Search Results (14)

Lubricating greases with varying proportions of gold mine tailings or SiO₂ as additives were prepared, and their friction and wear performance were evaluated using a four-ball tribometer. Scanning electron microscopy and three-dimensional surface profilometry were employed to analyze the thickener properties and wear patterns on the steel balls. The results indicated that the addition of gold mine tailings significantly improved the friction-reducing and wear-resistant properties of the base grease compared with SiO₂. At the optimal concentration of 3 wt%, the addition of gold mine tailings reduced the coefficient of friction and wear scar diameter of the base grease by 43.2% and 21.1%, respectively, yielding the best performance among the 11 tested samples. Further analysis revealed that silicate and calcium carbonate particles in the gold mine tailings were deposited on the surface, forming a protective layer. This layer, along with the grease film, contributed to substantial reductions in both friction and wear. Full article

EV motors and machine elements operate at higher speeds, generate significant heat and noise (vibration), and subject lubricants (bearings) to multiple degrading factors, requiring thermal stability, wear protection, mitigating wear mechanisms like pitting and scuffing, and low electrical conductivity to prevent arcing damage to bearings. This study evaluates the tribological performance of four types of greases—PUEs, PUPao, PUEth (polyurea-based), and LiPAO (lithium–calcium complex-based)—to determine their suitability for electric motor bearings. Key performance metrics include tribological properties, electrical resistivity, leakage, bearing noise, and wear behavior. A four-ball wear test ranks the greases by scar diameter as PUPao < PUEs < PUEth < LiPAO, while the coefficient of friction is observed in the range of 0.15–0.18, with LiPAO exhibiting the lowest friction. Electrical resistivity tests reveal that PUEs grease has the lowest resistivity. Electrical leakage tests, conducted with a voltage differential across bearings, assess pitting damage, with PUEth and LiPAO showing evidence of surface pitting. Optical microscopy and scanning electron microscopy analysis is carried out to examine the pitting. In bearing noise tests, PUEs demonstrates the lowest noise levels, whereas LiPAO produces the highest. Visual and microscopic examination of the greases further characterizes their lubricating properties. Based on overall performance, the greases are ranked in suitability for electric motor applications as PUEs > PUPao > PUEth > LiPAO. The findings highlight the critical need for selecting appropriate grease formulations to ensure optimal bearing performance under varying operational conditions. Full article

As public attention is increasingly drawn toward more sustainable transportation methods, the popularity of electric vehicles (EVs) as part of the solution is rapidly expanding. Operating conditions within EVs can be severe compared to standard combustion powertrains, and the risk of electrical arcing across mechanical surfaces from electric leakage currents incites additional concern. This study employed a series of electro-tribological tests utilizing various moving patterns to improve understanding of the driving conditions for electrically induced bearing damage (EIBD). Rolling ball-on-disk tests were performed with different polyurea-thickened greases. Rotational tests were initially run at various speeds and test durations, but electrical damage was limited. However, electrical damage was unmistakable when a reciprocating motion was used at different track lengths and speeds. These results suggest that the conditions associated with the track length, such as the number of directional changes and speed-dependent film thickness, play a considerable role in forming electrical damage. This work provides critical insights into the mechanisms of EIBD in EVs and other electrical systems. It highlights the importance of understanding the operational conditions that contribute to EIBD, which can lead to improved designs and maintenance practices, ultimately enhancing the efficiency and lifespan of these systems. Full article

To evaluate the impact of various proportions of erucamide and N-phenyl-α-naphthylamine on grease’s tribological performance for roller bearings, lithium complex grease (LCG) and polyurea grease (PG) were prepared with erucamide and N-phenyl-α-naphthylamine proportions of (0,0), (0,3), (1,2), (2,1), and (3,0). An investigation was conducted into the microscopic structures of the ten greases and their effects on the friction coefficients and wear scars of GCr15 steel. These findings were validated through bearing friction torque tests. The results indicate that the addition of 2 wt. % erucamide and 1 wt. % N-phenyl-α-naphthylamine to PG/LCG significantly enhances their tribological properties and reduces friction torque, with PG exhibiting superior performance. This enhancement was attributed to the synergistic interaction of erucamide and N-phenyl-α-naphthylamine with the lamellar thickener within PG. Erucamide contributed to friction reduction, while N acted as an antioxidant. Full article

In order to further extend the service life of calcium sulfonate complex–polyurea grease (CSCPG) while ensuring its tribological performance, this article starts with the production of raw materials and the preparation process of the grease and explores the factors that significantly affect the tribological performance and service life of CSCPG based on unreplicated saturated factorial design (USFD). The Kriging prediction model is used along with the optimization objectives of friction coefficient and service life, and nondominated sorting genetic algorithm II (NSGA-II) was used for a multi-objective optimization solution. The tribological and service life tests were conducted before and after optimization. The results show that the viscosity of the base oil and the content of the nano-solid friction reducers have a significant impact on the tribological properties of CSCPG. The content of polyurea thickeners and antioxidants, as well as the thickening reaction temperature, have a significant impact on the service life of CSCPG. When the friction coefficient and service life are optimized as objectives and are compared to the initial group, the friction coefficient of CSCPG could be reduced by 5.3%, and the service life could be extended by 3.8%. The Kriging prediction model based on USFD has high accuracy and can be used to guide the preparation and performance optimization of CSCPG. Full article

