By: Bill Bregar
July 8, 2014
ERIE, PA. — Attendees of Penn State Erie’s Innovation and Emerging Plastics Technologies Conference learned about the history of auxiliary equipment — and its future.
Speakers from auxiliary equipment makers Conair Group and Maguire Products Inc. gave updates on advances in interconnectivity and drying technology.
B. Patrick Smith, vice president of marketing and sales, said vacuum drying represents the next generation of drying. It’s a big change because vacuum drying doesn’t use dewpoint to measure the level of dryness — historically the key parameter.
“We’ve all grown up in an industry that only spoke of dewpoint,” he said. “Dewpoint is frequently misunderstood. Dewpoint refers to the dryness of the air, not the dryness of pellets.”
Maguire’s VBD series of vacuum dryers are six times faster, and use 50 to 70 percent less energy, than desiccant dryers. The VBD works on a continuous batch drying process, with no dessicant to change and no filters to clean, Smith said. Material moves from a heating hopper down to a vacuum vessel and then to a retention hopper. Load cells document material consumption.
VBD improves upon Maguire’s low pressure dryer, or LPD, that the company in Aston, Pa., introduced in 2000.
The vacuum reduces the boiling point of water. At 90 percent of full vacuum, water boils at 122° F, compared with 212° F at sea level and 203° F in Denver’s high altitude.
Once vacuum is applied, water vapor trapped inside the resin pellet instantly boils, because the high pressure inside the pellets combined with high pressure outside expels the moisture, in less than 15 minutes, Smith said. Pellets are ready for processing in about 35 minutes. It’s an active process, as opposed to the passive process of desiccant drying, he said.
Will vacuum material drying become the new industry standard? “It takes awhile to change a culture,” Smith said. “Our industry is made up of three generations of plastics processors who learned how to employ low-dewpoint air to reliably dry polymer. Wheel dryers have been dramatically improved in cost and efficiency, but vacuum dryer design has matured, costs have come down and superior technology will eventually win out.”
Chuck Morgan, Conair training manager, gave Erie conference attendees a history lesson. Closed loop control, and the ability to connect auxiliary equipment to the molding press, extruder and other equipment, has resulted in auxiliaries playing a larger role in the work cell. For example, in continuous extrusion of blown and cast film and sheet, auxiliary equipment such as blender and feeders can monitor and control the extruders, he said.
For drying, he said, closed loop control “has been a little nebulous for people taking a deep dive into drying.”
Morgan said that open-interconnectivity now can link production data to iPads and smart phones, “technology that we use ourselves without having to go to a third party.”
Morgan gave a history of desiccant wheel dryers. Desiccant in the revolving wheel gets regenerated automatically. “It is just far more efficient and, more important, it does not cycle,” like dryers that use tanks,” he said.
You can mount new super-compact desiccant wheels on a molding machine, he said.
The PET sector led the development in closed-loop control for dryers. Conair developed steel probe sensors that go into the drying hopper, measuring six different zones. The resulting data helps verify production accuracy. “We can tell before it happens that you’re going to make bad parts,” Morgan said.
Morgan said improved communication between machines also has moved into gravimetric blenders.
“The equipment is getting much smarter,” Morgan said. For example, a drying monitor can run up to 30 hoppers of any size or brand. Conveying systems can monitor up to 500 receivers and 40 vacuum pumps.
Erie conference attendees also got a history lesson from Smith, of Maguire. He said DuPont Co. first used vacuum drying in the late 1960s, to dry nylon. At GE Plastics, Lexan polycarbonate inventor Dan Fox said endorsed vacuum as the best way to dry hydroscopic polymers. Even so, vacuum drying did not become widely used because the pumps were expensive and cumbersome, pressure vessels were not as advanced and since there no microprocessor controls, it was hard to control the vacuum, he said.