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Mixing Screw Technology: Shear Flow Doesn't Cut It.

Rauwendaal Extrusion Engineering, Inc., reports that its recently introduced CRD mixer is being successfully implemented in a number of single-screw extrusion applications, including color concentrates, foamed plastic, reactive extrusion, heat shrinkable tubing and medical tubing, post-consumer reclaim, blown film extrusion, and injection molding.

Unlike typical existing mixers, the CRD mixer does not rely mostly on shear flow whereby the plastic receives only one high-stress exposure. Shear flow, explains Rauwendaal, does not achieve efficient dispersive mixing and causes high melt temperatures resulting from viscous dissipation. The CRD mixers are designed to create strong elongational flow to achieve efficient mixing, Rauwendaal says, adding that elongational flow reduces viscous dissipation, allowing CRD mixers to operate at lower melt temperatures. Thus, in addition to improving dispersion, the mixers are said to reduce the chance of degradation. CRD mixers are also capable of dispersing gels, which shear-based mixers cannot do, according to Rauwendaal.

An added benefit of the CRD mixer over shear-based mixers is its low cost, reports the manufacturer. Moreover, it is said to be easily incorporated into existing screw designs.
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Comment:Mixing Screw Technology: Shear Flow Doesn't Cut It.
Publication:Plastics Engineering
Geographic Code:1USA
Date:Nov 1, 1999
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