JP6446304B2 - Magnetic characteristic evaluation method and magnetic characteristic evaluation apparatus - Google Patents

Description

  The present invention relates to a magnetic property evaluation method and a magnetic property evaluation device, and more particularly to an evaluation method for evaluating the magnetic properties of a magnet material after magnetization in an unmagnetized state and a device used therefor. .

  Magnets having excellent magnetic properties such as high residual magnetic flux density have been developed centering on rare earth magnets (for example, Patent Document 1). This type of magnet is often inconvenient to handle in a magnetized state due to its high magnetic properties, and the manufacturer ships it from a factory etc. in an unmagnetized state. Are generally magnetized after acquisition. Generally, even if magnet materials are manufactured by the same method using the same materials, the magnetic characteristics after magnetization will inevitably vary. When a manufacturer ships from a factory or the like, it is required to select a magnet product that exhibits a predetermined range of magnetic characteristics after magnetization from a range of variations.

  Conventionally, because of the necessity of evaluating the magnetic characteristics after magnetization, even a magnet material that is shipped in an unmagnetized state has been magnetized by the manufacturer. For example, Patent Document 2 discloses a method of measuring a magnetic flux density distribution of a magnetized ferromagnetic material with an apparatus including a Hall element array.

  In this way, when magnetic properties are evaluated by magnetizing a magnet material to be shipped in an unmagnetized state, usually a portion of all products are extracted and magnetized, and the magnetic properties are inspected. Do. The majority of products that were not subject to sampling inspection are shipped without being evaluated for magnetic properties after magnetization.

Japanese Patent Laid-Open No. 11-329810 JP 2013-245958 A

  As described above, in the magnet material to be shipped without being magnetized, when magnetic and magnetic properties are evaluated by sampling inspection, a predetermined magnetic property is obtained after magnetization in an individual subjected to sampling inspection. Even in such a case, there may occur a situation in which a predetermined magnetic characteristic is not exhibited after magnetization in an individual that has not actually undergone a sampling inspection that has been shipped or the like. Thus, it is difficult for a manufacturer to select and ship a magnet material that stably exhibits good magnetic characteristics after magnetization in an unmagnetized state.

  Therefore, instead of sampling inspection, it is conceivable to magnetize all products to be shipped, evaluate magnetic characteristics, and select non-defective products. In this case, the product after inspection is demagnetized before shipment. As described above, it is not practical to ship all products through the steps of magnetization, inspection, and demagnetization, which requires a lot of time, labor and cost.

  The problem to be solved by the present invention is to provide a magnetic property evaluation method and a magnetic property evaluation device that can easily evaluate magnetic properties expressed by a magnet material.

  In order to solve the above-described problems, the magnetic property evaluation method according to the present invention has not yet performed electromagnetic induction measurement in which an induced current is generated in a sample by an alternating magnetic field, the induced current is detected by synchronous detection, and a synchronous detection signal is obtained. An evaluation sample measurement process executed for an evaluation sample made of a magnetized magnet material, and a standard sample measurement for performing the electromagnetic induction measurement on a plurality of unmagnetized standard samples formed in the same manner as the evaluation sample A magnetic property value measuring step of magnetizing the plurality of standard samples and measuring a magnetic property value, a synchronous detection signal obtained by the standard sample measurement for the plurality of standard samples, and the magnetic property Obtained for the evaluation sample in the evaluation sample measurement step based on the corresponding step for estimating the relationship between the magnetic property values obtained in the value measurement step and the relationship estimated in the corresponding step Synchronous detection signal Al, is summarized in that with an evaluation step of estimating the magnetic characteristic values of the evaluation sample. Detection of the induced current by synchronous detection can be easily performed by measuring the magnetic flux generated by the induced current as an electromotive force of a detection coil (or a coil also serving as an excitation coil for generating the alternating magnetic field). .

  Here, the magnetic measurement value is preferably a magnetic flux amount.

  The alternating magnetic field is generated by passing an alternating current through the exciting coil, and the induced current is an alternating current that flows through the exciting coil through a current that is also used as the exciting coil or separated from the detecting coil by electromagnetic induction. It is preferable to use the value of the real part of the signal detected by synchronous detection with current as a reference and detected by the synchronous detection as the synchronous detection signal in the corresponding step and the evaluation step.

