PETpla.net Insider 12 / 2010

Vol.6 PET planet print PREFORM PRODUCTION 20 PET planet insider Vol. 11 No. 12/10 www.petpla.net Long Gate Nub Chapter 17 of 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 pock- ets 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 17 of the guide. Symptom: The projected gate nub has extended beyond its normal length. Cause: The preform gate nub is deformed either during the initial mould opening sequence (core side separating from cavity side) due to the nub not releasing freely from the gate (photo A), or from poor formation due to the valve stem not closing properly (photo B). Solutions: 1. Check water cooling temperature. This should be 7 – 10ºC (45 - 50ºF) for optimum cooling. 2. Check water cooling flow to mould. This should be at the mould manufacturers rating (for a given preform size and cavitation). 3. Check dryer for alarms and correct as necessary. A high dewpoint (above –40ºC (-40ºF)) may cause extrusion prob- lems, leading to downstream melt strength problems and must be rectified. The resin must be dried below 50ppm of water to minimize IV loss and melt strength issues. 4. Check for adequate resin drying time in hopper (should be around 4h at 175ºC (347ºF) and up to 6h at 160ºC (320ºF)) 5. Check all temperature readings and correct if necessary. PET resin should be melted at about 280ºC (536ºF) +/- 10ºC (18ºF). 6. Check nozzle tip heat settings. This area has a major impact on gate nub quality. Settings too high may cause the dome and gate nub area to remain hot and easily deformable. The settings should be adjusted low enough to improve nub strength yet not too low to cause crystallinity to form. A: Holland Continued on page 25