What problems should be considered in the operation and maintenance management of clean rooms? (Original link: http://)
First, maintaining the appropriate air temperature and relative humidity in the clean room is crucial.
If the air temperature in the clean room is too low, it can hinder normal operations. Conversely, if the temperature is too high, workers may sweat excessively, and the evaporation of this sweat can release tiny particles into the air, increasing the number of dust particles and reducing the room's cleanliness level. This, in turn, compromises the required process conditions. On the other hand, if the relative humidity is too low, the dry indoor environment can cause protective coatings on equipment and surfaces to flake off, adding more particles to the air. High humidity, however, can cause small airborne particles to aggregate into larger ones, again increasing dust levels and affecting the cleanliness grade. Excessive humidity can also lead to rusting of certain components, creating further complications. Second, measures should be taken to ensure cleanliness within the clean room.
To achieve the necessary cleanliness, the clean air conditioning system must be operational, supplying filtered air into the clean room. Personnel and materials entering the clean room should also be cleaned where necessary to minimize the introduction of dust. 1. Personnel Netting
The cleaning measures for personnel primarily involve washing, changing clothes and shoes, and air showers.
Human-generated pollutants can be categorized into self-produced and carried pollutants. There are three main types of dust particles carried by humans: external environmental pollutants randomly attaching to hair, clothes, and shoes; residues left on clothes and shoes; and personal smears like oils, perfumes, and makeup. Additionally, wear and tear on garments can contribute to dust.
Humans are also significant sources of bacteria in clean rooms. Given this, individuals entering the clean room should undertake necessary cleaning steps. These measures include:
1) Washing
Using water to wash hands, face, and even the entire body’s epidermis to remove accumulated surface discharges.
2) Changing Clothes and Shoes
To reduce pollutants brought in from outside, individuals entering the clean room typically change into cleanroom-specific overalls and shoes. These garments should not only be highly clean but also easy to remove contaminants from, functioning as filters for dust particles released by the human body. They should also be less likely to produce static electricity. Shoes, which carry the most dirt, should be pre-treated at the entrance via washing, vacuuming, and adhesive application to prevent excessive contamination of the entryway.
3) Air Shower
An air shower uses high-speed clean air to remove temporary attachments from clothing and accessories. These cleaning measures can reduce external pollutants brought in by personnel and clothing to a certain extent, minimizing direct contact contamination and isolating most of the body and undergarments from the indoor air.
The duration of air showering depends on the wind speed; shorter durations require higher speeds, and vice versa. Typically, the air showering time ranges from 20 to 60 seconds.
Air shower rooms usually consist of a blower, pre-filters, HEPA filters, a static pressure box, nozzles, and other components.
4) Air Curtains and Air Locks
Since air shower rooms are often located at the entrance to clean areas, directly adjacent to the clean area, and the doors at both ends are frequently interlocked, they serve not only for personnel purification but also as air locks to prevent outdoor pollution. For clean room doors with lower personnel purification requirements, air curtains are sometimes used alongside air curtains. Units with medium and high-efficiency filters are installed at the top of the clean room, spraying air downward through slits to create a gas barrier against pollution.
2. Material Entry into the Clean Room
Materials entering the clean room should generally be cleaned and decontaminated before transportation to reduce the amount of dust generated within the clean room.
Small items entering the clean room are typically accessed through the transfer window between the clean room and the outer corridor or between clean rooms or adjacent rooms of different cleanliness levels. Transfer windows are generally box-shaped or rotary.
3. Clean Air Entering the Clean Room
In the purification air conditioning system, all levels of air filters used must be intact without damage or leakage. During the operation of the purification air conditioning system, to prevent the air supply system from introducing dust particles that should not enter the room, regular leak detection of the primary, intermediate, and final air filters used in the system must be conducted.
