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
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/12—Measuring magnetic properties of articles or specimens of solids or fluids
  • G01R33/1223—Measuring permeability, i.e. permeameters

Definitions

• the present invention relates to the determination of the magnetic component content, for example ferrite, of a material.
• the determined content of magnetic component is arbitrary and relative and does not necessarily correspond to the content of real or absolute magnetic component. For this reason, we will speak of a magnetic component index and not a percentage of magnetic component to express the determined content of it.
• Ferrite, magnetic phase is inserted into austenite, stainless phase and not magnetic.
• Various methods of determining the ferrite index have already been proposed, based on the magnetic effects of the ferritic phase.
• the most widely used device using a destructive method is called a sigmameter. This device measures the average ferrite index from the magnetic saturation of a sample, of known mass.
• the first group makes it possible to determine the index from static permeability using a device called magnégage. This device exploits the fact that the magnetic force of a permanent magnet on the material to be analyzed is a function of the ferrite index. The volume observed is a few mm 3 in the vicinity of the surface.
• the second group makes it possible to determine the index from the dynamic permeability.
• the devices of the second group exploit the fact that the magnetic induction produced in the material is a function of the index.
• the measurements are very superficial and vary with the thickness of the coating analyzed.
• the present invention now proposes a method and a device which make it possible to solve the problem defined above, and which allow an analysis of the index of magnetic component, in particular of ferrite, in situ, in three dimensions from the surface of the object to be analyzed and for depths up to 1 cm.
• a weighting coefficient H n defined in step iii) and associated with a given elementary function equal, a summation of parameters h n p representative s of the respective contribution of each layer p to the generation of said elementary function given in the signal and determined on standard samples receiving the known predetermined cycle of excitation, weighted respectively by the sought indices m p by magmetic component of the layers.
• the weighting coefficients H n defined in step iii) are the Fourier coefficients of harmonics of odd rank.
• the response detected in step ii) mentioned above and broken down in step iii) preferably consists of the derivative with respect to time of the flux of the magnetic field created by the material through a induced coil.
• steps i) to iv) are repeated for a plurality of excitation values.
• the determination, using standard samples of the same magnetic characteristic, that is to say of the same hysteresis cycle B (H) for the same index, as the material to be studied, parameters representative of the respective contribution of each layer to the generation of a given elementary function in the detected signal, used in step iv) comprises the steps consisting in: a) exciting, according to a known predetermined cycle , a standard structure formed of a plurality of superimposed layers of known index in magnetic component, using a probe, b) detecting, using the probe, the resulting magnetic induction produced in response by the structure, c) decomposing into elementary functions a signal derived from the response detected in step b) to define respective weighting coefficients H provisiontalon of the elementary functions intervene nant in the generation of said signal, d) repeat steps a), b) and c) after modifying the index by magnetic component of one of the layers of the standard structure, and e) determining the value of said parameters tr en solving a
• a magnetic probe able to excite the structure of the material according to a known predetermined cycle and to detect the resulting magnetic induction produced in response by the material
• decomposition means capable of decomposing into elementary functions a signal derived from the response detected by the probe to define respective weighting coefficients H n of the elementary functions involved in the generation of said signal and
• H n Zm p h p n
• H n Zm p h p n
• the probe comprises an inductor coil creating an alternating excitation field and two secondary detection coils placed symmetrically in the vicinity of the axial ends of the induction coil.
• the aforementioned determination device further comprises means for supplying the induction coil by capacitive discharge.
• the device for determining the indices of magnetic component advantageously comprises means capable of repeating the process of analysis of indices by magnetic component of the various superposed layers of the material for a plurality of excitation values.
• the determination device preferably comprises means able to move the magnetic probe over the structure of the material and to repeat the analysis process in synchronism.
