WO2000024535A1 - Vertical continuous casting installation with optimized measurement of the metal level - Google Patents

Abstract

A vertical continuous casting installation comprising at least one ingot mould (10) with a bottom (14) that can be lowered onto a casting table (16), a launder system (20) for conveying molten metal from a furnace into individual ingot moulds (10) and a measuring device for each ingot mould (10) in order to determine a time-dependent level of said molten metal N(t), in addition to a flow control device (30) that controls the supply of metal that is fed into the individual ingot moulds (10) on the basis of the difference between a predetermined setpoint flow Nsoll(t) and a measured time-dependent level of molten metal N(t). The measuring device consists of two measuring systems (22, 26) that work in a different physical manner. Said systems are respectively provided with a sensor (24, 28). The sensors (24, 28) are placed at a predetermined fixed distance in relation to the ingot mould (10). The first measuring system (22) has a measuring accuracy of at least ± 2 mm in a measuring range of at least 200 mm and is used to measure the level N(t) during a first filling phase of the ingot mould (10) and the second measuring system (26) has a measuring accuracy of at least ± 0.1 mm in a measuring range of at least 20 mm and is used to measure the level N(t) during the final phase of the filling process and the lowering phase of the casting table (16).

Description

Vertical continuous casting machine with optimized metal level measurement

The invention relates to a vertical continuous casting system, in particular a vertical continuous casting system for the automatic continuous casting of aluminum alloys, comprising at least one mold with a start-up base arranged on a lowerable casting table, a pouring channel system for transporting a molten metal from an oven into the individual molds, and a measuring device for determining each mold of the time-dependent metal melt level N (t) and a flow control device for controlling the metal supply into the individual molds as a function of the difference between a predetermined setpoint curve N _so n (t) and the measured time-dependent metal melt level N (t).

The invention further relates to a method for vertical continuous casting of metals, in particular aluminum alloys, in a casting plant comprising at least one mold, in which method the liquid metal is fed from an oven to the individual molds via a trough system and into the mold via a flow control device closed molds are initially guided during a filling phase from start-up floors arranged on a lowerable casting table, starting from an initial level of the metal melt, at which metal melt level control begins, to a predetermined start level, at which the lowering of the casting table to generate the metal strands begins, and during the entire lowering phase the time-dependent metal level N (t) in each mold is measured with a measuring device and compared with a time-dependent setpoint specification N _so u (t), and the metal supply into the individual molds by means of a through flow control device is controlled according to the time-dependent difference between the actual and target value of the metal level.

Such a method, as well as such a vertical continuous casting installation containing several molds are known for example from DE-OS 32 05 480 AI. According to the teaching described in DE-OS 32 05 480 AI, the detection of the metal level takes place by means of a float as a measuring sensor, which rests on the surface of the metal column and consists of a heat-resistant material, which must be selected such that absorption of molten metal or contamination is avoided.

Patent EP-B 0 517 629 also describes an apparatus described at the outset and a corresponding method for vertical continuous casting of metals, a capacitive sensor being used to record the time-dependent metal melt level in the individual molds. The capacitive level measurement takes place between the surface of the molten metal and one at a certain distance from it located plate, which is adjusted in its distance from the metal surface by means of a servo motor in such a way that the capacity is constant and equal to a reference capacity.

In the case of a multi-strand continuous caster, the control of the start-up process, i.e. the optimal control of the metal supply to the individual casting units until the actual casting start, which is initiated by lowering the casting table, is crucial. In order to regulate the metal level in the individual molds during the start-up phase as quickly as possible to a level predetermined for the beginning of the lowering of the casting table without the risk of metal freezing, WO 98/32559 describes a method according to that the metal level in all molds is controlled simultaneously according to a setpoint curve that is identical for all molds, the gradient of which is greater at the beginning of the cleaning process than the average gradient and is smaller than the average gradient at the end of the start-up phase.

The filling level of the molds for the start of the lowering process is typically between 120 and 200 mm. The precise control of the metal level is of crucial importance for trouble-free operation of a casting system, especially in the lowering phase. The precise control of the metal level in the individual molds requires a correspondingly precise measurement of the fill level. As a result, the precise metal level control of a casting system requires precise and reproducible level measurement over a large measuring range of typically 200 mm. The importance of a precise metal level determination is greatly increased, in particular in the further developed controls of multi-mold continuous casting plants, such as, for example, controls according to WO 98/32559, in which the level control takes place with non-linear setpoint curves.

