Three Key Indicators Affecting Plastic Quality

1. Plastic Shrinkage

• Causes: Thermal shrinkage, cooling shrinkage, molecular orientation, and phase changes.

• Stages:

• From injection to holding pressure;

• From cooling to before demolding;

• After demolding.

• Causes of Deformation: Uneven shrinkage, caused by:

• Uneven cooling,

• Uneven wall thickness,

• Uneven pressure distribution,

• Molecular orientation,

• Uneven demolding force.

  
  

2. Plastic Crystallization

• Definition: The orderly arrangement of molecules.

• Influencing Factors: Mainly cooling speed—the faster the cooling, the lower the crystallinity.

• Impact on Product Performance: Higher crystallinity leads to greater density, strength, shrinkage, and surface finish, but reduced toughness.

3. Plastic Viscosity

• Definition: A measure of a fluid’s resistance to flow; higher values indicate poorer flowability.

• Influencing Factors: Temperature, shear rate, and pressure.

• Note: These three factors interact; different materials respond differently, and their dominant effect varies with injection speed.