JP5968658B2 - Film thickness measuring method and film thickness measuring apparatus - Google Patents

Description

  The present invention relates to a film thickness measuring method and a film thickness measuring apparatus for measuring the film thickness of a film by applying an alternating electric field from the outside to the surface of a measurement object and detecting the strength of an induced eddy current. It is about.

  Conventionally, as an eddy current type film thickness measuring apparatus, an AC electric field is applied from the outside to the surface of a measurement object, and the strength of the induced eddy current is detected to detect the film formed on the base material. A film thickness measuring device for measuring the thickness is known. This eddy current film thickness measuring device uses the principle of electromagnetic induction. When a probe equipped with a coil that generates an alternating electric field is brought close to the surface of the measurement object, the eddy current film thickness measurement apparatus is brought into the measurement object. Therefore, the thickness of the coating is measured by detecting the eddy current with a coil.

  The above-mentioned eddy current film thickness measurement device does not require advanced measurement skills, and can be damaged even if the measurement object is a fragile material by simply operating the probe tip on the surface of the measurement object. The film thickness of the coating can be measured non-destructively without giving a film, and is therefore widely used for the measurement of the thickness of a coating film or a oxidization film at a work site. Nowadays, it is possible to measure a thin film thickness of, for example, nanometer order with a small portable measuring device.

  As an example of the use scene of the eddy current type film thickness measuring device, there is a periodic inspection of an open rack type vaporizer used for vaporizing liquefied natural gas. In the open rack type vaporizer, liquefied natural gas flows in the heat transfer tube of the vaporizer, while seawater flows on the outer surface of the heat transfer tube, and the liquefied natural gas is heated by the seawater.

  Therefore, heat transfer tubes that are always in contact with seawater are prone to corrosion, so in order to protect the base aluminum alloy from corrosion, conventionally, an aluminum-zinc alloy film having a thickness of about 400 to 600 μm is sprayed onto the surface of the heat transfer tube (metallicon). ), The sacrificial protection of the base material is achieved. Such sprayed coatings may be consumed at unexpected speeds due to the abrasion caused by seawater corrosion and solid matter such as shellfish and mud sand in the seawater. When the film thickness is about 100 μm or less, repair work such as respraying is performed.

  As an example of a conventional eddy current film thickness measuring apparatus, there is an eddy current film thickness measuring apparatus described in Patent Document 1. The principle of film thickness measurement by a conventional general eddy current film thickness measuring apparatus is as follows.

  In advance, a plurality of standard samples are prepared in which the measurement object and the base material are the same, the film thickness of the film is different, and the film thickness of the film is known. Next, an AC electric field is applied to the surface of each standard sample, and the conductivity is measured by inducing an eddy current in the standard sample and measuring its strength. The conductivity of the object to be measured and the film thickness of the coating A standard curve (calibration curve) showing the correlation with is prepared. During actual film thickness measurement, an AC electric field is applied to the surface of the measurement object, and the conductivity of the measurement object is measured by inducing an eddy current in the measurement object and measuring its strength. The film thickness of the film is derived from the measured conductivity value using the standard curve.

JP 2007-298292 A

  However, in the conventional eddy current film thickness measuring apparatus, when the coating film of the object to be measured is a sprayed film, accurate film thickness measurement is difficult for the following reason.

  That is, when a coating is formed by spraying, the film quality of the formed sprayed film varies greatly depending on the spraying conditions. Even if the material of the thermal spray material is the same, for example, if the thermal spraying conditions such as thermal spraying speed, thermal spraying temperature, thermal spraying distance, thermal spraying atmosphere, thermal spraying gas pressure, etc. are different, the formation density is different, the oxide is involved, etc. As a result, films having different film quality are formed. Therefore, the film quality of the formed sprayed film depends on the characteristics of the apparatus for performing the spraying process and the working environment, and may vary depending on the production lot, for example. Furthermore, the film quality of the sprayed film may change depending on the ambient temperature and aging deterioration.

  However, as described above, the conventional eddy current film thickness measurement device does not consider or correct the difference in film quality between the standard sample and the measurement object for actually measuring the film thickness. The standard curve that does not necessarily show the correct correlation between the electrical conductivity of the actual measurement object and the film thickness of the film, so every time the measurement object changes, the derived film film thickness has a measurement error. Has occurred.

  The present invention has been made in view of the above circumstances, and for example, even when there is a variation in the film quality of the coating film of the measurement object, such as when the coating film on the measurement object is a sprayed film. An object of the present invention is to provide a film thickness measuring method and a film thickness measuring apparatus capable of measuring a film thickness of a film with little error.

  The film thickness measurement method of the present invention provides an AC electric field from the outside to the surface of a measurement object composed of a base material and a coating on the base material, thereby increasing the intensity of eddy currents induced in the measurement object. The present invention relates to a film thickness measuring method for measuring the film thickness of the coating film by detection.

The film thickness measuring method of the present invention is
A film conductivity measuring step for detecting the intensity of the eddy current and measuring the specific conductivity of the film based on the detected intensity of the eddy current;
Corresponding to the different specific conductivity of the film, the correlation between the measured conductivity of the measurement object and the film thickness when the frequency of the AC electric field is a predetermined fixed value, and the measurement object The film conductivity is measured from a plurality of standard curves according to film quality prepared in advance using a standard sample group in which the material and shape of the base material are substantially the same and the film quality is different, and the film thickness of the film is known. A standard curve selection step for selecting a standard curve for measurement used for measuring the film thickness of the coating film based on the intrinsic conductivity of the coating film measured in the step;
In the state where the frequency of the AC electric field is set to the predetermined fixed value, the intensity of the eddy current is detected, the conductivity of the measurement object is measured based on the detected intensity of the eddy current, and the measurement object is measured. A film thickness measuring step for measuring the film thickness of the coating film using the electrical conductivity of the object and the standard curve for measurement is provided.