  In the corresponding step, the range of the synchronous detection signal corresponding to the magnetic characteristic value in a predetermined range is set as a non-defective range, and in the evaluation step, if the synchronous detection signal of the evaluation sample is in the non-defective range, The evaluation sample may be evaluated as a good product.

  The magnet material may be a magnet material for a hot work magnet.

  An apparatus for evaluating magnetic characteristics according to the present invention includes a magnetic field generating means for generating an alternating magnetic field and applying the alternating magnetic field to the sample, and an induced current detecting means for detecting the induced current generated in the sample by synchronous detection. The gist is to execute such a magnetic property evaluation method.

  In the magnetic property evaluation method according to the above invention, a standard sample that is not an object for evaluating magnetic properties is magnetized and the magnetic properties after magnetization are measured. The evaluation sample, which is the object for evaluating the magnetic characteristics, is not magnetized, but is only subjected to electromagnetic induction measurement in an unmagnetized state. Based on the relationship between the magnetic properties after magnetization obtained using the standard sample and the synchronous detection signal in the electromagnetic induction measurement in the non-magnetized state, from the synchronous detection signal obtained in the evaluation sample, The magnetic properties of the evaluation sample after magnetizing are estimated. In this way, the magnetic properties after magnetization can be easily evaluated for an evaluation sample made of an unmagnetized magnet material without performing magnetization before evaluation or demagnetization after measurement. Since all products shipped from factories can be evaluated without requiring large costs and long time, unlike the case of sampling inspection, even if there are fluctuations in manufacturing conditions etc. A non-defective product exhibiting a predetermined magnetic property after magnetism can be selected with high accuracy and used for shipment or the like.

  Here, when the magnetic measurement value is the amount of magnetic flux, the magnetic characteristic value shows a good correlation with the synchronous detection signal, so that the magnetic characteristic of the evaluation sample can be evaluated with high accuracy.

  In addition, an alternating magnetic field is generated by flowing an alternating current through the exciting coil, and an induced current is a current that flows through the induction coil in a separate detection coil that is also used as the exciting coil or the alternating current that flows through the exciting coil. When the value of the real part of the signal detected by the synchronous detection is used as the synchronous detection signal in the corresponding process and the evaluation process, the induced current flowing through the sample can be simply detected synchronously. can do. The real part value thus obtained shows a better correlation with the magnetic property value than the imaginary part value and absolute value. Therefore, by using the real part value as an index, the evaluation sample Can be evaluated with high accuracy.

  Then, in the corresponding step, the range of the synchronous detection signal corresponding to the magnetic characteristic value in the predetermined range is set as a non-defective range, and if the magnetic characteristic value of the evaluation sample is in the non-defective range in the evaluation step, the evaluation sample is regarded as a non-defective product. In the case of evaluation, a non-defective product having a magnetic property value in a desired range can be easily selected from a large number of individual magnetic materials, and can be used for shipment or the like.

  When the magnet material is a magnet material of a hot-worked magnet, a uniform magnetic material is easily formed by hot working, so there is a good correlation between the magnetic characteristics and the synchronous detection signal in electromagnetic induction measurement. Is obtained. Thereby, the magnetic characteristics of the evaluation sample can be evaluated with high accuracy.

  If the magnetic characteristic evaluation apparatus concerning the said invention is used, the above magnetic characteristic evaluation methods can be applied, and the magnetic characteristic of a magnet material can be simply evaluated with the state which is not magnetized.

It is sectional drawing which shows the outline of the electromagnetic induction measuring apparatus with which the magnetic characteristic evaluation apparatus concerning one Embodiment of this invention is equipped. (A) is the direction along the axis | shaft of a test | inspection coil, (b) has shown the cross section of the direction perpendicular | vertical to the axis | shaft of a test | inspection coil. It is a block diagram which shows the signal processing in the said electromagnetic induction measuring apparatus. It is sectional drawing of the direction along the axis | shaft of a test | inspection coil which shows the detail of an electromagnetic induction measuring apparatus. It is sectional drawing which shows the outline of the electromagnetic induction measuring device concerning another example, (a) is the direction along the axis | shaft of a test | inspection coil, (b) has shown the cross section of the direction perpendicular | vertical to the axis | shaft of a test | inspection coil. It is a figure which shows an example of the relationship between the real part of the synchronous detection signal in a standard sample, and the magnetic flux amount after magnetization.

