JPH0593619A - Method and apparatus for measuring thickness of coating film on metal by Compton scattering X-ray method - Google Patents

Abstract

(57) [Summary] [Purpose] When measuring the thickness of a coating film that covers a metal by the Compton scattering X-ray method, eliminate measurement errors due to fluctuations in the inclination of the measurement surface. [Arrangement] Using a device in which a pair of X-ray generation sources 1 and 2 are provided at positions symmetrical to each other with respect to a normal line at a measurement point O of a measurement surface 21, a plane including an expected maximum inclination angle α of the measurement surface is used. The pair of X-ray generation sources 1 and 2 are positioned on the (paper surface) and irradiated toward the measurement point O. [Effect] Even if the optical path length of one incident X-ray passing through the coating film changes due to the variation α of the inclination of the measurement surface, the optical path length of the other incident X-ray passing through the coating film also changes, and these optical path lengths are mutually different. Since it changes so as to cancel out the change of, the measurement error is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The Compton scattering X-ray method is one of the techniques for measuring the thickness of a coating film coated on a metal substrate such as a steel plate or a plated steel plate, and is concerned with improving the accuracy of this measurement technique.

[0002]

2. Description of the Related Art The methods of measuring the thickness of a coating film on a metal include the micrometer method, the weight method, the electromagnetic method, the infrared reflection method, and the like. The micrometer method and the gravimetric method are methods in which the coating film is peeled off and the coating film thickness is determined from the dimensional difference or weight difference before and after the peeling, which is an absolute method in which the thickness is directly determined, but the measurement requires time.

The electromagnetic method and the infrared reflection method are relative methods,
Electromagnetic intensity or infrared absorption is converted into thickness based on the above absolute method. These relative methods are excellent in that they can be measured quickly and non-destructive measurement is possible, but they have the drawback that they can be measured only under limited conditions. A Compton scattering X-ray measurement method is a measurement method that overcomes this drawback.

For example, in JP-A-64-41810, the intensity of Compton scattered X-rays generated by irradiating a metal coated with a coating film with X-rays has a linear relationship with the thickness of the coating film. Reveals that the intercepts of the are associated with the base metal and the gradients are associated with the coating. That is, when the primary X-rays pass through the coating film, the secondary X-rays that collide with the atoms and are scattered are Compton scattered X-rays, and the amount thereof depends on the length of the passage of the primary X-rays.

[0005]

Therefore, there is no problem when the incident angle of the primary X-rays is constant, but when the incident angle fluctuates due to tilting of the measurement surface, X which passes through the coating film. There remains a problem that the length of the line fluctuates and an error occurs in the measurement.

The present invention has been made to solve this problem. It is possible to measure the coating film thickness with high accuracy by using a plurality of X-ray tubes to cancel the fluctuation of the incident angle. The purpose is.

[0007]

Means for achieving the object is to use two X-ray generation sources when irradiating a measurement point with X-rays and measuring secondary X-rays generated. ,
This is a method of canceling fluctuations in the incident angle due to fluctuations in the tilt of the measurement surface, but these two X-ray sources are located in the plane including the maximum tilt angle of the measurement surface and at the measurement point of the reference measurement surface. A method for measuring the thickness of a coating film on a metal by the Compton scattering X-ray method, which is arranged at a position symmetrical with respect to the normal line, thereby canceling out the fluctuation of the incident angle, and an apparatus suitable for using this method. In a measuring device for irradiating a point with X-rays and measuring secondary X-rays generated, Compton scattering X in which a pair of X-ray generating tubes are arranged at positions symmetrical with respect to a normal line at a measurement point on a reference measurement surface And a device for measuring the thickness of a coating film on a metal by the line method.

[0008]

In the Compton scattering X-ray method, a metal body coated with a resin film such as a coating film (hereinafter, simply referred to as a coating film) is irradiated with X-rays and the generated secondary X-rays are captured to obtain the thickness of the coating film. The intensity is measured. Of the secondary X-rays, the Compton scattered X-ray intensity is the main information, and the fluorescent X-ray information is the reference information.

Compton scattered X-rays are scattered by colliding with atoms as X-rays pass therethrough, and the intensity thereof and the coating thickness have a linear relationship. This relationship is shown in FIG. In FIG. 6, the vertical axis represents the Compton scattered X-ray intensity and the horizontal axis represents the coating thickness. The vertical axis intercept of the straight line showing the relationship between the two is the Compton scattering X generated when there is no coating, i.
It is the line strength. As the coating thickness increases, the X-ray line passing through it becomes longer and the Compton scattered X-ray intensity also increases. Therefore, if the relationship of FIG. 6 is obtained in advance as a calibration curve, the thickness of the coating film can be calculated from the Compton scattered X-ray intensity.

