The first fluidized bed powder coating machine used by the U.S. Navy was certified April 26 for use in the Southwest Regional Maintenance Center (SWRMC) corrosion control shop.

The machine improves the longevity of the primer and topcoat application while simultaneously reducing process cycle time compared to traditional methods.

"The real value of the new process is the quality of the application," said Terry Thompson, SWRMC corrosion control product family manager. "We estimate the coating will last 4-5 years compared to using traditional methods which typically last 1-2 years."

Application of primer and topcoat powder coating for watertight fixtures is fully automated by the fluidized bed powder coating machine. When a watertight fixture is ready for powder coating, it is attached to a hanging device outside of the machine. Once the operating area around the machine is free of personnel, the machine transfers the fixture into the first bed where it receives an encapsulating primer coating. The watertight fixture is then transferred to a second bed where a top coat of ultraviolet resistant powder coat is applied. After the process is complete, the fixture is placed back on the conveyor monorail where it can be manually moved to the curing oven and then inspected at the quality assurance station.

Traditional powder coating is applied in a powder coating booth using a line-of-sight spray-on method called electrostatic powder coating. Electrostatic powder coating often leaves hidden crevices exposed, which poses a risk of corrosion because oxidation can occur anywhere the metal is untreated. This proved to be an issue with exterior watertight doors because even the tiniest of exposed surfaces can result in major corrosion, which was occurring consistently in the rubber seal channel.

"What we are seeing with traditional methods is when an exterior watertight door is exposed to moisture all the time, the moisture builds up inside the lower half of the channel and begins eating it away," said Thompson. "Once it gets underneath the powder coating, doors are rotting away in the bottom half."

Combating corrosion issues like the watertight door channel are where Thompson believes the Navy will see the biggest advantage of the fluidized bed powder coating process.

"When the watertight fixture is completely encapsulated, we prevent moisture from reaching the areas where traditional powder coating guns cannot achieve proper coverage of the area and that is what is going to make the doors last longer," said Thompson. "All of those areas that were formerly exposed are now completely coated."

The application of the powder coating is more uniform than previous methods, yielding a more durable product. Uniformity and durability help reduce surface deterioration, adding to the oxidation fighting power.

Prior to SWRMC receiving the Fluidized bed powder coating system, the proof of concept was tested on DDG louvers for several years. DDG louvers are used on Navy ships to prevent debris from entering the gas turbine air intake system. They have several voids that are difficult to powder coat completely when using the electrostatic method. Traditional coatings resulted in having to recoat the louvers every two years.

"The Navy now sends all DDG louvers to Automatic Coatings Limited (ACL) in Canada" said Thompson. "Once coated using their fluidized bed powder coating machine, the louvers are shipped back to the U.S. to be reinstalled on the ship. Those same louvers are now lasting 9-15 years."

The fluidized bed powder coating machine installed at SWRMC is much smaller than the machine at ACL, and is intended for watertight doors, scuttles and hatches. Due to their massive size, DDG louvers will continue to receive powder coating at ACL, which houses a much larger machine to do the job.

Not only does the fluidized bed powder coating process save time and improve quality, it helps improve safety onboard the ship. Watertight fixtures such as doors, scuttles and hatches are critical to preventing water intrusion onboard the ship. These fixtures also ensure containment in the event of a fire.

As the corrosion control center of excellence, SWRMC was chosen to receive the first fluidized bed powder coating machine. With over 23,000 watertight doors and thousands of additional fixtures, there is no shortage of customers pier side in San Diego.

"Corrosion control is a 24/7 job, 365 days a year," said Thompson. "Rust never rests."

SWRMC's mission is to provide superior ship maintenance, modernization, technical support, and training for the Pacific Fleet.

For more information about SWRMC visit our website at www.swrmc.navy.mil/index.html

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