One of the necessary conditions for the clean room to meet the cleanliness level requirements

10/08/2020

    In order to obtain a good cleaning effect in a clean room, it is necessary not only to take reasonable air-conditioning purification measures, but also to take corresponding measures in crafts, architecture and other professions: not only reasonable design, but also careful construction and installation in compliance with specifications, And the correct use of clean rooms and scientific maintenance management. One of the necessary conditions for the cleanroom to reach the cleanliness level-the the cleanliness of the air supply.

    To ensure that the air supply cleanliness meets the requirements, the key is the performance and installation of the final filter of the purification system.

    The final filter of the purification system generally uses a high-efficiency filter or a sub-high-efficiency filter. According to China's standard [1], the efficiency of high-efficiency filters is divided into four grades: Type A is ≥99.9%, Type B is ≥99.9%, Type C is ≥99.999%, and Type D is (for particles ≥0.1μm) ≥99.999% ( Also known as the ultra-high-efficiency filter); sub-high-efficiency filter[2] is (for particles ≥0.5μm) 95~99.9%. The higher the efficiency, the more expensive the filter. Therefore, when choosing a filter, you should not only meet the air supply cleanliness requirements but also consider the economy and reasonableness. Considering cleanliness requirements, the principle is to use low-performance filters for low-level clean rooms and high-performance filters for high-level clean rooms. Generally speaking: 1 million grades can choose high and medium efficiency filters; less than 10,000 grades can choose sub-high efficiency or A-type HEPA filters; 10,000 to 100 grades use B type filters; 100 to 1-grade use C type filters. There seem to be two types of filters for each cleanliness level. The choice of high performance or low performance depends on the specific situation: when the environmental pollution is serious, or the proportion of indoor exhaust air is large, or the cleanroom Particularly important, a larger safety factor is required. In these or one of the cases, a higher class filter should be selected; otherwise, a lower performance filter should be selected. For clean rooms that require control of 0.1μm particles, no matter how high or low the concentration of particles is to be controlled, a Class D filter should be selected. The above is only from the point of view of the filter, in fact, to choose a good filter, we must fully consider the characteristics of the cleanroom, the characteristics of the filter, and the characteristics of the purification system [3].

    To ensure the cleanliness of the air supply, only qualified filters are not enough, but also to ensure: a. The filter is not damaged during transportation and installation; b. The installation is tight. To achieve the a, it requires well-trained construction and installation personnel, not only must have the knowledge of installing purification systems but also have more proficient installation skills, otherwise, it will be difficult to ensure that the filter will not be damaged. There are profound lessons in this respect... Secondly, the problem of installation tightness mainly depends on the quality of the installation structure. The design manual [4] generally recommends: use the surface-mounted type for a single filter, so that even if leakage occurs, it will not leak into the room; use the finished high-efficiency air outlet, Tightness is easier to guarantee. For the tuyere of multiple filters, liquid tank sealing and negative pressure sealing are often used in recent years. The liquid tank seal must ensure that the liquid tank joints are tight and the overall frame is on the same level. Negative pressure sealing means that the outer periphery of the joint between the filter and the static pressure box and the frame is in a negative pressure state, and it will not leak into the room even if it leaks, like the surface mounting type. In fact, as long as the installation frame is flat and the end face of the filter is in uniform contact with the installation frame, it should be said that it is not difficult for any installation type to meet the tightness requirements of the filter.