Less material or more air, that is the question..
#11
  
I sprayed some clear finish (2 part catalyzed lacquer) and had some problems with poor atomization.  I'd say about 3/4 of the spray patter is decently atomized but the rest is small drops. I'm still really new at spraying finish with an HVLP and am still learning all the ins and outs.
 
From all the research I've done, I'm still not clear on when to increase the air flow and when I'm supposed to reduce the material flow. It seems like the symptoms of the two issues are awfully similar. How do you decide when to adjust either the air or material?
How do you know you're learning anything if you don't screw up once in awhile?

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#12
  Re: Less material or more air, that is the question.. by mr_skittle (I sprayed some clear...)
(01-12-2018, 06:36 PM)mr_skittle Wrote: I sprayed some clear finish (2 part catalyzed lacquer) and had some problems with poor atomization.  I'd say about 3/4 of the spray patter is decently atomized but the rest is small drops. I'm still really new at spraying finish with an HVLP and am still learning all the ins and outs.
 
From all the research I've done, I'm still not clear on when to increase the air flow and when I'm supposed to reduce the material flow. It seems like the symptoms of the two issues are awfully similar. How do you decide when to adjust either the air or material?

First... some stuff just doesn't spray well. It's sticky and seems to build up at the spray tip and the "spittle on the tip" spits on the work piece. Not saying that's what's happening but it does happen.

A couple things you can try. Open up the air valve some. Not sure which gun you have but one of the knobs lets more air through. Another thing to try is thinning your finish a little more. It may not take much to make a difference. You can also try to open up the fluid volume valve to allow more finish through the gun. I'd try one at a time so you don't loose track of your bench-mark. Try one, if it doesn't work, put it back to where it was and try the other. If that doesn't work, try both.

Make sure your tip, needle and air-cap are clean.

A fellow woodnetter came by my house with a a problem spraying a particular finish. I was sure we could figure it out. His gun, my gun, my experience, his lack of experience, changed settings on both guns, added thinner... etc etc etc.. never got the stuff to spray well. It was the finish.

Another thing about catalyzed lacquers, they have a limited shelf life once catalyzed and stop spraying well after a certain time mixed. Not sure how long it's been mixed. With automotive, 2 part clear-coats, I have about 10 minutes before I have to throw it out. I've shot cat lacquers that were good at 5 days but were worthless on day 6.

Hope this helps.
Good judgement comes from experience.
Experience comes from poor judgement.

Neil Summers Home Inspections
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#13
  Re: Less material or more air, that is the question.. by mr_skittle (I sprayed some clear...)
What's the viscosity?  What N/N size are you using?  Normally, when I get the N/N matched to the viscosity a finish sprays well w/o thinning and w/o much change to the air pressure.  About the only thing I have to do is adjust the fluid flow until I get a good oval pattern on a piece of cardboard or scrap when I shoot a burst.    

One universal thing.  If you have one of the those little plastic filters at the inlet of your gun take it out and throw it away.  Run your finish through a cone filter before pouring it into the cup. 

Also, if you don't have a regulator within about 20 feet of your gun, or one at the gun inlet, you should.  I set the air inlet on my guns wide open and adjust the air pressure as needed.  With my Qualspray gun I spray nearly everything at 29 psi at the gun inlet, which is 10 psi at the nozzle.  As I said, normally the only thing I need to adjust is the fluid flow.  

John
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#14
  Re: Less material or more air, that is the question.. by mr_skittle (I sprayed some clear...)
Here's a thread that talks a little about my setup. It's a CapSpray HVLP unit https://forums.woodnet.net/showthread.php?tid=7331248

The gun is totally cleaned out. I figured out the difference between pretty clean and totally clean last time I used it. It has some latex residue in it and the powerful solvents from the lacquer set it free to clog up my nozzle. I originally had a problem with a little "spittle on the tip" that was due to an unclean setup, but that was full-on drips of material off the gun. The problem I'm having now is different. Every indication from the material manufacturer and the HVLP units instructions says that I am using the right needle and tip setup so I don't think that's the prob. The one thing I haven't tried yet is to thin it a bit. I can imagine that being a possible fix. I am aware that cat lacquers have a shelf life once mixed. The stuff I'm using puts it about 24-36 hrs. I'm using it freshly mixed.

