WITH LOEHLE ULTRA-FLEX TECHNOLOGY
Spray Gun Tips
by Mike Loehle
Questions regarding spray guns come up on a regular basis and we will attempt to explain what we have learned… especially about the modern HVLP (high volume low pressure) type guns.
The older standard paint guns that were used for years were siphon feed guns with the paint cups below the air trigger. These guns used a lot of air to mix with the paint to properly atomize the particles. This was necessary to have the paint particles "busted up" or thin enough to flow out evenly on the surface being painted. This resulted in a lot of paint being sprayed into the air (overspray), which the EPA (government) didn’t like. They mandated that the paint be reformulated with much less thinner used and thus HVLP type guns were created.
The modern HVLP guns will spray paint that is much thicker, with theoretically much less air. This results in more paint being directly applied to the surface and less overspray… which pleases the government. The problem is that even with HVLP guns, the paint droplets that come from the gun are normally bigger and create craters like "orange peel" on the surface being painted when first applied … especially by novice painters. It is also quite common to see some orange peel on brand new factory automobiles because of these thicker type coatings. It is somewhat the "nature of the beast" as they say. Also vehicles that look 100% smooth probably had the final clear coating machine buffed to remove any texture or over spray. Our Clear Top Coat chemical is formulated to be buffed out to remove any blemishes and dirt particles. We can provide all the buffing agents if required.
Our chemicals have specially formulated thinners that will allow the paint to flow out (drop to drop) before the paint sets up. This is accomplished with thinners that are designed for various temperature ranges. This makes our paint products EPA compliant, as a minimum of thinner is used. Thinner evaporates into the atmosphere and makes the EPA upset…
Most of the printed literature that novice painters receive with any of their paint guns will have recommended air pressures to use for their guns. Many talk about "low pressure" and are measured at the cap end of the gun (front). Most novice painters do not even have the equipment to measure "cap end" pressure. This "low pressure" is normally in the 8 – 10 psi range and really looks low for EPA type matters.
The reality is that most novice painters measure air pressure with a regulator at the compressor or at the incoming end of the gun. Some literature will give settings for this type of measurement, but are really only recommendations to start with. Novice painters especially want these psi numbers to be "set in stone" for them and it is virtually impossible for any paint manufacturer or spray gun manufacturer to provide these.
What we have found is that the pressures that come into the guns are required to be somewhat higher than most folks think to allow the modern paints to be "busted up" or atomized. We have also discovered that if a recommendation of 45 psi is given, they mean 45 psi at the gun as the air enters into the end and not at the compressor. The pressure will drop dramatically from the compressor to the gun based on the length of air hose and its inside diameter. Also it is important to learn that the pros use this air pressure recommendation with the trigger pulled and watch for the air pressure to drop and then become stabilized. This is when they want the say 45 psi that is talked about… not with the gun at idle. We learned this first hand in a demonstration by a long time pro painter that even has NASCAR (race car) experience.
Well we learned that day that a big problem with orange peel and the large paint drops is that the air pressure most novice painters use is generally way too low. The amount of overspray created was much greater than we had ever seen with the new type HVLP guns. It reminded us of the overspray we used to see with the older siphon cup guns. The difference was that the particles were paint particles and not mainly thinner particles like the old days. The heavier paint particles seemed to end up where they belong… on the painted surface. The correct atomization with more air pressure created smaller (finer) paint droplets that flowed out smoothly. The correct temperature range thinner allowed the particles to then completely flow out and virtually eliminate any orange peel.
Other factors definitely enter into the picture and we will now discuss them.
The first is that the paint gun must be adjusted properly. This can require a learning curve. The fluid adjustment knob is the one that will govern how much paint comes out and how large or small the droplets will be once the air pressure is proper. The tendency is to "open up" the fluid knob to put out a lot of paint and allow the painter to move along rather quickly. This is the typical problem that a novice will have. The "wide open" fluid knob will result in large droplets or again, orange peel.
