Injection Molding
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PET Preform Short Shot Material Shortage
Problem Phenomenon
The preform body or threaded neck is incompletely filled, with material shortage and incomplete contour, and the weight is lower than the set value.
Cause Analysis
Insufficient injection pressure, low melt temperature, blocked gate or abnormal hot runner valve pin action, causing the melt to not fill the cavity; unbalanced filling of each cavity in multi-cavity molds also causes short shots in individual cavities.
Solution
①Increase injection pressure and speed; ②appropriately raise the melt temperature to improve flowability; ③clean the gate and check valve pin action; ④weigh preforms cavity by cavity and balance hot runner temperature.
Key Takeaway
Preform short shots are directly scrapped, and need to be quickly located from the three aspects of pressure, temperature and gate; multi-cavity molds should monitor the weight cavity by cavity to ensure filling consistency of each cavity.; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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