Hardness can be defined as a material’s resistance to permanent deformation. In the coatings industry, hardness measurement can be used to determine the resistance of the coating to scratching from general wear and tear and also if a coating is fully cured.
Depending on the requirements, there are various methods for testing hardness. Some are dedicated to characterise coatings and others are more suitable for testing bulk materials such as metals, plastics, rubber or elastomers.
Scratch Resistance: To assess a coating’s resistance to scratch there are a number of different instruments that can be used: Pencil Hardness Tester (Wolff-Wilborn), Sclerometer, Clemen Apparatus, Scratching and Shearing Instrument.
Resistance to Indentation: There are many instruments available to assess the resistance to penetration. For coatings in particular, there are three common methods where the depth of penetration of a weighted tool is used to show the coating’s resistance to penetration: Buchholz, Barcol, Shore.
Pendulum Hardness Test: Another way to determine a coating or substrate’s hardness is to use the pendulum method. The pendulum method (Persoz & König) uses the concept of friction. Essentially, a pendulum of a fixed weight rests on the coated surface via two ball bearings. The softer the material, the more the bearings will sink into the surface or coating.