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From Powder Coating 1998: PTFE Membrane Cartridge Case History
Membrane cartridge filters make saving powder a snap for toolmaker
When paper and polyester cartridge filters throw a monkey wrench into a Midwestern toolmaker's finishing line, the company turns to membrane cartridges. The outcome: Improved powder recovery, lower energy costs, and less down time.
Snap-on, a 78-year-old company based in Kenosha, Wis., manufactures hand and power tools, diagnostics and shop equipment, tool storage products, and diagnostics software at plants throughout North America. At its Algona, Iowa, plant, operators spray 34 colors of powder coatings on tool chest components for businesses like Harley-Davidson and the National Football League. "Handling so many colors and projects keeps the plant's 450 employees on their toes," said Dwayne Anderson, the plants paint technician.
Doors opened in 1956 at Snap-on's 417,000-square-foot plant in Algona. Operators powder coat thousands of tool-chest parts daily in runs ranging from 2 to 1,500 pieces, not including a few pieces e-coated with red paint. Nearly 6 years ago, the company decided to use more powder coatings instead of e-coat to accommodate customers growing demands for different colors, as setting up e-coat dip tanks with extensive color selections wasn't a feasible alternative. Last year the company used more than 300,000 pounds of powder.
Wasting powder with paper and polyester cartridges
Wanting to reclaim the multiple colors sprayed on its main powder line, the company installed paper cartridge filters in its spray booth. But complications soon cropped up. "Several years ago, during our learning curve," Anderson said, "we found paper filters were contributing to powder contamination and poor product finish. Operators encountered rejects because paper fibers ended up in the powder after operators pulsed the filters clean. Moreover, pulsing rates were at 90 to 100 pounds per square inch, causing wear and tear on the cartridges, which eventually blew apart.
Next, the company tried polyester cartridge filters. Polyester proved more promising than paper, but left something to be desired. The polyester cartridges didn't lint like the paper ones, according to Anderson, but they still took 100 psi to pulse clean and retained 50 to 60 pounds of powder when changed every 2 months. "We were throwing away a lot of costly powder," he said. "We knew there had to be a better way."
Taking a tip from a customer
Anderson resolved to take a tip from one of Snap-on's customers, Harley-Davidson. The motorcycle manufacturer had a different kind of cartridge filter on its powder coating lines, one designed specifically for powder coating. The filter includes a slick, GORE-TEX® polyester laminate membrane. The exterior of the filter is covered with an expanded polytetrafluoroethylene membrane that resists clogging, requires lower air compression levels for cleaning than paper or polyester cartridges, and reduces the noise of powder booth systems.
The membrane cartridge filters have lasted 3-1/2 years and saved the company nearly 18,000 pounds of powder.
Anderson ordered 20 of the 36-inch membrane cartridges. The cartridges were installed on the fully automated main powder coating line, which handles large runs of tool chests as well as sheet metal for other electrical components the company makes.
When entering the finishing area, parts first pass through a multistage automated washer, encompassing two reverse-osmosis stages, an iron phosphate coating, an immersion phosphate treatment, and a chrome rinse to ensure the powder will adhere to the metal substrate and provide a long-lasting, durable finish.
Next, parts pass through a drip-off station and enter a dry-off oven. Then, the parts enter the powder booth, where 16 coronacharging guns spray powder at film thicknesses of 2 mils. Operators touch up inside and outside corners of tool chests with three manual guns. After powder application, parts enter an infrared oven where they're heated to 375°F for 10 minutes. After the parts cure, employees inspect and assemble the parts, then inspect them again before and shipping to distributors.
Holding up under pressure
The quality of the membrane cartridges soon registered with Anderson. "We originally purchased them because the manufacturer promised better powder reclamation without linting," he said. "That was an understatement."
Linting and rejects stopped. Pulsing the filters for cleaning required only 40 to 60 psi, reducing energy costs and saving on wear and tear of air compression equipment. The paper and polyester cartridges needed changing every 3 months; Anderson didn't have to change the for 3% years. Although he didn't do a formal cost analysis, Anderson estimates the plant has saved $27,000 in replacement filter costs and 18,000 pounds of powder since switching to the membrane filters. Productivity is also a part of the big picture. Said Anderson: "I can't remember the last time I had to shut down for a filter-related problem."
As customers requested more powder colors, Anderson saw the need for additional cartridge filters. He recently ordered 40 newer versions of the membrane cartridges already in place. The newer cartridges offer a slick, polytetrafluoroethylene over an aluminized, non-woven polyester substrate. The conductive membrane allow for greater powder transfer efficiency, less powder retention, and fewer filter changeouts. Anderson sends the cartridges out once a year to be cleaned. In that time, he said, the cartridges retain about 20 pounds of powder, a vast improvement over the 50 to 60 pounds of powder retained in 2 months with previous polyester cartridge types.
The filters need no seasoning to reach their full capacity capturing 100 percent of particles 1.0 micron or larger. Another advantage of the newer filter is that less powder reaches final exhaust Filters, which can be costly and time-consuming to replace. The cartridges are unaffected by high-moisture conditions, another feature favorable to the Algona plant. Said Anderson: "In July and August, Iowa is very hot, with humidity oftentimes over 80 percent."
Anderson said the membrane cartridge Filters paid for themselves in the first year. "It's been my experience that you can use the membrane cartridges and replace them every 3 years," he said, "or use anything else and replace them every 3 months."
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From Powder Coating 1998: PTFE Membrane Cartridge Case History