Harmonized System Subheading Verification Using Immersion Density Protocols
Immersion density testing verifies polymer tariff subheadings by resolving specific gravity at 23 °C on void-free annealed plaques.
ISO 293 Annex C
Meaning
Specific guidelines for the compression moulding of thermoplastic test specimens are found in the technical supplement known as iso 293 annex c. This section provides the precise cooling rates and pressure sequences required to produce consistent crystal structures in materials like polyethylene or polypropylene. Standardized sample preparation ensures that a datasheet value from one laboratory matches the results from another.
Deviations from these procedures can lead to variations in density or mechanical strength that mask the true properties of the resin.
Cooling Rate
Rapid cooling through the glass transition or melting point can freeze in internal stresses and alter the crystallinity of the polymer. Under the rules of iso 293 annex c, the mould temperature is dropped at a controlled rate of 15 degrees Celsius per minute. This slow reduction allows for a more uniform grain structure and reduces the risk of warping in the final plaque.
Pressure Sequence
Maintaining a constant load during the cooling phase compensates for the volumetric shrinkage that occurs as the melt solidifies. The standard dictates the contact pressure and the full moulding pressure to ensure that no voids or sink marks form.
Property Correlation
Results obtained from plaques made using these methods serve as the baseline for material selection and design calculations. Because injection moulded parts often cool much faster and experience higher shear, the values from iso 293 annex c represent a more relaxed and ideal state of the material. Designers apply appropriate safety factors when moving from a test plaque to a complex mass produced component to account for these structural variations.