EP3744440A1 - Method and device for continuous casting - Google Patents

Abstract

The present invention relates to a method for continuous casting, wherein a cast strand is cast. The cast strand has at least a first and a second surface section. At least one thermal image of the cast strand is recorded after secondary cooling of the cast strand by means of a device for secondary cooling. The method is characterized in that the at least first and second surface section is captured with the thermal image (s). A first actual temperature of the first surface section of the cast strand is recorded by means of the thermal image or images. A second actual temperature of the second surface section of the cast strand is also recorded by means of the thermal image or images. Depending on a first difference between the first actual temperature and a first setpoint temperature, a cooling nozzle field of the device for secondary cooling that is assigned to the first surface section is regulated. Depending on a second difference between the second actual temperature and a second setpoint temperature, a cooling nozzle field of the device for secondary cooling that is assigned to the second surface section is regulated. The invention also relates to a corresponding device for continuous casting.

Description

The present invention relates to a method and an apparatus for continuous casting.

A device for continuous casting typically comprises a mold and a strand guide with a plurality of strand guide rollers, which is arranged downstream of the mold in the casting direction. First, liquid metal, in particular liquid steel, is poured into the mold. This is cooled at the edges of the mold with the aid of a device for primary cooling, so that a cast strand with an initially still liquid core but already solidified, load-bearing strand shell is formed inside the mold. After the cast strand has left the mold with a stable shell, it is guided within the downstream strand guide and cooled by means of a device for secondary cooling until it is finally completely solidified. The solidification length indicates the length of the metal strand from the exit from the mold to the location of the device for continuous casting at which the cast strand has completely solidified. The guide within the strand guide takes place between opposite strand guide rollers, the cast strand typically being bent over from the vertical to the horizontal. The solidified, continuous cast strand is regularly divided into individual slabs, thin slabs, billets or blooms at the outlet of the device for continuous casting.

In the EP 2 753 439 B1 a simulation method for determining the temperature distribution in the cast strand and the solidification length is described, on the basis of which the known device for continuous casting, in particular the secondary cooling and the casting speed, is controlled, since a continuous temperature measurement by means of a pyrometer is due to the spraying of the surface of the cast strand with water occurring splash water is not reliably possible. In the DE 10 2011 077 454 A1 it is also proposed to improve a modeled temperature distribution in the cast strand by individual measurements of the temperature along the strand guide.

In addition, the JP 2014 037001 A proposed to determine the degree of solidification of a cast strand using a heat transfer model taking into account the cooling conditions of the secondary cooling. The temperature distribution in the width direction of the cast strand is measured with a thermometer. When measuring the temperature distribution, a surface of the cast strand is recorded with a camera and the temperature distribution is determined based on the brightness distribution of the recorded image.

Finally, in the WO 2017/144481 A1 discloses an array of nozzles for applying coolant to the cast strand. This is intended for installation in roller gaps between two strand guide rollers. The known nozzle row arrangement has nozzles with different control ratios. The control ratio indicates how far the volume flow of the coolant discharged by means of the nozzle can be reduced compared to the nozzle-specific maximum value without there being a significant change in the jet cone.

It has been shown that with the known methods and devices for continuous casting, cracks can occur on the surface of the cast strand and consequently on the surfaces of the subsequently divided semi-finished products.

Proceeding from the known prior art, the present invention is consequently based on the object of specifying a method and a device for continuous casting with which the process reliability can be increased and a qualitatively improved semi-finished product can be obtained.

According to the invention, this object is achieved by the subject matter of the main and subsidiary claims. Advantageous refinements are given in the subclaims.

A method for continuous casting is proposed, in which a cast strand is cast. The cast strand has at least a first and a second surface section. At least one thermal image of the cast strand is recorded after secondary cooling of the cast strand by means of a device for secondary cooling. The method is characterized in that the at least first and second surface section is recorded with the thermal image (s). A first actual temperature of the first surface section of the cast strand is recorded by means of the thermal image or images. A second actual temperature of the second surface section of the cast strand is also recorded by means of the thermal image or images. As a function of a first difference between the first actual temperature and a first setpoint temperature, a cooling nozzle field of the device for secondary cooling that is assigned to the first surface section is regulated. As a function of a second difference between the second actual temperature and a second setpoint temperature, a cooling nozzle field of the device for secondary cooling that is assigned to the second surface section is regulated.

