JP2006234807A - Defect detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely detect a defect having a low reflection echo intensity existing in a body to be inspected. <P>SOLUTION: A part from which a reflection echo above a predetermined intensity is measured continuously more than a predetermined distance in the rolling direction of the body to be inspected is detected as a defect. In the case where two or more detected defects exist adjacent to each other within a predetermined or less interval in the rolling direction of the body to be inspected, two or more defects are detected as one continuous defect. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a defect detection method for detecting defects present in an object to be inspected.

In general, if there are defects such as inclusions or processing flaws on the rolling surfaces (orbital surfaces and rolling surfaces) of the rolling parts that make up a rolling bearing, the quality of the rolling bearing (for example, rolling fatigue life and acoustic life) ) Is well-known.
For this reason, steelmakers that manufacture bearing steel that is the material for rolling parts should inspect steel materials such as round bars by ultrasonic flaw detection and ship only non-defective products for which no defects have been detected. Yes. However, steelmakers' inspections are performed on steel materials with coarse crystal grains immediately after rolling and a large surface roughness, and ultrasonic testing is performed at high speed from the viewpoint of productivity. Therefore, it is difficult to detect unless the inclusion is a large inclusion having a length of several tens of millimeters or more. Therefore, in steelmaker inspections, cracks, wrinkles, etc. caused by rolling, drawing, etc. on the surface of the object to be inspected (the surface when the object to be inspected is a round bar, the internal surface when the object to be inspected is a pipe) It is currently determined whether the product is a non-defective product or a defective product depending on whether or not there are defects such as inclusions having a length of several tens of millimeters or more.

  For example, in Patent Document 1, it is determined that a defect exists when both oblique and vertical flaw detections are performed at the same portion of a steel material such as a steel pipe and the obtained reflected echo intensity exceeds a predetermined threshold value. It has been proposed. Also, equipment used in the next process of ultrasonic flaw detection when the continuity in the circumferential direction and / or the axial direction of the steel pipe is determined and the part determined to have a defect continues beyond a predetermined threshold. It is also described that it is determined to be harmful.

  On the other hand, in steel rolling bearings, it is known that inclusions having a length of less than several tens of millimeters affect the rolling fatigue life. For this reason, in the Patent Documents 2 to 4, the present inventors specify inclusions that affect the rolling fatigue life, and perform inspection by ultrasonic flaw detection on the finished rolling parts. It is proposed that these inclusions should not be present in the part.

In addition, data of defects existing in the inspection object detected by ultrasonic flaw detection are usually recorded for proof of inspection or investigation of the cause of defective products.
For example, in Non-Patent Document 1 and Non-Patent Document 2, as a method for recording data of defects detected by ultrasonic flaw detection, the reflected echo intensity obtained is converted into an analog signal and taken on the vertical axis, A method is described in which time is plotted on the horizontal axis and recorded in an analog chart format.
Further, in Patent Document 1 described above, the reflected echo intensity for each flaw detection pitch in the axial direction and the circumferential direction of the object to be inspected is measured and converted into a digital signal. A method is described in which the flaw detection pitch in the direction is taken on the horizontal axis and recorded digitally.

JP 2003-222617 A JP 2000-130447 A JP 2002-317821 A Japanese Patent Application No. 2002-293750 Special Steel, Vol. 46, No. 6, 1997, p14 Special Steel No. 51, No. 2, 2002, p27

  By the way, in order to detect inclusions having a length of less than several tens of millimeters using the method described in Patent Document 1, the flaw detection for evaluating the continuity in the axial direction and the circumferential direction of the object to be inspected. It is necessary to subdivide the pitch to increase the flaw detection sensitivity and lower the threshold value of the reflected echo intensity determined as a defect. However, if the flaw detection pitch is subdivided and the flaw detection sensitivity is increased, it is assumed that the electrical noise signal also increases, making it difficult to distinguish between defects and noise.

