JP7776302B2 - Magnetic particle liquid for magnetic particle testing and magnetic particle testing method - Google Patents

Description

The present invention relates to a magnetic particle liquid for magnetic particle testing and a magnetic particle testing method. Specifically, the magnetic particle liquid is a magnetic particle liquid in which the magnetic particles and the dispersion liquid in which the magnetic particles are dispersed have different colors, and the magnetic particle liquid and magnetic particle testing method make it easy to distinguish between defects and liquid pools.

Magnetic particle testing is a flaw detection testing method that applies a magnetic field to the object being inspected, generating magnetic poles in areas with cracks or other defects, causing colored iron powder (hereafter referred to as "magnetic powder") to adhere to the magnetic poles, and then detecting defects by observing the magnetic powder that has adhered to the defective areas.

However, in actual magnetic particle testing, magnetic particles may remain in areas other than the magnetic pole generating area.

These remaining magnetic particles are called "liquid pools." Because the presence of "liquid pools" reduces the contrast between the defect indication area and other areas, back-cleaning methods such as immersion in water are used.

However, this method has the drawback of increasing equipment costs and reducing detection power.

If defect detection is performed using image processing while the "puddle" remains, the background brightness increases, making it difficult to set a threshold for determining whether or not a defect exists.

Furthermore, because the liquid pools are not uniform across the entire test object, it is necessary to apply a blur filter or the like to the image to determine the brightness change across the entire test image, and then correct the brightness depending on the location or change the threshold depending on the location, which results in poor work efficiency.

In addition, it is difficult to remove locally adhered liquid using the correction methods described above, and there is a risk that areas that are not defective may be detected as defective, resulting in reduced defect detection accuracy.

Furthermore, if the liquid pool contains air bubbles, the air bubbles may be mistakenly detected as defects, further reducing defect detection accuracy.

Therefore, there is a need to develop a magnetic particle liquid that can easily determine whether it is a defect or a liquid pool.

JP 2000-11528

Patent Document 1 describes a method for separating defects from noise components by attaching fluorescent magnetic particles to the surface of a magnetized piece of steel, capturing an image of the fluorescence emitted by the fluorescent magnetic particles attached to the piece of steel, generating a differential image of the captured image, extracting defect candidate areas from the differential image, and identifying defects from the defect candidate areas based on the size and shape of the areas that appear in a binarized image of the captured image.

However, while the method described in Patent Document 1 can separate defects from noise caused by liquid pools, it has the problem of requiring many steps and being time-consuming.

The inventors set out to solve the above-mentioned problems as their technical challenge, and after much trial and error and extensive trial and error, they discovered that if the magnetic powder liquid has a different color combination between the magnetic powder and the dispersion liquid in which the magnetic powder is dispersed, then image processing can be used to calculate the ratio of the magnetic powder color components to the dispersion liquid color components contained in the hue of the indication pattern, and indication patterns in which the ratio of the magnetic powder color component is increased compared to the ratio of each color component of the magnetic powder liquid can be identified as defect indication patterns. This makes it possible to remove noise caused by liquid pools and detect defects, thereby achieving the above-mentioned technical challenge.

This invention is a magnetic particle liquid for magnetic particle testing in which the color of the magnetic particles and the color of the dispersion liquid in which the magnetic particles are dispersed (excluding the color of uncolored water) are different colors.

The present invention also relates to the magnetic particle liquid for magnetic particle testing, wherein the color combination is a two-color combination of one color and another color that is at an angle of 45° or more and 315° or less from the first color on the color wheel.

The present invention also relates to the magnetic particle liquid for magnetic particle testing, wherein the color combination is a combination of two colors selected from red, green, and blue.

The present invention also relates to a magnetic particle testing method that uses the above-mentioned magnetic particle liquid for magnetic particle testing.

The present invention also provides a magnetic particle testing method that detects defects by calculating the ratios of the color components of the magnetic particles and the dispersion liquid contained in the hue of the indication pattern.

