- 08 June 2006 -
Spray Gun Cleaning Made Easy
By Barry Thomas, President, BECCA Inc., Kennesaw, Ga.

Most operations that spray liquid coating on their products require the spray gun apparatus to be cleaned. Historically, cleaning was done manually over a 55-gallon drum.

The result was evaporation of solvents into the environment and generation of excessive hazardous wastes. The environment and businesses paid a high cost. The environment has been potentially damaged by these pollutants. Businesses have had large expenses and, worryingly, many workers have been exposed to toxins.

If spray guns are not properly maintained, however, the result is poorly painted products, which may need to be repainted, costing extra work on the unit and lost production. Today's production environment requires first through quality while continually improving the speed of every process, including painting and quality of spray guns. New spray gun cleaning systems are available to improve on the quality, results, speed, cost, and liability of an operation. Below is a review of these systems.

Figure 1: Automatic gun cleaner.

Cleaning Methods
Enclosed automatic paint gun washers: This process involves an enclosure with a manifold of multiple spray nozzles spraying the outside of a spray gun, while another nozzle directs a flow of solvent through the fluid passageway of the gun (see Figure 1). A clip holds the spray gun trigger in its compressed state, allowing the flow of the cleaning fluid all the way through the gun, and exiting through the fluid tip.

Some designs provide the ability to use previously used solvents to pre-clean the gun and clean solvents to rinse the gun. Such a method minimizes solvent use in the overall process.

A system also exists to protect the air passageway from solvents and residues, and to protect seals on the air passage side of the spray guns.

Enclosed automatic paint gun cleaners are the best way to reduce evaporation and protect workers from exposure to toxins. When it comes to cleaning a spray gun to a level needed by a technician, enclosed automatic paint gun cleaners have proven average.

Figure 2: Manual gun cleaning

Manual paint gun washers: This process typically involves a flow brush with stiff bristles and a flow of solvent to remove paint residues from the spray gun (see Figure 2). Some systems also include a spigot or shower flow to manually rinse off the remaining residue. This is the simplest system for cleaning a spray gun.

Solvents are exposed more within this design, meaning there is more evaporation and greater potential for workers to be exposed to toxins. When it comes to cleaning, however, manual paint gun washers can clean guns more effectively than enclosed automatic cleaners. Some designs provide the ability to use previously used solvents to pre-clean, and clean solvents to rinse. This process minimizes solvent use by up to 50%.

Manual cleaning: This is where an operator manually cleans the spray gun, using two 55-gallon drums. Clean solvent is in one drum while waste goes into the other drum. The operator manually removes the residue by using a flow of solvent from a hand pump or a cup with brushes.

In paint operations today, manual cleaning is still the most common way to clean spray guns. The downside of this method is two-fold: a large loss of solvent to evaporation and workers whose health may be compromised due to maximum exposure to toxins. Most operations have relied on this process to clean their spray guns.

Many operations found that early versions of automatic spray gun cleaners did not properly clean their spray guns. In response, these organizations switched back to the manual method for more satisfactory results.

Figure 3: Solvent filter in manual gun cleaner.

Cleaning workstations: These paint gun washers combine manual and enclosed automatic processes to provide the best results in cleaning capability—exactly what technicians want and require. Spray guns are cleaned with superior results, and both the environment and operators are exposed to less solvent vapor. Workstations include larger working areas and multiple cleaning capabilities, including the ability to clean with used solvent and rinse with clean solvent.
Workstations have automatic, manual, and spray out features. These systems give operations and their operators all the cleaning capabilities in one large workstation area—a huge advancement when it comes to cleaning spray guns.

Pressure pot and fluid line cleaning systems: Pressure pots can be hooked up to spray gun cleaners. Pressure pot cleaner systems were designed to handle the cleaning of the pressurized pot and fluid lines typically found in large or high production operations. Some systems pre-clean and rinse through the fluid line, while turbulent compressed air is added, providing the turbo cleaning effect.

The compressed air can then dry the lines. Two methods of cleaning are available: a quick clean, spraying out through the spray gun, or a detailed clean, using the closed loop system. This process, too, utilizes used solvent for pre-cleaning, cleaning solvent for rinsing, and compressed air for purging any remaining solvent.

