ISO 7902-3-2020 pdf download

ISO 7902-3-2020 pdf download.Hydrodynamic plain journal bearings under steady-state conditions一 Circular cylindrical bearings一 Part 3: Permissible operational parameters. 7 Operational parameters to avoid excessive thermal loading The maximum permissible bearing temperature, Tim , 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, Tg, or by the lubricant outlet temperature, Tex , provided they do not exceed, Tim . Table 4 gives general empirical values for Tim in which it is taken into account that the maximum value of the temperature field is greater than the calculated bearing temperature, Tg, or than the calculated lubricant outlet temperature, Tex . From the total quantity of lubricant available for bearing lubrication, there is always only a small proportion for a limited period within the clearance gap and hence at an increased temperature level.This means that Tp or y is important for the service life of the lubricant flow rate. This ratio is, in general, more favourable for circumferentially-lubricated bearings than for self-lubricated bearings. 8 Operational parameters for the bearing clearance The bearing clearance greatly influences the operational behaviour of the plain bearing. Although its magnitude would actually be determined taking into account all other operational data, in practice, the following approximate formula has proven of value. According to this formula, the mean relative bearing clearance, iii, in thousandths, is calculated as a function of the peripheral speed, U1, in metres per second, only: ,Ji=O,409 6.Ji Experience has shown that it is sometimes difficult to realize an appropriate clearance fit using the tolerances specified in ISO 286-2. Sometimes deviations greater than the mean value calculated using this formula occur. For this reason, the bearing clearance should preferably be 0,56; 0,8; 1,12; 1,32; 1,6; 1,9; 2,24; 3,15 (%o) in which the main relative bearing clearances are in steps based on the preferred number...