Density Testing Protocols under ISO 1183 for Customs Classification
ISO 1183 density testing determines customs tariff lines under Chapter 39; accurate classification demands exact fluid temperature control and plaque molding.
Microvoiding
Meaning
A physical defect consists of microscopic cavities that form within a polymer matrix during cooling or mechanical stress. The presence of microvoiding reduces the density of a moulded part and creates internal weak points that can lead to premature failure. It often occurs when the outer skin of a part freezes before the interior has fully densified, leaving small pockets of vacuum or gas.
Gas Entrapment
Rapid processing or insufficient venting can trap small amounts of air in the melt. If these bubbles are not compressed by sufficient packing pressure, microvoiding appears as a dispersed phase of tiny holes. This reduces the effective cross-sectional area of the part, making it less resistant to tensile loads and impact.
Structural Weakness
These internal gaps act as stress concentrators where cracks can easily start to grow. Over time, microvoiding can cause a component to fail well below its rated strength, especially if the part is exposed to vibrations or fluctuating temperatures. Identifying this issue requires cross-sectional analysis or high precision density testing to detect the loss of material volume.
Visual Alteration
Light scattering occurs when the internal cavities become large enough to interfere with photon transmission. While the resin itself remains clear, the presence of microvoiding gives the plastic a whitened or opaque appearance. This change in optical properties is a common indicator that the part has been subjected to excessive stress or environmental degradation.
Eliminating this defect requires a careful balance of injection speed, hold pressure and cooling time in the moulding cycle.