Founded in 1947, Metlon Corp. (Cranston, RI) provides high-precision slitting capabilities for a wide range of materials including plastic films, papers, metal foils, impregnated fabrics, and laminations of these and other flexible materials. The company serves industries ranging from aeronautics and automotive to wild game control and wire. Its custom-built machines can hold tolerances below ± .001 in.

Metlon's pneumatic edge guides use air from the plant's main compressed air system to execute extremely accurate registration in very narrow width slitting. In the past, moisture built up in the air lines, causing valves and solenoids in the edge guides to rust. "It was a constant problem," recalled Wayne Etchells, Metlon vice president. "At least every other day, one of the machines was down while we took apart and lubricated the valves. And in some cases, we had to replace the valves." The maintenance took about one hour, at an estimated cost of $75/hr in lost productivity.

One possible solution to this problem was a refrigerated air system that dried the air as it cooled it. This was an expensive option, however, costing between $5,000 and $6,000. Operating costs would also be high due to the electricity needed to run the system. Another option was presented by a Parker Hannifin Corporation Filtration and Separation Division (Tewksbury, MA) salesman, who suggested a new type of compressed air drier. The Balston membrane air driers he demonstrated used membrane filter technology.

Less expensive, more effective

Metlon installed a Balston Model 76-50-35 membrane air drier, which produces a flow rate of 50 scfm. It cost approximately $2,600 including installation. Compressed air goes into the system but prior to entering the membrane-drying portion of the system, it passes through two high-efficiency coalescing filters.

The filters remove water droplets and particulate contamination with an efficiency of 99.99% at 0.01 micron. Next the air passes into Balston dehydration membranes. These consist of bundles of hollow membrane fibers, each permeable only to water vapor.

As the compressed air passes through the center of these fibers, water vapor permeates the walls of the fiber, and dry air exits from the other end. A small portion of the dry air (regeneration flow) is redirected along the length of the membrane fiber to carry away the moisture-laden air that surrounds it. This moisture-laden sweep gas is vented to the atmosphere while the remainder of the dry air is piped to the pneumatic edge guides and other applications in the plant that use compressed air. The drier delivers air with a dewpoint of 35 degrees F.

"This new type of drier was just what we needed to eliminate problems with water building up in compressed air lines," said Etchells. "This has totally eliminated downtime. At an estimated rate of $75 per hour for the production rate of the machines, the drier saves us more than $200 each week. At that rate, it paid for itself in just over three months."

Saving three hours production time each week

Metlon had been using nitrogen in a particular cutting application to clean dust off of cores cut by its machines. "These cores are reels that eventually go into a Class-10 cleanroom, so they have to be perfectly free of dust," explained Etchells. "We were using compressed nitrogen to do this because the compressed air, even though we had gotten it free of moisture with the air drier, still had particulates. It wasn't clean enough to use for this job." Metlon had compressed nitrogen delivered daily for this application at a cost of about $200 per month.

The Parker Hannifin representative suggested an alternate solution - an air filter downstream from the air drier that would trap the particulates. He recommended the A 15/80, which costs $1,600. Metlon installed it downstream of the air drier in the cutting machine line. "The filter removes 99.9% of the impurities from the compressed air, making it pure enough to clean those reels," said Etchells. The company halted its nitrogen deliveries, providing savings that paid for the air filter in eight months.

"Our compressed air system is now completely dry and clean at a very reasonable cost," said Etchells. "And we gain at least three hours of production time each week by not having to shut down to clean rusted valves. To us that is worth hundreds of dollars, making these products an excellent investment." ES