JP2008180536A - Apparatus and method for inspecting leakage of housing and the like - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a leakage inspection apparatus capable of inspecting leakage of housings or containers having holes or openings and performing accurate inspection in a short time without being affected by external noise. <P>SOLUTION: A compressed gas is filled in an object to be inspected, and the object to be inspected is placed in an inspection container. A microphone for detecting leakage sound generated from the object to be inspected is mounted to the inspection container, and another microphone is mounted to the outside of the inspection container. The leakage inspection apparatus is provided with a frequency analyzer for displaying the frequencies of sound detected by both microphones and a computer for comparing power spectra generated by the frequency analyzer with each other. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an apparatus and an inspection method for inspecting leakage of housings of machine parts and other containers by detecting leakage sound.

  There are innumerable containers for storing liquids and gases, and these containers are sealed so that the stored liquids and gases do not leak. Therefore, sealed containers such as fuel tanks and drums and housings constituting the mechanical device need to be inspected for leakage of liquid or gas contained therein. Conventionally, the inspection of leakage of objects such as containers and housings has been performed by various methods.

(1) In a method called foam leak inspection, a viscous liquid is sprayed on a joint portion of a pipe to which air or gas is pumped, and the leak inspection is performed from the state of generation of bubbles.
However, the foam-type leak inspection in which a viscous liquid is sprayed on the leak inspection section requires a lot of inspection steps and requires operations such as wiping after the inspection is completed, which is a troublesome operation. In addition, there is a risk that an erroneous inspection such as an oversight or the like, and a leak inspection is difficult in the case of a minute leak.

(2) In a method called submersion type leak inspection, air or nitrogen gas is injected and sealed inside the object to be submerged, and the leak inspection is performed from the state of occurrence of bubbles.
However, the submersion type leak inspection, in which air or nitrogen gas is injected into the interior and submerged, is a troublesome operation that requires a lot of man-hours, such as drying after the inspection. There is a problem that it is difficult to detect.

(3) In a method called helium type leak inspection, the inside of the inspection object is evacuated and the leak inspection is performed by the helium concentration.
However, in the helium type leak inspection in which the inside is in a vacuum and the leak inspection is performed with helium, the inspection apparatus is very expensive, and the helium used for the inspection is also very expensive and cumbersome.

(4) A method for inspecting leakage by detecting the ultrasonic wave generated when the pressure of the air inside the container is increased and the air inside leaks outside through a small hole has been invented.
However, the method of detecting the ultrasonic waves generated when high-pressure air is sealed inside the container and the air leaks makes it difficult to distinguish the leaking ultrasonic waves from the ambient noise because the amplitude of the ultrasonic waves is extremely small. For this reason, it is necessary to place the object to be inspected in a sealed container and to provide sound insulation. However, even if sound insulation is performed in this way, fine vibrations transmitted through surrounding objects such as the floor surface are transmitted as noise into the shielding container, affecting the inspection. In addition, since ultrasonic waves have a strong straightness, the inspection accuracy decreases when the leaked portion is blocked by the inspection object as viewed from the microphone.

  The “beer barrel leakage inspection device” according to Japanese Patent No. 3338777 has a fixed sound insulation device in which a recess capable of accommodating the entire beer barrel and a hole for holding by hand among the top and bottom surfaces of the beer barrel. A surface on which the provided side is placed, a table that forms a space for sealing the entire beer barrel in close contact with the recessed opening end surface of the fixed sound insulation device, and a fixed sound insulation device, which is filled with compressed air. A first ultrasonic detector and a second ultrasonic detector for detecting whether or not the beer barrel leaks by detecting an ultrasonic wave generated by an air leak in the beer barrel; An acoustic wave detector is provided in the vicinity of the surface of the beer barrel opposite to the surface facing the table, and the second ultrasonic detector is on the surface side of the beer barrel placed on the table. Provided near the hole, front Each of the first ultrasonic detector and the second ultrasonic detector includes a sound wave sensor that picks up a sound wave, and an ultrasonic frequency band that is determined as an air leak from a sound wave signal picked up by the sound wave sensor. The beer keg can be detected from the signal that has passed through the band pass filter.

The “ultrasonic leak inspection device” according to Japanese Patent Application Laid-Open No. 11-142279 facilitates the work of measuring leaks of pipe joints, containers such as fuel tanks or rubber or synthetic resin bags, This is an ultrasonic leak inspection device that accurately detects leaks. Therefore, an ultrasonic detector for detecting leakage sound, a band filter for inputting an output signal of the ultrasonic detector and passing only a predetermined narrow band frequency, and a detector for detecting the output signal of the band filter And.
"Leak inspection device for beer barrels" according to Japanese Patent No. 3387777 “Ultrasonic Leak Inspection Device” according to Japanese Patent Application Laid-Open No. 11-142279

  There are various known methods for inspecting leakage in this way, but there are problems as described above. The problems to be solved by the present invention are these problems, and provide a leakage inspection apparatus and a leakage inspection method which can easily detect leakage of housings and containers of a mechanical device accurately and easily in a short time.

