The herringbone-grooved oil-film-lubricated mechanical face seals were experimentally studied on aspects of the leakage and thermal features. The outer-diameter pressured test assembly was utilized to measure the leakage and the stator temperature of the seals at rotation speeds of 500 ~ 2500 r/min and medium pressures of 0.35 ~ 0.80 MPa. A novel method is proposed to obtain the radial temperature distribution of the stator face by fitting the measured temperatures of three spots inside the stator. Results indicate that the outer-grooved seal and the middle-grooved seal present acceptable leakage suppression effect, but the temperature increment is larger; the inner-grooved seal maintains zero leakage at lower pressure, and the temperature increment is only half of that of the rest; at higher pressure, the leakage of the inner-grooved seal is overly large; the fitted face temperature distributions contribute to explaining the abnormal phenomena (dark and bubbled) of the collected oil leakages. The mechanism of the leakage and thermal features are analyzed and discussed in aspects of the low-pressure, high-pressure, pumping, cavitation blocking effects of the grooves, as well as the convergent-sealing-gap effect due to uneven temperature profile.

In this work, the degradation of selected lubrication oil parameters until the specified threshold is predicted based on Gaussian process regression (GPR) to extend the oil change interval. Kinematic viscosity (40°C) and total acid number (TAN) was selected based on Mahalanobis-Taguchi Gram-Schmidt (MTGS) analysis. Kinematic viscosity (40°C) degradation prediction model presented a better result with an R squared of 0.61835, RMSE of 0.97142 and predicted maximum oil age of 31.9 months. The predicted maximum oil age value is validated by modelling the degradation of remaining lubrication oil parameters namely water content and particle counts, these parameters are within its threshold value at 31.9 months. The study proves that the degradation of kinematic viscosity (40°C) can be predicted based on GPR modelling. The corresponding oil age at threshold of parameter was identified to be longer than the actual duration of lubrication oil in service and the oil change interval can be extended beyond 26 months.

Fourier transform infrared (FTIR) spectroscopy is a well-established primary qualitative screening tool for Condition Monitoring (CM) of in-service lubricants, with three key determinative ASTM methods often used to accept their continued use or condemn them. These include Acid Number (AN), Base Number (BN) and moisture (H₂O), all tedious and environmentally problematic titrimetric methods. The latter have been developed into FTIR quantitative methods through the use of targeted stoichiometric reactions to produce infrared-active products readily and accurately quantified. FTIR CM is discussed in the context of these methods, their tribological significance and the basic analytical concepts examined and compared. The evolution of new FTIR qualitative and quantitative methodology is reviewed from its origins in edible oil analysis to the high-throughput analytical FTIR systems used by commercial CM laboratories to produce ASTM-comparable data in lieu of titration. Comparisons of chemometric vs. stoichiometric approaches are made, including implementation, applications, and instrumentation. Commercial implementation and performance of proprietary quantitative FTIR/IR systems are discussed with a focus on the stoichiometric approach. Current developments include generic, manual FTIR methods combining simplicity, universality, and practical environmental benefits in being able to serve as alternatives to titrimetric procedures. A new methodological approach that could unify the three deterministic FTIR methods under a single, IR-active reaction product is also presented.

Total wear in transient regime consists of transient wear and linear wear components. Within the transient regime metal possess higher wear rates than the steady state. FEM computational based wear models ignore transient regime which leads to higher error. This paper emphases on predicting the total wear in transient regime of 316 stainless steel pin against AISI 52100 bearing steel disc for 20 N and 30 N.Novel methodology is proposed to calculate individual wear components. Linear component by FEM based Abaqus software using an extrapolation technique to reduce computational time without compromising the accuracy. Transient component is calculated using Gauss Newton regression method. Further, total wear is modelled by addition of linear and transient wear components. Simulated total wear has good agreement with experimental wear error within 11% for both the loads. Corresponding transient wear rate was found to be approximately 2.5 times higher than steady state wear. This establishes the robustness of proposed methodology.

The Japanese Society of Tribologists is pleased to announce that the 2021 Best Paper Award of the Society was awarded to the following papers from Tribology Online. The Award was presented to the authors by Prof. Joichi Sugimura, the President of the Japanese Society of Tribologists, at the award ceremony in the JAST Annual Meeting on 24th May, 2022, held online.

The titles and the authors of the awarded papers:

◊“Estimation Method of Micropitting Life from S-N Curve Established by Residual Stress Measurements and Numerical Contact Analysis,” by Naoya Hasegawa, Takumi Fujita, Michimasa Uchidate, Masayoshi Abo, and Hiroshi Kinoshita, Tribology Online, Vol. 14, No. 3 (2019) 131-142.