I assume every gun is a bit different but I'll detail my setup anyways. The air control knob has an arrow on it and when it points straight up (12 o'clock) it's off. I've been running it just a bit open somewhere around 1-2 o'clock. For the material knob, I'll turn it about 1-1.5 turns.

My thinking is, (and correct me if I'm wrong) with this setup if I'm getting less than 100% atomization of the material, turning the air up should lead to more turbulence at the nozzle and lead to better atomization. On the other hand, leaving the air the same but decreasing the material flow should lead to the same results. Running less material with the same amount of air should lead to more air per unit of material and lead to better atomization. Weather I turn the air up or the material down, it seems like the same results. Am I missing something?

What I really want to hear is that I should set one of the two adjustment at "so-and-so" and just fiddle with the other one. That's what it sounds like John has going on but I think he's got a different setup.
How do you know you're learning anything if you don't screw up once in awhile?

My blog: http://birdsandboards.blogspot.com/
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#15
  Re: Less material or more air, that is the question.. by mr_skittle (I sprayed some clear...)
I own the 9100 and maxim 2 gun. Bottom dial is the needle flow control. You can feel when the point is fully open. So screw down bottom dial to close needle 100% gently, then back it off till the needle fully opens and just. Also make sure your tube and one way check valve inline in clear tube are working good and clear, then once you are ready to test spraying, fill the cup (use lacquer thinner to test, its cheaper. I also use cup bags to make cleanup easier), make sure tube faces forward in cup, make sure the cap over nozzle Is horizontal or vertical, you should be able to click turn it, just test fans for now ( pattern will be opposite the turn), connect hose, turn on pump, test the spray pattern, and adjust top dial till correct air atomizes the lacquer thinner in a nice even pattern. Test on rosin paper hung in your booth setup. Once happy try finish and adjust top dial again if needed.

Clean gun, disassemble bottom dial, spring, needle, then unscrew front ring, remove disc and its spring, and use socket to remove nozzle - soak all that in a lacquer thinner, (I use a clean empty paint can to soak), scrub everything down with lacquer thinner and bristle brush (toothbrush and cleaning kit). Once everything is spotless i lightly coat all the threads in Vaseline in nozzle and rear dial. If long term storage is needef i clean and dry needle stuff and store in a viewtainer. I seal my gun up in a bag so zero nothing can get to it. I pay attention to my hoses, cup seals, flow control valves, etc.

Sorry if its overkill, it was big money for me, its how i was shown, its worked for 12 years for me and i bought it used from the original owner that taught me. Its a sweeeet setup. I pretty much only use it for ml Campbell pre and post cat lacquer.

John, no compressor or air regulation with this setup. Also that is a check valve in the outer clear hose and there is no filter on inlet tube.


Glad its my shop I am responsible for - I only have to make me happy.

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#16
  Re: RE: Less material or more air, that is the question.. by BloomingtonMike (I own the 9100 and m...)
(01-13-2018, 12:07 AM)BloomingtonMike Wrote: I own the 9100 and maxim 2 gun. Bottom dial is the needle flow control. You can feel when the point is fully open. So screw down bottom dial to close needle 100% gently, then back it off till the needle fully opens and just. Also make sure your tube and one way check valve inline in clear tube are working good and clear, then once you are ready to test spraying, fill the cup (use lacquer thinner to test, its cheaper. I also use cup bags to make cleanup easier), make sure tube faces forward in cup, make sure the cap over nozzle Is horizontal or vertical, you should be able to click turn it, just test fans for now ( pattern will be opposite the turn), connect hose, turn on pump, test the spray pattern, and adjust top dial till correct air atomizes the lacquer thinner in a nice even pattern. Test on rosin paper hung in your booth setup. Once happy try finish and adjust top dial again if needed.

