WO2011054903A1 - Method for regulating the temperature profile and the speed of a cast strand in a continuous casting system, and continuous casting system for carrying out the method - Google Patents

Abstract

The invention relates to a method for detecting properties, in particular surface properties, of a cast strand in a continuous casting system using a laser source (13) for creating a laser beam directed onto the surface of the cast strand (4) and using a measuring tool (10) for analyzing signals reflected from the surface of the cast strand. The reflected laser beam reproduces information from the cast strand (4). Said information is obtained by creating an eddy current in the cast strand (4), and surface acoustic waves are created in the cast strand, said surface acoustic waves being received by a detector.

Description

 Method for controlling the temperature profile and the speed of a casting strand in a continuous casting plant and continuous casting plant for carrying out the process

The invention relates to a method for determining properties, in particular surface properties, of a cast strand in a continuous casting plant using a laser source for generating a directed onto the surface of the cast strand laser beam and a measuring device for the evaluation of reflected from the surface of the cast strand signals.

In addition, the invention relates to the quality optimization during the ongoing production operation of continuous casting plants due to the determined surface properties in the cast strand.

After a cast product has left the continuous casting plant, in the further course of production, in particular after a cooling process that may take several days, the slab separated from the cast strand or the separated block or billet is fed to the next processing step. As a rule, the products are inspected here in order to check the quality produced in each case.

This can be detected errors such. As surface cracks, internal cracks and segregation cracks that lie on or below the product surface. The errors are documented in order to be able to repair the product if necessary. The inspection is performed by various methods, such as visual inspection, sampling or surface finishing, to perform surface or interior quality control. For this purpose, the product to be tested must have cooled to a certain temperature, for example below 100 ° C., in order to carry out the required inspection operations. An inspection is not possible at the CSP Process (= Compact Strip Production), ie the process for casting thin slabs, in which the product produced is fed directly to the next processing step.

From DE 29 1 1 578 A1 a method and a device for checking the surface of a moving metal band have become known in a continuous casting process. Here, a compact device and a method for determining on a surface of a steel strip, such as a steel plate or a steel ingot in the course of the continuous casting at any desired location or preferably in a cooling chamber resulting overlaps of the casting strand are specified without any appreciable Impaired by cooling water or cooling steam occurs. The known device includes a light generating device with a light source emitting light beams with short wavelengths or other waves. Furthermore, a light detector with a filter is provided, which allows the passage of light beams having only short wavelengths. In addition, a flat hood is provided, which surrounds an extending between the light generating device and the light detector light path. Finally, an image memory device is provided, to which an electrical signal is supplied. This characterizes the shadow of a steel strip in the continuous casting process which is supplied to the light detector in the case where the areas of a light path are cleaned by compressed air introduced into the hood, the shadow of the steel strip after processing by the image memory I am played on a television monitor system. In this way, any overlaps that may be present on the surface of the steel strip are determined. The main part of a strip surface testing device can be accommodated in a cooling chamber. The outer end of the flat hood is located between two adjacent support rolls turned into a steel strip which is manufactured by continuous casting.

This known method is intended to determine the surface condition of a steel strip. and continuously monitor the wide surface area of the steel strip on the TV monitor. Moreover, the surface condition of the steel strip is to be examined in an initial stage of steel strip movement, which is intended to quickly eliminate the causes leading to the occurrence of overlaps by supplying data to a control section as a result of the inspection to adjust the casting speed of the steel strip. The strip surface testing device is intended to allow the inspection of the surface of a steel strip in the course of performing the continuous casting process. From WO 91 17009 A1 a method for continuous inspection of a metal casting strand has become known. In this method, a laser source for generating a pulsed laser beam is used, which is irradiated on the extruded from the continuous casting mold strand and generates an acoustic wave in the strand in or on the surface. Furthermore, means are provided which detect the interaction of the acoustic wave with the strand and generate corresponding signals. There is also means for analyzing the waves and generating signals indicative of the condition of the casting strand. It is also possible to arrange a plurality of laser sources at the periphery of the strand. The detector may also include an interferometer.

According to WO 91 17009 A1 it is proposed to regulate the water flow in the region of the continuous casting mold, the secondary cooling, the casting speed, the roll contact pressure and the energy consumption on the basis of the information obtained during the measurement of the surface waves.