• FIG. 1 represents a schematic view in the form of functional blocks of a determination device in accordance with the present invention
• FIG. 2 schematically illustrates, and in enlarged view, the structure of a probe used in the device according to the present invention
• FIG. 3 schematically represents, as a function of time, the shape of the excitation current applied to the induction coil
• FIG. 4 represents the magnetic induction B in a material as a function of the excitation H
• FIG. 5 represents, as a function of time, the derivative of the magnetic induction for a low excitation value H, in the range of linear variation of the induction as a function of the excitation.
• FIG. 6 also represents, as a function of time, the derivative of induction B, but for a higher excitation value H, beyond the range of linear variation between induction B and excitation H, - the FIG. 7 represents another general schematic view in the form of functional blocks of the determination device in accordance with the present invention and illustrates in particular various options of the device,
• FIG. 8 represents in the form of a schematic flow diagram the analysis method in accordance with the present invention, and
• the magnetic component content, in particular the ferrite content, in accordance with the present invention are based on 3 main components: - a magnetic probe with small differential measurement with spatial excitation gradient and maximum excitation illustrated in particular in figure 2,
• FIG. 1 shows a magnetic probe 100 placed opposite a weld bead C to be analyzed, and means for analyzing the signal generated by the measurement probe 100, bearing the general reference 200.
• the magnetic probe 100 makes it possible to excite the structure of the material C to be analyzed and to record a hysteresis cycle of the excited material.
• the probe 100 comprises an inductor coil 101 generally cylindrical of revolution, the longitudinal axis of which is referenced 102.
• the inductor coil 101 is connected to a generator 201 belonging to the analysis means 200 to create an alternating excitation field on the material C to be analyzed, for example in the form of half-sinusoids each having a period of 20 msec.
• the generator 201 can be adapted to supply the probe 100 by capacitive discharge.
• the amplitude of the excitation current applied by the generator 201 to the induction coil 101 can vary from one ampere to several hundred amperes.
• the probe 100 also comprises two secondary detection coils 103, 104 placed symmetrically in the vicinity of the axial ends of the induction coil, coaxial with the axis 102 above.
• the induced coils 103, 104 are connected in opposition so that when no magnetic material is close to the probe 100, the total potential difference taken across the induced coils 103, 104 remains zero.
• the presence of a magnetic substance C in the vicinity of one of the induced coils 103, 104 unbalances the assembly and creates an electromotive force characteristic of the material, as a function of the excitation current in the coils 103, 104 connected in series.
• the probe 100 in the form of a zero device by placing on the upper induced coil 104, or the coil opposite to the material C to be analyzed, a homogeneous standard 105, schematically illustrated in FIG. 2, of index equal to the index of the material C to be analyzed, more or less 5.
• the generator 200 is adapted to modulate the amplitude of the sinusoidal excitation current applied to the induction coil 101 and schematically illustrated in FIG. 3 to create an alternating excitation field composed of half-periods of sinusoids of amplitude variable.
• the excitation in the axis 102 of the probe reaches the Tesla in the vicinity of the induced coils 103, 104.
• the induced field produced by the amperes of the magnetic material C creates an electromotive force alone detected by the induced coils 103, 104 connected in series .
• the low frequency of 50 Hz preferably chosen as the excitation frequency, makes it possible to attenuate the eddy currents, the amplitude of which is also low due to the high resistivity of stainless steels.
• the central volume of the induction coil 101 contains only air, so that the probe does not contain magnetic material in order to obtain a sinusoidal excitation excitation without generation of harmonics.
• the induction coil 101 can have an internal diameter of the order of 2 mm and include around 120 turns.
• the signal detected at the terminals of the induced coils 103, 104 connected in series is applied to a variable gain instrumentation amplifier, preferably integrated into the probe, referenced 202 in FIG. 1.
• This amplifier 202 is preferably followed by an analog / digital converter. As shown in FIG. 4, and as is well known to those skilled in the art, for a ferromagnetic material, for example ferrite, the relationship between the excitation H and the magnetic induction B is not linear for high values of excitation. The signal detected at the terminals of the induced coils
• FIGS. 5 and 6 corresponds to the derivative with respect to time of the magnetic field induced by the magnetic material C to be analyzed.