Third, ensuring the air supply volume of the purification air conditioning system
That is to ensure the number of air changes in the clean room meets the needs of the indoor airflow organization. When the air conditioning system is cleaned, the air supply volume of the system should be measured regularly. The measurement points can be selected at the air inlet and outlet of the blower and at the air supply openings. Because the air supply volume of the system is designed considering energy consumption, indoor airflow organization, and other factors, if the air supply volume of the system is too low, the airflow speed at the air supply openings in the clean room will decrease, thereby destroying the airflow organization in the room, preventing the polluted air from being discharged, and failing to meet the indoor cleanliness standards.
The reduction in system airflow may have the following factors:
1) After the belt-driven fan runs for a period of time, the fan speed decreases due to belt elongation, resulting in a reduced air volume.
2) The dust-holding capacity of the air filter reaches its maximum value, increasing air resistance and preventing air from being sent out.
Therefore, during the operation of the clean air conditioning system and the clean room, regular inspections should be carried out to check the air filters and air resistance at all levels (a differential pressure gauge is installed before and after the air filter) and the dust-holding capacity, or the differential pressure gauge can be used for regular inspections (there is no pressure difference meter before and after the air filter); or judge by experience to determine whether the air filter of each level should be replaced, so that the air supply volume of the system is basically guaranteed.
Fourth, maintaining the positive static pressure value in the clean room as required
In the operation of the clean room, it is generally required to maintain a certain positive static pressure difference between adjacent rooms and corridors (including the outer corridor), that is, the static pressure value in the clean room is higher than that in adjacent rooms (rooms with different cleanliness levels) and corridors. Static pressure to avoid contamination of the air outside the clean room with high dust concentration in adjacent rooms, corridors, etc. Therefore, in the operation of the clean room and the purified air conditioning system, attention should be paid to the inspection, maintenance, maintenance, adjustment, and repair of the residual pressure valve (also known as the micro differential pressure Regulating Valve) in the system, as well as the pressure sensors, transmitters, regulators, and actuators to maintain the required positive static pressure in the chamber.
In the national standard GBJ73-84 "Code for Design of Clean Plants", the static pressure difference between clean rooms and clean areas and non-clean areas of different grades is required to be not less than 0.5mmH2O, and the static pressure difference between clean area and outdoor should not be less than 1.0mmH2O. However, it is not necessarily better to have a greater static pressure difference. If the static pressure difference is too large, it may damage the seal of the clean room, causing excessive energy consumption, and the indoor staff will feel pressure.
Fifth, try to reduce the amount of dust in the clean room
In the clean room, there are two factors that generate dust; one is the operation of the equipment, and the other is the activity of the operator.
In the clean room, people are the biggest dusting factor. Therefore, workers in the clean room must wear specially prepared dust-free overalls suitable for use in the clean room. As for the dusting of the clean room operating equipment, it is inevitable, but the amount of dust generated by the rotating equipment should be kept to a minimum from the time of reducing the vibration and the idling of the operating equipment.
6. Regular cleaning in the clean room
After the clean room has been running for a period of time, it will inevitably accumulate some dust on some dead corners, walls, and countertops. If it is not cleaned in time, the dust will re-enter the indoor air under the impact of a large airflow or some other disturbance. In this way, the cleanliness level of the indoor air is increased, and the process cannot be guaranteed. Therefore, regular cleaning of the clean room is indispensable.
Cleaning of the clean room is generally not allowed with brooms and mops, and can be carried out by means of decentralized or concentrated vacuum sweeping.
VII. Clean room indoor cleanliness detection and evaluation of test data
1. Selection of testing instruments
Although the measurement of the cleanliness in the clean room can be carried out by using a light scattering particle counter, a condensation tube counter, an electron microscope, and an optical microscope, the light scattering particle counter is currently the most used. Since the particle counter can measure the dust content of indoor air automatically, continuously and timely in use, and can directly display the instantaneous dust concentration, it can also measure the dust concentration of different particle sizes. Simple, convenient, timely and flexible. The counter can be roughly divided into two types: one is a side scatter type in which the optical axis of the illumination system is arranged to intersect the optical axis of the detection system; and the other is a forward scatter type in which the two optical axes are arranged on the same straight line.
