Spray booths...

[davyowen]

Ok, so I know there are a number of trade users on here, and perhaps a number of hobbyists who spray on their finishes.

For a while I've been using pleated cardboard filters with a spun mesh to reduce the amount of mist that gets circulated back into the air, but so far this has not been effective. I still get a large amount of mist lingering in the air and some very pretty colours on the ceiling mounted air filter.

I don't have space for a dedicated room or sealed booth but I do need something that is going to catch the vast majority of overspray.

So here is my idea and I need those in the know to tell me if its going to work ;D

Get three of these, two more plate fans and some 1"x6"

Here's a very technical drawing of what I see in my head



So in orange you have a plate fan, in lime green you have some ply/mdf that the fan is attached to. The blue is the filters I linked to above, the red is the spun mesh stuff and the black line is the pleated cardboard thingy. The whole lot should fit inside a 1x6 frame and repeat that two more times. Slap on some loose pin hinges and let the spraying commence... maybe...

What do you think? ;D

[engineerone]

when i used to spray lots of model cars, etc, i made up a box with a ceiling extractor fan and a turntable in side. a filter in front of the fan seemed to work quite well.

were i to spray furniture, the biggest problem would i think be the bounce back of the over spray. so you would need a top as well as sides. and of course it depends on how large the bits you spray are

it is said to be the reason for using hvlp since the bounce back is lower.

i also wonder whether there is an advantage to creating a kind of vortex to draw the overspray upwards and then into the collectors.

your idea seems interesting, but i think stopping bounce back is the most important thing. ;D
paul

[davyowen]

Well I'm spraying guitars... my current 'booth' which isn't a booth at all is just a 0.9m x 1.2m frame with the pleated filters and a 350mm fan blowing throught them and into an old cartridge filter... All held up with a workmate



I'm just about to start spraying 4 guitars so I decided today that I needed to sort something out so that I could continue using the workshop without needing to mask up constantly.

I thought about adding sides and a top but I doubt it would make much of a difference because I don't feel there is enough airflow to catch the mist before it floats away.

I'm using low pressure guns and they are significantly better than the HP guns I used to use but I still get bounce-back and when spraying the sides for example only a small portion of the overspray gets caught by the filters.

I need the 'booth' to be reasonably easy to move about, freestanding with all the extraction contained within it. I'm contemplating just getting 2 filters/fans and then mounting my existing 350mm fan with filter to a board ontop of the 2 sides.



Meaning it would take up less space in use and could then fold up when I don't need it. I'm just not sure whether I can get a good result without doing it 'properly' but I don't have the space or the money to go all out. At the same time I don't want to waste time/money building something that isn't going to be as effective as I need.

[jfc]

You need a few of these minus the plants .








When done just zip them up .

[cnc paul]

Davy,

Those filter are for Powder coating and would probable not be suitable for cellulose or water based paints.

What are you spraying
What direction is the air direction in your drawing

The fans are always behind the filter, The fans will need to be explosion proof.


Paul

[davyowen]

I did wonder about that, and thats why I'm going to be keeping the cardboard/mesh filters infront of them to catch the majority of the wet overspray, and I'll confirm their suitability with the supplier tomorrow.

Im using waterbased lacquers and the air direction will be through the pleated filters first, then the powderbooth panels and then through the fan.

[engineerone]

davy, couple more thoughts.

looking at your photos the guitar seems to be very near the rear, so i think you are getting more bounceback than necessary.

secondly have you tried making the paint slightly "drier" to spray.

when painting the racing cars, i found that a better finish was obtained by the paint being almost dry when it hit the surface.
i learnt this originally when using cellulose on resin kits, which would with "wet" paint tend to deform because of the "bite" of the cellulose.

however, one benefit of dryer spraying was less bounce back.

so i would tend to think of a design like those flower houses that jason has shown but make sure that the guitar is at least in the middle of the space. but i do think you need a roof, as well as maybe a triangular set of sides. then two filters before the extractor.

paul

[davyowen]

Can you explain what difference the distance between the guitar and filter would make?

I'm assuming bounce-back is when the paint particles hit a surface and then bounce back off without sticking? Whereas overspray is paint that actually misses the target? Also, by a drier coat I assume you mean a lower fluid delivery rate rather than perhaps moving the gun further away from the piece or increasing the temperature of the room?

The reason the guitar is reasonably close to the filters (about 10") is because I don't feel there is sufficient airflow to capture the mist if I were to be spraying any further away. The filter area would need to be twice the size just to catch the directional spray, and thats before you factor in draughts and bounceback.

You seem to have knowledge of this so I'm not saying you are wrong, just that it seems to go against my logic, which frankly, is based on nothing more than the idea that the closer to the extraction point the more airflow you get, this logic itself may be totally irrelevent for a spray booth

[engineerone]

to an extent davy you are right.

but let me see if i can explain my thoughts more clearly.

when you start and finish spraying, you are i guess to one side or the other of the item being sprayed, thus the back wall will as it were get the full force of the paint, and if you are too near it will bounce back.

hence my feeling you should have the guitar further away from the back.

in relation to the "drier" coat what you are looking for is what i guess would be called a "mist coat". less paint and more thinners which in the days of cellulose, evaporate and put the paint on the body in such a way as it almost dry as it touches the guitar body. that way you can build up the colour.

in most pro spray booths, there are top mounted filtered fans
which capture the mist going up in the air.

does that make more sense??

paul

[davyowen]

Aug 17, 2008 18:41:49 GMT engineerone said:

does that make more sense??

