Ash on the parts is caused when powder coatings are blown fromtheparts and hangers into the oven airstream or by contaminantsenteringthe oven from the plant airspace that have catalyzed orburned.Adjusting the velocity of the air seals or circulation air at theovenentrance will reduce the problems of blowing the powder coatingfrom theparts and/or the hangers. A little known cause of thisphenomenon ispoor part grounding. If the part is improperly grounded,then theelectrostatic force that holds the powder onto the part'ssurface islower. The lower the electrostatic force, the more likely thepowdercoating will be displaced by the oven airstream. Frequenthangercleaning and conveyor maintenance will improve the ground (lessthan 1megohm resistance) and eliminate this as a cause to yourcontamination problem.
If you are sucking airborne contaminants into your oven fromtheplant airspace, then you must isolate their sources or use filterstoremove them. Filtration is available to clean air that is introducedbythe combustion blower in convection ovens. These filters arelocatedoutside the oven and do not have to be high-temperatureresistant.Isolating the cure oven from your plant airstream may berequired toprevent airborne contaminants from entering the partentrance/exit ofthe oven. Walling off the oven and providing an outsideair supply willsufficiently isolate your oven from the dirty plantairspace. However,isolating the specific plant area that is causing thecontamination maybe easier than isolating the cure oven.
