Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
  • G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
  • G01N27/90—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents
  • G01N27/904—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents with two or more sensors
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
  • G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
  • G01N27/90—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
  • G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
  • G01N27/90—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents
  • G01N27/9006—Details, e.g. in the structure or functioning of sensors

Definitions

• the invention relates to the detection of surface defects on a slab or, more generally, on a metal product, in particular steel, raw of continuous casting. More specifically, the invention relates to the detection of surface defects on a raw metal product of continuous casting using a sensor by eddy currents with separate emitter-receiver placed opposite and close to the surface to be inspected.
• a sensor of this type also called “CdF sensor with anisotropic probes", the probes of which are separate transmitting and receiving coils, spaced from each other on a line oriented perpendicular to the travel of the slab going on underneath.
• Such a sensor is thus sensitive to changes in the circulation of eddy currents generated by the presence of a long transverse defect on the surface of the product inspected. It thus makes it possible to discriminate in particular the transverse edge cracks since the induced currents generated under the transmitter by the magnetic field of the latter do not circulate as far as under the receiver in the absence of faults which propagate from one to the other.
• the distance which separates the two transmitting and receiving coils being fixed by construction, we therefore miss the detection of short cracks if we do not scan a sufficiently wide slab edge region, ie by multiple passages of the sensor with an incremental lateral offset adjusted accordingly, either by placing a series of multiple sensors side by side so that the whole covers the region considered.
• the invention seeks to resolve these difficulties by using recent high-speed imaging technologies using arrays (or rows) of aligned elementary mini-coils (or cells), which can be activated separately by programmed multiplexing.
• arrays or rows
• eddy current sensors of this type can be found for example in the following documents: FR 9300984, USP 6,339,327 or USP 5,237,271, used for the inspection of metal plates, sheets, strips or blades in many technical fields.
• each cell is thus capable of generating or detecting eddy currents on the surface of the metal product to be inspected.
• the pair of controlled cells is shifted by one cell on the row at each iteration of this control step, so as to scan and inspect the entire surface of the plate metal facing this row of cells without moving either the plate to be inspected or the sensor.
• the size of the cells is of the order of a few square millimeters.
• the metal plates inspected with such sensors must be smooth and the measuring cells are placed at a distance less than 1.5 millimeters from the surface of the plate to be inspected. At such a distance from the surface of the plate, the sensors quickly and precisely detect any surface defect resulting in a break in electrical conductivity. Beyond this distance, however, these sensors become imprecise and cannot be used. Attempts to use these same sensors to detect cracks on the surface of steel slabs coming directly from continuous casting have so far been unsuccessful, to the knowledge of the Applicant. In fact, the roughness of the surface of the slab, as well as the high temperature of this slab, generally higher than 550 ° C., make it hardly possible to keep the sensor permanently below 1.5 mm of the surface to be inspected.
• the invention aims to remedy such a handicap so as to be able to use these CdF sensors with rows of cells controlled by multiplexing on a metallic product in the raw state of continuous casting. It thus relates to a method for detecting surface defects of a raw metal product of continuous casting using an eddy current sensor of the "separate transceiver" type with rows of aligned measuring cells.
• said sensor comprising a matrix of measurement cells distributed in rows and columns, said matrix having at least one first and second parallel rows of at least three measurement cells each, the multiplexing is adjusted according to successive command steps so that, - at a given command step, a first and second cell are activated on each row which are separated from each other by at least one inactive measuring cell, the first cell being controlled to generate eddy currents t on the surface of said metal product, the second cell being controlled so that it detects the eddy currents generated by the first cell whose circulation on the surface has been modified by the presence of surface defects, and in that, at predetermined time interval, the two controlled cells are made inactive and said control step is repeated with two following cells which are offset by at least one cell along the same row relative to the two cells made inactive, and so on until the entire surface area to be inspected has been checked.
• said control step is executed simultaneously for the cells of the first and second rows, said first cells of each row belonging to the same column and said second cells of each row belonging also in the same column, said second cells of each row being configured to produce signals of opposite polarities when a fault is detected.
• the cell which generates the eddy currents must always be spaced from the cell which detects them on the same row by at least one inactive cell. It has in fact been discovered that increasing the spacing between the two controlled transceiver cells makes it possible to increase the distance separating these cells from the surface to be inspected while retaining sufficient sensor performance for the selected application.
• the control step is executed simultaneously and in exactly the same way on two adjacent rows, the pairs of cells active on the second row being however configured to produce signals of reverse polarity with respect to the pair of cells. active in the first row, which makes it possible by addition of the signals to avoid the inevitable disturbances originating for example from the oscillation wrinkles present on the surface of the poured slab and deliver to the inspector a very clean fault detection signal with minimal background noise.