  In the above configuration, at the coating film conductivity measurement stage, an AC electric field is applied from the outside to the surface of the measurement object, and the intensity of the eddy current induced in the measurement object is detected. Based on this, the intrinsic conductivity of the coating is measured.

In the film conductivity measurement step, the eddy current intensity is detected by applying the alternating electric field while gradually changing the frequency from the outside to the surface of the measurement object, and based on the detected eddy current intensity. , together with measured values of the conductivity of the measurement object for each of the frequency, the values measured conductivity is saturated with respect to an increase of the frequency, that determine the intrinsic conductivity of the coating.

  It is known that as the frequency of the AC electric field is increased, the eddy current or measured conductivity reflects the conductivity state of a shallower region of the measurement object. Therefore, when changing the frequency from a low value to a high value while detecting the intensity of the eddy current or measuring the conductivity of the object to be measured, the conductivity measurement at a low frequency, the base material and the The conductivity value reflecting both the conductive state with the film is obtained, but the conductivity value reflecting only the conductive state of the film is obtained in the conductivity measurement at a frequency equal to or higher than the predetermined frequency. Therefore, the measured conductivity becomes a substantially constant value saturated with the increase of the frequency, and this saturation value is considered to indicate the intrinsic conductivity of the coating.

  If the present invention focuses on the intrinsic conductivity of the film or the saturation value of the measured conductivity with respect to the increase in the frequency, as long as it affects the eddy current film thickness measurement, the film quality difference and manufacturing variation ( A new technical idea of accurately discriminating the density, hardness, variation in the mixing degree of impurities, etc.) is provided and technically realized.

  In particular, when the coating is a sprayed coating formed on the base material, for example, the spraying material is the same, for example, spraying speed, spraying temperature, spraying distance, spraying atmosphere, spraying gas pressure, etc. Depending on the thermal spraying conditions, different film quality films are formed. Therefore, in general, the film quality of the coating may differ depending on the characteristics of the apparatus for performing the thermal spraying process, the working environment, the production lot, and the like. According to the present invention, the coating resulting from the difference in the film quality. It is possible to effectively suppress the error in film thickness measurement. Further, according to the present invention, even if the coating is either a coating film or a clad layer formed on the base material, an error in measuring the thickness of the coating due to a difference in film quality can be effectively prevented. Can be suppressed.

  In the above configuration, it is also preferable that the base material is a nonmagnetic metal and the coating is made of a nonmagnetic material. As the nonmagnetic metal constituting the base material, any nonmagnetic metal such as aluminum or copper can be used, and these alloys may be used. Moreover, as a nonmagnetic material which comprises the said film, arbitrary nonmagnetic materials, such as a coating-film material and plating other than the nonmagnetic metal different from a base material, can be used.

  In the standard curve selection step, based on the intrinsic conductivity of the coating measured in the coating conductivity measurement step, or the saturation value of the measured conductivity with respect to the increase in frequency, the measurement object and the base material and Actually used for film thickness measurement from a plurality of standard curves according to film quality prepared in advance using a group of standard samples having the same shape but different film quality and known film thickness. A standard curve for measurement is selected. This standard curve according to film quality shows the correlation between the measured conductivity of the measurement object and the film thickness when the frequency of the alternating electric field is set to a predetermined fixed value.

  For example, a plurality of standard curves according to film quality prepared in advance using a standard sample group in which the material and shape of the measurement object and the base material are substantially the same, the film quality of the film is different, and the film thickness of the film is known. From a standard sample having the saturation value of the conductivity in the measurement object for actually measuring the film thickness of the film, or the closest value to the specific conductivity of the film as the saturation value or the specific conductivity One standard curve created and associated with the intrinsic conductivity or saturation value is selected as the standard curve for measurement.

  That is, among the standard sample group, while using a standard curve for measurement created using a standard sample having a film quality that is closest to the film of the measurement object that actually measures the film thickness in terms of electrical characteristics In a state where the frequency of the AC electric field is set to the predetermined fixed value, the intensity of the eddy current is detected and the film thickness of the coating film of the measurement object is measured.

  It is preferable that the material of the film of the standard sample group is the same as the material of the film of the measurement object that is actually the object of film thickness measurement, but the present invention excludes various properties of the film. Since only the specific electrical conductivity in terms of electrical characteristics is used for identification, the present invention can be applied to the case where the material of the standard sample film is different from the material of the film of the object to be measured. It is possible to apply.

  With the above configuration, if the film thickness measurement method of the present invention is used, the film thickness of the film is measured based on a standard curve that more accurately shows the correlation between the conductivity of the actual measurement object and the film thickness of the film. can do. As a result, even when there is a variation in the film quality of the film to be measured, it is possible to realize film thickness measurement of the film with less error.

Moreover, the film thickness measuring apparatus of the present invention is
By applying an AC electric field from the outside to the surface of the measurement object consisting of the base material and the film on the base material, and detecting the intensity of the eddy current induced in the measurement object, the film of the film The present invention relates to a film thickness measuring apparatus for measuring thickness.