◊“In Situ Raman-SLIM Monitoring for the Formation Processes of MoDTC and ZDDP Tribofilms at Steel/Steel Contacts under Boundary Lubrication,” by Hikaru Okubo, Chiharu Tadokoro, and Shinya Sasaki, Tribology Online, Vol. 15, No. 3 (2020) 105-116.

Congratulations!

The Best Paper Award is given annually to the author(s), either the JAST members or non-members, of the paper(s) judged as the best paper(s) published in Journal of Japanese Society of Tribologists (Toraiborojisuto) and Tribology Online (TROL) for the previous three years. All papers that appeared in Toraiborojisuto and TROL for the three years are reviewed by the JAST Awards Committee.

This paper proposes a new THL bearing design method based on an improved version of a precedent method. The precedent method used a model expression prepared in advance to easily and quickly find a crucial predicted data of the maximum bearing temperature. Three expressions were prepared for three different values of journal eccentricity ratio, 0.25, 0.50, and 0.75. Which one of the three should be used was determined, based on the preliminarily obtained value of journal eccentricity ratio derived from the initially analysis and t–test, for the crucial temperature for any value of journal eccentricity ratio. Furthermore, the new expression explicitly includes the four well-known dimensionless numbers used in THL analysis, that is, Sommerfeld number, bearing width-to-dimeter ratio, Peclet number and Khonsari number. The model expressions for other bearing characteristic performances were obtained in the same way. Compared with some measurements in test rigs of cylindrical bearings, the new improved method is confirmed to predict reasonably accurate bearing performances of cylindrical bearings faster and more easily than the precedent method over a wide range of operating conditions.

In the modelling and characterization of changes undergone by engineering surfaces from tribological processes, an automatic detection system is often required to minimize subjective elements of the assessment in the analysis. Microgeometry changes in tribological surfaces are indentations, scratches, micro-pits, micro-smearing marks and mild wear. The current paper presents some effective methods to detect depressions on machined surfaces (e.g. indentations, scratches and micropitting) and also mild wear (small changes in the actual surface topography). The theoretical background of the methods is discussed and application examples are illustrated. With this, it is expected that the reader can easily develop computer programs to implement the methods described here.

This paper presents a modified Reynolds equation for analyzing thin film lubrication with a saturated high-viscosity surface layer on a solid surface. The saturated high-viscosity characteristics of engine oil blended with additives of metallic detergents and friction modifiers were expressed using new viscosity functions with various orders termed “viscosity model 2,” which is different from the previous model, termed “viscosity model 1.” The viscosity function was then incorporated on the moving surface, and the fluid flow in the bearing gap was determined in a closed-form solution for order numbers N of 2 to 5. Subsequently the modified Reynolds equation was formulated by numerically integrating the flow equation. The modified Reynolds equation was applied to analyze the tapered pad bearing, and different features of the load capacity and friction coefficients from those for viscosity model 1 were clarified. The effects of the order number N, viscosity ratio, bearing length, and high-viscosity layer thickness on the load capacity and friction coefficient were elucidated. It was found that when the order number N was increased to 5, the friction coefficient decreased to a minimal value, subsequently increased to the maximum value, and then decreased to the lowest value with a decrease in the trailing gap.

The friction coefficient when a Fe surface was lubricated with an additive mixture of N-Oleoyl sarcosine (NOS), a commercial organic friction modifier, and zinc dialkyldithiophosphate (ZDDP) was measured at 100°C using a ball-on-disk tribometer under boundary lubrication conditions. The sliding surface was observed with a 3D laser microscope to investigate the tribo-film morphology and to evaluate the anti-wear performance. The findings indicate that this additive mixture enhanced tribological lubrication behavior in terms of friction-reducing and anti-wear properties under extended sliding cycle conditions. Scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDX) studies were conducted to analyze the elemental composition of sliding surfaces after tribo-tests and to estimate the friction reduction mechanism of the additive mixture. The EDX results revealed a noticeable decrease in S, suggesting that the NOS suppresses ZDDP decomposition and reduces the adsorption of the decomposition products.

The tribological properties of a mixture of a commercial organic friction modifier, N-oleoyl sarcosine (NOS), and a commercial anti-wear additive, zinc dialkyldithiophosphate (ZDDP), were investigated. The results suggest a synergistic effect between these two additives, resulting in a mixture that exhibited the lowest and most stable friction coefficient as well as the smallest wear area. X-ray photoelectron spectroscopy was performed to investigate the chemical composition of the tribo-films formed using this mixture. The results suggest that the tribo-films lacked S as well as PO₄³⁻ species. They also suggest that ZDDP mitigates degradation of the NOS, and improve the tribo-film durability thus improving anti-wear/friction-reducing performance. These results elucidate the synergistic friction-reducing tribological mechanism of the NOS+ZDDP mixture.