Good morning,
Seems to be a morning for coating related questions.

Like many high-performance manufacturers, we use silicone RTV materials
around high mass components, such as them big honkin' electrolytics, to
give vibration resistance.  Our coating specifications has us coat over the
RTV materials with acrylic coating (Humiseal 1B31).  Our normal product
acceptance screen is a thermal cycle of -55C to +125C.  You can guess some
of the adhesion related problems we have from the differential expansion
rates and from the problems of trying to get anything to stick to
silicones, as well as to the halo region around the cured silicones.  Here
are my questions:

1.  Do you coat over silicone RTVs?
2.  If you do, do you preclean the silicone and surrounding areas?  If so,
with what?
3.  If you coat over silicones, do you use a primer material to promote
adhesion?

I imagine that this will be a dragon that I joust with regularly over this
coming year, till I slay the beast (Mountain Dew starting to kick in
folks).  Tis an unwholesome creature............

Doug Pauls
Rockwell Collins

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