How to Stop Powder Coatings from Drifting from Spray Booth
Nordson’s Frank Mohar says the main function of any powder booth is to contain excess powder overspray.
Q: Why is powder always drifting from my booth?
A: We get this question quite often and, even when the question is not asked, it should be as it is an all too common occurrence in many powder coating shops.
The first thing we need to understand is that the main function of any powder booth is to contain any excess powder overspray and, in some cases, give the customer the ability to reuse that overspray on their parts to utilize as much of the powder in the system as possible. With that being said, sometimes we find that, as time goes on, your booth (which used to be the cleanest area in the shop) is now the cause of powder being spread throughout the entire area. There are quite a few things that should be looked at when solving the problem. Below are a few common problems you can check:
Cartridge filters are blinded or plugged up: On systems with cylindrical cartridge filters, there should be a “pulse feature” that has a series of pulse valves to blow short bursts of air into the cartridge filters which will, in turn, knock any excess powder off the filters and allow them to breathe more easily. Be sure that you hear a solid “pop” noise, which tells you the filters are being blown down. There is an “on” time, which is the duration of the air being released into the filters. Typically, this is set to 0.2 seconds, give or take. The other set point is the “off” time. This is the duration between pulses (when nothing is happening, except for the air manifold being replenished with air). This setting is usually around 20 seconds, but can vary depending on the booth make and model. If the timing is correct, but the sound seems inconsistent, it could be that the bladder has a tear and needs replacing or the timer board is not firing all outputs. Refer to the manufacturer’s specifications for more information on the pulse system. If the pulsing is operating correctly, there should be magnehelic gauges on the collector itself, which measures the filter pressure (one for the cartridge filters and one for the secondary/final filters). The readings and operating parameters will vary between manufacturers, but all are there to display what the pressure readings are at any given time. These readings should be recorded on a regular basis so that you can refer to the data if there is a problem. For simple troubleshooting ideas, if the pressure on the cartridge gauge rises, that means powder is building up on them and should be replaced as needed. If you do not see any rise in the gauges, then potentially there is a leak or hole in the filters. This could also be determined if the secondary/final filter gauge shows a rise in pressure, as this means powder is leaking through the primaries and blinding the secondary.
Modifications were made to the booth after the design phase: As mentioned above, a standard cartridge powder booth is designed to contain powder with an airflow range anywhere from 80 to 150 fpm, depending on the booth design, parts being sprayed, number of guns being used and many other factors. Look for the original specifications on the booth itself and see that no openings were modified (usually made larger to accept bigger parts or conveyor changes). If the openings were enlarged without any fan design changes, then the booth airflow will go down, resulting in powder drifting out the openings.
Foreign air movement: What this means is that there is air being blown or pulled across any of the openings or even into one of the booth openings. This can be done inadvertently when using fans to keep operators cool, opening and closing shipping garage doors, or operating any air handling systems. Regardless of how the outside air is being introduced, this needs to be kept to a minimum — 60 fpm of airflow or less by any outside influences is standard practice in order to keep powder from being pulled or blown from the booth. If the outside air cannot be reduced, then a good option is to redirect that air so that it is not being directed toward any booth opening.
The above are just a few ideas of what to initially look for if your booth does not seem to keep powder in, but there are countless other variables that should be considered. Some include the booth being undersized, the number of powder guns is more than what the booth can handle, the fan motor is running in the wrong direction, the parts that are in the booth are too hot and causing the heat to carry the powder up and out of the booth, along with many other factors. As with all finishing equipment, please consult your manufacturer before performing service.
Frank Mohar is a powder systems specialist at Nordson. Visit Nordson.com
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