Overview
EN ISO 20274:2017 (ISO 20274:2017) specifies procedures for preparing vitreous and porcelain enamel samples and for measuring their thermal length change to calculate the thermal expansion coefficient. The standard targets reproducible sample production and measurement so that enamel thermal behaviour - a key factor in stress and adhesion in enamel/substrate systems - can be reliably assessed.
Key topics and technical requirements
- Scope: Procedure for sample preparation and measurement of thermal expansion (thermal length change).
- Normative references: ISO 7991 (glass - determination of mean linear thermal expansion) and ISO 19496‑1 (enamel terminology).
- Apparatus
- Standard laboratory instruments in accordance with ISO 7991.
- Dilatometer: pushrod dilatometer is specified; an optical dilatometer may be used as an alternative.
- Melting crucible: non‑contaminating materials (e.g., corundum, porcelain), approx. 55 mm height × 40 mm diameter.
- Casting moulds: ceramic (corundum, porcelain) or metal (tool steel) - see Annex A.
- Laboratory furnace: 800 °C to 1 100 °C, controllable to ±5 °C.
- Test specimen requirements
- Rod-shaped, straight; either approximately circular or square cross-section.
- Diameter/edge length constant to ±1 mm over length; faces plane‑parallel and within ±3° to the longitudinal axis.
- Initial length matched to reference sample within ±0.5 mm and sized to suit the dilatometer.
- Sample production methods
- Casting (G): melt frit, pour into mould, controlled cooling, removal of release agents, cut and polish to dimensions.
- Drawing from the melt (Z): melt at typically 900–980 °C (depends on enamel), draw rod from melt to form specimen, cool and temper.
- Sintering (S): form negative mould (e.g., kaolin), fill with sintering enamel (slip or powder), dry and sinter.
- Stress relief / tempering: heat ~30 °C above the transformation temperature, slow cool (~2 °C/min) to ~150 °C below transformation temperature, then to room temperature in draft‑free air to avoid measuring artefacts.
- Measurement and calculation: thermal expansion determined per the procedures; results calculated and reported (see Clauses 7–9).
Applications and users
- Quality control and R&D for vitreous and porcelain enamels.
- Materials scientists and coatings engineers assessing thermal compatibility, stress assessment, and failure analysis of enamelled components.
- Test laboratories performing standardized dilatometry and reporting thermal expansion coefficients for product specification, coating formulation, and substrate-enamel matching.
- Manufacturers of enamel frits, enamelled cookware, sanitaryware, and industrial enamel coatings.
Related standards
- ISO 7991 - Glass: determination of coefficient of mean linear thermal expansion.
- ISO 19496‑1 - Vitreous and porcelain enamels: terms and definitions.
Keywords: EN ISO 20274:2017, ISO 20274, thermal expansion coefficient, vitreous enamel, porcelain enamel, dilatometer, sample preparation, casting, drawing, sintering, melting crucible, laboratory furnace.
