Molds & Tooling
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Material Factors of PC Stress Cracking
Problem Phenomenon
Under the same mold and same process, the cracking rate of certain batches or grades of products is significantly higher
Cause Analysis
PC molecular weight determines the crack resistance: high molecular weight means more chain entanglement, strong crack resistance but poor flowability; low molecular weight high-flow grades and excessive regrind ratios both reduce the crack resistance
Solution
①For stressed parts, prioritize low MFR high molecular weight grades; ②regrind not exceeding 20% and clean and dry; ③compare the melt index and impact for batch changes; after adjustment, take samples continuously to verify the effect, and resume mass production only after confirming stability
Key Takeaway
Crack resistance is first a material property; MFR selection and regrind control are the source, and the process can only be optimized on this basis; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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