Since the invention of automobiles, they have become an essential travel tool for people, and automobile manufacturing has become one of the most essential industries in modern industries.
General introduction
During production, the car will pass four major processes: stamping, welding, coating, and assembly. Coating is one of the links that is more special than the other three major processes.
Because the requirements of the coating on the environment are more stringent, the quality of the coating environment directly affects the quality of the product.
Painting in an uncontrolled environment, fibers and particles will contaminate the paint surface and cause shrinkage of the paint.
At this time, designing and installing a filtration system with air filters of different performances is necessary to create a clean painting workshop.
Before I go into more detail about this air filtration system, I would like to briefly introduce some information about automobile spraying as a basic knowledge.
What is the automobile painting shop?
The workshop that completes the process from body-in-white to complete paint spraying is usually called an automotive spray shop. There are more than 20 steps from pre-treatment to finish painting.
As I mentioned above, the perfect birth of a car requires four processes: stamping, welding, painting, and final assembly, commonly known as the “four major processes” of automobile manufacturing.
Among them, stamping and welding form the shape and structure of the car; the final assembly is to complete the group of various parts of the car, and painting ensures the anti-corrosion and appearance of the vehicle.
What’s the function of automobile coating?
Automobile coating has two essential functions. One is to safeguard the underlying material (like steel and plastic), while the other aims to improve the visual aesthetics.
The coating works with a thin film of about 0.1mm, which is very effective compared to other ways.
Most customers are very interested in car paint color and spray quality. So it is also essential to increase the value of the car.
What causes car spray painting to fail?
Suspended particles above 10um can cause dirty spots and particle defects on the paint film’s surface, destroying the paint surface’s flatness.
Where does the dust come from in the painting shop?
During spraying operations, a large amount of dust is generated in the workshop. In addition to the paint, these dust particles include suspended dust in the coating environment and dust deposited in ventilation ducts, drying rooms, drying chambers, and dust adhering to conveyor devices. These particles will all affect the painting effect.
What is the cleanliness level of a car paint shop?
According to the regulations of ISO14644, different areas of the paint shop have different cleanliness standards. Typically, from ISO 7-8 level.
Painting is an essential process in automobile manufacturing. The process is complex and highly technical. It is one of the critical factors determining the car body’s good quality. Therefore, the clean environment of the paint shop needs to be strictly controlled.
The painting workshop is a relatively closed space. The air-conditioning air supply system is mainly used to ensure the balance of air supply and exhaust in the workshop and maintain a slight positive pressure. Therefore, the air filter is an essential part of maintaining the cleanliness of the air in the paint shop.
Clean area 1 (cleanliness level: ISO level 7)
It refers to the spray booth, drying area, drying oven, paint mixing room, and other areas in the coating workshop. The particles in these areas come into contact with the wet film of car body paint, which directly affects the quality of the paint film on the car body.
Clean area 2 (cleanliness level: ISO level 7)
Here refers to the pre-treatment line, electrophoresis line, PVC line, and other areas. Particles in this area come into contact with the bottom layer of coatings, such as phosphate car bodies, or with spray-related materials, seriously affecting the quality of the paint film on the surface of the car body.
General clean area (cleanliness level: ISO level 8)
These general clean areas are logistics channels, polishing rooms, and wax spray rooms.
The particles in this area generally only come into contact with the dried primer. Before entering the spraying process, the vehicle body can be restored to a clean state through cleaning measures to avoid any influence on the paint film on the surface of the vehicle body.
Use air filters to ensure the cleanliness level of a car paint shop
Generally speaking, the minimum cleanliness level required for paint shops is ISO Class 8, equivalent to Class 100,000 cleanliness.
Conventional paint film thicknesses are electrophoretic paint film 18-24um, mid-coat paint film 25-35um, color paint film 12-18um, and varnish film 30-45um. Any dust of 5-10um falling on the paint film will cause defects.