Other considerations: Size of solvent containers—your container size should correspond to the number of people cleaning spray guns. For instance, in an operation in which four or five people use the same spray gun cleaner, it is advisable to have a 10- gallon tank rather than a five-gallon tank. Cans, tanks, and drums hold anywhere from five to 55 gallons of solvent.

• Cover doors: Certain states require that a gun cleaner, when not in use, has a cover door closing all opening areas.
• Carbon absorption: Carbon absorption will absorb the volatiles that vent to the exhaust from a gun cleaner and capture them until breakthrough occurs. When the carbon is saturated, it will need to be regenerated off-site, or it can be disposed of as hazardous waste. Such filters can usually be retrofitted to a gun cleaner and for a large unit, the filter can cost up to $1,000.
• Protective coatings: You can cover equipment with a clear film coating known as "Protect Film" (www.beccainc.com) that protects the cleanliness and aesthetics of the equipment, and can be peeled off.

Alternative solutions: For the last three to four years, plastic cup systems for gravity feed spray guns have been widely used, especially in North American body shops. These disposable cups hold and spray the paint. When painting is finished, so are the cups.

Once there is no further use for the paint left inside the cup, the cup is thrown into the regular garbage as opposed to the correct location—hazardous waste. The cups are popular because of their price and convenience (although many operations spend $700 to $1,000 per month on these containers). Because they are disposable, the cups do not need to be cleaned—a bonus for painters. They should be placed in the solid hazardous waste container (they are considered hazardous waste per RCRA until proven different).

Common misconception holds that the paint left within the cup dries and then the cup can be thrown into the regular trash. Actually, the paint remaining within these cups is flammable. In short, our landfills now contain millions of seemingly harmless cups, all of which constitute hazardous waste, as specified by national requirements on the subject.

Spray Gun Cleaners Combined (COMBO) with Solvent Recycling
Today's environment requires operations to consider all aspects of the spray gun cleaning process, including the waste generated. Many operations look at how they can reduce both the cost and liability of this process. There are COMBO systems that include the direct connection, creating a closed loop operation of the spray gun cleaner and a waste solvent recycler.

Distillation: This is a form of recycling that heats solvents or wastes. The heat creates a vapor, which condenses. It leaves behind waste paint residue and captures good, clean solvents. These solvents are reused again in the cleaning process.

Filtration: Filtration is another form of recycling, in which solid wastes are filtered out. Using filtration, you can filter to 25 microns (about the size of a red blood cell.) This means you can clean effectively, although less effectively than with distillation.

Existing in the waste solvent are substances such as pigments, which are less than 25 microns in size. The filtered solvent will be colored but will effectively clean a spray gun. Filtration units cost less than distillation units. In many cases, the filters can be retrofitted to older solvent cleaning units. Filtration units typically cost about $1,500, while small distillation units for an average size gun washer sell for about $5,000.

For example, the author has experienced a case in which one painter was cleaning his spray gun three to four times per day and the filter life was five to six months. In another case, four painters were cleaning their guns three to four times per day and the filters lasted more than three months.

The use of such filters can easily be demonstrated to be cost effective.

Solvents: There are public health and environmental concerns with cleaning solvents—many operations use paint thinners or exempt solvents that have not been regulated to clean spray guns. Shop practices include the following: using solvents in an enclosed automatic gun washer; manually cleaning guns using solvents; or using a combination of manual and automatic cleaning. One can get manual cleaning stations that vent vapors outside, thereby reducing worker exposure to solvent vapors.

• Most solvents used for gun cleaning are VOCs that evaporate quickly when exposed to the atmosphere. Because it is difficult to control vapor emissions from these solvents, workers using such solvents significantly risk their health and safety.
• Exempt solvents, which do not contribute to smog formation, are generally not regulated. These exempt solvents can, however, be volatile and may compromise workers’ health if proper protection is not used.
• Spent thinner and exempt solvents are hazardous wastes due to their flammability and toxic characteristics. The shop owner is responsible for proper management of all hazardous waste.