With the rapid development of modern industry, the technical content of its products is more complex. In order to adapt to more and more industries relying on the production and assembly of their own products in clean and dust-free rooms, and to ensure stable quality and high service life of equipment. The modern cleanrooms are constantly being used in all walks of life. How to ensure that the cleanliness level of the modern cleanroom always meets the requirements of the production process.
Modern cleanroom technology divides the cleanroom into three categories: cleanroom design and construction, cleanroom testing and inspection, and cleanroom operation. To understand the positive pressure differential control mechanism in the cleanroom and ensure the efficient and energy-saving operation of the cleanroom is to meet the urgent requirements of modern industrial production for the cleanroom environment.
The cleanroom is first designed by the architectural design institute according to the requirements of the construction unit and the environmental requirements and characteristics of the products in the industry to match the corresponding cleanliness level. This is a prerequisite work for the design and construction of a clean room, and it is also a basic work.
1. Establishment of pressure difference in cleanroom
The test and inspection of the clean room is that the construction unit designs the construction drawings according to the design unit. After all the ventilation and air conditioning design and installation are in place, the sub-items are tested and measured for some items, mainly including air volume adjustment and pressure difference adjustment, cleanliness test, measurement of indoor temperature and humidity in cleanroom.
(1) Air volume debugging: According to the design and construction drawing design and calculation of the return pipeline, the size of the designed air volume, the opening state of the return air valve of each pipeline, and the air volume of each branch to test.
(2) Cleanliness test: It is divided into tests under empty conditions, tests under static conditions, and tests under dynamic conditions, respectively testing the dust content in the cleanroom.The test under empty conditions means that the system (cleanroom) is already in normal operation, but the process equipment and production personnel have not yet entered the test.
The test under static conditions means that the system (cleanroom) is already in normal operation, the process equipment has been installed but not in operation, and the test is carried out without production personnel in the room.
Testing under dynamic conditions means that the system (cleanroom) is already in normal operation, and the process equipment and production personnel are all working.
According to the above test results, the construction unit shall test the dust content concentration under different production environment conditions to achieve the cleanliness level required by the construction designer and the construction unit, and ensure that the dust concentration is always lower than this value. Qualified delivery to the construction unit for use.
(3) Differential pressure debugging: In order to prevent external pollutants from entering the cleanroom and increase the indoor cleanliness, it is required that the indoor pressure be kept higher than the external pressure. That is to say, in the clean room, rooms with different cleanliness must maintain a certain pressure gradient, which can effectively prevent the clean room from being polluted or polluted by the adjacent room under the condition of maintaining a certain pressure difference in the room. The process of differential pressure debugging is to ensure the number of air changes in the cleanroom and the effect of equipment exhaust and dust removal, and try not to change the air supply volume and the air volume of the equipment exhaust fan and dust removal fan. The pressure difference is adjusted mainly by adjusting the return air volume and the system exhaust air volume.
Each functional room in the man-cleaning area should follow the man-cleaning route: unclean corridor, changing shoes, primary changing room, secondary changing room, buffer room, and clean inner corridor.
Maintain a positive pressure difference of at least 30Pa between the cleanroom corridor and the unclean area.
The basic principle of this pressure difference is that the supply air volume is greater than the return air volume, exhaust air volume, and leakage air volume to maintain positive pressure. The pressure difference is established through the balance between the air volume sent into the cleanroom and the exhaust air volume + differential air volume (residual air volume).
For fresh air system: fresh air volume = exhaust air volume + differential pressure air volume
For circulating air system: fresh air volume + return air volume = return air volume + exhaust air volume + differential air volume
In the final analysis, the pressure difference in the cleanroom, that is, fresh air volume = exhaust air volume + differential air volume, and a balanced relationship between them is established.
In short, design, construction and commissioning are three important links to ensure the normal operation of the purification system. Through commissioning, we can understand the problems that arise during the operation of the system, so that we can improve the design plan, standardize the construction operation, and avoid the above problems. Debugging is an important and necessary link to ensure whether the pressure difference and cleanliness in the clean room are up to standard. The normal operation of the system belongs to the normal use and production link.2. Interfering Factors and Control Methods of Differential Pressure Fluctuation in Clean Room
Changes in outdoor wind pressure and wind speed cause changes in the pressure difference between the cleanroom and the outsideCoastal cities and cities with relatively high wind speeds must conduct face-to-face wind speed pressure recheck calculations and adjust pressure differential values.
As the air conditioning system runs over time, the resistance of the system will change, mainly due to changes in the resistance of the filter, which will cause changes in the air supply volume and affect the establishment of the pressure difference in the clean room, because the air conditioning system will run for a certain period of time. When the resistance changes to a certain value, the resistance of the system increases, which affects the reduction of the total air supply volume, the actual air supply volume is less than the set air supply volume, and the establishment of the original indoor pressure difference cannot be guaranteed. At the same time, due to the flow of people in the cleanroom, the doors and windows of the cleanroom are frequently opened and opened, the original sealing performance of the cleanroom is reduced, and serious air leakage will eventually affect the establishment of the original pressure difference in the cleanroom. For the above problems. In order to ensure that the cleanroom always maintains a certain pressure difference, certain measures must be taken to maintain the positive pressure in the room.
(1) Install an air damping layer at the air return port;(2) The exhaust pipe is equipped with an electric airtight valve medium-efficiency filter;
(3) The residual pressure valve is generally installed on the downwind side wall of the cleanroom. When taking such measures, it is required that there must be sufficient residual air volume in the room;
(4) Adjust the return air valve or exhaust air valve;
(5) Adjust the fresh air valve;
(6) Fan and air valve interlock control;
(7) Regularly replace some necessary filters.