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Barrier screw designs
Barrier screws for extrusion
Barrier screws for extrusion- Extrusion equipment maker Davis-Standard says it has taken barrier screw technology for extrusion a step further with its new DSB-V and DSB-V1 barrier screws, introduced at NPE. These screws incorporate a new complicated geometry that is said to enhance melting and performance. They can be used on any brand of extruder.
The DSB-V uses a variable-pitch barrier flight with a new design for the melt mechanism incorporating a modified solids channel that is actually divided into two channels, each with a variable depth. The variable depth is said to assist melting through heat generation via plastic energy dissipation while improving the quality of the mix.
Deformation of the solid bed creates a driving force for flow re-arrangementresulting in early mixing within the melt zone of the screw. At NPE, companyengineers noted that experimental evaluations of the new design havedemonstrated that excellent melt temperature uniformity across a wide range ofscrew speeds is attained, a result they have not seen in other screw designs.
The DSB-V1 is a similarly designed screw developed specifically for groove-feed extrusion. In the DSB-V1, the barrier section creates a balanced radial force aimed at minimizing wear within the highly aggressive environment of a groove feed extruder. Davis-Standard says it creates high output rates that are not attainable with smooth-feed screws.
The design of the DSB-V1 offers similar solids conveying capacity to the DSB-V in groove-feed extrusion but increases melting capacity by some 40%. A variable-lead design for the barrier improves the polymer melting rate, which results in improved stability in head pressure and melt temperature.
The DSB-V1 also has provisions to fit numerous mixing sections to the screw for production of uniform melt properties in order to homogeneously disperse additives, colorants, and polymer blends. Davis-Standard has applied for a patent on both screw designs.