  Hereinafter, a magnetic property evaluation method and a magnetic property evaluation device according to embodiments of the present invention will be described with reference to the drawings.

[Magnetic property evaluation equipment]
The magnetic property evaluation apparatus according to an embodiment of the present invention includes an electromagnetic induction measuring apparatus 1 that performs electromagnetic induction measurement on a sample S that is not magnetized. 1 and 2 simply show the configuration of an electromagnetic induction measuring apparatus 1 according to an embodiment of the present invention.

  As shown in FIG. 1, an electromagnetic induction measuring apparatus 1 provided in a magnetic property evaluation apparatus according to an embodiment of the present invention includes an inspection coil 10 that is a combination of an excitation coil 11 and a detection coil 12. The exciting coil 11 is formed of a substantially cylindrical coil that can be disposed by passing a substantially cylindrical sample S through the hollow portion, and functions as a magnetic field generating means. The detection coil 12 is a substantially cylindrical coil disposed coaxially with the excitation coil 11 inside the excitation coil 11, and functions as an induced current detection means. Such a detection device having the excitation coil 11 and the detection coil 12 coaxially and based on the principle of electromagnetic induction is also used as an eddy current flaw detection device, and the conventional eddy current flaw detection device is diverted as the electromagnetic induction measurement device 1. You can also

  In the electromagnetic induction measuring apparatus 1, an alternating current is passed through the exciting coil 11 by an oscillator 21 as shown in FIG. The current flowing through the detection coil 12 is amplified using the amplifier 22 and then input to the synchronous detection circuit 23 as a detection current. The reference signal is input to the synchronous detection circuit 23 as two reference signals: an output from the oscillator 21 and a signal in which the output from the oscillator 21 is passed through a 90 ° phase shifter 24 and the phase is shifted by 90 °. To do.

  In the synchronous detection circuit 23, the detection current input from the detection coil 12 via the amplifier 22 is synchronously detected (phase detection) with reference to the alternating current passed through the excitation coil 11. Specifically, by processing the waveform of the detected current by multiplying the current waveform of each of the two reference signals, the current component and the imaginary part of the detected current, that is, the current component in phase with the alternating current used for excitation ( The resistance component) is separated from the current component (reactance component) that is 90 ° out of phase, and is detected as a synchronous detection signal. Furthermore, the absolute value (amplitude) and phase difference of the detected current can be calculated from the values of the real part and the imaginary part. The amplifier 22, the synchronous detection circuit 23, and the phase shifter 24 may be integrated as a lock-in amplifier or the like.

  As will be described later, the sample S to be subjected to electromagnetic induction measurement by the electromagnetic induction measuring apparatus 1 is an evaluation sample and a standard sample, and both are made of an unmagnetized magnet material. When an alternating current is passed through the exciting coil 11 with such a sample S placed in the exciting coil 11, an alternating magnetic field is generated in the hollow portion of the exciting coil 11. Then, when the AC magnetic field is applied to the sample S, an induced current (eddy current) is generated on the surface of the sample S. Further, an induced magnetic field is formed by the induced current, and the induced current flows through the detection coil 12 by the induced magnetic field. The induced current flowing through the detection coil 12 is synchronously detected by the synchronous detection circuit 23 as a detection current.

  FIG. 3 shows a specific structure of the electromagnetic induction measuring apparatus 1 briefly described above. In the electromagnetic induction measuring apparatus 1 of FIG. 3, the inspection coil 10 is fixed to the tip of the support portion 17 that is erected on the gantry 16. Further, a positioning jig 13 made of an insulating material such as resin is erected on the gantry 16 so as to be coaxial with the inspection coil 10. The positioning jig 13 has a substantially cylindrical insertion portion 13a at the tip. The insertion portion 13a has an outer diameter slightly smaller than the cylindrical inner diameter of the sample S. Furthermore, the positioning jig 13 has a retaining portion 13b having an outer diameter larger than the inner diameter of the sample S on the proximal end side of the insertion portion 13a. The position of the tip of the retaining portion 13b (the boundary between the insertion portion 13a and the retaining portion 13b) substantially coincides with the position where the lower end of the sample S reaches when the sample S is arranged at the center in the axial direction of the inspection coil 10. ing.

