Method for calibrating an ultrasonic measuring device intended to analyze liquid metals

Abstract

A method for calibrating an ultrasonic measuring device (1) intended to characterize a liquid metal, said probe comprising: - a measuring emitter (11) configured to emit incident ultrasonic waves into the liquid metal; - a receiver (21) configured to detect ultrasonic waves reflected or diffracted by inclusions in the liquid metal after emission of said incident ultrasonic waves; - a processing unit configured for determining the amplitude of the detected ultrasonic waves; said method being characterized in that it comprises a phase of calibrating the probe by imposing upstream of the probe a standing acoustic wave that propagates within the liquid metal in order to trap inclusions by the effect of acoustophoresis.

Description

Technical Field

[0001] The technical field of this invention is to characterize liquid metal castings (such as aluminum alloy castings) using ultrasonic waves.

[0002] Existing technology In the field of metal casting, it is necessary to inspect the quality of molten metal in order to detect inclusions. This is especially true for aluminum. Certain industries, such as beverage can manufacturing, have very high requirements for the quality of molten aluminum alloys. The quality of molten metal is determined by the amount of inclusions present in the metal. These inclusions may be trace components of gases, oxides, nitrides, carbides, fluorides, or borides. Common inclusions encountered in molten aluminum include Al₂O₃, MgAl₂O₄, Al₄C₃, MgO, CaO, CaF₂, TiB₂, TiVB₂, and SiO₂.

[0003] Ultrasonic measurement technology can be used for online monitoring of casting quality. According to this method, ultrasonic waves propagate through liquid metal. If inclusions are present, some of the emitted sound waves are reflected and can be detected. The amplitude of the reflected or diffracted waves can be used to determine the size of the inclusions in the metal. Ultrasonic technology allows for the characterization of a portion (typically 2%) of the liquid metal.

[0004] Probes that allow for ultrasonic measurement of castings have been described in patents EP3204764B1 and EP3204763B1.

[0005] Document EP1194772B1 describes a method for calibrating a probe in which a reflector is arranged at the end of a rod, which is then placed in liquid metal. The reflectors can have different sizes. Therefore, a correlation can be established between the size of each reflector and the amplitude of the detected sound wave. This method needs to be applied to each probe individually. Furthermore, it implies arranging the calibrated reflector in liquid metal, which can prove complex.

[0006] The described document US20190145939 relates to a method and apparatus that allows for the quantitative determination of the quantity and size of particulate components contained in a medium flowing along a flow path; ultrasonic waves are coupled to the flowing medium and at least partially reflected by the particulate components, the reflected portion of the ultrasonic waves being detected in an ultrasonic time signal, and the quantitative determination is based on said ultrasonic time signal.

[0007] Document US4770699 describes a probe for testing or ultrasonically processing molten metal, comprising: an ultrasonic transmission rod having one end as a "downstream" end adapted to contact the molten metal to be tested or processed; a piezoelectric crystal adapted to provide ultrasonic waves to or receive ultrasonic waves from the rod; and means for cooling the rod located near the downstream end of the rod.

[0008] Document US5604301 describes a method for separating liquids, particularly liquid metals, using heterogeneous components in a liquid. The method includes the steps of providing a channel for a liquid flow containing heterogeneous components and guiding ultrasound in the channel.

[0009] Another possible approach to estimating inclusion size is to use a correlation curve between measurements obtained using an ultrasonic probe and measurements obtained using a method considered as a reference method. For example, the reference method could be a "LIMCA" (Liquid Metal Cleanliness Analysis) type analytical method, based on the analysis of the electrical resistance of a liquid metal sample. It could also include the method described in EP1194772B1, which involves calibrating a reflector. Therefore, a correlation function can be established between the inclusion size measured by the reference method and the amplitude of the ultrasonic signal.

[0010] One difficulty associated with using ultrasound probes is that their response can vary from probe to probe. However, it is difficult to calibrate each probe using a reference method (such as the LIMCA-type reference method or the reference method described in EP1194772B1). Such calibration takes time.

[0011] The variability in response between two probes with identical structures is attributed to differences that may affect the electronic circuitry or the materials used. When encountering the same inclusion, two different probes with the same design may produce detection signals of different amplitudes due to the variability in instrument response.

[0012] It is preferable, or even necessary, to consider this variability, for example, if one seeks to apply the same correlation curve to measurements produced by different ultrasound probes.

