Cleanroom (Clean Room), also known as clean rooms or clean rooms. It is the basis for pollution control, no clean room, contamination-sensitive parts can not be mass-produced. In the FED-STD-2 inside the clean room includes an air filter is defined as the distribution, optimization, operating room procedures and materials of construction of the apparatus, wherein the specific rules to control the concentration of suspended particles in the air, so as to achieve an appropriate level of particulate cleanliness .
  Clean room to get a good cleaning effect, not only to focus on air purification take reasonable measures, but also requires technology, construction and other professional take appropriate measures: not only have a rational design, but also careful construction compliant installation and the correct use of clean room maintenance and scientific management. In order to get good results cleanroom, there are many domestic and international literature from a different perspective made elaborate. In fact, it is difficult to achieve the ideal fit between different professions, and the designer is difficult to grasp the quality of construction and installation as well as the use and management of cases, particularly the latter. On clean room decontamination measures, many designers, or also the construction side, often not been enough attention to its necessary condition, resulting in a clean result is not satisfactory. This article will discuss the clean room decontamination measures to achieve the four necessary conditions for a brief discussion cleanliness requirements.
First, the air cleanliness
To ensure the cleanliness of the air supply to meet the requirements, the key is the final stage filter cleaning system performance and installation.
End-stage purification system filters generally use high efficiency filter or sub-high efficiency filter. According to our standard [1] provides efficient filter efficiency four positions: A class of ≥99.9%, Class B is ≥99.9%, class C is ≥99.999%, Class D is (for ≥0.1μ m particle) ≥99.999% (also known as ultra-high efficiency filter); sub-high efficiency filter [2] is (for ≥0.5μm particles) from 95 to 99.9 percent. The higher the efficiency, the filter more expensive price. So when selecting a filter spirit necessary to meet the air cleanliness requirements, but also consider the economic rationality. From the cleanliness requirements to consider a low-level clean room use low-performance filters, high-level clean room use high-performance filter principle. In general: 1000000 efficiency filters can be used in high school; less than 10 000 can be used efficiently or A sub-class efficiency filter; 10 000 - 100 Class B filter selection; 100 to a selection of class C filter . Where each level of cleanliness seems to have two types of filters are available, choose high-performance or low performance, depending on the specific circumstances: when the serious environmental pollution, or a large proportion of indoor ventilation, or the clean room particularly important, a larger safety factor, or one of them under these circumstances, have to select a class of filters; otherwise select a lower performance filters. 0.1μm particle control requirements for clean room, regardless of the level of control of particle concentration have to select a class D filter. The above only from the perspective of the filter, in fact, to choose your filter clean room but also take full account of the characteristics, properties and purification systems filter characteristics.
To ensure the cleanliness of the air supply, only qualified filters is not enough, but also to ensure: a transportation, installation process does not damage the filter; b installed tight... To do the first a, construction and installation requires trained personnel, we must have the knowledge to install purification systems, but also to have more skilled installation skills, otherwise it will be difficult to ensure that no damage to the filter, in this area there is a profound lesson . Secondly, the installation tightness problem, depending on the merits of the mounting structure type, design manual is generally recommended: For single filter uses surface mounted type, so even if leakage occurs, it will not leak into the room; use of the finished product and efficient delivery outlet, tightness also relatively easy to be guaranteed. For more filters wind □, in recent years, often using sealed and vacuum sealed tank. Sump tank seams tight seal must be guaranteed and the overall framework are on the same horizontal plane. Vacuum seal is to make the outer periphery of the filter and the plenum chamber and the frame joints in the vacuum state, and the same type of surface mounted even if leakage does not leak into the room. In fact, as long as the flat mounting frame, the filter end face of the mounting frame exposure evenly, any installation type of the filter to achieve strict requirements should be said that the installation is not difficult.
Second, the air distribution
Airflow clean room and general air-conditioned room is different, it requires the cleanest air is first sent to the operating site, its role is to limit and reduce pollution of the workpiece. For this reason, the design airflow should consider these principles: to minimize eddy currents, to avoid contamination outside the work area into the working area; try to prevent secondary dust flying in order to reduce dust pollution opportunity workpiece; airflow to the workspace as even as possible, and the wind speed to meet the technical and health requirements, when airflow to the return air flow to make the dust in the air can effectively take away. Depending on the cleanliness requirements, choose a different delivery, return air mode.