Here, since the electrical noise signal often appears periodically, it is sufficient to analyze and remove the periodically generated signal after measuring the total reflection echo intensity. However, the labor and cost required for the measurement increase. There is a problem of doing.
Further, in order to accurately detect inclusions having a length of less than several tens of millimeters, it is necessary to reduce the surface roughness of the object to be inspected and suppress the attenuation of ultrasonic waves. However, if the surface of the object to be inspected is subjected to processing such as turning or grinding in order to reduce the surface roughness, a processing flaw may occur in the circumferential direction of the object to be inspected. Unlike the electrical noise signal, the noise signal due to this processing flaw is not generated periodically, so it is difficult to distinguish it from a defect.

Furthermore, since the reflected echo intensity obtained from inclusions having a length of less than several tens of millimeters is weak, it is difficult to detect with high accuracy. For this reason, as described in Patent Document 1 described above, when the inclusion is determined only by the continuity in the axial direction or the circumferential direction of the object to be inspected, one long inclusion is two or more inclusions. Or the inclusion itself may not exist.
In addition, in Patent Documents 2 to 4 described above, detection of inclusions by ultrasonic flaw detection is described, but there is no mention of a method for determining the inclusions.

Further, in the above-described Non-Patent Documents 1 and 2, since all data of detected inclusions are stored, there is a problem that it takes time and cost to manage the data.
Therefore, the present invention has been made in view of such circumstances. For example, a defect determination that can accurately detect even a defect having a low reflection echo intensity, such as an inclusion having a length of less than several tens of millimeters. The challenge is to provide a method.

  In order to solve such a problem, as a result of intensive studies by the present inventors, “the reflection echo from the inclusions present in the object to be inspected is in the rolling direction (for example, the axial direction) of the object to be inspected. There must be continuous, and various noise signals must be continuously present in a direction perpendicular to the rolling direction of the object to be inspected (for example, in the circumferential direction) ”and“ two or more inclusions in the rolling direction at predetermined intervals. When it exists adjacently in the following range, it is found that it exists as one continuous inclusion ”, and the present invention has been made.

  That is, a defect detection method according to the present invention is a defect detection method for detecting a defect by irradiating an inspection object with ultrasonic waves and measuring a reflected echo from a defect present in the inspection object. The reflected echo of intensity or more detects a portion measured continuously in the rolling direction of the inspection object as a predetermined distance or more as the defect, and two or more defects are predetermined in the rolling direction of the inspection object. Two or more of the defects are detected as a single defect when they are adjacent to each other within a range of an interval or less.

According to the present invention, since the continuity of the reflected echoes in the rolling direction of the test object is used as a criterion for the defect, various noises extending in the direction perpendicular to the rolling direction are difficult to detect, and defects extending in the rolling direction are detected. It can be detected accurately.
In addition, in the case where two or more defects are adjacent to each other in the rolling direction within a predetermined interval or less, by detecting two or more defects as one continuous defect, even a defect having a weak reflected echo intensity It can be detected accurately.

In the present invention, the “rolling direction” refers to the direction in which the object to be inspected is rolled. For example, when the object to be inspected is a round bar or a ring, it is often the axial direction thereof.
Further, in the present invention, “continuous in the rolling direction” is not limited to the case where the linear direction L1 parallel to the rolling direction is continuous, as shown in FIG. , 45 °), and the case where it continues in the linear directions L2 and L3 inclined.
Furthermore, in the present invention, the “predetermined intensity” of the reflected echo used as a criterion for detection as a defect, the “predetermined distance” in which the reflected echo of the predetermined intensity or more continues, and two or more defects are detected as one defect The “predetermined interval” between two or more defects that are used as criteria for determination is appropriately changed according to the defect to be detected and the size of the inspection object.

