BS ISO 7905-1:2021

What is ISO 7905‑1 about?   

ISO 7905‑1 is the first part of the multi-series of the document that is applicable to the plain bearings for bearing fatigue. 

ISO 7905‑1 specifies a method of improving test result comparability by evaluating the stresses in the bearing layers leading to fatigue. A similar evaluation is required in practical applications. Because the stresses are the result of pressure build-up in the hydrodynamic film, it is essential to fully state the conditions of operation and lubrication. In addition to dynamic loading, dimensional and running characteristics, the inclusion of the following adequately defines the fatigue system: 

• Under conditions of dynamic loading the minimum bearing oil film thickness as   a function of time and location to ensure no excessive local overheating or   shearing as a result of mixed lubrication when running in 
• The distribution of pressure circumferentially and axially with time under   dynamic loading 
•  From this the resulting stresses in the bearing layers as a function of time and location, especially the maximum alternating stress 

ISO 7905‑1 applies to oil-lubricated plain cylindrical bearings, in test rigs and applications running in conditions of full hydrodynamic lubrication. It comprises dynamic loading in bi-metal and multilayer bearings. 

Note: The number of practical applications with different requirements has led to the development of many bearings test rigs. If the conditions of lubrication employed on these test rigs are not defined in detail, test results from different rigs are generally neither comparable nor applicable in practice. Different test rigs can yield inconsistent ranking among equal materials.  

Who is ISO 7905‑1 for?  

ISO 7905‑1 on bearing fatigue is useful for:  

•    Manufacturers and designers of bearings 
•    Manufacturers of bearing test rigs 
•    Machinery industries 
•    Mechanical engineers 

Why should you use ISO 7905‑1?   

ISO 7905-1 provides a method for improving test result comparability by assessing the stresses in the bearing layers that cause fatigue. Moreover, mixed lubrication, wear, dirt, tribochemical reactions, and other phenomena experienced in use, can all contribute to bearing fatigue, aggravating the situation. As a result, this paper is limited to fatigue under full hydrodynamic separation of the bearing surfaces by a lubricant film. 

ISO 7905-1 specifies in creating fatigue failure in high strength material without wear or seizure. ISO 7905-1 evaluates hydrodynamic properties (clearance, lubricant viscosity, and very low surface roughness) that must be chosen to provide a sufficient minimum oil film thickness to prevent metallic contact. This can avoid substantial damage from excessive temperature and frictional shear stress, both of which can induce surface microcracks.   

By obedience to ISO 7905-1, you can select the appropriate bearing for the application at hand in order to avoid premature bearing fatigue, and verify the dynamic performance and service-life of the bearing.