Inductive or capacitive sensors are suitable for the exact level determination. The required accuracy can only be achieved with inductive sensors in a measuring range of approx. 30-50 mm. The vertical continuous casting plants known from the prior art therefore use most devices in which such sensors are tracked by means of a precision mechanism in cooperation with a servo or stepper motor in such a way that the measuring range permitted for the required measuring accuracy is not exceeded. Capacitive sensors can be used for large measuring ranges of up to 300 mm, for example; however, they show a great dependency on the external measurement conditions, so that frequent recalibration is necessary. In principle, laser-optical, ultrasound and microwave methods are also known for level and distance measurements.

Laser-optical methods can only be used to a limited extent for the level measurement of highly reflective samples. Such methods are in principle suitable for level measurement of metal alloys, for example aluminum alloys, during the filling phase of the mold and at the beginning of the lowering phase. During the lowering phase - at least with aluminum alloys - a highly reflective oxide layer forms after a few minutes after the start of the lowering phase, which severely impairs or even makes it impossible to use laser-optical methods for level measurement.

Ultrasound and microwave methods based on the radar principle have a large measuring range and allow contactless level measurement, but do not show the required measuring accuracy, at least not for the lowering phase of the continuous casting process. In addition, the ultrasonic level measurement methods are strongly temperature-dependent, and the microwave level measurement methods are sensitive to the measurement environment.

The invention is therefore based on the object of providing a vertical continuous casting installation of the type mentioned at the outset with a precise, functionally reliable and inexpensive fill level measurement and of specifying a method of the type mentioned at the outset in which the metal level measurement is carried out in a simple manner with high precision can be.

According to the invention, the object on which the vertical continuous casting installation is based is achieved in that the measuring device consists of two physically different working measuring systems with one sensor each, the sensors of each measuring device are fixed at a predetermined and fixed distance with respect to the mold, and the first measuring system in a measuring range of at least 200 mm has a measuring accuracy of at least ± 2 mm, and the second measuring system has a measuring accuracy of at least ± 0.1 mm in a measuring range of at least 20 mm.

The invention advantageously relates to vertical continuous casting plants with several molds. However, the device according to the invention also comprises vertical continuous casting plants with only a single mold. The solution according to the invention is based on the idea that at the beginning of the continuous casting process, that is to say during the first filling phase of the mold which is initially closed by the start-up floor, and during the remaining filling phase, and during the lowering process of the casting table, different level measuring devices can be used which meet the specific requirements Optimally take into account requirements during the basically different phases.

The invention is further based on the knowledge that a large measuring range of approx. 200 mm is only required during the first filling phase of the mold, which is initially closed by the start-up floor, and in the subsequent filling and lowering phase of the casting table, a smaller measuring range of, for example, 15- 20 mm is sufficient. In addition, less high measuring accuracy is required during the start phase than in the subsequent filling and lowering phase, since the filling level changes very quickly in the first filling phase. On the other hand, a very high measuring accuracy is required during the subsequent filling and lowering phase.

The term measuring range means a measuring range in which the values in the entire range can lie between a maximum and a minimum measuring value, the difference between the maximum and the minimum value corresponding to the measuring range in terms of amount. For example, the measured values with a measuring range of 200 mm are in a range between 0 and 200 mm.

A measuring device is preferred in which the first measuring system is based on an optical, capacitive, ultrasonic or microwave method, and the second measuring system is based on an inductive, capacitive or optical method.

A measuring device is particularly preferred in which the first measuring system is based on an optical or an ultrasound or microwave method, and the second measuring system is based on an inductive or capacitive method.

