Purging, injection molding machines

Standard reciprocating screw injection molding machines can be used Process on clean machines, avoid purging... 

Decomposition, or burning, of the plastics material in the injection molding machine will cause color changes and will then result in the subsequent injection moldings being rejected. When this happens a complete shut down and clean out may be necessary. To prevent this it may be necessary to purge a heat sensitive resin with another, more heat stable, plastics material as this will withstand subsequent reheating. 

Typically, the injection molded article has low crystallinity upon molding with increased crystalhnity within 24 hours. Polyethylene plastic is an excellent purge material for injection molding machines. PHA plastics should be dried for 4 hours at 85 ° C prior to molding for improved mechanical properties. 

Blends of PCTG with PC or SMA are typically injection molded into business machine, appliance and automotive parts but can also be extruded. Eilms of thickness 0.025 mm can be extruded and sheet thickness up to 3.2 mm is possible when conventional extrusion equipment is used. Typical processing conditions vary depending on film or sheet thickness. PP, HOPE or an acrylic compound is used for purging. 

The dark TPE was the first material to be run. The material was purged through the screw and barrel to allow for a homogeneous melt. The optimal injection velocity, for the dark TPE, was keyed into the molding machine the shot size then needed to be manipulated to create the short shot. The study used short shots of the impact disc to have a visual representation of the flow front as the melt flows across the part. The short shot was molded at approximately 40 percent of the full part. The process being used was then recorded, and the process was left to stabilize for five to ten minutes. 

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