Method and measuring instrument for measuring the level of casting in a mould

Abstract

Method and measuring instrument for measuring the casting level in a mold. Method for measuring the casting level in a mold (1) with the following steps: a) applying a time current curve (i(t)) to a transmitting coil (2) arranged at the mold (1) during a measuring time interval (MZI), b) measuring a time signal curve (Ue(t)) generated in a receiving coil (3) during the measuring time interval (MZI), wherein the receiving coil (3) is inductively coupled to the transmitting coil (2), c) selecting a time window (ZF) within the measuring time interval (MZI), and d) evaluating the measured time signal curve (Ue(t)) within the selected time window (ZF) to determine the casting level (L).

Description

[0001] This invention relates to a method and measuring instrument for measuring the casting level in a mold.

[0002] The present invention is based on the objective of providing a method and measuring instrument for measuring the casting level in a mold, the method and measuring instrument enabling reliable measurement of the casting level.

[0003] The method for measuring the casting level in a mold includes the following steps.

[0004] Step a), that is, during the measurement time interval, a defined time current profile is applied to the transmitting coil arranged at / on the mold (i.e., a defined time current profile is generated in the transmitting coil).

[0005] Step b), which is to measure the time signal curve that appears in the receiving coil during the measurement time interval, wherein the receiving coil is inductively coupled to the transmitting coil via the mold and its contents.

[0006] Step c), which is to select a time window within the measurement time interval.

[0007] Step d) involves evaluating the time signal curve measured within the selected time window to determine the casting level.

[0008] In an embodiment, the time signal curve appearing in the receiving coil is the time voltage curve induced in the receiving coil as a result of the time current curve applied to the transmitting coil.

[0009] In this embodiment, the predefined time-current curve is ramp-shaped, particularly a linear ramp-shaped current curve. The current ramp can extend, for example, from a current amplitude of zero amperes up to a specific maximum current amplitude, where the current amplitude decreases back to zero after reaching the maximum current amplitude. This then results in, for example, a sawtooth current curve.

[0010] In this embodiment, the predefined time-current curve is a non-sinusoidal current curve. Specifically, the predefined time-current curve is not purely sinusoidal and / or not purely rectangular.

[0011] In an embodiment, the method includes the additional steps of: determining the gradient of the measured time signal curve or current curve within a selected time window, and evaluating the determined gradient to determine the casting level.

[0012] In one embodiment, applying a predefined time-current curve to the transmitting coil during the measurement time interval includes the following steps: specifying a time-current-setpoint-value curve and adjusting the current flowing through the transmitting coil to match the time-current-setpoint-value curve.

[0013] In the embodiments, steps a), c), and d) are repeated continuously, particularly periodically. Of course, it is also possible to repeat steps a) to d) continuously, particularly periodically.

[0014] In an embodiment, the method includes the additional steps of: e) measuring a time signal curve appearing in at least one additional receiving coil during a measurement time interval, the at least one additional receiving coil being inductively coupled to a transmitting coil via the mold and its contents, and f) evaluating the additional time signal curve measured within a selected time window to determine the casting level.

[0015] In one embodiment, the time window within the measurement time interval is selected based on the geometry of the mold.

[0016] The measuring instrument is used to measure the casting level in a mold and includes: at least one or exactly one transmitting coil; at least one or exactly one receiving coil; at least one controllable current source designed to realize a predefined time-current curve in one or more transmitting coils arranged at the mold; a measuring device designed to measure a time signal curve, particularly a time-voltage curve, in one or more receiving coils inductively coupled to the transmitting coil; and an evaluation device designed to evaluate the measured time signal curve to determine the casting level.

[0017] In this embodiment, the measuring instrument is designed to perform the method described above.

[0018] Measuring the level of molten metal in a casting plant (casting level measurement) is one of the most important measurements in the casting process. Besides preventing overfilling and breakthrough during casting, the fastest, most accurate, reliable, and continuous measurement is often crucial to the quality of the final product (crystal structure, microstructure). Due to the typically high temperature of the molten metal, casting level can usually only be measured non-contactly.

[0019] Electromagnetic measurements based on induced eddy currents have been developed for large casting formats (slabs). Compared to radiation measurements, this method has the advantages of not requiring radioactive isotopes and being independent of any casting powder or oil that may be present. However, a drawback of this method is its high sensitivity to the presence and changing electrical properties of other conductive materials near the sensor system. Therefore, the molds are often complex, with metallic structures (coated molds for copper, containers for steel), tundishes containing molten metal, and ladles found in very close proximity, while the molten metal is also present in the casting tube, etc. Temperature variations significantly impair this measurement principle because the electrical properties of the material and therefore the eddy current response are highly temperature-dependent. Vibrations of the mold, necessary to prevent agglomeration during casting, also have a significant interfering effect. The use of magnetic stirrers and brakes, along with their very strong electromagnetic fields, also have an interfering effect on this measurement technique. In the case of large formats, it is generally found that the sensor position is sufficiently far from all interfering structures, thus minimizing their influence. However, in small-scale applications, everything is so compact that the previous eddy current method cannot be used effectively due to the aforementioned disturbances. Another drawback of this method is the highly complex calibration, which typically cannot be performed using the liquid metal used for casting but must be performed using alternative materials during cooling, thus making it inherently impossible to account for the temperature-dependent effects of the surrounding environment.

