Cleaning, regular testing and maintenance are keys to keeping spray booths running smoothly.
Not too many years ago, a spray booth was considered a luxury in the collision repair industry. Today, many believe that without an efficiently operating spray booth, collision repair businesses would not refinish enough vehicles to be profitable.
Ask almost any painter why the shop has a spray booth and he'll tell you the reasons: for fast curing and a clean environment to refinish their customer's vehicles. Spray booths were first introduced, though, mainly to protect workers from harmful fumes outside the booth. Especially during the early days of collision repair, vehicles were sprayed in open areas where they were repaired, or at best moved to a designated spray area to be refinished.The technician who was spraying the vehicle may have used a respirator but others in the shop did not. Dust, fumes and danger of explosive accidents were ever-present, and many technicians suffered from diseases brought on by years of breathing paint fumes in these environments.
Today, in many areas of the country, shops that paint are required by law to have paint booths. Shops also have discovered that a properly operating spray booth will speed up the refinishing process to where six to 10 paint jobs can be done in a normal day.
Here's what to expect from a properly operating spray booth: safety, a clean environment, temperature control, fire and explosion protection, color match and production speed.
How does a spray booth work? That depends on how sophisticated its design is. Booths can be either a water filtration or dry type, but most are dry filtration. The more simple ones will filter the air coming into the booth from the outside and filter it again before the air goes out to the atmosphere.
More sophisticated booths might filter air four times — before it is heated, before it passes into the booth, as it leaves the booth and before it is discharged into the atmosphere. Even with booths that filter the air multiple times, what is taken out is the particulate matter or what are known as hazardous air pollutants, not the solvent vapors that contain volatile organic compounds (VOCs).What makes spray booths safe is that all the hazards, both hazardous air pollutants (HAPs) and volatile organic compounds (VOCs), are contained and either filtered out or directed away from the work environment. That containment keeps highly flammable vapors in an area that is free from sparks and other potential ignition sources.
Booths also protect the spray environment from dirt that could contaminate the finish. Sanding dust from the shop, outside dirt from agricultural and manufacturing activities, and other airborne contaminants can be filtered out before they reach the spray area. Most modern booths can be balanced, keeping the airflow into the booth at a slightly greater pressure than the air flowing out, thus keeping contaminants in the air outside the spray area.
Booths equipped with heating units both control the spray temperature and can raise the temperature during the cure cycle to speed up catalyzation, reducing dry time. Lastly, booths provide a brightly lit work area for spraying. When equipped with color-corrected lights, booths also can aid with evaluating the correct color match.
So how does a paint technician know that everything is working at its best to accomplish these tasks?
A shop's spray booth might be a cross-draft booth, a downdraft booth, or semi-downdraft type. In a cross-draft booth, air is brought in from one end and exhausted out the other. It operates to direct airflow along the length of the booth.
In a downdraft booth, air is brought in from the top of the booth and flows down over the vehicle, creating an envelope of air around the vehicle, while in a semi-downdraft booth air is often brought in from one end of the ceiling, drawn down over the vehicle, and then exhausted out from the lower part of the other end of the booth. A downdraft booth, with its envelope of airflow, is generally the more efficient and preferred type of booth.Booths require regular maintenance to operate at their peak. Procedures include balancing, cleaning, temperature checking, filter changing, airflow check and light maintenance. Each day when a painter starts the booth, the temperature setting should be verified. There may be as many as three settings to check: spray temperature, purge and baking.
Balancing
A booth equipped with two air flow systems, as most downdraft booths are, has a fan that brings air in from the outside and forces it through filters, then into the booth. A second fan system draws the air in the booth through more filters, then out.
A properly balanced booth will maintain slightly greater pressure being forced into the booth than is being sucked out; this is called positive airflow. With positive airflow present, the booth does not have a vacuum that draws air into the booth. However, if the booth is not balanced and a negative airflow is present, outside air will be sucked into the booth along with contaminants.
Most booths are equipped with a magnehelic gauge that will measure the level of vacuum in the booth. If that level is not slightly positive, it can be adjusted to achieve the proper positive flow. Booths that can no longer be adjusted often are in need of filter changing, and though this should not be the only indicator for filter changing, it is certainly an indication that a booth is not operating properly.
Cleaning
Booths by their nature become dirty, and the floors, walls, and lights must be cleaned regularly. Vacuuming is the best way to clean floors. If vacuuming is not available, they should be swept with a fine bristle broom. The walls should be blown off, then tacked to eliminate dust, with the booth closed and running as it is being cleaned so the dust that is dislodged will be drawn into the filter system and not just re-deposited on another part of the booth.