  In the defect detection method according to the present invention, it is preferable that the predetermined intensity of the reflected echo used as a determination criterion when detecting as a defect is determined according to the size of the object to be inspected. For example, when the object to be inspected is a round bar or a ring, the curvature of the outer peripheral surface decreases as the outer diameter decreases, and the reflected echo intensity decreases. On the other hand, the curvature of the outer peripheral surface increases as the outer diameter increases. Therefore, the reflected echo intensity tends to increase. For this reason, when a round bar, raceway, or the like is an object to be inspected, when the outer diameter is thin, the predetermined intensity of the reflected echo intensity used as a criterion is reduced, and when the outer diameter is increased, the criterion is used as a criterion. By increasing the predetermined echo intensity, defects extending in the rolling direction can be accurately detected regardless of the size of the object to be inspected.

In the present invention, the defect can be detected with higher accuracy by using the reflection echo intensity obtained by subtracting the allowable value in consideration of the continuity of the defect as a criterion for detection as a defect. The allowable value refers to measurement variations due to differences in the width and thickness of defects, and is calculated according to the dimensions of the object to be inspected.
Further, in the present invention, in addition to the continuity of defects in the rolling direction of the inspection object, the direction from the surface of the inspection object toward the inside is used as a criterion for detecting two or more defects as one continuous defect. By using the continuity of the defect in the depth direction, it is possible to accurately grasp the size and position of the defect, so that even a defect having a weak reflection echo intensity can be detected with high accuracy.

In the defect detection method according to the present invention, in the inspected object in which the defect is detected, all data of the measured reflected echo is recorded, and the inspected object in which the defect is not detected In this case, it is preferable to record data of the measured maximum value of the reflected echo.
According to this, it is possible to efficiently record defect data existing in the inspection object.

  According to the defect detection method of the present invention, the reflected echo of a predetermined intensity or more detects a portion measured continuously over a predetermined distance in the rolling direction of the inspected object as a defect, and two or more defects are at a predetermined interval. When two or more inclusions are detected as one inclusion when they are adjacent in the following range, the reflected echo intensity is, for example, an inclusion having a length of less than several tens of millimeters. Even a weak defect can be accurately detected.

The best mode for carrying out the present invention will be described below with reference to the drawings.
<First embodiment>
First, after rolling a material made of SUJ2 having a poor cleanliness into a predetermined shape, turning, quenching and tempering, and grinding are performed to roll with a nominal number NU322 (outer diameter: 240 mm, inner diameter: 110 mm, width: 50 mm). An inner ring for a bearing was produced.

Next, the obtained inner ring was installed in the ultrasonic flaw detector shown in FIG. 2, and ultrasonic flaw detection was performed on the inner ring raceway surface under the following conditions.
As shown in FIG. 2, this ultrasonic flaw detector is a probe for ultrasonic flaw detection while rotating an object to be inspected 11 immersed in a storage tank 10 in which an ultrasonic transmission medium is stored in the circumferential direction. By moving 12 in the axial direction of the inspection object 11 (rolling direction, Z direction shown in FIG. 2), the entire surface of the track surface of the inspection object 11 is flawed.

Further, when the raceway surface is a curved surface, flaw detection is further performed by rotating the probe 12 in the axial direction along the raceway surface (rolling direction, θ direction shown in FIG. 2), thereby detecting the raceway surface and the probe surface. It is possible to keep the distance and the angle with the toucher 12 constant.
Here, the reflected echo of the ultrasonic pulse transmitted from the probe 12 to the inspection object 11 is analyzed by the ultrasonic flaw detector 20. Then, by synchronizing the reflected echo signal for each flaw detection pitch in the axial direction and the circumferential direction of the inspection object 11 and the pulse signal from the servo motor 14 for synchronously rotating and driving the turntable 13 and the inspection object 11, Reflected echoes for each flaw detection pitch in the axial direction and the circumferential direction are measured and digitally displayed by the control device 30.

