Machine Builder Slashes Cost, Time with 'Purging Packet'
Coperion find iD Additives purging compound expedites changeovers and saves material.
Processors aren’t the only ones using purging compounds. Sometimes machine builders need them too. Especially those with laboratory lines used by their customers for testing, R&D and scale-up.
Such was the case with Coperion Corp., a leading supplier of twin-screw compounding extruders. At its lab in Sewell, NJ, the machine manufacturer has three lines from its ZSK series of co-rotating twin screw extruders equipped with various types of pelletizing systems. “The lab is typically busy with customers running trials or testing formulations,” says Justyn Pyz, Process Engineer for Coperion. “Sometimes customers run multiple tests over the course of several days. They may do a Design of Experiments (DOE) on one formulation one day, then come back the next day for another.” At the Coperion test lab, this means doing a complete clean-out between runs, which sometimes includes even screw pulls. Complete tear downs are done when the customer is finished with their trials.
For several years, Coperion had been purging with a, low-melt-flow PE that was left over from a customer trial. The material was in powder form, so before using it as a purging compounding the resin had to be pelletized. As the supply of that material started to dwindle, Coperion went looking for options, and ran into iD Additives at a conference in 2017, Pyz recalls iD Additives was displaying its QuickShots line of single-dose compounds. They come in individual packets and allow operators to purge their machinery by dropping the packets into the feed/throat/hopper of their machine. They are said to work with all resin types on all plastics machinery including injection molding, extrusion, and blow molding. Typical dosage is one oz./in. of screw diameter. No soaking or temperature adjustments are necessary.
Coperion and iD Additives conducted a trial in Coperion’s test lab and found that QuickShots reduced purging times from 4-5 hours to less than one hour, and sometimes even eliminated the need for a screw pull, says Nick Sotos, iD Additives president. Adds Pyz, “We certainly evaluated other suppliers, but found that QuickShots fit our needs. We find they’d been really good when purging Polyolefins and high-temperature engineering resins such as PPS, PPA and PEEK.” While Coperion still doses the PE as part of the purging process, Sotos maintains the machine builder has reduced use of the resin by more than 65%.
With vented extrusion, small amounts of melt can hang up on the screw and degrade, eventually resulting in streaks or specks that hurt the appearance of the extruded product.
For blow molders of HDPE parts, this is an all-too familiar sight at start-up time on Monday morning: The machine is purging leftover material onto the floor.
Maintenance departments often clean screws wrongly, causing serious and expensive damage.