PETpla.net Insider 10 / 2011

Vol.6 PET planet print PREFORM PRODUCTION 18 PET planet insider Vol. 12 No. 10/11 www.petpla.net Short shots The rapid guide to perfect preforms - part 24 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. 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 pos- sible. 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 24 of the guide. Symptom: The preform thread finish is incompletely formed. The degree of incompleteness can range from a slight absence of the TSS (top sealing surface) and upper threads to a complete missing neck finish and/or main body section. Cause: There was not enough melt injected to completely form the preform. 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 high (injection rate too slow) and adjust if necessary. Injection rate should be about 10 – 12g/sec/cavity. 3. 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 neck finish con- tour and TSS. 4. Check that the hold (packing) time isn’t too little for the preform being moulded. Increase as necessary to optimize part weight. 5. Check that the valve stems are open- ing properly. A partially open valve stem may restrict melt flow. 6. Check to ensure that the valve gate compressed air pressure is sufficient 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