Preheating the Polymer…

A customer asked me this question the other day…

We are using a screw specifically designed for our grade of PP, we have performed the tact temperature study, and have optimized both injection and packing. All these have helped, yet our cycle time is still limited by the screw recovery time, do you have any suggestions?

My Response
Once the process and screw have been optimized, the next step you can undertake is to preheat the polymer. Even though this material does not need drying, a simple hot air hopper dryer can be used to preheat the material to reduce he amount of heat necessary to melt the material. The more heat that is added to the material before it enters the barrel, the less energy that is required by the screw and heater bands.
Semi-crystalline polymers benefit most from pre-heating since the polymer will typically endure more preheating due to their sharp melting point.
Additional Thoughts
Always be cautious of your temperature in both the feedthroat and rear zone of the barrel. Since preheating hastens the melting, you may need to repeat the tact temperature study.

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