  2 designates a servo motor drive control amplifier, and similarly, 16 designates the position of the probe 12 in the XYZ directions in the figure, and the axial direction and circumferential direction of the inspected object 11. And an XYZ stage that is moved along the track surface of the inspected object 11, 17 is a support part that supports the probe 12, and 18 is an attachment that attaches the probe 12 to the support part 17, Reference numeral 19 denotes a rotary encoder that detects the rotation state of the object to be inspected 11, and 40 denotes an alignment control amplifier for an XYZ stage.

[Ultrasonic flaw detection conditions]
Probe: Focus type probe Flaw detection frequency: 5 to 20 MHz
Vibrator diameter: 6 mm
Ultrasonic flaw detector: HIS3 (Nippon Kraut Kramer)
Incident angle: 19 ° (diagonal flaw detection method, refraction angle 45 °), 28 ° (surface wave flaw detection method, refraction angle 90 °) Ultrasonic transmission medium: water (including rust preventive agent)
Flaw detection gate: 2 mm depth position from the surface Flaw detection pitch: 0.5 mm pitch in the circumferential direction of the test object, 0.5 mm pitch in the axial direction of the test object

And the ultrasonic flaw detection result of different to-be-inspected object 11 is shown in FIG.3 and FIG.4, respectively. Here, FIG. 3 and FIG. 4 are diagrams showing the reflected echo intensity for each flaw detection pitch in the range of the 1/4 width in the axial direction of the object to be inspected and the 1/8 width in the circumferential direction.
Next, as shown in FIG. 3 and FIG. 4, the defect inspection is actually performed on the inspection object 11 in which the defects A to M are detected, and the defect inspection result is compared with the above-described inspection result by the ultrasonic flaw detection. Went.

  As a result, in FIG. 3, the defects A to C in which the reflected echo intensity of 30% or more is continuously measured in the axial direction of the inspection object 11 by two pitches or more are detected as inclusions that become defects even in the actual defect inspection. In the defects D and E, in which the reflected echo intensity of 30% or more was continuously measured for two or more pitches in the circumferential direction of the inspection object 11, no defect was detected in the actual defect inspection.

From the above results, it was found that a defect can be detected with high accuracy by detecting a portion where a reflection echo having a predetermined intensity or more continuously exists in the axial direction of the inspection object 11 for a predetermined distance or more as a defect.
Moreover, as shown in FIG. 5, the defect F and the defect G which adjoin via the distance of 1 pitch in the axial direction of the to-be-inspected object 11 were the defects by one continuous inclusion. Similarly, the defect J and the defect K were also defects due to one continuous inclusion.

On the other hand, as shown in FIG. 6, the defect H and the defect I which are adjacent to each other through a distance of 2 pitches in the axial direction of the inspection object 11 are two defects due to different inclusions. Similarly, the defect L and the defect M were two defects caused by different inclusions.
From the above results, it was found that when two or more defects exist adjacent to each other within a predetermined interval or less, the defects can be detected with high accuracy by detecting them as one continuous defect.

<Second embodiment>
First, after rolling a material made of SUJ2 having poor cleanliness into a predetermined shape, rolling, quenching, tempering, and grinding are performed, so that a rolling bearing having a nominal number of 6202 (outer diameter: 35 mm, inner diameter: 15 mm, width: 11 mm). An inner ring and an outer ring were produced.
Next, the obtained inner ring and outer ring were respectively installed in the ultrasonic flaw detector shown in FIG. 2, and ultrasonic flaw detection was performed on each track surface under the following conditions.

