2014 Buyers' Guide - Filtration News

Cartridge | Filtrationcles. Commercially, a series of circumferentialcuts is made into the cartridge.However, the cartridge may also beturned on a machine tool to produce aspiral groove on the outer surface.However, grooves in the surface substantiallyweaken the physical strengthof the filter. In addition, the operationcreates circular lands, i.e., the regionsthat are left between the grooves. Toomany grooves in a given length of thecartridge will leave lands that are notthick enough to support themselves orto resist minor blows without breaking.This is particularly true in filters inwhich the outer surface into which thegrooves are cut is comprised of relativelylarge fibers. These fibers have relativelyfew intersections at which theycan be bonded together by the resin.Consequently, these lands are more susceptibleto breakage.In addition, the grooving processcreates particulate debris as well as altersthe surface structure of the filter.These minute particles often adhere tothe outer surface of the filter. Theirpresence is obvious. A common salestechnique is to tap a grooved cartridgeon a white sheet of paper placed on apotential customer’s desk. The appearanceof the dark particulate debris isoften sufficient to convince theprospective buyer that selection of anon-grooved competitive cartridge isthe wiser choice.One attempt to eliminate this sourceof media migration is to post-dip themachined cartridge in a resin bath tofurther saturate the outer surfaces 4 . Althoughthis process does fix the minuteparticles to the fiber matrix, it also altersthe cartridge’s void volume andhence its performance. Therefore, thecure may be worse than the disease.Resin bonded filter cartridges are operatedwith the flow direction from theoutside to the inside. Therefore, the30 • August 2013 • www.filtnews.comvast majority of these particles are removedfrom the filtrate as it passesthrough the cartridge matrix.A less obvious and more sinistercontributor to media migration is theuse of short fibers, i.e., those less than1/2” in length. Short filters have fewerintersections or points of contact thando longer fibers. Therefore, they can bemore readily separated from the cartridgematrix. Furthermore, they canexist anywhere within the element’sstructure. These particles do not haveto migrate through the entire cartridgeto contaminate the filtrate as do theparticles generated on the outer surfaceby the grooving operation.This problem is particularly acute inresin-bonded cartridges produced bythe vacuum deposition process. Theaqueous dispersions are often preparedusing both chopped linters and reclaimedfiber. Although incorporationof linters and reclaimed fiber providessignificant manufacturing cost reductions,the resultant cartridges exhibit ahigher degree of media migration thanequivalent cartridges produced by theother processes using higher-gradefibers. Neither can these cartridges bemarketed as “silicone free”, a necessityfor many coatings applications.IMPREGNATED MAT PROCESSESIn this section, the processes used toform fiber glass resin bonded cartridges,and compound layer resinbonded cartridges are discussed.Fiber Glass Resin Bonded Cartridges:In the process for producing fiberglass filter cartridges, molten glass is firstdrawn into thin glass fibers. These fibersare both extremely thin and uniform.The fibers are sprayed with an adhesivebinder as they are blown into a collectionchamber, in which the coated fibersare formed into uniform mats. Thesemats are then cut into sheets of predeterminedsizes to be rolled on a mandrelto form fiberglass tubes.After the cartridges are cured in anoven, they are first ground to the requiredouter diameter and subse-