Feed Screws and Barrels

Glycon and Westland develop innvative feedscrews

TECUMSEH, MI, July 2 -- Two competitors in the feedscrew market have teamed up to develop proprietary mixing and melting technology. At NPE 2003, Glycon Corp., based here, and Westland Corp., Wichita, KS, exhibited a Glycon DM2 feedscrew that incorporates a Westland Eagle mixing section. The two companies expect the new design will produce a consistent homogeneous melt, at high rates, with improved dispersion of color concentrate and liquid colorants.
The companies think the combination could potentially create a sort of ‘super’ screw,” says Jeff Kuhman, president of Glycon. They hoped that the exposure at NPE would help identify processors interested in the technology.
“For years, processors have said that they like the savings they get with liquid colorants,” explains Westland resident Dave Larson, “but getting consistent color mixing at high throughput rates has always been a challenge. We think this marriage between the DM2 and the Eagle might just be the solution they have been looking for.”
The DM2 name refers to a dynamic mixing/melting action that has been shown to produce more output than a typical barrier screw without the shear that can degrade many of today’s heat-sensitive engineering polymers. A thermal “cross-over zone” is positioned along the screw at a point where 70% to 80% of the polymer is melted.
This unique configuration of channels and undercut flights allows melt, as well as pellets, to interact without excessive pressure build-up. As the plastic crosses over the undercut flights, it tumbles into the next channel. The crossover is repeated several times, resulting in an unwinding effect such that the inner or core layer in one channel becomes the outer or skin layer in the other. Unmelted pellets are continuously mixed with melted material so that thermal energy is transferred from the molten polymer to any unmelted pellets, producing a very homogeneous melt, says the company.
To achieve the highest levels of additive dispersion, the DM2 is often paired with a supplemental mixing section. The Westland Eagle mixing section, which is normally about three diameters in length, would be positioned downstream from the DM2 mix/melt section. Alternating helical barrier and wiping lands convey and mix the melt. Mixing is enhanced by the use of two or three notches in each of the barrier lands. These notches (between 1/4- and 3/4- inch wide) bottom out on the root diameter and allow some of the melt to avoid crossing the barrier lands, changing direction of the melt flow as it moves through the mixer. The Eagle section is designed to accept at least 95% (and as much as 98%) of the melt that is conveyed into it without restricting the flow of the material.