Multi-impact testing for stone-chip resistance: EN ISO 20567 1 revised
Grit, road metal and other materials can damage automotive coatings so that individual layers come off or the whole coating delaminates from the substrate. Stone chipping can be simulated by means of single- and/or multi-impact tests. ISO 20567 1 has now been revised.
The latest edition of EN ISO 20567‑1, Paints and varnishes — Determination of stone-chip resistance of coatings — Part 1: Multi-impact testing, published in June 2017 specifies a new particle size distribution of the grit used for the test. The grit used is chilled-iron grit conforming to the requirements of EN ISO 11124‑2, Preparation of steel substrates before application of paints and related products — Specifications for metallic blast-cleaning abrasives — Part 2: Chilled-iron grit (see Figure 1).
Figure 1: Chilled-iron grit for multi-impact stone-chip testing. Source: DIN Standards Committee Coatings and Coating Materials
The required particle size distribution of the grit in accordance with EN ISO 20567‑1 was changed from 4 – 5 mm into 3,55 – 5 mm. The reason for this was a change in the production process of the chilled-iron grit which was necessary for an improvement of the delivery quality. The results obtained with the new particle size distribution should correspond to results obtained before the change in the production process of the grit. To ensure the comparability of test results between different users, the designation and particle-size distribution of the grit batch used for the test should always be stated in the test report. Both can be found in the acceptance test certificate of the grit manufacturer.
