ISO 5940-2:2007

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.