Injection Molding
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Low weld strength of general-purpose polyethylene injection molded products
Problem Phenomenon
The strength of the product at the weld line is significantly lower than that of other parts, and it breaks from the weld line when stressed.
The weld strength is usually 50-80% of the base material strength, and affects the use safety in stressed and sealed products.
Cause Analysis
（1）The melt convergence temperature is low, and the two melt streams are not fully fused
（2）The injection pressure transmission is insufficient, and the holding and feeding at the weld line are not enough
（3）The mold temperature is low, and the melt convergence cools rapidly
（4）The cavity venting is poor, and the gas at the convergence hinders fusion
（5）The weld line is located in the stressed part of the product
Solution
（1）Raise the melt temperature to the higher value within the range of 160-260°C
（2）Raise the mold temperature to the higher value within the range of 30-80°C
（3）Increase the injection pressure and holding pressure to ensure that the weld line is fully compacted
（4）Improve the mold venting, and set venting grooves or overflow grooves at the weld line
（5）Adjust the gate position to move the weld line to a non-stressed part
Key Takeaway
Low weld strength is caused by insufficient melt fusion, and the welding quality needs to be enhanced by increasing the temperature, pressure, and improving the venting.
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