JPH07159270A - Leak test method and apparatus for vessel - Google Patents

Abstract

PURPOSE:To check leakage accurately and automatically by detecting an ultrasonic wave generated by vibration when the compressed air in an hermetically sealed vessel leaks through a hole. CONSTITUTION:A drum 1 is laid on a chain conveyor 2 and carried into an hermetically sealed leak tester 3 where it is supported by an elevating/lowering frame 4. The drum 1 is set vertically at a predetermined position and secured at its top plate 6 side and bottom plate side by means of a jig, e.g. a disc 5 opening to the right and left. The disc 5 holds the drum 1 through an elastic material, e.g. a rubber plate 7, thus preventing the mixing of noise. A narrow rubber plate 7 is preferably employed because a wide rubber plate 7 chokes the entire surface of the top and bottom plates making detection of a hole impossible. Mouthpieces for injection port 9 and ventilation port 10 are fixed to the top and bottom sides of the drum 1 and compressed air is fed through a piping fixed to the disc 5. Acoustic emission(AE) caused by a hole or a crack is then detected by touching a 200kHz resonance AE sensor 11 having frequency band of 50kHz-1MHz to the drum 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an airtight leak test method and apparatus for containers such as steel drums.

[0002]

2. Description of the Related Art Conventionally, a steel drum is JIS Z-160.
As specified in 1 (steel drum), after forming a steel plate into a cylindrical shape, the top plate with the inlet and ventilation caps attached to the upper and lower ends of the welded body and the bottom plate It is manufactured by winding it up. The container is usually 20 to 200 liters and is used as a liquid container. The most important function of this container is to prevent the contents from leaking during transportation or storage after the contents are stored in the drum. Therefore, the airtightness test performed during the manufacturing process of containers such as drums is an important quality control test.
Also in 1901, compressed air with a gauge pressure of 30 kPa is sent into the container and immersed in water (submersion test) or soap water is applied to inspect for leaks by inspecting for leaks and water is injected into the container at 250 kPa. There is a provision of a water pressure test for checking for leaks by conducting a test for 5 minutes under a gauge pressure.

Further, it is general that 100% of airtightness tests are conducted in a production line for containers such as steel drums. The method used for the test in this line is to enclose compressed air in the container and apply soap water to the test place to visually inspect for bubbles that occur when there is a leak. Helium gas sealed in the container with compressed air, or by depressurizing the closed outer cover that covers the outside of the container to detect pressure changes in the container and inspect for leaks. There are three types of helium leak testers that detect the degree of leakage and inspect for leaks.

[0004]

Among the above-mentioned leak tests that have been widely used, the soap water test is an extremely sensitive test method performed by a trained inspector, and the diameter of the container Even small holes of about 0.005 mm can be detected, and there is no problem in practical use. However, since the presence or absence of leakage is inspected by visually observing minute bubbles of soapy water generated from a leaked portion, there is a problem in that the inspection result varies depending on the skill level and fatigue level of the inspector.

Further, when the holes formed in the container are large holes having a diameter of about 1 mm, the amount of air leaking is large, and bubbles of soapy water are immediately destroyed, so that there is a drawback that the leak can be easily overlooked. The differential pressure type leak tester is effective when the detectable hole is relatively large with a diameter of 0.2 mm or more,
The detection accuracy is poor in the case of small holes. In addition, a sharp pressure sensor is required to improve the detection accuracy. On the other hand, the helium-type leak tester can detect even small holes with a diameter of about 0.005 mm and is excellent as an inspection device, but the device cost is high and the container There is a drawback in that the cost of using helium enclosed inside is high compared to other test methods.

