PETpla.net Insider 05 / 2010

PREFORM PRODUCTION 29 PET planet insider Vol. 11 No. 05/10 www.petpla.net Symptom: The outer surface of the preform gate / dome area has indenta- tions, usually formed in a circular pattern around the nub. The depression can be smooth or wrinkled in appearance. Cause: The gate area is deformed during the initial mould opening sequence (core side separating from cavity side) due to the preform not releasing freely from the cavity. 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 manufacturers rating (for a given preform size and cavitation). 3. Check that the cooling time is sufficient 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 shrinkage for better release. 4. Check that the hold (packing) time is not excessive for the preform being moulded. Reduce as necessary to minimise swelling. 5. Check that the hold (packing) pressure is not too high to cause excessive swelling, especially in the last zone. Reduce as necessary. 6. Check that transition position is set to about 13% of shot- size + cushion. Lower values may result in overfilling. 7. Check all temperature readings and correct if necessary. PET resin should be melted at about 280ºC (536ºF) +/- 10ºC (18ºF). 8. Check that all thermocouples are properly inserted and contacting the bottom of the wells. 9. Check that the decompression (pullback) time and position is not too little. This should be set high enough to ensure the melt pressure is being released, yet as low as possible to minimise the risk of drawing in air. Typical settings for valve gated moulds are: Time = 0 – 1sec; Distance = 0 – 10mm. Non-valve gated moulds may require higher values to mini- mise gate stringing. 10. Check the valve gate open delay timer and increase as necessary to release preform pressure. Typical settings are 0 – 0.3sec. This adjustment must work together with decompression (pullback) time. 11. Check hardware for worn, damaged or failed compo- nents, specifically the mould gate inserts, valve stems, and clogged core / cavity cooling channels. 11. GateDepressions PETplanet print Vol. 6: The Rapid Guide to Perfect Preforms by Rick Unterlander and Ottmar Brandau fax: +49 (0) 6221-65108-28 [email protected] www.petpla.net Order your copy now! 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 prices in EUR + VAT. 1- 3 exemplar each 129,- € 4 - 10 exemplar each 99,- € > 10 exemplar each 69,- € 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