• the regime is no longer linear and the response is periodic with a generation of harmonics of odd rank all the more important as the excitation H is stronger, as shown schematically in the figure 6 attached.
• the excitation field is greater than in depth.
• the amperians in the upper layers produce more harmonic responses than those in the deeper layers, the response of which tends to become sinusoidal.
• the resulting excitation is the excitation produced by the amperes inducing turns increased by that produced by the amperians.
• the excitement produced by the Amperians is sensitive for an index greater than 10.
• the analysis process according to the present invention is based on the fact that after decomposition into elementary functions of the response of a given material to an excitation generated by the induction coil 101, the respective weighting coefficients (Fourier coefficients) H n of said elementary functions can be expressed in the form of a summation of parameters h p n representative of the respective contribution of different superimposed layers of the material (as referenced 0, 1, 2, ... p ... r on the bottom of FIG. 2) on the generation of said elementary function, weighted respectively by the indices m p by magnetic component of the layers.
• the standard samples used for the determination of the tr parameters can be, for example, secondary molten metal standards usually used for the calibration of ferrite measuring instruments and prepared for example for commission II of the IIS by the Welding Institute (United Kingdom). -United Kingdom) and VEWBöhler- (Austria). These samples have the same hysterisis B (H) cycle as the material to be studied for a leading index.
• H hysterisis B
• the first step 21 0 of the method consists in placing the probe 1 00 on a standard sample of known index x.
• the structure of the standard sample is then excited as illustrated diagrammatically in FIG. 8 by step 21 1 using the probe 1 00.
• the coils 1 03, 1 04 allow the measurement of the resultant magnetic induction response produced by the structure (step 21 2 in FIG. 8).
• the analysis means 200 then allow, as illustrated in step 21 3 in FIG. 8, the decomposition of the response by Fourier transform formed to obtain the non-standard Fourier H coefficients which constitute the respective weighting coefficients of the elementary functions. involved in the generation of the response produced by the standard sample tested.
• steps 211, 212 and 213 can be repeated for a predetermined number of excitations Y, by modifying, with each cycle of excitation 211 and measurement 212, the amplitude of the excitation current applied to the coil inductor 101 (steps 214 and 215).
• the above steps 211 to 215 allow, for a given excitation value, using the Fourier coefficients H 1 and H 3 weighting the harmonics 1 and 3 respectively, to describe the following relationships: (3)
• x represents the known index of the magnetic component in the standard sample
• the parameter h 1 1 represents the contribution of the surface layer 1 of the standard sample to the generation of the harmonic 1
• the parameter represents the contribution of the layer deep 2 to the generation of the same harmonic 1
• the parameter represents the contribution of the layer superficial 1 to the generation of harmonic 3
• the parameter represents the contribution of the layer deep 2 to the generation of harmonic 3.
• the standard sample is then moved away from the probe 100 by a step equal to the thickness of the above-mentioned surface layer 1, before resuming the steps
• steps 216 and 217 in FIG. 8 it is necessary to repeat p times the cycle of steps 211 to 215 by moving between each cycle the sample relative to the probe 100 by a step equal to the thickness of the layers considered, to obtain systems of equations similar to equations (3), (4), (5) and (6) above allowing the parameters h p n to be determined .
• step 218 is followed by step 219 during which the parameters h p n are stored.
• the parameters h p n being able to be introduced permanently by the manufacturer in a mass memory 203 of the analysis means 200.
• the previously described process for determining the parameters h p n applies the state superposition theorem and assumes that the index of the standard samples is low, for example less than 10.
• the superposition theorem is applicable after linearization around an experimentally defined average value, which amounts to saying that we only consider variations around of a determined average index.
• the standard sample when moving the standard sample relative to the probe 100, illustrated by step 217 in FIG. 8, it is advisable not to leave free the space defined between the standard sample and the probe, but to fill this space with standard samples having a known index different from that used during the first test.
• the actual analysis process of the magnetic component content of a material corresponds to the steps referenced 220 to 228 in FIG. 8, insofar as, as mentioned above, the parameters h p n can be permanently stored in a mass memory 203 of the analysis means 200.
• the analysis process begins with the placement of the probe 100 on the part C to be analyzed, as illustrated in step 220 in FIG. 8.