It is the object of the invention to specify a method for use in a continuous casting plant and a continuous casting plant, in which the material properties of the casting strand can be determined in a simple manner and the casting process is continuously optimized on the basis of the data obtained thereby. In a method of the type mentioned, this object is achieved in that the reflected laser beam reproduces information from the cast strand, which are obtained by generating an eddy current in the cast strand.

It is the object of the invention to present a novel method with corresponding devices for direct quality determination, even under so-called hot conditions, which via a non-contact measuring method directly during the generation or near to the generation of information about the quality generated, d. H. provide the surface or internal quality, a steel strand for the process automation control or the operator to then define the further production steps without requiring a material-destroying inspection. Furthermore, timely indications of a quality decline with the localized fault location with appropriate location and material allocation should be obtained.

In the last-mentioned application, which also applies to CSP plants, a measure plan according to the invention, which can also be partially automated in the automation system, a direct adaptation of product parameters, such as an adaptation of the casting speed, the change in cooling water amounts, the adaptation of Gießpulverzuordnung, the adaptation of the software reduction parameters, targeted and based on experience quality improvement.

This results in several advantages: Compared with the prior art, fewer manual inspections of both the cooled product and the continuous strand are required. Immediate and early quality control is possible, resulting in lower losses and a lower product scrap. It comes to a lesser extent material devaluation. Prozesssch ritte for further processing can be initiated without delay, as it results from a possible after cooling quality inspection. This is especially true for the hot-charging of the products. Especially when used with CSP plants, the surface quality of the precursor can be improved early.

The invention is characterized by a non-contact and non-destructive measuring method for determining the product surface and product quality at a surface temperature of the product, which is for example in the range between 400 and 1000 degrees Celsius.

The measurement is carried out on the passing material in the current production operation; no stopping of the product is required for the test or measurement. The measurement is preferably carried out on the broad sides of the product, ie slabs, thin slabs, billets and block plants. In the case of profiles, the measurement is carried out on the metrologically accessible surfaces. In the case of round or polygonal products, the measurement can take place on all accessible surfaces. The recorded error situations, especially in comparison to recorded Gutsituationen or to a still acceptable quality result, visualized for the operator at the control room or at appropriately designated operator stations. There are procedural execution provisions, so-called routing, for further processing, for. For example, the sorting out of products with detected frequent defects or the direct further processing of the products, defined treatment steps with minor errors, direct further processing with defect-free products, due to the determined test condition, derived. From this, an action plan for systematic quality improvement is derived for the operator when detecting errors. The action plan for fault detection, which can also be partially automated, includes a systematic quality improvement for the operator, for example an adjustment of the casting speed, the cooling or the hydraulic adjustment values for the segment adjustment.

According to the invention, a preferably stationary measuring device and also a preferably fixed measuring system are installed. Both are arranged, for example, behind the strand guide in an area where the cast product has not yet passed through the separating or cutting device, that is, for example, behind a bending driver or in or behind the straightening device or directly in front of the separating device.

Alternatively, the stationary measuring device and the measuring system can be arranged in a subsequent finishing device, with the product moving past the measuring device in the still hot state.

The number of measuring sensors used to measure a product page depends on the product dimensions and the detection range of the sensor. Thus, several sensors in an array next to each other can cover an extended measuring range.

Preferably, the continuous casting plant also comprises an automation system for data acquisition and data processing, for quality representation as well as for receiving and processing the inspection data or the measuring signals originating from one or more measuring sensors. Likewise, electronic memories for data backup and data archiving of the operator can be provided, with which the values measured during production can be completely documented.

From the data obtained via the cast strand can be optionally derive an automated execution specification for the further processing of the product.

It is also possible to derive an automated action plan to improve product quality, preferably the gradual adjustment of the casting speed, the gradual adjustment of the cooling or the gradual adjustment of the soft reduction parameters.

Advantageous developments of the invention will become apparent from the dependent claims and the description.

Overall, the invention provides a method according to which generates signals in a detector due to the reflected laser signals and a controller of a control loop for controlling process variables, in particular the cooling water flow, the roll contact pressure, the Gießpulverzufüh- tion, the energy supply, the temperature and / or supplied to the speed of the casting strand and the temperature or the speed of the casting strand are controlled accordingly.

