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Injection molding screenchanger permits constant filtration.

Injection Molding Screenchanger Permits Constant Filtration

One eye-catching development at June's NPE in Chicago is a true industry first: a continuous injection molding screenchanger from Gneuss Inc., Langhorne, Pa., that changes filters without interrupting the molding process. The ISF screenchanger - developed for a major European molder that needed to run recycled resins for beer and milk crates - is said to permit trouble-free use of reclaim while protecting sensitive mold surfaces against damage from foreign particles.

The ISF screenchanger is a rotary disk filter that is mounted on the tiebars up against the nozzle side of the stationary platen. Among its major components is the rotary transport disk, which is sandwiched between two plates and is fitted with multiple removable filter elements (the unit displayed at NPE contained nine such filters). In an arrangement similar to that of Gneuss's continuous-filtration system for extrusion, each screen pack is mounted in a supporting breaker plate, which itself sits in a removable filter cassette. The rotary disk is situated eccentrically in the feed plate, so that one screen pack is always in direct line with the melt channel. Gneuss claims that the optimum layout of the ISF filter minimizes pressure drop and eliminates dead spots that can cause polymer to degrade.

The ISF filter allows the active screen surface to be changed semiautomatically, on the fly, during a production run. Screens are changed between shots on a signal from the operator via a hydraulically operated ratchet-like mechanism. As each new screen pack is indexed counter-clockwise into place in the melt flow path, two dirty screen packs become accessible at the side of the feed plate for manual removal and cleaning.

The frequency of changing filters depends on the particular process and such factors as material cleanliness and pressure drop. The ISF screenchanger does not require constant supervision. Once the acceptable pressure drop is determined for a process, indexing can be based on time, number of shots, or pressure differential, and these monitoring tasks can be programmed into a PLC.

Gneuss says the ISF screenchanger is retrofittable to any injection machine, and the size and shape of the plates can be customized to particular equipment. Eight screen diameters from 0.8 to 5.9 in. are available. A wide range of filtration fineness can be chosen, and all models can be operated to 40,600 psi.

MULTIPLE BENEFITS

Protection against mold damage and clogging of runners or narrow mold passages offers the possibility of using lower-cost reclaimed materials and reduces downtime and expensive repairs, according to Gneuss v.p./general manager Joseph Altimari. Moreover, this same added mold protection may make the screenchanger attractive for running virgin materials as well, he adds. Although field data are yet limited, the company claims that the ISF may also contribute an extra mixing effect, thus aiding the processing of reclaimed materials where small deviations in color and viscosity are encountered. The company declined to discuss price of the unit. (CIRCLE 4)

Further evidence of the increased attention of injection molders to filtering is the Super Cycle system from Spear System, Inc., Camarillo, Calif. The system, first shown at JP90 and again at NPE (PT, Aug. '91, pp. 36-37, 43), consists of a filtration ring behind the screw tip, which blocks foreign particles in the melt stream and traps them in a reservoir area, where they reportedly do not cause pressure drop. Accumulated particles are purged by retracting the injection carriage and advancing the screw. Though periodic purging involves some interruption of the molding cycle, the device does not require screen packs to be removed and cleaned. The filtration system is available for about $10,000. (CIRCLE 5)

PHOTO : The ISF screenchanger reportedly protects sensitive molds against damage from foreign particles. Developed for use with reclaim, it may also be effective in filtering contaminants of virgin resins borne through the handling systems.
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Title Annotation:Gneuss Inc.
Author:De Gaspari, John
Publication:Plastics Technology
Article Type:product announcement
Date:Sep 1, 1991
Words:643
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