• a subject of the invention is also a fault detection system comprising an eddy current surface fault sensor, of the "separate transceiver" type, comprising at least two rows of at least three measurement cells each. contiguous and controllable, and a programmable multiplex control unit capable of controlling said measurement cells, each cell being capable of generating or detecting eddy currents, characterized in that the two rows of cells are arranged side by side parallel l 'to one another and in that said control unit is a multiplexer capable of controlling a first and a second cell of a row which are separated from each other by at least one inactive and order the same, but in reverse polarity, the pairs of corresponding analog cells in the second row.
• the sensor is provided with a flat sole in which are housed said rows of cells flush with the surface, said sole being intended to be placed at a distance of at least three millimeters from the surface to be inspected;
• the sensor comprises a circuit for cooling the sole by circulating fluid;
• the cooling circuit comprises at least one blade made of ceramic material arranged opposite the sole so as to provide a circulation space for the cooling fluid;
• FIG. 1 represents a system 2 for the continuous detection of surface defects of a steel slab 4 coming directly from a continuous casting installation.
• the slab 4 is arranged horizontally and it is in this arrangement that it arrives in a slow scrolling movement (barely a little more im / min) under the sensor 2.
• the slab 4 is what is called a crude product of continuous casting.
• the slab typically has a temperature even higher than 550 ° C.
• Its upper surface opposite the sensor 2 is irregular, has numerous local roughness and reliefs such as oscillation wrinkles of the ingot mold or islets of scale, as well as, if necessary, long surface defects to be detected such as cracks.
• the system 2 includes a sensor 10, a sensor control unit 12 and a pump 14 for cooling fluid delivery.
• the sensor 10 is able to detect conductivity faults on the surface of the slab 4 using eddy currents.
• the operating principle of such a sensor being known, it will not be detailed here.
• the reader can refer to European patent application EP 0 195 794 for more information on the principles implemented in such sensors.
• the sensor 10 has the shape of a rectangular parallelepiped oriented perpendicularly to the direction of movement F and of which one face (called “active face” because the measurement cells are flush with the surface) is arranged parallel to the surface of the slab 4.
• This sensor 10 is placed so that its active face overlaps the edge of the slab 4 "on horseback" so as to be sure that it can always inspect the extreme edge, even if the moving product would suffer slight lateral deviations during its movement.
• the active face of the sensor 20 is formed by a sole 20 in which are housed measurement cells 21. The bottom surface of this sole 20 is shown in FIG. 3.
• This sole 20 comprises, by way of illustration, two identical rows 22 and 24 of measurement cells 21 all identical to each other. These two rows are located parallel to each other in the length direction of the sensor 10. These rows 22 and 24 are also arranged as close to each other as possible so that their respective cells are placed next to each other and touch at least on one side. To simplify the illustration, only six measurement cells 21 have been shown in each row. In reality, a row can have up to thirty two cells or more.
• the cells of row 22 are designated in order and starting from the bottom upwards respectively by the references Cl, C3, C5, C7, C9 and Cl 1.
• the cells of row 24 are designated in order and starting from the bottom up respectively by the references C2, C4, C6, C8, C10 and C12.
• Each of the measurement cells 21 is adapted to be configured, under the control of the unit 12, either as an emitting cell or as a receiving cell.
• the cell 21 is configured as an emitting cell, the latter is capable of creating eddy currents in the surface of the slab 4.
• each cell comprises a coil 26 supplied by an alternating current. The axis of this coil 26 is perpendicular to the active face of the sensor 10.
• the cell When the cell is configured as a receiving cell, the latter is capable of detecting eddy currents present in the surface of the slab 4 in the case, and only in the case where the eddy currents created by the transmitting cell have been deflected towards the receiving cell by a surface defect which propagates from one to the other, according to the principle explained in EP 0 195 794 already mentioned.
• the coil 26 forms a closed electrical circuit used to detect electromagnetic fields.
• the contiguous cells of rows 22 and 24 are also able to be mounted in differential with one another on the two rows so as to be free from measurement or detection errors due to surface irregularities of slab 4, like swing wrinkles.
• the cel- The cells in each row 22 and 24, configured as receiving cells, are capable of generating signals for detecting a surface defect, of opposite polarities. This has the consequence that when a receiving cell of row 22 detects a fault, it generates a signal, for example, of positive polarity, while the corresponding receiving cell of row 24 generates a detection signal of negative polarity when it detects the same fault.
• the cells 21 are contiguous and the coils 26 of the adjoining cells are separated from each other by an edge to edge spacing X of less than 0.5 mm and preferably about 0.2 mm. This proximity of the different windings 26 ensures almost continuous scanning and inspection of the surface of the slab over the entire length of the rows 22 and 24.
• the cells 21 are shaped square as well as their internal winding 26. In addition, to detect surface defects or cracks whose length hardly exceeds 4 millimeters, each of these windings has a square section of 4 x 4 mm 2 .
• the sensor 10 is also equipped with a device 30 (FIG. 2) for cooling the sole 20.
• This device 30 comprises a circuit 32 for circulating a cooling fluid. This circuit 32 descends along a vertical wall 36 of the sensor 10, passes below the sole 20 and rises again along another vertical wall 38 of the sensor 10.
