Dave Finkelnburg on sat 2 mar 02
Martin,
Dear friend, you are right of course! The dust does go somewhere. You
point out one of the moral dilemmas to spraying glazes.
As a practical matter, you know virtually no studio potter has the
capability to capture air sprayed into the booth, filter the air and recycle
that air into the compressor suction. Also, for the booth to work it must
still be under negative pressure, so some air must be exhausted.
I have to stand by what I said. Perhaps it's better stated this way --
if you choose to spray, don't exhaust your spray booth air into your studio.
Respectfully,
Dave Finkelnburg
From: Martin Howard
>>away from any door or window that could pull air into your work area. >
>
>No necessarily so. If you can arrange that the air, which is warm because
>you have heated your pottery, is recycled and filtered and passes again
into
>the pressurised air system and through the spray gun, then that is fine.
And
>you save on heating costs.
>
>I just do not know of a commercial firm that works in that way, yet.
>One near me is trying it out.
>
>If you pass the spray booth air outside, just where is it going and who is
>it going to affect? Your neighbour?
>We don't consider that kind of question enough? We just think:- "We've got
>rid of it." That is not good enough, IMHO.
vince pitelka on sun 3 mar 02
> The compressor pulls the waste and new air from the back of the booth,
> through a filter, into the compressor. Then it send it out again via the
> sprayer into the booth.
> So the booth IS under negative pressure, which is stored in the
compressor.
> The waste dust is captured in the filter and can be re-used, safely.
> I cannot see the fault with that system. You could add a water screen as
> well to capture waste glaze.
Martin -
The air movement through the compressor is extremely minute in comparison to
the air movement required through the spray booth in order to draw off the
overspray and/or dust. The air intake of the compressor would not even make
a dent in the required air movement, so unfortunately this idea will not
work at all. It requires a LOT of air movement to create the necessary
negative pressure in the spray booth.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Dave Finkelnburg on sun 3 mar 02
Hello Martin!
You wrote, >The compressor pulls the waste and new air from the back of
the booth,
>through a filter, into the compressor. Then it send it out again via the
>sprayer into the booth.
>So the booth IS under negative pressure, which is stored in the compressor.
I know you mean well here. Your system is a step forward. What you
have written just is not correct, though.
If the compressor suction and discharge are both within the spray booth
system, then the pressure at the system opening is neutral, not negative.
You still need some ventilation to give the booth a negative pressure.
Otherwise glaze dust from the booth will get into the room.
Picture a booth with a LOT of glaze dust in the air, and picture it in a
studio which has, we hope, very clean air. How do you keep some dust from
the booth out of the studio air. Only with a strong "wind" being sucked
through the booth opening all the time by a ventilation fan.
IF you can get a good filter system, so the dust doesn't wipe out the
compressor, AND you use a ventilation fan which exhausts enough air outdoors
to keep the "face velocity" of air at the booth opening high enough the
capture all the dust and not let it into the room, then you will have a
workable system.
By the way, a typical spray gun uses 5 to 50 cubic feet per minute of
air. A 2-foot by 2-foot glaze booth opening requires 400 to 600 cubic feet
per minute of air flow to keep the dust captured. Reducing that amount by
even 50-CFM is all you can accomplish with the compressor suction hooked to
the spray booth. At least that is the system the way it looks to me.
I am really glad you think about these things because we are on a small
planet.
Regards,
Dave Finkelnburg.
Martin Howard on sun 3 mar 02
Dave wrote the
capability to capture air sprayed into the booth, filter the air and recycle
that air into the compressor suction. Also, for the booth to work it must
still be under negative pressure, so some air must be exhausted.>
Right, we are thinking along similar lines here.
The compressor pulls the waste and new air from the back of the booth,
through a filter, into the compressor. Then it send it out again via the
sprayer into the booth.
So the booth IS under negative pressure, which is stored in the compressor.
The waste dust is captured in the filter and can be re-used, safely.
I cannot see the fault with that system. You could add a water screen as
well to capture waste glaze.
Martin Howard
Webbs Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
01371 850 423
martin@webbscottage.co.uk
http://www.webbscottage.co.uk
Updated 8th February 2002
WHC228@AOL.COM on mon 4 mar 02
Dave
Your spray booth explanation is really good about moving the air.
My comment is about capturing the dust. Too many people believe that they can
use some kind of dry filter to capture the dust. My belief is that in order
to capture the submicronic particles the dry filters have to be so fine that
they will not allow enough volume of air through to work. The other problem
is that the plug up if they are going to be effective.
Industry uses waterfall type booths for much of its spraying. These booths
can be gotten from companies like Binks, and DeVilbus [sp]. They are probably
too expensive for the average potter, however can be homemade. I have made
several and they work well. They work well enough to have passed inspection
by OSHA, and the PA Dept. of Environmental Protection inspectors. They tested
the person spraying, and the air being evacuated from the building.
It would be a good idea for schools, and public workshops to have this kind
of equipment.
If you are interested in the waterfall type of spray booth, my suggestion
would be to take a good look the catalogues that these companies have for
their booths. I was able to construct my booths from their drawings and parts
found in a Grainger catalogue.
The booth is simple enough to make if you have some basic welding skills. The
mechanical parts include a tubeaxiel fan with a 3/4 HP. motor, and a sump
pump.
Having air that is free from the kind of dust that we shoot from our spray
equipment is a must.
We all know the kind of danger that it creates for the user and those people
down wind from us. I cringe when I see how little protection that is used in
public places where ceramics is taught.
Bill Campbell
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