Clean room pollution sources and control methods

1、 Indoor air pollution source and its transmission way 1 Indoor staff dust is the main source of Zui, accounting for 80% ~ 90% The amount of dust produced by human movement is quite complex The difference between the amount of dust produced by human static and the amount of dust produced by intense activities is about 10 times It is impossible for a person to be active indoors If we take the average of these actions, we can think that the amount of dust produced by a person when he is active indoors is 5 times of that when he is still, that is: 5 × 105 grains / (min · person) According to the process properties, the number and strength of human actions, this multiple is different It can be divided into two categories: lower and higher, which are three times and seven times of the static dust amount, respectively, corresponding to 3 × 105 particles / (min · person) and 7 × 105 particles / (min · person) Of course, the amount of human dust also has a lot to do with clothing, as well as the washing, airing, and drenching of clothing According to the actual use and experimental measurement, the dust emission of nylon silk clean clothes is less than that of cotton Dacron clean work clothes If a cotton Dacron overalls is added to the nylon silk overalls, the dust emission of the nylon silk overalls will be further reduced In addition, clean work clothes should not be rubbed and washed, and should be dried in a clean environment after washing 2 The dust production of equipment and process dust generating equipment is especially prominent in rotating equipment Motor, gear rotating parts, servo mechanical parts, hydraulic and pneumatic starter switches or manually operated equipment will generate particles due to friction between moving surfaces Japan and western industrial countries have carried out the corresponding experimental research on the typical actions of the common mechanical equipment with different operation modes, different speeds and different materials in the clean room and the dust production of some electrical appliances Some reference values of dust emission are given for the pollution sources of machinery and electrical appliances in the clean room, which provides the calculation basis for the ventilation design of the clean room 3 The pollution area adjacent to the clean room is adjacent to or connected with the surrounding area of the clean room, and the area with lower cleanliness or non clean area Because the polluted air carried in and out by the personnel and materials, or the pollutants settled on the personnel and materials are brought in, it is another important pollution source that affects the cleanliness of the room Reasonable positive pressure difference is an important measure to reduce the air pollution through the gap of enclosure structure, transfer window, door, opening of conveyor belt and other holes The airlock chamber, buffer chamber and air shower chamber at the door also play a certain role However, it is also difficult to completely avoid the interference and impact of surrounding pollution areas on the clean room environment, especially the area near the outer door of the clean room Therefore, the key process area should be far away from the outer door 4 Under normal conditions, if the air supply without filter is newly built or rebuilt or the final filter is replaced, strict acceptance test is carried out according to the specification requirements, and if there is any leakage on the filter itself and the contact surface between the filter and the support frame, it shall be found out and treated At this time, there is no unfiltered air entering the clean room in the air supply system It should be noted that the fragile filter paper core or filter is not touched in accordance with the operation regulations during the production process Because of the vibration of the support frame, or the aging and deterioration of the sealing gasket, the sealing gasket or rubber strip on the contact surface between the filter and the frame appears cracks, thus leaking unfiltered air and polluting the clean room, which is also the focus of daily monitoring work 5 Raw materials, packaging, etc the pre cleaning, unpacking place and method of the equipment, materials, containers, packaging, etc entering the clean room, as well as the procedures for entering the clean room, etc shall be carried out in accordance with the relevant specifications of the clean room operation management However, even if the operation is strictly in accordance with the relevant specifications and procedures, it is still difficult to completely prevent the pollutants adhering to the raw materials, containers, packaging, especially the small components of some products that are difficult to clean from being brought into the cleaning room They constitute another important source of pollution in the production process, which is often ignored When there is a problem, we usually focus on finding the defect of air conditioning purification system 2 Control methods for pollution sources 1 Control process equipment and dust production of process The process equipment in clean room should be well selected, clean and wear-resistant Those rotating and sliding parts are particularly important, and wear and dust production should be reduced as much as possible As far as possible, the process of dust production should be closed or enclosed, supplemented by ventilation, to form a local negative pressure relative to the clean room, so as to limit the diffusion of pollutants to other areas of the clean room It is necessary to clean and wipe the indoor machinery and equipment regularly, and it is also an effective measure to reduce the dust secondary flying 2 Pressure difference between adjacent clean rooms of different levels The main method to prevent the spread of pollution from the adjacent area with low cleanliness to the clean room is to maintain a proper positive pressure value between the high cleanliness area and the low cleanliness area, between the low cleanliness area and the service area, and between the service area and the outdoor According to different situations, the positive pressure value of adjacent rooms of different levels is about 5pa-10pa Keep the pressure difference of different levels of rooms with different cleanliness The purpose is that when the room door is closed, the air flow through the gap flows from the clean room to the low-level clean room, from the low-level clean room to the corridor and service area, and then to the outside In this way, the suspended pollutants in the air can be reduced from the room to the service area, from the service area to the low-level clean room, and from the low-level clean room to the other clean room The positive pressure value is not the greater the better Many theoretical research and practice have proved that when people and materials pass through the door, even if the pressure difference between the two sides of the door is as high as 50pA ~ 60Pa, it is still difficult to avoid the air flow carrying pollution into the room when people and materials move inward Especially when there is a temperature difference between the two sides of the door, even if there is no one walking around after the door is opened, there is also reverse air flow in part of the area of the opening section, which brings pollutants into the air In addition, the high positive pressure difference will make the door of the clean room hard to open and close The air flow at the door gap will cause Whistler noise, and the air volume will be increased due to excessive air flow overflow, which will waste energy and increase the burden of filters at all levels 3 Filtration of air supply in clean room air filter or super air filter, the end device of air supply system in clean room air conditioner, can effectively filter the particle pollutants in the fresh air and return air treated by air conditioning unit under normal conditions After being treated by super air filter and super air filter, the clean air is sent into the room, which can effectively displace and dilute the indoor pollutants, so as to maintain the indoor cleanliness However, if the final filter is damaged or the seal between the filter and the support frame is cracked or the air tightness fails, then the air that is not filtered by the air filter may carry a large number of pollution particles into the room and spread with the air flow, with a large range of harm Therefore, it is very important to detect, plug or replace the final filter before the clean room is put into use It is also very important to prevent the damage of the final filter during operation It should also be noted that the filter should be replaced in time after reaching the service life Shanghai Sujing Industry Co., Ltd if you have any need, you can pass with us at any time Thank you very much for your support and look forward to cooperating with you Thank you & 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Suing Jinghua