[0020] In order to apply the inductive measurement principle to small mold forms, a method is needed that is sensitive only in a limited spatial region, that is, in a region where only the liquid metal to be measured is detected.

[0021] Except for the case of eddy current measurement, the inductive measurement principle according to the invention does not operate with sinusoidal or rectangular excitation of the transmitting coil (at one or more frequencies), but with, for example, ramp excitation.

[0022] According to the present invention, in order to measure the filling level of liquid metal in a mold, a suitable (e.g., ramp-shaped) current profile is applied to one or more transmitting coils appropriately attached to the mold. Using a suitable measurement of the coil current, the current through the transmitting coil(s) precisely tracks the setpoint profile. As a result, the temperature-dependent resistance of the transmitting coil(s) no longer has almost any effect on the magnetic field generated by the excitation current.

[0023] The magnetic field generated in this way now induces a time-voltage curve in one (or more) receiving coils. If this time-voltage curve is read with very high resistance, it is independent of the resistance of the receiving coils and therefore independent of the temperature of the receiving coils, since only negligible current flows in the receiving coils.

[0024] If there is no conductive material in the vicinity of the transmitting coil(s) and the receiving coil(s), a time-voltage curve is induced in the receiving coil(s), which corresponds to a constant voltage in the case of ramp excitation. In the presence of a conductive material (metal), the time-voltage curve changes in a peculiar way depending on the type, quantity, and location of the material, as described, for example, in DE 10 2018 120 912 A1.

[0025] It has been found that the change in the time-voltage curve along the t-axis (time axis) is related to the distance along the z-axis (the spatial axis perpendicular to the coil surface). The maximum range (penetration depth) is determined here by the duration of the excitation ramp and by the amplitude of the current passing through the excitation coil.

[0026] If a suitable region or a suitable time window along the t-axis is now selected to evaluate the time-voltage curve, the sensitive region for measurement can thus be limited in such a way that it is sensitive only to the region of the liquid metal to be measured. If suitable parameters for the time-voltage curve are determined within this time window (e.g., the gradient of the time-voltage curve in the case of ramp excitation), then this is related to the filling level of the liquid metal.

[0027] The precise form of the time-voltage curve depends in particular on the form of the transmitting and receiving coil(s), the position of the coils in the mold, the mold itself, and also on the composition of the material being measured, and may be learned once or multiple times in each case.

[0028] The present invention will now be described in detail with reference to the accompanying drawings, wherein: Figure 1 A schematic block diagram of the height of the measuring instrument according to the present invention is shown. Figure 2 The characteristics of the voltage curves induced in the receiving coil based on different casting levels are shown. Figure 3 An embodiment of a measuring instrument according to the invention, having multiple receiving coils, is shown, and Figure 4 A fill level calibration curve with two reference points is shown, each determined by differential readings from two receiving coils.

[0029] Figure 1 A schematic block diagram of a measuring instrument 100 according to the present invention is shown, which is used to measure the casting level of liquid metal or casting metal 9 in mold 1.

[0030] The measuring instrument 100 includes a transmitting coil 2 arranged at / on the mold 1.

[0031] The measuring instrument 100 further includes a receiving coil 3, which is also arranged at / on the mold 1 and is inductively coupled to the transmitting coil 2 via the mold 1 and the liquid metal 9 that may be located in the mold 1.

[0032] The measuring instrument 100 further includes an adjustable current source 6, which is designed to realize a time-linear ramp-shaped current curve i(t) in the transmitting coil 2 during the measurement time interval MZI.

[0033] The measuring instrument 100 further includes a measuring device 7, which is designed to measure the time voltage curve Ue(t) induced in the receiving coil 3 as a result of the current curve i(t).

[0034] The measuring instrument 100 further includes an evaluation device 8, which is designed to evaluate the measured time-voltage curve Ue(t) to determine the casting level L.

[0035] A time window ZF is selected within the measurement time interval MZI to measure the casting level, and the time voltage curve Ue(t) generated or induced in the receiving coil 3 during the time window ZF is evaluated. The time window ZF within the measurement time interval MZI is selected based on the geometry of the mold 1.

[0036] Figure 2 The characteristics of the voltage curve Ue(t) induced in the receiving coil 3 are shown in the form of gradients m1 or m2, depending on the different casting levels of L1 or L2—see also [link to relevant documentation]. Figure 4 To measure the casting level L, evaluation unit 8 determines the gradient m1 or m2 obtained during the time window ZF, and then determines the casting level L based on the gradient m1 or m2.

[0037] To continuously measure the casting level L, repeat the above steps continuously.