[0006]

[Means for Solving the Problems] Therefore, the inventors of the present invention have made an earnest effort.
As a result of repeated husbands, these problems should be solved
When the compressed air enclosed in the container leaks from the hole,
Whether there is a leak by detecting the ultrasonic waves generated by vibration
A method and apparatus for automatically inspecting. The invention
(1) Enclose or decompress compressed air in the container, or
Enclose or decompress compressed air in the closed outer lid to cover the container.
The difference between the internal pressure and the external pressure is 0.5 to 2.0 kgf / cm ²Sir
Empty the container from the inside to the outside or in the opposite direction.
Propagation through the container body that occurs when air leaks 100-30
0 kHz wave is detected by the sensor that touches the container
The container is characterized by inspecting the container for airtight leaks.
Airtight leak test method.

(2) The top plate and the bottom plate of the container are held and fixed by a jig with an elastic material interposed therebetween, and compressed air is supplied into the container while vibration from other mechanical devices is blocked. Inject or discharge the air in the closed outer lid that covers the container outside the container,
A container airtight leak testing device, which is characterized by inspecting a container airtight leak. (3) It is possible to confirm in advance whether the operating state of the wave detecting device is normal by detecting the wave generated when injecting compressed air into the container or discharging the air in the closed outer lid that covers the container. An airtight leak test device for a container, which detects a wave caused by a leak of air in the container after the operation. (4) The container according to any one of (1), (2) and (3), characterized in that the container is inspected for airtightness while the inner surface or outer surface or a part or whole of the inner or outer surface of the container is wet with a liquid material. Airtight leak test equipment.

[0008]

The present invention will be described in detail below. Sound is emitted when an object is destroyed, but a weak ultrasonic wave of several kHz to several MHz that cannot be heard by humans is generated due to the small deformation and vibration before the destruction of the solid and the generation and development of minute cracks. To do. This is called acoustic emission (hereinafter abbreviated as AE) and is defined as "a phenomenon in which energy released by deformation and destruction of a solid becomes an acoustic pulse and propagates". Until now, it has been applied to research for elucidation of plastic deformation and fracture mechanism of materials and for monitoring tool damage during cutting / polishing, but it is the AE of the present invention that this AE is applied to an airtight leak testing machine for containers. With the air-tightness leak tester, it is possible to prevent the vibration of the minute container body that occurs when air leaks from the inside of the container and the minute breaking sound that occurs when the liquid film that wets the surface of the container breaks through the container body. This is a method of detecting leakage of the container by detecting it.

FIG. 1 is a schematic diagram of an AE type airtight leak tester. FIG. 1 (A) is a transverse sectional view of the AE type airtight leak tester, and FIG. 1 (B) is a front sectional view thereof. A block diagram and a flow chart of an AE type airtight leak tester using this AE type airtight leak tester will be described with reference to FIGS. 2 and 3 based on an example of application to a steel drum. That is, FIG. 2 is a signal processing block diagram of the AE type airtight leak tester. Further, FIG. 3 is a flow chart of the inspection. In addition, in the following description, the drum is a can manufacturing process in which the drum is conveyed horizontally,
This is not limited to horizontal placement, and in the can manufacturing process in which the drum is conveyed vertically, it is sufficient to take appropriate measures, and the drum is not particularly limited. Then, as shown in FIGS. 1A and 1B, the drum 1 is conveyed horizontally on the chain conveyor 2 and then to the airtight leakage tester 3. Here, after the height of the drum is set at a predetermined position by being supported by the pedestal 4 which moves up and down, the drum top plate 6 is opened or closed by hydraulic or pneumatic pressure to the left or right by a jig such as a disk 5 or an arm.
And the main plate side is held and fixed, and the gantry descends.

The fixing jig holds and fixes the drum through an elastic substance such as a rubber plate 7. When the disk and other metal parts that make up the other device parts are in contact with the drum, the ultrasonic waves generated by the movement of the conveyor, the movement of other machinery in the same factory, or the contact between the drums may occur. It is not preferable because it propagates and enters as noise and reduces the inspection accuracy. The rubber can block the vibrations and noises around it, but on the other hand, it must have a hardness that it is not compressed by the pressure that clamps the top and bottom plates of the drum.
A material having a hardness of 0 to 90 is preferable.

