Reprinted from Industrial Paint and Powder, January, 1998

DESIGNING A FLAW-FREE FINISHING LINE

By Claire Craig, Assistant Editor

Some OEMs are reluctant to outsource the coating operation, fearing they will lose control of the finish quality. Bill Andro, general manager of the Kentwood Powder Coat (Grand Rapids, MI), is proud to say his job specializes in “fussy” work from customers who consistently demand a cosmetically perfect, zero-defect finish. With the help of a new, multi- million dollar powder coating line opened in August 1996, Kentwood has been able to satisfy the fussiest among them with nearly flaw-free finishes.

Kentwood’s customers include companies such as Moen, General Electric, Whirlpool, and Amana.

Brass forgings, zinc and aluminum die castings, and aluminum extrusions comprise much of its business.

Kentwood saw its “fussy” finishing business growing long before opening the doors to the new facility. “We knew that if we built another line and really went after higher quality, we could do better,” Andro says. “It’s working out pretty well.”

Improving quality is at the heart of Kentwood’s philosophy, and it showed in the planning stages of the 31,000-square-foot expansion that doubled production capacity. Both Andro and plant manager Gerald Eddington had been through several major line installations before. Together with the help of Rodger Talbert, an industrial finishing consultant based in Grand Rapids, MI, they reviewed every aspect of the new line for quality and efficiency. “A lot of skill and technology was involved in the planning, which minimized the errors,” Andro says.

After the order was placed with turnkey installer Belco Industries (Belding, MI), Kentwood held weekly meetings with Talbert and all project contractors to maintain tight control and keep the project on course. Belco designed and built the permanent system, dry-off oven, conveyor, and convection oven.

The new addition, Kentwood II, is dedicated to white powder application, the most challenging finish Kentwood applies. The 7 foot-per-minute line uses an Allen-Bradley (Milwaukee) PC-based programmable logic controller (PLC) that monitors adjustments in detail, providing lot traceability for every part Kentwood finishes. “It gives us a good control record of what happens, so we can go back and look at these records to ask which process works the best for certain parts,” Andro says.

The steel pretreatment washer is the first stage of the line and incorporates the following seven steps, with all pretreatment chemicals supplied by BetzDearbon (Horsham, PA):

The design team considered a number of issues surrounding the best way to configure the new washer. They decided on mild steel as opposed to stainless steel for all washer tanks except stage seven. Not only is it less expensive, but experience has shown them that solution in the washer tanks limits oxidation, and breakdown and maintenance problems.

Each chemical stage of the washer has two drains. One is flush with the bottom of the tank for complete drainage, while the other is located a foot above the bottom drain. This enables the top two-thirds of the tank to be drained to the sewer. If heavy-metal buildup becomes unacceptably high, only the bottom third of settled sludge needs to be waste hauled as required by the local municipality. The washer also incorporates a square marine door at the bottom of each tank that can be removed to flush out the tank floor.

prevent chalking from exposure to sunlight. The coatings are supplied by Ferro Corp. (Cleveland), Fairboil Co. (Baltimore), and Protech Chemicals Ltd. (St. Laurent, Quebec).

Manual spray stations are located at the front of the booth, so parts with Faraday cage areas receive special attention before advancing to the automatic application zone. Andro explains that by predicting and coating Faraday areas before automatic application, manual touchup guns encounter less charge while spraying uncoated parts and can reach target areas more easily. Most of Kentwood’s products, however, are coated without manual touchup.

An electric eye activates the automatic powder guns in the ITW Gema powder booth shown with its recovery module. The booth is contained in Kentwood's environmentally controlled powder room. (Photos courtesy of Kentwood.)

As parts move into the booth, they are recognized for size and position by a photo eye linked to the PLC. The 10 corona guns turn on automatically, pivoting on radial oscillators before shutting down once parts have exited the spray zone. Automated triggering of the guns minimizes powder output and compressed air consumption. Andro says that the amount of powder Kentwood uses has decreased compared with the older line, indicating increased first-pass transfer efficiency.

Coated parts enter a PLC activated infrared oven supplied by PED Technologies (Erlanger, KY). Four zones of six vertical medium-wave quartz infrared emitters line the oven. Kentwood finishes parts with variable geometry and mass, necessitating adjustable oven zones. These variables also affected Kentwood’s decision to use a convection oven in addition to IR.

“We do a variety of parts. IR is basically line-of-sight heat, and sometimes you get parts with hidden surfaces that would not be exposed to IR directly,” Andro says, also citing concern about yellowing white coatings with over baking. Kentwood’s consultant Talbert also justifies the choice to incorporate both convection and IR. “The infrared oven has to be controlled more precisely than convection,” he says.

The IR oven gels the powder before parts enter the convection oven, providing a “soft shell” to resist the convection oven’s turbulence and possible contaminants.