PETpla.net Insider 07+08 / 2011

PREFORM PRODUCTION 15 PET planet insider Vol. 12 5. Reduce the initial mould opening speed (for the first few mm only) or increase the mould break valve to minimize the stress when the pre- form is released from the cavity. 6. Check that the hold (packing) time isn’t too short for the preform being moulded. Increase as necessary to improve solidification. 7. Check that the hold (packing) pres- sure isn’t too high to cause exces- sive swelling, espe- cially in the last zone. Reduce as necessary. 8. Check that transition position is set to about 13% of shotsize + cushion. Lower values may result in overfill- ing. 9. Check all temperature readings and correct if necessary. PET resin should be melted at about 280ºC (536ºF) +/- 10ºC (18ºF). Mini- mize as necessary to reduce cooling require- ments. 10. Check that the decom- pression (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 minimize 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 minimize gate string- ing. 11. Check the valve gate close delay timer and decrease as low as possible to restrict any melt backflow into the nozzle tip area. 12. Check that the mould core half (moving platen side) doesn’t drop slightly during the unclamp and initial mould open sequence. This could scratch the bottom surface of the preforms. 13. Check that no anomalies are present on the moulding surfaces and robot cooling receptacles. Repair if neces- sary. 14. Ensure the mould / robot alignment is accurate. 15. Check hardware for worn, damaged or failed components, specifically the mould cavities, and clogged neck insert, cavity and robot receptacle cooling channels. www.petpla.net