Different air distribution, have their own characteristics and scope:
1) The vertical unidirectional flow: downward airflow can obtain a uniform, easy to process equipment layout, and strong self-purification capacity, simplify the common advantages of personal purification facilities and other common facilities, the four air supply as well as their respective advantages and disadvantages: full high efficiency filter cloth have a low resistance, long filter replacement cycle, etc., but the roof structure is complicated, high cost; efficiency filter cloth top side delivery, and sent the whole plate covered with top efficiency filter top pros and cons of sending the contrary, wherein the whole plate in the top of the system to send a non-continuous operation, the inner plate surface is easy to dust, poor maintenance, some impact on cleanliness; dense diffuser top delivery, due to the need for some mixed layer, so only applies to more than 4m big clean room, which features a full plate with top send similar; the lower plate and on opposite sides of the wall evenly arranged on opposite sides of the return air grille return air method is applicable only on both sides of the net spacing of less than 6m clean room; and one-sided back to the lower portion of the wall fabric wall outlet only applies to the smaller spacing (eg ≤ <2 ~ 3m) cleanroom.
2) the level of one-way flow: cleanliness only reached 100 in the first work area, when the air flow to the other side of the dust concentration in the process of gradually increased, so only apply to the same process has different room cleanliness requirements of cleanliness room; local air wall covered with relatively high efficiency filter cloth feed can reduce the level of the amount of the high efficiency filter, saving the initial investment, but the local area has a vortex.
3) airflow turbulence type: top send dense diffuser plate and top with the aforementioned features to send the same: the advantages of easy-to-side delivery piping without technical dissection, low cost, is conducive to the transformation of the old plant, the disadvantage is the work area speed larger than the downwind side of the windward side of the dust concentration; efficient filter outlet top delivery systems with simple, efficient filters after no pipeline, clean air direct service work area, etc., but slow diffusion of clean air, the air flow than the work area uniform; but when uniformly arranged with a plurality of outlet or use a diffuser plate to high efficiency filter outlet, also can make the workspace more uniform airflow; but in non-continuous operation of the system to the case, the diffusion plate is easy to dust.
  Discussed above belong to an ideal state, but also the relevant national norms, standards or recommended design manual. The actual project or restricted to objective conditions, or due to subjective reasons designer without good airflow design, common are: vertical unidirectional flow adjacent to the lower part of both sides of the wall to take back to the wind, using a local one hundred to send back (ie local delivery downwind not add sagging around the curtain), turbulence type clean room high-efficiency air filter top next time to send back or one side (of the wall spacing is larger), etc., which is organized by the airflow measurement, its clean Most degrees are lower than the design requirements. As the current specification [6] provides empty static state or acceptance of such individual clean room in an empty state or static at barely reached cleanliness level design, but contamination is very low interference, once the clean room into operation amounted to no to requirements. Correct airflow around the local area should be set to the working area curtain hanging height, 100,000 should not be sent back to use on. Most factories also with diffuser plate HEPA, the diffusion plate are just decorative plates and can not afford to diffusion flow, please pay special attention to designers and users.
Third, the air supply or wind speed
A sufficient amount of ventilation to dilute and remove indoor air pollution, according to the different requirements of cleanliness, clean room when high clear height, and appropriately increase the number of ventilators. Among them, the ventilation rate of one million clean room purification system is considered efficient by high school [7], and the rest are by efficient purification system to consider; when 100,000 clean room efficiency filter disposed in the engine room or centralized system at the end with sub-high efficiency filter , it may be appropriate to improve the ventilation frequency of 10-20%.
