Overview
ISO 3927:2017 - "Metallic powders, excluding powders for hardmetals - Determination of compressibility in uniaxial compression" - specifies a laboratory method to measure how metallic powders compact under uniaxial compressive loading in a confining die. The standard applies to most metallic powders used in powder metallurgy but excludes powders for hardmetals. Results are used either at a single specified compacting pressure or across a series of pressures to produce a compressibility curve (density versus compacting pressure).
Key topics and technical requirements
- Principle: Double‑action uniaxial pressing in a confining die; density determined after ejection.
- Test specimens and tooling:
- Cylindrical compacts: diameter 20–26 mm, height/diameter ratio 0.8–1.0 (example tooling provided).
- Rectangular compacts: 30 × 12 mm, thickness 5–7 mm (example tooling provided).
- Mating parts must be fitted and lapped; dies preferably cemented carbide or tool steel.
- Apparatus:
- Press capable up to ~500 kN, accuracy ±1%, force increase ≤50 kN/s.
- Scale readable to 0.001 g; micrometer readable to 0.005 mm (dimensions measured to 0.01 mm, mass to 0.01 g).
- Lubrication options:
- Die wall lubrication (example: zinc stearate solution in acetone).
- Powder lubrication by admixing solid lubricant (typically 0.5–1.5 % zinc stearate or synthetic wax).
- Powders with/without lubricant can be tested in dry or lubricated dies per clauses 8.2–8.3.
- Compacting pressures:
- Recommended series for compressibility curves: 200, 400, 500, 600 and 800 N/mm² (or agreement between parties for single-pressure tests).
- Results and expression:
- Density ρ = m / V (report to 0.01 g/cm³).
- Report compressibility as average of three density determinations (to 0.01 g/cm³).
- Precision:
- Repeatability r = 0.025 g/cm³; reproducibility R = 0.07 g/cm³ (from referenced ASTM data).
- Test report must reference ISO 3927 and include sample ID, test piece type, lubricant details, pressures, results and any deviations.
Applications and users
- Typical users: powder metallurgists, materials engineers, QC laboratories, R&D teams, and manufacturers of pressed metal components.
- Practical uses:
- Characterizing powder compaction behaviour for process design (pressing parameters, tooling selection).
- Comparing powder formulations or lubricant blends.
- Quality control on incoming powders to predict green density and dimensional control.
- Generating compressibility curves to model sintered part density and performance.
Related standards
- ASTM B331-95 is cited for precision data and offers complementary methodology.
- Prepared by ISO/TC 119 (Powder metallurgy) - useful for locating related powder metallurgy test standards.
Keywords: ISO 3927:2017, metallic powders, compressibility, uniaxial compression, powder metallurgy, compaction, compressibility curve, green density, die lubrication, test method.
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