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April 2002

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Subject:
From:
David Douthit <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 15 Apr 2002 13:09:25 -0700
Content-Type:
text/plain
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text/plain (110 lines)
Phil,

You are in a nasty position!
When moisture combines with motor oils, fuels, or most other man made hydrocarbon compounds
numerous acids are formed due to the chemistry of the additives. I have seen cases where this
combination will
"eat" aluminum, permeate double "O" rings,  sealants, and torqued down screw combinations in 3 years.

The only choice you have is to apply a replaceable sacrificial coating over the "sealed" area and
periodically
remove and replace it (it will be fairly thick!). The main problem is finding something that will
withstand the vibration
and temperature as well as the chemical issues for a year or so.

If the rest of the CCA housing is hermetically sealed then you may have a fighting chance. If not then
you will need parylene coating on the CCA.

Good luck and please don't forget to do some serious testing of the design under operating conditions.

David a. Douthit
Manager
LoCan LLC

Phil Bavaro wrote:

> Sorry, definitely Class 2.
>
> Warranty period of 3 years is acceptable although would like something
> longer if possible.
>
>   At 09:55 AM 4/15/2002 -0700, David Douthit wrote:
> >Phil,
> >
> >What class product is this? (2 or 3)
> >More importantly what is the "warranty" period for this product?
> >(Anything longer than 3 years will be a problem!)
> >
> >David A. Douthit
> >Manager
> >LoCan LLC
> >
> >David A. Douthit
> >Manager
> >LoCan LLC
> >
> >phil bavaro wrote:
> >
> > > Ok, I've been around the sealant, conformal coating, potting, and general
> > > adhesive world for 20 years and I have my own opinions and preferences when
> > > it comes to specifying a compound for a production assembly, but I would
> > > like to see what this group will suggest for this new assembly we are
> > > designing:
> > >
> > > We have a CCA on which is mounted a very large bulkhead type connector
> > > which requires a form in place sealant around it where it interfaces with
> > > (sticks through) the chassis.  The connector is mechanically fastened to
> > > the chassis with four screws but the application will see very tough
> > > vibration exposure.  The bond is between  the connector flange (plastic)
> > > and the chassis (cast aluminum) and must be capable of resisting constant
> > > outdoor environment abuse such as high pressure water spray cleaning, motor
> > > oils, fuels, and general dirt.
> > >
> > > The temp range is -40 C to +85 C, and it will not be submerged (at least
> > > not intentionally) for long periods of time but moisture is the primary
> > > culprit that we are trying to defeat as the CCA will not be sealed with
> > > conformal coating.
> > >
> > > Please select your choice and tell me why?  Remember, this is for
> > > production so cure time, cost, and application ease are very important
> > > factors.  Please include whether or not the cast aluminum chassis  needs to
> > > be chem filmed, primed, or painted to seal its surface.
> > >
> > >
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