Overview
ISO 20567-4:2023 - Paints and varnishes: Determination of stone-chip resistance of coatings - Part 4 specifies a mobile multi-impact testing method on a small testing area. The procedure evaluates the resistance of automotive finishes to simulated stone chipping by projecting chilled-iron grit at 90° using compressed air. Results from this mobile method are explicitly not comparable with results from ISO 20567-1.
Key topics and technical requirements
- Test principle: Multiple small, sharp-edged impact bodies (chilled-iron grit) are projected onto a confined test window to produce localized stone-chip damage.
- Grit specification: Chilled-iron grit shall conform to ISO 11124-2, with particle-size determination per ISO 11125-2 and ISO 565. A 25 g fraction shall contain 340 ± 20 grit particles.
- Apparatus requirements:
- Mobile stone-chip tester with dosing device that delivers grit in (10 ± 1) s.
- Compressed air supply with oil and water separators; output pressure min. 400 kPa; connection hose inner diameter min. 9.52 mm (3/8 in).
- Projection mask (example: 20 mm × 20 mm) and grit-accelerating pipe details as specified.
- Calibration device and illuminated 10× magnifier for evaluation.
- Test procedure:
- Two test runs per location (each test run = projection of 2 × 100 g); grit replaced after max. 25 test runs (i.e., projected 50 times).
- Remove loose coating fragments (methods per Annex B) before evaluation.
- Evaluation and scoring:
- Visual comparison against normative pictorial reference standards (Annex A) using a 0–4 rating scale.
- Damage includes delamination, flaking or displacement of layers; scratches/indentation without flaking are excluded.
- Reporting: Report must include coating ID, substrate preparation, application and curing details, film thickness (ISO 2808), ambient test conditions, grit details, removal method, pictorial standards used, rating, deviations, and tester identity.
Applications and users
- Primary users: automotive OEMs, vehicle refinishers, coating manufacturers, independent test laboratories, and quality assurance teams.
- Practical uses:
- On-site or field assessment of vehicle body finishes and small repair areas.
- Quality control for production and refinish processes where a mobile, small-area stone-chip simulation is required.
- R&D and comparative assessment of coating systems for stone-chip durability.
Related standards
Keywords: ISO 20567-4, stone-chip resistance, mobile multi-impact testing, chilled-iron grit, automotive finishes, coating testing, pictorial reference standards.
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