Orlando, Fla. — "Do you have anything for PVC?"
That is a question Don Macnamara, general manager for PSI-Polymer Systems Inc., can recall customers asking since his first NPE, he estimates, in 1985.
"Our question to them is always, 'Well, how highly stabilized is it?' because if it's highly stable, we can run it," Macnamara said during a May 9 interview at the company's booth at NPE2018. "If it's not, then it's going to degrade, and once it degrades, it gives off gases that are corrosive and it forms carbon."
The Conover, N.C.-based supplier of polymer filtration equipment, gear pumps, static mixers and other products used for plastics extrusion began a project about a year ago in preparation for this year's NPE to find an answer.
"[We wanted to] try to come up with some products that we thought would be able to handle a much, much more difficult process range of PVC, so effectively the rigid PVCs that are not really stabilized," he explained.
At NPE2018, PSI responded to customer requests with the launch of two products designed specifically for PVC, or hard vinyl, applications: the Expansion Plate Screen Changer and Chlorinated Gear Pump.
"The problem with the screen changers has always been that they have mechanical seals, and when the polymer goes over the mechanical seal, it sees different steps and so forth and … different changes in flow rate. You can begin to form carbon on the seals surface, which ultimately causes degradation," Macnamara said of conventional screen changers.
"So, we said, all right, we can't use a polymer seal. We can't use a mechanical seal. We can't have a seal," he added. "So, how do we seal it?"
The Expansion Plate Screen Changer features two body halves that clamp on to a slide plate. The screen change process relies on programmable logic controllers, which control the expansion spacer bars that separate the body halves from the slide plate in the middle.
Once the spent screen has been replaced, the spacer bars contract, bringing the body halves back against the slide plate to recreate a seal.
"The entire screen changer effectively became the seal," Macnamara said.
The company said its patent-applied-for screen changer can tolerate temperature swings up to 20-40° F and comes standard with corrosion-resistant stainless steel components and chrome-plated flow bores to reduce surface friction and eliminate hang-up areas.
The product is currently being beta tested by three of PSI's customers, Macnamara said, adding that roughly 15 percent of his leads from the show are PVC-related.
"What we really want to do is get into a broader exposure of different PVC recipes to find out where do we have a sweet spot and where do we start to cross into regions where maybe the technology just isn't developed far enough yet," he said. "That's what the beta testing is about."
Additionally, the company launched the Chlorinated Gear Pump for PVC applications. The design features modified components that improve heat transfer and more tightly control temperature shifts common in gear pumps.
"People are producing PVC profiles and they're trying to maintain the wall thickness on the profiles, but the extruders don't always deliver a stable output, so if you have any pressure swings at the die, that effectively shows up as a weight change — linear per foot weight change — in the end product, and so they try to control that by measuring devices and by speeding up or slowing down the haul-offs," Macnamara explained.
PSI's objective, however, is to "never have to adjust anything," he said.
"We put a melt pump on there, and it delivers an absolutely rock steady output, and so the linear weight per foot never changes. The walls never change," he added.
PSI's Chlorinated Gear Pump has dual-extended gear shafts to help push heat out of high-load areas of the gears, the company said. Cooling channels placed in the body further improve heat control by wicking heat off the gears and away from the bearing areas.
"We're maintaining very, very stable temperatures across the entire gear pump," Macnamara said. "And this is all done with internal jackets, and then we're wicking the heat off anywhere where it's really starting to build up so we can get that PVC to run through there."
The Chlorinated Gear Pump is currently being beta tested by one customer.
"With the excitement that [these products] have generated — both with the people who have seen it and internally for us — I think this is a project we're going to continue along with and put a lot of horsepower behind to make it happen," he said.
