Extrusion & Post
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Excessive Thermal Shrinkage of CMC Film
Problem Phenomenon
Thermal shrinkage of CMC film at 80°C is >12%, exceeding the 5% dimensional stability requirement
Cause Analysis
CMC extrusion orientation is released after heating, causing large shrinkage; CMC thermal expansion coefficient is large; film cooling freezes a large amount of orientation stress
Solution
1)Reduce extrusion draw ratio to reduce orientation freezing; 2)Film annealing at 60-80°C to release orientation stress; 3)Add 5-10wt% rigid resin to reduce thermal shrinkage; 4)Biaxial stretching process to balance orientation
Key Takeaway
Film thermal shrinkage is caused by orientation freezing; reducing draw ratio and annealing treatment are the key
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