Chemical, mechanical purging combined

A joint development from Spirex and Asaclean-Sun Plastech has led to a patent-pending self-cleaning injection system that is said to remove resin from screws and barrels without having to disassemble them, eliminating leftover resin that can discolor parts or affect mechanical properties. The PowerPurge system allows molders performing quick color and material changes to reduce scrap thanks to high scrubbing capability. On most machines, PowerPurge can be programmed for one-touch operation into the existing controls. The system reduces the need for chemical purging compound, and it can be used on commodity or engineering grades of resin, including optical lines.

In the past, molders chose between disassembling the barrel and screw or using chemical purging compounds. PowerPurge combines these, with a three-piece valve featuring retainer body, check ring, and lock, as well as a specially formulated purging compound. The valve acts as a nonreturn device that also handles the self-cleaning PowerPurge mode. The PowerPurge formulation has low adhesion to metal surfaces, leaving less residue, and it can be used in smaller volumes.

Outside normal molding, where the valve acts in a nonreturn manner, the injection unit is moved away from the mold to remove resin through an air shot. Next the PowerPurge compound is put in place after a purge plug is inserted. The valve then locks into an open position, and the screw moves forward, creating high-pressure backflow and turbulent scrubbing and cleaning.

Demag Plastics Group will offer the technology as an option on its machines with a modified controller that allows the technology to run at the touch of a button. Spirex Corp., Youngstown, OH, US; +1 330-726-4000; www.spirex.com; Asaclean-Sun Plastech Inc., Parsippany, NJ, US; +1 800-787-4348; www.asaclean.com