JP3046188B2 - Method and apparatus for testing airtight leakage of containers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, steel drums have been used in accordance with JIS Z-160.
As specified in 1 (steel drum), after a steel plate is formed into a cylindrical shape, a top plate with a base serving as an inlet and a vent is attached to the upper and lower ends of the welded fuselage, and a base plate serving as a bottom is attached. It is manufactured by winding. The container usually has a capacity of 20 to 200 l and is used as a liquid container. The most important function of the 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 in the manufacturing process of containers such as drums is an important quality control test, and JIS Z
Also in 1901, compressed air with a gauge pressure of 30 kPa is sent into the container and immersed in water (submerged test) or applied with soapy water to check for leaks, and water is injected into the container, and water is injected into the container at 250 kPa. There is a provision of a water pressure test for testing for 5 minutes at a gauge pressure to check for leaks.

[0003] In a production line for containers such as steel drums, it is common practice to carry out a 100% airtightness test. The method used for testing in this line includes a soap water test, in which compressed air is sealed in a container, and when a test solution is applied with soapy water, bubbles generated when there is a leak are visually inspected. A differential pressure type leak tester and a helium gas sealed in a container, in which compressed air is filled in, or the inside of a sealed outer lid that covers the outside of the container is depressurized to detect a change in pressure inside the container and to check for leaks. There are three types of helium-type leak testers that detect the degree of leakage and check for the presence or absence of leakage.

[0004]

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

[0005] Further, when the hole formed in the container is a large hole having a diameter of about 1 mm, a large amount of air leaks, and there is a disadvantage that the leak is easily overlooked because the soapy water bubbles are destroyed immediately. The differential pressure type leak tester is effective when the detectable hole is relatively large with a diameter of 0.2 mm or more,
In the case of minute holes, the detection accuracy is poor. In addition, a sharp pressure sensor is required to increase the detection accuracy. On the other hand, the helium-type leak tester is capable of detecting holes as small as 0.005 mm in diameter, and is excellent as an inspection device, but the equipment cost is high, and The disadvantage is that the cost of using helium encapsulated inside is higher than other test methods.

[0006]

Means for Solving the Problems Therefore, the inventors have eagerly worked.
As a result of repeated husbands, we developed to solve these problems
When the compressed air enclosed in the container leaks from the hole
Leakage is detected by detecting ultrasonic waves generated by vibration
And a device for automatically inspecting the data. The invention
(1) Enclose or decompress compressed air in the container, or place the container
Enclose or reduce the pressure of compressed air in the sealed outer lid to
The difference between the internal pressure and the external pressure is 0.5 to 2.0 kgf / cm ^TwoNasu
To empty from the inside of the container to the outside or in the opposite direction.
Propagating the container body that occurs when air leaks 100-30
0kHz wave is detected by a sensor that contacts the container.
Inspection of the container for leaks.
Airtight leak test method.

(2) With the top and bottom plates of the container held and fixed by means of a jig via an elastic material, compressed air is blown into the container while vibrations from other mechanical devices are cut off. Inject or vent the air in the sealed outer lid that covers the container outside the container,
An airtight leak test apparatus for a container, which inspects the airtight leak of the container. (3) In the airtight leak test according to (1),
Liquid inside or outside or part or whole of inside and outside
It is characterized by inspecting the airtightness of the container while wet with the body
The leak test method .

[0008]

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

FIG. 1 is a schematic view of an AE type airtight leak tester. FIG. 1A is a cross-sectional view of the AE type airtight leak tester, and FIG. 1B is a front cross-sectional view of the same. A block diagram and a flow chart of the AE type airtight leak tester using the 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. FIG. 3 is a flowchart of the inspection. In the following description, the drum making process in which the drum is transported in a horizontal state,
This is not limited to the horizontal placement, and the drum making process in which the drum is transported in the vertical position may be performed in accordance with the process, and is not particularly limited to any one. Thus, as shown in FIGS. 1A and 1B, the drum 1 is conveyed on the chain conveyor 2 in a state of being laid horizontally, and conveyed to the airtight leak tester 3. Here, the height of the drum is set at a predetermined position while being supported by the gantry 4 that moves up and down, and then the top plate 6 of the drum is set by a jig such as a disk 5 or an arm that opens and closes left and right by hydraulic or pneumatic pressure.
Then, the base plate is held and fixed, and the gantry descends.

The fixing jig holds and fixes the drum via an elastic material such as a rubber plate 7. If the drum is in contact with the metal parts that make up the disc or other device parts, 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 This is undesirable because it propagates as noise and lowers the inspection accuracy. The rubber can block the vibration and sound of the surroundings. On the other hand, the rubber needs to have a hardness not to be compressed by the pressure for clamping the top plate and the base plate of the drum.
Materials with a hardness of 0 to 90 are preferred.