The determination of the respective actual temperature of several surface sections of the cast strand by means of one or more thermal images after the secondary cooling, in particular at the outlet of the continuous caster, and the targeted influencing of the temperature of these surface sections by the respectively assigned cooling nozzle fields allow a targeted setting of the temperature profile of the cast strand for the subsequent one Machining. A homogeneous temperature profile of the cast strand can have a very positive effect on the material properties of the further processed semi-finished product.

In contrast to the previously usual temperature measurements by means of a pyrometer, not only the temperature of individual surface points is determined, but also entire, more or less large surface sections. When recording the thermal images, use can be made of thermal imaging cameras, in particular in the form of infrared cameras, for example. The measuring thermal imager can, for example, have a resolution between 600 x 400 pixels or heat dots and 1650 x 1250 pixels or heat dots, in particular 640 x 480 pixels or heat dots, with which one between half a square meter and one and a half square meters, in particular a one square meter Surface portion of the cast strand can be detected. On the one hand, this allows the effort involved in evaluating the measurement to be kept low. On the other hand, a sufficient data basis for the regulation of the cooling nozzle fields of the device for secondary cooling is obtained. The surface sections evaluated by means of the thermal images can have a circular geometry in order to further simplify the evaluation. In addition, it is also conceivable that the geometry of the surface sections is freely specified by the user. The use of a thermal imaging camera enables the temperature to be measured synchronously at different points on the measured object. In particular with the moving cast strand, a simultaneous measurement of the temperature of different Surface sections of the cast strand guaranteed perpendicular to the conveying direction and the control of the temperature distribution simplified. In contrast to previous temperature measurement methods, the thermal imaging camera can also be suitable for measuring the surface temperature in the presence of fog, water vapor or smoke in the vicinity of the cast strand. The cooling nozzle fields can be, for example, sections of one or more of the in the WO 2017/144481 A1 Acting nozzle row arrangements described. To regulate the first difference and / or the second difference, the water pressure or the volume of water dispensed and, if applicable, the air pressure or the amount of air dispensed by the single-substance nozzles (pure water cooling) or two-substance nozzles (water-air Cooling) can be controlled.

If the first and second surface sections are adjacent and the amount of the difference between the first target temperature and the second target temperature is less than 150 Kelvin (| first target temperature - second target temperature | <150 Kelvin), the risk of The formation of surface cracks can already be significantly reduced. A good quality of the semi-finished products produced can be obtained in particular with an amount of the difference between the first target temperature and the second target temperature of less than 100 Kelvin (| first target temperature - second target temperature | <100 Kelvin).

A choice of the first and / or second target temperature of more than 800 ° C. can simplify the further processing of the cast strand. In particular, less energy is required for further processing (for example in a rolling mill) the semi-finished products (for example slabs), since the semi-finished products have to be heated to a lesser extent. The first and / or second target temperature is preferably greater than 900 ° C.

It can further be provided that a core temperature of the cast strand is determined by means of the first actual temperature and the second actual temperature. The core temperature can provide an indication of the position of the sump tip in the cross-section of the cast strand. This can enable verification of simulation calculations or other metrological methods by converting the measured temperatures.

In particular, an average temperature of the first surface section can be determined as the first actual temperature. The use of average temperatures can reduce the risk of the temperature control being influenced by individual extreme values, which e.g. Measurement errors. However, it is also conceivable to determine a maximum temperature or a minimum temperature of the first surface section. Similarly, actual temperatures in the form of average, maximum or minimum temperatures can also be determined from the further surface sections.

The upper side of the cast strand and / or the underside of the cast strand and / or the left side of the cast strand and / or the right side of the cast strand and / or the end face of the cast strand can be detected by means of the thermal image (s).

In particular, a thermal image that records the end face of the cast strand can enable the core temperature of the cast strand to be determined more precisely. The core temperature measured on the front side, which is the highest temperature that can usually be found in the center of the cross-section, can be an indication of a possible increase in the casting speed. If, for example, a defined maximum limit temperature in the cross-sectional core at the end face of the cast strand, ie the separation point of the separated semi-finished product, of 1200 ° C., for example, is not reached, Casting speed can still be increased safely until this limit is reached. The risk of breaking out (breakthrough of liquid steel on the face, broad side or narrow side) can be reduced in this way while increasing production at the same time. Correspondingly, one embodiment of the method provides that the casting speed is regulated as a function of the first and / or second actual temperature.

