Method and measuring device for measuring the casting level in a mold

Abstract

To provide a measuring method and a measuring device for casting levels in a mould.SOLUTION: A method for measurement of a casting level (L) in a mould (1) includes the steps of: a) impressing a temporal current profile (i(t)) into a transmitting coil (2) arranged at the mould (1), during a measuring time interval (MZI); b) measuring a temporal signal profile (Ue(t)) generated in a receiving coil (3) during the measuring time interval (MZI), wherein the receiving coil is coupled inductively to the transmitting coil (2); c) selecting a time window (ZF) within the measuring time interval (MZI); and d) evaluating the measured temporal signal profile (Ue(t)) within the selected time window (ZF) to determine the casting level (L).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and device for measuring the casting level in a mold.

[0002] The present invention is based on the object of providing a casting level measurement method and a measurement device which allow reliable measurement of the casting level in a mold. Summary of the Invention

[0003] The method for measuring the casting level in the mold comprises the following steps:

[0004] a) Passing a defined time-varying current profile through a transmitter coil placed in / on the mold during a measurement time interval (i.e., inducing a defined time-varying current profile in the transmitter coil).

[0005] b) measuring a time-varying signal profile occurring in a receive coil during a measurement time interval, said receive coil being inductively coupled to the transmit coil via the mould and its contents;

[0006] c) selecting a time window within the measurement interval;

[0007] d) Evaluating the measured time-varying signal profile within a selected time window to determine the casting level.

[0008] In one embodiment, the time-varying signal profile produced in the receive coil is a time-varying voltage profile induced in the receive coil as a result of a time-varying current profile being passed through the transmit coil.

[0009] According to one embodiment, the predefined time-varying current profile is a ramp-type current profile, in particular a linear ramp-type current profile. For example, the current ramp can extend from a current magnitude of zero amperes to a certain maximum current magnitude, and the current magnitude is reduced to zero again after reaching the maximum current magnitude. This results in, for example, a sawtooth-shaped current profile.

[0010] In one embodiment, the predefined time-varying current profile is a non-sinusoidal current profile, in particular a predefined time-varying current profile that is not purely sinusoidal and / or not purely rectangular.

[0011] In one embodiment, the method includes the further steps of identifying a slope of the time-varying signal profile or current profile measured within a selected time window and evaluating the identified slope to identify the casting level.

[0012] In one embodiment, energizing a predefined time-varying current profile through the transmit coil during the measurement interval includes specifying the time-varying current-setpoint profile and adjusting the current through the transmit coil to match the time-varying current-setpoint profile.

[0013] In one embodiment, steps a), c) and d) are repeated continuously, in particular periodically. Of course, it is also possible to repeat steps a) to d) continuously, in particular periodically.

[0014] In one embodiment, the method further comprises the steps of e) measuring a time-varying signal profile occurring during the measurement time interval in at least one further receiver coil inductively coupled to the transmitter coil via the mold and its contents, and f) evaluating the further time-varying signal profile measured within the selected time window to ascertain the casting level.

[0015] In one embodiment, the time window within the measurement interval is selected according to the shape of the mold.

[0016] The measuring device is used for measuring the casting level in the mold and comprises at least one or precisely one transmitting coil, at least one or precisely one receiving coil, at least one controllable current source designed to achieve a predefined time-varying current profile in one or more transmitting coils arranged in the mold, a measuring device designed to measure a time-varying signal profile, in particular a time-varying voltage profile, in one or more receiving coils inductively coupled to the transmitting coil, and an evaluation device designed to evaluate the measured time-varying signal profile to ascertain the casting level.

[0017] In one embodiment, a measurement device is designed to perform the above-described techniques.

[0018] Measuring the fill level of liquid metal in a foundry (casting level measurement) is one of the most important measurements in the casting process. In addition to avoiding overfilling and breakthrough during the casting process, the fastest, most accurate, most reliable and continuous measurement possible is also often crucial for the quality of the final product (crystal structure, microstructure). Due to the normally high temperatures of the liquid metal, casting level measurement is usually only possible without contact.

