Overview
ISO 20567-2:2023 - "Paints and varnishes - Determination of stone-chip resistance of coatings - Part 2: Single-impact test with a guided impact body" - specifies a laboratory method to evaluate stone-chip resistance of automobile finishes and other coatings. The method uses a wedge‑shaped, hardened-steel impact body driven by the energy of a compressed‑air‑accelerated steel ball to simulate the effect of a single stone impact. Results are reported by measuring the total width of delamination produced, enabling objective comparison of coating systems for stone‑chip performance.
Key topics and technical requirements
- Test principle: A guided wedge impact body transmits a pulse from a steel ball (driven at 300 kPa) to the coated panel, producing a wedge‑type defect equivalent to multi‑impact damage patterns.
- Impact body: Hardened steel, 60–66 HRC; replace after a maximum of 500 impacts.
- Test panels: Minimum size 100 × 100 mm, substrate thickness ≥ 0.7 mm; prepare panels per ISO 1514 and measure dry film thickness per ISO 2808.
- Conditioning and environment: Condition panels at (23 ± 2) °C and (50 ± 5)% RH for ≥16 h (ISO 3270); perform tests at 18–28 °C.
- Procedure: Compressed-air set to 300 kPa; typically three test runs per sample unless otherwise agreed. Remove loose paint using agreed method (Annex A: brushing, adhesive tape, etc.).
- Evaluation: Measure the total width of the delaminated coating (mm) and, where possible, identify the separation level or interlayer failure.
- Precision: Repeatability limit r = 1.4 mm; reproducibility limit R = 2.2 mm.
- Calibration and annexes: Annex B covers apparatus calibration; Annex A gives examples for removing loose paint.
Practical applications
- Quality control and acceptance testing for automotive OEM finishes and aftermarket coatings.
- Coating formulation development to compare stone‑chip performance during R&D.
- Supplier certification and batch verification in automotive and transportation coatings supply chains.
- Failure analysis to identify interlayer adhesion weaknesses following impact damage.
Who should use this standard
- Automotive manufacturers and OEM paint engineers
- Coating formulators and R&D laboratories
- Independent test laboratories and certification bodies
- Quality assurance teams in vehicle and parts manufacturing
Related standards
This standard provides a repeatable, quantitative single‑impact test for stone‑chip resistance, supporting robust comparison of coating systems and informed coating selection for high‑impact exposure applications.
Open preview (PDF)Paints and varnishes — Determination of stone-chip resistance of coatings — Part 2: Single-impact test with a guided impact body