[0038] Figure 3 An embodiment of the invention is illustrated, wherein the measuring instrument 100 includes three receiving coils 3, 4, and 5. In this embodiment, the time-voltage profiles induced in the receiving coils 3, 4, and 5 during the time window ZF are measured and evaluated.

[0039] The precise form of the time-voltage curve Ue(t) in the corresponding receiving coils 3, 4 and 5 depends in particular on the form of the transmitting coil 2 and the receiving coils 3, 4 and 5, the position of coils 2 to 5 in the mold, the mold itself, and to some extent also on the composition of the liquid metal 9 to be measured, and must be learned once in each case.

[0040] The position and shape of the fill level calibration curve can then be adjusted by increasing the differential readout receiving coils 4 and 5. That is, it has been found that the differential evaluation signal AS1 or AS2 based on the receiving coil pairs 3 / 4 and 4 / 5 reaches its maximum value when the fill level L is precisely positioned between the two differential readout receiving coils of receiving coil pair 3 / 4 or 4 / 5, see [link to relevant documentation]. Figure 4 Since this position is precisely mechanically determined by the known positions of receiving coils 3, 4, and 5, the fill level calibration curve can then be adjusted with sufficient accuracy, especially during injection port casting.

[0041] Figure 4 A fill level calibration curve is shown, where the fill level L is plotted relative to the gradient m of the voltage curve Ue(t). The differential signal AS1 between the voltage curves of receiving coils 3 and 4 has its maximum value at reference point R1, such that the gradient m1 at reference point R1 can be assigned to the known fill level L1. The differential signal AS2 between the voltage curves of receiving coils 4 and 5 has its maximum value at reference point R2, such that the gradient m2 at reference point R2 can be assigned to the known fill level L2.

[0042] This invention provides an inductive measurement principle not based on eddy currents for non-contact measurement of the filling level of conductive material in a mold, particularly the filling level of liquid metal, with locally selective resolution and highly independent of temperature.

[0043] This invention enables reliable measurement of casting quality independent of interfering conductive materials near the coil system, and it can be easily calibrated. The invention is also applicable to small mold configurations because the sensitive area can be easily specified by selecting the time window ZF.

Claims

1. A method for measuring the casting level in a mold (1), comprising the following steps: a) During the measurement time interval (MZI), the time-current curve (i(t)) is applied to the transmitting coil (2) arranged at the mold (1), b) Measure the time signal curve (Ue(t)) generated in the receiving coil during the measurement time interval (MZI), wherein the receiving coil is inductively coupled to the transmitting coil (2). c) Select a time window (ZF) within the measurement time interval (MZI), and d) Evaluate the time signal curve (Ue(t)) measured within the selected time window (ZF) to determine the casting level (L). Among them, the time-current curve (i(t)) is a non-sinusoidal and / or non-rectangular time-current curve.

2. The method according to claim 1, characterized in that... - The time signal curve (Ue(t)) generated in the receiving coil is the time voltage curve (Ue(t)) induced in the receiving coil as a result of the time current curve (i(t)) applied to the transmitting coil (2).

3. The method according to any one of claims 1 or 2, characterized in that... - The time-current curve (i(t)) is a ramp-shaped current curve, especially a linear ramp-shaped current curve.

4. The method according to claim 1 or 2, characterized by the following steps: - Determine the gradient of the measured time signal curve (Ue(t)) within the selected time window (ZF), and - Evaluate the determined gradient to determine the casting level (L).

5. The method according to any one of claims 1 or 2, characterized in that... - Applying the time-current curve (i(t)) to the transmitting coil (2) during the measurement time interval (MZI) includes the following steps: -Specified time current setpoint curve, and - Adjust the current (i(t)) flowing through the transmitting coil (2) to track the time current setpoint curve.

6. The method according to any one of claims 1 or 2, characterized in that... - Repeat steps a), c), and d continuously, especially periodically.

7. The method according to claim 1 or 2, characterized by the following steps: e) Measure the time signal curve appearing in at least one additional receiving coil inductively coupled to the transmitting coil (2) during the measurement time interval (MZI), and f) Evaluate the additional time signal curves measured within the selected time window (ZF) to determine the casting level (L).

8. The method according to any one of claims 1 or 2, characterized in that - Select the time window (ZF) within the measurement time interval (MZI) based on the geometry of the mold (1).

9. A measuring instrument (100) for measuring the casting level in the mold (1), comprising: -At least one transmitting coil (2) -At least one receiving coil, - A controllable current source (6) is designed to realize a predefined time current curve (i(t)) in at least one transmitting coil (2). - Measuring device (7), which is designed to measure the time signal curve (Ue(t)) in at least one receiving coil inductively coupled to at least one transmitting coil (2), and - Evaluation device (8), which is designed to evaluate the measured time signal curve (Ue(t)) to determine the casting level (L). Among them, the time-current curve (i(t)) is a non-sinusoidal and / or non-rectangular time-current curve.

10. The measuring instrument (100) according to claim 9, characterized in that... - The measuring instrument (100) is designed to perform the method according to any one of claims 1 to 8.

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