  Further, an elevating device 15 such as an air cylinder is fixed to the gantry 16 outside the positioning jig 13. And the magnet protrusion jig | tool 14 is connected with the raising / lowering apparatus 15, and the magnet protrusion jig | tool 14 is raised / lowered by the raising / lowering apparatus 15 in the up-down direction (direction along the axis | shaft of the test | inspection coil 10). The magnet protruding jig 14 is formed in a cylindrical shape having an inner diameter slightly larger than the outer diameter of the retaining portion 13 b of the positioning jig 13. In the state where the magnet protruding jig 14 is lowered by the elevating device 15, the position of the tip is substantially coincident with the position of the tip of the retaining portion 13 b of the positioning jig 13. FIG. 3 shows a state where the magnet protruding jig 14 is lowered.

  With the configuration as described above, the sample S is attached to the positioning jig 13 so that the tip of the insertion portion 13a penetrates the cylindrical portion of the sample S as shown in FIG. Is lowered by the lifting device 15, the sample S has a retaining portion of the positioning jig 13 in the hollow portion of the inspection coil 10 at the center position in the axial direction and the direction perpendicular to the axis of the inspection coil 10. 13b and the end surface of the magnet protruding jig 14 are stably supported. Thereby, it is possible to reduce the influence of the mismatch of the position of the sample S for each measurement and the temporal variation of the sample position during the measurement, and to perform the electromagnetic induction measurement with high accuracy and reproducibility. On the other hand, in a state where the positioning jig 13 is raised by the lifting device 15, the sample S comes out of the hollow portion of the inspection coil 10 and is placed above the inspection coil 10. Thereby, attachment of the sample S to the electromagnetic induction measuring apparatus 1 and replacement | exchange of the sample S can be performed easily. Since the attachment and replacement of the sample S can be automated, it is easy to automatically perform electromagnetic induction measurement sequentially for each individual mass-produced magnet material.

  As described above, the electromagnetic induction measuring apparatus 1 detects an induced current generated in the sample S by applying an AC magnetic field to the sample S, and diverts the measurement unit of a conventional general eddy current flaw detector. be able to. The present invention is not limited to the same configuration as that of the electromagnetic induction measuring apparatus 1, and any apparatus can be applied as long as it can generate an alternating magnetic field and synchronously detect the induced current generated in the sample S by the alternating magnetic field.

  For example, in the electromagnetic induction measuring apparatus 1, the measurement was performed by passing the substantially cylindrical sample S through the hollow portion of the inspection coil 10 including the substantially cylindrical excitation coil 11 and the detection coil 12. If the inspection coil 10 is plate-shaped, the inspection coil 10 may be formed into a flat and substantially rectangular tube shape, and the sample S may be passed through the inspection coil 10. Thus, the shape of the inspection coil 10 that penetrates the sample S may be arbitrarily selected according to the shape of the sample S so that the magnetic field can be applied and detected with high uniformity in the entire sample S. Further, as shown in FIG. 4, a probe type electromagnetic induction as well as a through coil type electromagnetic induction measuring device in which the sample S is disposed through the hollow cylindrical inspection coil 10 as shown in FIG. It can also be set as the measuring apparatus 1 ′. That is, the inspection probe 10 ′ including the inspection coil 10 may be disposed in a partial region on the surface of the sample S so as not to contact the sample S, and electromagnetic induction measurement may be performed on the region. . In addition, from the viewpoint of eliminating measurement errors, it is preferable to perform measurement in the vicinity of the center portion, avoiding the end portion of the sample S, in both the penetration coil type and the probe type.

  Further, unlike the electromagnetic induction device 1, in the inspection coil 10, it is not necessary to provide the detection coil 12 as a separate body from the excitation coil 11, and a single coil is also used as the excitation coil 11 and the detection coil 12. Both detections may be performed. In this case, the modulation component given to the alternating current flowing through the coil by electromagnetic induction in the sample S may be detected by synchronous detection. Such a form using a single coil can be suitably used particularly in the probe type electromagnetic induction measuring apparatus 1 '.

[Magnetic property evaluation method]
Next, a magnetic property evaluation method according to an embodiment of the present invention will be described. The present inventors have found that there is a good correlation between a synchronous detection signal obtained by performing electromagnetic induction measurement in a non-magnetized state on a magnet material and a magnetic characteristic value after magnetization. . Then, the present magnetic property evaluation method was constructed to estimate the magnetic property value after magnetization without actually magnetizing by performing electromagnetic induction measurement on an unmagnetized magnet material.

