Novasys Group offers Model 291 scratch hardness testers from Erichsen, a leading supplier of testing equipment for quality management.
Based on the pencil method, Erichsen scratch hardness testers are a range of scratch hardness testing instruments that employ a simple and quick method for testing the surface hardness of coatings with regard to stresses inflicted by scratching with sharp edges, or other rough surfaces.
Erichsen scratch hardness testers are supplied with 17 standardised pencils, a special sharpener and a sheet of emery paper. Pencils of various grades of hardness are moved over the painted surface at an angle of 45º to the horizontal with a force of 7.5 ± 0.1 N. An assortment of pencils with 17 degrees of hardness from 6 B to 9 H is used for the test.
The pencil hardness is defined by the two grades of hardness, the softer one of which just produces a writing trace while the next harder one leaves a perceptible scratch on the coating.
Design and Function
The scratch hardness tester enables the test to be carried out technically equivalent to Wolff-Wilborn and ensures that the specified force and angle remain constant throughout the test. Guidance of the instrument is easy and excludes manual influences of the pencil pressure.
The sharpened pencil point is clamped into the holder block so that the graphite point protrudes about 5mm. The instrument is now placed on the test specimen with the hubs of the wheels held using the thumb and forefinger. The instrument is moved over the specimen in the direction the pencil point shows at a speed of about 10 cm/s.
The appropriate pencil hardness is established empirically. It is recommended to start testing with a medium soft pencil or medium hard one and narrow down to the most suitable pencil type. The numbers of the two pencil types defined are indicated as pencil hardness. A pencil hardness of 2 H...3 H for example, means that pencil type 2 H still writes on the surface while pencil type 3 H already slightly scratches the film.