[0013] The inventors have proposed a method that allows for consideration of the variability in the responses of two different probes. The aim is to ensure that, in the presence of identical inclusions, two probes with the same design produce the same signal, or can be considered to produce the same signal. Summary of the Invention

[0014] The first object of the present invention is a method for calibrating an ultrasonic measuring device designed to characterize liquid metals, the device comprising: - A measuring transmitter configured to emit incident ultrasonic waves in liquid metal; - A receiver configured to detect ultrasonic waves reflected or diffracted by inclusions in the liquid metal after the incident ultrasonic waves are emitted; - A processing unit configured to determine the amplitude of the detected ultrasonic wave; The method is characterized by comprising the following steps: a) The ultrasonic tool head is placed in liquid metal, and the device is arranged such that the measuring transmitter and the receiver are placed in or facing the liquid metal; b) Activate the ultrasonic tool head during the activation cycle to generate standing sound waves that propagate through the liquid metal; c) Powering on the measuring transmitter so that the measuring transmitter emits incident ultrasonic waves propagating in liquid metal at different calibration times, the calibration times forming a calibration period; d) At each calibration time, the receiver detects the ultrasonic waves reflected or diffracted by the liquid metal under the action of the incident wave, and determines the amplitude of the ultrasonic waves detected by the receiver; e) Calculate the normalized amplitude based on the amplitude measured at each calibration time; f) Calculate a normalization function configured to normalize each ultrasonic amplitude detected by the receiver by the normalized amplitude.

[0015] The standing sound wave can be an ultrasonic wave.

[0016] The device can be positioned at a distance of less than 2 meters from the ultrasonic tool head.

[0017] The frequency of the standing sound wave is different from the frequency of the incident wave.

[0018] The calibration period can be after the activation period.

[0019] According to one possible approach, the ultrasonic tool head forms the measuring transmitter. Then, the method causes: - During step b), the measuring transmitter emits the standing sound wave; - During step c), the measuring transmitter and the receiver of the device are activated to determine the amplitude of the ultrasonic waves detected by the receiver.

[0020] According to one possible approach, the calibration period is extended based on a duration of less than 1 second.

[0021] According to one possible approach, the frequency of the standing sound wave generated during step b) is greater than the frequency of the incident ultrasonic wave emitted during step c).

[0022] According to one possible solution: - The frequency of the standing sound wave generated during step b) is different from the frequency of the incident ultrasonic wave emitted during step c); - The calibration cycle includes all or part of the activation cycle, and steps b) and c) are performed simultaneously.

[0023] A second objective of this invention is a method for characterizing liquid metals, the method employing an ultrasonic measuring device, comprising: - A measuring transmitter configured to emit incident ultrasonic waves in the liquid metal; - A receiver configured to detect ultrasonic waves reflected or diffracted by inclusions in the liquid metal after the incident ultrasonic waves are emitted; - A processing unit configured to determine the amplitude of the detected ultrasonic wave; The method includes the following steps: - (i) Arrange the device such that the measuring transmitter and the receiver are disposed in or toward the liquid metal; - (ii) Powering the measuring transmitter so that it emits incident ultrasonic waves propagating in the liquid metal; - (iii) The receiver detects ultrasonic waves reflected or diffracted by inclusions in the liquid metal under the action of the incident wave; - (iv) At the measurement time, the receiver measures the ultrasonic waves reflected or diffracted by the inclusions in the liquid metal under the action of the incident ultrasonic waves, and determines the amplitude of the ultrasonic waves detected by the receiver at each measurement time; The method is characterized in that it includes: -(v) Apply a normalization function to the amplitude determined at the measurement time, the normalization function being defined by the first objective method according to the invention.

[0024] According to one possible solution: - The liquid metal flows along the tank; - The transmitter and the receiver are arranged facing the slot.

[0025] According to one possible solution: - The measurement transmitter is coupled to a first waveguide immersed in the liquid metal; - The receiver is coupled to a second waveguide immersed in the liquid metal.

[0026] A third objective of the present invention is an ultrasonic measuring device, comprising: - A measuring transmitter configured to emit incident ultrasonic waves in the liquid metal; - A receiver configured to detect ultrasonic waves reflected or diffracted by inclusions in the liquid metal after the incident ultrasonic waves are emitted; - A processing unit configured to implement steps e) and f) of the method according to the invention.

[0027] The invention will be better understood by taking into account the accompanying drawings and by reading the disclosure of the embodiments presented in the following description. Attached Figure Description

[0028] Figure 1A A first embodiment of the probe capable of implementing the present invention is shown.