When the fixing jig is a disc, a rubber plate of about 30 mm thicker than the height of the drum chime 8 is attached, and is held and fixed on the top plate of the drum. If high-pressure compressed air is sealed in the drum, the top and bottom plates expand first, and then the body expands and causes permanent deformation, so it is necessary to set an appropriate pressure. It has the effect of suppressing the expansion of the top plate which is easily deformed, so that the inspection can be performed with a relatively high internal pressure, so that the inspection accuracy is improved. The rubber plate may hold the drum at the tip of the chime portion, but it is better to hold the drum on the top surface of the top plate because the rubber plate is pressed by a large pressure and the rubber plate is greatly worn. In this case, the rubber plate does not come into contact with the entire surface of the top and bottom plates, but may partially penetrate the rubber plate.

If the rubber plate is in contact with the entire surface of the top plate, if there is a hole in the top plate, the hole is closed with the rubber plate and the hole cannot be detected. It is desirable that the contact be as narrow as possible in terms of strength for holding the drum. Further, a base serving as an inlet 9 and a ventilation opening 10 is attached to the top and bottom sides of the drum, and compressed air injected by a pipe attached to the top side disk is sealed in the drum from the base or the air is supplied. In order to discharge the air, it is necessary to open the hole corresponding to the base portion in the rubber plate so as not to cover the base and to secure an air passage.

When the fixing jig is an arm, the drum is held and fixed at the tip of the arm covered with rubber, so that the area of the open portion of the drum surface is large and the area of the container that can be inspected is large. . However, in this method, if the pressure of the compressed air to be filled becomes large, the deformation of the top plate of the drum cannot be suppressed, so that the internal pressure must be reduced.
In addition, in the case of holding and fixing the container on the top and bottom sides by this method, the ventilation port side of the base is sealed in advance, and a device for directly injecting or discharging air from the injection port side is used as a device. .

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 and uses a class of L to H.
The outer surface of the drum is generally coated, but the inner surface may be left as it is after the chemical conversion treatment or may be coated after the chemical conversion treatment. Further, some steel sheets are made of galvanized steel sheet or stainless steel sheet, and the inner and outer surfaces are unpainted. Based on the results of tests performed on these various drums under various conditions, when compressed air is sealed inside, the pressure is 0.5 to 2.0 kgf / gauge.
The air of cm ² , desirably 0.7 to 1.2 kgf / cm ² is enclosed. The higher the air pressure, the higher the leakage inspection accuracy.On the other hand, if the internal pressure increases, the hydraulic mechanism of the disk holding and fixing the top and bottom plates to prevent deformation of the drum must have a large capacity. It is desirable to select.

Further, for various drums, a steel plate, a welded portion,
Alternatively, a leak test was performed on the size of the leaked portion and the hole generated in the tightened portion, and as a result of analyzing the generated AE signal,
Ultrasonic waves from 100 kHz to 400 kHz are generated, and there is a difference 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 generation of signals around 200 kHz was remarkable in each case. . That is, 2
It was found that if a filter that preferentially detects a signal of 00 kHz is used, noise due to other machines or collision noise can be removed relatively effectively, and inspection accuracy improves.

The AE sensor 11 converts an elastic vibration propagating through the container body into an electrical signal by contacting the surface of the container, and is a circular body having a diameter of about 10 mm made of a ceramic piezoelectric body. . It is omnidirectional so that AE signals in any direction can be detected. When contacting the sensor with the surface of the container, if there is an air layer between the sensor and the surface of the container, signal attenuation will occur, so provide a thin layer of glycerin or a surfactant aqueous solution or water on the sensor surface. There is a need. The embodiment of the present invention employs a method of providing a thin layer of water so that a continuous inspection can be performed in a drum production line. That is, a rubber ring high by 0.8 mm in height and a water injection pipe connected to the rubber ring are provided around the sensor, and a certain amount of water supplied from the water injection pipe is distributed on the surface of the sensor surrounded by the rubber ring. Remains, and the excess is discharged by overflowing 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. When the sensor is pressed from the lower part of the container body, the sensor is placed at a fixed interval corresponding to the thickness of the rubber ring, and water is supplied to the container. It will come in contact through the layers. Container 1 to be inspected if it is a steel drum
Although one sensor is sufficient for each sensor, 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 the sensors is provided. If a leak is detected by one of the above, it is determined to be rejected. In addition, a sensor having an appropriate frequency characteristic and sensitivity is selected according to the frequency of the generated ultrasonic wave. In the present embodiment, the frequency of 200 kHz is most prominent in the steel drum as described above. , 200k in the frequency band of 50kHz to 1MHz
Hz resonance type and waterproof type are used.

Next, as shown in FIG. 2, a minute voltage obtained by converting the elastic vibration into an electric signal by the sensor is amplified by a preamplifier, and then the surrounding mechanical noise coming in with the AE signal is passed through a filter. Suppress the disturbing noise and extract only the signal of the necessary frequency component. Many environmental noises such as mechanical vibrations have low frequencies, so that a filter blocks a frequency signal of several tens of kHz or less. A noise that is likely to be erroneously determined at a frequency most similar to a signal based on leakage of a container in ambient noise is noise generated when compressed air is injected into the container. Therefore, as will be described later, while injecting the compressed air, a device diagnosis for testing whether or not the operation of the sensor is normal is performed. In other words, if the AE signal is detected within 0.5 to 0.7 seconds during which compressed air is injected, the sensor operation is determined to be normal, and if no signal is detected, the sensor operation is determined to be malfunctioning and the device is inspected. I'm going to do.