The first filling phase of the mold closed with the start-up floor usually takes place at the highest possible speed, so that the metal level rises very quickly at the beginning of the mold filling. As a result, a turbulent flow is formed in the mold at the beginning of the filling phase, so that there is no flat melt surface at the start of the filling process, as a result of which the reflective properties of the melt surface are significantly lower compared to a flat surface of the same metal. For this reason, as well as those not yet formed in this phase of the process Oxide skin allows the first filling phase to be measured using laser-optical methods. For the subsequent casting process, ie during the remaining filling phase and during the lowering process of the casting table, the use of a laser-optical level measurement process is not suitable for all alloys due to the high reflection of the essentially flat molten metal surface.

According to the invention, the first measuring system can relate to sensors or sensors which are based on one of the level measurement methods described below: a) ultrasound method b) optical method c) microwave method according to the radar principle d) capacitive method

A level measurement with ultrasound is based either on measuring the transit time of a sound pulse or on measuring sound absorption. Measurement of the transit time of an ultrasonic pulse, i.e. the distance from the melt surface is calculated from the transit time between the transmitted and received signal. The runtime method usually works on the principle of the echo sounder, i.e. An electrical pulse is converted, for example, by a piezoelectric oscillator attached to the start-up floor or to a lower region of the mold into an ultrasound pulse which is emitted into the melt and is partially reflected by the melt-air boundary layer, the reflected ultrasound pulse (echo) being of a similar type hits the piezoelectric oscillator by converting the echo back into an electrical pulse. The fill level results from the transit time of the sound pulse and the speed of sound. The level can also be measured using the same sonar principle if the ultrasonic transmitter and receiver are located in the air space above the melt surface. The temperature of the measuring media must be taken into account when measuring the ultrasound level, since the speed of sound is temperature-dependent.

For a level measurement with microwaves based on the radar principle, microwave transmitters and receivers as well as an antenna are attached above the mold. The surface of the molten metal partially reflects the usually frequency-modulated, electromagnetic waves or pulses emerging from the microwave transmitter. The distance between the antenna and the melt surface is measured according to the radar principle. In a preferred embodiment of this method, a microwave signal of constant amplitude is emitted and again after the reflection received and mixed with part of the transmission signal; the frequency of the mixer output signal is proportional to the transit time and thus a measure of the distance between the transmitter and the melt surface.

An optical level measurement can relate to an interf erometric distance measurement, a laser runtime method or a triangulation method.

With interf erometric distance measurement, the distance of the reflecting melt surface is measured by a sensor. Either the phase angle difference between the reflected and unreflected, modulated laser beam is evaluated as the measurement signal, or the displacement of the reflector surface (melt surface) is measured with a counting laser interferometer. In the interferometric distance measurement, a monochromatic laser beam is expediently split into a measuring and a reference beam on a semitransparent mirror. Both beams are reflected by one reflector, one fixed and one movable. The reflected rays are superimposed on the semi-transparent mirror, creating interference fringes that lie across the receiver and are analyzed by it. A change in the distance of λ / 4 from the melt surface (λ = wavelength of the laser beam) causes a maximum change in the light intensity, so that the change in the melt level results from the number of registered maxima or minima and the wavelength.

In the laser transit time method, the level measurement can be carried out by a direct transit time measurement of a light pulse or by a phase measurement. In the phase measurement, the transmission signal is expediently modulated onto a carrier signal, for example in the MHz range, the phase shift being measured in the receiver after demodulation. The direct transit time measurement is based on the radar principle, whereby the smallest time differences in the nano to picosecond range are measured.

In the triangulation process, the level measurement is traced back to an angle measurement. A highly concentrated beam of light from a laser hits the melt surface at an acute angle and is reflected there. Depending on the fill level, the reflected light beam strikes a specific point on the receiver, ie, for example a position detector. The position detector can represent, for example, a CCD line (Charge Coupled Device), which consists of a large number of light-sensitive components (pixels) arranged in a line. This position can be recorded with a CCD line and converted into the level using the angle or path difference. The The location of the reflected laser beam on the position detector shifts depending on the distance of the melt surface from the sensor.

In the case of capacitive level measurement, the capacitance is measured as a function of the melt height. The capacity changes, for example, through the degree of coverage or the distance between two given surfaces. However, the capacitance also changes due to a change in the dielectric constant (e.g. the air) due to the introduction of the molten metal. A change in capacitance is detected, for example, by changing the capacitive resistance.

