Molds & Tooling
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PET preform sprue stringing
Problem Phenomenon
Sprue stringing sticks, the robot fails to take the preform, and the strings enter the next mold cavity to form impurity spots
Cause Analysis
Hot runner nozzle unable to close or worn, nozzle temperature too high, gate valve delayed closing too long, and valve pin control failure can all cause sprue stringing; during on-site troubleshooting, verify item by item according to this mechanism, and avoid blindly adjusting the machine based only on experience
Solution
① Maintain the hot runner cylinder or replace the nozzle; ② lower the nozzle heating temperature; ③ reduce the gate valve delayed closing time; after adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability
Key Takeaway
Sprue stringing is a health indicator of the hot runner system; valve pin timing and nozzle condition checks should be included in the daily maintenance list; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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