In this specification, the term "indication pattern" refers to an area that has developed a colored pattern, and is used to include not only defect indication patterns, but also areas that have developed a colored pattern due to liquid pooling or other causes.

The present invention uses a magnetic powder liquid in which the magnetic powder and the dispersion liquid in which the magnetic powder is dispersed have different color combinations. Image processing is used to calculate the ratio of the magnetic powder color components contained in the hue of the indication pattern to the ratio of the dispersion liquid color components, and indication patterns in which the ratio of the magnetic powder color components is higher than the color components of the magnetic powder liquid hue are identified as defect indication patterns. This simple method allows for the removal of noise caused by liquid pools and the detection of defects with high detection accuracy.

Furthermore, by combining the two colors of the magnetic powder and the dispersion liquid, such as a combination of one color and another color that is at an angle of 45° or more and 315° or less on the color wheel to the first color, or a combination of two colors selected from red, green, and blue, the colors can be easily separated using image processing, making it possible to more accurately distinguish between a defect indication pattern and noise caused by a liquid puddle.

1 is a grayscale image of an example and a comparative example. 10 shows images in which red and green components are extracted in the embodiment. 10 is an image in which the red component and the green component are extracted, respectively, in a comparative example. 10 is an image showing defects, liquid pools, and bubbles.

The present invention is a magnetic powder liquid in which the color of the magnetic powder and the color of the dispersion liquid in which the magnetic powder is dispersed are different colors.

In this invention, "different colors" refers to colors that are different at least under the observation conditions used for defect detection in magnetic particle testing.

Furthermore, the colors and hues referred to in this invention may be colors and hues under visible light, or may be colors and hues due to fluorescence induced by invisible light such as ultraviolet light.

Furthermore, the color wheel used in the present invention is not particularly limited and may be any color wheel.

Note that "combinations of different colors" in this invention exclude combinations with the color of uncolored water.

Magnetic particle liquid is usually managed so that the magnetic particles are uniformly dispersed in the dispersion liquid, resulting in a hue where the colors of the magnetic particles and the dispersion liquid are evenly distributed.

In the magnetic pole generating area, the magnetic particles are attracted to the magnetic pole, whereas the dispersion liquid is not directly affected by the magnetic pole. Therefore, in the magnetic pole generating area caused by the defect, the magnetic particles are more concentrated than in normal magnetic particle liquid, and the color of the magnetic particles becomes darker than the hue of the magnetic particle liquid.

Therefore, the proportion of magnetic powder color components increases in the defective area compared to normal magnetic powder liquid.

If the color of the magnetic powder and the color of the dispersion liquid are a color combination that can be separated using image processing, it is possible to determine whether the indication pattern obtained by magnetic particle testing is a defect indication pattern formed in a defective area or noise caused by a liquid pool based on the respective ratios of the color components of the magnetic powder and the color components of the dispersion liquid contained in the hue of the indication pattern, making it possible to set a more appropriate threshold than before.

It is preferable that the colors of the magnetic powder and the dispersion liquid are easily separable from each other in the color space used.

Easy-to-separate colors are, for example, color combinations that are not analogous hues on the color wheel.

Color combinations that are not analogous hue combinations are preferably those in which one color is more than 45° and less than 315° apart on the pigment wheel.

When using an RGB image, simply select two colors from red, green, and blue for the magnetic powder and dispersion liquid.

This is because it is easy to separate from color images using image processing.

For example, magnetic particles that emit green fluorescence when irradiated with ultraviolet light can be dispersed in a dispersion liquid that emits red or blue light when irradiated with ultraviolet light.

The ratio of magnetic particles to dispersion in the magnetic particle liquid of the present invention is preferably a concentration at which the dispersion emits fluorescence at the same level as the magnetic particles.

For example, it can be produced by dispersing 0.3g to 1.5g/L of magnetic powder and 0.28g/L to 1.0g/L of red phosphor in 1L of dispersion liquid.

The magnetic powder liquid of the present invention may contain a dispersant.