According to the invention, the second measuring system can relate to sensors or sensors which are based on one of the level measurement methods described below: e) capacitive f) inductive g) optical

The inductive sensors are preferably based on measuring the change in the inductive resistance X _L , with:

N ² -μ- A

X _L = ω L, where L = and N = number of turns ss = path length of the magnetic field lines

A = the one penetrated by the magnetic field lines

Area, m = permeability of the material.

According to the invention, the sensors are arranged at a predetermined and fixed distance with respect to the mold, i.e. the two measuring systems have no device for height adjustment of the sensors.

In addition, preference is given to measuring systems which have no mechanically movable parts, and in particular no mechanical precision parts. Measuring systems which operate in a contactless manner with regard to the molten metal are further preferred.

A measuring device for each casting unit (mold) is particularly preferred, in which the first measuring system is based on an optical method, in particular on a triangulation method, and the second measuring system is based on an inductive method. A first measuring system with a measuring range of up to 200 mm is very particularly preferred, with a measuring accuracy of ± 1 mm being achieved in the entire measuring range.

The measuring accuracy of the first measuring system is typically between ± 0.1 mm and ± 2 mm, preferably between ± 0.1 mm and ± 1 mm.

The measuring range of the second measuring system is typically 20 to 50 mm, the measuring accuracy typically being between ± 0.01 mm and ± 0.1 mm, preferably between ± 0.01 mm and ± 0.08 mm.

The combination of an optical sensor with an inductive sensor allows the provision of a compact and powerful measuring device which, on the one hand, does not require expensive, sensitive and elaborately designed mechanical sensor tracking devices and, on the other hand, has a sensor characteristic that is adapted to the individual casting phases in terms of measuring range and measuring accuracy efficient level measurement of the molten metal allowed with sufficiently high accuracy. The continuous casting installation according to the invention is also particularly suitable for a control algorithm for introducing metal into the individual molds, in which non-linear setpoint curves are used to control the level of molten metal.

By avoiding mechanical tracking devices of the sensors, significantly less space is required for level measurement with regard to the vertical dimensions, so that the casting installation can be made more compact.

The solution according to the invention to the problem relating to the method is that the measurement of the time-dependent metal level N (t) is carried out with a measuring device consisting of two physically different measuring systems, starting from the initial level until reaching a predetermined melt level by a first measuring system with a first Sensor happens, and for the further measurement of the time-dependent metal level curve N (t) during the subsequent filling and lowering phases, a second measuring system with a second sensor is used, and the sensors of the two measuring systems with respect to the mold are fixed and throughout Continuous casting process take a constant position.

The filling phase begins with the introduction of liquid metal onto the start-up floor and ends with the start of lowering the start-up floor, ie when the start level N _{s is reached} at time t _s . The metal level control usually only starts when a certain metal level N _a at time t _a in which the mold, which was initially closed by the start-up floor, is reached. The first filling phase denotes the period from the start of the introduction of liquid metal into the mold until the time t _w , at which the change from the first to the second measuring system for the metal level determination takes place, where t _w denotes the time at which the metal level in the first a mold closed by the start-up floor reaches a predetermined height N _w . The period between t _w and t _s describes the second or the further filling phase, or that of the first filling phase that follows. The lowering phase begins when the start level N _{s is reached} at time t _s and lasts until the end or the termination of the continuous casting process.

The flow control device is controlled as a function of the difference in the measured metal level curve N (t) from the setpoint curve N _so n (t) by means of a control unit, the flow control device determining the amount of metal melt flowing into the mold. The control unit determines, for example, the starting time t _{a of} the mold filling, the time t _w for changing the measuring system, the starting time t _{s of} the lowering process, the filling of the mold or the amount of metal to be introduced into the mold per unit of time during the filling phase and during the Lowering process, the lowering speed of the casting table and the control of the measuring system responsible for level measurement N (t). However, the control unit may also be used to monitor and control further process parameters, such as cooling water supply, CO ₂ supply, grain refining agent supply, EMC power supply, and automatically initiate the lowering process of the casting table, for example.