  The leak inspection apparatus according to the present invention places an object to be inspected in an inspection container (measurement chamber) prepared in advance, and fills the object to be inspected with predetermined compressed air (or any compressed gas). The compressed air is filled from the openings and holes provided in the object to be inspected. When there are a plurality of openings and holes, the other openings and holes are closed except for one place. Therefore, when a minute hole exists in the object to be inspected, air flows out from the inside of the object to be inspected into the inspection container, and a leakage sound is generated at this time. On the other hand, by closing an opening or a hole provided in the inspection object and filling the inspection container with compressed air, the inspection can be performed so that air enters the inspection object from the minute hole.

  In the present invention, the microphone can be attached outside the inspection object inside the inspection container, or can be arranged inside the inspection object to detect leakage sound. By the way, this leaking sound does not have a single frequency, but has a vibration spectrum distributed between several KHz to several tens of KHz. In the present invention, it is not an ultrasonic wave but an audible vibration of 20 KHz or less. Detect leaking sound with several sound waves. As a result, a decrease in inspection sensitivity resulting from the strong straightness of ultrasonic waves is avoided, and unevenness in inspection accuracy is eliminated.

  The leaked sound wave has a very small amplitude, so it is very important to distinguish it from ambient noise. Therefore, in the present invention, a test container for sound insulation is used. It is essential to process the signal. In order to detect leaking sound, it is common to distinguish a microphone signal from noise by amplitude, but in the present invention, noise signal is distinguished by using frequency instead of amplitude.

  Therefore, in addition to the microphone attached in the inspection container, a noise recording microphone is provided outside the inspection container, and signals are simultaneously collected from the two microphones. Then, the frequency spectrum is obtained by applying each signal to two frequency analyzers. Next, the peak of the signal spectrum in the cuvette is examined to determine whether the frequency of each peak is included in the frequency spectrum of ambient noise.

  If the same frequency appears in both the cuvette and the ambient noise, the noise is determined regardless of the amplitude. If it appears only on the microphone in the cuvette, it is determined as a leak sound. Therefore, frequency peak comparison means (computer) for checking the presence / absence of a peak at the same frequency is provided. Further, the accuracy and reliability of the leak inspection are improved by making a determination on a plurality of peaks instead of only one.

  The leak inspection apparatus of the present invention has a defect (micro hole) in the inspection object by installing the inspection object in the inspection container and supplying compressed air inside the inspection object or outside the inspection object. In this case, air flows and the sound generated at this time can be detected as a leaking sound. The inspection method of the present invention is superior to the conventional inspection method in that it can be instantaneously inspected, and does not require a long time for performing the inspection. The system is highly reliable with no mistakes such as misjudgment due to human error.

  And since the leak test is equipped with two microphones inside and outside the test container, it is possible to distinguish the real leak sound from the outside noise, and it is highly accurate and reliable. Leakage determination can be performed. In particular, even in a noisy environment such as a factory, it is possible to accurately inspect leakage sound without being affected by the noise.

  FIG. 1 is an embodiment showing an overall configuration diagram of a leakage inspection apparatus according to the present invention, where (a) shows a case where the inspection container 1 is open and (b) shows a case where the inspection container 1 is closed. Although the specific shape and size of the cuvette 1 are not limited here, the cuvette 1 is composed of the base 2 and the lid 3, and the lid 3 can be lifted and opened without having a bottom. Therefore, the inspection object 4 is installed at a predetermined position of the base 2, and the lid 3 is lowered to be closed and sealed.

  The lid 3 can be moved up and down by an air cylinder 5. Therefore, the support column 6 stands vertically from the base 2, and the upper plate 7 is attached horizontally to the upper end of the support column 6, and the air cylinder 5 is attached to the upper plate 7. The piston rod 8 of the air cylinder 5 extends downward, and a frame 9 is attached to the tip (lower end) of the piston rod 8.

  The frame 9 has a structure in which an upper plate 10 and a lower plate 11 are connected by a plurality of rods 12, 12..., And the upper plate 10 is connected to the tip of the piston rod 8. An air supply unit 13 is provided at the center of the frame, and the lid 3 of the cuvette 1 is attached to the lower plate 11. Therefore, the lid 3 can move up and down with the frame 9 as the piston rod 8 of the air cylinder 5 expands and contracts. When it is raised, it can be opened as shown in FIG. 1 (a), and when it is lowered, it can be closed as shown in (b).

  A guide rod 14 is attached in parallel with the piston rod 8, and the guide rod 14 fits and slides on a bearing provided on the upper plate 7, so that the frame 9 does not rotate and change its orientation. By the way, the inspection object 4 placed on the base 2 is a container made by welding cast iron, aluminum alloy, or an iron plate, and has a space in which gas or liquid can be accommodated. And the hole 15 used as an opening part is formed in at least one place.

  The hole 15 is closed by the lid 3 being lowered and closed at the same time as the air supply unit 13. In this state, air is supplied from the air supply unit 13, and the internal space of the inspection object 4 is filled with compressed air. Is done. If there is a minute hole somewhere in the inspection object 4, air leaks from the minute hole, and a leakage sound generated due to the air leakage is detected.