2, the arrangement of the detection points
According to the National Standard of the People's Republic of China GBJ73-84 "Code for Design of Clean Plants": When cleaning the clean room, the test point should be within 1.00m from the indoor floor; for the one-way flow type clean room test The total number of points should be no less than 20 points, and the distance between the measuring points is 0.5-2.0m. The horizontal one-way flow clean room measuring point is only arranged in the first clean working area; the non-unidirectional flow clean room is arranged in five measuring points according to the clean area less than or equal to 50 m2.
3. When the clean room is cleaned, the sample amount of the light scattering particle counter is used.
Regarding the air sampling amount when the dust particle counter is detected, it is specified in the national standard GBJ73-84: for a clean room of class 100, the sampling amount should be greater than or equal to 1L each time. For a clean room of 1000~10000 class, the sampling amount should be Greater than or equal to 0.3L, for a clean room of class 10000, the sample volume should be greater than or equal to 0.1L.
For Class 100 cleanrooms, high flow particle counters should be used for testing. If not, a particle counter with a sampling amount of not less than 1L should be used.
In the clean room inspection of clean rooms, although the minimum sampling amount of air is specified, in actual work, we should use large-flow dust particles according to the existing testing equipment under the premise of ensuring the minimum sampling amount. counter.
4. Questions about equal power sampling
The so-called equal-power sampling is that when the detection, the inlet direction of the sampling tube of the particle counter coincides with the direction of the sampled unidirectional airflow, and the average velocity of the air entering the inlet of the sampling tube is the same as the average velocity of the unidirectional airflow at the position.
Because of the detection of clean rooms, we mainly care about two particle sizes, namely 0.5um and 5um. Non-equal power sampling has little effect on particles ≤0.5um. If the sampled air is used to calculate a particle size concentration greater than or equal to 0.5 um, if the particles are not affected by the non-equal dynamic conditions, the calculation results are not affected. Therefore, unequal dynamic sampling in clean areas is only meaningful for particles larger than or equal to 0.5 um.
5, clean room cleanliness detection
According to the above method, the measuring points are arranged in the clean room, and the dust particle counter used and corrected has been selected. At the same time, the floor plan of the clean indoor measuring point is drawn, and the measuring point number is performed, so as to prepare for the recording.
For the unidirectional flow clean room, the sampling counter of the particle counter should respond to the airflow direction; for the non-unidirectional flow clean room, the sampling port should be upward, so that the airflow velocity at the sampling port is as close as possible to the airflow velocity in the room.
At the same time, it should be noted that the sampling nozzle must be clean and there should be no leakage at the joint. The length of the sampling tube should be based on the allowable length of the instrument. If it is not specified, it should not be greater than 1.5m.
The sampling times of each sampling point are not less than 3 times, but the sampling times of each sampling point may be different. Under the stable operating conditions of the test instrument, each measurement data should be recorded on the record sheet.
Eight, the role of the blower and circulation fan, the duty fan in the air conditioning system
1. Purifying the air blower and circulating fan in the air conditioning system
In order to meet the airflow organization in the clean room and the airflow speed in the working area, the air supply volume in the clean room is relatively large, and the number of air changes is high. The large amount of air is treated in the temperature and humidity range required by the clean room, which is bound to increase. The capacity of the air handling equipment in the system increases the area of ​​the air handling equipment, increasing the investment cost, operating cost, equipment maintenance and repair costs, and increasing energy consumption. Therefore, in the air conditioning system, a set of air handlers (ie, air conditioners, mainly heat and humidity treatment) is used as an air treatment device for air conditioning, as a hot and humid treatment and purification pretreatment for replenishing fresh air and part of the return air, and A large part of the return air is only used as a recycling process to meet the requirements of indoor air supply. Therefore, the blower for purifying the air conditioning system is also called the heat and humidity treatment fan, and the circulation fan is only to ensure the air supply volume of the system.
