Air for powder coating is practically of no real consequence. The raw powder
is essentially a "plastic material powder" (I've forgotten the actual
makeup). The low pressure air is used to transport the powder from the
source to the area of the item. The actual powder adheres (temporarily)
because a static charge is built up by the powder transport and the part is
of opposite charge. This is why you will have a "ground wire" attached to
any part you are coating. The powder comes out of the gun at one electrical
charge and the part has the opposite electrical charge. The powder then
"adheres" to the part due to the electrical charge (just like dust particles
do to anything in your house!!) long enought for you to have it in the oven.
The oven temperature then bakes on the powder (i.e., melts it) into a more
or less (almost) non-porous finish.
In the automotive industry, the static charge transport method for powder
coating is also sometimes used for some higher quality paint finishes as
well. The EPA is driving all this because they want to reduce the VOC's
(Volatile Organic Compounds) that are evaporated when traditional paint
finishes are applied, dry and/or cure. Lacquer is going away because of all
the VOC's (i.e., solvents) that have to be used and end up in the
atmosphere. Enamels cure by chemical reaction but also still have some VOC's
in them which is why they take so long to "dry" (i.e., cure). Polyurethanes
are catalyzed for curing but still have VOC's although can be lower VOC than
enamel. Powder coat is the ultimate because it has almost eliminated the
VOC's. This is the wave of the future.
Roy
'60 TR3 TS63103LO (in restoration)
techman@metrolink.net
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