When the fixing jig is a disk, a rubber plate having a thickness of about 30 mm, which is thicker than the height of the drum chime 8, is attached and held and fixed on the surface of the top plate of the drum. When high-pressure compressed air is filled in the drum, the top plate side expands first, and then the body part expands, causing permanent deformation, so it is necessary to set an appropriate pressure, but this holding and fixing method is the most important. Since it has the effect of suppressing the expansion of the top and bottom plate, which is easily deformed, the inspection can be performed with a relatively high internal pressure, and the inspection accuracy is high. The rubber plate may hold the drum at the tip of the chime portion, but since it is pressed with a large pressure and the rubber plate is greatly worn, it is better to hold it on the flat portion of the top plate. In this case, the rubber plate may not be in contact with the entire surface of the top and bottom plate, but a hole may be partially bored in the rubber plate.

If the rubber plate is in contact with the entire surface of the top plate, and if there is a hole in the top plate, the hole will be blocked by the rubber plate and the hole cannot be detected. It is desirable that the contact is as narrow as possible in terms of strength for holding the drum. In addition, a mouthpiece serving as an inlet 9 and a ventilator 10 is attached to the top and bottom sides of the drum, and compressed air injected by a pipe attached to the top and bottom side disk is sealed from the mouthpiece into the drum or air is supplied. In order to discharge, it is necessary to secure a passage for air by hollowing the hole corresponding to the mouthpiece in the rubber plate so as not to block the mouthpiece.

When the fixing jig is an arm, since the drum is held and fixed by the tip of the arm covered with rubber, the open area of the drum surface is large and the area of the container that can be inspected is large. . However, in this method, when the pressure of the compressed air to be enclosed becomes large, the deformation of the top plate of the drum cannot be suppressed, so the internal pressure must be lowered.
Further, in the case of holding and fixing the top and bottom sides of the container by this method, the ventilation port side of the mouthpiece is previously sealed with a cap, and a device for directly connecting a pipe for injecting or exhausting air from the injection port side is used. .

One type of steel drum having a capacity of 200 liters uses a steel plate having a thickness of 1.0 mm to 1.6 mm, from L grade to H grade.
There are up to grades, and the outer surface of the drum is generally painted, but the inner surface is the case where the chemical conversion treatment is left as it is and the case where it is painted after the chemical conversion treatment. Further, there is a steel sheet which is made of galvanized steel sheet or stainless steel sheet and whose inner and outer surfaces are unpainted. Based on the results of tests conducted on these various drums under various conditions, when compressed air is enclosed inside, the pressure is 0.5 to 2.0 kgf / gauge pressure.
Enclose with air of cm ² , preferably 0.7 to 1.2 kgf / cm ² . The higher the air pressure, the higher the accuracy of leak inspection, but on the other hand, when the internal pressure increases, it is necessary to make the hydraulic mechanism of the top plate holding and fixing disk to prevent deformation of the drum large capacity, so appropriate pressure should be set. It is desirable to select it.

Further, steel plates and welded parts of various drums,
Alternatively, as a result of performing a leakage test on the leakage portion and the size of the hole generated in the tightening portion and analyzing the generated AE signal,
Ultrasonic waves of 100 kHz to 400 kHz are generated, and there are differences in strength depending on the presence or absence of coating on the drum, the leakage location, and the size of the hole, but it was found that the signals around 200 kHz were remarkable. . Ie 2
It has been found that if a filter that preferentially detects a signal of 00 kHz is used, noise caused by other machines and collision noise can be relatively effectively removed, and the inspection accuracy is improved.