High-performance greases typically consist of a base oil and polyurea as a thickener material. To date, few alternatives to polyureas have been investigated. Polyesters could be one such alternative; however, little is known about the gelation of such polyesters because, unlike polyureas, they cannot form hydrogen bonds between the polymer chains. Here, we present studies on the gel formation of a polyester based thickener poly(hexane dodecanoate) with 1-octanol endgroups in three different base oils, i.e., a mineral oil (Brightstock 150), a synthetic Polyalphaolefin (Spectrasyn 40) and castor oil (85 to 90 wt.% ricinoleic acid triglyceride). Small- and wide-angle X-ray scattering measurements indicate a strong interaction of the polyester with castor oil and an increase in the crystalline fraction, with an increasing polymer amount from 5 to 40 wt.%. Moreover, infrared analysis of the polyester in castor oil showed gel formation at a minimum concentration of 20 wt.%. The strong interaction of the polyester with castor oil compared to the other two base oils led to an increase in the yield point γ_F as a measure of the mechanical stability of the gel, which was determined to be 5.9% compared to 0.8% and 1.0% in Brightstock and Spectrasyn, respectively. Full article

In order to improve the tribological properties of calcium sulfonate complex–polyurea grease, WS₂ nanoparticles were used as additives to prepare WS₂ calcium sulfonate complex–polyurea grease. The tribological behavior of WS₂ grease on the GCr15 surface was systematically studied. The results indicate that WS₂ nanoparticles can significantly improve the extreme pressure performance of calcium sulfonate complex–polyurea grease. When the concentration of WS₂ nanoparticles is 2 wt.%, the friction coefficient decreases by 14.94%, and the maximum nonseizure load PB increases by 31.41%. As the temperature increases, the friction coefficient and wear rate of WS₂ grease first decrease and then increase. This is mainly attributed to the adsorption and frictional chemical reaction between WS₂ nanoparticles and the matrix. Full article

China’s rapid industrial development requires more energy consumption based on non-renewable energy resources. The energy consumption caused by unnecessary friction accounts for about 4.5% of the GDP in China. Although grease effectively lubricates machines, lubrication failure may occur under severe conditions. Nanomaterials exhibit intriguing tribological performances and have received much attention regarding lubrication. In this study, oleylamine-modified Ni nanoparticles (OA-Ni) were synthesized and used as lubricant additive in four kinds of commonly used greases: lithium, calcium, composite calcium, and polyurea grease. The OA-Ni were uniformly dispersed in the greases through electromagnetic stirring, ultrasonic vibration, and three-roll grinding. The physicochemical properties and the structure of OA-Ni-doped grease were investigated, while the feasibility of OA-Ni as various grease additives at different contact modes was evaluated by a four-ball friction tester and a UMT-tribolab tester. Tribological tests results revealed that the friction-reducing and anti-wear properties of point-to-point contact were increased by 56.7% and 70.3% in lithium grease, respectively, while those of the point-to-face contact were increased by 59.5% and 68.9% in polyurea grease, respectively. The present work provides not only theoretical guidance of nano nickel modification but also a practical reference for the application of modified nanomaterials to various greases. Full article

The rheological properties of lithium grease and polyurea grease at different temperatures and consistencies were determined with a rotary rheometer. The plateau moduli of the greases were calculated, and the mechanism of influence of consistency and temperature on the rheological properties of the greases was explained. The tribological and wear properties of the two greases were measured by high-temperature friction and wear tester. The friction and wear mechanisms are probed by the rheological properties of lubricating grease. The results show that the plateau modulus G_N can be used to assess the structural strength of different greases, but it can only assess the degree of entanglement of the same grease. The higher the consistency of the grease, the larger the apparent viscosity, structural strength, and yield stress. The rheological properties of PAO-polyurea grease are greatly affected by temperature, but its structural strength is better than that of mineral oil-lithium grease. The consistency of mineral oil-lithium grease is expected to affect the friction coefficient and wear through its influence on the grease’s structural strength and film-forming ability. For PAO-polyurea, the consistency in a certain range has little effect on the friction coefficient and wear resistance. Full article