In a preferred embodiment of the method according to the invention, the metal supply into the individual molds is only regulated directly up to the starting time t _s by the time-dependent difference between the actual and the setpoint value of the metal level. Furthermore, the direct control of the metal supply takes place after the start of the lowering process as a function of the bar length, ie as a function of the vertical casting table position, and on the basis of the difference between the actual and target value of the metal level. Accordingly, the control of the metal supply takes place after the start time t _s by the bar length-dependent difference between the actual and target value of the metal level. Since the lowering process usually takes place at a constant speed, the bar length increases linearly with time, so that the regulation of the metal supply is also regulated during the lowering process in accordance with the time-dependent difference between the actual and target value of the metal level. The time t _{a of} the start of the level control is preferably determined by measuring the metal level, in particular by level measurement using a laser-optical method. The level measurement by means of the second measuring system, ie the time of the change of the measuring systems, can either be triggered by a control unit on the basis of the measured metal level, or according to a preferred embodiment, in particular when using a second measuring system with an inductive measuring method, directly are triggered by the melt level by changing the measuring system at a time at which the melt enters, for example, the cavity formed by an inductively operating measuring coil.

The method according to the invention is suitable for casting plants with only one mold; however, it is particularly suitable for vertical continuous casting plants with several molds.

According to the invention, the sensors of the two measuring systems of a casting unit have a fixed position with respect to the mold and are constant during the entire continuous casting process, i.e. the measurement is carried out without any mechanical tracking device, for example in the form of a height adjustment of the sensors. The level measurement is preferably carried out without contact during the first filling phase with respect to the molten metal.

The measuring systems include continuously and discontinuously operating level detection systems. Accordingly, the method according to the invention can be carried out by a continuous and / or discontinuous level measurement. A continuous metal level measurement is preferred for level measurement with the second measuring system. The measurement with the first measurement system is preferably carried out at discrete times, in particular with 3 to 10 measurement values, the level measurement being carried out continuously with the second measurement system.

In casting plants with several molds, the lowering of the casting table with the start-up trays expediently begins as soon as the start level is reached in a mold.

The metal level in the casting trough is also preferably kept at a constant level from the start of the filling phase of the start-up trays and the molds up to and with the stationary casting phase (lowering phase).

Further advantageous developments of the method according to the invention result from the subclaims. The continuous casting installation according to the invention and the method according to the invention are suitable for the casting of all continuously castable metals, but preferably for the continuous casting of aluminum, magnesium and copper alloys. However, the continuous casting installation according to the invention and the method according to the invention are particularly suitable for the continuous casting of aluminum alloys.

Further advantages, features and details of the invention result from the exemplary embodiments shown in FIGS. 1 and 2 and from the description of the figures.

FIG. 1 schematically shows a simplified cross section through part of a mold with the approach floor retracted.

Figure 2 shows schematically a setpoint curve of the time course of the metal level in a mold.

The vertical continuous casting installation shown in FIG. 1 contains a mold 10 with a start-up floor 14 arranged on a lowerable casting table 16, a lifting / lowering device 11 for the casting table, which is driven by a motor 12, the motor being controlled by a control unit 34, a metal level measuring device consisting of two measuring systems 22, 26, a pouring channel system 20 for transporting a molten metal 18 from a furnace (not shown) into the mold 10, a flow control device 30 controlled by the control unit 34 determining the quantity of molten metal to be introduced into the mold. The control unit 34 determines, among other things, the starting time t _{a of} the mold filling, the starting time t _{s of} the lowering process, the filling of the mold or the amount of metal 18 to be introduced into the mold 10 per unit of time during the filling phase and during the lowering process and the lowering speed of the casting table 16 wherein the control unit 34 _so ιι in dependence of the metal level measurement N (t) and a predetermined setpoint curve N (t) is working.

The flow control device 30 shown by way of example in FIG. 1 essentially consists of an inlet opening 33 located in the casting trough 20, which can be closed by a vertically movable stopper 32. The stopper 32 can be brought into the closed position on the one hand by lowering it into the inlet opening 33, or by lifting the opening cross section and thus the supply of molten metal 18 into the mold 10 can be increased accordingly. The stopper 32 has a stopper rod which is guided by a holding device and driven by a motor 31, the motor being controlled via the control unit 34. Before a casting begins, all settings on the casting system are checked during a test phase. When all starting conditions are met, the trough 20 is filled to a predetermined metal level by tilting the furnace containing the liquid metal. As soon as a sensor - for example an inductive sensor - indicates a predetermined fill level in the trough 20, the inlet opening 33 of the trough 20 is opened by lifting the stopper 32 of the flow control device 30 and the filling of the approach floors 14 and the molds 10 begins with the liquid metal 18 . The metal level N (t) in the approach floor 14 or in the mold 10 takes place, for example PID-controlled, via a measuring device containing two measuring systems 22, 26.

