Blow Molding
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Bottom Pinch-Off/Flash of High-Density Polyethylene Blow Molded Products
Problem Phenomenon
Flash or pinch-off marks appear at the bottom of the blow molded products, requiring trimming.
Bottom flash affects the appearance, and improper trimming leads to 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 design is improper 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 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, and 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 30-80°C range
Key Takeaway
Bottom flash is caused by an excessively long parison or pinch-off edge problems, and the parison length needs to be adjusted and the pinch-off edge maintained.
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