Overview
ISO 18771:2019 specifies a practical test method to determine the surface abrasion resistance of anodic oxidation coatings on aluminium and its alloys using glass-coated abrasive paper. Intended mainly for evaluating external architectural coatings, the standard is a production control method that relies heavily on operator skill and instruction. It can be applied to whole articles (non‑destructive for passing items) and provides a simple pass/fail assessment of whether a coating is harder or softer than the validated abrasive paper.
Key topics and technical requirements
- Scope and purpose: Evaluates sulfuric‑acid anodized coatings for external architectural use; used primarily for quality control.
- Test principle: Abrade the anodized surface with glass‑coated abrasive paper and assess transfer of a chalky white powder (coating abrasion) or measure coating loss.
- Two methods:
- Method 1 - Visual/qualitative: wrap abrasive around a resilient block, apply firm pressure and make 10 double strokes (25–30 mm amplitude). Dense powder on the abrasive = coating softer than abrasive.
- Method 2 - Quantitative: perform 50 double strokes, fresh abrasive area every 10 strokes, then measure coating thickness by eddy‑current (ISO 2360). A loss > 2 µm indicates the coating is less wear resistant than the abrasive.
- Apparatus requirements:
- Glass‑coated abrasive paper validated per Annex A (P240 equivalent noted as suitable).
- Resilient support block: recommended 6–8 mm thick, ~30 × 40 mm, hardness 30–70 IRHD (ISO 48‑2).
- Validation (Annex A): Lot validation using two standard anodized specimens - one more wear resistant and one less - prepared under specified anodizing and sealing conditions (e.g., sulfuric acid ~180 ±2 g/L, coating ~22–23 µm, anodizing at 20 °C for the more wear resistant specimen and 26 °C for the less).
- Test report: Must reference ISO 18771, specimen ID, method used, abrasive details (manufacturer/lot), test location, results and date.
Applications and users
- Who uses it: Anodizing process engineers, quality control technicians, finishing shops, architectural metal fabricators, and coating specifiers.
- When to use:
- Routine production control for external architectural anodized components.
- Verifying lot acceptance and troubleshooting process changes (bath concentration, temperature, time).
- Quick field checks on assembled articles where non‑destructive evaluation is desirable.
Related standards
Keywords: ISO 18771:2019, anodizing, aluminium, surface abrasion resistance, glass-coated abrasive paper, architectural coatings, production control, test method, Annex A validation.
Open preview (PDF)Anodizing of aluminium and its alloys — Method to test the surface abrasion resistance using glass-coated abrasive paper