Stefan Trethan wrote:
> On Tue, 28 Jun 2005 00:50:28 +0200, Adam Seychell
> <a_seychell@...> wrote:
>
>
>>I've never notice actual mist from bubbling etchant. However, if your
>>trying to minimize gaseous fumes then a sealed system is the only
>>option. Bubbles do create a lot of splashes and fine droplets that will
>>travel a surprising long distance. If you can sufficiently cover the
>>etchant so that droplets run back in to the tank, then that should solve
>>most of your problems. My spray etcher does creates a heck of lot of
>>mist and it is not "closed loop". There is an air bubbler in the spray
>>chamber for aerating the etchant and I get virtually no etchant escaping
>>even though the "air" is continuously escaping. By far most etchant
>>escapes from spillage as I withdraw the PCB. The trick was to install a
>>double walled opening. The theory is that mist will immediately settle
>>upon contact with a surface. So you all you have to do it make sure the
>>mist is very likely to contact a surface.
>>Now you won't be limited to corrosion resistant air pumps. And even
>>aquarium pumps don't like acid. They usually have a zinc screw
>>connecting the diaphragm to the oscillating arm, and I've found the
>>valve flap material breaks down too. I can guarantee you'll get more
>>problems then you'll solve trying to recirculate the etchant chamber
>>gases.
>>Adam
>
>
>
> well, i have taken the pump apart, cleaned it, and you were right the
> liquid did affect it, it "sticks" the valve flaps. They are silicone so i
> wouldn't worry and the screw was protected with silicone too.
>
>
> In a way i want to run it open loop and avoid all the problems, but in a
> way i also want to avoid the fumes. If there is enough droplets in the air
> to clog the pump it will corrode my tools. My tank is more or less
> airtight, with a rubber seal.
>
>
> Now the pump works better again, and would even be strong enough to power
> the bubbler (tho i can use shop air open loop).
>
> What i wonder is if there is a way to make sort of a filter, maybe a
> bottle with cotton wool in it or something like that to catch the
> droplets. Maybe it would help to soak it in some weak NaOh, and let dry,
> to neutralize and droplets.
>
> What do you think?
>
> ST
If tools are corroding several meters away then it must be HCl gas,
rather than splashes or wouldn't travel so far. What etchant are you
running ? There should be almost no oder from a open jar of etchant at
room temp. Keep HCl concentration under 2 Molar. If your stuck with a
fuming etchant,(i.e an open container of etchant will corrode steel in
its vicinity) then you have to keep it sealed. All I can recommend is
keep the place well ventilated during etching, and seal air tight when
not in use. You must of course also eliminate exterior splashes due to
bubbles.