Riding the Plastisol Carousel
An indexing carousel finishing system has resulted in good repeatability and more efficiency . . .
Greenfield Products, Greenfield, Ohio, was founded in 1959 by J. Paul Gessner, who hoped to manufacture a line of marine accessories. The company began by making outdoor cookware and aluminum-painted anchors, products that are still part of the company's product mix. However, Greenfield established itself as a serious player in the marine market with the first PVC-coated anchor in 1962. The product quickly caught on with marine distributors as well as national retailers, including Kmart, Wal-Mart, L.L. Bean and others.
Today, Greenfield remains a manufacturer of anchors and other marine accessories. The company operates three conveyorized production lines, the largest of which produces 3,000 anchors per shift. It manufactures a variety of anchors, including several cast-iron anchors, anchors for jet boats and fisherman outriggers and traditional Danforth-type (mechanical) anchors for yachts up to 45 ft long.
The anchors are coated with a vinyl compound plastisol that is applied approximately 50 mils thick. Plastisols are rubber-like coatings that are soft to the touch and generally found on grips and tool handles. Greenfield uses them to coat its anchors because they help to protect the boat's finish. This is especially important to Greenfield because it sells many anchors to antique and luxury boat owners.
Despite its success, the company could not keep its production lines operational year round due to the seasonal nature of the marine accessory business. In 1993, building on its knowledge of plastisol applications, Greenfield offered its dip coating and dip molding services to other manufacturers. The company took on a variety of plastisol manufacturing and finishing jobs, including grips for Mac Tool (now Stanley Mechanics Tool), underhood components for General Motors Corp., seat control levers for Ford, specialty dip-molded parts for Fairchild Industries and underhood components for Chrysler.
The dip coating process is quite simple. Parts are coated with a primer; pretreatment is generally not necessary. The parts are then heated and dipped into a plastisol chemistry, hence the term dip coating. After dipping, the parts go through a short cure cycle. Dip coating is performed when the plastisol should adhere to the part. Dip molding is different in that the plastisol does not adhere to the part. During dip molding, a positive mold of the part is made. This mold is then coated with a lubricant and filled with the plastisol. The lubricant facilitates the removal of the plastisol from the mold. After the mold is filled with the plastisol, it goes through a short cure cycle. The molded plastisol is then slipped onto the part.
Although Greenfield now had enough work to keep its plastisol lines busy year round, the new work was not suited to the company's current plastisol lines. Its current lines were designed to finish anchors, which meant they were suited to large parts in low volumes. However, much of Greenfield's new work involved small parts in high volumes.
In order to compete more aggressively and build on its success as a Tier II supplier, Anne Gessner-Pence, Greenfield's owner/manager since 1990, invested in a new plastisol application technology in 1995. She also believed that the improved application technology could open doors to new applications that demanded good aesthetics, better ergonomics, electrical resistance, corrosion and abrasion protection, high impact strength or a combination of these traits.
The new finishing equipment, manufactured by Corrotec Inc., is called Corrocoat. Greenfield uses the automated system for both dip coating and dip molding of high-volume, small parts. It is a non-conveyorized system engineered to operate within a small footprint. The system has a six-position indexing carousel that is approximately 10 ft in diameter.
The process starts with parts either being primed or coated with a lubricant. They are then loaded onto fixtures, and the fixtures are loaded onto the indexing carousel. After loading, parts proceed through two (540 and 525F) gas convection preheat ovens. Both preheat ovens have a fast ramp-up burner design that minimizes utility expenses. The preheat ovens facilitate the coating bond and cook off minor surface oils or forming materials. It also eliminates the need for any pretreatment, provided that the parts are not heavily contaminated. Following the preheat stage, the carousel moves the parts to the coating tank. Depending on the frequency of color changes, the system incorporates one or more 80-gal tanks. Greenfield uses a number of colors, including red, white, blue, purple, teal, yellow and a few others. Parts are immersed in a plastisol bath at ambient temperature for about 70 seconds. The carousel then moves the parts to the gas convection curing oven. Parts are cured for about two minutes on average. After curing, the parts are ready to be unloaded and packaged.
The indexing carousel has greatly improved the efficiency of Greenfield's operation. At any one time, one position on the carousel is loaded, two are preheated, one is dipped, one is cured and one is unloaded. The indexing carousel has allowed the company to decrease the time required to finish a part and reduce the number of workers needed. When the system was first installed, two workers ensured that the system operated correctly. Now, only one worker is needed to operate the system. This is a dramatic decrease over the number of workers it takes to operate one of the company's conveyorized lines.
This system has not only made Greenfield more efficient; it has also provided excellent repeatability and accuracy. How is this accomplished? Instead of the carousel lowering the parts into the tank, the tank is raised by a PLC up to the parts. The tanks move up and down because the carousel needs to be kept in single plane. The PLC controls both the speed and the angle at which the tank moves up to the parts. This is important because plastisols are extremely viscous. The PLC control allows the operator to slowly raise and lower the tanks, providing a drip-free finish.
The system was first used at Greenfield to coat automotive seat control bars at a rate of 5,000 pieces per hour. Other applications include nozzle covers, biomedical components and hand tools.
"Plastisol's inherent ability to build films, combined with an application system that offers highly consistent results and operates with virtually 100% transfer efficiency, indeed opened new doors," said Ms. Pence. "At present, we're working with about a dozen truck, appliance and recreational products that are good candidates for plastisol dip coating or dip molding."
The company also tried the new system on some of its anchors, specifically small anchors used on jet skis. "At the time of the retail purchase," explained Ms. Pence, "the jet ski and all of its components, including the anchor, are very visible. And just like on an appliance, or motorcycle, the manufacturer demands that the finish on everything the customer can see be Class A, virtually flawless.
"Clearly," said Ms. Pence, "Class A finishing has become the norm for more parts, or more products, than ever before. The system has allowed us to step up to the plate and deliver what customers demand."
To learn more visit Corrotec Inc..