Exploration of steel barrel leak tester
Wuhan Metal Container Factory 2 Wang Lin
In the production of steel drums, the type inspection is generally carried out by means of sampling inspection. Due to the leakage inspection of the steel drum, the full inspection is carried out. Therefore, in the barrel production line, the sealing machine is generally equipped with equipment for non-leakage inspection. We call this equipment a leak test machine. There are three types of leak detectors, namely water immersion, soap liquid and air pressure change, depending on the leak test method. The structure, working process or basic principle of the three types of leak testers and their advantages and disadvantages are analyzed and compared.
1. Immersion
The more advanced leak test equipment in China is an immersion test leaking device. It consists mainly of a pool and a clamp that introduces compressed air into the barrel. It is specially used for sampling sample barrels, such as the airtight leak tester used by the Export Packaging Testing Center of the Hubei Provincial Commodity Inspection Bureau. The machine consists of a transparent glass basin (with a row of sealed incandescent lamps at the bottom of the pool), a special clamp that can open compressed air into the bucket, and a special positioning and turning device for pressing the bucket without lifting it. The working process is as follows: firstly, a through hole with a diameter of about 60 mm is drilled in the center of the top of the barrel, and a special ventilation clamp is screwed, and then the horizontally placed blessing is manually placed into the pool, and then the special positioning turning device is operated (it makes the barrel On the one hand, not all floated, the floating volume accounts for about 1/3 of the barrel volume, and on the other hand, the bucket is slowly flipped). Then, observe the presence or absence of bubbles in the pool. Since the bottom of the glass pool is equipped with a row of incandescent lamps and the glass is transparent, it is easier to see the foaming or leakage. It is convenient for the remedial work of the follow-up “prescription medicineâ€. In addition, it is able to check the leakage of the steel drum in all directions, including the injection port, the sealing at the vent and the leakage caused by the crack of the steel plate. Since it can strictly inspect all the leaking parts of the barrel, it is not easy to miss the inspection. The machine controls the air pressure mode is electronically controlled, which is more advanced and precise. Because the glass pool is easy to be crushed, the inspection time is long (about a few minutes), and the manufacturing cost is high. It is a destructive test to require the person to lift the bucket in the center of the bucket top. The application of the machine in mass production is only applicable to the type inspection of the sample barrel in the inspection room.
2. Soap liquid
The soap liquid type leak test equipment is mainly composed of a pneumatic system, a rotating support frame of the barrel and a soap liquid pump. The basic structure and pneumatic system principle of soap-liquid leak detection equipment commonly used in mass production are shown in Figure 1. The working process is as follows: the sealed bucket is placed between the top plate and the tail plate of the leak tester by the bucket rack on the conveyor chain, and the top of the bucket is opposite to the top plate. Operate the reversing valve 1 so that the compressed air enters the left chamber of the cylinder, the piston is on the right, and the tail tray is followed by the right line, and the barrel is pressed between the top plate and the tail plate. Then, the 2/2-way valve 12 is operated to allow compressed air to pass through the through hole at the center of the mandrel, and enter the barrel from the inlet and the vent of the barrel. When the pressure value in the barrel reaches the test leak requirement (the pressure value in the barrel can be indicated from the pressure gauge 13), the soap liquid pumped from the soap tank by the pump 5 flows from the hose to the straight seam of the barrel and its barrel The top of the top and the bottom of the barrel. For the convenience of observation, the barrel should be rotated to observe the occurrence of blistering in the above parts. If there is air leakage and foaming, it must be leaking steel drum. Mark it with chalk at the leak. After the inspection is completed, the valve 12 is operated to cut off the compressed air, and at the same time, the valve 1 is operated to make the piston in the cylinder go to the left, the tail plate is taken out of the barrel, and the conveyor chain will pass the qualified bucket. A next process. For barrels that have been marked for leak detection, they are removed from the conveyor chain by the vertical barrel mechanism.
Figure 1 Schematic diagram of soap liquid leak test machine
1, reversing valve; 2, oil mister; 3, pressure gauge; 4, pressure reducing valve; 5, soap tank; 6, air compressor; 7, shut-off valve
8, gas tank; 9, gas filter; 10, pressure reducing valve; 11, oil mister; 12, two-position two-way valve; 13, pressure gauge
In the figure, the pressures of the pressure reducing valves 4 and 10 are not equal. Generally, the pressure of the valve 4 should be greater than the valve 10 (ie, the pressure indicated on the pressure gauge 3 should be greater than the pressure indicated on the pressure gauge 13). value). Especially for large barrels, the diameter of the cylinder is often smaller than the barrel diameter. If the pressure of the two valves is equal, the thrust generated in the un-cylinder will be less than the thrust generated during the leak test in the barrel. The compressed air in the barrel will leak from the contact between the top of the barrel and the gasket. The air pressure in the barrel drops below the standard. Value (according to GB325-84 "200L closed steel drum" national standard, the steel drum does not leak to check the air pressure value, the light barrel is the steel drum with the thickness of 1.25 mm is 4.903 × 10 (4) Pascal, the heavy barrel is the steel plate The forging bucket with a thickness of 1-50 mm is 6.865 × 10 (4) Pascals, thus causing a missed inspection. So you must pay attention to this when designing.
