The choice of the correct paint booth filters has beneficial effects on product quality, worker safety and operating costs.
Outside air filters
Outside air filters are the first barrier against possible impurities entering the paint booth and are used to filter the larger particles present in the airflow coming from outside.
They are generally pre-filters and usually take the form of filter cells, polyester panels or washable aluminium panels.
Outside air filters are the first element to check when there are problems with the filtration system: if the airflow in the booth is too low, they may be clogged; if the airflow in the painting area is too high, they may be incorrectly installed or missing.
Outside air filters can also be configured as a multi-pocket filter with several sections.
Supply air filters
Supply air filters ensure that all particles that can cause paint defects are removed from the airflow in the booth.
Even contaminants with a diameter of 10 microns (10 thousandths of a millimetre) can cause visible paint defects.
The main task of these filters is to provide clean, particle-free air to the painting area, in order to prevent defects and blemishes on the finished product.
In vertical-flow booths these filters are installed in the upper part, which is why they are called ceiling filters.
Ceiling filters should be at least in M5 class and, where possible, installed as frameless ceiling panel filters.
The absence of a frame makes installation easier and helps avoid leaks and bypasses of contaminated air.
Exhaust filters
The air leaving the painting process must be filtered to protect the environment and worker safety.
Filters for removing the solid part of the overspray can be made from different materials and installed in a wide variety of ways.
They can be standard under-grid glass fibre paint-stop filters, pleated cardboard inertial filters, often used in horizontal-flow booths, or high-capacity, low-pressure-drop Raccoglivernice® multi-layer filters, which are self-extinguishing.
In addition to these filters, in vertical-flow booths – especially in spray/bake booths for body shops – a final section of pocket exhaust filters is installed.
Activated carbon filters
Once the solid part of the overspray has been filtered, it is necessary to remove the volatile organic compounds (VOCs) in the paints, i.e. the solvents that are primarily responsible for the spread of odours outside the painting department.
Filtration of the organic molecules that make up the solvent takes place by adsorption on a bed of activated carbon.
Activated carbon for painting typically comes in the form of pellets, extruded cylinders of 3–4 mm.
These pellets are contained in the cavity of cylindrical or square-section cartridges through which the air to be purified is conveyed.
For proper operation, the activated carbon bed must be protected against any solid overspray residues, so activated carbon cartridges are often equipped with a pre-filtration section for the solid part of the overspray, in the form of socks or sleeves for activated carbon.
Filter maintenance
Filtration systems are made up of several sections and are crucial to achieving good results in painting operations.
Timely, scheduled maintenance helps avoid occupational safety issues, reduce defects on painted parts and save energy.
Clogged filters are not only a possible cause of pollution and production defects, but also create unnecessary resistance to airflow, with non-negligible energy costs.