The AE sensor 11 contacts the surface of the container and converts the elastic vibration propagating through the container body into an electrical signal, which is a circular body made of a ceramic piezoelectric body and having a diameter of about 10 mm. . It is omnidirectional so that AE signals in any direction can be detected. When the sensor is in contact with the surface of the container, an air layer between the sensor and the surface of the container causes signal attenuation, so the surface of the sensor is provided with a thin layer of glycerin or an aqueous solution of surfactant or water. There is a need. The embodiment of the present invention employs a system in which a thin layer of water is provided so that continuous inspection can be performed in the drum manufacturing line. That is, a rubber ring with a height of 0.8 mm and a water injection pipe connected to it are installed around the sensor, and the water supplied from the water injection pipe is distributed on the surface of the sensor surrounded by the rubber ring by a certain amount. Remains, and the excess is overflowed and discharged from a slit provided in a part of the rubber ring.

The sensor having such a structure can be moved up and down by the air cylinder 12, and when the sensor is pressed from the lower part of the container body, the sensor is placed at a constant interval by the thickness of the rubber ring, and water is put in the container. It comes in contact through the layers. Container 1 to inspect if it is a steel drum
One sensor is sufficient for each sensor, but in order to avoid an inspection error due to a malfunction of the sensor, in this embodiment, two systems including a sensor and an electric circuit described below are provided, and at least one of them is provided. If a leak can be detected by one of the above, it will be judged as a failure. Further, the sensor is selected to have appropriate frequency characteristics and sensitivity according to the frequency of the generated ultrasonic wave. In this embodiment, however, the frequency of 200 kHz was the most prominent in the steel drum as described above. , 200k in the frequency band of 50kHz to 1MHz
It uses a Hz resonance type and a waterproof type.

Next, as shown in FIG. 2, after a minute voltage obtained by converting elastic vibration into an electric signal by a sensor is amplified by a preamplifier, mechanical noise around the AE signal and the surrounding mechanical noise are passed through a filter. Suppress the interfering noise and extract only the signal of the required frequency component. Since environmental noise such as mechanical vibration often has a low frequency, a frequency signal of several tens of kHz or less is cut off by a filter. It is the noise generated when injecting compressed air into the container that is most likely to be misjudged at the frequency most similar to the signal due to the leakage of the container in the ambient noise. Therefore, as will be described later, while injecting compressed air, device diagnosis is performed to test whether the operation of the sensor is normal. That is, if the AE signal is detected within 0.5 to 0.7 seconds after injecting compressed air, it is judged that the operation of the sensor is normal, and if the signal is not detected, it is judged that the operation of the sensor is defective and the inspection of the device is performed. I am going to do.

Leak inspection is started 0.1 to 2 seconds after the compressed air is injected and a predetermined pressure is reached. The inspection is performed for 1.0 to 2.5 seconds, and the number of times a signal larger than a preset threshold is detected is measured every 100 msec (the number of peaks exceeding the set value is ringed down, RD for short).
That is, the cumulative value within the inspection time is automatically obtained, and further compared with a preset alarm set value, and if the RD value is larger than that, it is determined as a failure and an alarm is issued. In the case of leakage from a large hole, RD exceeds the alarm set value in a short time, but in the case of a small hole, RD does not reach the warning set value within a predetermined inspection time even if wet. Judge as pass. Therefore, the longer the inspection time is, the smaller the size of the hole that can detect the leakage becomes, and the better the inspection accuracy becomes. However, the inspection time directly affects the productivity, so it is necessary to decide the inspection time at an appropriate time. is necessary.

When compressed air is injected when the inner or outer surface of the leaking container is wet with a liquid such as water or an aqueous solution of a surfactant, the container leaks before the air leaks from the leaked portion. The film of liquid wetting the
At that time, the same AE signal is emitted. Therefore, even if the container has a minute hole that does not generate the RD value that reaches the predetermined alarm set value in the inspection time of 2 seconds, if the inner surface or the outer surface of the container is wet with the liquid, the alarm set value can be set in a short time. Signals that exceed can be detected. That is, by wetting the inner surface or the outer surface of the container with the liquid, the limit of the size of the hole that can be detected is improved, and the inspection time can be shortened.

