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6 ROTATIONAL MOULDING APPENDIX 1 – ROTATIONAL MOULDING TROUBLESHOOTING GUIDE Problem /Issue Air Entrapment Corners do not fill Cause(s) Potential Solution(s) /Action(s) Failure during Chemical Storage Flashing Insufficient Rigidity in Moulding Odour, shiny yellow- ish internal surface Parts Stick in Mould Poor Impact Properties Wall Thickness Variation Warpage Insufficent heating Powder quality Cycle time too short Design – sharp corners or small gaps between walls Powder has poor dry flow Contents not compatible with container Design – Stress concentrators present Thickness insufficient Service temperature too high Contamination in part line MFI of polymer too high Unevenly clamped mould Poor venting Wall thickness too thin Density of Resin too low Design Overcuring Insufficient mould release due to inadequate application Mould release diminished with number of shots Design Mould damage Poor mould finish Design Undercure – Small voids are present in wall sections Overcure – Internal surface is shiny Choice of Polymer Poor powder quality. Tails and poor flowability Incorrect rotation Variable heating of the mould walls Uneven Cooling due to large thickness variations Uneven Cooling due to premature separation from mould surface Poor Venting Cook to a higher peak internal air temperature Powder may be too course or contains tails. Consult powder supplier Increase heating time Redesign mould Contact Powder supplier Discontinue or revise service life appropriately Redesign mould Increase shot weight Increase shot weight, reduce maximum exposure temperature Ensure good cleaning practices Change to a lower MFI grade Check clamping mechanism Check vent is not blocked and is of sufficient size Increase shot weight Trial higher density resin Design stiffening features or ribs may be required Reduce temperature or heating time. Reduce peak internal air temperature Reapply mould release Reapply mould release Check for undercuts Inspect mould and repair if required Inspect mould and repair if required Review Design, minimising any sharp corners or areas of stress concentration Cook to a higher peak internal air temperature Cook to a lower peak internal air temperature Lower Density and/or lower MFI grades may enable increased impact resistance Contact Powder supplier Alter rotations Check for thickness variation of the mould wall. Check for shielding effects Alter rotation ratio. Review design Reduce mould cooling or apply internal cooling. Reduce mould release Check vent is not blocked and is of sufficient size Disclaimer The proposed solutions in this guide are based on conditions that are typically encountered in the manufacture of products from polyethylene. Other variables or constraints may impact the ability of the user to apply these solutions. Qenos also refers the user to the disclaimer at the beginning of this document. 18 QQeennoossTTeecchhniicallGuidesPDF Image | ROTATIONAL MOULDING Guide
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