The film thickness measuring device of the present invention is
An alternating voltage application unit that applies an alternating electric field to the surface of the object to be measured by applying an alternating voltage to the coil;
An eddy current intensity detector that detects the intensity of eddy current induced in the measurement object by an AC electric field applied by the AC voltage application unit;
Based on the intensity of eddy current detected by the eddy current intensity detection unit, a conductivity measurement unit that measures the conductivity of the measurement object;
A frequency adjusting unit that gradually changes the frequency of the AC voltage applied to the coil;
A frequency-specific conductivity storage unit that stores, for each frequency, a conductivity value of the measurement object measured by the conductivity measurement unit when the frequency adjustment unit gradually changes the frequency;
A saturation conductivity determining unit that determines a saturation value of the conductivity of the measurement object with respect to an increase in the frequency from a value of the conductivity of the measurement object for each frequency stored in the conductivity storage unit for each frequency; ,
Corresponding to the different specific conductivity of the film, the correlation between the measured conductivity of the measurement object and the film thickness when the frequency of the AC electric field is a predetermined fixed value, and the measurement object A standard curve group storage unit for storing a plurality of standard curves according to film quality, which are prepared in advance using a standard sample group in which the material and shape of the base material are substantially the same, the film quality of the film is different, and the film thickness of the film is known. ,
Based on the saturation value determined by the saturation conductivity determination unit, a standard curve for measurement used for measuring the film thickness of the coating is selected from the plurality of standard curves according to film quality stored in the standard curve group storage unit A standard curve selection unit,
Based on the measurement standard curve selected by the conductivity of the measurement object measured by the conductivity measurement unit and the standard curve selection unit, with the frequency of the alternating electric field set to the predetermined fixed value, A film thickness measuring unit for measuring the film thickness of the coating.

  With the above configuration, the film thickness measuring apparatus of the present invention has the same effect as the film thickness measuring method, and even when there is a variation in the film quality of the film of the object to be measured, Film thickness measurement can be realized.

  According to the film thickness measuring method and the film thickness measuring apparatus according to the present invention, it is possible to realize the film thickness measurement of a film with few errors even when there is a variation in the film quality of the film of the measurement object.

It is the functional block diagram which showed the control block of the film thickness measuring apparatus which concerns on one Embodiment of this invention. It is an external view of the film thickness measuring apparatus of FIG. It is a flowchart which shows the flow of a film thickness measurement process. It is a flowchart which shows the flow of film conductivity measurement. It is a graph which shows the relationship between the frequency of the alternating voltage provided to a coil, and the measurement electrical conductivity of a measuring object. The graph of FIG. 5 was experimentally obtained for a plurality of types of measurement objects (sample A and sample B). It is a flowchart which shows the flow from standard curve selection to film thickness measurement. It is a list | wrist which shows the classification | category of several standard curve according to film quality. It is a graph which shows the relationship between the electrical conductivity according to frequency of an alternating electric field, and a film thickness. It is a flowchart which shows the flow of a film thickness measurement.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

[1. Configuration example of film thickness measuring device]
FIG. 2 is a diagram showing an appearance of the film thickness measuring apparatus 1 according to one embodiment of the present invention. As shown in the figure, the film thickness measuring device 1 is composed of a housing and a probe 10 connected to the housing. The probe 10 is brought close to the surface of the measurement object, and has a built-in coil for applying an alternating electric field to the surface.

  FIG. 1 is a functional block diagram showing main control blocks of the film thickness measuring apparatus 1. The film thickness measuring device 1 applies an AC electric field to the surface of the measurement object composed of the base material M and the coating F on the base material M by the probe 10, and the intensity of the eddy current induced in the measurement object. The film thickness of the film F is measured by detecting. As shown in the figure, the control block of the film thickness measuring device 1 includes an AC voltage application unit 11, an eddy current intensity detection unit 12, a conductivity measurement unit 13, a frequency adjustment unit 14, a frequency-specific conductivity storage unit 15, and a saturation. It comprises a conductivity determination unit 16, a standard curve group storage unit 17, a standard curve selection unit 18, and a film thickness measurement unit 19. The film thickness measuring apparatus 1 also includes, as a user interface, an input / output unit 20 including various input / selection keys that accept input instructions from the user and a display that displays various information.

  The AC voltage application unit 11 is connected to a coil built in the probe 10 and is a power supply unit that applies an AC voltage to the coil. The coil built in the probe 10 is designed to be used when the coating film F of the measurement object is thick and to be used when the coating film F of the measurement object is thin in order to adjust the output or detection sensitivity. It is also preferable to change the specifications.

  The eddy current intensity detector 12 detects the intensity of the eddy current induced in the measurement object due to the AC electric field applied by the AC voltage of the AC voltage application unit 11 through a coil built in the probe 10.

  The conductivity measuring unit 13 measures the conductivity of the measurement object based on the eddy current intensity detected by the eddy current intensity detecting unit 12. Note that the conductivity measuring unit 13 may not be configured to measure the conductivity of the measurement object as an absolute value, but may be configured to relatively measure a value proportional to the conductivity. This is because the eddy current intensity detected by the eddy current intensity detection unit 12 varies depending on the detection sensitivity.

  The frequency adjustment unit 14 adjusts the frequency of the AC voltage applied to the coil built in the probe 10 by the AC voltage application unit 11 to an arbitrary value. By the function of the frequency adjusting unit 14, an AC electric field having an adjusted frequency can be applied to the surface of the measurement object facing the probe 10. As will be described later, the frequency adjusting unit 14 can gradually increase the frequency of the AC voltage applied to the coil built in the probe 10 from a low frequency to a high frequency.

  The frequency-specific conductivity storage unit 15 is a value of the conductivity of the measurement object measured by the conductivity measurement unit 13 when the frequency adjustment unit 14 gradually increases the frequency of the AC voltage applied to the coil built in the probe 10. Is a storage unit for storing each frequency. That is, the frequency-specific conductivity storage unit 15 stores, for each frequency, the measured conductivity when the AC voltage is set to a low frequency, the measured conductivity when the AC voltage is set to a high frequency, and the like.