Specifically, it is measured by the optical system shown in FIG. In FIG. 7, 1 is an X-ray tube, 11 is a coating film, 12 is a base metal, 13 is a secondary X-ray, 14 is a detector, 15 is an amplifier, 16 is a counting circuit, and 17 is an arithmetic unit. A high voltage is applied to the X-ray tube 1 to generate X-rays, and the coating film 11 is irradiated with the X-rays. When irradiated with X-rays, the X-rays, the coating film 11 and the base metal 1
Secondary X-rays, such as Compton scattered X-rays and fluorescent X-rays, are generated by the interaction with 2. The detector 14 receives the secondary X-ray 13, the amplifier 15 amplifies the received signal, the counting circuit 16 counts the intensity of the X-ray, and the computing device 17 computes the coating thickness.

The above is an outline of the Compton scattering X-ray method. In the conventional method, the X-ray source was provided at one place as shown in FIG. In this case, when the inclination of the measurement surface changes, the incident angle of the irradiation X-ray changes and an error occurs in the measurement. This state is shown in FIG. In FIG. 5, when the incident angle changes from α to β, the distance of the incident X-ray passing through the coating film (hereinafter referred to as the optical path length) changes from d ₁ to d ₂ . When the optical path length changes, Compton scattering X
Since the line strength also changes, the calculated value of the coating thickness changes accordingly.

FIG. 4 shows the Compton scattered X-ray intensity with respect to the variation of the incident angle. In FIG. 4, the vertical axis represents the Compton scattered X-ray intensity and the horizontal axis represents the variation amount of the incident angle. When the incident angle is changed to be small, the Compton scattered X-ray intensity is increased, and when the incident angle is changed to be large, the Compton scattered X-ray intensity is decreased.

FIG. 4 shows a large variation range of the incident angle, but the variation that actually occurs is small, and the relationship between the variation amount of the incident angle and the Compton scattered X-ray intensity can be regarded as a linear relationship. I can. For example, in the continuous measurement of the coated steel strip, the fluctuation range is within 2 degrees, and the relationship in such a case is shown in FIG. In FIG. 3, the vertical axis represents the Compton scattered X-ray intensity and the horizontal axis represents the variation of the incident angle, and the variation is within 2 degrees, but the graph relating them is extremely close to a straight line.

Compton scattering X due to the variation of the incident angle
Fluctuations in line intensity can be offset by using a pair of X-ray sources. This will be described with reference to FIGS. 2 and 3.

In FIG. 2, the reference measurement surface 21 is determined, and the inclination is considered based on this, and the paper surface shown in FIG. 2 is taken as the surface containing the maximum inclination angle of the measurement surface. The X-ray generation source 1 and the other X-ray generation source 2 forming a pair are both in the plane including the maximum inclination angle of the measurement surface, that is, on the paper surface, and with respect to the normal line 22 at the measurement point O of the reference measurement surface 21. They are located symmetrically to each other. When the measurement surface is the reference measurement surface, the optical path length passing through the coating film 11 of X-rays emitted from the X-ray generation source 1 passes through the coating film 11 of X-rays emitted from the X-ray generation source 2. The optical path length is equal to OC, and the Compton scattered X-ray intensities scattered by them are twice as large as I shown in FIG.

When this measurement surface is inclined by α, the X-ray source 1
The optical path length of X-rays emitted from
A, the X-rays emitted from the X-ray generation source 2 are OB, and the Compton scattered X-ray intensities scattered by these are I-kα and I + kα, respectively, as shown in FIG.
That is, the fluctuation amount kα of the Compton scattered X-ray intensity scattered by the X-rays emitted from both X-ray sources is canceled out, and twice the Compton scattered intensity I measured in the state of the reference measurement surface is measured.

An apparatus suitable for carrying out the above measuring method will be described below. Online measurement is one of the cases where the inclination of the test piece is a problem. When the steel strip is measured on a continuous line for continuous processing, the measuring surface is not stationary, and the degree of inclination of the measuring surface constantly fluctuates. The plane including the maximum inclination angle may be parallel to the steel strip traveling direction or may be perpendicular to the traveling direction depending on the measurement location, line operating conditions, and the like.

When the direction of the plane including the maximum tilt angle is constant in one direction, it is a target position with respect to the normal line at the measurement point of the reference measurement plane, and the X-ray generation source is located in this plane. In addition, if it is an apparatus provided with a pair of X-ray generating tubes, the above-mentioned measuring method can be carried out.

