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Old 06-25-2004, 10:23 AM
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More on Orange Peel

I am an occasional painter and new to the forum.

I've always had good results with Dupont Centauri etc. - but I am having difficulty with urethane enamel. It seems no matter what I do, I end up with orange-peel.

I've used a Binks conventional siphon gun, an Accu-Spray HVLP gravity feed, and most ecently a Devilbiss Plus gravity feed gun. I've tried different pressures, air caps and tips. I also verified the viscosity using a viscosity cup, as well as trying different reducers. Either I haven't hit upon the right combination, or this paint is just prone to orange peel(?)

I read in another message here that perhaps my fluid is not opened far enough. However I did begin to experience sags and runs by opening up the flow.

Does anyone have any input?

Oh yes.. my best results recently have been with PPG Concept single stage urethane. It happened to be a 90 degree day and all I had was mid-temp reducer. It flashed pretty fast, but came out much smoother. This is the exact opposite of what I would have expected - but it's what happened!

My results are ok after sanding and buffing but I'm looking to improve my technique.

Any ideas and thoughts would be most appreciated!

-- Ken

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Old 06-25-2004, 03:35 PM
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a good painter once said and I quote: "a good coat of paint is, too much paint to get orange peel and not enough to make it run or sag" (he finished that sentence with the words "now how hard can that be? not hard not hard at all!YEAH right!!!)
I have never forgotten that sentence.
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Old 06-25-2004, 03:52 PM
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You evidently haven't hit the correct combo of paint flow and atomizing pressure. If you are setting pressure based on a reading at the compressor, pressure at the gun is WAY too low. I am admittedly an extreme amateur at painting but usually get pretty good results, save the spots where I drag my T-shirt across the paint, get a huge drip, have a blob of water plop smack in the middle of a hood, etc. I have found that orange peel is too little paint and too little atomization pressure. Crank up the pressure and flow on your last coat and it should flow smoothly with any type of paint. The last coat can be pretty heavy 'cause the first two will have tacked up and can hold the final coat from running and sagging. Can't get any more specific than that and it doesn't mean gallons/minute and hundreds of psi but that is the direction you need to head to eliminate your problem.
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Old 06-25-2004, 04:01 PM
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I too am an amateur, but I really would like to get a handle on this.

I have a pressure regulator at the gun. With my HVLP accu-spray I've cranked it up as high as 60psi (way higher than it should be) in an attempt to see how things change.

The interesting thing is that on CURVED surfaces, such as the end of my S10 bed at the gate - or all along the top of the bed rail - these areas come out PERFECT. I'd like to know what's happening there to cause the paint to flow out correctly and yet still form orange peel on the wider flatter areas.

Just as a sanity check I am tempted to get some centauri and load up and try that. I remember painting bumper covers with centauri and not even having to sand or buff - it could come out mirror smooth. That is what I'm after.
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Old 06-25-2004, 04:15 PM
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That sounds like your are shorting volume of paint on the flats. The same gun speed on a curved surface will by definition pile on a little thicker coat that will flow. Have you any problems with sags or runs? If not, see how much you can pile on a flat until you get a run. I usually end up with a couple of small runs that scrape easily off once the paint is cured but I get zero orange peel. If you get a run, leave it alone until the paint dries. Then take a single edge razor and bend it in a very slight curve so the ends won't dig into the surface. Then holding it almost at a 90 degree angle to the surface, LIGHTLY drag it across the drip like you would use a cabinet scraper. Let the sharp blade do the work. A couple of localized drips are much preferable to all over orange peel. The former can be fixed in minutes, the latter takes most of a day to remedy.
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Old 06-25-2004, 04:21 PM
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Yeah unfortunately I did get a couple of runs on this last job. But it may have been at the point where I had increased the flow of material AND slowed slightly at those spots.

I think I am going to approch this problem from the other direction - in other words open the gun way up FIRST and then close it down gradually - I'll try some test panels etc. I also have a feeling that the single stage urethanes I've been shooting are more orange peel prone than the older enamels. Time will tell, but I am irritated enough to keep scratching until I figure this out.

I may not be able to get back on the computer again until Monday but I will be back. There is a lot of wisdom on this board.
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Old 06-25-2004, 06:46 PM
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"Basics of Basics" Atomization and gun set up.
By Brian Martin

Being HVLP and low VOC products are the way the industry’s going I will be referring to them in this discussion on painting and paint guns. Most all basic issues dealing with HVLP can be applied to conventional guns, atomization is atomization. The HVLP just arrives at it differently.

The object of the spray gun is to break up the primer/sealer/paint/clear (I will call this “PSPC” from here out) into small particles and lay them in neat little rows on the panel being PSPRed. So the whole outcome rests on how well the gun is doing this. Picture the droplets of PSPC coming out of the fluid tip of the gun and then the air “slapping” them into smaller droplets.

