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The problem of substandard effectiveness of high efficiency filters
The problem of substandard effectiveness of high efficiency filtersDue to the strict requirements of the place of use, filters must be tested unit by unit before they leave the factory and can only be put into use after passing the test. There are factory tests and field tests for filters. In these two testing processes, the reasons why the filters do not meet the standards may be the following.I. Reasons that can be identified by visual inspection and simple tests Visual inspection. 1) The surface of the filter media is broken or slightly damaged. The naked eye simple to see the filter media broken, a small amount of broken repair is relatively simple, and this repair is very good in the filter production plant. Some minor damage is not easy to see with the naked eye and can only be detected by testing on a test bench. 2) The filter material is damaged by excessive weight or some human factors during the production process. If it is only damaged in individual places and is not serious, it is possible to repair it with qualified products, but the quality of repair should meet the standard requirements. 3) Sealing defects, and air leakage from the combined parts of the filter material and the outer frame of the filter. In the production inspection, most of the efficiency failures are caused by this kind of air leakage. Most such cases can be repaired, but the appearance after repair should not have obvious defects. Air leakage at the seam of the filter sealing tape. Many high-efficiency filters have sealant strips on their frames. Sometimes, poor handling of the interface can cause air leakage. Some manufacturers adopt on-site foamed polyurethane sealing strips without joints, and there is no air leakage problem. If you use adhesive strips with joints, it is good to make a labyrinth form at the joints. II. Reasons for the raw materials themselves 1) Low efficiency of the filter material itself. If the efficiency of the filter material itself does not meet the requirements (definition of high-efficiency filter material: tested at 5.3cm/s wind speed, the filtration efficiency of 0.3μm dust ≥ 99.97%), it is impossible to manufacture a qualified filter. This reasoning is understood by all, but the market is labeled as high efficiency, the actual failure to achieve high efficiency of the filter material. 2) Dusty material. Traditional high-efficiency filters with a partition, if the paper partition and the manipulation of raw materials are not strict, the paper partition has the risk of dust. Poor filter material production environment, the filter material itself with a large number of possible off dust, and the filter made may also be dusty. It is worth noting that some tests are unable to detect this type of dust emission. III. Problems with the test itself 1) When the factory inspection is carried out, if the scanning inspection method is used, there may be eddy currents on the air outlet side of the filter, and the dust around it will enter the scanning area with the eddy currents. If the eddy current exists, the dust will exceed the standard when scanning, at this time, you will not be able to determine whether the dust is from the filter leakage point or eddy current, and the operator who lacks experience may judge the good filter as a waste product. To eliminate the misjudgments caused by eddy currents, the filter test bench is placed in the clean room. We had to find a way to eliminate eddy currents. 2) In many cases, after the filter is installed, people use the downstream dust concentration to deduce whether the filter is qualified or not. In this case, even if the filter efficiency is qualified, it may be misjudged as unqualified due to the high downstream concentration. |
