Innstøtningsporer

Innstøtningsporer, sometimes referred to as sink marks or sinkholes, are surface depressions or indentations that can occur in molded plastic parts. They are typically found on thicker sections of a part, often opposite to a reinforcing rib or boss. The formation of innstøtningsporer is a consequence of the cooling and solidification process of the plastic material during injection molding.

During injection molding, molten plastic is injected into a mold cavity. As the plastic cools and solidifies, it shrinks. The material on the surface of the part cools and solidifies first, forming a solid outer shell. However, the material in the thicker interior sections cools and shrinks more slowly. As this interior material solidifies and shrinks, it pulls away from the outer shell, creating a void or depression on the surface. This phenomenon is exacerbated when there is a significant difference in wall thickness within the part, as the thicker areas will experience more shrinkage than thinner areas.

The presence of innstøtningsporer can affect the aesthetic appearance of a molded part and, in some cases, can compromise its structural integrity if they are particularly deep or extensive. Several factors can influence the severity of innstøtningsporer, including the type of plastic material used, the melt and mold temperatures, the injection pressure, the cooling time, and the geometry of the part itself. Design considerations, such as minimizing drastic changes in wall thickness and strategically placing gates, can help mitigate their formation.