Material Drying
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Insufficient impact strength of homopolymer polypropylene injection products
Fenómeno del problema
The product breaks in drop tests or impact tests, with impact strength lower than standard requirements.
The fracture shows brittle fracture characteristics with no obvious plastic deformation, and is easily damaged by impact in actual use.
Análisis de la causa
(1) Melt temperature too low; severe molecular chain orientation, large residual internal stress
(2) Mold temperature too low; rapid cooling causes low or uneven crystallinity
(3) Holding pressure too high; over-packing produces residual stress
(4) High material moisture content; hydrolysis at high temperature reduces molecular weight
(5) Regrind ratio too high or too many regrind cycles; each heat history of the material reduces molecular weight
Solución
(1) Increase melt temperature to the higher value within the 200-280°C range, reduce molecular orientation
(2) Increase mold temperature to the higher value within the 40-90°C range, improve crystallization quality
(3) Appropriately reduce holding pressure, avoid residual stress from over-packing
(4) Fully dry raw material, control homopolymer polypropylene moisture content below 0.02%
(5) Control regrind ratio not exceeding 20%, regrind used no more than 2 times
Conclusión clave
Insufficient impact strength is usually caused by excessive internal stress or material degradation; it needs to be addressed from temperature parameters, drying, and regrind control.
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