Roughness
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Roughness Han Haitjema Mitutoyo RCE, Best, The Netherlands
Synonyms Surface roughness
Definition
difference between “gloss” and “mat” of, e.g., pictures or paint is determined by the surface roughness. For the final optical properties of an object also the shape is essential. For good adhesion of coatings to a surface, a certain roughness may be needed. A simple example is the grinding of a surface before it is painted. Chemical reactions with a surface depend on the roughness. A reflective surface of a lapped gauge has very little corrosion under normal circumstances, even if it is made from a rapidly corroding steel.
Dimensional irregularity of a surface, its deviations from a mathematical flat.
Interaction Between Two Surfaces We give here some aspects and properties that are affected or determined by the surface roughness:
Theory and Application
• The coefficient of friction between two bodies • The presence/remain in a liquid film between two bodies (lubrication) • Sealing by means of a threaded connection or a pen/hole connection • Stiffness of a connection • Plastic or elastic deformation at contact between two bodies • Thermal conductivity between two bodies • Electrical conduction between two bodies • Wear/fatigue contact between surfaces
Importance of Roughness for the Function of a Workpiece Functional aspects that are affected by surface roughness can be described by 1-, 2-, and 3-body interactions. Interaction with a Single Surface The transmission and reflection of electromagnetic waves is determined by the surface geometry (see entry “▶ Reflectivity”), especially the scattering by the surface. One can look through window glass due to the fact that the surface roughness Ra (
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