S25 (ZVV)

S25 (ZVV) refers to a specific surface roughness parameter, commonly used in engineering and manufacturing to characterize the three-dimensional texture of a surface. The abbreviation "ZVV" indicates that the roughness value is calculated based on vertical deviations from the mean surface and is derived from the ISO 25178 standard.

In more detail, S25 is a material ratio parameter. It represents the percentage of the surface area that is above a certain height threshold (specified as a percentage) of the entire assessed surface height. This height threshold is calculated as 25% of the Sz value (maximum height of the surface). Sz is the sum of the maximum peak height (Sp) and the maximum pit depth (Sv) within the defined area.

Therefore, S25 essentially describes the portion of the bearing surface which is significantly high relative to the total height variation of the measured area. It provides insight into the load-bearing capacity of the surface and can be used to predict wear characteristics and tribological behavior. A higher S25 value suggests a surface with more material at higher elevations, potentially implying a greater initial contact area.

The S25 parameter is usually determined by optical or tactile measurement methods. It is particularly relevant when controlling surface finish for sealing applications, adhesive bonding, and other situations where the surface topography significantly influences performance. Other S parameters from ISO 25178 such as Sa (arithmetical mean height), Sq (root mean square height), and Sz can be used in conjunction with S25 to provide a more complete assessment of surface texture.