Stefan Trethan wrote:
> On Mon, 27 Jun 2005 18:11:47 +0200, Leon Heller
> <leon.heller@...> wrote:
>
>
>>If it's only for occasional use, why not pump up an old car wheel and
>>tyre.
>>That should have plenty of pressure and capacity to etch a few boards.
>>Can't
>>be a closed system, of course.
>>Leon
>
>
>
> closed system is main requirement or i would use shop air. I'm not
> spreading any more etchant mist than needed.
>
> thanks
>
> ST
>
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