Yes actually, that seems to makes a lot of sense to me - basically moving the piece being sprayed back a few inches will mean there is a greater distance for the overspray particles to lose their kinetic energy so when they hit the filter they are far less likely to rebound, and are far more likely to be picked up by the airflow through the filters.

Cheers Paul, I'll give it a try next time it's due a coat (in about 1/2 hour) and see what difference it makes. Tomorrow I'll also see about adding removable sides/top/bottom.

If anyone else wants to come in with suggestions on how to build an effective, yet easily movable spray booth though, I'm still very interested.

[davyowen]

Well I tried moving the guitar away from the filters and I did notice a reduction in bounce-back. Unfortunately I still got large amounts of mist in the air but more airflow, better filters and enclosing the area as much as possible should cut that down considerably.

I'll post some pictures of the build when I get around to it in a few days time, but until then keep the suggestions coming

And thanks to everyone who has replied.

[engineerone]

glad to get you pointed in the right direction ;D

paul

[engineerone]

actually davy have had a couple of extra thoughts.

why not make the equivalent of a metal beading tank. they are what is used in the metalworking industry to clean up metal.
it is an enclosed tank with gloves to keep all the waste within the tank.

so i think you might consider the following. make something like an old fashioned door screen with a rear, that holds the filters and fan, two sides and a top, all of which fold together when collapsed. at the front you have two or three strips of that flexi plastic that they have in for instance cold stores to keep the cold in.

then you stick your hand and the gun in the gap and spray. most then of the spray will be caught within the box, but you will be able to move around properly.

paul

[engineerone]

you could make it with a plastic frame and i seem to think that it is possible to get some kind of hinged connections for plastic too.

try polypipe and see what they have. and you could use plastic sheet for the side surfaces and top and front too.

paul

[ivan]

There's a useful design here:
www.highlandwoodworking.com/index.asp?PageAction=Custom&ID=88

I have made a slightly bigger version which works well with pleated card. The filter holders were made by "ripping" 3" galv electrical trunking in two.

Note the fan airflow required in example at Highland - 6000 cu ft min. The resistance of the filter will reduce this to around 3000 cu ft min in situ, so through 20 sq ft of filter, about 2.5 ft second which seems to be in the right ballpark (apparently capture is velocity dependant in pleated filters, too slow and droplets don't hit the cardboard?)

More useful stuff here:
www.itwifeuro.com/Training/Technical%20articles/Equipment_hook-ups.asp
www.highlandwoodworking.com/index.asp?PageAction=Custom&ID=156

[engineerone]

davy, been thinking more, and if you think out of the box, maybe this will explain more.

don't know if you have an scms, but i do, i also have a decent extractor, which i connect to said saw, even though i have not at this time got it mounted on a stand. frankly the hose out of the back of the blade may as well not be there, it only collects maybe 30-45 % of the dust, the rest is thrown every where.

when i get round to building the stand, i will have a back behind the saw, that is probably octagonal or at the least semicircular, it will also have a top and sides reaching to the fixed part of the saw. but for extraction, i will have two holes one at the top, and one at the bottom. because of the way the air moves, this will i think capture more of the dust.

when spraying the same applies, in principle, the spray seems to go up in the air (not sure whether it is lighter or just the action of spraying ) so it makes sense to have a fan at the top of the box to capture more if possible.

i would also go for some kind of cyclonic activity to direct the over spray toward the collectors.

paul

[davyowen]

Well the new fans and filters arrived and I decided it was time to do a sort out... I ended up buying a shed and relocating anything that would fit through the door. I can now see some floor, and theres a nice empty space which conveniently, is the perfect size for the spindle moulder Jason brought to my attention... ;D

Anyway, onto the spray booth...

I got myself 2x new 250mm Vortice fans and attached it to a 12mm sheet of MDF either side of the 350mm fan I was using previously. I mounted that to the wall via 2x angled pieces of timber...



I then glued the 2 filters together...



I rested them on some 2x4 timber that I hot-glued to the wall at the right place and sealed the gap between the filters and fans with some hardboard I had laying around...

After thinking about the workshop plan I decided to put my workbench infront of the filters due to the fact that they are suitable for dry dusts down to 0.2microns so I can use it as a sort of 'backdraft' table when I'm sanding/routing etc.



For spraying I just need to clamp on the pleated cardboard filters to provide protection from the wet particles and after a quick test with some smoking newspaper it's proved to be very effective at pulling from quite a distance from the filters and a test spray showed all visible particles being caught and no particles lingering in the air.

I'm considering the need for sides, but for now I can't be arsed

Specs (direct from fan manufacturer):

Airflow: 1115m³/h + 3110m³/h + 1115m³/h = 5340m³/h
Noise level: 53dB + 64dB + 53dB = 64.6dB

[engineerone]

nice one davy.

roof for booth might be good though ;D

paul

[davyowen]

Yeh, I am going to see about fitting a roof but I didn't have any hardboard big enough and I really didn't want to use anything heavier because at the moment the filters are just resting on the 'legs' and are held in place by the edge of the shelf, the hardboard that bridges the gap and the bench...

I'm finding that because there is significantly more airflow and the filters are larger and more effective that all the particles (and smoke in my test) was pulled in, even at the extremities so for not I'll just leave it as it is. The exhaust air from the fans that exits at the top and bottom will push anything that the filters miss well clear of me and the air filter can deal with that

[engineerone]

you could always use cardboard for the roof

you had enough empty boxes ;D

paul