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WATER GETS SUPER CLEAN WITH FILTERS HOUSED IN DUPONT ZYTEL
USFilter is meeting needs for a strong, long-lasting filter housing for its water microfiltration systems with DuPont Zytel nylon resins. Used for municipal water treatment and industrial uses, USFilter's Memcor Continuous Microfiltration system is based on microporous membrane technology. It provides filtration down to 0.2 micrometer, less than 8 millionths of an inch, which is sufficient to separate out virtually all solids and harmful microorganisms. Filter modules made of DuPont Zytel PA612 nylon resins are mounted in frames, which are linked to form high-capacity systems to filter municipal or industrial water supplies. USFilter's Memcor Products subsidiary molds the system's filter housing components from Zytel nylon resins based on PA612 polymer. "We chose this type of Zytel for our filter module housing for a number of reasons, but most critical was its ability to remain strong and tough when exposed to water over long periods of time." says John Crapper, Memcor's managing director. "If parts become weakened, they can potentially fail as a result of dynamic flexing under water pressure. Leaks and failures aren't tolerable to the customer or us," says Crapper. The Memcor CMF system consists of banks of vertically suspended tubular filter modules containing thousands of hollow microporous fibers. Unfiltered water enters the module under pressure, surrounding the outside surfaces of the fibers. It passes through the fibers' porous walls, depositing suspended solids and microorganisms on their outside surface. Filtered water flows through the inside of the hollow fibers and exits at each end of the module. The module's housing measures 175 centimeter (5 feet 9 inches) long. Its molded parts include a center tube with a diameter of 130 millimeter (5 inches), large upper and lower head pieces, and end caps, spacers and outer sleeves. USFilter's Memcor microfiltration system employs a unique patented self-cleaning gas backwash. Filtration is halted periodically and compressed air is injected into the hollow fibers. The air passes rapidly through the fibers' porous walls dislodging accumulated solids from the outside surfaces. The solids are then flushed away using feed water rather than filtrate. Because backwashing and other aspects of the filtration process generate strong pressure pulses, USFilter set a burst strength requirement of 3000 kiloPascal (435 pounds per square inch) for the module's head pieces, center tube and other parts under pressure. To meet this requirement, DuPont scientists developed Zytel FE5448 GYB493. It combines PA 612 polymer, 33 percent by weight of glass fiber reinforcement and proprietary DuPont toughening technology. DuPont scientists also met a formidable challenge of optimizing the toughened resin to the molding challenges posed by the filter module's head pieces. "The head piece is a very intricate, heavy and hard-to-mold design, but DuPont worked with us to adjust the formulation of Zytel to meet this particular challenge," comments Crapper. Each head piece weighs around 3 kilograms (6.6 lbs.) and has walls averaging 5.5 mm (0.22 in.) thick. The part is cube-shaped, with each dimension measuring 180 mm (7.1 inches). Memcor molds other parts of the module housing, for example, the filtrate cups and outer sleeves –with Zytel 77G33L, a standard 33 percent glass reinforced PA612 resin.
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