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Date: | Mon, 9 Jun 2008 16:34:40 +0100 |
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You see - there are all the "Depends" you could wish for - despite the
poor spelling.
Only one little extra titbit - urethanes often/usually contain
isocyanates that would require/mandate you to provide the operators
with artificial respiration equipment, not entirely dissimilar to what
Buzz Aldrin had to wear on the moon! I exaggerate just a tad.
Graham N
On 9 Jun 2008, at 13:53, Douglas O. Pauls wrote:
> Mike,
> As others have said, the two don't mix. I have tried to clean
> silicones
> from spray equipment and you can never get it down enough such that it
> does not cause fisheyes and other coating problems. Save yourself a
> whole
> lot of problems and simply get new equipment. If you cannot go this
> direction, then I would suggest that you use naphtha as a cleaning
> solvent. It seems to be more effective than other solvents on
> silicone
> residues. Then follow the naphtha cleaning with alcohol cleaning.
> You
> would probably need to clean your exhaust stacks too. Replacing
> might be
> easier and cheaper in the long run.
>
> You did not say what kind of silicone you were going from (solvent
> vs 100%
> solids) and what kind of urethane you are going to (solvent-borne
> (notice
> the proper spelling) vs. two part reactive). Where you may not have
> had
> an environmental exhaust permit issue before, you may have one now
> if you
> are going to a VOC-based solvent urethane. Check with your local
> EPA or
> DNR.
>
> Someone else brought up the dreaded "O word" - OSHA. Check what
> personal
> protective equipment you will need. Many of the urethanes have
> higher
> health impact ratings than silicones.
>
> Urethanes and silicones have dramatically different properties in
> terms of
> chemical resistance, thermal performance and rigidity. Have you
> checked
> with the designers to determine if there is any impact to form, fit or
> function that this change represents?
>
> Urethanes and silicones flow differently, have you figured in the
> time to
> retrain your operators on the new methods?
>
> Urethanes and silicones look and feel different in their finished
> form.
> Are you ready for the change in workmanship standards? Have you
> accounted
> for the re-training time for your inspectors?
>
> Urethanes and silicones have completely rework and repair procedures.
>
> What does the end user think about the change?
>
> Are you ready for the culture change? The material switch is
> relatively
> easy. It's changing the culture that is a cast iron *^%*#^(*#.
>
> Doug Pauls
>
>
>
>
> Mike Johnson <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
> 06/06/2008 10:04 AM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> Mike Johnson <[log in to unmask]>
>
>
> To
> [log in to unmask]
> cc
>
> Subject
> [TN] Changing conformal coating from silicone to urethane...
>
>
>
>
>
>
> We are considering changing our pcb conformal coating process from a
> silicone base material to a urethane base material. Other than a
> thorough
> cleaning of our machine, replacing material delivery lines, complete
> disassembly and cleaning of nozzles, ordering new nozzles to meet
> viscosity requirements of new material if necessary, are there other
> concerns we should be addressing?
>
> Mike
>
>
>
>
>
>
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