Overview
ISO 501:2012 specifies a standardized laboratory method to determine the crucible swelling number (CSN) - also known as the free swelling index (FSI) - of hard coal. The method measures the swelling properties of a 1 g coal sample heated in a covered silica crucible under controlled time and temperature conditions. The shape and strength of the resulting coke button are compared with standard profiles to assign a CSN value that characterizes coal coking/swelling behaviour.
Key topics and requirements
- Scope: Test for swelling properties of hard coal when heated in a covered crucible (CSN / FSI).
- Sample preparation:
- Use general analysis test sample prepared per ISO 13909-4 and ISO 18283.
- Grind sample to pass a 212 μm sieve; avoid over‑pulverization.
- Perform test within 24 hours of preparation to avoid oxidation; equilibrate moisture with lab atmosphere.
- Apparatus:
- Specified silica crucible and lid (dimensions, mass and capacity defined).
- Pierced lid for thermocouple, silica triangle support, draught shield, burner (Teclu/Meker or electrical alternative), sheathed thermocouple, 500 g weight and sight tube for profile comparison.
- Heating profile:
- Standard heating to reach 800 °C ±10 °C in 1.5 min and 820 °C ±5 °C in 2.5 min (gas burner conditions adjusted accordingly).
- Procedure:
- Weigh 1.00–1.01 g of sample, tamp level, cover with lid, heat until volatile flame dies (minimum 2.5 min), cool and remove residue.
- Evaluate residue: non‑coherent = CSN 0; non‑swollen but strong/weak buttons = 1 or 1/2; swollen buttons matched to standard profiles (1.5–9 or >9).
- Perform tests in triplicate (or up to 5/10 per reproducibility rules) and follow averaging rules; report mean to the nearest 1/2 unit.
- Precision:
- Repeatability: for three determinations the range should not exceed 0.5 unit; for five determinations not exceed 1 unit.
- Reproducibility: means between different laboratories should not differ by more than specified precision (see Clause 9/Table 1).
- Safety: Standard warns about hazardous materials and operations; users must adopt appropriate safety practices.
Applications and users
- Used by coal testing laboratories, coke producers, metallurgical and steel industry quality control, power utilities and research organisations to:
- Assess coal suitability for coke production and metallurgical processes.
- Classify coals by swelling/coking behaviour for blend design.
- Support procurement, quality assurance and compliance testing.
- Valuable for engineers, lab managers, coal analysts and standards/QA personnel.
Related standards
- ISO 13909-4 - Hard coal and coke - Mechanical sampling - Part 4: Preparation of test samples
- ISO 18283 - Hard coal and coke - Manual sampling
Keywords: ISO 501:2012, crucible swelling number, CSN, free swelling index, hard coal, coal testing, swelling properties, covered crucible, coal analysis.