BS ISO 21250-1-2020 Rolling bearings一Noise testing of rolling bearing greases Part 1: Basic principles, testing assembly and test machine.
5 Basics
In the case of grease lubrication, many factors can affect the degree of cleanliness during operation. For the initial lubrication and relubrication, clean grease is always required. Also, in applications where the fatigue life is not an issue (e.g. at very low load), the use of clean greases can be extremely important, for example, as a contribution to a low bearing noise, which is required for applications such as electric motors, fans, etc.
The purpose of assessing grease noise is the determination of the grease noise quality or identifying low-noise (quieter) greases. It can contribute to the development and improvement of low noise grease as well as support.
The comparison of damping properties of different lubricants shall be made on one bearing type and size, and the bearing shall be mounted in the same way. If all these provisions are followed, the selection of the lubricant with optimum damping characteristics can be performed successfully.
It has been found that many factors within the lubricant contribute to the attenuation. For greases, the main parameters are the viscosity, the type of base oil and additive types used. An improvement
of damping characteristics can be observed when increasing the base oil viscosity. In addition, the thickener type and its micro-structure, as well as additives, can cause irregular damping properties.
NOTE 1 When abrasive or hard particles (impurities) are over-rolled, raceways (tracks) are damaged It can result in indentations and increase the stress level (see also ISO 15243). Thus, the fatigue process is accelerated, leading to surface distress including asperity related micro-cracks and micro-spalls where material is released. This in turn leads to noise increase and finally bearing fatigue and bearing failure. In ISO 281. the existence of contamination is described by the factor e and incorporated in the life modification factor
NOTE 2 Currently. no sufficient evidence about noise testing of used greases is existing. Therefore, this document is primarily intended for testing of unused greases.
6 Grease noise evaluation method
6.1 General and overview
The evaluation method o[the grease noise is as follows:
— rotate the deep groove ball bearing in which testing grease is enclosed, and
— analyse the vibration frequencies of the bearing.
The analysis method of grease noise varies with each method. Table 3 gives an overview of the features
of the methods.BS ISO 21250-1 pdf download.