• the device 30 comprises a rectangular blade 40 disposed opposite and parallel to the sole 20 so as to protect the measurement cells.
• This blade is, for example, made of ceramic material so as to be permeable to the electromagnetic waves generated and received by the coils 26 of the different measurement cells.
• This blade 40 is, for example, spaced about 1 millimeter from the surface of the sole 20. It is held in position by two horizontal tabs 42 and 44 fixed along its long sides. The legs 42 and 44 are intended to slide on the surface of the slab 4 and act as pads. These horizontal tabs 42 and 44 are each secured to a vertical metal plate 46 and 48 respectively.
• the plates 46 and 48 extend along the walls 36 and 38 of the sensor 10. They are spaced apart from the vertical walls 36 and 38 so to provide space for the passage of the circuit 32. In order to resist heat, the legs 42 and 44 as well as the plates 46 and 48 are, for example, made of stainless steel.
• the thicknesses of the legs 42 and 44 as well as the thickness of the blade 40 and the thickness of the circuit 32 below the sole 20 are chosen so that the height H separating the sole 20 from the upper surface of the slab 4 is greater than or equal to three millimeters and preferably greater than 4 millimeters.
• the arrows shown in circuit 32 indicate the direction of circulation of the cooling fluid.
• the coolant is water.
• Each ex- end of the circuit 32 is connected to the pump 14 suitable for circulating the cooling fluid in the circuit 32.
• the control unit 12 is a multiplexer capable of individually controlling each of the cells of the sole 20. This control unit is, for example, produced from a conventional programmable electronic computer associated with a memory 50 comprising instructions for the execution of the method of FIG. 4.
• the slab 4 runs flat under the sensor 10 in the direction of the arrow F.
• an edge crack 6 arrives under the sole 20
• one of the cells of the row 24 detects this crack and generates a corresponding signal.
• the crack 6 is detected by at least one of the cells of the other row 22, which also generates a corresponding signal, but of opposite polarity.
• the operation of the sensor 10 controlled by the multiplexer 12 is divided into numerous time windows, each time window corresponding to a predefined time interval. In each time window, only a pair of cells in row 22 and a pair of cells in row 24 are controlled, while all the other cells in rows 22 and 24 are inactive.
• the control unit 12 proceeds as follows. During a first time window, the unit 12 configures, in a step 60, the cells C1 and C2 as emitting cells so that these generate eddy currents in the upper surface of the slab 4. At the same time, the unit 12 configures cells C5 and C6 so that they detect eddy currents in the surface of the slab 4. By thus controlling the sensor 10, the emitting and receiving cells are spaced from one another by an inactive cell, in this case cells C3 and C4.
• the edge-to-edge spacing between the emitting and receiving cells is therefore greater than four millimeters. It has been found experimentally that the height at which the sole 20 can be placed relative to the surface of the slab 4 increases in proportion to the edge-to-edge spacing between the emitting cells and the receiving cells. Thus, by providing, in step 60, a spacing between the emitting and receiving cells of at least four millimeters, the operation of the sensor 10 is not degraded while the latter is placed about three millimeters from the surface in which one seeks to detect faults.
• step 62 the unit 12 configures, during a step 62, the cells C3 and C4 and the cells C7 and C8 so that that cells C3 and C4 work at the same time as emitting cells, while cells C7 and C8 work at the same time as receiving cells.
• the other cells and in particular, the cells previously ordered that is to say the cells C1, C2, C5, C6, are rendered inactive.
• step 62 is repeated during a step 64 by shifting the controlled cells by one cell upwards. Consequently, during this step 64, it is the cells C5 and C6 which work as emitting cells and the cells C9 and CIO which work as receiving cells.
• step 66 identical to the previous ones except that it is the cells C7, C8, C11 and C12 which are controlled. Then, the method returns to step 60. Steps 60, 62, 64 and 66 are repeated as long as the system 2 is operating. It can thus be seen that by shifting the cells ordered during each of the steps 60, 62, 64 and 66 by one cell, it is possible to scan the whole of the surface portion of the slab with respect to the sole 20 with a high resolution, since the section of the cells is of the order of 4 mm 2 , and without thereby displacing the sensor 10.
• the emitting cells and receptors on the same row can be separated from one another by one, two, three, four or five inactive cells. It is also possible to increase the detection capabilities of the device by providing a number greater than two of rows of cells. In addition, the rows of cells do not have to be contiguous. A spacing can be provided between them.
• System 2 has been described in the particular case where it is placed in an environment where the temperature can be above 550 ° C. The same system can of course also be used to inspect a slab at room temperature. In this variant, the device 30 for cooling the sole is no longer useful and can therefore be omitted.
• each winding may have an oblong or even exactly rectangular section, the small and the long side of this rectangle having a length of between 2 and 10 mm.

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• Chemical & Material Sciences (AREA)
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• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)
• Continuous Casting (AREA)

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• 2003
  • 2003-11-18 FR FR0313498A patent/FR2862384B3/fr not_active Expired - Lifetime
• 2004
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