The image editing software used in this invention may be any known image editing software, such as GIMP or Photoshop (registered trademark).

The present invention will be explained in more detail using examples and comparative examples, but the present invention is not limited to these.

A fluorescent pigment that emits red light under ultraviolet light (SINLOIHI COLOR FZ-6037 Pink, manufactured by SINLOIHI Co., Ltd.) was mixed with 500 mL of water at a ratio of 0.5 g to prepare a dispersion at a concentration of 1 g/L.

The magnetic powder liquid used in this example was a 1:1 mixture of fluorescent magnetic powder LY-30 (manufactured by Marktec Co., Ltd.) and the dispersion liquid prepared.

The comparative examples were a fluorescent magnetic powder LY-30 (manufactured by Marktec Co., Ltd.) solution and a magnetic powder solution with a concentration of 1 g/L in uncolored water.

Fluorescent magnetic powder LY-30 emits green light under ultraviolet light.

The specimen used for testing was a test piece with a simulated defect that resembled a gear with a slit cut into it.

The specimen was magnetized using the axial current method, and magnetic particle testing was performed by applying the test liquid using the continuous method.

After the flaw detection test, the specimen was photographed using a color CMOS (Complementary Metal Oxide Semiconductor) camera sensitive to RGB.

(Image Processing)
Image processing was carried out using image editing software according to the following steps (1) to (4).
(1) Open the resulting image. (2) Use the selection tool to select the target area. (3) Use the histogram dialog to obtain the average luminance (8-bit pixel value) of the red component from the area selected in (2). (4) Use the histogram dialog to obtain the average luminance (8-bit pixel value) of the green component from the area selected in (2).

Figure 1 shows a color image of the test piece taken after the flaw detection test, which was then converted to grayscale.

Figure 2 shows a color image of the test object after the flaw detection test in this example, with the green and red components extracted.

Figure 3 shows a color image of the specimen after the comparative example flaw detection test, with the green and red components extracted.

Tables 1 and 2 show the 8-bit pixel values of the red and green components of each simulated defect, puddle, and bubble (Figure 4) in the example and comparative example.

With the magnetic powder liquid of the example, defective areas where magnetic poles occur have higher values for the green component than for the red component, while puddles and bubble areas where no magnetic poles occur have roughly the same values for the red and green components. This proves that it is possible to distinguish between defect indication patterns and noise caused by puddles, and to remove the noise.

Since the present invention uses a magnetic particle liquid in which the color of the magnetic powder and the color of the dispersion liquid in which the magnetic powder is dispersed are different colors, the color of the magnetic powder in defective areas where magnetic poles are generated is darker than the hue of the magnetic particle liquid, compared to puddles where no magnetic poles are generated.Therefore, by using image processing to calculate the ratio of the color components of the magnetic powder and the color components of the dispersion liquid contained in the hue of the indication pattern, and by distinguishing indication patterns in which the ratio of the color component of the magnetic powder is increased compared to the ratio of each color component of the magnetic particle liquid, as defect indication patterns, it is possible to separate out the noise caused by puddles and detect defective areas, resulting in a magnetic particle liquid and magnetic particle inspection method that allows for highly accurate magnetic particle inspection testing in a simple manner.
Therefore, the present invention has high industrial applicability.

Claims (4)

A magnetic particle liquid for magnetic particle inspection testing, in which the color of the magnetic particle and the color of the dispersion liquid in which the magnetic particle is dispersed (excluding the color of uncolored water) are different colors, and the color combination is a combination of two colors, one color and another color that is at an angle of 45° or more and 315° or less from the first color on the color wheel . 2. The magnetic particle liquid for magnetic particle testing according to claim 1 , wherein the color combination is a combination of two colors selected from the group consisting of red, green, and blue. A magnetic particle testing method using the magnetic particle liquid for magnetic particle testing according to claim 1 or 2 . 4. A magnetic particle testing method according to claim 3 , wherein defects are detected by calculating the ratio of the color components of the magnetic particles contained in the hue of the indication pattern to the color components of the dispersion liquid.