Powder Coating defects
Outgassing                                               Back to Powder-Coater Home Page


The term outgassing is a reference to the release of trapped air in a

cast substrate during the cure cycle. Porosity in the casting traps air.

When the casting is heated, the air expands and blows through the

partially gelled coating, leaving a small defect like a pinhole.

Outgassing is a serious problem for powder coaters. The severity of

the problem is dependent on the type of casting and the quality of the

casting. Generally, aluminum is not too bad, while zinc die cast can be more of a problem and sand castings are the worst.

Methods for dealing with this problem are limited.

If a manufacturer has control over the casting process, they can work

to minimize the contamination in the casting process, x-ray castings

for porosity as a process control measure and use an impregnator to

fill open porosity in the cast surface. Many times these measures are

not available or not practical.

Two widely used methods of dealing with outgassing are preheating

and the use of "outgassing forgiving" powders.

Preheating means bringing the part to a temperature in excess of the

cure temperature prior to coating. For example, running the part

through the dry-off oven at 450 °F and curing at 350 °F. The theory

is that the trapped air will escape in the preheat and no more will

come out in the cure oven.

Actual field evidence is that this can be an effective way to reduce the damage of outgassing by a large margin.

Outgassing forgiving powders are designed to provide a longer flow

cycle so that the air can escape before the powder has gelled. This

also has been demonstrated to be an effective way of reducing



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abrasive blasting   adhesion problems  caps and plugs

chemical cleaning  cure ovens  defects  fluidized bed

infrared oven  masking  outgassing  powder formulations

pretreatment  quality  tape  powder selection

powder vs. liquid  spray booth  spray gun  substrates

hi-temp tapes  types of powder

June 14, 2012