PETpla.net Insider 10 / 2010

PREFORM PRODUCTION 45 PET planet insider Vol. 11 No. 10/10 www.petpla.net 15. Internal Sinks 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 Symptom: Small round dimples that occur on the interior of the preform. Cause: Internal shrinkage has occurred after the external surface has solidified. Occurs while the preform is contained within the mould, typically due to better cavity side cooling vs. core side cooling. Solutions: 1. Check water cooling temperature. This should be 7 – 10ºC (45 – 50ºF) for optimum cooling. 2. Check water cooling flow to mould, especially the core side. This should be at the mould manufacturers rating (for a given preform size and cavitation). 3. Check that the valve stems are opening properly. A par- tially open valve stem may restrict melt flow. 4. Check to ensure that the valve gate compressed air pres- sure is sufficient to open the valve stems properly. Typical pressures are in the range of 8 – 10bar (120 – 145psi). 5. Check that the cooling time isn’t excessive for the preform being moulded. This typically ranges from about 1 to 3sec depending upon the preform wall thickness. Reduce time 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 fax: +49 (0) 6221-65108-28 [email protected]  www.petpla.net Order your copy now! prices in EUR + VAT. 1- 3 exemplar each 129,- € 4 - 10 exemplar each 99,- € > 10 exemplar each 69,- € if necessary to minimize the risk of non-uniform shrinkage while contained in the mould. 6. Check to ensure hold (packing) pressure isn’t too low, especially near the beginning of hold time. Adjust higher if necessary to fully fill out the preform. 7. Check that the hold (packing) time isn’t too little for the preform being moulded. Increase as necessary to optimize part weight. 8. Check all temperature readings and adjust as necessary. PET resin should be melted at about 280ºC (536ºF) +/- 10ºC (18ºF). 9. Check that the decompression (pullback) time and position is not excessive. This should be set as low as possible to minimize the risk of melt backflow into the nozzle tips, yet enough to eliminate drooling into the cavity from excess melt pressure. Typical settings for valve gated moulds are: Time = 0 – 1sec; Distance = 0 – 10mm. Non-valve gated moulds may require higher values to minimize gate stringing. 10. Ensure the mould neck insert and lock ring vents are clean. This will minimize melt flow resistance due to gas entrapment. 11. Check to ensure that no moisture exists on the moulding surfaces, either from water leaks or condensation. This may obstruct normal melt flow and cause filling problems. The environmental dewpoint should be below the chilled water temperature to eliminate the risk of condensation. 12. Check hardware for worn, damaged or failed components, specifically the core cooling tubes, valve stems, valve stem seals, and clogged core cooling channels.