[0029] Figure 1B Another embodiment of the probe capable of implementing the present invention is shown.

[0030] Figure 2 The diagram schematically illustrates the sound waves detected at the measurement time point.

[0031] Figure 3 The diagram schematically illustrates a standing sound wave extending through a groove.

[0032] Figure 4 The correlation curve between the detected wave amplitude and the inclusion size is shown.

[0033] Figure 5 The main steps of the method according to the invention are illustrated schematically.

[0034] Figure 6A An ultrasonic tool head is schematically shown immersed in a tank.

[0035] Figure 6B The results show the changes in the concentration of inclusions of different sizes in the casting over time during the first test, with and without the application of standing acoustic waves.

[0036] Figure 6C The diagram shows the change in the concentration of inclusions larger than 20 µm in the casting over time, with and without the application of standing acoustic waves, during the second test.

[0037] Figure 6D and Figure 6E Histograms showing the size distribution of inclusions with and without the application of standing acoustic waves are presented.

[0038] Figure 6F The diagram shows the change in the concentration of inclusions larger than 20 µm in the casting over time, with and without the application of standing acoustic waves, during the third test.

[0039] Figure 7A and Figure 7B The images are obtained from PODFA (Porous Disk Filter Analysis) analysis of samples taken from the casting with and without the application of standing sound waves.

[0040] Figure 8A The changes in the detection signal generated by the probe during the experimental test are shown.

[0041] Figure 8B It shows Figure 8A Enlarged view of the area within the Chinese box.

[0042] Detailed Implementation Plan The first embodiment of the ultrasonic probe capable of implementing the present invention has been combined with Figure 1A As shown. The probe includes a measuring transmitter 11 and a receiver 21. In this embodiment, the measuring transmitter 11 and the receiver 21 are formed by the same acoustic transducer. For example, the acoustic transducer is a piezoelectric transducer known to those skilled in the art.

[0043] For example, the transducer is a piezoelectric material wafer that emits sound waves at a frequency of 15 MHz. Typically, the frequency of the emitted sound waves is preferably between 1 MHz and 20 MHz.

[0044] The probe is designed to detect inclusions 4 in the liquid medium 2 to be analyzed, and more specifically, to detect inclusions in liquid metal, such as aluminum alloys. Figure 1A In the diagram, the horizontal dashed line represents the interface between liquid metal 2 and the ambient medium 3, such as air.

[0045] The probe 1 includes a waveguide 13 designed to be immersed in liquid metal 2. This waveguide is configured to facilitate the propagation of acoustic waves between the transducer, which acts as a transceiver, and the liquid metal 2. For example, the waveguide 13 is formed of a silicon nitride or silicon oxynitride (SiAlON) type material, or more generally of a metallic or refractory ceramic type material, which are considered inert to the liquid metal 2. The use of such a waveguide has been described in EP3204763B1 or EP1194772B1.

[0046] Figure 1AThe ultrasonic field 5 is schematically shown, corresponding to a portion of the liquid metal being examined by probe 1. As inclusion 4 passes through the ultrasonic field, a portion of the sound waves emitted by measuring transmitter 11 is reflected or diffracted toward receiver 21. The characteristics of the reflected waves, particularly their amplitude, enable the detection and characterization of the inclusions, such as estimation of their size.

[0047] Preferably, the probe may include a power transmitter 12 configured to emit high-power acoustic waves, i.e., greater than 10W, preferably greater than 50W or 100W, such as 120W, as described in EP3204764. In practice, applying high-power acoustic waves allows for the wetting of the first waveguide 13 by the liquid metal 2. The power transmitter 12 is activated at regular time intervals to allow for maintaining good wetting of the waveguide 13 by the liquid metal 2.

[0048] Figure 1B A preferred configuration is shown, in which the probe includes a measuring transmitter 11 and a receiver 21. The measuring transmitter 11 is connected to a first waveguide 13. The receiver 21 is connected to a second waveguide 23, which is preferably identical to the first waveguide 13 (same material, same dimensions), but separate from the first waveguide 13. For example, the length of each waveguide is between 10 cm and 50 cm. Preferably, the first and second waveguides are straight and extend around a first central axis Δ1 and a second central axis Δ2, respectively. The central axes Δ1 and Δ2 intersect and are inclined relative to each other according to an angle α. This angle is, for example, between 20° and 40°, preferably between 25° and 35°. For example, angle α is equal to 28°. This configuration has been described in EP3204764B1.

