Overview
ISO 4897:1985 - Cellular plastics: Determination of the coefficient of linear thermal expansion of rigid materials at sub-ambient temperatures specifies two laboratory methods to measure how rigid cellular plastics contract/expand at temperatures below ambient. Method A (preferred) determines the coefficient at a chosen sub‑ambient temperature on a large specimen and is more representative where anisotropy exists. Method B gives an average coefficient across a temperature interval (typically from a cryogenic bath to ambient) and is designed for economy and simplicity. An annex describes suitable test apparatus in detail.
Key topics and technical requirements
- Two test methods
- Method A: large rectangular board specimen (900 ± 2 mm length; 100–300 mm width; 25–50 mm thickness). Uses a well‑insulated test chamber with controlled cooling (liquid nitrogen commonly used), a reference length material (silica rod, 880 ± 5 mm), and a travelling microscope (resolution 0.01 mm).
- Method B: small parallelepiped specimens (50 ± 1 mm length; 20 × 20 ± 1 mm cross‑section). Uses immersion in a cryogenic bath (Dewar), a silica tube/piston system and a micrometer (resolution 0.001 mm).
- Specimen conditioning: 23 ± 2 °C and 50 ± 5 % RH for at least 16 hours prior to testing.
- Temperature control and measurement: thermometer devices calibrated to within 1 °C; temperature stability and measurement tolerances specified (e.g., ±2 °C in Method A measurements).
- Data treatment: results plotted as length vs. temperature; mean coefficient calculated from measured ΔL over ΔT with formulae provided. Report must include sample ID, conditioning, anisotropy direction, temperature range, graph, and mean coefficient to two significant figures.
- Anisotropy considerations: the standard warns many rigid cellular plastics are anisotropic; sampling direction must be recorded and multiple specimens used.
Applications and practical value
- Provides standardized tests for assessing thermal contraction/expansion of rigid cellular plastics used in:
- Cryogenic insulation and tanks
- Building and pipe insulation materials
- Aerospace, cold‑storage and refrigeration components
- Quality control, material specification and R&D for foam plastics
- Helps manufacturers, materials laboratories and product designers quantify thermal dimensional stability at sub‑ambient conditions and compare materials in a repeatable way.
Who should use this standard
- Testing laboratories and QA/QC departments
- Materials engineers and product developers working with cellular plastics
- Specifiers and procurement teams requiring certified thermal‑expansion data for cold‑temperature applications
Related standards
- ISO 291 - Plastics: standard atmospheres for conditioning and testing
- ISO 1923 - Cellular plastics and rubbers: determination of linear dimensions
Keywords: ISO 4897:1985, cellular plastics, coefficient of linear thermal expansion, sub-ambient temperatures, Method A, Method B, liquid nitrogen, cryogenic testing, thermal expansion testing, rigid cellular plastics.
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