JP2533190B2 - Automatic ultrasonic flaw detection method for solid insulators - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a solid porcelain body such as a solid porcelain insulator and a long porcelain insulator, which is provided with a plurality of shades (hereinafter referred to as solid porcelain) ) Relates to an automatic ultrasonic flaw detection method for solid insulators used for flaw detection inside.

(Prior Art) In general, both ends of a solid porcelain porcelain body are cut and polished to remove unnecessary portions after firing, thereby forming smooth end faces. Therefore, in order to inspect the presence or absence of defects inside the porcelain of the solid insulators, the ultrasonic flaw detector test is conducted by bringing the probe of the ultrasonic flaw detector into contact with these polished both end surfaces.

The directivity angle of such a probe can be generally obtained by the following equation.

θ ₀ ≈ 70 × λ / 2a (degrees) where θ ₀ is the directivity angle of the probe, a is the radius of the probe, and λ
Indicates the wavelength of ultrasonic waves. According to the measured data, the sound velocity inside the solid insulators is 5900 m / sec, the radius of the probe used is 10 mm, and the vibration frequency is 2.0 MHz, so substitute these values into the above formula. Then, the directivity angle θ ₀ of the probe is about 10
This is shown in FIG. 4. The maximum diameter of solid insulators is 225 mm, and the total length is 1218 mm, but the spread of sound in products of this maximum size is a circle with a diameter of 225 mm equal to the body diameter at a distance of 638 mm from the end face as shown in FIG. Therefore, if flaw detection is performed from the upper and lower end faces, the entire porcelain body can be set as the defect detection range, and it is understood that the probe can be placed at the center of the insulator end face. Therefore, conventionally, the presence or absence of defects inside solid insulators has been inspected by such a method.

However, since solid insulators have many shades in the body,
Even if there is no defect inside, the flaw detection waveform by the flaw detection method described above is a special waveform with a forest echo as shown in FIG.
It is considered that this is because the echoes from each shade interfere with each other. If there is a defect inside, the second
As shown in the figure, defect echoes F ₁ , F ₂ , and F ₃ are generated in the forest echo, so these defect echoes are automatically detected and judged as defective. However, since the defect echo is hidden when the height of the forest echo increases, there is a problem that the internal defect detection accuracy is low.

(Problems to be solved by the invention) An object of the present invention is to solve the above-mentioned conventional problems and to suppress the height of forest echoes that are unavoidably generated in solid insulators to reduce internal defects. An object of the present invention is to provide an automatic ultrasonic flaw detection method for solid insulators whose detection accuracy is significantly improved.

(Means for Solving the Problem) In order to solve the above-mentioned problems, the present inventor repeatedly tested the occurrence status of the forest echo in solid insulators, and found that the contact position of the probe is a conventional common sense. On the contrary, it was found that the height of the forest echo can be reduced by setting the eccentric position off the central axis of the insulator.

The present invention has been completed based on such knowledge, and the probe is brought into contact with the eccentric position deviated from the insulator central axis on the upper and lower end surfaces of the solid insulator, and the probe is rotated around the insulator central axis. It is characterized in that the inside of a solid insulator is ultrasonically flaw-detected while rotating once.

As described above, in the present invention, the contact position of the probe with the upper and lower end surfaces of the solid insulator is the eccentric position deviated from the insulator central axis. As a result, the height of the forest echo can be reduced to 1/2 or less of that when the probe contact position is on the insulator central axis. However, when an appropriate eccentricity amount was investigated using a sample in which it was known that there was an internal defect in the center, 100% defect echo could be detected at a position 10 mm from the insulator center axis, but at a position 15 mm. However, the defect echo could not be detected at a rate of about once every five times. Therefore, the amount of eccentricity should be 15 mm or less for regular size solid insulators.

Further, as shown in FIG. 4, if the flaws are detected from the upper and lower end surfaces of the solid insulator, the whole body is in the detectable range, so it seems that the position of the probe may be fixed. When observing the defect echo while rotating the probe around the central axis of the insulator, the defect echo sometimes disappeared at a certain angle. It is thought that this is because the echoes from each shade interfered with each other due to the bending of the solid insulators in the axial direction and the variation in the distance between the shades, and the defect echo happened to disappear. Therefore, in the present invention, by performing ultrasonic flaw detection while rotating the probe once around the central axis of the insulator,
Made it possible to detect 100% of internal defects.

Thus, according to the present invention, since the height of the forest echo generated by the shade of the solid insulator can be 1/2 or less of the conventional one, it is possible to detect the defect echo hidden in the forest echo. It becomes easy, and the detection accuracy of the internal defect can be greatly improved.

 Next, a preferred embodiment of the present invention will be described.

(Example) As shown in FIG. 3, the porcelain body has a diameter of 200 mm and a total length of 1
Both upper and lower end faces (2) of 000mm solid insulators (1),
The transducers (3) and (3) are automatically brought into contact with the positions eccentric to the insulator center axis of (2) by 5 mm, respectively, and the vibration frequency exceeds 2.0 MHz while rotating 360 degrees around the insulator center axis. An ultrasonic flaw detection test using sound waves was performed.

During the test, the multiplexers (4), which are electronic switching devices, alternately select the probes (3) and (3) on both end faces (2) and (2), and the flaw detection waveform is transmitted through the ultrasonic flaw detector (5). It was output. The output analog waveform of the ultrasonic flaw detector (5) was digitized by the A / D converter (6), taken into the computer (7) and subjected to software processing, and only the defective waveform was detected.

According to the method of the present invention as described above, an internal defect 100
Ultrasonic flaw detection of a solid insulator in a book was able to detect internal defects with 100% accuracy. On the other hand, when the probe (3) was fixed on the insulator central axis as in the conventional case and the same ultrasonic flaw detection was performed, the internal defect detection accuracy was 87.
%.

(Effects of the Invention) As described above, the present invention, in the automatic ultrasonic flaw detection test for solid insulators, places the probe at a position eccentric from the insulator central axis and also 1 By rotating it, the height of the forest echo was reduced and the accuracy of detecting internal defects was significantly improved. Therefore, the present invention contributes to industrial development as an automatic ultrasonic flaw detection method for solid insulators suitable for detecting internal defects in solid insulators that cause forest-like echoes such as solid SP insulators and long stem insulators. However, it is extremely large.

[Brief description of drawings]

Fig. 1 is an ultrasonic flaw detection waveform diagram for solid insulators without defects inside, and Fig. 2 is an ultrasonic flaw detection waveform for defective products containing defect echoes F ₁ , F ₂ and F ₃ in the forest echo. FIG. 3 and FIG. 3 are block diagrams illustrating an embodiment, and FIG. 4 is a cross-sectional view showing the relationship between the spread of sound waves and the defect detectable range inside solid insulators. (1): Solid insulators, (2): Both end faces, (3): Probe.

Claims (1)

(57) [Claims] 1. Upper and lower end surfaces (2) of a solid insulator (1),
The probe (3) is placed at an eccentric position off the insulator central axis of (2).
And the probe (3) is rotated once around the central axis of the insulator to perform ultrasonic flaw detection on the inside of the solid insulators, which is an automatic ultrasonic flaw detection method for solid insulators.