Special Delivery

Article From: Products Finishing, ,

Posted on: 6/1/2009

Finishing of large diesel engines benefits from paint system improvements

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Completed diesel engine

Completed diesel engine receives final inspection and fitting out before being prepared for shipment

New paint pumps

New paint pumps operate with extremely low pulsation in material flow, which allows for consistent paint viscosity and atomization and improved quality.

Revamped paint delivery system

Revamped paint delivery system requires minimal involvement from engineers or paint line operators.

Painting for military and defense applications involves a lot more than just chemical agent resistant coatings (CARCs).

Case in point: Cummins Inc.’s Seymour, IN, plant, where they use only waterborne coating materials to paint large diesel engines used in military and other applications. When plant engineers realized that engine finishing was a production bottleneck, they took a hard look at their paint process and focused targeted improvements in the paint delivery system and paint room.

Opened in 1976, the 381,000- ft2 Seymour plant produces 19-L inline 6, 30-L V-12 and 14.8-L V-8 diesel engines on three assembly lines. Applications for the diesels, which produce from 500–1,500 hp, include construction, mining, rail/locomotive, power generation and marine propulsion in addition to military vehicles.

The company is certainly no slouch in military power applications: Cummins diesel engines currently power roughly 30,000 military vehicles worldwide, and the approximately 600 employees at the Seymour plant built every engine used in U.S. Army Bradley fighting vehicles deployed in Iraq during operations Desert Shield and Desert Storm.

The plant can turn out 15 of the 19-L engines and 10, 30-L engines per shift. Seymour produces engines from start to finish, from machining of engine block and other components to tube fabrication and assembly. Completed engines contain cast iron, cast aluminum and steel components. All engines are hot-tested after assembly, and all run through a single paint line for finishing.

Paint line capacity is 15 engines per shift, and a recent reduction from two shifts to one on the paint line has created some production issues, according to manufacturing engineer Dan Wiederholt. “We went to a single shift on the paint line, but we were also being hindered by frequent problems with paint delivery and other issues,” he explains.

Paint Process

After hot testing, engines are hung on hoists that travel on a monorail through an upfit line, then to the plant’s paint system, which includes pretreatment, paint and curing, Wiederholt says. After paint and final fitting, engines are tagged, inspected and prepared for shipping.

“In upfit, parts that do not have to be on the engine for testing, such as air cleaners, exhaust connections, special engine supports and so on are added,” Wiederholt explains. “The next step is pretreatment, which consists of a three-stage washer that we recently switched to a zirconium-based, non-phosphate chemistry.”

Stage 1 of the pretreatment process consists of a cleaner and the zirconium-based pretreatment chemical. Stage 2 is a chemical-free rinse, and Stage 3 applies a zirconium-based sealer.

After a quick blow-off, engines are masked and sent to the paint line for a water-based prime coat. “The line cycles every 24 min, so an engine is in the primer booth for 24 min. The engine then sits between the primer booth and paint booth for a cycle to allow the primer to dry before receiving its top coat,” Wiederholt explains.

Both primer and top coat are applied by hand using HVLP spray equipment. Finish coats are one of four main colors or seven secondary colors. “Back to back engines taking the same color are rare,” Wiederholt says.

Completed engines are cured for one cycle in a dryer at 145°F, and a second cycle in an unheated dryer completes curing. Finally, additional parts such as belt guards, exhaust shields and air intake connections are added to the engines along with stickers, decals, and data plates. Masking is removed, and engines are ready for final inspection and shipping.

Paint Delivery Issues

Several factors were complicating efficient finishing of the plant’s products. For one thing, the plant layout featured two paint booths on the line and one off-line booth for touch-ups and smaller components. “The biggest problem with that is that the main paint booths are about 250 ft from the mix room,” Wiederholt explains. “At one time, the paint booths were actually right next to the mix room. The booths were moved, but the paint mix room never was.

“This required pumps that could provide consistent pressure to properly feed the paint through relatively long paint lines and recirculate the paint back to the paint room,” he continues. “It also made problem-solving difficult, because you could work on something on one end of the system and have to wait for a response from the other end. We just had constant issues with paint delivery.”

Unfortunately, paint pumps in use at Seymour were anything but consistent. The plant’s hydraulic paint supply system was in bad shape, and there were constant problems with the pumps. “It became apparent that a paint delivery system upgrade was necessary for numerous reasons,” Wiederholt explains. “The old equipment, originally installed in the 1970s, was worn out, rebuilds were becoming less effective and some parts were not even available any more.”

As a result, he says, the old equipment was not able to maintain consistent pressure in the paint lines or to properly recirculate paint through lines. The leaky hydraulic system also posed a safety and environmental threat and required constant attention, Wiederholt adds. “And, we wanted an upgrade that required less user involvement to minimize time operators spent attending to the paint system.”

Paint Delivery Improvements

Seymour’s paint delivery system came in for multiple upgrades that, taken together, made a big difference in finishing productivity and quality.

Replacing the plant’s worn-out hydraulic paint pumps were Puma piston pumps supplied by Wagner Industrial Solutions (Elgin, IL). The wall-mounted units use a vertical reciprocating piston capable of consistently delivering nearly 20 gal/min of paint material. The pumps are specifically designed to operate with extremely low pulsation in material flow, which allows for consistent paint atomization and improved quality.

Also in the new paint delivery system, patented agitators provide good mixing at lower speeds and reduced air consumption than the previous hydraulic and air-powered agitators. Instead of drawing paint directly from 55-gal drums as the previous system had, the new system draws paint from custom bottom-outlet stainless steel mix tanks that eliminate pumping of air into the circulation piping.

This eliminated quality issues resulting from air intake and allowed more uniform agitation and viscosity control. “Once in the system, air was difficult to bleed off and caused downtime, paint defects, and other issues,” Wiederholt explains.

Pneumatic level control systems from Wagner distributor FinishLine Technologies (Columbus, IN) and Wagner double-diaphragm pumps automatically keep the 30-gal mix tanks topped off and prevent any air from entering the new circulation system. The “hands-free” filling system allows Cummins paint line operators to forget about monitoring and replenishing paint levels, allowing them to concentrate on more productive activities.

The plant’s four main colors are supplied to the top coat booth from the new paint room equipment. “Switching between those colors is as easy as picking up a different gun,” Wiederholt says.

Secondary colors are still painted using pressure pots. “For those, color changes take more time, because paint has to be poured, mixed, poured into the pot and plugged into air. And the pot has to be cleaned after each use,” he adds.

Paint mix room layout was also completely revamped to allow easy access to all system components. As a result of the upgrades, the mix room now operates virtually unattended on a daily basis. An engineer who formerly spent a large chunk of his time dealing with paint room issues is now free to work on other projects and only needs to check the mix room periodically to verify that everything is working as designed.

Design and installation of the automatic paint level control system, as well as integration and installation of the other new paint room equipment, were handled by FinishLine Technologies. The project was completed over a single three-day holiday weekend.

In addition to the finishing process operating improvements, paint quality also improved in multiple ways. The old pumps were unable to circulate paint at the correct velocity, resulting in material separating in the lines. Because the new system paint circulates paint correctly, quality has significantly improved. “We really do not have anything to quantify the quality improvements,” Wiederholt says. “But inspectors noticed right away that the painted engines looked better.

“The painter is most responsible for coverage, because everything is painted by hand. However, with the new equipment we are assured that the painter is reliable receiving a consistent flow of paint to the gun,” he concludes.

 


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