In particular, the secondary cooling can initially be increased, whereby the cross-sectional temperature is reduced in order to subsequently increase the casting speed. The productivity of the apparatus for continuous casting can thus be improved.

A pictorial representation of the temperature profile of the cast strand obtained by means of the method described above can simplify operation, quality assurance and maintenance for the user of the device for continuous casting.

Furthermore, a device for continuous casting with a device for secondary cooling of a cast strand and with at least one thermal imaging camera for recording at least one thermal image of the cast strand after the device for secondary cooling of the cast strand is proposed, the device for secondary cooling having a first cooling nozzle field which is a first surface section of the cast strand is assigned, and wherein the device for secondary cooling has a second cooling nozzle field which is assigned to a second surface section of the cast strand. The device is characterized in that it is set up to record the at least first and second surface section with the thermal image (s), to determine a first actual temperature of the first surface section of the cast strand by means of the thermal image or images, by means of the or the thermal images to determine a second actual temperature of the second surface section of the cast strand, depending on a first difference between the first actual temperature and a first target temperature to regulate a cooling nozzle field of the device for secondary cooling assigned to the first surface section, and depending on the second difference between the second actual temperature and a second target temperature, on the second To regulate surface section associated cooling nozzle field of the device for secondary cooling.

With regard to the advantages associated with such a device and possible further refinements, reference is made to the statements on the method for continuous casting.

Fig. 1

eine Vorrichtung zum Stranggießen;

Fig. 2

einen Ausschnitt der Vorrichtung nach Fig. 1; und

Fig. 3

ein Ablaufdiagramm eines Verfahrens zum Stranggießen.

The invention is explained in more detail below on the basis of exemplary embodiments. They show schematically:

Fig. 1

an apparatus for continuous casting;

Fig. 2

a section of the device Fig. 1 ; and

Fig. 3

a flow chart of a method for continuous casting.

The ones in the Fig. 1 The device shown for continuous casting comprises a pan P, in which liquid metal, in particular steel, can be transported to an intermediate container Z and poured into it. The liquid metal flows from the intermediate container Z to a mold KO, at the edges of which the liquid metal is cooled with a primary cooling device (not shown), so that there is a cast strand G with an initially still liquid core, but already solidified, inside the mold KO. more stable strand shell.

After the cast strand G has left the mold KO, it is guided by means of a strand guide in such a way that, starting from the cast, it is bent in the direction of gravity and in a horizontal conveying direction F. is transported further. For this purpose, the strand guide has a plurality of strand guide rollers R lying opposite one another.

Nozzle row arrangements SK1, SK2, SK3 for secondary cooling are provided between the opposite strand guide rollers R. The cast strand G is cooled by means of the device for secondary cooling formed by the row arrangements SK1, SK2, SK3 until it has solidified. The cast strand G is then divided into semi-finished products B using a device not shown in the figure. In the exemplary embodiment shown, the semi-finished product B is a slab B.

Furthermore, at least one thermal imaging camera K is provided in the outlet of the device for continuous casting.

In the Fig. 2 is an excerpt from the Fig.1 shown device for continuous casting. The device for secondary cooling comprises cooling nozzle fields SK1, SK2, SK3, SK4 of which four cooling nozzle fields are assigned to four surface sections W1, W2, W3, W4 of the cast strand G. In the four surface sections W1, W2, W3, W4 of the cast strand G, the three surface sections W1, W2, W3 are surface sections of the upper side of the cast strand G, ie a broad side of the strand, and a surface section W4 is a surface section of a narrow side.

Like in the Fig. 2 is shown, a thermal imaging camera K is used to record at least one thermal image of the cast strand G after the device for secondary cooling. Actual temperatures of surface sections W1, W2, W3, W4 are determined by means of the thermal image. The actual temperatures are average temperatures of the surface sections W1, W2, W3, W4.

In addition to the surface sections W1, W2, W3, W4 to which the cooling nozzle fields SK1, SK2, SK3, SK4 are assigned, the temperature of surface sections Q1, Q2, Q3 on the end face of the cast strand G is also recorded.

4 shows a greatly simplified flow diagram of a method for continuous casting. First, the parameters of the semifinished product B to be produced, in particular its dimensions and its material properties, are recorded (step 301).

Based on these parameters, control specifications for the device for continuous casting are determined in an automated manner (step 302). In particular, the target surface temperatures of the cast strand G at the outlet of the device for continuous casting and the target cross-sectional temperatures of the cast strand at the outlet of the device for continuous casting are determined.

