Management at Freightliner’s Truck Manufacturing Plant in Portland, Oregon, decided to reconfigure its entire chassis production line, which included relocating its paint operation. In late 1994, space was assigned for new booths an ovens where chassis would be cleaned, topcoated and cured. By the end of 1995, the entire paint system was up and running, totally integrated into the chassis assembly line.

At the time of the project, the plant was operating three shifts a day, five days a week. At freightliner’s request, Portland-based systems integrator Ken R. Humke co. took on the task of designing a turnkey paint system that could be installed without stopping normal production at the plant. To do so, Humke had to complete all the major on-site work during weekend and holiday shutdowns, including the fourth of July, Labor Day, Thanksgiving and even Christmas.

Tom Gertz, Freightliner’s senior manufacturing engineer and project manager for this system, says the installation “definitely a challenge.” Accomplishing such a major changeover without shutting down the facility was a tribute to everyone involved. The company is pleased with the production efficiencies of the new paint line and the improved quality of finish, he adds.

Todd Elmer, vice president of Humke, attributes the success to the teamwork of everyone involved. “We worked closely with Freightliner, with JBI, the manufacturer of the paint booths and cure ovens, and with the other suppliers. Suring the final phase of installation and debug, there were about 110 people in the plant every day – all committed to completing the system in those nine days. And it happened.”

Side-by-side operations

Approximately 100 trucks are produced during a three-shift day at the plant. Prior to the changeover, Freightliner had a single line for chassis assembly and finishing. It started at one end of the plant and stopped at the other. When chassis production was rearrange, two floor conveyor lines were installed to take parts through the new paint line, where parallel work areas provide two complete systems.

The dimensions of the chassis are 8 feet wide, from 17 to 40 feet ling, and 10 feet high at the tallest point. The first section of the paint line is comprised of two 20-foot-long wash/rinse booths, side by side. Two 35-foot-loong dry-off ovens are next, followed by two down-draft spray booths measuring 75 feet long. The chassis go from the paint booths into 50-foot cure ovens, and then into cool-down booths that re 15 feet long. Construction of the booths and ovens features 6-inch steel I-beams and 16-gauge steel panels. From beginning to end, the paint line measures 214 feet, including spaces between booths and ovens. It is 40 feet wide and 20 feet high.

This “double-wide” approach allows Freightliner to run two lines at once, each with different models or different colors. The company can also run just one line when two aren’t needed. The two are attached, but a common wall down the center separates them.

Jervis B. Webb Co. (Farmington Hills, MI) built the floor conveyors that tow the chassis on steel dollies through the two paint lines at an average speed of 2 feet per minute. The chassis continue to move down two lines after cool down for truck hose routing and engine hang operations. The two conveyor lines then merge back into one before cabs are hung on the chassis. Jervis B. Webb also built the transfer conveyor that accomplishes the merge.

Prior to entering the paint tunnels, a chassis begins its life as frame rails. During prepaint assembly, cross members, brackets, air tanks, front and rear axles, suspensions and drive lines are attached as the conveyor pulls the chassis along. At this point, the chassis have grease, dirt and other contaminants on them.

So into a wash/rinse booth they go for a 10-minute cycle. Two operators use high-pressure, heated wash systems manufactured by the Hotsy Corp. (Englewood, CO) to spray the parts with a mild alkaline cleaner. A thorough water rinse follows. This procedure represents and important change at the plant. Previously, cleaning had been accomplished by a solvent spray that produced VOC emissions.

The conveyor then moves the chassis into the 190°F dry-off oven. Because water can easily collect in the chassis’ channels and cavities, getting them dried thoroughly is essential. Gertz reports that the system design includes manual air nozzles to blow off excess water, but Freightliner has not had to use them. He says another concern was that the dried-off chassis would be too hot to paint as they exit the oven and enter the spray booth. JBI customized the dry-off oven specifically for this installation; its 17-minute cycle, combined with complex air changes, provides the needed cooling.

Down-draft spray booths

After dry-off, the truck chassis are ready to receive their topcoat. Two painters in each spray booth, on each side of the conveyor track, are equipped with a JGA spray gun, supplied by ITW DeVilbiss (Maumee, OH). As the chassis moves through the booth, the workers apply a topcoat. For standard products, this is black, water-reducible enamel with 2.0 pounds per gallon VOC made by Akron Paint and Varnish (Akron, OH). When the customer has specified a color, the painters use Imron 5000, a solventborne urethane manufactured by DuPont Automotive (Troy, MI). It has a slightly higher gloss than the standard black coat. In both cases, cycle time in the paint booth is typically 35 minutes.

Humke’s Elmer explains how this project differed from others his company has done: “Normally we design and construct the pit for the paint booth. In this case, Freightliner gave us a drawing of the existing pit and said it needed to e utilized for the booth. Although conditions were not ideal, we worked together with JBI to engineer the system so that the pit draws air well and everything works right”

Gertz concurs. “The biggest challenge with the spray booth was air flow. Routing and ducting the system within the space available was quite tricky. Sizing he booths to give the operators enough room for spraying was also important. And working around existing electrical and gas lines also presented a challenge.”

Four air makeup units manufactured by Rupp Industries (Burnsville, MN) are mounted on the plant’s roof. Fresh, conditioned air is brought into the booth through the roof; it travels past the painters and chassis down through the booth’s floor, which is made of grating. The pit underneath the booth houses paint-collection filters and the exhaust ductwork.

As air flow through the booth, taking the overspray with it, paint particles re collected bye the filters, which are changed daily. The system has variable-frequency drives and controls that adjust the air flow to the paint booth as filters accumulate overspray during the day. Each both is kept in balance so that no shop air is being pulled into the booth from the building, nor is contaminated air being sent from the booth into the plant.

When the chassis exit the spray booth, they are moved into the 200°F cure oven. The typical cycle time is 25 minutes. After the topcoat has been cured, the conveyor moves the chassis into the last section of the paint line, a cool-down booth. High-velocity, 65°F air is routed through this enclosure to return the chassis to touchable temperatures. Paint is set, and there is no tackiness, so workers can resume assembly operations. They begin attaching the chassis’ hoses during cool-down.

The old assembly line was arranged so that all truck air hoses were already attached to the chassis before it went into the paint booth. And although the hoses were different colors initially, when the chassis came out of the paint booth the hoses were all painted the same. This made it difficult later to trace back mechanical, component or air problems through those lines. Now, with the hoses being attached after chassis are painted, they keep their designated colors, which facilitates tracing line problems.

The new paint line has accomplished every objective Freightliner set when it determined that redesign was needed. Truck chassis move through each of the five stages smoothly, receiving excellent pretreatment, dry-off, topcoating, cure and cool-down. Air quality in the plant is healthy, space is being used efficiently, and production continues uninterrupted.