  The saturation conductivity determining unit 16 determines the saturation value of the conductivity of the measurement object with respect to the increase in frequency based on the measured conductivity value for each frequency stored in the frequency-specific conductivity storage unit 15. The significance of the saturation value of the conductivity will be described later.

  The standard curve group storage unit 17 is a standard sample group in which the film thickness of the coating film F is known and the measurement object that actually measures the film thickness is substantially the same as the base material M and the film quality of the coating film F is different. It is a data storage unit for storing a plurality of standard curves according to film quality that are created in advance. This standard curve according to film quality corresponds to the different saturation values, and shows a correlation between the measured conductivity of the measurement object and the film thickness of the coating F. The standard curve group storage unit 17 can store, for example, hundreds to thousands of patterns of standard curves classified by film quality by a digital storage configuration, and can easily call data of standard curves classified by film quality.

  Based on the saturation value determined by the saturation conductivity determination unit 16, the standard curve selection unit 18 selects a film of the actual coating F from the plurality of standard curves according to film quality stored in the standard curve group storage unit 17. In this configuration, a measurement standard curve used for thickness measurement is selected. More specifically, the standard curve selection unit 18 saturates closest to the saturation value (the specific conductivity of the coating F) in the measurement object that actually measures the film thickness from among the plurality of film quality standard curves. One standard curve associated with the value (the intrinsic conductivity of coating F) is selected as the standard curve for measurement. Thereby, among the above-mentioned standard sample group, the standard curve created by using the standard sample provided with the coating F of the measurement object for actually measuring the film thickness and the coating F having the closest property in terms of electrical characteristics. Is used for the film thickness measurement of the coating film F of the measurement object.

  The film thickness measurement unit 19 is configured to measure the film thickness of the coating F based on the conductivity of the measurement object measured by the conductivity measurement unit 13 and the measurement standard curve selected by the standard curve selection unit 18. . The film thickness measurement result of the coating F by the film thickness measuring unit 19 is appropriately displayed on the display of the input / output unit 20. In addition, the film thickness measuring unit 19 has a function of integrally controlling each control operation of the film thickness measuring device 1 as a center control unit that controls the entire control operation of the film thickness measuring device 1.

[2. Flow of film thickness measurement process
Next, the details of the film thickness measurement process performed by the film thickness measurement apparatus 1 will be described with reference to FIGS.

  FIG. 3 is a flowchart showing the flow of the film thickness measurement process (film thickness measurement method) executed by the film thickness measurement apparatus 1. In the present embodiment, a case where the film thickness of the coating F is measured on a measurement object (a part of an open rack vaporizer) composed of the base material M and the coating F (metallized) sprayed on the base material M is considered. . In the present embodiment, the base material M is made of a nonmagnetic metal aluminum alloy (for example, Al—Mn, Al—Mg, or Al—Mg—Si not containing Zn), and the specific composition is as follows. For example, A3004, A5052, A5083 material is used. For the coating F, a sprayed aluminum-zinc alloy film is used as an example of a nonmagnetic material.

  As shown in FIG. 3, this film thickness measurement process is composed of three steps: a film specific conductivity measurement process S 1, a standard curve selection process S 2, and a film thickness measurement process S 3.

  The measurement process S1 of the intrinsic conductivity of the coating is a vortex induced in the measurement target while applying an AC electric field from the outside to the surface of the measurement target composed of the base material M and the coating F on the base material M. In this process, the current intensity is detected, and the intrinsic conductivity of the coating F is measured based on the detected eddy current intensity.

  The standard curve selection process S2 corresponds to the intrinsic conductivity of different coatings F, and correlates the measured conductivity of the measurement object with the film thickness of the coating F when the frequency of the alternating electric field is set to a predetermined fixed value. This is a process of selecting a standard curve for measurement used for actual film thickness measurement from a plurality of standard curves according to film quality. Such a standard curve for each film quality is prepared in advance using a standard sample group in which the material and shape of the measurement object and the base material M are substantially the same, the film quality of the film F is different, and the film thickness of the film F is known.

  In the coating film thickness measurement process S3, an AC electric field is applied from the outside, the intensity of the eddy current induced in the measurement object is detected, and the conductivity of the measurement object is measured based on the detected intensity of the eddy current. Then, the film thickness of the coating F is measured using the measured conductivity of the measurement object and the standard curve for measurement.

  FIG. 4 is a flowchart showing in more detail the flow (subroutine) of the measurement process S1 for the intrinsic conductivity of the film.

  The measurement process S1 of the intrinsic conductivity of the film is a process of measuring the intrinsic conductivity of the film F as described above, and is mainly executed based on the command of the saturation conductivity determining unit 16 of the film thickness measuring device 1. Is done. Specifically, the film thickness measurement apparatus 1 is used as a measurement object while gradually increasing the frequency of the AC electric field by each process of S10 to S13 shown in FIG. 4 based on the command of the saturation conductivity determination unit 16. The intensity of the eddy current is detected, and based on the detected intensity of the eddy current, the conductivity value of the measurement object is measured for each frequency. The saturated value is determined as the intrinsic conductivity of the coating F.

