Too much airflow in booth?

K

keith_y

My shop has a side downdraft booth, non-heated, with the fans mounted directly on each plenum. Booth is this model -https://www.paint-booths.com/product/SDD-1000.html We keep it clean and get the cleanest jobs of any shop Ive worked for, but we've had problems with delamination and clear not laying as smooth as I am able to spray elsewhere.

Number one, when the boss and I both spray a car simultaneously, with RP guns, The overspray disappears immediately. Ive been in properly maintained, expensive booths that cant remove the overspray of one RP as fast as this booth does with 2.

This is a restoration shop and we take meticulous preparation versus the collision that Ive done, yet we've had delamination problems ranging from base releasing from primer to flow-coated clear releasing from the previous layer of sanded clear.

Also, I cannot get clear, no matter what brand with proper reducer/hardener to lay as smooth in this shop as I can at other shops, even on the flow coat. We have a large screw compressor and refrigerated dryer with high flow fittings in booth.

I had to paint a large work van roof last week. I had to use a different brand sealer for this particular job. The panel temp and air temp were all about 65*. I used slow reducer with a RP jet 100 at about 22 psi and it made nasty overspray on the roof as I was spraying. Im afraid it might delaminate later. Also, the boss and I both cleared the roof since he was available to help. With both of us spraying, the overspray didnt want to melt it. Like it had flashed already. This was with HOK per the customer request. Im not familiar with it.

Is any of this normal? Could the booth be flowing too much air causing too quick flash times? When we open the booth door, it is under pressure and hard to open. When it is opened, a giant rush of air comes in blowing the masking paper around. There is no adjustments that Im aware of. We just have an on/off switch for fans. Nothing for dampers, if there are any.
 
It can be a problem and if this is the problem its time to change the fan or motor pulley to reduce the air flow or add more intake area in the door.
 
Sounds like you have a booth set up for a water system, the heavier overspray needing a quicker airflow. I have seen little 110 transformers with a big dial for speed control we used on a flow coating machine in the past, and there are ways to do it with three phase http://www.tcf.com/docs/fan-enginee...horsepower-motors---fe-1000.pdf?Status=Master to reduce the current going to the motors and slow them down. Is it possible to get enough flow if you just turn one fan on? Otherwise, maybe a dampner on the outlet side will slow down flow so you can have the exhaust when you want it and lower it when you dont.

Otherwise, are you immediately stopping the fan after each coat?
 
You don't want negitave pressure in your booth and I can't imagine that it was this way the whole time since the booth was installed. Something else has to have happened, I'm guessing that there is no intake fan just the exhaust fan pulling shop air into the intake correct? I would look into the intake side and make sure the air pathway is free and not clogged. Were the motors ever changed? If they were they should have been the exact rpm as the ones taken out and like Barry said with the pullies they should have been the same size as
what came with it if they were ever changed.

The first thing I would look at would be the intake. With nothing blocking the intake on the outside and nothing in it start the booth and see if the negitave pressure is there if so try removing an intake filter and see if it changes if it does they need changed or cleaned.

With those types of booths you also need enough free air in the building or you could create negitave pressure in the building.
 
Thanks for the responses! The booth was bought brand new from mfg as a kit in 2013. I wasnt there when it was installed. There is a huge neg pressure inside shop when turning on fans. The doors slam shut if they are open. In the winter when they are already shut the building makes a noise from having the air sucked out of it.

For now, there is no intake fan. Just one exhaust on each side pulling air down from the ceiling of the booth. Depending on temp, humidity and what Im spraying, I decide to keep fans on or turn off between coats.
 
airflow through a booth should be about 100fpm +-25. its pretty easy to calculate in a crossflow if you know the cfm of the fan. downdraft is a little more difficult. i stand in middle my booth and you can feel air movement but not a breeze. only if im standing right by the intake filter on the one end. if you know an hvac guy he will have a little fan tool that can tell you air speed. easiest way to turn this down has already been said....change the pulleys. there are a few extremely nice clears though that i know of that are for high flow booths. you need a baking clear. sikkens hs+ or superior 250 would fit the bill in your booth perfect. in my booth they just stay wet forever and flow out really nice. they do still air dry just fine but very very slow flash.
 
Intake air in the form of an air makeup unit that matches the CFM of all the fans in your building bringing outside air in are what is usually recommended. I really dont know why that would make a difference other than not slamming your doors and not sucking your roof in..

This is a type of speed control I would recommend. http://www.ebay.com/itm/1-5KW-2HP-7A...25.m3641.l6368 just the first one I found. That way you dont have to change pulleys if you go to water system and can slow the fans to your liking. Even if you eventually want to change pulleys, its not like you are gonna hit it right the first time and this would tell you what you want. There are different models for different horsepower motors.
 
Makeup air is a must! Some shops have actually sucked in flue gasses by running too negative, that can be dangerous, deadly at worst or a bad headache at best.
 
Again, thank you guys very much! Eventually, we will get heat and AMU. I was just wondering if that was part of my issues Ive been having. Sounds like a resounding, yes.
 
I run a VFD like Anotheridiot posted. Easy to hook up and I run a pot switch from radio shack for infinite adjustment. You will need one for each motor. I picked another one up off ebay for my blast cabinet that was under 200 dollars. I've used an AC-tech brand for over 8 years without any problems.

These will be a nice tool for the future upgrade of an air makeup because you can dial all three fan speeds for a slightly positive pressure.

Other options are out there for makeup air also. If your happy with your booths performance and don't want to spend 10k for makeup then you can just heat the incoming air. I basically use a large radiator with hot water passing through it from a boiler. It doesn't make hot air in the building but it keeps the building a constant temperature when I'm spraying. A couple grand would go a long ways in making a good system. Not as fancy as a makeup but it's efficient and only takes few seconds to turn the boiler one and remove insulation board from the radiator. With 2 fans you would probably want 2 large 24" by 24" heat exchangers.
 
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