[0019] Electromagnetic measurements based on induced eddy currents have been established for large casting molds (slabs). In contrast to radioactive measurements, this method has the advantage of not requiring radioactive isotopes and being independent of any casting powder or oil that may be present. However, a disadvantage of this measurement method is its high sensitivity to the presence of other conductive materials in the vicinity of the sensor system, which changes their electrical properties. Thus, casting molds are usually complex metal structures (copper-coated molds, steel vessels), with tundishes and ladles containing liquid metal found nearby, while liquid metal is also present in the casting tube. Material electrical properties, especially temperature changes, significantly impair this measurement principle, since the eddy current response is highly temperature-dependent. Furthermore, the vibration of the casting mold required during the casting process to prevent caking also has a significant disruptive effect on this method. The use of magnetic stirrers and brakes, which have very strong electromagnetic fields, also disrupts this measurement technique. For large molds, a small sensor location can usually be found that is far enough away from all disturbing structures to minimize their varying influence. However, for small molds, everything is so compact that the aforementioned disturbances make it impossible to effectively use the previous eddy current method. A further drawback of this approach is the highly complex calibration, which cannot usually be performed with the liquid metal used in casting, but must be performed with alternative materials when cold, making it essentially impossible to take into account the temperature-dependent effects of the surrounding environment.

[0020] Therefore, in order to be able to use the inductive measurement principle in small casting moulds, high sensitivity is required only in a defined spatial region, i.e. in the region where only the liquid metal to be measured is found.

[0021] Besides eddy current measurements, the inductive measurement method according to the invention operates with, for example, ramp-type excitation rather than sine wave or square wave excitation (at one or more frequencies) of the transmitting coil.

[0022] To measure the fill level of the liquid metal in the mold, a suitable current profile (e.g., ramp type) is passed through one or more transmitter coils appropriately mounted in the mold. Using appropriate measurements of the coil current, the current through the transmitter coils is made to accurately track the setpoint profile. As a result, the temperature-dependent resistance of the transmitter coil(s) has little effect on the magnetic field generated by the excitation current.

[0023] The magnetic field thus generated now induces a time-varying voltage profile in the receiving coil(s), which is read at a very high resistance, and is therefore independent of the electrical resistance of the receiving coil and therefore of the temperature of the receiving coil, since negligible current flows in the receiving coil.

[0024] In the absence of conductive materials in the vicinity of the transmitter and receiver coils, a time-varying voltage profile corresponding to a constant voltage is induced in the receiver coil during ramp excitation. In the presence of conductive materials (metals), this time-varying voltage profile is modified in a characteristic manner depending on the type, amount and location of the material, as described, for example, in DE 10 2018 120 912 A1.

[0025] The change in the time-varying voltage profile along the t-axis (time axis) is found to correlate with the distance along the z-axis (spatial axis perpendicular to the plane of the coil). The maximum range (penetration depth) is here determined by the duration of the excitation ramp and the magnitude of the current through the excitation coil.

[0026] Now, if an appropriate region or an appropriate time window along the t-axis is selected for evaluation of the time-varying voltage profile, the sensitive region of the measurement can be limited thereby to be sensitive only to the region of the liquid metal being measured. If an appropriate parameter of the time-varying voltage profile is determined in this time window (this is, for example, the slope of the time-varying voltage profile in the case of a ramp-type excitation), this will correlate with the fill level of the liquid metal.

[0027] The exact shape of the time-varying voltage profile depends, among other things, on the configuration of the transmit and receive coils, the position of the coils within the casting mold, the mold itself, and the composition of the material being measured, and can each be learned once or multiple times.

[0028] The present invention will now be described in detail with reference to the drawings. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a schematic block diagram of a measuring device according to the present invention; [Figure 2] FIG. 10 illustrates the characteristics of the voltage profile induced in the receiving coil at different casting levels. [Figure 3] FIG. 1 illustrates an embodiment of a measurement device of the present invention having multiple receive coils. [Figure 4] FIG. 10 shows a fill level calibration curve with two reference points each determined by differential reading of two receiving coils. DETAILED DESCRIPTION OF THE INVENTION

[0030] FIG. 1 shows a highly schematic block diagram of a measuring device 100 according to the invention for measuring the casting level of liquid or casting metal 9 in a mould 1 .

[0031] The measuring device 100 comprises a transmitting coil 2 arranged in or on the mold 1 .

[0032] The measuring device 100 further comprises a receiving coil 3 disposed on or above the mold 1 and inductively coupled to the transmitting coil 2 via the mold 1 and a liquid metal 9 which may be disposed within the mold 1 .

[0033] The measurement device 100 further comprises an adjusted current source 6 designed to drive a time-varying linear ramp-type current profile i(t) in the transmission coil 2 during the measurement interval MZI.