  That is, based on the command of the saturation conductivity determining unit 16, the film thickness measuring apparatus 1 measures the conductivity of the measurement object by applying an alternating electric field of a low frequency (for example, about 100 KHz) as shown in FIG. (S10), applying an alternating electric field of medium frequency (for example, about 250 KHz) to measure the conductivity of the measurement object (S11), applying an alternating electric field of high frequency (for example, about 500 KHz) The conductivity is measured (S13). These measurement results are stored in the frequency-specific conductivity storage unit 15 for each frequency. Note that the frequency at which the conductivity should be measured may be appropriately set in consideration of the time required for the measurement and the number of data necessary for deriving a saturation value (specific conductivity) described later. In general, as the number of data increases, the derivation of the saturation value (specific conductivity) becomes more accurate.

  Thus, the reason for measuring the conductivity of the measurement object while changing the frequency of the AC electric field is that the measurable depth of the eddy current film thickness measurement is inversely proportional to the square of the frequency of the AC electric field. Because it is known. That is, the value of the measured conductivity reflects the conductive state of the shallower region of the measurement object as the frequency of the alternating electric field is increased. Therefore, when the conductivity of the measurement object is measured while increasing the frequency of the AC electric field from a low value to a high value, the conductivity of both the base material M and the coating F is measured in the low frequency region conductivity measurement. Although the conductivity value reflecting the state is obtained, it is considered that the conductivity value reflecting the conduction state of only the coating F can be obtained in the conductivity measurement in the high frequency region above the predetermined frequency.

  FIG. 5 is a graph conceptually showing the relationship between the frequency of the AC voltage applied to the coil (the frequency of the AC electric field applied to the measurement object) and the measurement conductivity of the measurement object. As shown in the figure, in a region where the frequency of the AC voltage is equal to or higher than a predetermined value, the measured conductivity is saturated (saturated) with respect to the increase in frequency and has a substantially constant value. This saturation value is considered to indicate the conductivity of the coating film F only, that is, the intrinsic conductivity of the coating film F. In this way, by measuring the saturation conductivity while increasing the measurement frequency from a low frequency to a high frequency, it is possible to accurately measure the specific conductivity of the coating F even when the coating F is thin. Become.

  In addition, if the frequency of the AC electric field is too high, the surface roughness of the measurement object will become stronger, and the measured conductivity will reflect the state of only the surface layer, and appropriate intrinsic conductivity will not be obtained. There is. In general, when the thickness of the measurement object is thick, it is preferable to set the measurement frequency lower, while when the measurement object is thin, it is preferable to set the measurement frequency higher.

  In FIG. 4, the determination of the saturation conductivity (S13) is performed by obtaining the saturation value of the conductivity with respect to the frequency increase based on the value of the conductivity for each frequency measured in each process of S10 to S12. Is called.

  FIG. 6 is a graph showing the results of actual measurement of the relationship between the frequency of the alternating electric field and the measured conductivity for different objects to be measured (the coating of sample A is a cladding layer and the coating of sample B is a sprayed coating). . Referring to FIG. 6, depending on the configuration of the sample, the measured conductivity may increase when the frequency of the alternating electric field increases, and the measured conductivity may decrease when the frequency of the alternating electric field increases. Recognize. This difference is caused by the difference in magnitude between the conductivity of the base material M and the conductivity of the coating F.

  However, for both Sample A and Sample B in FIG. 6, the value of each measured conductivity is saturated as the frequency of the AC electric field increases, and from this saturation value, the conductivity of a very shallow region of the object to be measured, that is, the film The intrinsic conductivity of F can be read. The saturation conductivity determining unit 16 of the film thickness measuring apparatus 1 may use a sufficiently saturated high-frequency conductivity value as the saturation value as a specific calculation method of the saturation value, or may perform a predetermined calculation. The saturation value may be calculated by applying an appropriate fitting process or interpolation process according to an equation.

  FIG. 7 is a flowchart showing in more detail the flow (subroutine) of the standard curve (calibration curve) selection process S2.

  As described above, the standard curve selection process S2 is for measurement used for actual film thickness measurement from among a plurality of film quality standard curves indicating the correlation between the measurement conductivity of the measurement object and the film thickness of the film F. This is a process of selecting a standard curve, and is mainly executed based on the command of the film thickness measuring unit 19 of the film thickness measuring apparatus 1. Specifically, the film thickness measuring device 1 selects the measurement standard curve by each process of S20 to S22 based on the command of the film thickness measuring unit 19.

  As shown in FIG. 7, the film thickness measuring unit 19 includes an input / output unit 20 as a base material selection (S 20) and a base material shape selection (S 21) of an object to be measured actually. An input instruction from the user is accepted via Such selection is necessary in eddy current film thickness measurement, in principle, the material and shape of the base material M of the measurement object is the material of the base material M of the standard sample that obtains the standard curve for measurement. This is because the information on the material and the shape of the base material M is necessary to accurately select the measurement standard curve used for the film thickness measurement.

  Here, the standard sample is a sample for creating a standard curve used for film thickness measurement, and the material and shape of the measurement object and the base material M are substantially the same, and the film thickness of the coating F is known. Say things. As a specific preparation procedure of such a standard sample, for example, the coating F is sprayed on the same base material M as the object to be measured with the number of spraying being changed once, twice, three times, etc. Thus, samples having different film thicknesses are prepared, and the film thickness of the film F of the sample may be actually measured. For example, the film thickness can be measured by a destructive test after creating a standard curve described later. In obtaining a standard curve to be described later, the more the thickness variation of the standard sample, the more data is preferable.

  Due to the instability of the thermal spraying process described above, if the equipment, the thermal spraying lot, and the working environment that perform the thermal spraying process are different when creating a standard sample, a standard sample group with different film quality can be created. If the standard sample group sprayed by the apparatus A, the standard sample group sprayed by the apparatus B, the standard sample group sprayed by the factory C, or the standard sample group sprayed by the factory D is prepared, the base material M and the coating Even if the material of F is the same, a standard sample group in which the film quality state of the coating F is different can be prepared. Such a standard sample group is preferably prepared according to the material and shape of the base material M to be measured, and other types or a large number of samples having different film quality states of the coating F are prepared as much as possible.

