Injection Molding
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General-purpose polyethylene injection molded products underfill/short shot
Fenómeno do problema
The product fails to completely fill the cavity, with underfilled areas, incomplete edges or local voids.
Short shots directly cause product scrapping, usually occurring first at parts with long flow distances, thin walls or poor venting.
Análise das causas
（1） Injection pressure insufficient or injection speed too slow, the melt solidifies prematurely during filling\
（2） Barrel temperature too low （below the 160-260°C lower limit）, melt viscosity high and flowability poor\
（3） Mold temperature too low, the melt cools rapidly after contacting the mold wall and the flow distance is shortened\
（4） Gate size too small or runner too long, melt flow resistance large\
（5） Poor cavity venting, trapped gas hinders melt filling
Solução
（1） Increase injection pressure to 80-150MPa, increase injection speed, shorten filling time\
（2） Increase barrel temperature to the higher value within the 160-260°C range, reduce melt viscosity\
（3） Increase mold temperature to the higher value within the 30-80°C range, delay melt cooling\
（4） Enlarge gate and runner dimensions, shorten runner length, reduce flow resistance\
（5） Check and improve mold venting, add vent grooves or vent pins at the filling end
Conclusão principal
Short shot is the result of insufficient melt flowability or excessive filling resistance, and needs to be solved by increasing temperature, pressure and improving the gate and venting system.
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