Surface finishes - Characterization

The properties of solids and their behavior often depend more on the characteristics of their surfaces than on their mass or volume properties. The surface of a solid body is the part of that solid that limits it in space and separates it from its surrounding environment. It plays a key role in ensuring functions such as friction capacity, resistance to wear or corrosion, thermal and electrical conduction, resistance to mechanical stress, static or dynamic sealing, appearance, etc.

Industrial surfaces produced by technical means always have irregularities compared to the ideal surface. To describe them accurately, a continuous function z (x, y) would need to be used, giving the altitude of each point relative to the ideal surface.

Understanding the influence of a surface's condition on a part's performance and behavior over time requires the ability to characterize its geometry, macro, micro, and even nano-geometry in some cases.

Only the characterization of surface conditions carried out on a profile is standardized. Advances in technology and equipment now make it possible to obtain a three-dimensional representation of the surface (topography). Although this approach is currently the most accurate way of characterizing a surface, it is not yet recognized and cannot be used in production.

Problems relating to surface geometry arise at three levels:

• Design: What surface finish is suitable for the function to be performed, and how should it be specified on a technical drawing?

• surface finish: what methods should be used to achieve the desired surface condition?

• Surface measurement: what measurement methods and conditions should be used to verify that the surface meets specifications? This aspect will be addressed in the dossier.  .

This file and the next one  primarily studies the industrial aspects of characterizing and measuring surface conditions, based on current standards and ongoing work.

Issues concerning imperfections (pits, scratches, pores, etc.) and the appearance (color, shine) of surfaces are not addressed in this document.

The characterization of surface conditions on a profile is currently the only standardized method.

The current standardization is a real step forward, with the GPS (Geometric Product Specification) concept recognized and adopted by the main industrial countries. It should therefore be used to specify and measure surface conditions, particularly in commercial transactions.

While this system is well suited...