  This evaluation method is executed by using a magnetic property evaluation apparatus including an electromagnetic induction measuring apparatus capable of performing electromagnetic induction measurement on an unmagnetized magnet material by synchronous detection. Here, the case where the magnetic flux amount (flux) after magnetization of a certain evaluation sample is evaluated using the magnetic characteristic evaluation apparatus provided with the electromagnetic induction measuring apparatus 1 described above will be described.

  In this evaluation method, as a sample S for performing electromagnetic induction measurement, a plurality of standard samples are used as a reference for measuring the magnetic properties of the evaluation sample, in addition to the evaluation sample that is the target of magnetic property evaluation. . Both the evaluation sample and the standard sample are magnet materials that become permanent magnets when magnetized. The standard sample is a magnet material formed in the same manner as the evaluation sample. In other words, it is a plurality of magnet materials manufactured with the same component composition as the evaluation sample and manufactured by the same manufacturing method within the range of manufacturing error. Both the evaluation sample and the standard sample are prepared in an unmagnetized state, and electromagnetic induction measurement is performed. As will be described later, the magnetic properties of the magnet material after magnetization vary within the range of manufacturing errors of the magnet material, but from the viewpoint of improving the accuracy of evaluation, a plurality of standard samples can have magnetic properties after magnetization. It is preferable to select so that it is distributed over as wide a range as possible.

  In this evaluation method, (1) evaluation sample measurement step, (2) standard sample measurement step, (3) magnetic characteristic value measurement step, (4) corresponding step, and (5) evaluation step are executed. Each will be described in turn.

(1) Evaluation sample measurement process First, an evaluation sample which is a target for magnetic property evaluation, such as a magnet material to be shipped as a product, is prepared in an unmagnetized state, and the sample S is synchronized using the electromagnetic induction measuring device 1. Perform electromagnetic induction measurement by detection. As a result, the real part and imaginary part values of the detection current output from the detection coil 12 are obtained. Here, the value of the real part is recorded.

(2) Standard Sample Measurement Step Next, for each of the plurality of standard samples, the sample S is subjected to the same conditions as the sample S using the same electromagnetic induction measuring apparatus 1 as in the step (1). To perform electromagnetic induction measurement. Then, the value of the real part of the detected current obtained for each standard sample is recorded. Here, since the electromagnetic induction measuring apparatus 1 has the positioning jig 13 as shown in FIG. 3, the measurement conditions change between the evaluation sample and the standard sample and between the standard samples. Is prevented.

(3) Magnetic characteristic value measuring step Next, in the magnetic characteristic value measuring step, each of the plurality of standard samples is magnetized under the same conditions. Here, the conditions for magnetization are aligned with the conditions assumed when the evaluation sample to be an actual magnet product is magnetized. Magnetization may be appropriately performed using a static magnetic field, a pulse magnetic field, or the like.

  Next, the amount of magnetic flux is measured and recorded as a magnetic characteristic value for each magnetized standard sample. The amount of magnetic flux can be measured using a known measuring device such as a flux meter. At this time, from the viewpoint of improving the evaluation accuracy, it was confirmed that the obtained magnetic flux amount was distributed both inside and outside the magnetic flux amount range required when the evaluation sample as a product was magnetized. It is preferable to keep it. In addition, you may perform each process of the above (1)-(3) in arbitrary orders.

(4) Corresponding Step Next, in the corresponding step, with respect to the standard sample, the real part value obtained by the electromagnetic induction measurement in the above (2) standard sample measuring step and the above (3) magnetic property value measuring step The relationship between the obtained magnetic flux values is estimated. In other words, the real part value measured for each individual standard sample is associated with the value of the magnetic flux, and the magnetic flux after magnetization is obtained when a certain real part value is obtained in the electromagnetic induction measurement in the unmagnetized state. Estimate the correspondence of the value of the quantity.

  FIG. 5 is obtained by electromagnetic induction measurement in a non-magnetized state with respect to a plurality of standard samples made of a hot-worked Nd—Fe—B magnet material similar to that disclosed in Patent Document 1 above. The relationship between the obtained real part value and the amount of magnetic flux obtained after magnetization is shown. The amount of magnetic flux is expressed in units of mWb · T, and T indicates the number of turns T of the search coil of the flux meter used for measuring the amount of magnetic flux. According to FIG. 5, the larger the value of the real part of the electromagnetic induction measurement, the smaller the amount of magnetic flux. Between the value of the real part of the electromagnetic induction measurement in the unmagnetized state and the value of the magnetic flux amount after magnetization. It can be seen that there is a strong linear correlation. This means that the amount of magnetic flux after magnetization can be predicted and estimated using the value of the real part obtained by electromagnetic induction measurement in an unmagnetized state as an index.

