Several points that affect the quality of Plastic injection mold
Jul 15, 2021
1), Plastic materials
The complexity of the properties of plastic materials determines the complexity of the injection molding process. The properties of plastic materials vary greatly depending on the variety, grade, manufacturer or batch. Different performance parameters can lead to completely different molding results.
2), Injection temperature
The melt flows into the cooling cavity and dissipates heat due to heat conduction. At the same time, depending on the injection molding conditions, heat is generated by shear, which can be more or less than heat transfer. As the temperature increases, the viscosity of the melt becomes lower. Therefore, the higher the injection temperature, the lower the viscosity of the melt and the smaller the required filling pressure. At the same time, the injection temperature is also limited by the thermal degradation temperature and decomposition temperature.
3) Mold temperature
The lower the mold temperature, the faster the heat loss due to heat conduction, and the lower the temperature of the melt, the worse the fluidity. This phenomenon is especially noticeable when using a lower injection rate.
4), Injection time
The impact of injection time on the injection molding process is manifested in three aspects:
(1) To shorten the injection time, the shear strain rate in the melt also increases, and the injection pressure required to fill the cavity also increases.
(2) Shorten the injection time, increase the shear strain rate in the melt, and reduce the viscosity of the melt due to the shear thinning properties of the plastic melt, and the injection pressure required to fill the cavity is also required.
(3) To shorten the injection time, the shear strain rate in the melt increases, the shear heat increases, and the heat loss caused by heat conduction is small. Therefore, the melt temperature is high, the viscosity is low, and the pressure required for injection filling the cavity should also be reduced. Due to the combination of the above three conditions, the injection pressure curve required to fill the cavity presents a "U" shape. In other words, there is an injection time that requires a small injection pressure.