  And it classify | categorizes beforehand with each material and each shape of the base material M of a measuring object, About the standard sample of different film quality, it carries out the said saturated electric conduction according to the procedure similar to the measurement process S1 of the intrinsic | native conductivity of the said film. The rate or the intrinsic conductivity of the coating F is measured in advance. Thus, each standard sample can be identified by its saturated conductivity or the intrinsic conductivity of the coating F, and this saturated conductivity or the intrinsic conductivity of the coating F is a representative value reflecting the film quality of the coating F. .

  Next, the film thickness measuring unit 19 of the film thickness measuring device 1 sets the frequency of the AC electric field to be the same as the frequency of the AC electric field (measurement frequency) used at the time of actual film thickness measurement. A standard curve indicating the correlation between the conductivity and the known film thickness is measured, and stored in the standard curve group storage unit 17 in the form of a numerical value group created in a database or a graph of numerical values plotted. These standard curves are different for each standard sample, and correspond to the saturated conductivity of each standard sample or the specific conductivity value of the coating F. The frequency (measurement frequency) of the alternating electric field used at the time of actual film thickness measurement is a predetermined fixed value, and details of the setting procedure will be described later.

  Thus, based on the standard sample group, it is classified for each material and shape of the base material M of the measurement object, and corresponds to the specific conductivity of the different coating F, and the measurement conductivity and measurement of the measurement object. A plurality of standard curves according to film quality showing a correlation with the film thickness of the coating film F of the object can be obtained.

  A feature of the present invention is that the film quality (including density, hardness, etc. in addition to the material) of the coating F, particularly the sprayed coating F, can be accurately indicated by the saturated conductivity or the intrinsic conductivity of the coating F. The present inventors have found and verified that this is the case. In other words, if the arrangement is focused on only the saturated conductivity or the specific conductivity, a standard curve for measurement that accurately reflects the film quality of the coating F that is actually measured from the data of the standard curve for each film quality prepared in large numbers. Can be selected accurately.

  FIG. 8 is a list showing an example of standard curve classification stored in the standard curve group storage unit 17 of the film thickness measuring apparatus 1. In the film thickness measuring device 1, the standard curve selection unit 18 holds the list of FIG. 8, and the list is based first on the material of the base material M and secondly on the shape of the base material M (measurement target member). The standard curve is classified.

  “A3004”, “A5052” and “A5083” in FIG. 8 indicate the material of the base material M (composition name of the aluminum alloy described above), while “fin”, “root” and “header” in FIG. It shows which member of the rack type vaporizer is to be measured for film thickness, and the names of these members correspond to the shape of the base material M. Specifically, “fin” indicates the shape of a flat plate (width of about 10 mm) corresponding to the fin portion of the open rack type vaporizer, and “root” is a pipe corresponding to the tube root portion of the open rack type vaporizer. The shape of (about 30 mmφ) is shown, and “header” shows the shape of a pipe (about 200 mmφ) corresponding to the lower header portion of the open rack type vaporizer.

  In the list of FIG. 8, the standard curve data (No. 1 to 27) of the standard sample group is classified based on the material and shape of the base material M as a premise, so the selection of the material of the base material M in S20 is performed. After narrowing down the standard curve data based on the result (for example, “A3004”) and the selection result of the shape of the base material M in S21 (for example, “fin”), the saturation conductivity or the characteristic of the coating F is further reduced. One standard curve data can be selected based on the conductivity. As a result, a standard curve for measurement actually used for measuring the film thickness of the coating F is selected from among a large number of standard curves (standard curves classified by film quality) stored in the standard curve group storage unit 17.

  For example, a plurality of standard curves according to film quality prepared in advance using a standard sample group in which the measurement object and the base material M have substantially the same material and shape, the film quality of the film F is different, and the film thickness of the film F is known. A standard sample having, as the saturation value or the intrinsic conductivity, the value closest to the saturation value of the conductivity in the measurement object for actually measuring the film thickness of the coating F or the intrinsic conductivity of the coating F. A standard curve that is created and associated with these intrinsic conductivity or saturation values is selected as the standard curve for measurement.

  Referring to the list of FIG. 8, for example, for the base material shape “fin” of the base material “A3004”, standard curves according to film quality respectively associated with three different types of saturation conductivity values A, B, and C. No. 1 to 3 exist. The film thickness measuring unit 19 of the film thickness measuring apparatus 1 has a standard curve No. by film quality. A standard curve (No. 1) having a saturation conductivity (for example, A) having the closest saturation conductivity value of the measurement object determined in S13 from 1 to 3 is used for measurement of film thickness described later. It selects as a standard curve (S22 of FIG. 7).

  The data relating to the standard curve obtained using the standard sample group includes the classification of the base material M shown in FIG. 8 according to the material, shape, and saturation conductivity, as well as the difference in the thermal spraying apparatus on which the coating F is formed. It may be subdivided by element. Of course, in such a case, in order to select an appropriate standard curve, the user needs to input an instruction not only for the material, shape, and saturation conductivity of the base material M, but also for the above-described subdivision items. .

  As described above, the design and specifications of the coil of the probe 10 are mainly used when the coating film F of the measurement object is thick, and when the coating film F of the measurement object is thin. In the case of using differently, the standard curve of each standard sample group is prepared by classifying each type of probe 10.

