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Plastic Mould Problems Solution_2
Plastic Mould Defects-Dark Spots
Different factors can cause the formation of dark spots or speckled:
1) process-related causes:
e.g. melt temperature too high or residence time in the plasticizing unit too long.
Wrong temperature in the hot-runner system
2) mold-related causes:
e.g. dirty gate system or wear ((dead spot)) in the hot-runner system
3) machine-related cuases:
e.g. dirty plasticizing unit or wear of screw and cylinder
4) caused by polymer or dyeing:
e.g. impurities in the granule, high reclaim content or unsuitable dye / master batch
Impurities in the granule? If yes, then
(1) check granule for impurities
Do dark spots appear after a change of material? If yes, then
(1) clean plasticizing unit
Is the melt temperature exceeding the processing range? If yes, then
Reduce melt temperature:
(1) vary cylinder temperature (-)
(2) vary screw speed (-)
(3) reduce back pressure
Is the residence time of the melt within the critical range? If yes, then
(1) reduce cycle time
(2) increase plasticizing time delay
(3) check dimensil on of plasticizing unit
If no, then
(1) check hot-runner temperature
(2) reduce reclaim content
(3) check dye for compatibility
(4) check plasticizing system, gate system and hot-runner for impurities, wear and dead spot
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