Contamination control a key element in automobile painting integrity
Whether on the new-auto assembly line or in a retrofit shop, a paint booth requires contamination-control techniques and technologies that ensure a flawless, finished product.
by Patrick McLaughlin
The need to protect manufacturing processes from the harmful intrusion of particles goes beyond the oft-noted and much-publicized industries of semiconductor manufacturing and pharmaceutical development. While not every environment requires a cleanroom by the strict definition of the word, contamination control issues are nonetheless critical.
One such environment is an automobile painting facility. Whether on the new-auto assembly line or in a retrofit shop, a paint booth requires contamination-control techniques and technologies that ensure a flawless finished product.
CleanRooms magazine invited Duane McKinnon, president of Simplex Strip Doors (Fontana, Calif.; www.simplexstripdoors.com), to elaborate on this type of environment. Simplex provides soft-walled structures that are increasingly being deployed in paint booths.
CR: Please describe a typical automobile-painting set-up, in terms of the levels of contamination control at each step along the line.
DM: In most cases, the auto bodies or parts thereof will go through several steps before the painting process. Today, the bodies are dipped several times in solution to protect them from rust and corrosion. Once these steps are complete, it becomes important to ensure the parts are kept clean. One hazard that is particularly common in automobile factories is called "shakedown" from overhead structures and the factory roof. Dust and particles constantly are falling, and the automobile bodies must be protected from them. These environments also often have a lot of airborne mist from oils and welding operations, as well as the constant movement of robotics.
Typically, the production lines between the different processes will be covered, although there are no apparent standards or particular levels of cleanliness these manufacturers are trying to achieve. The most critical times in the paint process are immediately prior to priming, then after the priming and before entering the paint booths. The tunnels or enclosures used for protection at these points ideally will maintain a slight positive pressure, using either ASHRA or HEPA filters. A cleanliness level of Class 100,000 is more than adequate.
CR: How does a paint booth in a new-auto assembly line differ from an environment in which an existing automobile is getting a new paint job?
DM: As you might imagine, a body shop is a much less clean environment due to all the sanding and bodywork that is being done. The body shops try to keep the dirty areas secluded by using curtains. Once the vehicle is ready for painting, it will be moved to an area called the prep station, which will be an enclosure of some type that sits just in front of the paint booth. In this enclosure, the cars are masked and then wiped down using treated wipes that remove all the dust particles and oils from handprints. Then the car will be pushed into the paint booth. Typically, the car is wiped down again prior to painting. In an automated assembly plant, the automobiles generally are not touched again by anybody after they leave the priming area. Thus, it is important to keep the automobile or its parts clean before it enters the automated paint booth.
CR: What factors are most likely to determine the choice between a permanent and a temporary enclosure around a painting area?
DM: Because modern assembly lines must remain highly flexible and be able to adapt to the different vehicles and parts, the enclosures usually are a modular type. It is important to maintain quick access to the autos as they move down the production line. Workers also must be able to remove panels easily or gain access for maintenance. In these environments, we typically deploy our airlock modular enclosures. Because the frames are constructed of lightweight aluminum and use a compressing latch system, users can remove individual panels in minutes. This environment also calls for panels that are clear, providing a complete view of the line for both safety and quality. The walls in our airlock system can accept both soft vinyl inserts, and rigid hard panels of polycarbonate, ABS, or aluminum composite.
CR: What are the practical implications for an automobile that does not come through the painting process cleanly?
DM: We supplied tunnels and enclosures to a luxury-automobile plant that previously had an extremely high rejection rate. Each car that was rejected had to be hand-finished to repair the flawed area.
PATRICK McLAUGHLIN is a chief editor at PennWell ATD, Nashua, N.H. He can be reached at: firstname.lastname@example.org