Compressed Air Best Practices - November 2008 - (Page 37) Focus In ustry STEEL METALS Foc s Indu Focus Industry STEEL & METALS ocus ndustry EEL METALS L METALS METALS METAL | 11–12/08 | Aluminum Foil Casting Stations Require Blow-off Air to Remove Aluminum Chips. Problem A major United States manufacturer of light gauge aluminum decided in 2006 that it had to address the efficiency of its energy use in its manufacturing plant in western Tennessee. They found in their audit that one of the main culprits was the unrestricted and unmonitored usage of compressed air at the aluminum foil casting stations. The casters utilize a continuous casting method, in which two large rollers solidify and roll a feed of molten aluminum into a 0.200" thick sheet. As the sheet cools, a jagged, irregular edge is left on the sides. A rotary mill on each side removes the rough portions, creating a smooth, straight edge to the sheet. Most of the metal chips created by the milling fall to the floor. However a significant amount falls back onto the sheet. Later, the sheet is rolled into six-foot diameter spools. If these chips are not removed the aluminum will be damaged, causing rejects by their customers’ quality control departments. To remove the chips, the plant was using a series of multi-channel, flat fan nozzles attached to ¼" feeds from the plant’s compressed air line. The pressure and flow was measured at each nozzle to be 7.7 cfm at 87 psi. Assuming 4 cfm per kW, it was determined that the plant was requiring 96 kW for each of its four casters to remove the metal chips from the surface. Operating 24 hours a day, 350 days a year, the total energy usage is 804,300 kW-hrs per year per caster. At a rate of $0.046 per kW-hr and with maintenance costs, assumed at 10% of the total energy costs, the plant was spending $40,698 a year to remove the chips from the aluminum at each of four casting stations. w ww .a rb es tp ac tic e s. co m ww w. air be stp ra ct ic es .c om w ai e st pr ce c o 37 37 http://www.airbestpractices.com
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