[0049] In this embodiment, the probe may include a first power transmitter 12 and a second power transmitter 22, as described in conjunction with the first embodiment. The first and second power transmitters are periodically activated to improve the wetting of the liquid metal 2 on the first waveguide 13 and the second waveguide 23, respectively.

[0050] The probe includes a control unit 31 configured to enable control of the measuring transmitter 11 to emit sound waves, and when the probe includes such a transmitter, to enable control of the power transmitter 12 to emit power sound waves.

[0051] The sound waves emitted by the measuring transmitter 11 are typically emitted in series. In practice, each series of sound waves is emitted by the measuring transmitter 11 at a regular frequency (e.g., 0.1 Hz). A series includes at least one sound wave, preferably several consecutive sound waves. Within the same series, the emission frequency of the sound waves can be between 100 Hz and 300 Hz, corresponding to the excitation frequency of the piezoelectric transducer of the measuring transmitter.

[0052] Figure 2 The diagram schematically illustrates three waves detected by receiver 21 after transmitter 11 emits a series of three waves. Parentheses indicate that the three waves belong to the same series. Figure 2 In the diagram, the vertical axis corresponds to the signal S(t) detected by receiver 21, while the horizontal axis corresponds to time t.

[0053] The probe includes a processing unit 32 configured to calculate the amplitude of waves detected by the receiver 21 in response to a series of sound waves emitted by the measuring transmitter 11. The calculated amplitude can be the average of the maximum amplitude of each detected sound wave, or the maximum amplitude of all sound waves detected after a series of wave emissions. The calculated amplitude is then labeled as follows: . The measurement time corresponds to the detection of a series of sound waves by receiver 21.

[0054] When the amplitude When a certain threshold is exceeded, inclusions 4 are present in the liquid metal. Amplitude Inclusion size can be estimated using reference methods (such as LIMCA or methods based on calibrated reflectors) based on experimentally plotted correlation curves, and these methods are described in conjunction with existing techniques.

[0055] The same correlation curve can be used for different ultrasound probes with the same design, provided that the amplitudes produced by the ultrasound probes are comparable. However, as mentioned earlier, it is necessary to consider the variability of the probes, even if they are similar to each other: the same size and using the same materials.

[0056] Processing unit 32 includes an amplifier designed to amplify the signal from receiver 21, and the amplification gain G0 of the amplifier is typically set at the factory after the probe is manufactured. This gain is generally not modified during the process. It can be adjusted according to the conditions of probe use.

[0057] Probe 1 is designed to be immersed in molten metal 2 flowing from a furnace. For example, the molten metal flows along a tank. The waveguide of the probe is immersed in the tank.

[0058] Due to cost and time constraints, it is impractical to generate correlation curves for each probe using a reference method. However, it is necessary to consider the variability in the response of each probe. The inventors propose a method for obtaining comparable responses for each probe, enabling the use of the following combination... Figure 4 The correlation curve described.

[0059] An important aspect of this invention is the ability to obtain liquid metal with controlled inclusion concentrations in castings for so-called calibration measurements using ultrasonic probes. The basic idea is that for the same inclusion concentration, the measurement amplitude should be the same regardless of the type of probe used.

[0060] However, the inclusion concentration in castings varies with time and space. To obtain a controlled inclusion concentration, the casting is subjected to standing sound waves at at least one point. This places the inclusions in a sound pressure field and subjects them to a force called acoustic radiation force, which can cause inclusion displacement. Inclusions can concentrate at pressure nodes (i.e., the region with the smallest pressure wave amplitude) or pressure antinodes (i.e., the region with the largest pressure wave amplitude in the sample). Inclusion concentration has also been observed at interfaces, whether they are the walls defining a groove or the free surface of liquid metal. Therefore, using sound waves allows for the non-physical displacement of inclusions, thereby depleting the inclusions in the field of view, i.e., reducing the number of inclusions present in the field of view.

[0061] This invention is based on generating standing sound waves at certain points in the casting (upstream and / or downstream, or at the probe). According to the principle of acoustic migration, standing sound waves allow inclusions flowing in the casting to move and / or remain outside the observation field of view of probe 1. Therefore, the observation field of view of the probe can be considered to be free of inclusions.

