual coil diameter of the strip on the take-up coiler.
5. The method according to any one of claims 1 to 4,
   characterised in
   that at least one further redundant strip length measurement is made.
6. The method according to claim 5,
   characterised in
   that if a first strip length measurement used to determine the average strip thickness fails, there is an automatic switchover to a further redundant strip length measurement.
7. A device for correcting the thickness of a metal strip (1) during rolling using at least one roll stand (2) with adjusting elements to regulate the thickness of the strip, at least one take-up coiler (4) as well as means for measuring the strip length (5) and the extent of the dedicated rotation of the take-up coiler (6) and means (18) for controlling the adjusting elements of the roll stand (2) depending on an average strip thickness determined from the measured strip length and dedicated rotation of the take-up coiler (4) are provided, especially for implementing a method according to claims 1 to 6,
   characterised in
   that means (8, 9) for radiometric determination of the thickness of the metal strip (1) are additionally provided between the roll stand (2) and take-up coiler (3) and a laser Doppler velocimetry system (5) is provided for measuring the strip length.
8. The device according to claim 7,
   characterised in
   that means (5) are provided for redundant measurement of the strip length.
9. The device according to claim 7 or 8,
   characterised in
   that high-resolution incremental sensors (6) are provided on the axis of the take-up coiler (7) or the axis of the take-up coiler motor.

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