Rolled Filters Move Filtration in a New Direction
When selecting filtration technology, industrial users have long wrestled with the tradeoffs of dirt-holding capacity versus particle selectivity or quick-and-dirty change-outs versus process time. For many applications, a self-contained rolled filter offers an effective solution to both problems.
Constructed with polypropylene hardware and various media in a spiral-wound design, rolled filters create a tangential crossflow motion that sweeps particulates across the media and traps contaminants in special, non-permeable sections rather than in the media itself. Combining the capacity of depth filters with the selectivity of pleated filters, rolled filters solve many performance problems caused by surface blinding and gel slugs. Their encapsulated design also protects the operator from contact with process fluid and eliminates complicated, messy change-out procedures. Rolled filters are manufactured with different types of polymer membrane, much like a pleated filter, to suit the filter to the application. Housing types range from a disposable polypropylene housing in an inexpensive bracket for filtration of hazardous materials, to a wetted or non-wetted stainless steel housing for applications that require operating pressures up to125 psig.
SWEEPING ACROSS MANY APPLICATIONS
Originally developed for applications in the photographic film industry, rolled filters are effective in any application that requires high dirt-holding capacity and efficiency, good gel retention, and reduced operator contact with process fluids. Although rolled filters are typically more costly up front, they are often more economical over the life of the filter. The following are some examples of industries and applications that have successfully applied rolled filters.
When polymer solutions of a solvent and resin (or resins) are mixed, the resin will adhere to contaminants and create gel slugs. During filtration, these gel slugs tend to extrude through conventional filters. Depth filters may be able to retain some gel slugs, but the pressure drop is significant in viscous polymer solutions. Pleated filters cannot retain the gels and experience pleat collapse. Rolled filters provide little flow resistance and have no pleats to collapse. Since these gel slugs are not captured within the filtration media of a rolled filter, gel slug extrusion is minimized. And by removing additional contaminants, rolled filters efficiently prevent gel slug formation downstream. The fully encapsulated design, spring-loaded check valves and removable portcaps are added advantages when dealing with messy solutions. No cleanup is required during filter change-outs.
If you do not achieve sharp cutoff in the production of audio and videotapes and computer diskettes, you will produce unwanted results such as a snowy picture, lost memory, audio blips and angry customers. Rolled filters not only provide the sharp cutoff required to separate oversized particles from metal oxide slurry, they also handle the heavy load of contaminants typical in processing magnetic media emulsions. In addition, rolled filters can eliminate product imperfections and damage from gel slugs and particulates while increasing efficiency and longevity. And because these highly volatile emulsions polymerize quickly during change-outs, the encapsulated design is again an advantage.
Although standard printer's ink does not need a high degree of filtration, many specialty inks do. Inks used for ink jet printers, ball point or rollerball pens, and other specialty inks require highly efficient filters that can handle viscous fluids and achieve the fine separation of contaminants from pigments, or those printers and pens simply will not work. Not only can rolled filters keep specialty inks free of clogging particles, their encapsulated design is an advantage in dealing with inky waste.
In hard-resin lens manufacture, a refrigerated polymer is filtered to remove hard particles that can cause imperfections. However, gel slugs and air bubbles often cause other lens damage during lens curvature. Filter longevity is also a problem--hardening polymer during work breaks required filter changes two or three times per day at one manufacturer using disc filters.
The tangential flow of rolled filters increased gel slug retention and also purged air quickly to discourage bubble formation and reduce imperfections. At day's end, filters can be taken off-line, ports capped and the filter cold-stored for use the next day, increasing the average filter life to 20 days.
When working with biotech products such as blood serums or biological extracts, the removal of bacteria, protein and other unwanted matter is critical. Because rolled filters can hold a large volume of particulates, serial filtration--and thus, inefficiency--can be reduced. This provides greater longevity for a costly downstream or sterilizing filter or, in the case of bacterial extracts, provides a cost-effective final filter.
Once an enzyme produces the desired reaction during pharmaceutical or beverage production, it is vital to eliminate these organisms and other contaminants from the broth. However, these rich solutions can create a heavy load on the membrane, creating gel slugs or overwhelming the filter's dirt-holding capacity. Rolled filters solve these problems, separating organisms from filtrate efficiently and ensuring consistency, even over many batches.