[0062] According to one possible approach, the ultrasonic tool head is positioned at a distance from the probe (or more precisely, from the probe's field of view), either upstream or downstream of the probe, with upstream and downstream defined relative to the flow of the liquid metal. Inclusions are then trapped, particularly at the free interface (liquid / gas metal interface) or the wall of the tank. The distance between the probe and the ultrasonic tool head is preferably greater than 10 cm, for example, between 30 cm and 2 m. Those skilled in the art adjust this distance so that it is sufficient to prevent standing waves from being detected by the probe, while being close enough to allow for a filtering effect applied by the standing waves. Figure 3 A schematic diagram of standing sound waves Its perpendicularity to the groove The flow direction of the casting of liquid metal 2 extends in the middle. Inclusions move toward the free interface 2' (liquid / gas metal interface) or toward the wall 6 of the tank.

[0063] According to another possible approach, the ultrasonic tool head is formed by the transmitter 11 of the probe. In this case, the transmitter emits standing sound waves that displace the inclusions outside the field of view, at the free interface or the wall of the groove.

[0064] Regardless of the implementation scheme, standing sound waves are emitted at high frequencies, typically greater than 10 kHz, and greater than 20 kHz if noise pollution needs to be limited. This is considered more effective for small inclusions. Furthermore, the application of standing sound waves in the ultrasonic range allows for the limitation of noise pollution.

[0065] Standing sound wave generated upstream of probe 1 It acts as a filter, allowing inclusions to move or remain outside the field of view. Therefore, within the field of view, the mass of the liquid metal can be considered controlled, meaning the metal can be assumed to be free of inclusions or that inclusions have been sufficiently depleted.

[0066] One object of the present invention is to calibrate the probe by utilizing the filtering effect of standing sound waves to identify portions of the casting that are considered clean or at least have a controllable amount of inclusions.

[0067] The ultrasonic tool head (whether it is the same as or different from the measuring transmitter) is configured to emit standing sound waves during the activation cycle Ta. The activation cycle Ta can last for several seconds or minutes.

[0068] According to one possible approach, the activation period is followed by a calibration period Tc. During the calibration period, preferably no standing sound waves are emitted to avoid detection by the probe's receiver. The calibration period Tc is sufficiently close to the activation period Ta, so that the effect of the standing sound waves on the liquid metal is considered to still exist during the calibration period. Therefore, during the calibration period, the probe's field of view is considered to be free of inclusions, or that inclusions have been sufficiently depleted.

[0069] It should be understood that the calibration period is preferably as close as possible to the activation period in order to take advantage of the arrangement of inclusions located outside the probe's field of view during the activation period under the influence of the emitted standing sound waves.

[0070] According to another possible approach, the frequency of the standing sound wave differs sufficiently from the transmission frequency of the transmitter 11 of the probe, so that the influence of the standing sound wave on the sound wave detected by the receiver of the probe can be considered negligible.

[0071] Regardless of the implementation scheme, during calibration, the device to be calibrated is immersed in liquid metal, and at one or more calibration moments... Perform measurements. Calibrate the amplitude. For each calibration time, this calibration amplitude corresponds to the probe's amplitude at that calibration time. The amplitude of the detected signal. Based on the calibrated amplitude. Define the normalized amplitude and label it. It corresponds to the calibration amplitude. The average or median.

[0072] The duration of the calibration period Ta depends on the experimental conditions. It can last from several milliseconds to hundreds of milliseconds, or even several seconds.

[0073] With the normalized amplitude already determined Then, at the measurement time Each amplitude obtained from the probe All can be achieved through a normalization function. Normalization is performed so that: in: - This corresponds to the normalization function.

[0074] - It is the normalized amplitude.

[0075] - It could be, for example, 20. In this case, the normalized amplitude... It is expressed as a percentage. A value of 20% corresponds to a casting that is considered clean.

[0076] Once a normalization function has been defined for the probe, it can be used in the same way as a reference probe, whose response is known.

[0077] One advantage of this method is that, regardless of the type of probe used, the normalized value corresponds to... (e.g., 20%) normalized amplitude The value represents a clean casting. Normalization avoids affecting probe variability: the normalized amplitude for different probes. They can be compared because, for each probe, the normalized amplitude... It is established under comparable conditions (assuming the presence of clean liquid metal).

[0078] The normalization assumption assumes that liquid metal, generally considered clean (i.e., free of inclusions or fully depleted), produces sound waves whose amplitude is likened to noise. This amplitude corresponds to the normalized amplitude. .

