Injection Molding
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Weak PE '2079851475616104452 Weld Lines
Problem Phenomenon
PE products have obvious weld lines with low strength, cracking along the weld line under stress, and container products easily leak at the weld line.
Cause Analysis
PE crystallizes quickly, and when the melt fronts converge, they freeze quickly if the temperature is insufficient, with insufficient molecular chain entanglement; when venting is poor, the fronts entrain gas and cold material, further deteriorating the weld line strength and appearance.
Solution
①Increase the material temperature and injection speed to maintain the front temperature; ②open vent grooves at the convergence, with overflow wells if necessary; ③adjust the gate position to avoid stressed and sealing areas; ④appropriately increase the mold temperature to delay crystallization; ⑤select high-flow grades.
Key Takeaway
PE weld lines must 'entangle before crystallization': raise the temperature, increase the speed and vent all together, and design the weld line position to non-stressed areas; for sealing parts, the weld line position is more worth planning in advance than strength.
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