1, end filtering
The main function of the low-efficiency end air filter is equalization, not filtration. Those filters ensure that the airflow in the painting work area is uniform without turbulence and side flow to ensure the uniformity of painting. In the past, those filters were flat filters with fluffy glass fiber or synthetic fiber as the filter material. Later, those plate filters were replaced by top cotton. The function of the top cotton is the same as that of the previous plate filter: even flow.
"Top cotton" is a layer of dense and uniform polyester fiber non-woven fabric, which is laid over a large area above the working area of the spray booth. Compared with the flat filter, the ceiling air filter cotton has good current sharing effect, good reliability and easy replacement. The common top cotton is glued on the one hand to prevent possible fiber shedding and on the other hand to increase the ability to trap dust.
A good top cotton should at least: uniform material, low resistance, high dust holding capacity; three-dimensional dipping, no fibrous hairs that may fall off the air surface; no deformation during use; meet relevant fire standards. If the filtration efficiency is evaluated, the filtration efficiency of the top cotton is higher than that of the previous flat filter, and the common efficiency level of the top cotton is F5.
The setting of the filter efficiency of the spray booth is different from the setting of the conventional air conditioning filtering system. For ordinary systems, the efficiency is from low to high. For example, G3 → F5 → F8, but the paint booth is unreasonable G3 → F5 → F8 → F5. In fact, the last stage of the roof filter cotton, its role is to equalize the flow, the filtering function is secondary.
2, the last pre-filter
In the conventional design, the air filter setting method of the spray booth in the automobile factory is the key filter for purifying the air. The domestic and European settings are similar. When the budget allows, use high-efficiency filters as much as possible. Common filter levels are F7 ~ F9, but occasionally car manufacturers use lower or higher-level filters.
If only considering the factor of filtration level, as long as a filter higher than F5 is used as the pre-filtration before the top cotton, the purification requirements can be met. It can not only filter particles that damage the quality of the paint, but also effectively protect the top cotton. The reason is as follows.
First of all, the F5 filter can already meet the air purification requirements of the spray booth. The car spray booth needs to filter out dust particles larger than 15 μm. Laboratory experiments show that the filtration efficiency of F5 filter for particles larger than 10 μm is almost 100%. As long as a reliable F5 filter is used, the problem of filtering out particles that affect the quality of the paint has been resolved.
Second, high-efficiency filters mean high resistance. Selecting a filter with a too high level will cause a large burden on the system resistance and therefore reduce the air volume.
Third, top cotton already has a good filtering effect. Although the main function of top cotton is to equalize the flow, even without pre-filtration, its filtering effect has basically guaranteed the air cleanliness of the spray booth. At this time, the role of the pre-filter is to protect the top cotton to extend its service life. In a sense, some of the existing high-efficiency pre-filters are luxurious settings. Those filters mainly filter particles below 5 μm, and those particles do not affect the quality of spray paint.
Fourth, replacement cycle and cost control. Filtration costs include filter spare parts costs, maintenance costs, and filter energy consumption. Experience shows that the cost of filter spare parts only accounts for 10% to 15% of the filter cost, and the energy consumption of the filter accounts for the largest proportion of the filter cost. The luxurious use of high-level filters intercepts smaller particles that do not affect the quality of the paint, but have a great impact on cost. Owners may only notice the cost of spare parts and ignore the much larger proportion of energy and maintenance costs.
Choose according to the local environment. If the local environment is bad, you can choose G3 or G4. If the environment is good, you can directly choose F5. The use of a bag filter is better because of its high dust holding capacity and long service life.
4. Structural seal
No matter how good the filter is, the seal between the filter and the installation structure is not reliable, and it will also cause dust pollution. In many factories, I saw air leakage around the filter: due to broken seals, the metal structure itself leaked air, and the filter pressing device was lost. What's more, some filter installation boxes were found reversed. In these cases, the use of even the best filters does not help.