Lately I have noticed a great deal of companies ignoring the integrity of the material during screw recovery. During a recent on-site training visit, one student was encountering significant quality issues with a particular product molded from TPE. In reviewing the situation, it appears the material may be damaged or degraded during recovery which will contribute to the quality issues they are encountering.
When recovering the next shot, it is important that you consider the following factors.
1) Melt Temperature – Don’t rely on your barrel temperatures alone, actually measure the temperature of the polymer melt once the process has stabilized.
2) Rear Zone Temperature – The rear zone temperature has the highest influence on the material conveyance through the feed zone to the transition zone.
3) Screw Recovery Time – The recovery time should consume about 80% of the overall cooling time to maximize melting efficiency.
4) Back Pressure – The back pressure should remain low unless there are specific mixing issues or inconsistent recovery times.