Paint systems

[Tom Spurgeon]

I'm a long ways away from needing this information, but I'm researching a fairly new technology for painting. High-volume, low-pressure (HVLP) systems are being promoted as applying a "better" - "show-room quality" automotive finish than the traditional high-pressure, low-volume systems. I have some experience in developing a "show-room quality" finish from the traditional systems. However, as some of you may know, it requires a process of building up and taking down until the desired finish is achieved. I'm hearing that the HVLP system has benefits over the old system that achieves better results.
Has anyone researched this claim or had their finish applied in this manner?
Again, your help is always appreciated.
Sincerely,
Tom Spurgeon
corvettethomas67

[Chuck S.]

Re: Paint systems

Tom, I haven't heard that HVLP offers ANY advantages over conventional guns in reducing orange peel. In fact, my experience and from anecdotal reports is that HVLP guns INCREASE orange peel because the individual paint droplets are discrete macro droplets with little atomiztion or vaporization. If you want to talk about "show-room quality", you have to be talking about significant large orange peel...these days, everybody's new products seem to have some orange peel.

Eliminating the paint vaporization reduces emmissions introduced into the atmosphere. The original motivation for HVLP was to respond to the government's demand to reduce air-borne emmissions. A fringe benefit is that the process wastes very little paint; most of it goes on the target which reduces material consumption.

As I found out recently, you have to choose your fluid nozzle size carefully depending on what product you are painting, and you CAN'T ALWAYS GO with what the paint manufacturer recommends. The days of going down to Sears and buying a spray gun to apply everything from primer to clear are gone (if it was ever here).

Product response to fluid nozzle size varies according to manufacture of the gun; Therefore...consult the gun manufacter for the fluid nozzle best suited to a given product. The manufacturers have tested all the available products in their guns, so they already have identified the best choice fluid nozzle for any given product. Choosing your fluid nozzle correctly will improve your finish quality significantly; i.e. optimum dry-film-thickness with minimum orange peel.

Primer-surfacers require the largest fluid nozzles: PPG's K36 acrylic primer surfacer, for example, really needs a Size 97 (1.7mm/0.070") nozzle in a Binks M1-G gun...it is unsprayable using the Size 94 (1.4mm) fluid nozzle, even when one part reducer is added. It should be noted that PPG says 1.4 mm to 1.6 mm is suitable; maybe 1.4mm works OK in a Sata. DPLF epoxy primers should take a Size 94. Two-stage basecoats typically require a Size 93, and clears will take a 92. Purchasing all the optimum fluid nozzles for a Binks M1-G is no small investment...the nozzles cost about $70 apiece. I will probably use the just slightly non-optimum Size 94 for color and clear, but that Size 97 for the K36 IS REQUIRED.

[Tom Spurgeon]

Re: Paint systems

Chuck,
Thank you very much for your information. This post began with two pieces of information that I didn't include (on purpose). First, the first HVLP system that (I believe) I saw applying a finish coat was featured indiscriminately on an episode of "American Hotrod". The reason we believe it was this type of system was the large (app. 1") feeder hose and compressor sound (they sound like a loud vacuum cleaner). Second, my wife has an in-home business where she applies spray sun-tanning solution using an HVLP system with a gravity-feed Apollo brand gun. The gun is equipped with a .030 size needle/nozzle. The claim from the HVLP sources I've seen claim that: Overspray is reduced or almost eliminated resulting in less post work. Regarding the orange-peel, I can't claim to know what advantage or disadvantage the HVLP system offers over conventional automotive finish systems. I can only guess that, with enough reduction, you can spray almost anything. Your points about governmental requirements seems logical and your information regarding proper needle size is appreciated.
The last gun I owned was a DeVilbiss unit, and as to the model -I couldn't tell you. I just know at my cost (owning the parts store) it was close to $300. Of course, this was in 1971.
Sincerely,
Tom

[Chuck S.]

Re: Paint systems

Tom, the HVLP system with the 1" hose is a different type HVLP system than those used by most professional body and paint shops now. Conventional guns are sort of a misnomer; they may be "conventional" in name only, a legacy from the early days of HVLP. I expect "conventional" guns will be fading away. In some states, HVLP is mandated, and in the other states, painters are quickly changing over because the HVLP guns use less material and from what I can see, that's all the paint stores are pushing. Besides, Big Brother will be in your local neighborhood soon enough.

The 1" hose systems are sold by Eastwood and maybe Tip Tools. The sales poop says the air is heated (probably due to the single stage of turbine compression), and is advantageous to the process. The large hose has to be relatively short to reduce pressure losses because the pressure at the hose inlet is really low, er...like a vacuum cleaner. This contrasts with the more common HVLP guns that have a 3/8" supply hose with maybe 40 psi inlet pressure, that is regulated to 7-8 psi at the gun handle. I haven't used one of the large hose systems, but I figure hauling that little cart with the turbine "compressor" around a vehicle couldn't be much fun...dragging a single 3/8" supply air hose and watching that it doesn't get into the wet paint is pain enough.

While it is true that anything can be sprayed if reduced enough, over- reduction beyond the paint manufacturer's instructions should be avoided. The lesson I learned the hard way was that proper selection of typical HVLP fluid nozzles (Binks, DeVilbiss, Sata, et al) will eliminate the need to over-reduce.

[John H.]

