Hi Inge
I would suggest an angle of 45 degrees and a side to side (left/right/
left/right) action, spraying from all four sides, slowly building up
the wet film thickness and making sure the sides of components are
covered. RH is a concern however excessive humidity is likely to cause
a "milky bloom" rather than the phenomena you are witnessing. HumiSeal
recommend RH of <60% for this material and if the area you are using
is outside of this it might not be helping your problem.
This kind of process should be done in a draft-free area (for obvious
reasons) but if there is a flow of extraction/laminar flow it should
be in the same direction as the flow of material because it will help
the process. For example only, in the SB2900 batch spray coating
machine, air is extracted through 3 stages of particulate filtration
and an exhaust plenum from directly underneath the position where the
workpiece sits (in the horizontal plane - this is important too) So
when the material is flowing from the lower pressure aerosol, nozzle
the extraction is not working against the spray jet and all the
particulate "overspray" and nasty solvents are safely taken away from
the operator.
I hope this helps a little?
Best regards
Nick Plumb
_____
On 21 Aug 2009, at 12:48, Hernefjord Ingemar wrote:
> Nick,
> we have done tests today, same operator, same boards, same cans,
> same everything. Most boards get a clear, deep and nice look, but
> suddenly we get a greyish coating, quite matte!
>
> Q1: what spray angle do you recommend?
> Q2: what spray pattern do you recommend? Zig-zag, up-and-down, side-
> to-side or what?
> Q3: is the room RH of importance?
> Q4: is the process sensitive to laminar flow and if so, what level
> is critical?
>
> Inge
>
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Nicholas
> Redgrave-Plumb
> Sent: fredag 21 augusti 2009 12:31
> To: [log in to unmask]
> Subject: Re: [TN] Manual spraying
>
> The only way I can see for the propellant causing this kind of
> problem is if the nozzle of the spray can is too close to the
> substrate whilst spraying. I note several suggestions in the posted
> responses of expensive elevated IR curing ovens etc. for IB31 but
> these are really not necessary as this material is dry to the
> touch/"tack" dry in only minutes, dry in 24 hours and cured/fully
> optimised in 7 days. This would undoubtedly be accelerated by an
> elevated cure but it shouldn't really be necessary. So all you
> should really need is simple drying cabinet at ambient temperature
> just to take the solvent vapours away.
>
> Otherwise, it could be "champagning" or "solvent-popping" which are
> terms to describe a condition where the surface of the coating
> material partially cures leaving solvent still trapped inside the
> wet- film. The solvent has to go somewhere so it finds it's way out
> through the surface and in doing so makes multiple small holes.
>
> To avoid this problem should be a matter of going back to basics.
> Review the coating procedure, make sure the operators are properly
> trained (and not getting the spray nozzle too close to the substrate).
> If the volumes justify the use of a purpose-built spray booth for
> conformal coating with intrinsic safety features and laminar air-
> flow/ extraction then it might be worth going in that direction.
>
> But there should be a simple solution to this problem because the
> usage of HumiSeal 1B31 globally, in both liquid and aerosol cans is
> massive.
>
> Nick Plumb
> Gen3 Systems Limited
> Farnborough, United Kingdom
>
> _________________________________
>
>
> On 20 Aug 2009, at 19:17, Inge wrote:
>
>> Good Evening,
>> we use small cans filled with 1B1 conformal coating for handspraying
>> boards. The guys are not satisfied with the result, because sometimes
>> the result is matte. Microscope photos show thousands of microscopic
>> bubbles in the coating. I suspect that it's included driving gas. Or
>> wrong handling the spray can.Anyone out there with experience? How do
>> you avoid this problem?
>> /Inge
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