[Ultrasonic flaw detection conditions]
Probe: Focus type probe Flaw detection frequency: 5 to 20 MHz
Vibrator diameter: 6 mm
Ultrasonic flaw detector: HIS3 (Nippon Kraut Kramer)
Incident angle: 19 ° (diagonal flaw detection method, refraction angle 45 °), 28 ° (surface wave flaw detection method, refraction angle 90 °) Ultrasonic transmission medium: hydrocarbon-based cleaning liquid (including white kerosene and rust inhibitor)
Flaw detection gate: 2 mm depth position from the surface Flaw detection pitch: 0.5 mm pitch in the circumferential direction of the test object, 0.5 mm pitch in the axial direction of the test object

Then, the ultrasonic flaw detection results of the same specimen 11 were recorded by both the method shown in FIG. 7 as an example of the present invention and the method shown in FIG. 8 as a conventional example.
FIG. 7 is a diagram showing the reflected echo intensity for each flaw detection pitch obtained by ultrasonic flaw detection in the entire range in the axial direction and the circumferential direction of the inspection object. In the case of recording as shown in FIG. 7, the position and length of the defect present in the inspection object 11 could be determined at a glance.

  On the other hand, FIG. 8 is a diagram showing the relationship between the flaw detection time and the reflected echo intensity over the entire range in the axial direction and the circumferential direction of the inspection object. In the case of recording as shown in FIG. 8, the position at which the defect is detected based on the flaw detection time when the reflected echo having a predetermined intensity or more was obtained and the time for one rotation in the circumferential direction of the inspection object 11. Therefore, it is difficult to accurately determine the position and length of the defect present in the inspection object 11, and it takes time for the determination.

Further, data of the maximum value of the reflected echo obtained by the ultrasonic flaw detection of the inspection object 11 was recorded as shown in FIG. Note that FIG. 9 shows a record of the ultrasonic flaw detection results for two days, a sample whose reflection echo maximum value data is less than a predetermined intensity (50%) is determined as a non-defective product, and the maximum value is a predetermined intensity (50 %) Or more samples were judged as defective.
And sample No. determined as a defective product. 2, no. In FIG. 18, all the data of the obtained reflection echoes were recorded as shown in FIG.

  From the above results, all the data of the obtained reflection echo is recorded in the sample in which the defect is detected, and the maximum value data of the obtained reflection echo is recorded in the sample in which the defect is not detected. As a result, it was found that the defect information existing in the sample determined as a defective product can be grasped in detail, the result of the pass / fail determination of each sample can be easily recognized, and the proof of 100% inspection can be performed.

In addition, for samples determined to be non-defective, recording the maximum value of the obtained reflection echo, the average data of the maximum value of the reflection echo is larger on the second day than on the first day, etc. It turned out that the tendency for every lot can be recognized easily.
In the first and second embodiments described above, the defect detection is performed by dividing the reflection echo intensity into three stages. However, the present invention is not limited to this. For example, the defect detection is performed by dividing the reflection echo intensity into two stages. Alternatively, as shown in FIG. 10, the reflected echo intensity may be divided into four or more stages to detect a defect.

Here, as shown in FIG. 10, in the inspection object in which the defects a to n having the reflection echo intensity of 30% or more were detected, the defect inspection was actually performed in the same manner as described above. In the defects a, b, g, h, i, j, l, and m in which the echo intensity is continuously measured in the axial direction of the object to be inspected, defects due to inclusions are detected even in the actual defect inspection. It was.
Further, in the axial direction of the object to be inspected, a defect due to one continuous inclusion was detected in each of the defect c and the defect d, and the defect e and the defect f adjacent to each other through a distance of 1 pitch.
On the other hand, in the defects k and n measured at only one pitch in the axial direction of the object to be inspected, no defects due to inclusions were detected in the actual defect inspection. In addition, a defect due to two different inclusions was detected in the defect h and the defect i and the defect k and the defect l adjacent to each other through a distance of 2 pitches in the axial direction of the inspection object.

<Third embodiment>
First, after a rod-shaped material made of a spheroidized annealing material made of SUJ2 is processed into a predetermined shape, turning, quenching and tempering, and grinding are performed, so that the axial length is 200 mm with each outer diameter dimension shown in Table 1. An inspection object was produced. Then, on one end face in the axial direction of each object to be inspected, the distance from the outer edge portion to the core portion is 6 mm at a position of φ0. An artificial defect of 5 mm × 10 mm was formed.

