Spray booth for solvent based coating with a dust-free finish

A. Michael,

I am not a clean room expert ... which seems to me to be fairly expensive. But I've got some ideas and suggestions, if you don't mind.

1. Ensure that your room is always under positive pressure.
2. Maybe not have one access door but a 'double' one so that on entry, outside air isn't brought in, i.e., a door with an airspace leading to another door.
3. On the air inlet side, have a reasonably high efficiency low micron mist eliminator constantly sprayed. We're talking about a pressure drop of max. 1" for that. Blade material to be PVC. Horizontal airflow. I've heard of these being used in Europe to clean up the air before entering (University?) buildings. They just used a single bank, I'd opt for two. Your water WILL evaporate so you'd need a tank with an el-cheapo pump along with a water make-up float valve (a la toilet)and the water, if you use a decent unit, WILL get dirty, which will show it is working OK.

I used to demonstrate CT-120 mist eliminators of 12 micron capture in the USA at trade shows ... and learnt that the water sure does evaporate and gets nice and dirty even in a nice, clean building.

This would be a very inexpensive approach ... price? Well, that depends on the room size, doesn't it (& you didn't mention that) and I'd probably go for 10 or 12 air changes an hour.

A. Once you have set things up as Mr. Newton suggests, creating clean make-up air, be aware that when you are spray painting you will be generating dust in the form of tiny dry paint particles in the very area you are painting.

A. In Florida you could not add any extra humidity or several paints will blush. The first thing that I would do is add a HEPA filter for the incoming (makeup) air. You can get these units from places like Grainger's. The airlock would be second, if required. Third would be to put a cheap household type HEPA filter in the room at a mid height.

You do not want to stir up any floor dust.

A. Michael,

As James W said, don't stir up the floor dust ... and if you want a PROPER dust free room, then people will have to wear hair net coverings (as in food processing plants) and slip-on dust-free overshoes.

There's something to be said about a 'HEPA' in the main ducting. HEPA filters come in varying qualities! And if you get one for 2 micron dust and install it in the ducting, then
A. It will be, will have to be fairly large
B. It will generate quite a pressure drop and
C. Ah, it will plug up pretty soon .... which is why proper clean rooms have the whole ceiling made up of HEPA filters so that they DON'T plug up PDQ because the airflow is slow and languid.

I mentioned the European approach ... but they used a single blade bank @ 1,000 fpm and sprayed it whereas I'd opt for the slightly more expensive 2 blade bank approach @ 1,500 fpm which is, of course, not nearly as bulky.

It all boils down to the K.I.S.S. principle and NOT having to do maintenance.

A. The responses so far were good. One important item was left out. The largest source of "dirt" in a spray painting operation is fibers off of peoples clothing. Supply everyone in the booth with fiber-free overalls when spraying is being done.

A. Heck, what Ronald said is 'Elementary, My Dear Watson' and an el cheapo white coverall such as they use in food mfg. plants would be ideal.

Why didn't I say that before?

Lastly, Michael, we'd be very interested to know what route you took. Feedback would be most appreciated.

A. Actually, I believe that Tyvek overalls are more appropriate. Available thru safety equipment catalogues. Cost is minimal and they can be thrown in the dust bin when they become dirty or torn.

A. Yes there are, but since so few are sold, they are quite expensive. Lacquer will blush in high humidity, so on an island it would be highly probable that you would need help to be able to paint. Sermatel coatings require a specific RH range also, so I would guess that there are a number of other applications that also do.
Some companies filter and reuse the conditioned air, but that requires self contained or external breathing air.
Some people will condition the air in a larger room where they do not have to contend with overspray on the units or the controls. They then draw the paint booth air from this room.

It really helps to know exactly what you are trying to do, and why.