Paint - High Volume Low Pressure Paint Application
9216chevy10
Number: 91-334-10
Section: 10
Date: MAY 1991
Corporate Bulletin No.: 161701R
Subject:
HVLP-HIGH VOLUME LOW PRESSURE
PAINT APPLICATION
Model and Year:
1982-91 ALL PASSENGER CARS AND TRUCKS
VOC stands for Volatile Organic Compounds. Most solvents used in automotive refinishing paints are considered volatile organic compounds. Volatile organic compounds react chemically with sunlight and make a variety of pollutants generally referred to as "Photochemical Smog." VOC regulations seek to reduce the amount of VOC getting into the air and thereby limit pollution. One way to reduce the amount of volatile organic compounds being emitted into the air is to increase the transfer efficiency rate of the paint material being transferred between the spray gun and the surface being painted.
Different states throughout the country, such as California, New York, New Jersey, etc., are in the process of writing VOC emission regulations. As an example, the South Coast Air Quality Management District (SCAOMD) in Southern California has a Rule 1151 for automotive refinishing that stipulates that coating applications must be done with either electrostatic application, high-volume, low-pressure (HVLP) spray or "such other coating application methods that are demonstrated to the executive officer to be capable of achieving at least 65 percent transfer efficiency." HVLP spray is defined as "to spray a coating by means of a gun that operates between 0.1 and 10.0 psi air pressure."
What is the difference between the high pressure conventional spray guns now in use and the HVLP spray guns being stipulated in VOC regulations? In the conventional spray gun high pressure air leaves the air cap and rapidly expands. As this air expands, the paint from the fluid tip is blasted apart, sending small paint droplets in all directions at a high velocity. This explosion of paint causes much of the paint to pass or bounce off the surface being painted. Transfer efficiency on conventional spray guns is usually between 20 percent and 50 percent efficiency.
HVLP stands for (H)igh (V)olume (L)ow (P)ressure. HVLP spray guns utilize lower spray pressures upon atomization. The relatively low air pressure causes a much "softer" explosion. The resultant paint droplets are larger and slower. The large volume of air from the air caps can now better control the flight of the droplets. The paint spray tends to move in one direction. Bounce back and paint passing by the substrate are reduced, resulting in increased transfer efficiency. Transfer efficiency of HVLP guns is usually between 65 percent to 90 percent efficient. The amount of savings and transfer efficiency varies with the skill of the painter, gun adjustment, the air pressures, the size of the object being painted, and the viscosity of the paint.
Basically, there are three types of HVLP spray equipment available; turbine units, air conversion units, and spray guns with the air conversion units inside the gun.
The turbine unit is normally a portable or wall-mounted unit that generates a high volume of air at between 3 to 7 psi. Due to friction, the turbine generates heat. The amount of heat generated and the temperature of the air depend on the size of the turbine and length of hose. A large size diameter air hose is used between the turbine and the HVLP spray gun.
Air conversion units are normally portable or wall-mounted units that use high pressure air from an air compressor and then convert it to a high volume of air at a lower pressure set on a regulator. Most air regulators on these units do not exceed 10 psi. A large size diameter air hose is used between the air conversion unit and the HVLP spray gun. These units do not generate any heat, but can be purchased with a heat source.
HVLP spray guns with the air conversion units inside the gun use high pressure air from an air compressor and then convert it to a high volume of air at a preset pressure normally dependent on incoming air line pressure. The spray guns cannot exceed 10 psi no matter how high the incoming air line pressure is. There is no large diameter air hoses or heat to contend with. HVLP equipment that can maintain precise control and maintain close to 10 psi air cap pressure will provide better atomization of materials, especially low VOC paints.
A GM training course on HVLP Paint Application is currently available (Course # 22001.42). Please refer to the GM monthly training schedule for more information.
MANUFACTURERS of HVLP SPRAY EQUIPMENT
Accuspray System Binks
Bessam-Aire Binks Manufacturing Co.
26881 Cannon Road 9201 West Belmont Ave.
P.O. Box 46478 Franklin Park, IL 60131
Cleveland, OH 44146-0478 708-671-3000
216-439-1200
Can-Am Croix
Can-Am Engineered Croix Air Products
Products. Inc. 520 Airport Rd./Flemingfield
30850 Industrial Rd. So. St Paul, MN 55074
Livinoia, MI 48150 612-455-1213
313-427-2020
DevilBiss Graco Inc.
The Devilbiss Co. P.O. Box 1441
320 Phillips Ave. Minneapolis, MN 55440-1441
P.O. Box 913 1-800-367-4023
Toledo, OH 43962
419-470-2169
Lex-Air Turbine Spray Mattson
Lex-Air South 230 West Coleman
5874 Buford Hwy. P.O. Box 132
Doraville, GA 30340 Rice Lake, WI 54868
404-454-8417 715-234-1617
Sata Sharpe Mfg.
Sata Spray Equipment 1224 Wall St.
P.O. Box 46 Hwy. 16&63 N. P.O. Box 15042
Spring Valley, MN 55975 Los Angeles, CA 90015-0042
507-346-7102 213-749-4368
Xcel Spray
Smith Eastern Corporation
5020 Sunnyside Ave. #207
Beltsville, MD 20705
301-937-4548
We believe the sources listed in this bulletin and their equipment to be reliable. There may be additional manufacturers of such equipment. General Motors does not endorse, indicate any preference for or assume any responsibility for the products or equipment from this firm or for any such item which may be available from other sources.