You have two things that help you with this process, air and solvent. Solvent can mean something that is already in the PSPR from the manufacture or something the manufacture has told you to add to it. By the way, you should always mix in proper ratios as instructed in the tech sheet. The thinner (less viscosity) you get the PSPR or the more air you have at the fluid tip of the gun the more it will break up the PSPR. The target for you is getting the perfect balance needed. Too much solvent and the PSPR will have no body, fill, durability, etc. Too much air and you blow the PSPR everywhere but the car, poor adhesion, excessive texture, etc.

So, the answer is proper air supply and gun (and fluid tip) choice and how you adjust it.

With today’s high solids-low VOC (Volatile Organic Compound, you know the bad stuff that goes up into the air we breathe) products there is less solvent. And with HVLP guns there is less air at the cap to break up the PSPC, proper air supply and gun setup is more important than ever.

FIRST THINGS FIRST, your compressor and air supply.

An HVLP gun requires more VOLUME of air to operate (the V in HVLP, High Volume Low Pressure). Now you may notice that your HVLP gun is adjusted at maybe the same PSI as an old conventional gun, around 50 lbs at the gun (many HVLP guns are set at much lower though) so where is the “Low” in PSI they are talking about? It is at the actual air cap where the air and paint come out. An HVLP gun has only 10 lbs at the cap while a conventional has upwards of 50! So the VOLUME of air (CFM, Cubic Feet per Minute) is the key to proper atomization with an HVLP.

This 10 lbs I am mentioning is AT THE CAP where the air and paint comes out. It is not measurable without a special air cap that has a gauge built in to it. This air cap costs about $150.00 (and you would need a different one for every brand and model of gun you use) and is not needed to set up or tune your gun. Just looking at the droplet patterns will tell you everything you need. I only refer to it to make a point about HVLP operation.

If you have a gun that requires 15 CFM you will need a compressor and plumbing that will produce that at a very minimum. There are HVLP guns that need as little as 7.5 CFM so you can get good results even from a smaller compressor. Air supply is a complete subject by it’s self so lets assume that you have the air supply needed and move on to gun set up.

So atomization is the key, but why? Why can’t you just lay it out wet and let it “flow”, as an old painter will say. Picture a jar full of bb’s, they will represent well small, atomized droplets of PSPC. The gaps in between the bb’s is solvent. Now picture a jar filled with marbles, they will represent large, poorly atomized droplets of PSPC. The gaps in between are, you guessed it, solvent.

If you apply your PSPC in large poorly atomized droplets, what you will have is a film full of solvent. This can and will cause slow curing, shrinkage and dieback (the loss of gloss in the hours and days after application).

So, now that we have learned the need for gun set up, how do we do it? Lets start with the fluid tip choice. The newer high solids low VOC PSPC products need to be broken up more, so a smaller fluid tip is needed.
Basically you want the smallest fluid tip that will still allow you to PSPC the particular part you are PSPCing keeping the entire thing wet and in a fair amount of time. In other words a 1.0 tip would be beautiful for clearing one fender, but would be lousy to paint a complete. The application would be way to slow and the first panel would be way to flashed by the time you got around back to it. So you need to compromise, a 1.3 is a great all around tip, while a 1.5 though getting a little big, can get you by. If you read the tech sheet on the particular product you are shooting, it will have a recommendation for fluid tip size.
There are needs for other tips, for instance when shooting polyester primer you may need as big as a 2.3, but for urethanes and epoxies, the 1.3 or 1.4 will work great. If you plan on using a pressure pot or paint a bus, all bets are off and we would need to study a little bit more.

As an example of the use of a 1.3 tip I did a test once that proved the point well. I shot two panels of metal with a med solids urethane primer. One was shot with a 1.3 super high atomizing top of the line topcoat gun. The other was shot with a 1.5 (or a 1.7 I can’t remember) “hoser” primer gun. Three coats were applied and after a full cure (the one shot with the larger gun took MUCH longer to flash and cure by the way) the film thickness was measured. The one shot with the 1.3 tip was 2 tenths of a MIL thicker! The larger gun laid out the marble sized droplets full of solvent and when the solvent flashed the film shrank.

Air supply is a subject that could fill many pages by it’s self. So we are going to assume you have that covered and move on to gun set up.

You need to “tune” your gun EVERY TIME you use it just as you would tune a guitar before you perform. This is done with a very basic spray out pattern test. This very basic test tells you how your gun is atomizing and you adjust it to achieve the best atomization you can.

Lets do a spray pattern test:

Set the fan width as need (you don’t want to change it after you have “tuned” the gun). Turn out the material knob about 2 ½ turns. This is the “mixture” adjustment, kind of like the idle screw on a carburetor. The farther in it is screwed the lower the fluid to air ratio is and the smaller the droplets will be. The farther out it is, the higher the fluid to air ratio is and the larger the droplets.
Set the air pressure at the inlet to the gun to the manufactures specs. On an HVLP gun this spec is usually found on the gun and is the maximum PSI it can have while still maintaining the maximum 10 lb at the cap for legal HVLP transfer efficiency (68 %). You are now ready to do a test spray out.

