Effect of the specimen geometry on wear - combination of polyacetal (POM) and carbon steel for machine structures

Engineering plastics which have been shown to have good mechanical properties are now frequently used as materials for various machine elements. Engineering plastics are combined with other engineering plastics and metallic materials for machine construction. These machine elements are fabricated with contact surface forms, such as convex, concave, and plane surfaces. Therefore, when designing machines with a combination of materials containing engineering plastics, it is useful to know the wear and friction characteristics for various contact surface forms. In the present research, polyacetal (POM), an engineering plastic, and carbon steel, a metal often used for machine structures, were chosen as materials to study wear and friction. Wear tests were performed in the combination of a convex surface and a plane, and in the combination of a plane and a plane. As a result, some features of the wear and friction characteristic are clarified. (1) The worn mass when the flat specimen made of POM is rubbed by the POM pin specimen is larger than when with the pin specimen made of carbon steel. (2) When the flat specimen made of POM is rubbed by the POM or the carbon steel pin specimen, the same grade of wear is observed regardless of the pin specimen material. (3) The worn length of the steel spherical pin specimen on the steel flat specimen becomes close to the initial radius of the curvature of the pin specimen when the sliding distance is large. The initial condition of the spherical tip pin specimen on the flat specimen evolves toward a condition of the flat tip pin specimen on the flat specimen. So, the comparison between the two geometries is non-relevant. Such problem did not occur in POM pin specimen.