Injection Molding
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Low Welding Strength of Polypropylene Injection-Molded Products
Fenómeno del problema
The strength of the product at the weld line is significantly lower than that of other parts, and it breaks at the weld line when stressed.
Low welding strength is usually 50-80% of the base material strength, affecting use safety in load-bearing and sealed products.
Análisis de la causa
(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 shrinkage compensation at the weld line is not enough
(3) The mold temperature is low, and the melt at the convergence cools rapidly
(4) The cavity venting is poor, and the gas at the convergence hinders fusion
(5) The weld line is located at a load-bearing part of the product
Solución
(1) Increase the melt temperature to the higher value within the range of 200-280°C
(2) Increase the mold temperature to the higher value within the range of 40-90°C
(3) Increase the injection pressure and holding pressure to ensure the weld line is fully compacted
(4) Improve mold venting, and set vent grooves or overflow wells at the weld line
(5) Adjust the gate position to move the weld line to a non-load-bearing part
Conclusión clave
Low welding strength is caused by insufficient melt fusion, and the welding quality needs to be enhanced by increasing the temperature and pressure and improving venting.
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