Lubricating greases based on urea thickeners are frequently used in high-performance applications since their invention in 1954. One property that has so far been neglected in the further development of these systems due to their low solubility and the resulting difficulty of analysis, is to better understand how the degree of polymerization affect such polyurea lubricating systems. In this work, we prepared three different oligo- or polyurea systemswith different degrees of polymerization (DP) and investigated the influence of DP on rheological and tribological properties. The results showed that the DP has an influence on the flow limit in rheology as well as on the extreme pressure (EP) and anti-wear (AW) properties as examined by tribology measurements. By optimizing the DP for a thickener system, comparable EP and AW properties can be achieved through the use of additives. The DP showed an increasing influence on the flow limit. This could reduce damage to rolling bearings due to lateral loading at rest. Therefore, modifying the DP of the polyurea systems shows similar effects as the addition of external additives. Overall, this would reduce the use of additives in industrial applications. Full article

Due to the fact that the application of AW and EP additives in low-temperature greases may lead to worse high-temperature and anti-corrosion characteristics as well as additional burden on the environment due to the content of aggressive components, in this paper, the possibility of replacing these additives with NFA, which do not have these disadvantages, was investigated. The analysis of nanosized particles being used as functional additives in greases was carried out. The morphology of the following nanoparticles was studied: montmorillonite K 10, silica, calcium car-bonate and borate, halloysite, and molybdenum disulfide incorporated in halloysite tubes. The effect of nanostructured components on the physicochemical characteristics and anti-wear and anti-scuffing properties of complex lithium, polyurea, and polymer greases were studied. Maximal improvement of anti-wear and anti-scuffing characteristics of cLi-greases was reached when using silica and calcium borate. Maximal improvement of anti-scuffing properties of PU-lubricant was reached when using calcium carbonate and the two-component NFA based on halloysite, for anti-wear properties when adding silicon dioxide and halloysite. When the concentrations of silicon dioxide and calcium carbonate was increased from 1 to 3 wt.%, there was a decrease in yield stress of the structural frame of the PU-lubricant and its colloidal stability was worse. The increase of the concentration of calcium carbonate and borate nanoparticles in the studied range led to a significant improvement of the anti-wear and anti-scuffing characteristics of the PU grease, respectively. The greases properties’ dependence from the nanostructured functional additives’ introduction method and their concentration were investigated. Nanoparticles were added into the test lubricants before and after the thermo-mechanical dispersion stage. The addition of silicon dioxide and calcium carbonate NFA after the heat treatment stage led to worsening of the characteristics of the plastic material, and the increase of their concentration from 1 to 3 wt.% formed a harder structure of Li-grease. On the contrary, the addition of calcium borate NFA is recommended after the thermomechanical dispersion. The choice of nanoparticles and the method of their addition to the lubricants of various types was carried out according to the results of the previous stage of the research. Along with the analysis of the physicochemical characteristics and anti-wear and anti-scuffing properties of the lubricants, the structure of the dispersion phase of nanomodified lubricants were studied. Full article

One commonly used lubricant in rolling bearings is grease, which consists of base oil, thickener and small amounts of additives. Commercial greases are mostly produced from petrochemical base oil and thickener. Recently, the development of base oils from renewable resources have been significantly focused on in the lubricant industry. However, to produce an entirely bio-based grease, the thickener must also be produced from renewable materials. Therefore, this work presents the design and evaluation of three different bio-based polymer thickener systems. Tribological tests are performed to characterize lubrication properties of developed bio-based greases. The effect of thickener type on film thickness and friction behavior of the produced bio-based greases is evaluated on a ball-on-disc tribometer. Moreover, the results are compared to a commercial petrochemical grease chosen as benchmark. Full article

Greased bearings in electric motors (EMs) are subject to a wide range of operational requirements and corresponding micro-environments. Consequently, greases must function effectively in these conditions. Here, the tribological performance of four market-available EM greases was characterized by measuring friction and wear of silicon nitride sliding on hardened 52100 steel. The EM greases evaluated had similar viscosity grades but different combinations of polyurea or lithium thickener with mineral or synthetic base oil. Measurements were performed at a range of temperature and surface roughness conditions to capture behavior in multiple lubrication regimes. Results enabled direct comparison of market-available products across different application-relevant metrics, and the analysis methods developed can be used as a baseline for future studies of EM grease performance. Full article

Practical steady-state flow curves were obtained from different rheological tests and protocols for five lubricating greases, containing thickeners of a rather different nature, i.e., aluminum complex, lithium, lithium complex, and calcium complex soaps and polyurea. The experimental results demonstrated the difficulty to reach “real” steady-state flow conditions for these colloidal suspensions as a consequence of the strong time dependence and marked yielding behavior in a wide range of shear rates, resulting in flow instabilities such as shear banding and fracture. In order to better understand these phenomena, transient flow experiments, at constant shear rates, and creep tests, at constant shear stresses, were also carried out using controlled-strain and controlled-stress rheometers, respectively. The main objective of this work was to study the steady-state flow behaviour of lubricating greases, analyzing how the microstructural characteristics may affect the yielding flow behaviour. Full article