2. The role of the duty fan in the purification system
For the air-conditioning system with intermittent operation, in order to prevent the clean room from being polluted by the outdoor air when the air-conditioning system is shut down, the indoor cleanliness should be maintained. Therefore, when the system is out of service, the operation method of the duty fan is adopted, and the general duty room is used. The air volume of the fan is determined by the number of air changes required to maintain the positive pressure value in the room.
9. Replacement of air filter in clean room air conditioning system
The air filter used in the clean room air conditioning system will reach its maximum allowable dust and air resistance after a period of operation. At this time, it must be replaced, otherwise the clean air conditioning system will not operate normally, and the clean room will not reach its effect. Pay attention to the following issues when replacing air filters at all levels in a clean air conditioning system:
1. Air filter replacement cycle
The air filters of each level used in the purification air conditioning system should be replaced under what circumstances, according to their specific conditions.
1) Replacement of fresh air filter (also known as pre-filter or initial filter, coarse filter) and intermediate air filter (also known as medium-efficiency air filter), which can be twice the initial resistance of air resistance. Time to proceed.
2) Replacement of the end air filter (generally a sub-efficient, efficient, ultra-efficient air filter).
The national standard GBJ73-84 stipulates that the airflow speed is reduced to a minimum. Even after replacing the primary effect and medium efficiency filter, the airflow speed cannot be increased; the resistance of the high efficiency air filter reaches twice the initial resistance; the high efficiency air The filter should be replaced if there is an unrepairable leak.
2, the choice of air filter
After purging the air conditioner for a period of time, the air filter used in the system must be replaced. The following points should be noted for the replacement of the filter:
1) First, try to use an air filter that is consistent with the original filter model, specifications, and performance (even the manufacturer).
2) When adopting new models and specifications of air filters, the installation possibilities of the original installation frame should be considered, and the fire resistance performance should also be considered.
3, air filter removal and purification air conditioning system delivery, return air line cleaning
For the purification air conditioning system before the removal of the original air filter (mainly referred to as the end of the efficient or ultra-efficient air filter), the equipment in the clean room should be wrapped and covered with a plastic film to prevent the air filter at the end. After the dismantling and dismantling, the dust accumulated in the air duct, static pressure box, etc. falls, causing pollution to the equipment and the floor.
After the air filter in the system is removed, the installation frame, air conditioner, delivery, and return air ducts should be carefully and thoroughly cleaned.
When removing the air filter in the system, it is recommended to follow the order of the primary (new air) filter, the medium efficiency filter, the sub-high efficiency filter, the high efficiency filter and the ultra-efficient air filter, which can reduce the dust entering the clean room. the amount.
Since it is not easy to replace the air filter at the end of the air conditioning system and the replacement cycle is long, it is recommended to perform an overhaul of all the equipment in the system while replacing the end air filter.
4, remove fine dust particles
After the air filter is removed and completely removed in the system, the fan in the system can be started to blow off all the air ducts and the end filter installation frame and the clean room to remove the adhesion on the relevant surfaces. Fine dust particles.
5, the end (sub-efficient, efficient, ultra-efficient) air filter replacement
In the purification air conditioning system, the installation of the air filters at all levels, which plays a key role in ensuring the cleanliness of the clean room, is the end filter.
End filters in cleanrooms generally use high-efficiency, ultra-efficient filtration or low-permeability filters, which have very high dust filtration efficiency and therefore have the disadvantage of being easily clogged. Generally, in the operation of the clean room, it is often inconvenient to remove and replace the terminal filter in the main air supply duct in the clean room and the clean air conditioning system due to the relationship between the indoor work and the cleanliness of the clean room. The upper side of the device is designed to reduce the particle concentration to the concentration required for the cleanliness of the clean room, and to extend the life of the end filter, an intermediate filter is placed in front of the high efficiency or ultra high efficiency filter.
