Fairlawn, Ohio — Twin-screw extruders are well known for their compounding ability, but Keith Luker advocates single-screw extruders by his company, Randcastle Extrusion Systems Inc., dubbed “orderly mixers” under the SSE line.
“My point is, I'd like to create an orderly mix,” Luker said in a presentation at the Society of Plastics Engineers' TPE TopCon in Fairlawn. He is president of Randcastle, based in Cedar Grove, N.J.
Traditionally, he said, single-screw extruders have been “one-dimensional mixers” — basically taking a straight line and stretching it in a linear, simple shearing action. Twins do two-dimensional stretching.
The key to single-screw SSE compounding extruders is a screw design with a series of mixers with channels and pumping areas. The channels work to elongate the material, and the pumping area pulls it in another direction, so the plastic gets stretched. Luker said that's different than a barrier screw that pushes plastic through a conventional single-screw extruder.
Luker said a study by Dow Chemical Co. showed that the Randcastle single-screw compounder can do distributive mixing eight times better than twin-screw mixing of an immiscible polymer blend.
“We're not fussing with the barrel, we're just changing the screw design,” he said.