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Compressed Air Quality for Powder Coating

by Eric | Published May 20, 2013

Most facilities have after-coolers on their compressor along with water and oil removal systems for the main plant air system. These components will remove the bulk of the water, oil and particulate contaminants however in many cases an additional dryer/filter is necessary. This is especially true in your powder coating operation as the highest quality of compressed air is very important to the application process and final results, in addition to higher quality, you can expect dramatically lower maintenance costs for your powder coating system also. High voltage electrostatic equipment is especially sensitive to moisture and oil from compressed air. The un-sprayed powder absorbs moisture much like flour and when the powder application equipment (supply hoppers, hoses, gauges or guns) becomes contaminated with oil or moisture your equipment produces uneven coating, loss of transfer efficiency and many other inconsistencies that will result in all around poor quality.  Final air treatment at the “POINT OF USE” is usually necessary since this high level of filtration is not typically required for many other applications throughout the plant.

Here are some preventative measures that must be addressed in every compressed air system to be used in powder coating.

1 – AFTERCOOLER – All atmospheric air contains water vapor which begins to condense as the air is heated up and compressed. As an example by compressing air to 100 PSI we generate almost 10 times the amount of water per cubic foot.  Later in the process, as the air is cooled down, it begins to cool down and produce moisture in a liquid form. Aftercoolers are designed to cool the air to within 5 to 20 degrees F of ambient air temperatures.

2 – WATER SEPARATOR – After the aftercooler process, up to 75% of the water vapor condenses to a liquid and can now be removed from the system.  A quality separator trap will remove most bulk liquids and solids by centrifugally spinning the air stream allowing the heavier liquids and solids to drop out of the air stream while producing low pressure drops of 1 PSI or less. By removing the bulk liquids and solids at the separator trap, the particulate and coalescing filters downstream can do a better job of providing clean dry air, thus, lowering the pressure drop where it is not as noticeable. With every 2 PSI of pressure drop, you waste 1% of the energy used to compress the air at 100 PSI.  A Water Separator Saves Energy and Money!

3 – PARTICULATE CONTAMINANTS – A Particulate Filters is suggested to remove the pipe scale, rust and grit which will gather over time in the pipes of your compressed air system. In addition to particulates in your piping system, the compressor’s intake air can fall victim to particulates also which can be transferred to your powder. A low micron size filter will remove the vast majority of this type of contaminant. We suggest you use a 5 micron filter.

4 – WATER CONTAMINANTS –  A  Coalescing Filter will provide your equipment with clean dry air up to 99.997% when you use a .03 micron element. The bulk separator, discussed above, definitely plays its part in the compressed air system but it is not designed to remove the finer water droplets or mist from the downstream air system. This is especially true after the air has had a chance to sit in your pipes and condense even further. A good coalescing filter is recommended directly prior to the equipment to be used.

5 – OIL AEROSOLS – Oils from your compressor can infiltrate into your compressed air system. These can come from the crankcase, lubricants or just about anywhere. As a result of the high pressure and temperatures associated with compressing air, these oils are broken down into extremely small droplets or aerosols. Typically finer than tobacco smoke, these aerosols can pass through conventional filters and cause problems with gauges, valves or electrostatic components. Through the use of a hi-efficiency coalescing filter, like the one described above, up to 99.997% of these aerosols can be removed (down to .03 micron). Often times the same coalescing filter can take care of the water contaminants mentioned above as well as the oil aerosols mentioned here.

In most cases of paint or powder systems, a properly sized refrigerant dryer will provide air that is cooled down to a 35 degree dew point. Combined with the proper filters in the proper sequence you can drastically improve your system by providing clean dry air that is free of water, particulates and oil vapor. This should provide a good quality compressed air system at a reasonable cost to you.  Clean dry compressed air will pay you back every day through increased quality, higher transfer efficiency rates and lower maintenance costs.

For additional information on sizing your compressed air system, or for ordering information, you can contact Buy Rite Finishing toll free at 888-647-9929 or through info@buyritefinishing.com.