**1. Introduction**

It is a well-known fact that the appropriate test method could be one of the crucial conditions of the correct evaluation of a simulated process. One might presume that in some cases in which the subject matter is well-researched, only widely recognized methods are applied. However, in less familiar cases, or where one needs to evaluate some unusual values, the question of the appropriate methodology becomes far more significant. There are a number of papers in literature dealing with the analysis of the same phenomenon or process where tests were based on completely different methodological approach. As a result most papers quoted different results which caused serious controversy. In addition, it appears that even when the research was conducted according to the same procedure, but at different research units the results were still divergent.

As far as ball bearings are concerned there are numerous research methods to test these elements. For instance, using a four-ball pitting apparatus (T-03), a pitting ball-bearing tester (T-06), Amsler device or a ball-bearing testing platform. Most standards describe research methodology with the main focus on using particular testing devices, disregarding to a certain extent the very essence and purpose of the analysed object. The official standard for ball bearings in Poland is PN- 89/M-86410, however, it lacks a description of research methodology related to the external function of a ball bearing in "true-to-life" conditions. The description contains regulations concerning controlling the particular components of a ball bearing e.g. radial and axial run-out deviation, radial and axial clearance without paying any special attention to the working conditions of a ball bearing. Still, the standard allows applying other research methods which require prior acceptance of both the manufacturer and recipient of ball bearings.

In this context, the authors of the present section conducted tests on two-set ball bearings according to two different methods: their own methodology and the methods

© 2012 Nachimowicz and Jałbrzykowski, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Nachimowicz and Jałbrzykowski, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

recommended by the manufacturer (FŁT PLC in Kraśnik - Poland). Should add that all of the test, later in this chapter bearings are factory items and their designations are in accordance with PN, PN-EN and ISO standards. All tests were performed for three replicates at each point.

Performance Evaluation of Rolling Element Bearings Based on Tribological Behaviour 29

Before the tests were started, in the initial stage, normal force of N= 350 [kG] ≈ 3433 [N] was applied to the bearing. Next the apparatus was switched on for t=30 [min] at the speed of n= 1000 [rpm]. After that the rotational speed was increased to n= 1400 [rpm] and as soon as the system became stable the moment of friction was measured (Mt). Then, the rotational speed was decreased by 200 [rpm] in each step, and on each occasion after the friction node

Due to the extensive research material, the present section does not contain the results of

As far as MB-1 method is concerned, it should be noted that its results indicate diversification of tribological characteristics of the examined elements in relation to rotational speed. There is also a certain analogy in the course of characteristics for the two groups of the evaluated bearings. In the initial stage of the process the maximum value of friction moment was obtained (for all rotational speeds). In the subsequent stages it decreases and, in the final stages, the resistance of motion becomes stable. One should note that at the beginning of the process the highest value of the moment of friction was obtained at the speed of n = 1200 [rpm] while the lowest at n = 300 [rpm]. In the final stage of the

In the case of MB-2 method general diversification of the moment of friction was also noticed. It is logical considering different conditions of the external function. However the lowest value of the moment of friction was recorded for the lowest rotational speed n = 200 [rpm], while the highest for n = 1000 [rpm]. Further measurements, at higher rotational speeds, indicate the decrease of the value of the moment of friction. However, the most controversial conclusions

Fig. 2 and 3 shows selected comparative graphs of the courses and values of the moment of

The graphs above provide data concerning completely divergent results in the conducted tests. The analysis of the data in fig. 2. (MB-1 method) proves that both at the speed of n = 300 [rpm], and especially n = 1200, throughout the whole of the research cycle, one notices distinctly higher values of the moment of friction for the bearings from the 134-781TNG-2RS group. At the same time there are lower values of resistance to motion for the bearings from the CBK 441TNG group. Since these bearings have different dimensions of working elements one could assume that different values of the moment of friction is a natural phenomenon. When tests were carried out according to the other method similar trends in friction characteristics were expected. However, when the results obtained with MB-2 were analysed, quite contrary to expectations, they were in direct opposition to those obtained

friction obtained in tests according to MB-1 and MB-2 methods described above.

are drawn from the comparative analysis of the two research methods.

initial tests obtained with MB-1 and MB-2 methods, it only includes their description.

*1.1.2. Tests recommended by FŁT in Kraśnik (MB-2)* 

became stable the measurements Mt were taken.

**1.2. Test results and discussion** 

process the trend is reversed.

with MB-1 method.
