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Modular dies for blown film.

Stackable die components have emerged as one route to bringing more flexibility--and layers--to coextruded blown film. At the recent K'92 show in Dusseldorf, two suppliers showcased such modular die technologies.

Davis-Standard Div. of Crompton & Knowles Corp., Pawcatuck, Conn., introduced its new Stack-Pak line. These dies feature a complete reorientation of the spiral mandrel sections. Rather than the standard vertical arrangement of concentric mandrels fed by a separate distribution block, the Stack-Pak's individually fed spiral sections cant inward at a 15-20|degrees~ angle. Blown film die product manager Peter Gates says these conically shaped sections fit atop one another much like a stack of PS foam cups. "Layers can be added or subtracted at will," Gates says.

This angling of the spiral sections also allows all of them to have the same diameter, regardless of positioning in the die. In the past, explains Gates, the outer mandrel diameters were inherently bigger than the inner ones. These larger sections would then be prone to excessive heat transfer and polymer degradation from the increased residence times and greater wetted surface areas. The Stack-Pak, however, can offer up to 80% reduction in residence time and exhibits only one-sixteenth the heat transfer of a comparable conventional design, Gates adds.

Stack-Pak dies can be configured for up to eight layers in diameters from 3/8 in. to 15 in. For dies smaller than 5 in., the layers can be moved to any position within the stack or removed altogether. Larger dies need a more "hard-wired" structure, Gates says, because they use a flow-dividing network.

Meanwhile, Brampton Engineering Inc., Brampton, Ont., brought an eight-layer, 75-mm modular die to the K'92 show. This supplier relies on annular, or disc-like, modules for melt feeding and distribution. Here, too, the flow patterns remain independent of the layer position. According to John Perdikoulias of Brampton's R&D department, these modular dies have only half the residence times of conventional designs. Also, the company says it can achieve excellent temperature isolation between layers--even to the point of running adjacent layers 50|degrees~ F apart.
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Publication:Plastics Technology
Date:Dec 1, 1992
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