Overview
ISO 5940-2:2007 sets out the international standard method for determining the softening point of pitches-primarily coal-tar pitch-used in the production of aluminium electrodes, using the Mettler softening point method. This standard is applicable within a temperature range of 50 °C to 180 °C and is also suitable for other organic binder and impregnating materials falling within a softening point range of 50 °C to 150 °C. The standard provides clear and consistent procedures, ensuring the reliability and comparability of results in the global aluminium industry.
Key Topics
- Scope and Applicability: ISO 5940-2:2007 is focused on pitches used as binder and impregnating agents, covering both grindable and non-grindable materials within the specified temperature range.
- Test Principle: The standard details how a pitch sample is progressively heated in a controlled environment, with the temperature at which softened material interrupts a light barrier-19 mm below the cup outlet-defined as the Mettler softening point.
- Apparatus Requirements:
- Electrically heated furnace
- Sample cup and holder
- Resistance thermometer (50 °C to 180 °C)
- Light barrier
- Temperature control unit
- Material collector
- Calibration checks and specific sampling tools
- Sample Preparation: Both melting and pressing techniques for preparing pitch samples are covered, as well as requirements for sample size, handling, and consistency.
- Calibration and Precision: The standard describes calibration procedures and precision criteria, with repeatability and reproducibility guidelines to ensure accuracy across different laboratories.
- Reporting Requirements: A comprehensive list of the details required in the test report, including apparatus specifications, sample identification, test conditions, and full results.
Applications
Adopting ISO 5940-2:2007 in industrial and laboratory settings offers several practical benefits:
- Aluminium Production: Ensures that coal-tar pitch used for carbon anodes in aluminium smelting meets uniform quality standards, directly influencing process efficiency and product quality.
- Quality Control: Laboratories and manufacturers use this method to reliably assess the softening characteristics of raw or processed binder pitches, facilitating regulatory compliance and material selection.
- Comparability of Results: The use of an internationally recognized method supports consistent results between different manufacturers and testing facilities, aiding global trade and procurement.
- Material Innovation: Research institutions and industries developing new binder or impregnating materials for electrodes can use the Mettler softening point determination to benchmark performance and suitability.
- Calibration and Cross-Verification: The standard references conversion to other softening point methods (e.g., ring-and-ball, Kraemer-Sarnow, cube-in-air), supporting cross-validation in multi-method laboratories.
Related Standards
To complement ISO 5940-2:2007, the following standards are relevant within the field of carbonaceous materials and softening point determination:
- ISO 6257: Carbonaceous materials used in the production of aluminium - Pitch for electrodes - Sampling
- ISO 5940-1: Determination of the softening point by the ring-and-ball method
- DIN 52011 & DIN 52025: Methods for alternative softening point measurements (ring-and-ball, Kraemer-Sarnow)
- ASTM D2319: Standard test method for softening point of pitch (cube-in-air)
- ASTM D3104: Standard test method for softening point of pitches (Mettler method)
- DIN 51848-1: Testing of mineral oils - precision guidance for laboratory methods
Employing ISO 5940-2:2007 guarantees reliable, reproducible softening point measurements for pitches and organic binders, underpinning quality assurance and process control in the aluminium industry and related sectors.
Open preview (PDF)Carbonaceous materials used in the production of aluminium — Pitch for electrodes — Part 2: Determination of the softening point (Mettler softening point method)