  Next, as shown in S <b> 23 of FIG. 7, the film thickness measuring device 1 sets the frequency (measurement frequency) of the AC electric field used at the time of actual film thickness measurement based on the command of the film thickness measuring unit 19. In general, it is known that as the measurement frequency is set lower, information on a deeper region of the measurement object can be obtained, while the measurement sensitivity (accuracy) of the film thickness is deteriorated. On the other hand, if the measurement frequency is set too high, only information on a very shallow region of the measurement object can be obtained, so information around the boundary between the coating F and the base material M is not reflected well in the measurement result, and an appropriate film is obtained. Thickness cannot be measured. Therefore, in consideration of the above trade-off relationship, it is preferable to grasp the film thickness of the coating F on the measurement object to some extent and set the measurement frequency as high as possible within a range where the film thickness of the coating F can be appropriately measured. .

  FIG. 9 is a graph (standard curve) illustrating the relationship between the measured conductivity and the film thickness when the measurement frequency is changed within the range of 60 kHz to 480 kHz for the same measurement object. In the figure, the value of the measured conductivity is not converted to an absolute conductivity having a unit, but is described as a relative conductivity.

  Referring to the graph of FIG. 9, it can be seen that the conductivity value corresponding to the predetermined film thickness gradually increases as the measurement frequency increases to 60 kHz, 120 kHz, 240 kHz, and 480 kHz. In this figure, the graph is a monotonically increasing curve that rises to the right at all measurement frequencies, and the film thickness and the conductivity show a substantially one-to-one correspondence (however, in the graph of 480 kHz, In the film thickness region of about 300 μm or more, there is a decrease in conductivity with an increase in film thickness).

  Therefore, if the film thickness of the coating F of the measurement object is within the range of less than about 300 μm, setting the measurement frequency value to 480 kHz among the above will maximize the wide dynamic range of the measurement conductivity. The film thickness measurement with high sensitivity can be performed. In particular, if the film thickness of the coating F of the measurement object is within a range of less than about 100 μm, when the measurement frequency is set to 480 kHz, the film thickness is larger than when the measurement frequency is set to 60 kHz, 120 kHz, and 240 kHz. Since the change in conductivity with respect to the change in thickness increases, the sensitivity of film thickness measurement can be improved.

  The frequency (measurement frequency) of the alternating electric field used for the actual film thickness measurement used when measuring the standard curve stored in the standard curve group storage unit 17 is the measurement frequency set in S23. For example, when the film thickness measuring device 1 determines based on the command of the film thickness measuring unit 19 based on, for example, the graph of FIG. 9, the film thickness of the coating film F of the measurement object is assumed to be within a range of less than about 300 μm. (For example, referring to the value of the previous film thickness measurement result), the measurement frequency is set to 480 kHz, while the film thickness of the coating F of the measurement object is assumed to be in the range of about 300 to 400 μm. Then, the measurement frequency is set to 60 kHz (the measurement sensitivity is the best when the film thickness is in the range of about 300 to 400 μm).

  In S <b> 23, the film thickness measurement apparatus 1 uses the input / output unit 20 to provide information on approximate values, design values, and ranges of the film thickness of the coating F of the measurement object as prerequisite information for determining the measurement frequency. It is also preferable to accept from the user. Note that the film thickness measuring apparatus 1 may determine the measurement frequency based on a user's direct instruction or selection.

  FIG. 10 is a flowchart showing in more detail the flow (subroutine) of the coating film thickness measurement process S3.

  As described above, the film thickness measurement process S3 detects the intensity of the eddy current in a state where the frequency of the AC electric field is set to the predetermined fixed value, and performs the measurement based on the detected intensity of the eddy current. This is a process of measuring the conductivity of the object, and measuring the film thickness of the coating F using the measured conductivity of the object to be measured and the standard curve for measurement selected in S22. This is executed based on the command of the film thickness measuring unit 19 of the measuring apparatus 1. Specifically, the film thickness measuring apparatus 1 selects the measurement standard curve by each process of S20 to S22 shown in FIG. 7 based on the command of the film thickness measuring unit 19.

  The calibration process (S30) means that the measurement conductivity is within the allowable dynamic range (measurement range) as a preparatory stage for actually carrying out the film thickness measurement using the measurement standard curve selected in S22. In this process, the sensitivity is adjusted so that the measured conductivity is appropriately within a predetermined measurement range.

  The sensitivity adjustment described above can be realized by properly using the probe 10 as described above, in addition to the method of adjusting the electrical amplification amount. That is, by preparing a plurality of types of probes 10 incorporating coils with different winding numbers, the thick film probe 10 is used when the film F is thick, while the thin film probe 10 is used when the film F is thin. Sensitivity adjustment can be performed. When performing such sensitivity adjustment, the film thickness measuring unit 19 of the film thickness measuring apparatus 1 displays a message on the display of the input / output unit 20 to prompt the user to replace the probe 10 as appropriate. Generally, when the film F is thick, the value of measured conductivity tends to increase, and when the film F is thin, the value of measured conductivity tends to decrease.

  When performing the sensitivity adjustment described above, when measuring the film thickness using the measurement standard curve, the measurement conductivity value may be appropriately corrected taking into account the adjustment amount of the electrical amplification amount, or the measurement standard A process of changing the curve to another standard curve corresponding to a different type of probe 10 is required.

