The Scratching Tool acc. to van Laar is a ball-shaped hard metal pin with a tip diameter of 0.5 mm is mounted stably in a ballpoint pen-shaped holder made of anodised hard aluminium. This handy design ensures that the device can be guided stably during the scribing/scratching process. The stability of the ball tip is tested in a continual endurance test: A cylinder made of machining steel of approx. 100-mm diameter is scratched by a scribing needle at approx. 20 cm/s and with a load of 50 N on a rotary table. After a distance of 18000 cm, no damage to the ball end should be detected.
Purpose and application: Scratching-in of the St. Andrew’s cross into test panels is a well-known preparation for short-term and endurance corrosion tests, enabling the examination of the protection of the coating against rusting of the substrate underneath the coating (“underrusting”). The Sratching Tool acc. to van Laar is a handy universal tool: for producing accurately defined incisions on the surface of the coating in preparation of forced corrosion tests, such as salt spray, continuous or intermittent immersion, accelerated weathering, gas corrosion and humidtiy tests.