Re: Paint systems

Trivia - Assembly plant paint systems don't use "spray guns" any more, except for shooting-in jambs and openings prior to main color application; main basecoat and clear application is done (robotically) with air-driven electrostatic "bells" that spin at 15,000 rpm as they oscillate back and forth across the horizontals and vertically past the side panels. The extreme velocity when the paint leaves the periphery of the spinning "bell" instantly atomizes the paint into a very fine mist that's attracted directly to the oppositely-charged body surface; virtually no wasted material, and highly-controllable film build. The basecoat material is waterborne, so the basecoat booth temperature and humidity is controlled within 2 degrees and 2%. About the only place you'll find a spray gun any more is in a repair booth.

[Tom Spurgeon]

Thanks John and Chuck

Since the wife has one of the 1" systems, she's thinking that this unit would be similar to those used by today's "paint guys" -I'm still skeptical. As I stated earlier, just in the research stage now. All I can verify at this point is -when she fires that thing up, better be wearing earplugs!
Respecfully,
Tom

[Bill W.]

Re: Paint systems

I have been a painter for about 35 years and have been using HVLP guns (at work) for about 8 years .(its a law here). They do use a little less paint. I think there is more overspray. On modern high metallic paints I think it helps the paint match. They work great for primer .For my old cars I still use my old DeVilbis. If you plan on using an HVLP to paint a whole car you better have a major air compresor. large inside dia. air hoses, special hvlp air line fittings and as few in line obstructions ( filters,regulators etc.) as possible. ...Bill

[John M.]

Re: Paint systems

Tom,
I in my opinion, The HVLP gun DOES NOT offer any advantages in quality of finish. It will offer lower overspray and lower paint costs, butwill not improve quality over high pressure guns. I have tried several HVLP guns and have found each one to be very hard to achive the same level of finish as my old CA Technologies of Binks gun. The application of material is much slower which requires learning a new application process. I found it extremely hard to slow down enough to get smooth application. It is just tough to break 35 year old habbits.
That being said, I finally broke down and tried the new REDUCED PRESSURE Sata gun about 2 months ago, and I can tell you that in my opnion, it is probably the finest gun on the market today! It operates at a reduced tip pressure (approx 29 psi) and lays down paint smoother than any gun I have ever used. It is a lot of money for a gun, but I do not regret spending the money. It has a built-in digital air micrometer in the handle of the gun and you can repeat a particular setup with incredible accuracy.
The setup that you are talking about sounds like a turbine style HVLP gun and it usually uses a high speed low pressure turbine to supply the air instead of a compressor. These guns have never made any inroads into the the automotive refinish market, although several companies still sell them. Tip Tool and several of the woodworker tool suply companies sell them in their catalogs.
The knock that on them, is that because of the turbine source, the air at the tip tends to be substantially warmer than compressed air guns. High pressure air, when released through an orrifice, will drop it's temperature dramatically, while a turbine gun will not since it is supplying the full pressure of the turbine to the gun. This can be both an advantage and a disadvantage depending upon the use of the gun. Not having a pressure drop means that a turbine gun is almost immune to the moisture problems that plague compressed air guns. On a compressed air gun you will need an air dryer to prevent moisture drop-out in the cooler airstream created at the tip by the pressure drop. The dryer removes enough moisture to lower the dewpoint of the compressed air stream below the lowest possible discharge temperature (usually about 35 degrees F). The turbine gun however, will have problems with blushing of lacquer in humid enviroments as there is no way to dry the airstream. Also, since the airstream is warmer at the tip, the paint will tend to flow less and will have a tendency to really orange peel. This can be overcome to some degree with a very slow thinner, but it still remains a problem. The large hose is absolutely necessary to prevent pressure drop on the way to the gun, and you have a very limited distance that the turbine can be away from the gun.

Regards, John McGraw

[Warren L.]

Re: Paint systems

HVLP is not new technology. I first tried it 15 years ago and it was probably around well before that, it wasn't very good back then but has improved. HVLP can leave a smoother finish than some of the factory finishes but some of the factory finishes are pretty poor. Some painters say they get glass smooth finishes from their top quality HVLP's, others say that it is just not possible.

The variables are very important in how smooth a finish ends up, type of material, viscosity of the material related to ambient temperature, speed of air flow in the room, temperature of the material, temperature of the car, proper air pressure and eonough cfm for the gun, temperature of the air going through the room when you spray, speed of your reducer, etc all affect your final finish, and of course the painters technique.

Painters with HVLP only had a 9 percent increase in transfer efficiency over conventional spray guns, that went up over 20 percent when they were trained. So how the gun is used is important if your focus is transfer effeciency. Compliant guns are between conventional and HVLP, they offer the 65 percent transfer efficiency when used correctly and can give smoother finishes than HVLP, so can some of the old conventional guns.

Depends on your intentions, spray one car with Acryl Lacquer? or one car with base clear? or a bunch of cars over time etc. See some custom painters in your area and see what they are using, what material, gun etc then look at how smooth the finishes are.

Last week I stopped to see one guy up north who does stunning work,he uses all HVLP, then for final coat water sands the clear and flow coats with an old conventional gun, later in the week I stopped by a guy who uses all old conventional stuff and his work is top notch as well.

If you are intending to water sand and polish in the end then a good quality HVLP should work for well for you. The variables make a big difference and if they are all in your favour you will get better quality results from any spray gun.

Warren

[mac peppers]

Re: Paint systems

i've got a new high end hvlp gun and was planing to paint my car with lacquer. i've now heard that hvlp may not be very good for spraying lacquer, not enough pressure to atomize the lacquer. has anyone used hvlp for spraying lacquer and would you recommend it? i've still got my old gun around, but if the hvlp puts more paint on the car instead of the floor, i'm all for it.