Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 184 of 331

There are a wide range of powder cartridge filter products available today—dif- ferent media, various treatments, as well as customized manufacturing tech- nologies (i.e., special gasketing, variation in pleat count, design, depth and spac- ing, etc.). To ensure optimum performance and value, one must consider the design capabilities and limitations of the filter, in addition to the application fac- tors that might have an impact on a filter's performance. There are three media styles typically used in powder cartridges: cellulose, spun bond polyester and expanded polytetraflouroethylene (ePTFE) membrane; 100% cellulose and 80/20 blend (80% cellulose – 20% polyester) are "depth-load- ing" media constructed with tightly packed pleats and an outer wire mesh screen for support. This is the least expensive media style available, offers only moder- ate efficiency, and is best suited for low- to mid-volume, spray-to- waste powder operations. Pulse cleaning cellulose cartridges can be difficult at times because the powder has a tendency to become trapped between the pleats, resulting in very high powder retention within the filter (20–45 lbs.) and more rapid pressure drop. Cellulose-style cartridges would not be appropriate for high-moisture con- ditions or high-volume reclaim operations, as they tend to plug up much quick- er. One-hundred percent spun bond polyester is a continuous strand, "surface- loading" media that is tougher and slicker than cellulose and does not require out- er screen support to maintain pleat rigidity and strength. Spun bond polyester cartridges also require 50–70% less surface area than cellulose filters to handle a given air volume. This allows for a wider pleat spacing and fuller utilization of filter media, and together with the higher efficiency that polyester provides, re- sults in the following benefits in relation to cellulose: • Lower pressure drop and longer service life • Higher recovery rate of reclaim powder • Less powder retention within cartridge (80–90% less) • Less compressed air needed to pulse clean filters (40–60psi) • Less downstream contamination of system and plant air • No linting contamination of reclaimed powder or paint finish Better resistance to aggressive and abrasive powder (i.e., frit or porcelain) • Superior moisture resistance • Ability to wash and reuse filters Spunbond polyester media also offers several specialty treatments and mem- brane selections to enhance filter performance in more challenging conditions: Aluminized polyester (anti-static). This treatment coats the face of the media with a thin layer of aluminum, which dissipates the electrical charge of the fil- tered powder. This makes it an ideal filter for effective pulse cleaning when sta- tic electricity buildup is a concern. Hydro-oleophobic polyester (moisture-resistant). This type of cartridge is treated with a fluorocarbon or teflon bath that provides an oil and water repel- 183

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