Advances in Tribology

In this study, the conventional acid-clay method was used to evaluate its potential for recycling waste crankcase lubricating oil (WCLO). The results showed that the acid-clay method was effective in re-refining the WCLO and returning the oil to a quality comparable to oils produced from fresh lube oil stocks. This method has been reported to account for around 90% of the global waste crankcase lubricating oil treatment and is considered to be an inexpensive process. The results revealed that the acid-clay method improved the viscosity of the oil at 40°C from 104 cSt to 105.6 cSt. The flash point of the oil was also increased from 192°C in the WCLO to 204°C in the re-refined crankcase lubricating oil (RCLO). The water content reduced from 0.01% in the WCLO to 0% in the RCLO, indicating the effectiveness of the acid-clay method in removing water traces from the WCLO. Additionally, the contaminants present in the WCLO were reduced drastically, with iron and aluminum content reduced from 23.0% and 21.0% to 0.0% and 0.0%, respectively. The fuel ingress in the WCLO reduced from 4.0% to 1.0%. However, it was observed that the acid-clay method did not significantly impact the viscosity index, TBN, and density of the oil. The re-refined base oil produced by the acid-clay method can be fortified with appropriate additives and reused in vehicles, reducing environmental pollution, depleting fossil resources, and saving the country’s foreign exchange used in importing fresh lubricating oil.

Self-organization mechanisms of metastable dissipative structures during friction depending on base and oil functional additives for hypoid gears are considered. Research was conducted on a software-hardware complex with simulation of gears’ operation in rolling with slipping conditions in start-stop mode. Indicators of formation of wear-resistant dissipative structures include the following: improvement of antifriction characteristics, lubricant boundary layers’ formation, contact surfaces’ strengthening, and formation of heterogeneous deformation microrelief with a fine-grained structure. The formation of chemically modified boundary layers on 90% of the contact area of tribo-coupling elements ensures an increase in the wear resistance of leading and lagging surfaces by 2 and 1.4 times, respectively. The sclerometry method was used to establish that the formation of dissipative structures when lubricating tribo-coupling elements with various transmission oils can reduce deformation processes in metal near-surface layers by 23%. Highly viscous flavored lubricant with distillate oil and additive composition ensures wear-resistant dissipative structures with active components, including oxygen, sulfur, and phosphorus.

New lubricants based on vegetable oil were developed in this study. Different blends of canola oil mixed with fully synthetic two stock engine oils were developed (0, 20%, 40%, 60%, and 80% of synthetic oil).  The viscosity of the prepared blends was determined at different temperatures (20°C–80°C). Tribological experiments were conducted to investigate the effect of the newly developed oil on the wear characteristics of mild steel material compared with stainless steel when subjected to adhesive wear loading. The weight loss (WL) and the specific wear rate (SWR) of the mild steel using each of the prepared lubricants were determined. Scanning electron microscopy was used to examine the worn surface of the mild steel. The results revealed that pure canola oil as a lubricant performed competitively against a blend of 80% synthetic and 20% canola oils. The viscosity of the canola oil and its various blends with synthetic oil are controlled by the environmental temperature since an increased temperature reduces the viscosity. Also, the experimental results revealed that operating parameters play the main role in controlling the wear behavior of mild steel since increasing the sliding distances increases the weight loss. The specific wear rate exhibited a steady state after about 5 km sliding distance, and different blends influenced the applied loads and velocity differently. The mixing ratio of canola and syntactic oil was not particularly significant since the pure canola oil exhibited competitive wear performance compared with the blends. However, an intermediate mixing ratio (40%–60% synthetic oil mixed with 60%–40% canola) can produce a slightly low specific wear rate among other things.

The tribological behavior of Ni-based WC-Co coatings is analyzed. The coatings were deposited on gray cast iron substrates in a spray and fuse process using SuperJet Eutalloy deposition equipment, varying the oxygen flow conditions in the flame. The crystallographic structure of the coatings was characterized via the X-ray diffraction (XRD) technique. The microhardness was measured on the surface and in cross sections of the coatings by means of a Knoop microhardness tester. The topography and the morphological characteristics of the coatings and the tribo-surfaces were examined using scanning electron microscopy (SEM) and confocal microscopy, while the chemical composition was measured by means of energy-dispersive X-ray spectroscopy (EDS). The tribological behavior of the coatings was examined via a cohesion-adhesion scratch test, using cross sections of the coatings. Furthermore, two wear tests were carried out, using the pin-on-disk method under ASTM G99 standard and an ASTM standard G65 sand/rubber wheel abrasion wear test. The wear of the coatings showed a close relationship to the porosity in the metal matrix; since then, in the abrasive wear test, a high porosity is related with lower hardness in the coatings; likewise, a low hardness is related with a high wear.

In this paper, a state of the art on computer simulation and prediction of wear in mechanical components is reviewed. Past and recent developments as well as approaches employed in the simulation and prediction of wear are reviewed. In particular, the wear models, contact analysis schemes, and wear evolution prediction procedures as well as their application to the mechanical components (including cam-follower, gears, bearings, and cylinder/piston/piston ring wear) are reviewed. Recommendations and suggestions on possible directions for further research studies are also presented.

The aim of the present research is to characterize both experimentally and numerically journal bearings with low radial clearances for rotors in small-scale applications (e.g., microgas turbines); their diameter is in the order of ten millimetres, leading to very small dimensional clearances when the typical relative ones (order of 1/1000) are employed; investigating this particular class of journal bearings under static and dynamic loading conditions represents something unexplored. To this goal, a suitable test rig was designed and the performance of its bearings was investigated under steady load. For the sake of comparison, numerical simulations of the lubrication were also performed by means of a simplified model. The original test rig adopted is a commercial rotor kit (RK), but substantial modifications were carried out in order to allow significant measurements. Indeed, the relative radial clearance of RK4 RK bearings is about 2/100, while it is around 1/1000 in industrial bearings. Therefore, the same original RK bearings are employed in this new test rig, but a new shaft was designed to reduce their original clearance. The new custom shaft allows to study bearing behaviour for different clearances, since it is equipped with interchangeable journals. Experimental data obtained by this test rig are then compared with further results of more sophisticated simulations. They were carried out by means of an in-house developed finite element (FEM) code, suitable for thermoelasto-hydrodynamic (TEHD) analysis of journal bearings both in static and dynamic conditions. In this paper, bearing static performances are studied to assess the reliability of the experimental journal location predictions by comparing them with the ones coming from already validated numerical codes. Such comparisons are presented both for large and small clearance bearings of original and modified RKs, respectively. Good agreement is found only for the modified RK equipped with small clearance bearings (relative radial clearance 8/1000), as expected. In comparison with two-dimensional lubrication analysis, three-dimensional simulation improves prediction of journal location and correlation with experimental results.