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.
Hydrostatic Weighing
Meaning
A gravimetric technique determines the density of a solid object by measuring its mass in both air and a liquid of known density. Utilizing hydrostatic weighing provides a highly accurate way to verify the specific gravity of moulded plastic parts and resin pellets. It relies on the principle that the loss of weight in the liquid is equal to the weight of the liquid displaced by the object.
Archimedes Principle
The upward buoyancy force acting on the submerged specimen allows for the calculation of its volume. When performing hydrostatic weighing, the technician records the dry weight and then the submerged weight using a precision balance. This difference is the basis for identifying shifts in material composition or the presence of internal defects.
Apparent Mass
The reading on the scale decreases when the part is lowered into the water or ethanol bath. In hydrostatic weighing, any air bubbles trapped on the surface of the specimen will cause a false reduction in the apparent mass. A wetting agent is often added to the liquid to ensure that the measurement reflects the true volume of the plastic.
Specimen Submergence
Total immersion is required to obtain a valid result for the entire part. Hydrostatic weighing is the preferred method for quality control because it can be performed on finished components without destroying them. Comparing the result to the virgin resin datasheet helps a moulder detect if the material has been degraded by excessive heat or the addition of too much regrind.
This method remains the gold standard for density verification in polymer laboratories.