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Four Points That Affect The Quality Of Injection Molds
Jun 05, 2018

Core Tip: When injection molds are manufactured, there are often many factors that affect the quality of the products. There are four main points to summarize:

 

    1). Plastic materials

 

    The complexity of the properties of plastic materials determines the complexity of the injection molding process. However, the properties of plastic materials vary greatly due to different varieties, different brands, different manufacturers, and even batches. Different performance parameters can lead to completely different molding results.

 

    2). Injection temperature

 

    The melt flows into the cooled cavity and dissipates heat due to heat conduction. At the same time, due to the heat generated by the shearing action, this part of the heat may be more or less than the amount of heat lost by heat conduction, depending on the injection molding conditions. The viscosity of the melt becomes lower as the temperature increases. In this way, the higher the injection temperature, the lower the viscosity of the melt and the lower 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 dissipation due to heat conduction, the lower the melt temperature, the worse the flowability. This phenomenon is especially noticeable when using lower injection rates.

 

    4). Injection time

 

    Injection time affects the injection molding process in three ways:

 

    (1) When the injection time is shortened, the shear strain rate in the melt is also increased, and the injection pressure required to fill the cavity is also increased.

 

    (2) Shortening the injection time increases the shear strain rate in the melt. Due to the shear thinning property of the plastic melt, the viscosity of the melt decreases, and the injection pressure required to fill the cavity also decreases.

 

    (3) Shortening the injection time, the shear strain rate in the melt increases, the greater the shear heat generation, and the less heat is lost due to heat conduction, so the melt temperature is high, the viscosity is lower, the injection required to fill the cavity The pressure should also be reduced. As a result of the above three conditions, the curve of the injection pressure required to fill the cavity is “Ushaped. That is, there is an injection time when the required injection pressure is minimal.

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