By: Bill Bregar
March 25, 2014
CLEVELAND — About 150 extrusion enthusiasts at the Society of Plastics Engineers’ Continuous Compounding Topcon learned the 101 of twin-screw and single-screw technology and heard updates about simulation software and instruments that give in-line measurements of color and viscosity.
SPE’s Extrusion Division and the society’s Cleveland and Akron sections hosted the compounding conference March 11-13 at Case Western Reserve University in Cleveland. A snowstorm on the middle day forced the school to close early, and delayed a tour of CWRU’s Center for Advanced Polymer Processing, but the extrusion conference continued.
“Compounding is about transforming materials,” said Babu Padmanabhan, an Indian extrusion expert who founded twin-screw extruder maker Steer Engineering Pvt. Ltd. He said the technology takes an “innocent base resin” and combines property-improving additives, color and fillers to make something new.
Padmanabhan described a study Steer of retaining long fiber length of natural fibers, such as jute, during compounding on a co-rotating twin-screw extruder.
He said long fiber-reinforced parts may be able to replace sheet metal in some applications.
In another long-fiber presentation, Matt Sieverding, general manager for KraussMaffei Corp.’s extrusion division in Florence, Ky., said the Munich-based KM has built injection molding compounders big enough to process up to 105 pounds of plastic in a single shot. The IMC pairs a Berstorff extruder that compounds fiber-reinforced plastics, linked directly to a KraussMaffei injection molding press that injects the material into the mold. One application: an automotive front-end carrier from long-glass-fiber reinforced polypropylene.
Other parts made by the IMC include pallets containing 30 percent wood flour, medical tube inserts and even pet food.
Sieverding said there now are more than 65 IMCs in use around the world. That includes 22 in North America — 11 in the United States, nine in Canada and two in Mexico.
KraussMaffei also has sold several IMCs to the extrusion market — where there is no second injection molding step, Sieverding said. The process is used to make plastic pipe with a highly filled middle layer, which gives extra sound deadening.
Bob Furlan, sales manager of Equitech International Corp., said the company’s in-line color measurement for compounding extrusion uses fiber-optic probes with a sapphire window, which fits into the extruder barrel and the die lip. The spectrophotometer probes look similar to temperature and pressure transducers.
“More people are interested in using that feedback loop for closed-loop control,” Furlan said,
The color probes work on both single and twin-screw extruders, but not injection molding, because molding has too high of pressure and temperature, he said.
“We can pull out fibers out at any time without any disruption to the process at all,” Furlan said.
In-line color measurement for compounding allows for a company to get instant results continuously, avoiding the need to pull laboratory samples.
“For color-change lab samples, typically measurement can happen every two to three hours. A lot can happen in two or three hours,” Furlan said. “Here we’re giving you a reading every few seconds.”
It also allows you to diagnose feeder rates and performance, and find out potential problems like inconsistent heater bands and screw ear, he said.
Furlan said that one big application for the technology is PET pelletizing lines, before the PET is injection molded into preforms.
The increasing use of recycled content also makes instant color checking more important. “The product can vary, minute to minute,” he said.
Equitech is based in New Ellenton, S.C.
Continuous Extrusion Topcon attendees also heard Monika Gneuss, vice president of Gneuss Inc., discuss in-line viscometry.
Other speakers, from Century Extrusion, PolyOne Corp., Cloeren Inc. and the University of Maryland, explained new developments in process simulation.
Technical presentations covered co-rotating, intermeshing twin-screw extrusion; counter-rotating, non-intermeshing extrusion, long-fiber compounding, kneaders and mixing.