ISO 528:1983

Overview

ISO 528:1983 specifies a standardized method for determining the pyrometric cone equivalent (PCE) - commonly referred to as refractoriness - of siliceous, low‑alumina fireclay and fireclay refractory materials and products. The method compares test pieces with calibrated pyrometric reference cones to express refractoriness as the number(s) of the reference cone(s) that match the behaviour of the test material when heated under controlled conditions.

This procedure is primarily intended for fireclay refractories; it can also be used to obtain a rough refractoriness estimate for other refractory types, subject to the availability of appropriate pyrometric reference cones (see ISO/R 1146).

Key Topics

• Scope and applicability: Designed for siliceous and low‑alumina fireclay refractories. Useful temperature range depends on available reference cones (ISO/R 1146 cones are suitable in the 1 500–1 800 °C range).
• Reference cones: Pyrometric reference cones should preferably conform to ISO/R 1146; alternative cones may be used if their reference temperatures and mounting angles are documented by the manufacturer.
• Furnace and atmosphere: The furnace must reach required temperatures and maintain an oxidizing atmosphere (free oxygen). Temperature uniformity in the test zone shall not differ by more than 10 °C between hottest and coldest spots.
• Heating schedule: After an initial soak to 200 °C below estimated refractoriness, the temperature is raised at a constant mean rate (2.5 °C/min is the specified rate in the standard) until cone collapse criteria are met.
• Test pieces and stand: Test pieces are geometrically similar to the reference cones (height 100–120% of cone height). Shaped, cut or moulded pieces are prepared according to material type and fired or stabilised as required. Cones and test pieces are mounted on a refractory stand and arranged to allow unobstructed bending.
• Reporting: Results are expressed as the pyrometric cone equivalent (the number(s) of the reference cone(s)). Test reports must include identification of the tested product, test date, methods used, cone types, preliminary firing conditions (if any) and all individual results for repeated tests.

Applications

• Quality control of fireclay and siliceous refractory bricks and shapes
• Comparative material assessment for furnace lining and high‑temperature components
• Selection of refractories for processes requiring specific refractoriness levels

Benefits include standardized, reproducible refractoriness measurement, easier material comparison, and informed selection for high‑temperature applications.

Related Standards

• ISO/R 1146 - Pyrometric reference cones (specification of cones used as references)
• ISO 565 - Test sieves (used in sample preparation)
• ISO 5022 - Sampling and testing of shaped refractory products

For implementation, follow ISO 528:1983 step‑by‑step procedures for sampling, preparation, furnace control and reporting to ensure reliable and comparable refractoriness data.