Preferably, the method is characterized in that the laser source irradiates a laser light beam through a filled with a dielectric inner region of a transmitting coil for generating an alternating magnetic field for inducing eddy currents in the casting strand and that of the surface of the casting strand reflected laser beam after re-passing through the dielectric and a beam splitter and a polarization filter in an optical sensor generates a signal that provides information about the surface properties of the cast strand under the action of the alternating magnetic field and that the sensor generates output signals on the basis of the measured laser light intensity, which it passes on to the controller. This detection method utilizes the Faraday effect used in magneto-optic eddy current testing systems. In itself In a known manner, a magnetic alternating field is generated contactlessly by an excitation and transmitting coil brought into the vicinity of an electrically conductive substance, ie, which is operated with an alternating current. This penetrates into the material and induces eddy currents in it. The distribution and strength of the eddy current depend on the electrical and magnetic properties of the substance under investigation. The eddy current also generates a magnetic alternating field which attenuates the field of the transmitting coil according to the Lenz rule. This attenuation could be detected by a receiving coil introduced into the interior of the transmitting coil. Instead of the receiver coil, however, it is possible to replace it by another sensor with a high lateral resolution, ie a high resolution in the plane of the cast strand to be examined, which shows the Faraday effect. This property has an optical component that rotates the polarization direction of a light wave in response to a magnetic field. Rotating the polarization is a property of some crystals. The Faraday rotator consists of such a crystal in conjunction with a surrounding electromagnet, the transmitting coil. In the context of the invention, an increase in resolution has the effect that the rotation, which undergoes a polarized light beam passing through the crystal, is always doubled in a second passage through the rotator, independently of the running direction of the light.

The invention also relates to a further method for determining properties, in particular surface properties, of a cast strand in a continuous casting plant using a laser source. Also in this case, laser pulses are directed to the surface of the cast strand; and there is a meter for evaluating signals reflected from the surface of the cast strand.

This method is inventively characterized in that surface acoustic waves are generated in the cast strand, which are received by a detector. The method is based on the excitation of acoustic Surface waves in samples to be examined. They are generated by short, in particular perpendicular to the sample surface impinging laser pulses and received after covering a selectable distance with a suitable detector, preferably in the frequency range up to 200 MHz. From the resulting sound dispersion can then be concluded on the elastic Eigen- shafts in the investigated layer. As a result, it is already possible to examine layers with a thickness of 500 nm or less on substrates with low sound attenuation. Only the layer thickness and the transverse contraction number of the material of the casting strand must be known. Preferably, a piezo-ceramic detector is used to receive the surface acoustic waves. This measurement method allows the modulus of elasticity of the cast strand to be investigated to a thickness of several micrometers. This means that not only the surface quality of the cast strand is determined, but also the internal quality and the quality are determined. The sound propagation times are measured. The edge layers of the cast strand can be characterized in particular, in particular, an elastic anisotropy of the bulk material can be determined, if it is present. Advantageously, the values measured by the measuring device or by the detector are displayed on a monitor of a control station of the continuous casting plant.

Advantageously, the method is also characterized in that the temperature is controlled by the supply and the amount of coolant in the region of the strand guide segments.

Likewise, the invention also relates to a continuous casting plant for carrying out a method as described above. According to the invention, the continuous casting plant is characterized in that the continuous casting plant has a regulating device for regulating the temperature or the speed of the casting strand on the basis of the measuring device or the detector produced by the measuring device. th signals.

The invention will be explained in more detail in an embodiment with reference to the drawings.

These show:

Fig. 1 is a schematic representation of a continuous casting plant for casting a metal strand with an integrated measuring device and

Fig. 2 shows the meter in detail.

A continuous casting plant for casting thin slabs comprises a casting ladle 1 (FIG. 1) from which liquid metal, in particular liquid steel, is transferred via an intermediate container 2 into a mold 3. From the mold 3 is a hot strand 4, which is guided by a strand guide 5 with segments and rollers not shown here. Via driver units 6, 7 of the hot strand is continued to a separator 8 in the direction of arrow A. In the separator 8 arise from the hot strand 4 individual slabs. 9

For example, between the last driver unit 7 and the separating device 8, a measuring device 10 for measuring the material or structural properties of the hot strand 4 is arranged without contact with the strand surface and preferably also angle-adjustable with respect to the hot strand 4. The data obtained by the measuring device 10 are fed to a data acquisition, processing, evaluation and archiving as well as control or regulating unit 11. These are supplied by a (not shown here) control center via data lines process data and / or operating parameters, so that the control unit 1 1 this evaluates taking into account the transmitted from the meter 10 data to operating variables such as the supply of liquid metal in Area of the ladle 1 and the tundish 2, the cooling in the region of the mold 3, the secondary cooling in the strand guide 5 or in a (not shown) downstream cooling unit, the contact pressure of leadership or driver roles in the driver units 6, 7 and other operating variables. Data from the control unit 1 1 are forwarded to a monitor 12 and visualized for the operator.

