Air Filter Manufacturing
Raw Material
When manufacturing HEPA filters every single component is important with the filter media of paramount importance.
Every roll of glass filter media we use is tested to verify the compatibility of the following parameters as follows:
- Weight fluctuation
- DEHS penetration at o.3µm
- Pressure loss
- MPPS penetration
- Water repellence
- Thickness
- Tensile strength along the roll direction and perpendicularly
Manufacturing Process
As HEPA filters are used in critical environments where the highest air quality level is needed, they also need to be produce in a clean room to avoid any risk of contaminating any component or material during the manufacturing process.
In a ISO 7 clean room the media is pleated and spaced by hot melt separators from precisely calibrated nozzles, with all of them fed by the same tank to have the very same hot melt temperature and injection velocity to maintain the same mechanical characteristics of the spacers in every filter.
The pleated media packs are permanently bonded to the filter frame with a bi-component sealant with a sample of the sealant checked every hour.
The frame used for laminar air flow HEPA filters is made of extruded aluminium 20/10 with a high strength resistance to twisting.
Testing
The filter is then automatically delivered to the ISO 5 testing clean room where, according to the EN 1822 Standard, it is tested at the rated air flow to verify the overall efficiency and MPPS efficiency.
The test is carried out using a polydisperse aerosol and the total particle counting method is used with an optical particle counter which, in addition to counting the particles, is also able to determine their size distribution.
The downstream sampling is carried out directly behind the test filter using one moveable probe, which can scan the entire cross sectional area of the filter including the frame.
Once tested, the automatic testing machine produces a test report with the following information:
- Serial number and code of the filter
- Overall dimensions
- Filter medium type and MPPS value at the corresponding medium velocity
- Temperature, relative humidity and pressure of the test air
- Nominal air flow of the tested filter
- Challenge aerosol
- Particle counters model, brand and serial numbers
- Upstream particle concentration and dilution system
- Global and local MPPS efficiency
- Filter class
Labelling & Packaging
Every filter is labelled with the serial number and type of the filter, number of the standard to which the filter is compliant, class of the filter, nominal air flow rate at which the filter has been classified.
The filter is then packaged and sealed in a clean plastic protective bag together with its own test report and finally leaves the clean room to be boxed.
