Extrusion & Post
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PET Preform Black Speck Impurities
Problem Phenomenon
Black or brown dots appear in the transparent body of the preform; after blowing, the black specks are stretched and enlarged, forming visible contamination and stress concentration points.
Cause Analysis
PET retained long-term at dead corners of the barrel and hot runner carbonizes, falls off and mixes into the melt; incomplete cleaning during material change, contaminated raw material or regrind, and metal chips from equipment wear also form black specks.
Solution
①Thoroughly clean the barrel and hot runner, remove retained material at dead corners; ②standardize the material change process and the use of purging material; ③strengthen the cleanliness management of raw material and regrind; ④check the wear of the screw and check ring.
Key Takeaway
Black specks mostly originate from equipment cleanliness and thermal management problems; black-specked preforms cause weak points and poor appearance of the bottle body, so a regular machine cleaning system should be established and the effect of each cleaning recorded.
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