[0034] The measurement device 100 further comprises a measuring device 7 designed to measure the time-varying voltage profile Ue(t) induced in the receiving coil 3 as a result of the current profile i(t).

[0035] The measuring device 100 further comprises an estimator 8 designed to evaluate the measured time-varying voltage profile Ue(t) to ascertain the casting level L.

[0036] A time window ZF is selected within the measurement time interval MZI for measuring the casting level, and a time-varying voltage profile Ue(t) occurring 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 depending on the shape of the mold 1.

[0037] 2 shows the characteristic in the form of gradients m1 or m2 of the voltage distribution Ue(t) induced in the receiving coil 3 as a function of different casting levels L1 or L2 - see also FIG. 4. To determine the casting level L, the evaluation unit 8 ascertains the resulting gradients m1 or m2 in the time window ZF and then ascertains the casting level L as a function of the gradients m1 or m2.

[0038] The above steps are repeated continuously for continuous measurement of the casting level L.

[0039] 3 shows an embodiment of the invention in which the measurement device 100 comprises three receive coils 3, 4 and 5. In this embodiment, all of the time-varying voltage profiles induced in the receive coils 3, 4 and 5 during the time window ZF are measured and evaluated.

[0040] The exact shape of the time-varying voltage profile Ue(t) in each receiving coil 3, 4 and 5 depends, among other things, on the shape of the transmitting coil 2 and receiving coils 3, 4 and 5, the position of the coils 2-5 in the casting mold, the mold itself and, to some extent, the composition of the liquid metal 9 being measured, and must each be learned once.

[0041] The position and shape of the fill level calibration curve can then be adjusted by adding the differential read-out receiver coils 4 and 5. It has been found that the differential evaluation signal AS1 or AS2 (see FIG. 4) based on the receiver coil pair 3 / 4 and 4 / 5 reaches a maximum when the fill level L is located exactly between the two differential read-out receiver coils of the receiver coil pair 3 / 4 or 4 / 5. Since this position is precisely mechanically determined by the known positions of the receiver coils 3, 4 and 5, the fill level calibration curve can thus be subsequently adjusted with sufficient precision, especially when sprue casting is carried out.

[0042] 4 shows such a fill level calibration curve, where the fill level L is plotted against the slope m of the voltage profile Ue(t). The differential signal AS1 between the voltage profiles of receive coils 3 and 4 has its maximum at reference point R1, so that at reference point R1 the slope m1 can be assigned to a known fill level L1. The differential signal AS2 between the voltage profiles of receive coils 4 and 5 has its maximum at reference point R2, so that at reference point R2 the slope m2 can be assigned to a known fill level L2.

[0043] The present invention provides an inductive measurement principle that is not based on eddy currents for non-contact measurement of the fill level of conductive materials, in particular liquid metals, in casting molds with locally selective resolution and that is largely temperature independent.