In order to specifically utilize such effects, the present invention devises the following device. That is, in the case of a steel drum, the most leak inspection is required, and
Water is sprayed or dropped from the nozzles 13 and 14 provided on the lower and upper ends of the container immediately before the inspection on the welding line part of the body and the tightening part of the top plate and the bottom plate, which are likely to cause minute holes, Is soaked in water. Of course, there is a need for a device to wipe or dry the wet water after this. As a result, in the case of the dried container, the RD value was 13 within the inspection time of 2 seconds, but when it was wet with water, it was 2
It was 57. Since the generation degree of the AE signal is affected as described above, in the inspection at the factory where the production speed is high,
Since it is necessary to shorten the inspection time, increase the internal pressure,
A method of wetting the outer surface of the container is effective, but the equipment cost is correspondingly high. On the other hand, in a factory where the production speed is low, the inspection time can be lengthened, so that it is not necessary to reduce the internal pressure and to wet with water, so that the facility cost can be increased. Appropriate equipment specifications and inspection conditions can be set according to each situation.

[0022]

Example: According to the test method specified in JIS Z1601, a gauge pressure of 30 kPa (0.3 kgf / cm ² )
Steel drum 1 class M that failed the air tightness test in which compressed air was sent and immersed in water to inspect for leaks.
A can of grade (thickness 1.2 mm) with no coating on the inside and coating on the outside was moved to the airtight leak tester by the operation procedure shown in Fig. 3 and stopped, and after raising the sensor, the internal pressure was 0.7k.
The sensor test was started by enclosing compressed air of gf / cm ² , and after confirming that there was no abnormality, the sensor test was stopped and the leak inspection was subsequently started. R every 100 msec
D was measured, an abnormal alarm was output by comparing with the alarm set value, the inspection value was stored in the memory, and the result was that the RD value 335 was counted in 2 seconds and the result was a failure. After that, the leak inspection is stopped, the air in the container is removed, the sensor is lowered, and the process ends.

[0023]

As described above, according to the method of detecting the ultrasonic wave generated by the vibration when the compressed air sealed in the container leaks from the hole according to the present invention, the container can be automatically and accurately and easily without requiring human hands. It is an object of the present invention to provide an industrially extremely advantageous method and apparatus capable of inspecting the airtight leakage of the above.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an AE type airtight leak tester,

FIG. 2 is a signal processing block diagram of an AE type airtight leak tester,

FIG. 3 is a flowchart of inspection.

[Explanation of symbols]

 1 Drum 2 Chain Conveyor 3 Airtight Leakage Tester 4 Frame 5 Disc 6 Top Plate 7 Rubber Plate 8 Chime 9 Injection Port 10 Ventilation Port 11 AE Sensor 12 Air Cylinder 13, 14 Nozzle

Claims (4)

[Claims] 1. A container is filled with compressed air or decompressed, or a sealed outer lid covering the container is filled with decompressed air or decompressed so that the difference between the inner pressure and the outer pressure of the container is 0.5 to 2.0 kgf /.
By making it cm ² , it propagates through the container body that occurs when air leaks from inside the container to the outside or in the opposite direction 1
An airtight leak test method for a container, which comprises detecting a wave of 0 to 300 kHz by a sensor in contact with the container and inspecting the airtight leak of the container. 2. Compressed air is injected into the container while holding and fixing the top plate and the ground plate of the container with a jig having an elastic material interposed between them so as to block vibrations from other mechanical devices. Alternatively, an airtight leak test device for a container, which is characterized by discharging air in a closed outer lid that covers the container outside the container and inspecting the airtight leak of the container. 3. Whether or not the operating state of the wave detecting device is normal by detecting the wave generated when injecting compressed air into the container or discharging the air in the closed outer lid that covers the container. An airtight leak test device for a container, which detects a wave caused by leakage of air in the container after confirmation in advance. 4. The airtight leak of the container according to claim 1, wherein the airtightness of the container is inspected in a state where a part or all of the inner surface or the outer surface or the inner or outer surface of the container is wet with a liquid. Test equipment.