PETpla.net Insider 06 / 2012

Vol.6 PET planet print PREFORM PRODUCTION 12 PET planet insider Vol. 13 No. 06/12 www.petpla.net The rapid guide to perfect preforms - part 30 Thread flow lines 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 proposi- tion eating away at already tight margins. PETplanet’s “Rapid Guide to Perfect Preforms” takes a different approach. 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 Unter- lander and Ottmar Brandau, it gives concrete advice on 35 of the most common problems in preform manufacture, most illustrated by pic- tures. From high AA levels to wavy bodies pro- cessors can find help when they need it. Read chapter 30 of the guide. Symptom Translucent streaks on the outer surface of the neck finish. Usually found near a thread or neck feature. Cause The melt flow has been disturbed by the contour changes in the neck insert, caus- ing gas / air to fold over and become trapped. This defect is exacerbated with polished neck insert surfaces. Table of Contents i........................ About the Authors ii.................................Introduction Chapter 1.............................. AA Level High 2........................ Accordion Preform 3....................... Air hooks / Streaks 4............................... Black Specks 5...................................... Bubbles 6..................................Burn Marks 7...........................Colour Streaking ................................... /Peeling 8..................................Crystallinity 9.................................Drool Marks 10.......................................... Flash 11......................... Gate Depressions 12............................... Gate Peeling 13..................Gate Voids / Pin Holes 14......................... Internal Gate Sink 15................................Internal Sinks 16........................................ IV Loss Solutions 1. Check injection time isn’t too low (injection rate too fast), especially in the last zones when the melt flows into the neck finish area, and adjust if necessary. Injection rate should be about 10 – 12g/sec/cavity. 2. Check to ensure hold (packing) pressure isn’t too low, especially near the beginning of hold time. Adjust higher if necessary to improve thread formation. 3. Ensure the mould neck insert and lock ring vents are clean. This will minimize gas entrapment at the TSS (Top Sealing Surface). 4. Ensure the neck inserts are clean. This will eliminate any obstructions when the melt is forming. 5. Check to ensure hold (packing) pres- sure isn’t too low, especially near the beginning of hold time. Adjust higher if necessary to fill out TSS contour. 17............................ Long Gate Nub 18...............................Milky Preform 19............................ Moisture Marks 20................Neck Finish out of Round 21....................... Parting Line Crease 22.................Parting Line Deformation 23......................... Preform Yellowing 24.................................. Short Shots 25.......................................... Sinks 26......................................... Splay 27........................... Stretched Necks 28..................................... Stringing 29......................... Surface Blemishes 30.. ....................... Thread Flow Lines 31...............TSS (Top Sealing Surface) ......................................... Sink 32.......................................Unmelts 33.................Wall Thickness Variation 34.................................Wavy Body 35.................................. Weld Lines