PETpla.net Insider 12 / 2012

Vol.6 PET planet print PREFORM PRODUCTION 16 PET planet insider Vol. 13 No. 12/12 www.petpla.net The rapid guide to perfect preforms - part 35 Weld 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 now the last chapter of the guide. Symptom Tiny crevices formed on the TSS (top sealing surface) of the preform, usually observed through a 10X loop. Cause Two melt fronts that didn’t form together properly produce a minuscule slit at their intersection point. Typically occurs when the melt is split around an intrusive mould feature (such as a perform thread), then reunited imperfectly. Solutions 1. Check injection time isn’t too high (injection rate too slow) and adjust 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 if necessary. Injection rate should be about 10 – 12g/sec/cavity. 2. Ensure the mould neck insert and lock ring vents are clean. This will minimize gas entrapment at the TSS. 3. Ensure the TSS surface on the cores and lock rings are clean. This will eliminate any obstructions when the melt is forming. 4. 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. 5. Check all temperature readings and adjust higher if necessary. PET resin should be melted at about 280ºC (536ºF) +/- 10ºC (18ºF). 6. Check to ensure that no moisture exists on the moulding surfaces, either from water leaks or condensa- tion. This may obstruct normal melt flow and cause filling problems. The environmental dewpoint should be below the chilled water temperature to eliminate the risk of condensation. 7. Check hardware for worn, dam- aged or failed components, spe- cifically the mould neck inserts (col- lapsed vents), lock ring vents, and lock ring / core parting line. www.petpla.net 16........................................ IV Loss 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