Current Issue : October-December Volume : 2022 Issue Number : 4 Articles : 5 Articles
The article presents the results of tribological investigations into the steel/polymer/steel sandwich material LITECOR® developed by ThyssenKrupp Steel Europe for applications in the automotive industry. Friction tests were carried out by means of a strip drawing test with the use of a special tribotester mounted on a uniaxial tensile test machine. The influence of sheet deformation on the value of the coefficient of friction (COF) was considered. For this purpose, the samples were subjected to a pre-deformation of 4%, 8% and 12%. Friction tests were carried out with different force values and under different friction conditions, i.e., in dry friction conditions and lubrication of the sheet surface with L-AN 46 machine oil. The highest values of COF were observed for as-received sheets. In contrast, apart from the friction process under the conditions of the lowest force analysed, the lowest value of the COF was observed for pre-strained sheets with a deformation of 12%. The lubrication efficiency of the pre-strained strip specimens with ε = 4% was between 10.5% and 16.3%, with a trend of increasing lubrication efficiency with increasing force. For pre-strained sheets with deformation ε = 12%, there was a trend of decreasing effectiveness from 14.9% to 9.03% with an increase in force....
Mineral-based oils are the market leaders when it comes to their consumption in different types of rotating machines. Recently, a lot of attention has been given to the bio-oils and lubricants due to their better thermophysical, tribological, and environmental characteristics for use in journal bearing and other rotating machines. The superior physical properties of bio-oils have instigated this research in order to evaluate their dynamic characteristics that can cause the harmful dynamic instabilities in rotating machinery. The dynamic characteristics of the fluid film are influenced by temperature, eccentricity ratio, and rotational speed. In this work, the effect of temperature is experimentally measured on the dynamic viscosity of bio-oils and mineral-based oil. The dynamic viscosity measured is then computationally used to estimate the hydrodynamic pressure response of three bio-oils (rapeseed, palm olein, and soybean) and SAE40, a mineral-based oil, to check their performance in the rotor bearing system. It is found that at 40 ◦C, the hydrodynamic pressure for SAE40 is observed to be 2.53, 2.72, and 3.32 times greater than those of rapeseed, palm olein, and soybean oil, respectively, whereas, at 125 ◦C, the hydrodynamic pressure for SAE40 is observed to be 8% and 4.3% less than those of rapeseed and palm olein, respectively, but 14% greater than that of soybean oil. Hence, the increasing temperature has less effect on the viscosity and hydrodynamic pressure of bio-oils compared to SAE40. Therefore, for high-temperature applications, the bio-oils can be used with further processing. The superior response of bio-oils is also an indication for better dynamic characteristics....
To explore the effect of dents on the tribological behavior of the “washers-cage-rollers” system of rolling element bearings (REBs), the friction and wear properties of dents textured thrust cylindrical roller bearings (81107TN) with different diameters of dents (DAOD, 200, 250, 300 μm), depth of dents (DPOD, 4, 8, 12 μm) as well as circumferential interval angle (CFIA, 1.5◦, 2.0◦, 2.5◦) were researched under dry wear. The surface stresses of REBs and the influence mechanism of dents were also compared and discussed. The results show that: due to the nylon film formed and left on the raceways, the coefficients of friction (COFs) of dents textured bearings are all higher than the average COF of smooth ones, while their wear losses may become higher or lower, depending on the combination of pattern parameters. The influence of the DPOD on the tribological performance of textured bearings is more significant than that of the DAOD. The results show that, when the DAOD and DPOD are 250 and 8 μm, respectively, compared with the smooth ones, the mass losses of bearings can be reduced by up to 49.22% under dry wear, which would be an important reference for the optimal design of the “washers-cage-rollers” system of REBs....
WC‐(Fe‐Mn‐C) composites with γ‐iron and γ + α’ matrices were sintered and then tested at sliding speeds in the range 7–37 m/s. The coefficient of friction was exponentially reduced as a function of sliding speed reaching its minimum at 37 m/s. This behavior was provided by the mechanochemical formation of iron tungstate FeWO4 on the worn surfaces of composite samples. The lubricating effect of iron tungstate did not, however, allow for a reduction in wear. The worn surface was represented by a 3–10 μm‐thickness tribological layer composed of fine WC and iron particles cemented by FeWO4. This layer provided the self‐lubricating effect in high‐speed (high‐temperature) sliding because of its easy shear and quasi‐viscous behavior. The underlying 25–65 μm of thickness layer was composed of only heat‐affected WC and recrystallized iron grains....
In order to understand the surface and interface conditions of polycrystalline cubic boron nitride (PcBN) sliding against bearing steel in vacuum environments, the effects of different loads on the tribological behaviors of PcBN and bearing steel AISI 52100 were studied deeply in a vacuum tribometer. Furthermore, the wear tracks of PcBN and the wear scars of AISI 52100 were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the stable coefficient of friction (CoF) of the tribopair experiences a decrease first and then an increase with the increase in loads from 2 N to 15 N. The adhesive layer increases with the increase in loads, and the formation of adhesive layer contributes to the change of CoF and wear rate of counterpart balls. The adhesive layer is formed due to the combination of high contact stress and high temperature. Meanwhile, the exfoliated cubic boron nitride grains are embedded into the adhesive layer as abrasive grains, resulting in abrasive wear. Thus, the main wear mechanisms are adhesive wear and abrasive wear....
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