ISO 7902-3:2020 pdf download – Hydrodynamic plain journal bearings under steady-state conditions — Circular cylindrical bearings — Part 3: Permissible operational parameters.
6 Operational parameters to avoid excessive mechanical loading The maximum permissible specific bearing load, p lim , is the result of the requirement that a deformation of the sliding surfaces may not result in impairment of correct functioning and the formation of cracks. In addition to the composition of the bearing material, there are many other decisive influencing factors, such as the method of manufacture, the material structure, the thickness of bearing material and the geometry and type of bearing liner backing. Independently of these, a check shall be made as to whether the bearing is subjected to the full load when starting. If the specific bearing load during starting, p, is greater than 2,5 N/mm 2 to 3 N/mm 2 , it may be necessary to provide relief by pressurized oil (auxiliary hydrostatic device). Otherwise wear can occur on the sliding surfaces. Table 3 gives empirical values for p lim
7 Operational parameters to avoid excessive thermal loading The maximum permissible bearing temperature, T lim , is dependent on the bearing material and the lubricant. With increasing temperature, hardness and strength of the bearing material decrease. This is particularly noticeable for lead and tin alloys because of their low melting points. In addition, lubricant viscosity decreases as temperature increases. The load-carrying capacity of the plain bearing is therefore reduced, resulting, under certain circumstances, in mixed friction with wear. Furthermore, at temperatures greater than 80 °C, ageing of lubricants based on mineral oils increases. During steady-state operation of the plain bearing, the temperature field is constant. When carrying out the plain bearing calculation in accordance with ISO 7902-1, the thermal bearing load may be described by the bearing temperature, T B , or by the lubricant outlet temperature, T ex , provided they do not exceed, T lim . Table 4 gives general empirical values for T lim in which it is taken into account that the maximum value of the temperature field is greater than the calculated bearing temperature, T B , or than the calculated lubricant outlet temperature, T ex