Injection Molding
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Underfilling/short shot appearing on polypropylene injection molded products
Fenómeno del problema
The product fails to completely fill the cavity, with missing material parts, incomplete edges, or local voids.
Short shot directly causes the product to be scrapped, and usually occurs first at parts with long flow distances, thin walls, or poor venting.
Análisis de la causa
（1）The injection pressure is insufficient or the injection speed is too slow, and the melt solidifies prematurely during mold filling
（2）The barrel temperature is too low (below the 200-280°C lower limit), the melt viscosity is high and the flowability is poor
（3）The mold temperature is too low, the melt cools rapidly after contacting the mold wall, and the flow distance is shortened
（4）The gate size is too small or the runner is too long, and the melt flow resistance is large
（5）The cavity venting is poor, and the trapped gas hinders the melt filling
Solución
（1）Raise the injection pressure to 80-150MPa, increase the injection speed, and shorten the mold filling time
（2）Raise the barrel temperature to the higher value within the range of 200-280°C to reduce the melt viscosity
（3）Raise the mold temperature to the higher value within the range of 40-90°C to delay melt cooling
（4）Increase the gate and runner sizes, shorten the runner length, and reduce the flow resistance
（5）Check and improve the mold venting, adding venting grooves or venting pins at the filling end
Conclusión clave
Short shot is the result of insufficient melt flowability or excessive mold filling resistance, and needs to be solved by raising the temperature, pressure, and improving the gating and venting system.
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