However, if the plane containing the maximum tilt angle is in a plurality of directions, it is necessary to arrange a plurality of pairs of X-ray generating tubes according to these directions.

[0020]

EXAMPLE An apparatus in which an X-ray generating tube 1 and an X-ray generating tube 2 are arranged at predetermined positions, as shown in FIG. 1, for a coated steel sheet sample having a 0.35 mm thick steel sheet coated with a coating film. Was used to measure the thickness of the coating film 11. In the measurement, the test piece was tilted to change the incident angle φ up to ± 5 ° and the error due to the influence was examined. That is, the difference between the measurement value of the reference measurement surface and the measurement value of the inclined measurement surface is an error. The error was similarly examined and compared for the conventional example having only one X-ray generating tube.

The detector 14 is arranged on the normal line to the measuring point on the reference measuring surface, but it is not limited to this, and if it is difficult to install at this position in practice, it may be arranged at another position, or a plurality of detectors may be provided. A detector may be placed. When a plurality of detectors are used, the sum of the detected secondary X-ray intensities may be used for calculating the coating film thickness.

For the X-ray source tubes 1 and 2, Ag tubes having the same output were used, and the incident X-rays were monochromaticized into AgKα rays (λ = 0.5608Å) using a LiF monochromator. A semiconductor detector was used as the detector. The results of the examination are shown in Table 1.

[0023]

The error increases as the inclination of the measuring surface increases, but in the conventional example, even if the measuring surface is inclined by 0.5 °, the error is 2%.
As described above, when tilted by 2 °, an error of 9% or more occurs. On the other hand, in the embodiment of the present invention, the error is 0.4% or less even when tilted by 2 °. That is, in the embodiment, the error due to the inclination of the measurement surface is about 1/25 of that in the conventional example.

[0025]

As described above, according to the present invention, when measuring the thickness of a coating film on a metal using the Compton scattering X-ray method, a pair of X-ray generation sources are offset by the influence of the inclination of the measurement surface. Arrange as you would. For this reason, the measurement error was reduced to about 1/25 of that of the conventional measurement, and the measurement accuracy was greatly improved.

In the industrial world, the inclination of the measurement surface is often unavoidable as in the case of online measurement, and the effect of the present invention, which dramatically improves the measurement accuracy, is great.

[Brief description of drawings]

FIG. 1 is a diagram showing an arrangement of X-ray generating tubes according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a coating film for explaining the arrangement of a pair of X-ray generating tubes, the inclination of the measurement surface, and the cancellation of the optical path length of primary X-rays.

FIG. 3 is a diagram showing the relationship between the variation of the incident angle of primary X-rays and the Compton scattered X-ray intensity when the variation is small.

FIG. 4 shows variation in incident angle of primary X-ray and Compton scattering X
It is a figure which shows the relationship with a line strength.

FIG. 5 illustrates a primary X for explaining a measurement error generation principle.
FIG. 5 is a cross-sectional view of a coating film for explaining a change in incident angle of a line and a change in optical path length.

FIG. 6 is a diagram showing a relationship between a coating film thickness and Compton scattered X-ray intensity in the Compton scattered X-ray method.

FIG. 7 is a diagram showing an outline of an optical system for measuring a coating film thickness by a conventional Compton scattering X-ray method.

[Explanation of symbols]

 1 X-ray tube 2 Another pair of X-ray tube 11 Coating film 12 Base metal 13 Secondary X-ray 14 Detector 21 Reference measurement surface 22 Normal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takanori Akiyoshi, 1-2, Marunouchi, Chiyoda-ku, Tokyo Japan Steel Tube Co., Ltd. (72) Hiroyasu Yoshikawa, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside the Steel Pipe Corporation (72) Inventor Toshikazu Iwata 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Steel Pipe Corporation

Claims (2)

[Claims] 1. When measuring a secondary X-ray generated by irradiating a measurement point with X-rays, the two X-ray generation sources are arranged in a plane including the maximum inclination angle of the measurement plane and within the reference measurement plane. A method for measuring the thickness of a coating film on a metal by the Compton scattering X-ray method, which comprises arranging at symmetrical positions with respect to a normal line at a measurement point to cancel out fluctuations in the incident angle. 2. A measuring device for measuring a secondary X-ray generated by irradiating a measuring point with X-rays, wherein a pair of X-ray generating tubes are provided at positions symmetrical with respect to a normal line at the measuring point on a reference measuring surface. Compton scattering X characterized by the above arrangement
An instrument for measuring the thickness of coating films on metals by the wire method.