Process Parameters Affecting Plastic Molding

(I) Temperature

1. Cylinder temperature: It should be greater than the flow temperature of the plastic (melting point) and less than the decomposition temperature of the plastic.

＜When the barrel temperature is high - 'the plastic is easy to decompose and produce low molecular compounds decompose into gas, so that the surface of the plastic discoloration, bubbles, silver and mottled, resulting in performance degradation; 'high temperature' - the plastic inside and outside of the mold cavity is inconsistent, prone to internal stresses and dents. High material temperature' - the plastic inside and outside the mold cavity is not consistent, easy to produce internal stress and dents ﹒ 'High temperature of the melt, good fluidity, easy to overflow, overflow edge, etc.'.

＜2＞ When the barrel temperature is too low - 'Low material temperature' - poor fluidity, easy to produce defects such as weld marks, molding insufficiency, ripples, etc.; 'Uneven plasticization' - easy to produce cold lumps or stiff lumps, etc. ﹒'Low material temperature'-plastic cooling, easy to produce internal stress, easy to deform or cracked plastic parts.

2. Injection nozzle temperature

<1> Temperature is too high - the plastic is prone to decomposition reaction.

＜2＞ temperature is too low - nozzle clogging, easy to produce cold block or stiff block, etc.

3. Mold temperature: The actual melt flow in the mold cavity is non-isothermal, i.e., the temperature in each part of the cavity is not uniform.

<1> High mold temperature - slow cooling, easy to produce sticky mold, easy to deform the plastic parts when demolding, etc.

＜2＞ Low mold temperature-reduces the fluidity of melt, easy to produce molding shortage and fusion marks, when the melt cools down, the inner and outer layers do not cool down uniformly, easy to produce internal stresses ﹒ In a word, the temperature of the melt is high: easy to decompose, easy to produce internal stresses, the viscosity of the melt surface decreases, the fluidity is good, especially for the temperature-sensitive plastics, the mold is easy to fill up, easy to overflow and spill the edges, the shrinkage increases, easy to produce dents. Increase in shrinkage, easy to produce pits; in addition, decrease in crystallinity, decrease in orientation, etc. Uneven melt temperature: easy to produce internal stresses, e.g., in the actual mold cavity, the temperature is not uniform at all points, the melt flow is non-thermal flow. Low melt temperature: not easy to decompose; high surface viscosity, poor fluidity, difficult to fill the mold, easy to produce molding deficiencies, fusion marks, cold lumps, or stiff lumps.

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