Bearings surface finish

The most important stainless steel [12597-68-1] series are the 200-, 300-, and 400-series. The 300-series, primarily 302, 304, and 316, is used in the dairy industry, whereas the 400-series is used for special appHcations, such as pump impellers, plungers, cutting blades, scrapers, and bearings (Table 11). Surface finishes are specified from No. 1 to No. 8 (highly poHshed) the No. 4 finish is most commonly used. 

The low Mg -t- Si content of H9 facilitates the production of complex extrusions with a good surface finish making H9 a natural choice for glazing sections and other architectural features. Higher mechanical properties are obtainable with the H20 and H30 compositions, which are therefore more suitable for load bearing structures. 

The overall elements that contribute to the limiting of the PV factor are magnitude of pressure, speed of rotation, coefficient of friction of mating materials, lubrication, clearance between bearing and shaft, surrounding temperature, and surface finish, as well as hardness of the mating materials. Bearing wall thickness is also an element in the PV factor since it determines the heat dissipation. 

ABRASION. All metallic and nonmetallic surfaces, no matter how smooth, consist of minute serrations and ridges that induce a cutting or tearing action when two surfaces in contact move with respect to each other. This wearing of the sui faces is termed abrasion. Undesirable. abiasion may occur in bearings and other machine elements, but abrasion is also adapted lo surface finishing and machining, where the material is too hard to be cut by other means, or where precision is a primary requisite. 

Surface creep must be very low, both to restrict loss of lubricant from bearings, etc. and to avoid contamination of other components. Creep is a surface tension effect where oil surface tensions are typically in the range 18-30 mN/m. To mitigate surface creep, thermal gradients should be avoided or minimised and the surface finish of components should be optimised. Capillary creep occurs if Ra> 0.1 mm, thermal creep occurs if Ra < 0.6 mm. 

Therefore in laboratory tests it is common to choose specific combinations of load, speed, contact geometry (point, line or area), motion (continuous rotation, oscillation, reciprocation or fretting), counterface material and surface finish, ambient temperature and the presence or absence of lubricant or abrasive. The number of possible test combinations is therefore vast, and yet it is vitally important for the correct choice to be made if the results are to be of value in predicting in-service bearing life. 

Internal mirror-surface finish was possible for pieces made of bearing steel, alumina. Later studies (Qian et al., 2001) added some new conclusions that are presented here. 

The surface finish is also critical on many parts including shaft bearing interfaces, clutch hexagon interfaces, brake pins, etc. Relative motion between parts requires good lubrication, which is normally affected by the surface finish at the lubrication interface. Parts may need to be reworked to improve the surface finish. One half of the mating parts may need to be remade... 

The static friction coefficient of a solid material depends not only on the material but also on the nature of the substrate, its surface finish (e.g., roughness), its surface conditions (e.g., oxidized, etched), and the type of atmosphere (e.g., air, gas, vacuum). For most materials the static coefficient of friction is drastically increased when contact surfaces are put under vacuum because the lubricating action of molecules disappears. This explains why moving parts and bearing in a vacuum or under reduced pressure are technological challenges. On the other hand, the lubricating action of liquids is obvious except if they react chemically ... 

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