Injection Molding
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PSU Melt Fracture and Mold Filling Difficulty
Problem Phenomenon
When PSU is filled at increased injection speed, melt fracture appears on the product surface; the speed limit causes mold filling difficulty, and the contradiction is prominent for thin-walled long-flow parts.
Cause Analysis
PSU melt viscosity remains very high; excessive injection speed causes melt fracture, limiting the filling speed; the critical shear rate restricts the possibility of high-speed filling.
Solution
①Control injection speed in the medium range to avoid melt fracture; ②Increase melt temperature to reduce viscosity and assist filling; ③Optimize runners and gates to reduce flow resistance; ④Wall thickness not less than 1.5mm to ensure the flow length ratio.
Key Takeaway
PSU filling speed is limited by the melt fracture ceiling; temperature and structural compensation are more effective than forcibly increasing speed; a flow length ratio of 80 is a design constraint.; After confirming effectiveness, solidify the parameters and practices into the work instructions to prevent recurrence
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