One must reduce the amount of fluid coming out to reduce the droplet size. This will mean that the amount of paint coming out is reduced and one must slow down the speed the paint is applied. The tendency is to move too fast and this results in dry spots where not enough paint is applied. Also, moving too fast will generally have novice painters forgetting to properly use an overlap spray pattern, adding to the dry effect. This all sounds hard, but it’s not with a little practice and maybe some coaching from a painter friend… a PAINTER friend, not a guy who has only read articles about it!!
The next item to discuss is the size of the fluid needle/cap that the gun has. These numbers can be confusing at first, but they basically refer to the opening size that allows the paint to come through. Modern paints that are EPA compliant are generally thicker and require much less thinner than the old paints. This requires gun tips (needles/caps) to be larger and specially designed for these modern paints. Most guns are now manufactured for these paints. Most primers (also called surfacers, or as we call ours - Filler/UV Blockers) require larger size tips because they are thicker than most paints. This allows for more primer to be applied in one coat and results in less paint and fumes in the air… thus the EPA is happier.
Each paint and gun manufacturer have basic recommendations for the sizes of the tips for the type of chemical being applied. We find that our own Filler/UV Blockers (primers) chemicals can normally be applied very well with tips that range from 1.4 mm – 1.7 mm. The more professional guns seem to be more accurately made and will be closer to the 1.4 mm size. The cheaper import guns seem to be better in the 1.7 mm range.
Our Color Top Coats are much thinner than the Filler/UV Blockers or primers and will work very well with 1.3 mm – 1.4 mm tip sizes. Colors are normally thinner than primers or clear coats nowadays and still spray more like older (thinner) paints.
Our Clear Top Coats are possibly the thickest in any industry and are formulated to attempt to be applied with the fewest number of coats. They also resist runs as much as humanly possible. This was our largest complaint with early developed clear coat chemicals we experimented with. They were thin and would run very easily… not good for us novice painters. Our Clear Top Coats also will "flash off" (dry) rather fast to help prevent runs and having dust settle into the paint as it dries. Most novice painters do not have dust free, heated paint booths, so our formulation really helps folks in their workshops. We generally use 1.4 mm – 1.7 mm size tips for applying our Clear Top Coats. Also we have learned that painters that have experience with spraying can safely add one full part of thinner to the mixture without creating runs. The normal formulation to attempt to prevent runs uses 10% thinner… the one full part will help the clear flow out easier and allow the painter to utilize a gun with a smaller tip set up. By the time a novice painter gets to the Clear Top Coat application, they are usually pretty good with handling the spray gun and should be able to apply the chemicals with proper atomization and flow out.
Another point or two on guns is that normally professionals will use one gun to apply primers and another for colors and clears. The primers have abrasive particles in them and will wear out a paint gun if used repeatedly. This is not a problem for novice painters, because they do not spray everyday or enough paint to wear out their guns. Also one does not want a "chunk of primer" to come through the gun accidentally… especially when applying the final Clear Top Coat. We use two different guns in our shop and utilize a "primer gun" with a 1.7 mm tip to apply our Filler/UV Blockers. Our Color Top Coats are applied with a 1.4 mm tip, as is our Clear Top Coats. We do add the full one part thinner with the Clear Top Coats when using the 1.4 mm tipped gun.
We provide complete spray gun "kits" that can be used to apply our chemicals quite well. The kits are imported and come with three spray guns… one for Filler/UV Blockers with 1.7 mm tips, one for Color and Clear Top Coats and 1.4 mm tips. A smaller, handy touch up gun is also included and we use it for all our chemicals. The kits include two air regulators that fit on the paint guns and a cleanup brush package. Three different size spray cups that fit on the top are also included. The whole set comes in a plastic storage case. It is a good, economical setup and we honestly use one every few days ourselves in our shop. We’ve tried several of the import jobs… some are OK… some are junk. We finally found a setup that works well for the price.
We also sell medium and top of the line spray guns that professionals use everyday. We also handle fresh air respirators and wouldn’t even consider painting any chemicals without using it. Fortunately these have come down in price in recent years and are priced for the novice painter also.
The last item we want to mention is that most professional guns will apply our chemical very well with 1.4 mm tips. If they come with two tips, we choose a 1.5 mm for applying primer. Any suggestions that painters have for us are also welcome.
© 7-22-06 Mike Loehle
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