  When the calibration process is completed, the film thickness measuring unit 19 of the film thickness measuring apparatus 1 starts measuring the conductivity of the measurement object (S31), and the measured conductivity is within the allowable dynamic range (measurement range) described above. It is determined whether or not (S32). If the measurement conductivity is not within the measurement range as a result of the determination, the process returns to S30 and the calibration process is performed again. On the other hand, if the measurement conductivity is within the measurement range as a result of the determination, the film thickness is measured. The film thickness measurement unit 19 of the apparatus 1 proceeds to the process of S33, and sets the frequency of the alternating electric field as a fixed value set in S23, the standard curve for measurement selected in S22, and the conductivity value measured in S31. Based on the above, the film thickness of the coating F on the measurement object is calculated. And the film thickness measurement part 19 of the film thickness measurement apparatus 1 displays the calculated film thickness on the display of the input-output part 20, and complete | finishes a process (S34).

  As mentioned above, although specific embodiment of this invention was described, the aspect which this invention can take is not limited to these at all. For example, in the above description, a part of the processing that is automatically or autonomously executed by the film thickness measuring device 1 may be performed by the user instead of the film thickness measuring device 1. Moreover, in the above description, the embodiment for measuring the film thickness of the coating F made of a sprayed film has been mainly shown. In addition to the layer, any coating F can be used.

  As described above, the present invention is a film thickness measurement that measures the film thickness of a film by applying an AC electric field from the outside to the surface of the object to be measured and detecting the intensity of the induced eddy current. The method and the film thickness measuring device can be suitably used.

DESCRIPTION OF SYMBOLS 1 Film thickness measurement apparatus 10 Probe 11 AC voltage application part 12 Current intensity detection part 13 Conductivity measurement part 14 Frequency adjustment part 15 Conductivity storage part according to frequency 16 Saturation conductivity determination part 17 Standard curve group storage part 18 Standard curve selection part 19 Film thickness measurement unit 20 Input / output unit

Claims (5)

By applying an AC electric field from the outside to the surface of the measurement object consisting of the base material and the film on the base material, and detecting the intensity of the eddy current induced in the measurement object, the film of the film A film thickness measuring method for measuring thickness,
A film conductivity measuring step for detecting the intensity of the eddy current and measuring the specific conductivity of the film based on the detected intensity of the eddy current;
Corresponding to the different specific conductivity of the film, the correlation between the measured conductivity of the measurement object and the film thickness when the frequency of the AC electric field is a predetermined fixed value, and the measurement object The film conductivity is measured from a plurality of standard curves according to film quality prepared in advance using a standard sample group in which the material and shape of the base material are substantially the same and the film quality is different, and the film thickness of the film is known. A standard curve selection step for selecting a standard curve for measurement used for measuring the film thickness of the coating film based on the intrinsic conductivity of the coating film measured in the step;
In the state where the frequency of the AC electric field is set to the predetermined fixed value, the intensity of the eddy current is detected, the conductivity of the measurement object is measured based on the detected intensity of the eddy current, and the measurement object is measured. Using the electrical conductivity of the object and the standard curve for measurement, a film thickness measuring step for measuring the film thickness of the film ,
In the film conductivity measurement step,
Applying the alternating electric field to the surface of the measurement object while gradually changing the frequency from the outside to detect the intensity of the eddy current, and based on the detected intensity of the eddy current, the measurement object for each frequency with measuring the conductivity value of the object, the film thickness measuring method a value measured conductivity is saturated with respect to an increase of the frequency, characterized that you determined as intrinsic conductivity of the coating. The coating is sprayed film formed on the base material, the coating film, the film thickness measuring method according to claim 1 Symbol mounting, characterized in that either of the cladding layers. The film thickness measuring method according to claim 1 or 2, wherein the base material is a nonmagnetic metal and the coating is made of a nonmagnetic material. The base material is a film thickness measuring method according to any one of claims 1 to 3, characterized in that aluminum or an aluminum alloy. By applying an AC electric field from the outside to the surface of the measurement object consisting of the base material and the film on the base material, and detecting the intensity of the eddy current induced in the measurement object, the film of the film A film thickness measuring device for measuring thickness,
An alternating voltage application unit that applies an alternating electric field to the surface of the object to be measured by applying an alternating voltage to the coil;
An eddy current intensity detector that detects the intensity of eddy current induced in the measurement object by an AC electric field applied by the AC voltage application unit;
Based on the intensity of eddy current detected by the eddy current intensity detection unit, a conductivity measurement unit that measures the conductivity of the measurement object;
A frequency adjusting unit that gradually changes the frequency of the AC voltage applied to the coil;
A frequency-specific conductivity storage unit that stores, for each frequency, a conductivity value of the measurement object measured by the conductivity measurement unit when the frequency adjustment unit gradually changes the frequency;
A saturation conductivity determining unit that determines a saturation value of the conductivity of the measurement object with respect to an increase in the frequency from a value of the conductivity of the measurement object for each frequency stored in the conductivity storage unit for each frequency; ,
Corresponding to the different specific conductivity of the film, the correlation between the measured conductivity of the measurement object and the film thickness when the frequency of the AC electric field is a predetermined fixed value, and the measurement object A standard curve group storage unit for storing a plurality of standard curves according to film quality, which are prepared in advance using a standard sample group in which the material and shape of the base material are substantially the same, the film quality of the film is different, and the film thickness of the film is known. ,
Based on the saturation value determined by the saturation conductivity determination unit, a standard curve for measurement used for measuring the film thickness of the coating is selected from the plurality of standard curves according to film quality stored in the standard curve group storage unit A standard curve selection unit,
Based on the measurement standard curve selected by the conductivity of the measurement object measured by the conductivity measurement unit and the standard curve selection unit, with the frequency of the alternating electric field set to the predetermined fixed value, A film thickness measuring apparatus comprising: a film thickness measuring unit that measures the film thickness of the coating film.