6. Comprehensive performance test after end filter replacement
After cleaning the heat and humidity treatment equipment and the fan in the air conditioning system, the system fan should be started to put the purification system into operation, and the comprehensive performance test is carried out. The main contents of the test are:
1) Determination of system delivery, return air volume, fresh air volume, and exhaust air volume
The system sends, returns air volume, fresh air volume, and exhaust air volume are measured at the air inlet of the fan or at the air volume measuring hole on the air duct, and the relevant adjustment mechanism is adjusted.
The instrumentation used in the measurement is generally: a sub-management and micro-pressure gauge or an impeller anemometer, a hot ball anemometer, and the like.
2) Determination of airflow velocity and uniformity in clean room
The unidirectional flow clean room and the vertical unidirectional flow clean room are measured at 10 cm below the high-efficiency filter (30 cm in the US standard) and on the horizontal plane of the working area 80 cm from the floor. The distance between the measuring points is m2 m, and the number of measuring points is not less than 10.
The airflow speed in the non-unidirectional flow clean room (ie, the turbulent clean room) is generally measured at a wind speed of 10 cm below the air supply port. The number of measuring points can be appropriately arranged according to the size of the air supply port (generally 1 to 5 measuring points).
3) Detection of indoor air temperature and relative humidity
(1) Before the indoor air temperature and relative humidity are measured, the purified air-conditioning system should have been continuously operated for at least 24 hours. For places with constant temperature requirements, the measurement should be continuous for more than 8 hours according to the requirements of temperature and relative humidity fluctuation range. The interval between each measurement is not more than 30 min.
(2) According to the fluctuation range of temperature and relative humidity, the corresponding instrument with sufficient accuracy should be selected for measurement.
(3) Indoor measuring points are generally arranged in the following places:
a, send, return air outlet
b. Representative locations in the constant temperature working area
c, room center
d, sensitive components
All measuring points should be at the same height, 0.8m from the floor, or according to the size of the constant temperature zone, respectively, arranged on several planes at different heights from the ground. The measuring point should be greater than 0.5m from the outer surface.
4) Detection of indoor airflow patterns
For the detection of indoor airflow patterns, it is actually a key issue to check whether the airflow organization in the clean room can meet the cleanliness of the clean room. If the airflow pattern in the clean room cannot meet the requirements of airflow organization, the cleanliness in the clean room is also It will not or is difficult to meet the requirements.
Clean indoor airflow is generally in the form of a top-down. The following two issues need to be resolved during detection:
(1) Measuring point arrangement method
(2) Observe and record the flow direction of the airflow point by point using the cigarette lighter or the hanging monofilament thread, and mark the airflow direction on the sectional view with the measuring points arranged.
(3) Comparing the measurement record with the last measurement record, and finding that there is a phenomenon that is inconsistent or contradicts the indoor airflow organization, the cause should be analyzed and processed.
5) Detection of streamline misuse (for the detection of parallelism of streamlines in a unidirectional flow clean room)
(1) A single line can be used to observe the airflow direction of the air supply plane. Generally, each filter corresponds to one observation point.
(2) The angle measuring device measures the angle of the airflow away from the specified direction: the purpose of the test is to verify the parallelism of the airflow throughout the working area and the diffusion performance of the interior of the clean room. Equipment used; equal power smoke generators, plumb or level, tape measure, indicator and frame.
6) Determination and control of indoor static pressure
7) Inspection of indoor cleanliness
8) Detection of indoor planktonic bacteria and sedimentation bacteria
9) Detection of indoor noise
10) Detection of indoor microvibration
Data reference (portal):
Air shower: http://
High efficiency air filter: http://
Clean room: http://
High efficiency filter leak detection: http://
Operating room purification project: http://
Cleanliness level standard: http://
Cleanroom testing standards: http://
Clean factory design specifications: http://
Cleanroom management system: http://
Clean room ventilation frequency standard: http://
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