Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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lant to both sides of the media to ensure effective pulse cleaning ability in both humid and oily conditions. ePTFE laminated polyester (membrane). Another type of spunbound polyester, this consists of a thin membrane of expanded PTFE laminated over a polyester substrate that results in a slick and microporous surface providing 100% efficiency at 1 micron and above. Expanded PTFE membrane cartridges offer the highest efficiency and best powder release properties of any media choice in the powder cartridge market, making it the ideal filter choice for users needing to maximize the amount & quality of their reclaimed powder. PTFE cartridges also do not re- quire seasoning, and are an effective filter option when ultra-fines or high-mois- ture conditions exist. Another new technology, which is available only on spunbond polyester and treated polyester cartridges, is the "dual dimple" pleat design, which imparts opposing dimples along the entire length of each individual pleat. This dim- pling technology significantly optimizes the efficiency of pulse cleaning and the capacity of the filter by preventing the pleats from pinching together re- gardless of the conditions or dust load. (See Figures 2 through 5.) Once product options are reviewed, consideration must be given to the con- ditions or circumstances that make a given operation unique, since they, too, can affect the performance of cartridge filters. Possibly the biggest factor in cartridge filter selection is whether an opera- tion is reclaiming its powder or spraying to waste. One of the biggest advan- tages of switching from liquid to powder is the ability to reclaim and reuse the powder once it is sprayed. This benefit is lost, however, when using cellulose cartridges since they typically retain between 20–45 lbs. of powder over its use- ful life that cannot be extracted or reused. Polyester cartridges, on the other hand, only retain 4–8 lbs. of powder over the life of the filter, while ePTFE mem- brane filters retain only 1–2 lbs! (By simply multiplying the dollar cost per pound of powder by the weight gain in each cartridge, one can estimate the potential cost savings to be realized by using polyester or membrane cartridges.) Another primary concern for powder reclaim systems is reclaim powder con- tamination and "linting," which is the breaking off of fibers from cellulose-style cartridges during pulse cleaning. Lint and other sources of dirt that enter the booth air stream will not only contaminate the reclaim powder, but can also bounce back onto the parts being sprayed, causing rejects. Companies typically upgrade to spun- bond polyester or membrane-style cartridges to eliminate contamination or lint- ing issues. Some of the other key factors that should influence decision-makers to select polyester and membrane filters over cellulose style include: • Humidity or oil/moisture in compressed air "Fines" or small micron size powder (1-3 micron) common in reclaim systems and combination cyclone/cartridge collectors • Aggressive or abrasive powders, such as frit or porcelain • Heated powder, which tends to stick to filter media (i.e., pyrolytic powder) • Polyester powder, which tends to retain electrostatic charge more than other powder types 184

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