  Therefore, a leakage sound detection microphone 16 is attached to the lid 3 of the inspection container 1, and the leakage sound of air leaking from the inspection object 4 can be detected by the microphone 16. On the other hand, in the apparatus of the present invention, in addition to the microphone 16, a microphone 17 for detecting ambient noise is attached to the frame 9 outside the detection container 1.

  FIG. 2 shows a block diagram of the leak inspection apparatus. The inspection object 4 is installed in the internal space 18 of the inspection container 1 closed by the lid 3 being lowered on the base 2, and high-pressure air for inspection is supplied from the hole 15 of the inspection object 4. Therefore, if a minute hole exists in the inspection object 4, air flows out from the minute hole, and a leaking sound is generated along with the outflow. The microphone 16 can detect this leakage sound.

  A power spectrum is created by the frequency analyzer for the detected leak sound. Similarly, another microphone 17 attached to the outside of the cuvette 1 detects ambient noise, and a power spectrum is created from this by a frequency analyzer. FIG. 3 is a specific example showing the power spectrum of leakage sound detected by the microphone 16 and the power spectrum of noise detected by the microphone 17.

  The microphone 16 attached in the cuvette 1 detects a leak sound of air flowing out from the inspection object 4 and may contain external noise. Therefore, in the leak detection apparatus of the present invention, a microphone 17 is attached to the outside of the cuvette 1, and the frequency of the sound detected by both microphones 16 and 17 is analyzed to create a power spectrum as shown in FIG. To do.

  By the way, when both power spectra are compared, it can be seen that leakage sounds having frequencies A, B, and C exist in the power spectrum obtained by detecting the leakage sound with the microphone 16 and analyzing the frequency. These leakage sounds of frequencies A, B, and C are not detected from the microphone 17 that detected the noise. Therefore, it is considered that there are minute holes in the inspection object 4, and leakage sounds having the frequencies A, B, and C are emitted from these minute holes.

  These power spectra can be compared instantaneously by a computer. If there is a frequency that exists only in the power spectrum of the leaking sound, it is determined that a minute hole exists in the inspection object 4. . On the other hand, if all frequencies are present in the power spectrum in which noise is detected in the power spectrum of the leakage sound, it is determined that there are no micro holes in the inspection object 4.

The Example which shows the leak inspection apparatus which concerns on this invention. The block diagram of a leak inspection apparatus. The power spectrum detected by the microphone attached to the leak tester.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Test container 2 Base 3 Cover part 4 Inspected object 5 Air cylinder 6 Post 7 Upper plate 8 Piston 9 Frame
10 Upper plate
11 Lower plate
12 bars
13 Air supply section
14 Guide bar
15 holes
16 microphone
17 Microphone
18 Internal space

Claims (4)

In an apparatus for inspecting leakage of housings or containers having holes or openings formed by welding cast iron, aluminum alloy castings, or iron plates, etc., an inspection container for installing the inspected object as the housings or containers in an internal space The lid of the inspection container can be opened, and means for filling the inspection object installed in the inspection container from outside with a compressed gas is provided, while the inside of the inspection container and outside of the inspection container are provided. Leakage inspection characterized by having a microphone installed and a frequency analyzer for analyzing the frequency of the sound detected by each microphone, and a computer for comparing the power spectrum output from the frequency analyzer apparatus. In an apparatus for inspecting leakage of housings or containers having holes or openings formed by welding cast iron, aluminum alloy castings, or iron plates, etc., an inspection container for installing the inspected object as the housings or containers in an internal space The lid of the inspection container can be opened, and means for filling with compressed gas is provided in the inspection container from the outside so as not to enter the inspection object. A microphone is attached outside the container, and a frequency analyzer for analyzing the frequency of the sound detected by each microphone is provided, and a computer for comparing the power spectrum output from the frequency analyzer is provided. Leakage inspection device characterized. In the method for inspecting leakage of housings and containers having openings or holes on the surface, the inspection objects which are the housings and containers are installed in an inspection container that can be opened and closed. Air or other gas is filled from the outside to increase to a predetermined internal pressure. At this time, if there is a minute hole in the object to be inspected, the gas flows out from the minute hole to the inspection container, and the leakage sound at this time is detected as the inspection container. Detecting and analyzing the frequency with a microphone mounted inside, while comparing the power spectrum of both frequencies compared to the frequency of noise detected by a microphone mounted outside the cuvette, determine the leak from the microhole Leak inspection method characterized by performing. In the method for inspecting leakage of housings and containers having openings or holes on the surface, the inspection objects that are the housings and containers are installed in an openable inspection container, the inspection container is closed and the inspection object Air or other gas is filled from the outside so as not to enter, and the internal pressure is raised to a predetermined internal pressure. At this time, if there is a minute hole in the inspection object, the gas flows from the minute hole to the inspection object. The leakage sound is detected by a microphone installed in the object to be inspected and the frequency is analyzed. On the other hand, the power spectrum of both frequencies is compared with the frequency of noise detected by the microphone installed outside the inspection container. Leak inspection method characterized by performing leak judgment from minute hole.

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