The mold 10 shown in Figure 1 is shown in the closed state, i.e. the start-up floor rests on the mold 10, the lowering process not yet having started. However, the filling phase is almost complete since the mold 10 is already filled with liquid metal 18 up to close to the second sensor 28.

The first sensor 24 is at a greater distance from the approach floor 14 than the second sensor 28. This ensures that the first sensor 24, which is based on a laser-optical method, does not come into contact with the melt 18. However, the second sensor 28, which is based on an inductive measurement method, requires, at least in part, direct contact with the melt 18.

The sensors 24 and 28 are connected at a fixed distance to the respective other measuring system 22 and 26, respectively. In addition, the two measuring systems 22 and 26 are mechanically firmly connected to one another, i.e. The two measuring systems usually form a mechanical unit with one another.

The distance of the sensors 24, 28 from the mold is constant during the entire continuous casting process, ie the distance of the sensors 24, 28 from the metal surface changes constantly, in particular during the filling phase of the mold. Accordingly, at the beginning of the filling phase, the distance of the sensors 24, 28 from the molten metal surface, respectively. to the approach floor 14 is greatest, while this distance decreases continuously or discontinuously during the filling phase and remains essentially constant after reaching the start level N _s , ie at the beginning and during the lowering process. The exemplary embodiment shown in the drawing relates to continuous casting with a conventional mold. However, the vertical continuous casting installation according to the invention also includes other casting methods, such as, for example, casting in an alternating electromagnetic field (EMC), ie using an electromagnetic mold.

FIG. 2 shows an example of a setpoint curve N _so n (t) for the method _according to the invention. As soon as the metal in a mold 10 has reached a predetermined initial level N _a at the initial time t _a , the metal level control begins on the basis of the setpoint profile N _So iι (t) and the measured metal level N (t) until the metal level in the through the approach floor 14 closed mold 10 has reached the start level N _s at the start time t _s , where the lowering of the casting table 16 for producing the metal strands begins.

The setpoint curve N _so n (t) shown in FIG. 2 is polygonal and is suitable, for example, for discontinuous control of the metal level. In a region close to the initial level N _a , the setpoint curve N _sou (t) has a larger slope than the average slope ~ τr. In contrast, the setpoint curve N _soll (t) points in one against the

Starting level N _s nearby area has a smaller gradient than the average gradient.

At the time t _w, the set value N _so π (t _w) the amount N _w on. At time t _w , the switch from the first measuring system 22 to the second measuring system 26 takes place. In the second measuring system 26 shown in FIG. 1, which is based on an inductive measuring method, the point in time t _{w is} determined by the entry of the melt into the cavity formed by an inductively working measuring coil. Accordingly, the metal height N (t) above the approach floor 14 during the first filling phase, ie until the filling height has reached the value N _w , is determined with the first measuring system 22, which has a large measuring range. After the time t _w , the metal height is determined with the second measuring system 26, the measuring range of which is smaller than the first measuring system 22, but has a high measuring accuracy. The high measurement accuracy is particularly important from time t _w , since thereafter the setpoint curve N _thus ιι (t) is preferably flatter than the mean slope, and thus the metal supply to the individual casting units in a continuous casting installation having several molds 10 until the actual casting start t _s , which is initiated by lowering the casting table 16, can be optimally controlled. The starting level N _s , ie the height of the surface of the liquid metal 18 above the approach floor 14 at the starting time t _s , is typically between 100 and 200 mm and in particular between 120 and 190 mm. Starting level t _a - the starting level N _s is typically reached within a time of 20 to 90 s or preferably within 25 to 45 s.

