Purchasers of the new Mercedes M-Class SUV (sport utility vehicle) will love the trendy, soft-touch paint on the instrument panels and consoles, but they’ll have no idea of the amount of ingenuity that went into the application’s quality control.

Setting the Stage

The foundation of the tactile coating used by injected plastics molding/assembler Arkay Industries (Miamisburg, OH) at its Arkay Plastics plant (Prattville, AL) is a special two-part application of water-soluble paint compounds that produces a soft-touch finish. However, the formula’s application, color accuracy, and curing success depends on precise environmental conditions of 55% relative humidity (RH) and 75°F temperature in the twin 1,200-sq-ft paint booths.

“It’s temperature and humidity control in the application process that decides between a product that’s of the utmost quality and one that is less than acceptable and (has to be) produced again,” said Tim Henion, Mercedes model year 2000 program manager of Arkay Plastics. Arkay is a tier-two injection molding producer/assembler for tier-one supplier Delphi Automotive Interior Lighting Systems (Vandalia, OH).

To maintain tight humidity and temperature tolerances of 5% or less, Arkay created a design-build team led by mechanical contractor, Capital Refrigeration (Montgomery, AL); engineers from hvac manufacturer Dectron Internationale (Roswell, GA); manufacturer’s representative Derek Brown, president of Air Dynamics (Birmingham, AL); and consultants from Alabama Power Co.—A Southern Company (Birmingham, AL).

Closing the Door on Opening Problems

The production line of instrument panels, consoles, and various components are sprayed with the two-part paint process as they perpetually convey through separate 3- by 8-ft entrance and exit openings. It’s these openings, which could either potentially introduce contaminated air from the surrounding 50,000-sq-ft factory production floor and/or from the flash tunnels and infrared ovens further down line, that complicate the hvac design process.

While Arkay designed the application equipment for the booths, the hvac system was designed by Brown and Bonner Patrick, P.E., president of Capital Refrigeration. The key equipment for hvac is Dectron’s Dry-O-Tron® Series Model DK-450 — a series typically used in office buildings, hotels, and other structures requiring indoor air quality. The DK-450, which is really two separate systems packaged in one unit, has a capacity of 150 RT, 28,800 cfm, and 440 lb/hr of moisture removal. It is designed to introduce 100% outside air, which is dehumidified and cooled in the summer and heated in the winter months.

During Alabama’s seasonably dry winter season, a Nortec Industries (Ogdensburg, NY) humidifier that is custom-installed in the Dry-O-Tron® at the factory raises the humidity when needed.

While paint booth hvac might seem like a once-in-a-lifetime project for a contractor, Capital has designed and engineered several paint booths for other manufacturers such as Lockheed Martin. However, unlike past projects where Capital has combined different components to accomplish the hvac task, Dectron supplied Capital Refrigeration with a complete package where all components and options were factory installed and pre-tested.

“We’ve done plenty of paint booths in the past, but this is the most impressive because of the sophistication and high quality from the coils on down to the doors and control systems,” said Patrick, whose firm recently merged its $12 million full line mechanical contracting operation with hvac conglomerate, Comfort Systems USA (Houston).

A Coat of Success

So far, there have been minimal scraps and remakes, thanks to the hvac system’s engineering. Henion said the new dual paint booths, which cost approximately $250,000 to create, are state-of-the-art and totally unique for Arkay and for the rest of the industry as well. Few other applicators of the soft-touch paint, which is made by Red Spot Paint & Varnish Co. (Evansville, IN) control humidity and temperature so accurately.

Capital and Henion did have challenges with airflow within the booth, however. Ongoing daily statistical studies will determine someday whether automated damper systems, which are monitored by airflow sensors, will be needed to maintain the engineered target velocity of 150 ft/min. Presently, airflow is accomplished manually with one inlet and one relief damper installed in each booth’s supply duct. Regulating the current damper openings for greatest airflow efficiency was accomplished through testing/balancing metering.

Consequently, the booths presently are maintaining a positive pressure and excess air is relieved (via the relief dampers) into the factory, which improves the general IAQ of the surrounding open paint areas. The implementation of this paint process has been an engineering success, according to Henion, and it will undoubtedly impress future owners of the Mercedes 2000 SUV. ES