[0079] Normalization allows for the use of, for example Figure 4 The correlation curve is shown schematically. This correlation curve was experimentally established using the reference probe after applying the normalization function determined for this reference probe. Therefore, the y-axis corresponds to... ,in The amplitude corresponds to the measured amplitude in relation to the known inclusion size. The horizontal axis corresponds to the size of the inclusion, such as its diameter, which is measured using a reference method. Figure 4 The curve in the figure is a response function established for a reference probe: it establishes the relationship between the normalized measurement obtained from the reference probe and the known inclusion size established by a reference method (e.g., the LIMCA method).

[0080] The use of a normalization function allows for the readjustment of the response of each probe so that the response of each probe can be compared with the response of a reference probe.

[0081] The main steps of the present invention are now described, such as Figure 5 As shown in the illustration.

[0082] Step 100 Standing sound waves are generated during the activation cycle.

[0083] During this step, an ultrasonic tool head is used. Generation of standing sound waves The standing sound wave propagates in the liquid metal.

[0084] The ultrasonic tool head S may be different from the transmitter 11, in which case it may be located downstream or upstream of the transmitter. According to one possible scheme, the ultrasonic tool head S may be the same as the transmitter 11.

[0085] When the frequency of the standing sound wave differs sufficiently from the frequency of the sound wave emitted by the transmitter of the probe, the activation period Ta can be all or part of the same as the calibration period Tc.

[0086] When the standing acoustic wave might be confused with the acoustic wave reflected by the liquid metal in response to the transmitter of the probe, the calibration period Tc is followed by the activation period Ta. In this case, the time interval between the calibration period and the activation period should be as short as possible.

[0087] Step 110 Determine the normalized amplitude within the calibration period.

[0088] During this step, such as regarding Figure 1A and Figure 1B The probe described is positioned in the ultrasonic tool head. Downstream, so that at one or more calibration times Perform one or more calibration amplitudes At least one measurement. Based on calibrated amplitude. or multiple measurements The average (or median or other statistical measure) is used to determine the normalized amplitude. .

[0089] Step 120 Determine the normalization function Based on normalized amplitude The normalization function of the probe is defined according to equation (1). .

[0090] Steps 110 and 120 are implemented by processing unit 32.

[0091] Step 130 : Perform measurement Once the normalization function of the probe has been defined, the probe can be used at different measurement times. Perform the measurement. Measure the amplitude. For each measurement time, such as regarding Figure 2 As described.

[0092] Step 140 Normalization During this step, the measured amplitude is normalized according to equation (1) using the normalization function obtained from step 120.

[0093] Steps 100 to 120 are preferably performed for probes with the same design. This allows for the acquisition of a normalization function associated with each probe. The normalized measurements for each probe are then considered comparable because the variability of each probe has been corrected for using the normalization function defined for each probe.

[0094] A correlation curve can be established by comparing measurements from a reference method (such as LIMCA) with the normalized amplitude obtained from a probe considered as a reference probe. Such a curve can then be used for the normalized amplitude of all probes with a similar design to the reference probe.

[0095] Experimental test The inventors tested the capture of inclusions using sonication in a tank. They positioned the ultrasonic toolhead at the center of the tank, see [link to documentation]. Figure 6A The transmission power is 100 W. (Regarding...) Figure 6A The dimensions (in mm) are: P1=182, P2=166, L1=55, L2=146.

[0096] A sample of the casting is taken downstream of the probe, at a distance of 70 cm from the ultrasonic tool head. This sample is then subjected to LIMCA type measurement. Figure 6B The variation of inclusion concentration (vertical axis - number of inclusions, in thousands / kg) over time (horizontal axis - minutes) for inclusions of different sizes (20 µm, 40 µm, 60 µm, 80 µm in diameter) is shown. The ultrasonic tool head S was activated between t = 40 min and 50 min. A significant decrease in the detected particle concentration was observed during ultrasonic tool head activation. The inclusion concentration measured by LIMCA represents the inclusion quality of the casting downstream of the ultrasonic tool head. Activation of the ultrasonic tool head was accompanied by an improvement in inclusion quality for all sizes of inclusions. Small inclusions (20 µm) appear to be less sensitive to sonophoresis.

