ISO 6344-3:2021

Overview

ISO 6344-3:2021 - Coated abrasives - Determination and designation of grain size distribution - Part 3: Microgrit sizes P240 to P5000 defines laboratory methods and designation rules for measuring the grain size distribution of electro‑fused aluminium oxide and silicon carbide microgrits used in coated abrasives. The standard applies both to grits supplied for manufacture and grits extracted from finished coated abrasive products for test purposes. It extends grit designations up to P5000 and replaces earlier editions.

Key topics and technical requirements

• Scope and definitions: Defines “microgrit” (median equivalent diameter approx. 58.5 µm to 2.7 µm) and particle size distribution (PSD) terminology.
• Measurement principles: Grain size determination is based on gravitational liquid sedimentation and Stokes’ law to calculate equivalent grain diameters.
• Methods by size range:
  • P240–P1200: Tested by sedimentation using the US sedimentometer; measurement records volume vs time of settled particles.
  • P1500–P5000: Separate procedures and apparatus described (Clauses 6–7 cover method and calibration).
• Materials and reagents:
  • Sedimentation medium: methyl alcohol (95–99% purity).
  • Dispersing agent: e.g., EDTA (recommended dosage specified).
  • Checking mineral (320) for procedure validation and calibration.
• Evaluation criteria: Grain size distribution must meet four simultaneous d-value criteria (maximum d0, d3 at 3%, median d50 within tolerance, and minimum d95) - limit tables (e.g., Table 1 for P240–P1200) provide required d values.
• Procedure elements: Apparatus preparation, test portion preparation, dispersion, transfer, start of measurement, recording, calculation of d values, representation of PSD curves, permissible deviations.
• Reporting and designation: Requirements for test reports, product designation and marking of microgrit P sizes.

Applications and users

ISO 6344-3:2021 is intended for:

• Abrasive manufacturers - production control and specification of coated abrasive grits.
• Quality assurance and test laboratories - standardized PSD testing, calibration and validation of sedimentation equipment.
• R&D teams - correlating grain size distribution with abrasive performance, consistency, and formulation changes.
• Procurement and suppliers - verifying supplier grit conformity to P-size designations (P240–P5000). Practical uses include batch acceptance testing, supplier quality verification, product labelling, and process optimisation for grinding and finishing operations.

Related standards

• ISO 6344 series (other parts covering macrogrits and related tests)
• ISO 9138 - Abrasive grains - Sampling and splitting
• ISO 13317-3 - Particle size distribution by gravitational liquid sedimentation (X‑ray technique)

Keywords: ISO 6344-3, coated abrasives, grain size distribution, microgrit, P240 to P5000, sedimentation, US sedimentometer, electro‑fused aluminium oxide, silicon carbide.