Overview
ISO 14428:2019 specifies a laboratory method to determine expansion/shrinkage during baking of cold and tepid ramming pastes used in the production of aluminium. The standard defines the principle, apparatus, sample preparation and a stepwise test procedure that measures dimensional change up to 950 °C (with a 3 h hold) and quantifies shrinkage that can cause lining cracks in aluminium electrolysis cells.
Key topics and requirements
- Scope and principle: measure change in height of a rammed paste specimen while heating to 950 °C and during a 3 h hold; determine shrinkage between the non‑plastic transition and operating temperature.
- Apparatus: push‑rod dilatometer (vertical measurement), device for length measurement (±0.1 mm), disk and outer tube (preferably vitreous silica), thermocouple (type S recommended), furnace with ≤10 °C gradient over sample height, inert gas (N2/Ar).
- Accuracy and constraints: dilatometer capable of micrometre resolution (example: 1 μm for 50 mm); push‑rod contact force ≤ 2 N; gap between outer tube and sample 2–10 mm. Vitreous silica components require annealing before use.
- Calibration and correction: use a certified reference sample (ISO 17034 compliant) to derive correction terms for instrument thermal behaviour; perform at least three reference runs after any equipment change.
- Measurement and calculation: record temperature and length change at regular intervals (≥ every 5 min). Calculate corrected expansion/shrinkage (%) and defined reference points (e.g., average expansion 450–500 °C, 900–950 °C, and during hold). The standard prescribes formulae for correction and shrinkage calculation.
- Sample preparation: sampling and specimen preparation are referenced to ISO 14422 and ISO 14427; testing should begin preferably within 48 h of preparation.
Applications
- Assessing thermal behaviour of ramming pastes to prevent excessive shrinkage that leads to cracks, bath leakage and cell failure in aluminium electrolysis.
- Product development and quality control for refractory and lining materials used in primary aluminium production.
- Certification and comparison of cold and tepid ramming paste formulations for process reliability at high temperatures.
Who uses this standard
- Materials scientists and R&D teams in aluminium smelting and refractory industries.
- Quality control laboratories performing thermal characterization of ramming pastes.
- Suppliers of cold/tepid ramming pastes and refractory linings for electrolysis cells.
- Test laboratories certifying reference materials per ISO 17034.
Related standards
- ISO 14422 - Sampling of cold‑ramming pastes
- ISO 14427 - Preparation of unbaked test specimens and apparent density
- ISO 17034 - Competence of reference material producers
Keywords: ISO 14428:2019, ramming pastes, expansion/shrinkage, aluminium production, dilatometer, baking test, thermal expansion.