  In this way, in the corresponding step (4), the relationship between the value of the real part obtained by electromagnetic induction measurement by synchronous detection in an unmagnetized state and the amount of magnetic flux after magnetization is estimated. Here, with respect to the real part value corresponding to the area between the measurement points obtained for a plurality of standard samples, an interpolation operation such as linear interpolation is appropriately performed to obtain the corresponding magnetic flux amount. A value may be calculated, or, as indicated by a solid line in FIG. 5, curve fitting may be performed to calculate a correspondence expression between the value of the real part and the amount of magnetic flux. In FIG. 5, a linear expression is used as the corresponding expression, but an arbitrary mathematical expression may be used according to the distribution of measurement points.

  Furthermore, based on the relationship between the value of the real part obtained above and the amount of magnetic flux, the real part corresponding to the predetermined range of magnetic flux required when the evaluation sample to be shipped is magnetized. It is preferable to set the value range as a non-defective range. In FIG. 5, the non-defective product range thus defined is shown as a region between two broken lines.

(5) Evaluation process Finally, in the evaluation process, (4) Relationship between the value of the real part of the electromagnetic induction measurement in the non-magnetized state estimated for the standard sample in the corresponding process and the amount of magnetic flux after magnetization Based on the characteristics, (1) the amount of magnetic flux of the evaluation sample after magnetization is estimated from the value of the real part obtained by the electromagnetic induction measurement for the unmagnetized evaluation sample in the evaluation sample measurement step. Specifically, in order to determine whether or not the magnetic flux amount of the evaluation sample after magnetization is within a predetermined allowable range, (4) based on the relationship between the value of the real part and the magnetic flux amount in the corresponding step. (1) It is determined whether or not the value of the real part of the evaluation sample obtained in the evaluation sample measurement step is in the non-defective product range set in the above. When the value of the real part of the evaluation sample is within the non-defective range, it can be determined that the evaluation sample is a non-defective product that has a high probability of acquiring a predetermined allowable range of magnetic flux after magnetization. On the other hand, when the value of the real part of the evaluation sample is not within the non-defective range, it is possible to determine that the evaluation sample is a defective product having a high probability of not having a predetermined allowable range of magnetic flux after magnetization. it can. Furthermore, in addition to selecting whether the evaluation sample is a non-defective product or a defective product, when it is required to predict the magnetic flux amount of the evaluation sample after magnetization as a numerical value, (1) the actual value obtained in the evaluation sample measurement step The value of the part may be applied to the relationship between the value of the real part and the amount of magnetic flux as shown by the solid line in FIG. 5 to calculate the amount of magnetic flux when the evaluation sample is magnetized.

  In this magnetic property evaluation method having the above-described steps, the magnetic flux after magnetization is estimated only by performing electromagnetic induction measurement without magnetizing the evaluation sample without performing magnetization. Yes. The reliability of such estimation is, as shown in FIG. 5, because there is a strong correlation between the result of electromagnetic induction measurement using synchronous detection in an unmagnetized state and the amount of magnetic flux after magnetization. Guaranteed.

  Whether a magnet obtained by magnetizing a magnet material exhibits a desired performance depends largely on whether the magnetic characteristics including the amount of magnetic flux expressed in the magnet after magnetization are within a predetermined range. To do. However, in the magnetic material to be manufactured, there are unavoidably uncontrollable variations such as the size of crystal grains in the structure for each individual. Such unavoidable variations in the magnet material before magnetization may give large variations in the magnetic characteristics expressed after magnetization, including the amount of magnetic flux. In order to determine whether the magnet material to be shipped exhibits the desired performance, it is most direct to magnetize individual magnet materials and measure their magnetic properties. However, if the magnet material is subjected to shipment in a state where it is not magnetized, if it is once magnetized and inspected for all individuals, it will be inspected after being magnetized, and then demagnetized again. It takes a lot of time and money, and it is extremely difficult to carry out realistically. As is generally done in the past, when extracting and magnetizing only a part of all individuals, the time and cost required for the inspection can be reduced, but the magnetic properties of all individuals can be reduced. It becomes difficult to detect inevitable variations. On the other hand, in this manufacturing method, the magnetic properties of the evaluation sample after magnetization are estimated without magnetizing the evaluation sample. It is possible to easily and highly accurately select individuals whose magnetic characteristics fall within a predetermined range. In particular, if the electromagnetic induction measuring apparatus 1 suitable for automation as shown in FIG. 3 is used so that the evaluation sample can be exchanged and measured automatically, the magnetic material to be mass-produced can be obtained for all individuals. Inspection can be carried out efficiently.

