PSI-Polymer Systems, Inc. To Introduce New Products For PVC Applications at NPE2018 Conover, NC (May 7, 2018)
PSI-Polymer Systems Inc. (booth W5791) will introduce two new products designed for PVC applications at NPE2018. The new screen changer and gear pump are PSI’s first-ever products of their respective types to be developed specifically for hard vinyl. PVC is a particularly challenging material to work with due to its narrow process window and a need for a constant, steady flow, which keeps many processers of RPVC from using screen changers or gear pumps at all. PSI’s new products eliminate the usual concerns processors have about including screen changers and gear pumps in their process.
Expansion Plate Screen Changer (ESC)
Screen changers are often not applied to RPVC processes, as when the material travels through transitions or steps, shear heat is introduced and will often trigger localized burning of the material. PSI, however, was able to develop a workaround that enables their Expansion Plate Screen Changer (patent-applied-for) to tolerate temperature swings of up to 20-40° F.
“With our ESC we solved the chemistry issues relative to heat, flow, and thermal conductivity that make the use of a screen changer with PVC formulations so challenging,” says Don Macnamara, General Manager at PSI. “PSI has been solving challenging processing issues for nearly 20 years, but we’re really proud of this particularly tough solution.”
Generally used in sheet and profile applications, the screen changer requires a momentary shut down for a screen change, which eliminates the need for disassembling the die and the high scrap rates that result from that, especially on short runs. The screen change process itself is expertly engineered as well, with PLC control of expansion spacer bars that separate the body halves from the slide plate between them. Once the spent screen has been replaced, the spacer bars contract, bringing the steel body halves back tightly against the slide plate, recreating a seal through tight steel-on-steel contact. The ESC comes standard with corrosion-resistant stainless steel components, straight-through, chrome plated flow bores to reduce surface friction and eliminate hang-up areas, identical, interchangeable, and field repairable upstream and downstream bodies for easy repair or replacement, and zero mechanical seals to create less opportunity for things to go wrong. These attributes make this screen changer reliable, durable, and efficient in addition to its already impressive ability to thrive in an extremely challenging process.
Chlorinated Gear Pump (CGP)
It is not just screen changers that tend to be avoided for RPVC applications, however. Melt pumps are typically not used either due to the heat that’s generated in the axial clearances of the gears and the lubrication zones of the bearings. Many melt pumps today are capable of discharging material that is used for gear and bearing lubrication, but in doing so, they generally heat up to temperatures unsuitable for thermosensitive materials like RPVC. PSI’s new Chlorinated Gear Pump offers the solution.
“Our new CGP is highly effective at managing the temperature profile across the melt pump, which is so critical for PVC.” says Macnamara. “It took some hard work and several modifications, but our product will now allow our customers running a thermally sensitive polymer to take advantage of the die pressure stabilization, increased output, and reduction of extruder pressure benefits of a gear pump without worrying that their polymer will carbonize or degrade because of it.”
The new design modified several components to improve heat transfer and more tightly control the temperature shifts typical in a gear pump. The body and side plates of the CGP are jacketed for steam or oil heat transfer media, which travels through the entire pump in a single pass. To help push heat out of high load areas of the gears, the CGP has dual extended gear shafts which help transfer heat outward from the bearing journals into the cooler seal journals, and then on through the seals into the jacketed side plates. For optimal conductivity, all seals are contained within and are integral to the side plates. For further heat control, there are cooling channels placed in the body to wick heat away from bearing ODs and large, jacketed side plates help provide additional heat transfer from the bearings. Bleed material used for lubrication of the bearings and gears is evacuated from the process flow via internal ports to the outside of the pump in a constant bleed (approximately .01% of flow).