[0097] During the second experiment, the ultrasonic tool head was activated at different times. The inclusion concentration at a depth of 20 µm downstream of the ultrasonic tool head was measured using LIMCA. Figure 6CThe inclusion concentration (vertical axis - number of inclusions, unit: thousand / kg) at different measurement points distributed chronologically is shown. The ultrasonic tool head was activated between measurement points 43-47 and 53-57. Between measurement points 43 and 47, the power of the ultrasonic tool head was adjusted to 40% of its maximum power. Between measurement points 53 and 57, the power of the ultrasonic tool head was adjusted to 60% of its maximum power. It was also observed that, for different power levels, actuation of the ultrasonic tool head allowed for a reduction in the inclusion concentration downstream of the ultrasonic tool head.

[0098] Figure 6D and Figure 6E The inclusion concentrations (vertical axis - thousands of inclusions / kg metal) categorized by size (horizontal axis - units µm) are shown separately for the application of transverse acoustic waves (histogram a - black) and without application (histogram b - gray). Figure 6D and Figure 6E In the study, the power of the transverse sound waves was 40% and 60% of the maximum power. It was observed that the larger the size of the inclusions, the more significant the effect of the transverse sound waves, which is consistent with... Figure 6B The relevant observations are consistent.

[0099] During the third test, inclusion quality of the two castings at the furnace exit was measured over time using LIMCA: no ultrasonic tool head was used during the first casting. During the second casting, an ultrasonic tool head was used, immersed in the casting and located upstream (approximately 1 m) of the LIMCA measurement sampling area. Figure 6F The variation of inclusion concentration (vertical axis - thousands of inclusions / kg) with time for each type of casting is shown. For both types of castings, a gradual decrease in inclusion concentration over time was observed. It was observed that applying ultrasound to the casting allows for a significant reduction in inclusion concentration regardless of the measurement time.

[0100] exist Figure 6F In the diagram, each point corresponds to a measurement performed. Polynomial interpolation of the measured values ​​was performed on each of these castings, which allows for a continuous curve to be obtained for each casting: curve a: no ultrasound - curve b: ultrasound.

[0101] Figure 6F The observed pattern corresponds to the improvement in the quality of metal inclusions over time. The acoustic adsorption effect is particularly pronounced in the early stages of casting, when the metal is rich in inclusions.

[0102] Liquid aluminum samples were collected during a series of tests, including standard casting (i.e., without ultrasonic treatment) and experimental casting (downstream of the ultrasonic toolhead as described above). The samples were analyzed using a PoDFA (Porous Disk Filter Analysis) analyzer. Figure 7A and Figure 7BMetallographic images obtained from PoDFA analysis of the standard casting and the experimental casting are shown separately. A comparison between the two figures shows that the application of ultrasound significantly improves the inclusion state of aluminum: the oxide film on the experimental casting is significantly reduced.

[0103] about Figures 6A to 6F and Figures 7A to 7B The described experimental results confirm that applying ultrasound allows for castings with limited inclusion concentrations. This invention is based on the assumption that the inclusion quality of castings is comparable regardless of the type of casting, downstream of the standing acoustic wave propagating transversely to the casting flow. Therefore, downstream of the acoustic wave, the amplitude of the ultrasound wave reflected or diffracted by the metal allows for amplitude readjustment, as described with respect to expression (1).

[0104] In a series of experiments, the following were implemented: Figure 1B The probe described. Transmitter 11 is used as an ultrasonic tool head to generate standing sound waves. Figure 8A The diagram shows the change in wave amplitude detected by the probe's receiver 21 over time. During the activation period Ta, standing acoustic waves are emitted at high power to improve the wettability of each waveguide to the ultrasonic waves. This also allows for a reduction in the inclusion content within the probe's field of view by moving inclusions toward the free surface and / or toward the wall of the slot. During the activation period, the receiver is not used, which explains why the amplitude detected during the activation period is zero.

[0105] After the activation cycle, transmitter 11 transmits incident sound waves at a transmission power compatible with receiver 21 of the probe used. Figure 8B It shows Figure 8A Details were observed. After the activation period Ta, the measured amplitude was relatively low due to the depletion of inclusions within the field of view caused by the activation period. The initial moment after the activation period forms the calibration period Tc, during which the amplitude of the pulse measured by the receiver is considered to represent clean metal. In this embodiment, the calibration period lasts 100 ms.

[0106] This invention can be applied by implementing ultrasonic measuring devices of the same type (i.e., with the same structure), the variability of which is due to differences in the components affecting each device. Normalization allows for limiting the variability of response between ultrasonic measuring devices of the same type.