  Even if microscopic structural and compositional variations such as the size of crystal grains in an unmagnetized magnet material greatly affect the magnetic properties of the magnetized material, In many cases, the physical properties measured in the magnet material do not have a significant effect, and it is not easy to detect such variations in an unmagnetized state. However, in this evaluation method, the induced current generated on the surface of the magnet material is detected by synchronous detection sensitive to minute changes, and the influence on the induced current due to the above-mentioned microscopic variation is detected. Can be detected with high sensitivity. In particular, by using the electromagnetic induction measuring apparatus 1 capable of performing electromagnetic induction measurement with high reproducibility using the positioning jig 13 as shown in FIG. 3 above, a minute change in the induced current on the surface of the magnet material is achieved. Can be detected with higher accuracy.

  When performing the electromagnetic induction measurement, a magnetic field is applied from the exciting coil 11 to the magnet material, but this magnetic field is an alternating magnetic field and is negligible compared to the magnetic field used for magnetization. Therefore, the evaluation sample is not magnetized through the electromagnetic induction measurement. For example, the Nd—Fe—B based magnet material used in the example of FIG. 5 is magnetized in a magnetic field of about 30 to 50 kOe (about 2500 to 4000 kA / m), while at the time of electromagnetic induction measurement. For example, when measurement is performed by passing an AC current of 1 A through an excitation coil of φ50 mm and 100 turns, the AC magnetic field applied to the sample is estimated to be 2 kA / m or less, and the magnetic field during magnetization Of 1/1000 or less. In addition, the frequency of the alternating current passed through the exciting coil 11 is set to, for example, 100 Hz to 10 kHz from the viewpoint of obtaining a signal that can be detected with sufficient accuracy by synchronous detection measurement.

  In the above, the amount of magnetic flux is adopted as the magnetic characteristic value to be evaluated. As shown in FIG. 5, the amount of magnetic flux after magnetization has a good correlation with the result of electromagnetic induction measurement in an unmagnetized state. It was confirmed to have However, in addition to the amount of magnetic flux, various magnetic characteristic values expressed in the magnet material after magnetization can be evaluated by this magnetic characteristic evaluation method. In this case, in the (3) magnetic property evaluation step, a desired magnetic property value may be measured for the standard sample after magnetization instead of the magnetic flux amount and used in the subsequent steps. Examples of magnetic characteristic values that can be evaluated other than the amount of magnetic flux include magnetic permeability, coercive force, residual magnetic flux density, and the like.

Further, in the above, in the electromagnetic induction measurement, among the information included in the synchronous detection signal in which the current flowing in the detection coil 12 is detected with reference to the waveform of the alternating current flowing in the excitation coil 11, the value of the real part is used as an index. Although the magnetic characteristics after magnetization are evaluated, the information used as an index is not limited to the real part value (x). In addition, information such as an imaginary part value (y), an absolute value (z = (x ² + y ² ) ^1/2 ), and a phase difference (θ) can be used. Table 1 below shows the correlation coefficient obtained when linearly approximating the correspondence between the real part x, the imaginary part y, and the absolute value z obtained by a single electromagnetic induction measurement and the amount of magnetic flux. It shows a square value ^{R 2} of R. In addition, the measurement result of the magnetic induction after the electromagnetic induction measurement and magnetization used here is measured using a set of samples different from that shown in FIG.

  According to Table 1, it can be seen that when the real part x and the absolute value z are used, a better correlation is obtained with the amount of magnetic flux after magnetization than when the imaginary part y is used. In particular, good correlation is obtained when the real part x is used. This is because the imaginary part is more susceptible to fluctuations in measurement conditions such as the influence of the measurement position on the inspection coil 10 than the real part. Since the absolute value also includes an imaginary part component, it is easily affected to some extent by the measurement position. Thus, by using the real part of the electromagnetic induction measurement as an index, it is possible to accurately estimate the magnetic characteristics of the evaluation sample after magnetization.

