Injection Molding
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Low weld strength of low density polyethylene injection products
Fenómeno do problema
The strength of the product at the weld line is significantly lower than other parts, and it breaks from the weld line under stress.
Low weld strength is usually 50-80% of the base material strength, affecting use safety in load-bearing and sealing products.
Análise das causas
(1) Low melt convergence temperature; insufficient fusion of the two melt fronts
(2) Insufficient injection pressure transmission; inadequate holding pressure compensation at the weld line
(3) Low mold temperature; rapid cooling at the melt convergence
(4) Poor cavity venting; gas at the convergence hinders fusion
(5) Weld line located at the stressed part of the product
Solução
(1) Increase melt temperature to the higher value within the 160-220°C range
(2) Increase mold temperature to the higher value within the 30-60°C range
(3) Increase injection pressure and holding pressure, ensure full compaction at the weld line
(4) Improve mold venting; set vent grooves or overflow wells at the weld line
(5) Adjust gate position, move the weld line to a non-stressed area
Conclusão principal
Low weld strength is caused by insufficient melt fusion; weld quality needs to be enhanced by increasing temperature, pressure, and improving venting.
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