To improve the air cleanliness in the coating workshop, it is necessary to suppress dust and paint mist caused by solvent volatilization, and a large air exchange is required to ensure indoor airflow to suppress the spread of dust and prevent coating film defects caused by dust adhesion.
So we need to set different air filters to achieve the goal; here I list below:
| Paint Workshop | Air filter | Efficiency | Remark |
| Automotive painting workshop | Pocket filter | F5-F7 | Silicone free in air filter |
| Automobil paint baking workshop | High-temperature filter | F6-F7 | Silicone free in air filter |
| Automobile electrostatic spraying workshop | Pleated filter | F7-F8 | Silicone free in air filter |
Where are air filters located in the automobile painting workshop?
The car spray paint workshop is divided into a normal-temperature process area (spray room, work platform, etc.) and a high-temperature area (oven area). Therefore, the use area of the air filter is divided according to the process temperature and is divided into two types: regular temperature filters in the normal temperature area and high-temperature filters in the high-temperature region.
Ceiling mat location
The painting line is a very long tunnel. The car body is transported along the tunnel and undergoes various pre-treatment and spray processes.
The top of the coating tunnel is covered with a thick layer of non-woven fabric (filter ceiling mat). Fresh air passes through the ceiling mat and enters the tunnel evenly – the function of the filter ceiling mat is to dampen the flow, and its filtration level is generally F5. I commonly call it an F5 ceiling mat.
The important thing is that the filter ceiling mat itself should be uniform and lint-free.
Primary air filter location
The primary air filter of the spray painting line is located in the dynamic and static pressure chamber above the filter ceiling mat or in the air handling unit.
The primary filter is normally a pocket filter with an efficiency of F5 to F8 (depending on the level of the coating product). This level of the primary filter determines the cleanliness level of the spray painting environment, not the filter ceiling mat on the long tunnel.
If the outdoor air quality is poor, there should be a pre-filter before the primary filter. Since new automobile factory painting workshops in recent years are all international standards, most bag filters are of general specifications of 592×592mm (nominal size 24″ ×24″).
High-temperature filter location
In the baking production line of the coating workshop, the incoming air must be preheated to about 200°C. Since the heating device may generate dust, the air filter must be placed at one end of the hot air before entering the coating workshop, which requires the air filter to withstand 200-250°C for a long time.
The efficiency specifications of the air filters here are generally F7 to F8. All filters have a separator structure. The glass fiber filter paper is separated by corrugated aluminum foil. Due to the high-temperature resistance, the bonding and sealing issues between the filter paper and the filter metal frame are key. The sealing must be stable, and the cost of the sealing material should be reasonable.
The sealing gaskets on the high-temperature filter are mostly elastic fiberglass with a thickness of about 5mm. The overall dimensions of the air filter in the baking production line are 610×610×292mm or 610x610x78mm.
The pre-filter of the baking production line is located at the inlet of the air supply unit, where it is at normal temperature.
Standard bag filters with lower efficiency are often used as pre-filters. To facilitate management, the baking line’s pre-filters and the painting line’s pre-filters are often of the same specifications and models.
Do not use air filters with silicone sealant in automobile painting workshops
This issue is very critical so I will discuss it separately.
Silicone is an excellent material that is also used in many aspects of cars.
However, the automobile paint shop is particularly taboo about silicone because if a bit of silicone is stained on the paint, the paint will bubble.
Automakers have banned silicone, so you should check carefully with air filter suppliers or manufacturers about all materials they use in air filter manufacturing, especially adhesives, to ensure they do not contain silicone.
Last thought
The air filter is an effective measure in the coating workshop to prevent dust from contaminating the paint layer on the car’s surface. It is a necessary equipment for dust-free coating by automobile manufacturers.
Choosing suitable air filters can ensure the spray quality of the car body and the health and safety of workers to the greatest extent.
Taking this as the first principle, optimizing various parameters of the air filters can reduce the pressure difference under different equipment conditions, ultimately saving energy.