The leak inspection is started 0.1 second to 2 seconds after the predetermined pressure is reached by injecting the compressed air. The inspection is performed for 1.0 to 2.5 seconds, and the number of times that a signal larger than a preset threshold is detected every 100 ms is measured (the number of peaks exceeding the set value is ring-down, abbreviated as RD).
Then, the accumulated value within the inspection time is automatically obtained, and is compared with a preset alarm set value. If the RD value is larger than the set value, it is determined to be unacceptable and an alarm is issued. In the case of leakage from a large hole, the RD exceeds the alarm set value in a short time, but in the case of a small hole, the RD does not reach the alarm set value within a predetermined inspection time even if there is wetness. Judge as pass. Therefore, the longer the time taken for the inspection, the smaller the size of the hole where the leak can be detected and the higher the inspection accuracy, but the inspection time directly affects productivity, so it is necessary to determine the inspection time at an appropriate place. is necessary.

Further, when the 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 may leak before the air leaks from the leak location. The film of liquid wetting breaks down,
At this time, a similar AE signal is issued. Therefore, even if the container has minute holes so that the RD value does not reach the predetermined alarm setting 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 setting value is quickly set. It is possible to detect a signal exceeding it. 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 is shortened.

In order to specifically utilize such effects, the present invention devises the following apparatus. That is, in the case of a steel drum, the leak inspection is most necessary, and
Water is sprayed or dropped from the nozzles 13 and 14 provided at the lower and upper ends of the container immediately before the inspection at the weld line portion of the body where small holes are likely to be formed and the tightened portion of the top plate and the base plate. Is made to get wet with water. Of course, after this, a device for wiping or drying the wet water is required. As a result, the RD value of the dried container was 13 within the inspection time of 2 seconds.
57. Since the degree of occurrence of the AE signal is affected as described above, in the inspection at a factory where the production speed is high,
Since it is necessary to shorten the inspection time, raise the internal pressure,
The method of wetting the outer surface of the container is effective, but increases the equipment cost accordingly. On the other hand, in a factory where the production speed is low, the inspection time can be lengthened, so that the internal pressure is reduced and it is not necessary to wet with water, so that the facility cost can be simplified. Appropriate equipment specifications and inspection conditions can be set according to each situation.

[0022]

EXAMPLE According to the test method specified in JIS Z1601, the gauge pressure is 30 kPa (0.3 kgf / cm ² ).
1 type of steel drum M which failed in the airtightness test to send compressed air and immerse it in water to check for leaks
After moving the cans of grade (plate thickness 1.2mm) with no coating on the inner surface and painted on the outer surface to the airtight leak tester according to the operation procedure shown in Fig. 3, raising the sensor, the internal pressure was 0.7k.
The sensor test was started by injecting compressed air of gf / cm ² , and after confirming that there was no abnormality, the sensor test was stopped and the leak test was subsequently started. R every 100 msec
D was measured and compared with the alarm set value, an abnormal alarm was output, and the inspection value was stored in the memory. The result was that the RD value 335 was counted in 2 seconds and the result was rejected. After that, the leak inspection is stopped, the air in the container is eliminated, the sensor is lowered, and the process ends.

[0023]

As described above, according to the method of the present invention for detecting ultrasonic waves generated by vibration when compressed air enclosed in a container leaks from a hole, a container can be automatically and accurately and easily prepared without requiring any manual operation. It is an object of the present invention to provide an industrially advantageous method and apparatus capable of inspecting for airtight leaks.

[Brief description of the 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 an inspection.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Drum 2 Chain conveyor 3 Airtight leak tester 4 Stand 5 Disk 6 Top plate 7 Rubber plate 8 Chime 9 Inlet 10 Ventilation port 11 AE sensor 12 Air cylinder 13, 14 Nozzle

Continuation of the front page (56) References JP-A-63-249033 (JP, A) JP-A-50-2589 (JP, A) JP-A-4-25739 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) G01M 3/24 G01M 3/26

Claims (3)

(57) [Claims] 1. A method in which compressed air is sealed or decompressed in a container, or compressed air is sealed or decompressed in a closed outer cover for covering a container, so that a difference between an internal pressure and an external pressure of the container is 0.5 to 2.0 kgf /.
cm ² to propagate through the container body when air leaks from the inside of the container to the outside or in the opposite direction.
An airtight leak test method for a container, wherein a wave of 00 to 300 kHz is detected by a sensor contacting the container, and the airtight leak of the container is inspected. 2. Compressed air is injected into the container in a state where the container is held and fixed with a jig via an elastic material on a top plate portion and a base plate portion of the container, and vibration from other mechanical devices is cut off. Alternatively, an airtight leak test apparatus for a container, characterized in that the air inside the sealed outer lid that covers the container is discharged outside the container and the airtight leak of the container is inspected. 3. The airtight leak test according to claim 1,
Part or all of the inner or outer surface or inner or outer surface of the container
To inspect the airtightness of the container with the liquid wet.
Characteristic airtight leak test method.