Molds & Tooling
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PVDF High Shrinkage Causes Sink Marks and Shrinkage Voids
Problem Phenomenon
【Problem phenomenon】Surface sink marks and cross-section shrinkage voids on PVDF thick-walled sheets and rods, with dimensional deviation out of tolerance
Cause Analysis
PVDF's shrinkage of 2-3% is higher than most engineering plastics; insufficient shrinkage compensation during cooling and shrinking of thick-walled areas causes collapse into marks or internal voids; unreasonable gate design seals the compensation channel prematurely and aggravates the defect
Solution
Increase holding pressure to 80-120MPa and extend holding time; reduce material in thick-walled areas or set cooling inserts; enlarge the gate to delay freezing; anneal sheets and rods at 80-120℃ after molding to stabilize dimensions
Key Takeaway
2-3% high shrinkage is PVDF's nature; strengthened holding pressure plus structural material reduction is a two-pronged treatment; After confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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