PETpla.net Insider 09 / 2011

PREFORM PRODUCTION 23 PET planet insider Vol. 12 No. 09/11 www.petpla.net Symptom: Preforms have a yellow tint, not local- ized to a specific area but throughout the entire preform. Colouration may sometimes have a greenish hue. Cause: The resin has been thermally and/or oxi- datively degraded, but not to the point of black specks. Solutions: 1. Check dryer for alarms and correct as necessary. A high temperature (above 175ºC (347ºF)) may cause rapid degradation especially if resin flow is idle. 2. Check condition of resin and/ or regrind quality. Remove any degraded pellets or chips from dryer hopper and in-feed line. 3. Check for excessive resin drying time in hopper (should be around 4h at 175ºC (347ºF) and up to 6h at 160ºC (320ºF)). 4. Check all temperature readings and correct if necessary. PET resin should be melted at about 280ºC (536ºF) +/- 10ºC (18ºF). 5. Check all %-controlled temperature settings and minimize if possible. %-controllers provide no temperature feedback and require fine tuning. 6. Check that all thermocouples are properly inserted and contacting the bottom of the wells. 7. Check extruder back pressure and minimize if possible. Back pressure should be sufficient to provide good melt mixing, but not too little to cause bubbles to appear. Typical range is 15 – 20 bar (200 – 300 psi). 8. Check screw rpm and minimize if possible. Screw speed should be reduced as much as possible to minimize shear heating, yet still recover within the cycle time of the machine. The stopped time at the end of recovery should be about 2sec to offset any fluctuations during screw recovery. 9. Make sure the extruder screw cushion is not excessive. This should be a minimum of 25mm to compensate for any dynamic recovery fluctuations. (Two-stage machines only) 10. Check hardware for worn, dam- aged or failed components, spe- cifically the machine and mould heaters, and a misaligned shut-off nozzle. 11. For prevention, always: a.Reduce temperatures by about 40ºC (104ºF) if the machine stops for more than 15min b.Reduce %-controllers by ½ if the machine stops for more than 15min c. Shut off nozzle tip heats if the machine stops for more than 10min d.Never exceed start up tempera- ture soak times. Machine should be started within 15min of the temperatures reaching operat- ing settings. Nozzle tips should only be turned on 5 to 7min prior to start up. e. Always reduce the dryer tempera- ture to about 120°C if stopped for more than 30min and 80ºC (176ºF) if stopped for more than 2h. www.petpla.net 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 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 Eisbär Material Drying PRODUCER MODEL LOW ENERGY CONSUMPTION LOW ENERGY CONSUMPTION LOWEST ENERGY CONSUMPTION ON THE MARKET RATING AAA Energy A Eisbär B C D E F G All the others A WWW.EISBAER.AT WUHRMÜHLE 22 / A-6840 GÖTZIS T +43 5523 55558-0 / COOL@EISBAER.AT