Overview
ISO 7373:1987 specifies experimental methods for checking the precision of sample division for ferroalloys. The procedures apply to gross samples or sub-samples taken from a consignment according to the relevant ISO sampling standards. The methods are specifically applicable to crushable ferroalloys and are not intended for uncrushable ferroalloys where increments are taken by boring.
Key facts:
- Experiments are repeated at least 10 times for each ferroalloy type.
- Chemical analyses of experimental samples must follow the methods prescribed in the relevant ISO chemical analysis standards.
- Minimum consignment masses are given to ensure sufficient gross sample: for ferroalloys covered by ISO 4552-1 the consignment should be at least 100 t, and for those covered by ISO 4552-2 at least 5 t.
Key Topics
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Selection of experimental method: the standard distinguishes between methods of division in one or two stages and division in three or more stages. The choice depends on the physical properties of the ferroalloy and the practical crushing/division constraints.
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Division stages and particle sizes: examples of whole-through sieve sizes by division stage are provided. Typical examples include:
- Primary: -10 mm or -7.10 mm
- Secondary: -5 mm or -2.80 mm
- Tertiary: -1.0 mm or -250 µm
- Recommended whole-through sieve sizes to be divided are -2.8 mm or -1.0 mm, depending on the method chosen.
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Experimental design and data recording: one test sample is prepared from each divided sample. Chemical determinations are randomized (or analysed together in random order) and experimental data are recorded in a data log as exemplified in the standard.
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Data analysis and precision assessment: the standard provides formulas and guidance for estimating the precision of chemical analysis and the precision of sample division. If a calculated variance term under a square-root sign is negative, the standard instructs that the standard deviation be regarded as zero provided no attributable experimental defects are observed.
Applications
- Quality control of ferroalloy consignments through validated sampling procedures.
- Laboratory verification of division apparatus and crushing methods to ensure representative test portions.
- Demonstrating compliance with customer or regulatory requirements for sampling precision.
Practical benefits: improved sampling reliability, consistent test results, and clearer criteria for corrective action when measured precision does not meet the values referenced in the relevant ISO standards.
Related Standards
- ISO 4552 (Sampling and sample preparation for ferroalloys)
- ISO 7087 (Evaluation of quality variation and methods for checking sampling precision)
- Relevant ISO chemical analysis methods cited in the standard for specific elements
For implementation, consult ISO 7373:1987 alongside the referenced ISO sampling and analytical standards to ensure full procedural and analytical compliance.