[0044] The present invention allows reliable measurement of the casting level independent of interfering conductive materials in the vicinity of the coil system, and is easily calibrated, and is also applicable to small casting moulds, since sensitive areas can be easily identified by selecting the time window ZF. Some aspects of the invention are described below. [Aspect 1] A method for measuring the casting level (L) in a mold (1), comprising the steps of: a) energizing a transmitting coil (2) placed in the mold (1) with a temporal current profile (i(t)) during a measurement time interval (MZI); b) measuring, during said measurement time interval (MZI), the temporal signal profile (Ue(t)) occurring in a receiving coil (3) inductively coupled to said transmitting coil (2); c) selecting a time window (ZF) within said measurement time interval (MZI); d) evaluating the temporal signal profile (Ue(t)) measured within the selected time window (ZF) to determine the casting level (L). [Aspect 2] 2. The method of claim 1, wherein the temporal signal profile (Ue(t)) generated in the receiving coil (3) is a temporal voltage profile (Ue(t)) induced in the receiving coil (3) as a result of the temporal current profile (i(t)) being applied to the transmitting coil (2). [Aspect 3] 3. The method according to any one of the preceding aspects, wherein the temporal current profile (i(t)) is a ramp-type, in particular a linear ramp-type, current profile. [Aspect 4] The method according to any one of aspects 1 to 3, wherein the temporal current profile (i(t)) is a temporal current profile with a non-sinusoidal waveform and / or a non-rectangular waveform. [Aspect 5] determining the gradients (m1, m2) of the temporal signal profile (Ue(t)) measured within the selected time window (ZF); evaluating the identified gradients (m1, m2) to identify the casting level (L). [Aspect 6] The step of energizing the transmitting coil (2) with the temporal current profile (i(t)) during the measurement time interval (MZI) comprises: specifying a time current setpoint profile; and adjusting the current (i(t)) through the transmit coil (2) to track the time current setpoint profile. [Aspect 7] 7. The method according to any one of aspects 1 to 6, wherein steps a), c), and d) are repeated continuously, in particular periodically. [Aspect 8] e) measuring a time signal profile occurring during said measurement time interval (MZI) with at least one further receiving coil (4, 5) inductively coupled to said transmitting coil (2); f) evaluating a further time signal profile measured within the selected time window (ZF) to determine the casting level (L). [Aspect 9] The method according to any one of aspects 1 to 8, wherein the time window (ZF) within the measurement time interval (MZI) is selected depending on the shape of the template (1). [Aspect 10] A device (100) for measuring the casting level (L) in a mold (1), at least one transmitting coil (2); At least one receiving coil (3, 4, 5); a controlled current source (6) designed to energize the at least one transmitting coil (2) with a predefined temporal current profile (i(t)); a measuring device (7) designed to measure a time signal profile (Ue(t)) of the at least one receiving coil (3) inductively coupled to the at least one transmitting coil (2); an evaluation device (8) designed to evaluate the measured temporal signal profile (Ue(t)) in order to ascertain the casting level (L). [Aspect 11] The measuring device according to aspect 10, wherein the measuring device (100) is designed to perform the method according to any one of aspects 1 to 8.

Claims

1. A method for measuring the casting level (L) in a mold (1), comprising the steps of: a) energizing a transmitter coil (2) placed in the mold (1) with a temporal current profile (i(t)) during a measurement time interval (MZI); b) measuring, during said measurement time interval (MZI), the temporal signal profile (Ue(t)) occurring in a receiving coil (3) inductively coupled to said transmitting coil (2); c) selecting a time window (ZF) within said measurement time interval (MZI); d) evaluating the temporal signal profile (Ue(t)) measured within the selected time window (ZF) to determine the casting level (L), The method, wherein the temporal current profile (i(t)) is a ramp-type current profile.

2. 2. The method of claim 1, wherein the temporal signal profile (Ue(t)) generated in the receiving coil (3) is a temporal voltage profile (Ue(t)) induced in the receiving coil (3) as a result of the temporal current profile (i(t)) being passed through the transmitting coil (2).

3. The method according to claim 1 or 2, wherein the temporal current profile (i(t)) is a non-sinusoidal and / or non-rectangular waveform temporal current profile.

4. - ascertaining the gradients (m1, m2) of the temporal signal profile (Ue(t)) measured within the selected time window (ZF); A method according to any one of claims 1 to 3, characterized by a step of evaluating the ascertained gradients (m1, m2) to ascertain the casting level (L).

5. The step of energizing the transmitting coil (2) with the temporal current profile (i(t)) during the measurement time interval (MZI) comprises: specifying a time current setpoint profile; and adjusting the current (i(t)) through the transmit coil (2) to track the time current setpoint profile.

6. 6. The method according to any one of claims 1 to 5, wherein steps a), c), and d) are repeated continuously.

7. e) measuring the time signal profile occurring during said measurement time interval (MZI) with at least one further receiving coil (4, 5) inductively coupled to said transmitting coil (2); f) evaluating further time signal profiles measured within the selected time window (ZF) to determine the casting level (L).

8. The method according to any one of the preceding claims, wherein the time window (ZF) within the measurement time interval (MZI) is selected depending on the shape of the mold (1).

9. A device (100) for measuring the casting level (L) in a mold (1), comprising: At least one transmitting coil (2); at least one receiving coil (3, 4, 5); a controlled current source (6) designed to energize said at least one transmitting coil (2) with a predefined temporal current profile (i(t)); a measuring device (7) designed to measure a time signal profile (Ue(t)) of the at least one receiving coil (3) inductively coupled to the at least one transmitting coil (2); an evaluation device (8) designed to evaluate the measured temporal signal profile (Ue(t)) in order to verify the casting level (L), The measurement device, wherein the temporal current profile (i(t)) is a ramp-type current profile.

10. The measuring device (100) according to claim 9, wherein the measuring device (100) is designed to carry out the method according to any one of claims 1 to 8.

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