Claims

claims 1. Vertical continuous casting system, in particular vertical continuous casting system for the automatic continuous casting of aluminum alloys, comprising at least one mold (10) with a start-up floor (14) arranged on a lowerable casting table (16), a casting channel system (20) for transporting a molten metal from an oven into the individual Chill molds (10), for each mold (10) a measuring device for determining the time-dependent metal melt level N (t) and a flow control device (30) for controlling the metal feed into the individual molds (10) depending on the difference between a predetermined setpoint curve N _so n ( t) and the measured time-dependent molten metal level N (t), characterized in that the measuring device consists of two physically different measuring systems (22, 26), each with a sensor (24, 28), the sensors (24, 28) of each measuring device. tion with respect to the mold (10) si fixed at a predetermined and fixed distance nd, and the first measuring system (22) has a measuring accuracy of at least ± 2 mm in a measuring range of at least 200 mm, and the second measuring system (26) has a measuring accuracy of at least ± 0.1 mm in a measuring range of at least 20 mm. Vertical continuous casting installation according to claim 1, characterized in that the first measuring system (22) is based on an optical, capacitive, ultrasonic or microwave method, and the second measuring system (26) on an inductive, capacitive or optical method. 3. Vertical caster according to claim 1 or 2, characterized in that the first measuring system (22) is based on an optical or an ultrasonic or microwave method, and the second measuring system (26) on an inductive or capacitive method. 4. Vertical continuous casting installation according to one of claims 1 to 3, characterized in that the first measuring system (22) is based on an optical method, in particular on a triangulation method, and the second measuring system (26) on an inductive method. 5. Vertical continuous casting installation according to one of claims 1 to 4, characterized in that the first measuring system (22) of each measuring device operates in a contactless manner with respect to the molten metal (18). 6. A method for the vertical continuous casting of metals, in particular aluminum alloys, in a casting installation comprising at least one mold (10), in which method the liquid metal is fed from a furnace via a trough system (20) to the individual molds (10) and via a flow control device (30) into the molds (10), which are initially closed during a filling phase, from the start-up trays (14) arranged on a lowerable casting table (16), starting from an initial level (N _a ) of the molten metal (18), in which a molten metal Level control begins up to a predetermined start level (N _s ), at which the lowering of the casting table (16) for the production of the metal strands begins, and during the entire lowering phase the time-dependent metal level N (t) in each Mold (10) is measured with a measuring device and compared with a time-dependent setpoint specification N _So iι (t), and the metal supply to the individual molds (10) is regulated by means of a flow control device (30) according to the time-dependent difference between the actual and setpoint value of the metal level is characterized in that the measurement of the time-dependent metal level N (t) is carried out with a measuring device consisting of two physically different measuring systems (22, 26), starting from the initial level (N _a ) until reaching a predetermined melt level (N _w ) by a first measuring system (22) with a first sensor (24), and for the further measurement of the time-dependent Metal level curve N (t) during the subsequent filling and lowering phases, a second measuring system (26) with a second sensor (28) is used, and the sensors (24, 28) of the two measuring systems (22, 26) with respect to the mold (10) Assume a fixed position that is constant throughout the entire casting process. 7. The method according to claim 6, characterized in that the first measuring system (22) is based on an optical, capacitive, ultrasonic or microwave method, and the second measuring system (26) on an inductive, capacitive or optical method. 8. The method according to claim 6 or 7, characterized in that the first measuring system (22) is based on an optical method, in particular on a triangulation method, and the second measuring system (26) on an inductive method. 9. The method according to any one of claims 6 to 8, characterized in that the predetermined melt level (N _w ) at which the measuring system change takes place is determined by the vertical position of the lower opening of a cylindrical cavity formed by an inductively working measuring coil , wherein the longitudinal axis of the measuring coil is substantially perpendicular to the surface of the molten metal. 10. The method according to any one of claims 6 to 9, characterized in that the measurement of the metal level N (t) with the first measuring system (22) takes place at discrete times, and the metal level measurement N (t) with the second measuring system (26 ) happens continuously. 11. The method according to any one of claims 6 to 10, characterized in that the metal is fed into the molds (10) based on the corresponding difference between the setpoint _curve N _s0 , ι (t) and the metal level measurement value N (t).