The measuring device 10 (FIG. 2) comprises, for example, a Nd: YAG laser 13 having a wavelength of 532 nm as a source for generating polarized light. The laser beam generated by the laser 13 passes through a beam splitter 14 and then into a Faraday rotator 15, which comprises an optically active crystal 16 (dielectric) and a coil 17 surrounding it. To the coil 17, a particular high-frequency alternating current for generating a magnetic field is applied, which in turn generates eddy currents in the passing under the meter 10 hot strip 4. The eddy currents in turn generate magnetic fields which, together with the magnetic field of the coil 17, rotate the polarization of the laser beam reflected by a separate mirror layer or by the surface of the hot strand 4 itself. Then the back-reflected laser beam passes through the beam splitter 14 through a polarizing filter 18, which passes only light of a specific polarization direction. Only the component of the reflected laser beam having this polarization direction is transmitted and detected by an optical sensor 19, for example a photodiode or a CCD camera. Thus, the magnetic field distribution in the interior of the coil 17, ie in the crystal 16, is converted into a light intensity distribution which provides information about the properties of the hot strand 4 in the area of the surface and below the surface. It is also possible to tilt the entire measuring device or only the Faraday rotator 15, with respect to the surface of the hot strand 4 at a certain angle in order to carry out investigations for different angular ranges. LIST OF REFERENCE NUMBERS

1 ladle

 2 intermediate tanks

3 mold

 4 hot strands

 5 strand guide

 6 driver unit

 7 driver unit

 8 separating device

 9 slabs

 10 measuring device

 1 1 control unit

12 lines

 13 Nd: YAG laser

 14 beam splitter

 15 Faraday rotator

 16 crystal

 17 coil

 18 polarization filters

19 sensor

Claims

claims 1 . Method for determining properties, in particular of surface properties, of a cast strand (4) in a continuous casting plant using a laser source (13) for producing a laser beam directed onto the surface of the cast strand (4) and a measuring device (10) for evaluating it from the surface the cast strand of reflected signals,  characterized,  in that the reflected laser beam reproduces information from the cast strand (4) obtained by generating an eddy current. 2. The method according to claim 1,  characterized,  in that signals are generated in a detector (19) on the basis of the reflected laser signals and a controller (11) of a control loop for regulating process variables, in particular the cooling water flow, the roll contact pressure, the casting powder feed, the energy supply, the temperature and / or the speed of the cast strand ( 4) and the temperature or the speed of the casting strand (4) are regulated accordingly. 3. The method according to claim 1 or 2,  characterized, in that the laser source (13) radiates a laser beam through an inner region of a transmitting coil (17) filled with a dielectric (16) to produce an alternating magnetic field for inducing eddy currents in the cast strand (4) and that of the surface After repeated passage through the dielectric (16) and a beam splitter (14) and a polarization filter (18) in an optical sensor (19), the laser beam of the cast strand generates a signal, the conclusion about the surface properties of the cast strand under the action of the alternating magnetic field and that the sensor (19) generates output signals due to the measured laser light intensity, which it forwards to the controller (1 1). 4. A method for determining properties, in particular surface properties, of a cast strand (4) in a continuous casting using a laser source (13) for generating on the surface of the cast strand (4) directed laser pulses and a measuring device for the evaluation of the surface of the Cast strand of reflected signals, characterized  that surface acoustic waves generated by a detector are generated in the cast strand 5. The method according to claim 4,  characterized,  the surface acoustic waves are received by a piezoceramic detector. Method according to one of claims 1 to 5,  characterized,  in that the values measured by the measuring device (10) or by the detector are displayed on a monitor (12) of a control station of the continuous casting plant. Method according to one of claims 1 to 6,  characterized, the temperature is regulated by the supply and the quantity of coolant in the region of the strand guide segments. 8. continuous casting for carrying out a method according to one of claims 1 to 7 with a laser source (13) for generating a on the surface of the cast strand (4) directed laser beam and with a measuring device (10) and / or a detector for the evaluation of the O- surface of cast strand (4) reflected signals,  characterized,  the continuous casting plant comprises a regulating device (11) for regulating the temperature or the speed of the casting strand on the basis of the signals generated by the measuring device (10).