PETpla.net Insider 11 / 2010

Vol.6 PET planet print PREFORM PRODUCTION 24 PET planet insider Vol. 11 No. 11/10 www.petpla.net The Rapid Guide to Perfect Preforms by Rick Unterlander and Ottmar Brandau Troubleshooting guides have suffered in the past from being locked away in offices and not being available to the people that actually need them. Considering the high cost of machine and tools high scrap rates can be a costly proposition eating away at already tight margins. PETplanet’s “Rapid Guide to Perfect Preforms” takes a different approach. Bound in laminated paper that is easy to clean off, the small format of the book of 108mm by 151mm (4.25” by 6”) allows easy storage in back pockets or tool boxes. It has been written for the people on the floor of injection moulding companies to support their daily work in making the best preforms possible. The product of two industry experts, Rick Unterlander and Ottmar Brandau, it gives concrete advice on 35 of the most common problems in preform manufacture, most illustrated by pictures. From high AA levels to wavy bodies processors can find help when they need it. Read chapter 16 of the story... PET planet print vol.6 The Rapid Guide to Perfect Preforms machine no./name 16. IV Loss Symptom: The resin IV (Intrinsic Viscosity) has been reduced by more than 0.04dl/g between resin and preform. This cannot be seen in the preforms, rather it needs to be tested in a laboratory with an IV tester or melt viscometer. Cause: The melt has been hydrolytically or severely thermally degraded during processing. Solutions: 1. Check dryer for alarms and correct as necessary. A high dewpoint (above –40ºC (–40ºF)) may cause extru- sion problems and must be rectified. The resin must be dried below 50ppm of water to minimize IV loss during melting. 2. Check for adequate resin drying time in hopper (should be around 4h at 175ºC (347ºF) and up to 6h at 160ºC (320ºF)). 3. Check all temperature readings and correct if necessary. PET resin should be melted at about 280ºC (536ºF) +/- 10ºC (18ºF). Excessive temperatures may degrade the melt. 4. Check all %-controlled temperature settings and minimize if possible. %-controllers provide no temperature feedback and require fine tuning. 5. Check that all thermocouples are properly inserted and contacting the bottom of the wells. 6. Check extruder back pressure and minimize if possible. Back pressure should be sufficient to provide good melt mixing, but not too much to cause excess shear. Typical range is 15 – 20bar (200 – 300psi). 7. Check screw rpm and minimize if possible. Screw speed should be reduced as much as possible to minimize shear heating, yet still recover within the cycle time of the machine. The stopped time at the end of recovery should be about 2sec to offset any fluctuations during screw recovery. 8. Check to ensure incoming resin IV was within specification (resin supplier). 9. Check hardware for worn, damaged or failed components, specifically the resin handling and storage area for excess moisture (silos), dryer hopper (especially the cone), resin in-feed line, and machine and mould heaters.