Blow Molding
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Bottom Pinch-Off/Flash of Polypropylene Blow-Molded Products
Problem Phenomenon
Flash or pinch-off marks appear at the bottom of the blow-molded product, requiring trimming.
Bottom flash affects appearance, and improper trimming causes leakage.
Cause Analysis
(1) The parison length is too long, and there is much excess material at the bottom
(2) The mold pinch-off edge is designed improperly or worn
(3) The mold clamping force is insufficient, and the bottom sealing is poor
(4) The parison wall thickness is too thick
(5) The mold temperature is too low, and the material cutting is not clean
Solution
(1) Adjust the parison length to reduce the excess material at the bottom
(2) Check the mold pinch-off edge; repair it if worn
(3) Appropriately increase the mold clamping force
(4) Adjust the parison wall thickness to a suitable value
(5) Appropriately increase the mold bottom temperature to a reasonable value within the range of 40-90°C
Key Takeaway
Bottom flash is caused by an excessively long parison or pinch-off edge problems; the parison length needs to be adjusted and the pinch-off edge maintained.
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