Tape a piece of masking paper on the wall for the test. Hold the gun at a right angle to the wall, just as if you were going the wall. Hold the gun at a spread out hands distance (about 8” or 22cm). Pull the trigger to completely open for a split second and then close it. You want an ON-OFF wide open-completely closed in ONE movement. You should have a cigar shaped pattern with complete coverage in the center with fading coverage going away from the full coverage cigar shape in the center. The center should be fully covered without any runs. If you have runs, either you are holding the trigger too long, you are too close or the gun is simply applying too much material. In which case you need to screw in the material knob or turn the air pressure down. But most likely if you have turned the material knob out the 2 ½ turns and the air is set at the factory specs, you are just too close or holding the trigger open too long.

The droplets you see trailing off the center are what you will use to “tune” your gun.

Turn in the material knob to make the droplets smaller (and or raise the air pressure). The balance you need to attain is the smallest droplet size possible before you loose the coverage desired. In other words if you turn in the material knob too far, not enough material will be coming out to cover the panel!

Now, you’ll notice that I said, “raise the pressure to the gun”, while earlier I said to set it to manufactures specs. We are talking a very small adjustment. It is a fine balance in material to air ratio and a little more air than specified is okay. Even if it is an HVLP gun the inlet pressure recommended is to maintain the 10 lb limit at the cap. Well, about three quarters of the country has no regulations for HVLP use so if you go over the 10 lbs all it will do is atomize the material a little better. You may loose a little of the benefits of HVLP though. But remember you have a lot of control with the material adjustment knob.

After you are happy with the droplet size, DON’T TOUCH THE FAN CONTROL. It will change the PSI at the cap and will change the atomization you worked hard to get.
Do this spray out every time you spray as material change, temp, and humidity will necessitate a spray out droplet pattern test. Good luck!
Click here to see a sprayout pattern
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Old 06-26-2004, 12:57 PM
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Great post, Martinsr! You didn't mention anything about the air control screw at the bottom of most HVLP guns. Is there a fixed or optimal setting for that adjustment? Thanks.
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Old 06-26-2004, 01:21 PM
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>> Why can’t you just lay it out wet and let it “flow”, as an old painter will say. <<

Brian thank you for taking the time to post your response. I am printing it off and will study it further this afternoon - I plan to shoot some door panels later.

Your above quote sums up a good deal of my frustration, and would explain why I've had good results with older technology paints and aerosol cans of lacquer etc.

"I'll be back"
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Old 06-27-2004, 03:35 PM
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Why nbot just spend the extra time and make it perfect by wet sanding it.
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Old 06-28-2004, 08:09 AM
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Well Brian I did as you said. I used the smallest tip I had (1.2) and did a spray pattern test. I had adjusted for a small fan width because of the smaller area I was working with. The test had a run in it, so I kept adjusting down until the center of the pattern was wet but didn't run.

I was shooting Dupont Chroma-One urethane enamel and for the first time ever in my expereince, it came out nearly PERFECT! I was using my Devilbiss Plus gravity gun (which I am new to) and I was very impressed. (I found myself shooting a test pattern before each coat to verify my set-up)

I had gotten to the point where I thought putting this stuff on smoothly was impossible. Yet I realized that no production shop has the time to sand out orange peel so I knew there had to be a way.

I will look forward to trying this with a full-width fan!

-- Ken
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Old 06-29-2004, 09:58 AM
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good info *joinin in*

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Old 06-29-2004, 02:55 PM
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Brian if you're still reading, can this technique be applied so you can paint things like kitchen cabinets and the like? In other words, a thinner film build but still with the appropriate finish?
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Old 07-01-2004, 02:52 PM
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With an HVLP gun, slow down your arm speed. Half the speed of a conventional. If you are trying to adjust the amount of paint coverage with just the volume control, this will be futile. It takes me twice as long to paint with HVLP. With conventional you are moving fast because of the normal volume of paint output. If you don't move , you get run and sag. With HVLP you will not get enough coverage unless you slow down.

It only makes sense that you will use 30 -50 % less paint with HVLP because it is going on the surface rather than the atmosphere, but if you don't get good coverage there will be space between the paint droplets, and that is orange peel.

Most conventional gun painters don't like the switch initially, because of the time involved. Don't forget time is money to a production painter.

P.S. Watch the surface as you paint. That will tell you if you are laying enough paint. 10 - 15 pounds of pressure at the tip for HVLP.
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Old 07-02-2004, 02:47 AM
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Awesome post here by Willy and Martin. I've had good luck with my painting, the little I have done. I was taught the set-up like Martin described in my teens but had no idea why or how it worked. This is a printout. Thanks, Dan
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