Keeping it clean

There is a right way and a wrong way to maintain the paint technician's most important tool

There are about 60,000 collision repair facilities in the U.S., and therefore probably 60,000 different methods of cleaning spray guns. In the greater Portland, Ore. area there are nine facilities, both large and small and new and old, with at least 13 different methods of spray gun cleaning, everything from the immerse-it-and-leave-it-to-soak method to the simple clean-and-reload.

Today's spray gun is a very high-tech tool used to convert a liquid material into micron-sized droplets and deposit them onto the surface of a vehicle. Spray guns of the past were universal and almost any one brand or style would work for every product. Not today-now, the challenge is to match the proper atomization with the variety of different products being sprayed, including water thin primers, high solid surfacers, medium thickness sealers, multi-content colors and clears of all thicknesses. Waterborne products, which require specialized equipment, are used in certain geographic areas.

An example of this high technology is illustrated in a Geo G15 Aircap set up. The fluid tip is a combination of both an internal and external mix. It is internal because paint and air come together before the face of the aircap, and external when air and paint mix after the face of the aircap. This fluid tip is internally recessed with air holes around the perimeter edge, yet the fluid tip outer edge extends beyond the face of the aircap. The dump rate (ounces per minute) is low, but the breakup of particles and even layout on the surface offsets that concern.

Today's challenge is to select and properly use spray equipment that will help in the performance of paint application-like a high-performance race engine that requires the right fuel injection system to provide the perfect fuel-to-air mixture. Spray guns must properly mix the right amount of paint and air volume and pressure, depositing the perfect droplets on the surface.

Do You Believe in Magic?

The true magic of painting happens when the technician applies a coating in proper coverage, thickness and density, allowing each part to stratify. This stratification is the different materials going to their proper location: Resins for adhesion on the bottom; metallic flakes dispersed at the proper level; color evenly dispersed; resins and additives floating to the top to provide gloss and protection; and proper solvent content allowing for specific dry and cure. This stratification takes place in less than three minutes, after which the only action is the evaporation of solvents. Yes, this is the magic. Air atomization is the result of specific paths and functions of both air and paint inside and outside the spray gun. In a traditional (non-pressurized) spray gun, air entering the upper chambers is divided between the aircap, and the inner passages between the fluid tip and aircap. First, the inner chamber air is non-controlled, and provides the siphon at the end of the fluid tip that draws the material out of the fluid passage. In siphon and gravity feed, this air begins the breakdown of the stream flow. Secondary air holes near the center orifice also assist with the pattern development. Secondly, the controlled air exiting the horn holes meets with the fluid at the precise time and location and full pattern development occurs. This short distance is known as the atomizing envelope.

To perform and repeat this process on a regular basis, technicians must use an instrument that is clean, reliable and properly balanced for the task at hand. The objective then is to develop a process that returns a spray gun, after use, to a clean, precision instrument that will not require special attention before the next use.

Before beginning to establish a cleaning procedure, let's investigate what spray problems are the result of poor cleaning:

A horseshoe pattern is caused by a restriction in the airflow exiting the horn holes on one side. This restriction is generally larger in build up or may be completely plugging the air passage.
A teardrop pattern results from residue build up between the edge of the aircap center orifice and the fluid tip. Rotate the aircap 180 degrees. If the teardrop moved 180 degrees, the problem is on the aircap. If the teardrop didn't change, residue is on the fluid tip.
Paint starvation begins after spraying for a short period of time although the cup is almost full. Check the vent hole of the paint cup for plugging.
Fluttering or spitting is a common problem after a spray gun has been torn down for cleaning because air is being drawn into the fluid passage and mixing with the paint. Tighten the cup attaching nut, fluid needle packing nut, and/or the fluid tip.

Individual differences may vary the process, but the objective remains the same. Properly clean the tool so that it can be used next time without complications, using a minimum amount of solvent and generating the least amount of hazardous waste. Make sure to return the unused material to the appropriate container, uncatalyzed products to their original containers and catalyzed products in a separate container or the recycling unit. Place a small amount of solvent (3 oz. to 5 oz.) in the cup and shake or slosh it. This dilutes the remaining paint in the cup. Then, pour it into the recycler or holding container. Using clean solvent, brush off the outside of the gun and cup, and place the spray gun in the gun washer and start the cycle. Some materials may require a second or third cycle. Remove the spray gun, place a small amount of solvent in the cup (2 oz. to 3 oz.) and spray until no material comes out. This blows out any residue inside the gun and also rinses the fluid passages. Continue spraying until all solvent is gone. Finally, wipe, dry and properly store the gun.

If removal of a restriction is required, remember that only soft tools such as toothpicks or synthetic bristles can be used. Spray gun cleaning kits contain various brushes, toothpicks and plastic or nylon picks. Never use drill bits, welding wire or pocket knives to clean out a plugged passage.

Complete gun teardown should be avoided. Most often the only internal passage needing to be cleaned is the fluid tube and fluid tip (inside). Too many chances are taken in losing parts, cross threading, and over-tightening, which results in a malfunctioning spray gun. Removal of the air cap may be required but care should be taken since the fluid tip end is then exposed and subject to damage.

Lubrication to a spray gun is minimal since any lubricant will be removed the first time the unit goes through the gun washer. If needed, apply lubrication to the trigger hinge pin or air cap threads. These are the two major wear points on a spray gun. Almost all seals and O-rings today are neoprene and do not require lubrication. Use fine-weight oil, like sewing machine oil, or very sparingly apply fish eye eliminator.

Spray Gun Testing and Adjustment

Today's finish materials requires an art in operation of the spray gun. Some basic rules to follow that will help in achieving proper atomization are:

Open the fluid needle adjusting screw for full needle travel.
Adjust the spreader (pattern) control to full open.
Preset the air pressure based on the manufacturer's recommendations.
Spray a test pattern on a test panel. Make adjustments for pattern height, and even width throughout the pattern. Remember that the pattern height is equal to the distance being sprayed. For example, an 8-in. to 10-in. distance equals a pattern height of 8 in. to 10 in.
Rotate the air cap to spray a horizontal pattern. At the proper distance, spray a pattern for a count of four. Material should be flowing evenly across the length of the pattern. If not, minor adjustments are required in air pressure. These adjustments may be as little as 2 psi or 3 psi. If the pattern is not flowing at either end, this indicates a restriction around the center orifice. Check and clean the fluid tip end, or the air cap orifice.