Consider condensed moisture getting into the material during the spray
process, being trapped and later vaporizing during the cure process (or even
after?).  When we get bubbles it is usually because of a too heavy first
coat or not allowing solvent vapors to escape before the material gets too
hard to allow vapor escape (without making bubbles).  Perform a drying
bake-out before coating.  Allow a short time between coats for vapor
evaporation, cure at a lower temp to allow water vapor to escape before
material gets too viscous.

> Rainer G. Blomberg
> Honeywell -Space Systems Clearwater
> Staff Production Engineer
(727) 539-5534


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kelly Morris
Sent: Tuesday, January 24, 2006 10:25 AM
To: [log in to unmask]
Subject: [TN] Conforma Coat (Urethane) & bubbles

We've got a problem here, where we're hand spraying a urethane conformal
coat on over a rectangular inductor.
The inductor body is a plastic tube, with potting to fill.
The top is not always flat (sometimes concave).
The problem is that bubbles appear in the conformal coat on the potted
surface, sometimes right after bake and sometimes days after.

Any ideas on what the root cause is and how to prevent the bubbles?

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