PETpla.net Insider 05 / 2012

Vol.6 PET planet print PREFORM PRODUCTION 16 PET planet insider Vol. 13 No. 05/12 www.petpla.net Surface blemishes The rapid guide to perfect preforms - part 29 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 29 of the guide. Symptom Scratches, random smudges, and ellipti- cal marks that appear on the outside surface of the preform. Best observed under a polarized light fixture. Cause Preforms get marked when they con- tact each other (and other items) during handling. This consists of all forms of handling including part ejection, convey- ance, bulk collection, transportation of finished production, and unloading for 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 subsequent processing. The marks may be amplified if the preforms are insuf- ficiently cooled before handling begins, particularly if ejected above a 60°C (140°F) surface temperature. Solutions 1. Check water cooling temperature. This should be 7 – 10ºC (45 – 50ºF) for optimum cooling. 2. Check water cooling flow to mould and robot cooling receptacles. This should be at the mould manufactur- ers rating (for a given preform size and cavitation). 3. Check that the cooling time is suffi- cient for the preform being moulded. This typically ranges from about 1 to 3sec depending upon the preform wall thickness. Add time if necessary to increase solidification. 4. Maximize the cooling time of the robot. This should not be increased beyond the cycle time of the machine. 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