Claims

1. A method for calibrating an ultrasonic measuring device (1) designed to characterize liquid metal, said device comprising: - Measurement transmitter (11), the measurement transmitter being configured to emit incident ultrasonic waves in liquid metal; - Receiver (21), the receiver being configured to detect ultrasonic waves reflected or diffracted by inclusions in the liquid metal after the incident ultrasonic waves are emitted; - Processing unit (32), the processing unit being configured to determine the amplitude of the detected ultrasonic wave; The method is characterized by comprising the following steps: a) Arrange the ultrasonic tool head (S) in the liquid metal (2) and arrange the device (1) such that the measuring transmitter and the receiver are arranged in or toward the liquid metal; b) Activate the ultrasonic tool head during the activation cycle (Ta) to generate standing sound waves that propagate through the liquid metal; c) Power on the measurement transmitter (11) so that the measurement transmitter is energized at different calibration times (t). c An incident ultrasonic wave is emitted that propagates in liquid metal, and the calibration time forms a calibration period (Tc). d) At each calibration moment, the receiver detects the ultrasonic waves reflected or diffracted by the liquid metal under the action of the incident wave, and determines the amplitude of the ultrasonic waves detected by the receiver. ); e) Calculate the normalized amplitude based on the amplitude measured at each calibration time. ); f) Calculate the normalization function ( The normalization function is configured to normalize each ultrasonic amplitude detected by the receiver using the normalized amplitude.

2. The method according to claim 1, wherein the standing sound wave is ultrasound.

3. The method according to any one of the preceding claims, wherein the device is arranged at a distance of less than 2 meters from the ultrasonic tool head.

4. The method according to any one of the preceding claims, wherein the frequency of the standing sound wave is different from the frequency of the incident wave.

5. The method according to any one of the preceding claims, wherein the calibration period is after the activation period.

6. The method of claim 5, wherein the ultrasonic tool head forms the measuring transmitter, the The method makes: - During step b), the measuring transmitter emits the standing sound wave; - During step c), the measuring transmitter and receiver of the device are activated to determine the amplitude of the ultrasonic wave detected by the receiver. ).

7. The method of claim 6, wherein the duration of the calibration cycle is less than 1 second.

8. The method according to any one of the preceding claims, wherein the frequency of the standing sound wave generated during step b) is greater than the frequency of the incident ultrasonic wave emitted during step c).

9. The method according to any one of claims 1 to 4, wherein: - The frequency of the standing sound wave generated during step b) is different from the frequency of the incident ultrasonic wave emitted during step c); - The calibration cycle includes all or part of the activation cycle, and steps b) and c) are performed simultaneously.

10. A method for characterizing liquid metal, the method implementing an ultrasonic measuring device (1), comprising: - Measurement transmitter (11), the measurement transmitter being configured to emit incident ultrasonic waves in the liquid metal; - Receiver (21), the receiver being configured to detect ultrasonic waves reflected or diffracted by inclusions in the liquid metal after the incident ultrasonic waves are emitted; - A processing unit configured to determine the amplitude of the detected ultrasonic wave; The method includes the following steps: - (i) Arrange the device (1) such that the measuring transmitter and the receiver are arranged in or toward the liquid metal; - (ii) Powering the measuring transmitter so that it emits incident ultrasonic waves propagating in the liquid metal; - (iii) The receiver detects ultrasonic waves reflected or diffracted by inclusions in the liquid metal under the action of the incident wave; - (iv) At each measurement moment, the receiver measures the ultrasonic waves reflected or diffracted by inclusions in the liquid metal under the action of the incident ultrasonic waves, and determines the amplitude of the ultrasonic waves detected by the receiver at each measurement moment. ); The method is characterized in that it includes: - (v) Apply a normalization function to the amplitude determined at the measurement time, the normalization function being defined by the method according to any one of claims 1 to 9.

11. The method of claim 10, wherein: - The liquid metal flows along the tank; - The transmitter and the receiver are arranged facing the slot.

12. The method according to any one of claims 10 or 11, wherein: - The measurement transmitter is coupled to a first waveguide (13) immersed in the liquid metal; - The receiver is coupled to a second waveguide (23) immersed in the liquid metal.

13. An ultrasonic measuring device, comprising: - Measurement transmitter (11), the measurement transmitter being configured to emit incident ultrasonic waves in the liquid metal; - Receiver (21), the receiver being configured to detect ultrasonic waves reflected or diffracted by inclusions in the liquid metal after the incident ultrasonic waves are emitted; - Processing unit (32), the processing unit being configured to implement steps e) and f) of the method according to any one of claims 1 to 9.

Images