PETpla.net Insider 04 / 2012

Vol.6 PET planet print PREFORM PRODUCTION 16 PET planet insider Vol. 13 No. 04/12 www.petpla.net Stringing The rapid guide to perfect preforms - part 28 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 28 of the guide. Symptom Hair-like strands of plastic are emerging from the preform gate nub. Cause The preform gate is too hot, causing the nub to draw out. Typically observed on non valve gated moulds, but can also be found with valve gated moulds as caused by the valve stem not closing properly. 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 water cooling temperature. This should be 7 – 10ºC (45 – 50ºF) for optimum cooling. 2. Check water cooling flow to mould. This should be at the mould manufac- turers rating (for a given preform size and cavitation). 3. Check all temperature readings and correct if necessary. PET resin should be melted at about 280ºC (536ºF) +/- 10ºC (18ºF). 4. Check nozzle tip heat settings. This area has a major impact on gate nub stringing. Settings too high may cause the dome and gate nub area to remain hot. The settings should be adjusted low enough to solidify the nub yet not too low to cause crystallin- ity to form. 5. Check that the cooling time is suf- ficient for the preform being moulded. This typically ranges from about 1 - 3sec depending upon the preform wall thickness. Increase time if necessary to improve nub solidification. 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