The HEPA filters are mainly used to capture particulate dust and various suspended solids below 0.5um. Use ultra-fine glass fiber paper as the filter material, offset paper, an aluminum film, and other materials as the dividing plate, glued with wooden frame aluminum alloy. Each unit has been tested by the nano-flame method and has the characteristics of high filtration efficiency, low resistance, and large dust holding capacity. HEPA filters can be widely used in the air supply at the end of the air conditioner in the dust-free purification workshop of industries such as optical electronics, LCD liquid crystal manufacturing, biomedicine, precision instruments, beverages, and food, and PCB printing. Both high-efficiency and ultra-high-efficiency filters are used at the end of the cleanroom. According to their structure, they can be divided into high-efficiency with partitions, high-efficiency without partitions, high-efficiency with large air volume, ultra-efficient filters, etc.
The high-efficiency filter is the core equipment of the air-conditioning purification system. The filter forms resistance to the air. As the dust accumulation on the filter increases, the filter resistance will increase. When the filter has too much dust and the resistance is too high, the air volume of the filter will be reduced, or the filter will be partially penetrated. Therefore, when the filter resistance increases to a certain value, the filter will be scrapped. Therefore, to use the filter, it is necessary to grasp the appropriate life cycle. When the filter is not damaged, the service life is generally determined by resistance.
The service life of the HEPA filter
① The pros and cons of itself, such as filter material, filter area, structure design, initial resistance, etc.;
② It is related to the dust concentration in the air, the actual air volume used, and the final resistance setting.
The structure and filter material of the HEPA filter
① Structure: The outer frame is mainly used: aluminum alloy profile, multilayer frame, aluminum plate frame, galvanized steel frame, the most used is aluminum alloy profile frame, mainly made into a cubic structure.
② Filter material: glass fiber is mostly used, and chemical fiber is gradually being used. At present, some foreign manufacturers use electrostatically charged polytetrafluoroethylene fiber (electret) to manufacture HEPA filters, commonly known as PTFE.
There are partitions and partitions for efficient structures. No partitions mainly use hot melt as the separator of the filter element, which is convenient for mechanized production. In addition, it has the advantages of small size, lightweight, easy installation, stable efficiency, and uniform wind speed. At present, most of the large-volume filters required for clean workshops use a partitionless structure. ① There are partitions for high efficiency, and aluminum foil and paper are mostly used as filter element separators to form air channels. The partition board is made of high-quality kraft paper, formed by hot rolling or offset paper as the partition board. At present, coated paper with double-sided glue is often used as the partition board, the main purpose is to prevent the partition board from shrinking due to the influence of cold, heat, dry, and wet, thereby dispersing particles. However, according to the experience of Jiuding Air Conditioning Company for many years, when the temperature and humidity change, this kind of separator paper may emit larger particles, resulting in the unqualified cleanliness test of the cleanroom.
Comparison of HEPA filters with partitions and HEPA filters without partitions
The price of filters with partitions abroad is higher than the price without partitions, so there are fewer places with partitions abroad. In addition, compared with the rectangular channel with the partition filter, the V-shaped channel without the partition filter further improves the uniformity of dust holding and prolongs the service life. The partitionless filter for ventilation can avoid the use of metal parts, is easy to discard, and meets increasingly stringent environmental protection requirements. Except for some special occasions with high-temperature resistance and high safety requirements, filters without partitions can replace filters with partitions.