Next, the obtained object to be inspected was placed in the ultrasonic flaw detector shown in FIG. Then, the focal length (water distance) and the amplifier strength were adjusted so that the reflection echo intensity of the artificial defect formed on the inspection object having an outer diameter dimension of 60 mm or more and less than 65 mm was 100%. Ultrasonic flaw detection was performed on the surface of the body. The results are also shown in Table 1. Table 1 also shows the reflected echo intensity obtained by subtracting the allowable value calculated according to the outer diameter size of the object to be inspected.
In this ultrasonic flaw detector, as shown in FIG. 11, a probe 52 is disposed in a storage tank 50 in which an ultrasonic transmission medium is stored, and an artificial defect 51 a is formed in the storage tank 50. The surface of the inspection object 51 is flawed by immersing the inspection object 51 and rotating it in the circumferential direction.

[Ultrasonic flaw detection conditions]
Probe: Focus type probe Flaw detection frequency: 15 MHz
Vibrator diameter: 6 mm
Ultrasonic flaw detector: USD15 (manufactured by Nippon Kraut Kramer)
Incident angle 0 ° (Vertical flaw detection)
Ultrasonic transmission medium: water (including rust inhibitor)
Flaw detection gate: 2-20mm depth position from the surface

  As shown in Table 1, it can be seen that the smaller the outer diameter of the object to be inspected, the smaller the reflected echo intensity. From this result, it was found that the defect can be detected with higher accuracy by determining the predetermined intensity of the reflected echo as a determination criterion when detecting as a defect according to the size of the object to be inspected. Further, it was found that the defect can be detected with higher accuracy by setting the predetermined intensity of the reflected echo used as a determination criterion when detecting as a defect to a value obtained by subtracting the allowable value.

It is explanatory drawing which shows an example of the continuity of the rolling direction used with the defect detection method which concerns on this invention. It is a schematic block diagram which shows an example of the ultrasonic flaw detector used with the defect detection method which concerns on this invention. It is a figure which shows an example of the ultrasonic flaw detection result in 1st embodiment. It is a figure which shows the other example of the ultrasonic flaw detection result in 1st embodiment. 5 is an optical micrograph showing defects F and G detected in FIG. 4. 5 is an optical micrograph showing defects H and I detected in FIG. 4. It is a figure which shows an example of the ultrasonic flaw detection result in 2nd embodiment. It is a figure which shows the other example of the ultrasonic flaw detection result in 2nd embodiment. It is a figure which shows the other example of the ultrasonic flaw detection result in 2nd embodiment. It is a figure which shows the other example of the ultrasonic flaw test in 1st and 2nd embodiment. It is a schematic block diagram which shows an example of the ultrasonic flaw detector used with the defect detection method concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Storage tank 11 Inspected object 12 Probe 13 Turntable 14 Servo motor 15 Servo motor drive control amplifier 16 XYZ stage 17 Support part 18 Attaching tool 19 Rotary encoder 20 Ultrasonic flaw detector 30 Controller 40 Positioning control amplifier 50 Storage tank 51 Inspected object 52 Probe

Claims (3)

In the defect detection method for detecting the defect by irradiating the object to be inspected with ultrasonic waves and measuring a reflection echo from the defect existing in the object to be inspected,
The reflected echo of a predetermined intensity or more is detected as the defect a portion measured continuously over a predetermined distance in the rolling direction of the inspection object,
When two or more of the defects are present adjacent to each other in the rolling direction of the inspection object within a predetermined interval or less, two or more of the defects are detected as one defect. Method.   In the inspected object in which the defect is detected, all data of the measured reflected echo is recorded, and in the inspected object in which the defect is not detected, the measured reflected echo is recorded. The defect detection method according to claim 1, wherein data of a maximum value is recorded.   The defect detection method according to claim 1, wherein a predetermined intensity of the reflected echo that is used as a criterion for detection as the defect is determined according to a dimension of the inspection object.