Overview
ISO 10236:1995 defines a standardized laboratory method for determining the tapped bulk density of granular carbonaceous materials (green coke and calcined coke) used in the manufacture of carbon electrodes for aluminium production. The tapped bulk density is measured by determining the volume of a known mass of material after controlled tapping; this value is important for assessing porosity, handling, and electrode performance.
Key Topics
- Principle: The bulk density (tapped) is calculated by dividing a known mass of test portion by the tapped volume: pt = m / V (g/ml).
- Sample preparation:
- Sample in accordance with ISO 6375 for sampling.
- Dry sample in an oven at 120 °C ± 5 °C until consecutive weighings differ by ≤ 0.1% of the original mass; cool in a desiccator.
- Apparatus (summary of required equipment described in the standard):
- Bulk density measuring device with measuring cylinder (0–250 ml scale, readable to 1.0 ml) and cylinder holder with guided plunger.
- Plunger mass: 450 g ± 5 g.
- Tapping device capable of 250 ± 15 taps/min with a 3.0 mm ± 0.1 mm drop and counter; total tapping normally 1 500 taps.
- Feeder for controlled filling, test sieves (ISO 3310-1) and oven (120 °C ± 5 °C).
- Test portion: 100 g ± 5 g, weighed to 0.1 g.
- Size fractions: Typical screening fractions include 4.0–8.0 mm, 2.0–4.0 mm, 1.0–2.0 mm, 0.5–1.0 mm and 0.25–0.5 mm. The fraction tested should be recorded.
- Number of determinations: Two independent determinations; report the arithmetic mean to 0.01 g/ml.
- Precision: Repeatability r = 0.01 g/ml; reproducibility R = 0.02 g/ml (as reported in the standard).
Applications
- Quality control of green and calcined coke in electrode manufacture for the aluminium industry.
- Porosity assessment: comparison of tapped bulk density with real (true) density helps estimate granule porosity, which influences electrode performance.
- Material specification and acceptance: allows consistent comparison between batches and suppliers when the tested fraction is specified in the test report.
Related Standards
- ISO 6375 - Carbonaceous materials for the production of aluminium: sampling of coke for electrodes (referenced for sampling procedure).
- ISO 3310-1 - Test sieves: technical requirements for metal wire cloth (referenced for sieving).
- ISO 5725 - Precision of test methods (used to derive repeatability and reproducibility data in the standard).
Test report requirements (excerpt): include sample identification, reference to ISO 10236:1995, grain size distribution or fraction tested, oil-treatment history (if any), ambient temperature, test results (mean of two determinations), and any unusual observations or deviations from the method.
This concise, repeatable method ensures consistent measurement of tapped bulk density for use in production control and materials evaluation in the aluminium electrode supply chain.