Clean gun, disassemble bottom dial, spring, needle, then unscrew front ring, remove disc and its spring, and use socket to remove nozzle - soak all that in a lacquer thinner, (I use a clean empty paint can to soak), scrub everything down with lacquer thinner and bristle brush (toothbrush and cleaning kit). Once everything is spotless i lightly coat all the threads in Vaseline in nozzle and rear dial. If long term storage is needef i clean and dry needle stuff and store in a viewtainer. I seal my gun up in a bag so zero nothing can get to it. I pay attention to my hoses, cup seals,  flow control valves, etc.

Sorry if its overkill, it was big money for me, its how i was shown, its worked for 12 years for me and i bought it used from the original owner that taught me. Its a sweeeet setup. I pretty much only use it for ml Campbell pre and post cat lacquer.

John, no compressor or air regulation with this setup. Also that is a check valve in the outer clear hose and there is no filter on inlet tube.

Thanks Mike. Please don't apologize for overkill explanation. Much what you say isn't news to me except for the cup bags. I guess I know they exist but I'm soo concerned about getting a perfect spray that I'm not thinking about those detail. I'm sure they save some time and lacquer thinner. 

Considering that I have taken all the appropriate steps on cleaning and setup, I think my next step is to thin the material just a tiny bit. Before that I probably should go back to square one with some water and cardboard and tinker with all the adjustments.
How do you know you're learning anything if you don't screw up once in awhile?

My blog: http://birdsandboards.blogspot.com/
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#17
  Re: RE: Less material or more air, that is the question.. by mr_skittle (Here's a thread that...)
You would benefit from measuring the viscosity.  Guessing as to the correct N/N always leads to questions of what to do when something doesn't work right.

John
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#18
  Re: Less material or more air, that is the question.. by mr_skittle (I sprayed some clear...)
You know John, you were pushing 'the measuring the viscosity' idea in another post I had a few months back. I thought I was going to get away with skipping that part since I've been spraying the same material, but its time to make it happen.

Another thing I'm thinking about, as I look at my thermometer @ -15 degrees, is the viscosity of slightly cold finish. Before anyone freaks out at me, I've not sprayed at this temperature, but I am in MN and winter is winter. I can get my shop into the 60's to spray but its still gets a bit of a chill once I crack the door and set up a fan for ventilation. I keep the finish in the basement of the house to keep it from freezing but its pretty frigid down there too. Next time I'll have the finish and gun on the main level in the house to warm up. Will thinning it help compensate for working in a less than ideal temperatures?
How do you know you're learning anything if you don't screw up once in awhile?

My blog: http://birdsandboards.blogspot.com/
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#19
  Re: RE: Less material or more air, that is the question.. by mr_skittle (You know John, you w...)
I'd start by reading the documentation for the finish to find out the application temp. range.  I know you can spray shellac at nearly any temp., but WB products don't spray well and won't cure below about 60F.  I have no clue about your solvent based product.  It's probably somewhat more tolerant to low temps., but I'd be surprised if the viscosity isn't affected by temp., and maybe the curing.  Just makes sense.  

You might consider getting a carbon filter.  If you set up your vent fan to suck air through a furnace filter and then the carbon filter, it will absorb the VOC's and you won't lose temperature.  

John
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#20
  Re: Less material or more air, that is the question.. by mr_skittle (I sprayed some clear...)
Add a cap full or two of LT or even lacquer retarder to the full cup. Try a 1.3 to 1.5 needle. Turn your air volume on max flow. Now slowly open up your volume until you get a good spray pattern with no tails or larger “splatter” specks. Back your volume down a tad until the specks disappear. You should be good there.

Retarder with allow your specks to settle and flow into the finish before it dries into orange peel.

You will know if you’re over atomizing as the lacquer will land “dry” on the surface and look and feel like rough overspray. Over atomizing is much more common with an airless sprayer where you can pressurize the be-Jesus out of fast drying finishes.


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