PETpla.net Insider 11 / 2011

Vol.6 PET planet print PREFORM PRODUCTION 14 PET planet insider Vol. 12 No. 11/11 www.petpla.net Sinks The rapid guide to perfect preforms - part 25 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 25 of the guide. Symptom: Depressions of various shapes and sizes that occur randomly on the preform surface. Cause: Excessive shrinkage has occurred while the preform is contained within the mould. 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 for correct shotsize setting. The injection cushion should be about 3 – 5mm to compensate for any melt process fluctuations. 2. Check injection time isn’t too low (injection rate too fast) and adjust if necessary. Injection rate should be about 10 – 12g/sec/cavity. 3. Check that the cooling time isn’t excessive for the preform being moulded. This typically ranges from about 1 to 3sec depending upon the preform wall thickness. Reduce time if necessary to minimize the risk of non- uniform shrinkage while contained in the mould. 4. Check to ensure hold (packing) pres- sure isn’t too low, especially near the beginning of hold time. Adjust higher if necessary to fully fill out the preform. 5. Check that the hold (packing) time isn’t too little for the preform being 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