Overview
EN ISO 20567-4:2024 (identical to ISO 20567-4:2023) specifies a mobile multi‑impact method to assess the stone‑chip resistance of coatings, particularly automotive finishes. The procedure simulates stone chipping by projecting chilled‑iron grit at 90° onto a small test area using a portable tester. Results from this mobile test are explicitly not comparable with those from ISO 20567‑1 (stationary, large‑area testing).
Key topics and technical requirements
- Scope and principle
- Evaluates resistance of paints and varnishes to stone chipping using many small, sharp‑edged impacts (chilled‑iron grit).
- Damage depends on working pressure, grit characteristics, projection duration and tester design.
- Test equipment
- Mobile stone‑chip resistance tester with pressure regulator, dosing device and grit magazine.
- Projection mask: small testing window (example 20 mm × 20 mm).
- Calibration device: pressure plate and scale for functional checks.
- Illuminated 10× magnifier with graduated field for inspection.
- Compressed air and delivery
- Compressed air system with oil/water separators.
- Supply requirements noted (e.g., output pressure and hose dimensions referenced in the standard to ensure correct working pressure).
- Dosing device designed to deliver chilled‑iron grit in (10 ± 1) s per dose.
- Grit specification and lifecycle
- Use chilled‑iron grit conforming to ISO 11124‑2; particle size determined by ISO 11125‑2 and ISO 565.
- Example particle distribution (per standard): fractions on sieves 2.80 mm (15–20%), 2.50 mm (40–50%), 2.24 mm (30–40%); material through 2.24 mm discarded.
- 25 g sample should contain 340 ± 20 grit particles.
- Grit replacement after a maximum of 25 test runs (i.e., projected 50 times) or at end of the test series.
- Procedure and evaluation
- Projection at 90°, removal of loose coating fragments, and visual comparison against pictorial reference standards supplied in the standard.
- Test report requirements and apparatus functional checks are defined.
Applications and users
- Primary users: automotive OEMs, paint formulators, coatings laboratories, quality control teams and test houses needing a portable method to assess stone‑chip resistance on panels, assembled components or in‑field samples.
- Practical uses: on‑site evaluation of vehicle finishes, comparative screening of coatings, quality checks after repair or retrofit, and validation of protective topcoats against mechanical impact.
Related standards
Keywords: EN ISO 20567-4:2024, ISO 20567-4:2023, stone-chip resistance, mobile multi-impact testing, chilled-iron grit, automotive finishes, paints and varnishes, coating testing.