Thus it is axiomatic that almost all surfaces produced by common machining and fabrication methods are positively skewed. These positively skewed surfaces have an undesir- able effect on the bearing load of surfaces, negatively impact-
Figure 2
ing the performance of parts involved in applications where there is substantial surface-to-surface contact. Specialized high-energy finishing procedures can truncate these surface profile peaks and achieve negatively skewed surfaces (Fig 2.) that are plateaued, presenting a much higher surface bearing contact area. Application: The transition from Gaussian (Fig. 1) honed surfaces to carefully specified plateaued surfaces (Fig 2.) in diesel fuel injector bore and mating timing plungers resulted in eliminating a multi-million dollar war- rantee problem for an over-the-road diesel engine manufacturer. One in six injectors would “stick” and usually allow raw fuel to flow, misfire, and some- times cause that cylinder to seize. The plateaued surface has a high “bearing ratio” to distribute the high fuel pres- sure loads and a uniform valley lay that effectively distributes fuel (the fuel oil is the system’s lubricant). Today, these are “standard” two or three proces- honing techniques and mass finishing processes used by all high-performance fuel injector manufacturers that elimi- nate failures due to part-to-part contact through the lubricant film. 2) Directional vs. Random (Iso- tropic) Surface Texture Patterns: Somewhat related to surface texture