The corresponding temperatures at the outlet of the continuous caster are then regulated. For this purpose, default values for the device for secondary cooling are first determined on the basis of the target surface temperatures and the target cross-sectional temperatures, and the cast strand is cooled based on these values (step 303).

By means of the thermal imaging camera K, the actual surface temperatures and the actual cross-sectional temperatures are then measured and compared with the previously determined setpoint surface temperatures and setpoint cross-sectional temperatures (step 304). Depending on the deviation of the actual temperatures from the setpoint temperatures, the default values for the device for secondary cooling are then adapted (step 303).

Furthermore, the measured actual temperatures can then be made available to connection processes (e.g. rolling processes) and / or stored for purposes of quality assurance (step 305). A graphic representation of the temperature profile is also conceivable.

Claims (10)

Continuous casting process,
whereby a cast strand (G) is cast,
wherein the cast strand (G) has at least a first and a second surface section (W1, W2),
at least one thermal image of the cast strand (G) after secondary cooling of the cast strand by means of a device for secondary cooling (SK1, SK2, SK3, SK4) is recorded,
characterized,
that the at least first and second surface section (W1, W2) is recorded with the thermal image (s),
that a first actual temperature of the first surface section (W1) of the cast strand (G) is determined by means of the thermal image or images, that a second actual temperature of the second surface section (W2) of the cast strand (G) is determined by means of the thermal image or images, that as a function of a first difference between the first actual temperature and a first target temperature, a cooling nozzle field (SK1) of the device for secondary cooling assigned to the first surface section (W1) is regulated, and
that depending on the second difference between the second actual temperature and a second target temperature a second Surface section (W2) associated cooling nozzle field (SK2) of the device for secondary cooling is regulated. Method for continuous casting according to claim 1,
characterized,
that the first and second surface portions are adjacent, and
that the amount of the difference between the first target temperature and the second target temperature is less than 150 Kelvin, in particular less than 100 Kelvin. Method for continuous casting according to claim 1 or 2,
characterized,
that the first and / or second target temperature is greater than 800 ° C., in particular greater than 900 ° C. Process for continuous casting according to one of the preceding claims,
characterized,
that an average temperature, a maximum temperature or a minimum temperature is determined as the first actual temperature. Process for continuous casting according to one of the preceding claims,
characterized,
that by means of the thermal image (s) the top of the cast strand (G) and / or the bottom of the cast strand (G) and / or the left side of the cast strand (G) and / or the right side of the cast strand (G) and / or the end face of the cast strand (G) is detected. Process for continuous casting according to one of the preceding claims,
characterized,
that a core temperature of the cast strand (G) is determined by means of the first actual temperature and the second actual temperature. Process for continuous casting according to one of the preceding claims,
characterized,
that a casting speed is regulated as a function of the first actual temperature and the second actual temperature. Process for continuous casting according to one of the preceding claims,
characterized,
that a user is shown a pictorial representation of the temperature profile of the cast strand (G). Process for continuous casting according to one of the preceding claims,
characterized by
the secondary cooling is increased, and
subsequently the casting speed is increased. Device for continuous casting
with a device for secondary cooling (SK1, SK2, SK3, SK4) of a cast strand (G), and
with at least one thermal imaging camera (K) for recording at least one thermal image of the cast strand (G) after the device for secondary cooling (SK1, SK2, SK3, SK4) of the cast strand (G),
wherein the device for secondary cooling has a first cooling nozzle field (SK1) which is assigned to a first surface section (W1) of the cast strand (G),
wherein the device for secondary cooling has a second cooling nozzle field (SK2) which is assigned to a second surface section (W2) of the cast strand,
characterized,
that the device is set up to
to capture the at least first (W1) and second (W2) surface section with the thermal image (s),
to determine a first actual temperature of the first surface section (W1) of the cast strand (G) by means of the thermal image or images,
to determine a second actual temperature of the second surface section (W2) of the cast strand (G) by means of the thermal image or images,
as a function of a first difference between the first actual temperature and a first target temperature, to regulate a cooling nozzle field (SK1) of the device for secondary cooling assigned to the first surface section (W1), and
as a function of the second difference between the second actual temperature and a second target temperature, to regulate a cooling nozzle field (SK2) of the device for secondary cooling assigned to the second surface section (W2).

Images