Recommended values ​​for the above-mentioned ventilation think: unidirectional flow clean room by room sectional low wind speed, turbulence type clean room is a more adequate safety factor of the recommended values. Vertical unidirectional flow ≥0.25m / s, horizontal unidirectional flow ≥0.35m / s, in the empty state or under static detection cleanliness, although they would meet the requirements, but the anti-pollution ability is poor, once the interior into working condition, cleanliness it is possible to meet the requirements, such instances do not belong to the individual; at the same time, our fans the series has not been a more appropriate purification system with fans, the general designer of the system is often not as accurate calculation of air resistance, or noticed the choice of whether the fan is on the characteristic curve more favorable operating point, so that the system put into operation shortly after, the amount of wind or wind speed will reach the design value. US Federal Standard (FS209A ~ B) prior to October 27, 1987 has been such a requirement: unidirectional flow clean room air flow rate through the clean room sections usually remain in 9Oft / min (0.45m / s), in the room non-interference Under the conditions, the speed unevenness within ± 20% decline in any significant flow velocity will increase beyond all possibility of contaminated dust concentration after impact (enacted in October 1987 between FS209C purification time and work location parameter index were provided for). For this reason, I believe that it should be appropriately designed to improve the domestic value of the one-way flow velocity, our unit did do the same in the actual project, the effect is quite good. Chaotic flow type clean room is more fully recommended safety factor, but many designers still worried, do specific design will 100,000 clean room ventilation rate increased to 20 to 25 times / h, 1 万 step acceleration Great to 30 to 40 times / h, 1000 级 increased to 60 to 70 times / h, so do not increase the equipment capacity, increase the initial investment, but also increase maintenance costs in the future, in fact, there is no need to do so do. Clean air in the preparation of the technical measures [7] investigation had determined the country more than 100 clean room, a lot of the clean room or under the dynamic test results showed that: 100 000 ≥10 times / h, 1 万 ≥20 beats / h, 1000 级 ≥50 times / h ventilation is sufficient. US Federal Standard (FS2O9A ~ B) provides that: non-unidirectional flow clean room (100 000, 10 000), room high 8 ~ l2ft (2.44 ~ 3.66m), generally considered the whole room at least once every three minutes ventilation ( That is 20 times / h). Therefore, the design specification of the provisions of [6] have been considered a greater affluence factor, designers can safely follow the recommended values ​​in Table 1 air quantity selection.
Fourth, the static pressure difference
Clean room to maintain a certain positive pressure is to ensure a clean room is not less contaminated, in order to maintain essential one grade to conditions designed to cleanliness. Even negative pressure clean room, it must have its cleanliness level of not lower than to the adjacent room or suite to maintain a certain positive pressure, negative pressure clean room cleanliness can be maintained.
Clean room under positive pressure value is all the doors and windows closed, indoor static pressure is greater than the value of outdoor static pressure. It is through the air purification system is greater than the return air flow and exhaust volume method to achieve. In order to ensure a positive pressure clean room value, air, return air and exhaust fan interlock the best, when the system is turned to start the blower, and then start back to the fans and exhaust fan; first off ventilator when the system is off, then back off the fan and blower to prevent contamination of the clean room when the system is turned on and off.
Required to maintain a positive pressure clean room air flow is primarily determined based on the quality of maintenance of the structure airtight. The early construction of the clean room due to poor airtight building envelope, to maintain a positive pressure should ≥5Pa 2 to 6 times / h air volume; currently maintain airtight structure has been greatly improved, maintaining the same positive pressure only 1 ~ 2 times / h air volume; maintain ≥1OPa as long as 2 to 3 times / h air volume.
Our design specification [6] states: static pressure difference between the different levels of clean room and clean area and non-clean areas between not less than 0.5mmH2O (~ 5Pa), clean areas and outdoor static pressure difference should be not less than 1.OmmH2O (~ l0Pa). I believe that this value seems low, for three reasons: 1. The positive pressure clean room is suppressed by the slit windows ability to indoor air pollution, or to penetrate the interior of the pollutants in a short time when the ability to open windows and doors to reduce to a minimum, positive size indicates the strength of the pressure suppression capability of contamination, the bigger the better is certainly not a positive pressure (later to talk about). 2. Positive limited amount of wind needed, 5Pa 10Pa positive pressure and a positive pressure air volume required shy about 1 times / h, why not? Clearly positive pressure value lower limit l0Pa take some superior. 3. US Federal Standard (FS209A ~ B) provides: When all entrances closed, the lowest positive pressure clean room and any adjacent area between the low cleanliness is 0.05 inches of water (12.5Pa), which has been a lot of value countries have adopted.
However, the value of positive pressure clean room is not always better, according to the unit 30 years of practical engineering analysis showed that:! When the positive pressure value ≥30Pa, it is more difficult to open the door, close the door a little attention, bam surprise people; when positive pressure value ≥50 ~ 70Pa, the doors will be whistling gap, the infirm or those who have some discomfort without indications. But the relevant norms or standards at home and abroad in many countries were not specified on the limit of positive pressure, such a result, many units are just under the limit to meet the requirements, regardless of how much the upper limit is reached, the author encountered in actual clean Positive values ​​are up to the chamber 100Pa or more, resulting in a very bad effect. Positive adjustments actually not a difficult thing, it is controlled within a certain range is entirely possible. A country in Eastern Europe had the documents introduced positive pressure value defined as 1-3mmH20 (about 10 ~ 30Pa), I believe that this range is more appropriate.
For a clean room, the above four requirements must be met in order to ensure cleanliness to meet the requirements and have the proper anti-pollution interference.