Injection Molding
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PET Preform Gate Stringing
Problem Phenomenon
A slender material tail is dragged out at the preform injection point; during blowing, the material tail disturbs the material flow at the bottom, forming weak points at the bottle bottom or even leakage.
Cause Analysis
The nozzle or hot runner gate temperature is too high, and the melt is not fully solidified when the mold opens and is drawn into strings; holding time too long and insufficient gate cooling also aggravate stringing.
Solution
①Appropriately lower the nozzle and gate zone temperature; ②optimize the matching of holding and cooling time; ③check the gate cooling water channel; ④trim stringing preforms and evaluate whether to scrap them.
Key Takeaway
Gate stringing directly affects bottle bottom strength and may cause leakage; temperature control and cooling matching are the key, stringing preforms should be rejected and must not flow into the blowing process with defects.
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