In the barrel production line, the leak detection speed of the leak tester must match the sealing speed of the sealer. In order to ensure the leak detection speed of the leak tester without leaking, the specified leak test pressure must be reached within a relatively short period of time. Therefore, the piping of the pneumatic system should be calculated, not too thin.
At present, the use of soap-type leak test equipment in China is faster than the leak detection speed (about a few seconds), the leakage part is obvious, the operation is simple and convenient, and the labor intensity of the workers is low. However, it must be observed directly by the person on the barrel, and it is not possible to check for leaks such as leakage caused by the rubber ring not being pressed at the injection port and the vent, and it is relatively easy to miss the inspection.
There is also a leak tester that is actually a soap-type leak test device, but has a surface-like leak test device. It is mainly composed of a pool, a clamp for introducing compressed air into the barrel, a soap tank and a discharge. The working process is as follows: First, put the bucket into the pool, and turn the bucket by hand so that the seam of the bucket seam and its top with the top of the bucket and the bottom of the bucket face upward. Then, a jig that operates to introduce compressed air into the tub is operated to introduce compressed air into the tub. Then use the brush to smear the soap in the soap tank, and brush to the seam joint of the barrel and the top of the barrel and the bottom of the barrel to observe whether there are air bubbles at these three places. If there is, it must be leaking steel drums, marked with chalk at the leak. Then, take the bucket out of the pool and take remedial action. If there is no air bubble, take the bucket directly out and send it to the next process through the conveyor. The structure of the leak test device is the simplest, easy to repair and manufacture, the equipment cost is low, the leakage part is obvious, and it can be applied to the leak detection needs of multi-variety barrels. However, the labor intensity of the workers is large (it is necessary for people to move the buckets in and out of the pool) and it is easier to miss the inspection. It is generally suitable for multi-standard, small batch production.
3. Air pressure change
The air pressure change type leak tester is a leak test device that determines the leakage condition by detecting the change of the pressure inside the barrel. The basic principle is shown in Fig. 2.
In the figure, the bucket is placed vertically, the top of the bucket is up, and is rotated up. The leak detection positioning detecting device (ie, the leak detecting positioning plate) is located above the barrel, and the disc is equipped with a proximity switch and a mechanical positioning baffle. During the rotation of the barrel, when the proximity switch detects the inlet of the bucket top, a signal is sent, and after a delay, the mechanism positioning baffle is lowered to block the rotating barrel. At this time, the large and small positioning pins and barrels on the locating disc are tested. The injection port and the vent port are aligned, and the two pins are respectively inserted into the injection port and the vent port. The large pin is actually a test leak head. It is used for the ventilation test to detect the change of the air pressure in the barrel and to signal whether it leaks.
Figure 2 Working principle diagram of the pressure change type leak tester
The leak detection speed of such a leak tester for a single barrel is slower than the sealing speed of the sealer. In order to improve productivity and match the production speed of the sealing machine, the test leak machine should be made into a row of multiple stations. At the same time, multiple barrels are in the form of fully automatic leak test. Figure 3 is a schematic diagram of the transmission of a row of three-station test leaks. In the figure, the test leak is carried out in two steps: after the vertical barrel is input, it is first positioned, and then stepped to the test leak station for ventilation test leak. Finally, the bucket is sent to the next process.
Figure 3 A row of three-station test leak transmission diagram
The air pressure change type leak tester has been applied in the Maosai company barrel factory in West Germany. The gas that is introduced into the barrel from the injection port is not the general compressed air. The nitrogen is nitrogen, and the difference in the waveform displayed on the oscilloscope is used to automatically determine whether the barrel leaks. If it leaks, it can automatically remove the barrel from the production line without flowing into the next process.
The photoelectric control circuit and detection of the air pressure change type leak tester used by the West Dessert Co., Ltd., and the automatic rejecting leaky barrel system are all designed by West Germany Siemens Electric Company. This machine is the most advanced and automatic degree in the world (the single-machine unmanned operation has been realized), and the leak detection rate is zero. The steel barrel leak test equipment has the highest production efficiency and the most complete leak detection. However, the machine also has a high manufacturing cost, and the system is difficult to repair and manufacture due to the more precise and complicated system of control and detection.
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