Lights need to be cleaned to maintain proper color correction and brightness. After a booth is thoroughly cleaned, to maintain cleanliness, some technicians cover the floor with paper that can be changed as needed. Many technicians keep the booth fan running whenever someone is in the booth, and the doors closed at all times except for moving vehicles into or out of it, also to maintain cleanliness. Painters often keep everyone out of the booth if not properly clean themselves.
Temperature check
There may be from one to as many as three temperatures that a booth will control. Spray temperature, the temperature at which a booth is maintained while the coating is being applied, is quoted by most paint recommendations at 68 to 70 degrees Fahrenheit. However, most painters keep booths between 70 and 80 degrees, depending on season and humidity.
Remember that the booth is measuring air temperature, not the surface temperature of the vehicle in the booth, which could be significantly different. If a vehicle is moved from a cold area to a booth that is 80 degrees Fahrenheit, it will take several minutes for the vehicle to warm to 80 degrees. So if the booth temperature reading is the measurement of the air, not the vehicle, and it takes time for the surface of the vehicle to match the booth air, how can the true temperature of the vehicle be known?
The surface temperature of the vehicle should be monitored with a non-contact thermometer and then the booth air should be adjusted. For the surface temperature to get to 140 degrees, for example, the booth air temperature may need to be at 150 degrees. Once the difference is known, the booth temperature can be adjusted to achieve the desired result.
Filter change
Filters should be changed as often as needed to maintain the needed airflow and balance of the booth. Some filters must be changed more often than others. In booths that are equipped with a four-stage filtering system, there are pre-filters to clean the incoming air, and ceiling filters that filter air before it enters the booth. There also are floor filters that trap the particles as the air leaves the booth. Lastly, exhaust filters trap any remaining particles before the air is vented out the exhaust stacks.
Floor filters are generally changed the most often, because they filter air that contains overspray from the booth. As the floor filter becomes clogged, it requires more pressure from the fans to remove air from the booth, and the pressure differential change causes the booth to go out of balance. Paint technicians should check the balance before each paint job and adjust it as needed. When the booth can no longer be adjusted to maintain balance, filters must be changed.
If the booth will not balance after the floor filters have been changed, that indicates that others filters may be filled and also require changing. The exhaust filters should be checked next, then the intake filters, and the ceiling filters last.
Airflow
A velometer is used to measure the cubic feet per minute of airflow in a booth. Airflow will change depending on what is in the booth; the fuller the booth is, the higher the airflow. With a full-size vehicle in a booth the airflow will be at its highest, while with just parts in a booth the airflow will be lower.
Airflow should be checked at different spots within the booth and with the booth both loaded and unloaded, to check that the flow is even throughout the booth. One of the best ways to monitor airflow is with a smoke generator. Smoke should be generated at different spots in a booth then watched as it flows into the exhaust fans to assure that the airflow in a booth is even throughout.
Airflow evenness can be altered by what is in the booth and how a vehicle is placed. If the paint technician knows the normal air flow, he can place the object in a position to maximize the booth's airflow.
Light maintenance
Maintaining correct lighting in a booth is difficult and often poorly understood. Light needs to be monitored in two different areas. The first area is the brightness, or lumens, which needs to be maintained at 5-10K footcandles. The second area is the color rendering index (CRI), which to provide proper color-corrected light must be maintained at 85 percent to 92 percent.
What makes this difficult is that both of these parameters may deteriorate without light tubes going out. Lights will often need to be changed even though they appear to be in good working condition. Testing both the candlepower and color-rendering index regularly is necessary to determine when lights should be changed to maintain ideal conditions.
Testing equipment
Though most booths come equipped with a magnehelic gauge, many other booth-testing devices do not come with the booth. A non-contact thermometer is not expensive, and a technician would use it often enough to justify owning one. Other equipment, such as smoke generators, velometers and light meters, can be expensive. They are also only used on occasion, and most shops, unless very large with multiple booths, may not need to own them. Most paint booth suppliers either have them or can get them, though, to test equipment when they are needed.
Booths allow painters to work better, faster and cleaner, and to increase profitability if they are operating at peak efficiency. When spray booths are operating poorly, they can complicate the painting process, which can be a difficult and complex set of tasks. Cleaning, regular testing and maintenance (especially lighting, the condition of which cannot be seen with the naked eye), of shop paint booths can keep them operating at their optimum performance.
