Factors Affecting The Shrinkage Of Injection Molded Plastic Parts

- Aug 17, 2018-

  Shrinkage is an important factor considered in the processing of injection molded plastic parts. The main factors affecting the shrinkage of injection molded plastic parts are as follows: plastics in the plastic molding process due to the volume change of crystallization. The internal stress is strong, the residual stress in the plastic part is frozen, and the molecular orientation is strong. Therefore, compared with the thermosetting plastic, the shrinkage rate is large, the shrinkage rate is wide, the directionality is obvious, and the shrinkage, annealing or molding after molding is performed. The shrinkage rate after humidity control is generally larger than that of thermosetting plastics.

  When the plastic parts are molded, the molten material contacts the surface of the cavity and the outer layer is immediately cooled to form a low-density solid outer casing. Due to the poor thermal conductivity of the plastic, the inner layer of the injection molded plastic part is slowly cooled to form a high-density solid layer with large shrinkage. Thick, slow cooling, high-density layer thickness, large shrinkage. In addition, the presence or absence of inserts and insert layout, the number directly affects the flow direction, density distribution and shrinkage resistance, etc., so the characteristics of the injection molded plastic parts shrinkage The direction has a greater impact.

  The feeding port form, size and distribution directly affect the flow direction, density distribution, pressure-preserving and shrinking action and molding time. The direct feed port and the feed port have large cross-sections (especially thicker sections), but the shrinkage is small but the direction Largeness, the width of the feed port and the short length are small. The shrinkage is large when the feed port is close to or parallel to the flow direction.

  When the plastic parts are molded, the contact between the molten material and the surface of the cavity is immediately cooled to form a low-density solid outer casing. Due to the poor thermal conductivity of the plastic, the inner layer of the plastic part is slowly cooled to form a high-density solid layer with large shrinkage. Slow cooling, high density layer thickness, large shrinkage. In addition, the presence or absence of inserts and insert layout and quantity directly affect the flow direction, density distribution and shrinkage resistance, etc., so the characteristics of injection molded plastic parts shrink size, Directional influence is greater.