Chinese filter material performance test and standard development process

The filter material performance test method standard is different from the filter performance test method standard. The filter performance test should meet the characteristic requirements of the fluid system (or working position) where it is located, and the filter material should meet the filter performance requirements at the same time. It is also necessary to meet the technical requirements and physical and chemical performance requirements in the production process of the filter, so as to realize the long life of the filter, good technology, reliable strength and high efficiency of intercepting micro-sized particles. Among the many properties of filter materials, some properties are similar to those of filters, such as“Filtration accuracy”,“dirt holding capacity”and“flow resistance”etc., but the filter material is what makes the filter after all“Material”, it is necessary to test its performance according to the characteristics of the material, which is the so-called“Standard for Test Methods of Filter Material Properties”;and also—Items belonging to physical and chemical properties, such as flexural strength, bursting strength, compatibility with working fluid, etc., are related regulations that are beneficial to processing technology, finished product quality and life. 1. The main performance definitions and test methods of foreign oil-passing filter materials The definition of the filtration accuracy of modern oil-passing filters has gradually accepted the filtration characteristic evaluation method of hydraulic filters, that is, the filtration process of oil containing polluted particles. The ratio (efficiency) of the quantity before and after filtration is judged“Filtration accuracy”. This method is called“multiple pass test”. The multiple-pass test method was originally developed by Dr. Fitch from the Fluid Power Research Center of Oklahoma State University, and later became the American national standard. It was incorporated into the international standard in 1981. Now all filter elements used in industrial oil circuit systems and engineering vehicle oil systems are gradually adopting this standard, and the performance assessment of filter materials is also adopted abroad. The assessment method is: put the test powder into the test system according to the regulations, the polluted oil will establish a pressure difference in this test section through the filter element (or filter material) to be tested, and take samples and test before and after the filter element at several pressure difference points. The number of particles of at least 6 different sizes before and after filtration, and then divide the number of particles before filtration by the number of particles of the corresponding size after filtration to obtain the filtration ratio (β) (refer to Figure 1). During the process of establishing the filter differential pressure, the reduced number of particles in the contamination fluid of the test system will be slowly supplied by another contaminant injection system (high-concentration contamination fluid). The test is stopped when the differential pressure reaches the rated value. Filtration ratio of particles in 6 sizesβAmong the values, if there are up to 75, the accuracy value of the tested filter element is determined as the size. The multiple-pass test method is different from the glass ball test method before the 1980s. The automatic particle counter equipped with optical technology directly measures the size and number of passing particles, and finally evaluates the filtration ratio of particles of a certain size, and determines that the filtration accuracy is are dimensions (microns) at the specified ratios. In the early years, the glass ball method was used by Italian Boss Company and Belgium Bekaert Company in foreign filter material companies.“glass bead pass-through”. At that time, many companies used this standard to evaluate filters. China's aviation standards HB5825 and HB6146 (general technical conditions for aviation filters) clearly stipulated that F 9, F 13, F 15, F 17 and F 19 should be used in the maximum particle passing test. For glass bead powders with different size distributions, the test methods are equivalent to MIL F 8815D. After entering the 1990s, the more famous foreign filter material companies no longer use MIL F4 8815D, but adopt ISO4572 (changed to ISO16889 in 1995) standard, that is, the multiple-pass test method. Figure 1 is a system circuit diagram of the multiple-pass test shown on the sample by Bekaert. Lydall and Bekaert are the first filter material manufacturing companies in the world to learn from the filter filtration accuracy evaluation method. They directly equate the definition and evaluation method of the filter accuracy of the main performance of the filter with the filter materials produced by themselves, and are well received by filter manufacturers. , It has created great convenience for the design and selection of new filter materials and test stereotypes, and has avoided many detours. At present, there is no unified method standard for the performance testing method of filter materials in the world. It can be seen from the filtration accuracy test method alone: ​​in Bekaert's samples, the pore size test, air permeability test and dirt holding capacity test all indicate the standards used by the test method, but the column of filtration accuracy is not marked, although it is missing. Annotated by previous samples“MIL F 8815D”words, but it can be assumed that the Bekaert company is still following the old method. Unlike Lydall, the multiple-pass test bench in Figure 2 can be seen as a bench specially designed for multiple-pass testing of filter materials. And the big table of Fig. 3 Bekaert company cannot be used for the filtration accuracy test of the filter material, it is only used for the dirt holding capacity test, because the test needs to obtain the initial resistance value of the filter material and the resistance value after adding the test ash. American Pall Company is recognized as the world's top filter manufacturer. It has always claimed that the filter materials used are self-produced and used, and they must have their own filter material performance testing standards. The company has participated in the formulation of many filter performance test method standards organized by the international standardization organization ISO, and its own filter material test method will be very close to the filter, and will be different from other filter material manufacturers. From this, it can be judged that foreign companies have their own standards for the performance testing methods of filter materials.​​
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