• the probe 100 can for example be placed facing a weld bead C, the longitudinal axis 102 of the induction coil 101 extending transversely to the main outside surface of the weld bead C.
• the generator 201 then applies an excitation current to the induction coil 101 to excite the structure of the material C as illustrated in step 221 in FIG. 8.
• the induced coils 103, 104 detect the resulting magnetic response-induction produced by the material C, as illustrated in step 222 in FIG. 8.
• the analysis means 200 then proceed decomposing the detected response to define the respective weighting coefficients H (Fourier coefficient) of the elementary functions (harmonics of odd rank) involved in the generation of said signal (step 223).
• H Frier coefficient
• the cycle of steps 221, 223 can be repeated z times, by modifying for each cycle the amplitude of the excitation due to the probe 100.
• H 1 and H 3 represent the weighting coefficients Fourier coefficients determined in step 223, and - the parameters represent the parameters previously determined on the basis of equations (3), (4), (5) and (6) using standard samples.
• fine discretization can be carried out by cutting the material C to be tested in an area of 0.5 to 1 mm thick, the last area r being assumed to be formed of a homogeneous background.
• the position of the latter zone can vary for example from 0.5 to 1 cm.
• an automatic scanning of the probe 100 on the surface of the material C to be analyzed to allow a 3-dimensional analysis of the latter by correlating a result of the various measurement points.
• This automatic scanning is illustrated diagrammatically in FIG. 8 by the test step 226 which, if it is positive, induces a repetition of the steps 221, 222, 223, 224, 225 and 227 mentioned above.
• Such an automatic scanning of the probe allowing a 3-dimensional analysis is particularly advantageous in the case of the transverse analysis of the weld beads, in stainless steels for example, where the weld bead generally has a low index compared to the index of surrounding welded elements.
• the final stage of the analysis process consists in visualizing the indices m p , as illustrated in stage 228 in FIG. 8.
• the analysis means 200 illustrated in the figures can consist of conventional calculation means per se and will not be described in detail below. However, as is shown diagrammatically in FIG. 1, it will be noted that these analysis means 200 can include data management cards 204, managed by microprocessor, connected at the output of amplifier 202 and interacting with generator 201, output management cards 205 also managed by microprocessor, mass memory 203 and a keyboard 206 allowing the introduction of factors by the user.
• the results can be recorded on cassettes 207 and viewed on screen 208 as illustrated diagrammatically in FIG. 1.
• Analysis means 200 generally similar to those illustrated in FIG. 1 are represented in FIG. 7. However, on the latter, we see the analog-digital converter 209 interposed between the amplifier 202 and the data management card 204.
• a first option of this system as shown at the top right in FIG. 7 may consist of a microcomputer 230 comprising for example a floppy drive 231, a screen 232 and a keyboard 233.
• Two other options illustrated at the bottom right in FIG. 7 can be formed by a cassette player 234 and a plotter 235.
• a fourth option illustrated at the top left in FIG. 7 can be formed by a set of various probes comprising standards 105 of homogeneous index. known on the upper induced coil 104. This standard 105 makes it possible to increase the accuracy of the measurements in the case of strong indices, for example greater than 25, by transforming the analyzer into a zero device.
• a fifth option illustrated at the bottom left in FIG. 7 can be formed by a displacement sensor sensitive to the displacements of the probe 100 on the material C to be tested to allow a 3-dimensional analysis.
• the present invention is in no way limited to the embodiments which have just been described, but extends to any variant in accordance with its spirit.
• FIG. 9 represents the results of determination of indices on a sample of stainless steel plating on a ferrite bottom. Comparison of the appearance of the hatched area obtained in accordance with the present invention with respect to the rectilinear area obtained by means of devices conventional shows clearly the fineness of the measurement obtained through the analysis process according to the present invention.
• FIG. 10 represents the results of analysis on a sample of stainless steel plating with a thickness of 9.1 mm.
• FIG. 11 and FIG. 12 represent the results of two analyzes carried out on a stack of secondary standards from the Welding Institute.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Electrochemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=9320776

Family Applications (1)

Country Status (3)

Families Citing this family (10)

Family Cites Families (3)

• 1985
  • 1985-06-28 FR FR8509891A patent/FR2584190B1/fr not_active Expired
• 1986
  • 1986-06-26 WO PCT/FR1986/000227 patent/WO1987000293A1/fr unknown
  • 1986-06-26 EP EP19860904199 patent/EP0227767A1/de active Pending

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events