  As described above, this magnetic property evaluation method can be applied to any magnet material that becomes a permanent magnet by being magnetized. That is, the present invention can be applied to any magnet material such as a hot-worked magnet and a sintered magnet. However, in the case of a sintered magnet, the surface is often subjected to alteration such as oxidation during sintering, and this alteration of the surface gives large modulation to the detected signal in electromagnetic induction measurement using synchronous detection. . Therefore, there is a possibility that a signal derived from a variation in crystal grain size that affects the magnetic characteristics after magnetization is buried, making it difficult to detect. On the other hand, in the case of a hot-worked magnet, a homogeneous magnet material is easily formed by hot working and is not easily affected by surface alteration such as oxidation. Therefore, when this magnetic property evaluation method is applied to a hot-working magnet rather than a sintered magnet, the magnetic property after magnetization can be evaluated with higher accuracy. Similarly, since scratches on the surface of the magnet material have a large effect on the results of electromagnetic induction measurement using synchronous detection, the magnet material should not be subjected to mechanical processing such as polishing other than hot processing. preferable.

  As described above, this magnetic property evaluation method uses a magnetized magnet for a hot-worked magnet that is preferably inspected and shipped without being magnetized in order to give a large residual magnetic flux density after magnetization. It can be particularly preferably used for predicting characteristics. As such hot-working magnets having excellent magnetic properties, for example, magnets such as those described in Patent Document 1, specifically, Nd—Fe—B system, R-T-B system (R Is a rare earth metal, and R: 28-30% by mass, B: 0.85-1.10% by mass, T iron group transition metal), an anisotropic hot extruded magnet can be mentioned. .

  As mentioned above, although embodiment of this invention was described in detail, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the summary of this invention.

DESCRIPTION OF SYMBOLS 1 Electromagnetic induction measuring apparatus 10 Inspection coil 11 Excitation coil 12 Detection coil 13 Positioning jig 14 Magnet protrusion jig 15 Lifting apparatus S Sample

Claims (6)

An evaluation sample measurement step for generating an induced current in a sample by an alternating magnetic field, detecting the induced current by synchronous detection, and performing electromagnetic induction measurement for obtaining a synchronous detection signal on an evaluation sample made of an unmagnetized magnet material When,
A standard sample measurement step for performing the electromagnetic induction measurement on a plurality of unmagnetized standard samples formed in the same manner as the evaluation sample,
Magnetic property value measuring step of magnetizing the plurality of standard samples and measuring magnetic property values;
A corresponding step of estimating a relationship between the synchronous detection signal obtained in the standard sample measurement and the magnetic property value obtained in the magnetic property value measurement step with respect to the plurality of standard samples;
An evaluation step of estimating the magnetic property value of the evaluation sample from the synchronous detection signal obtained for the evaluation sample in the evaluation sample measurement step based on the relationship estimated in the corresponding step. A characteristic magnetic property evaluation method. The magnetic characteristic evaluation method according to claim 1, wherein the magnetic characteristic value is a magnetic flux amount. The alternating magnetic field is generated by passing an alternating current through the exciting coil,
The induced current is detected by synchronously detecting a current that flows by electromagnetic induction in a separate detection coil that is also used as the excitation coil, based on an alternating current that flows in the excitation coil,
3. The magnetic characteristic evaluation method according to claim 1, wherein a value of a real part of the signal detected by the synchronous detection is used as the synchronous detection signal in the corresponding step and the evaluation step. In the corresponding step, the range of the synchronous detection signal corresponding to the magnetic characteristic value in the predetermined range is set as a non-defective range,
4. The magnetic property evaluation method according to claim 1, wherein, in the evaluation step, if the synchronous detection signal of the evaluation sample is within the non-defective range, the evaluation sample is evaluated as a non-defective product. 5. .   The magnetic property evaluation method according to claim 1, wherein the magnet material is a magnet material of a hot-worked magnet. A magnetic field generating means for generating an alternating magnetic field and applying it to the sample;
Inductive current detection means for detecting the induced current generated in the sample by synchronous detection,
A magnetic property evaluation apparatus that executes the magnetic property evaluation method according to claim 1.

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