Search Results (63)

The rapid growth of electric vehicles and electrified systems has increased the risk of bearing failures due to combined mechanical and electrical stresses. This study investigated the performance of hexagonal boron nitride nanoparticle-enhanced lithium grease under electrified conditions. Experiments based on a Taguchi L9 orthogonal array were conducted on deep groove ball bearings using a full-scale test rig at 1200 rpm with varying loads (100–300 N), currents (6–10 A), and hBN concentrations (0.1–1 wt.%). The tribo-electrical performance of nano-enhanced grease was compared with the base grease and commercial grease. It was observed that the base grease exhibited superior performance with a lower current flow, reduced vibration, and minimal surface degradation. In contrast, the hBN-enhanced grease exhibited inferior tribo-performance, with high vibrations and surface damage in electrified conditions. The surface analysis revealed features morphologically similar to white etching areas and micro-pitting. The FTIR results indicated grease degradation, while ICP-OES confirmed higher wear debris generation in the commercial and hBN-added greases. The present work indicates that additives like hBN nanoparticles do not necessarily improve performance under electrified conditions, making it important to consider the type of additives to be added during lubricant formulation. Thus, the findings emphasize the importance of lubricant formulation for controlling electrically induced bearing failures and provide insights for developing advanced greases for electric machinery applications. Full article

The influence of BN particle size on lithium grease performance was systematically compared among a base grease (Li), a micro-BN (3 µm, 0.1 wt%) modified grease (Li + 0.1% mBN), and a nano-BN (50 nm, 0.1 wt%) modified grease (Li + 0.1% nBN). SEM shows that addition nano-BN leads to a more compact soap fiber networks, whereas micro-BN tends to agglomerate and provides limited reinforcement, leaving the base grease with a loose, porous network. Consequently, Li + 0.1% nBN outperforms both Li and Li + 0.1% mBN in dropping point (199.5 °C vs. 194.9 °C and 198.6 °C), oil separation (0.39% vs. 0.64% and 0.44%), and flow point (49% vs. 45% and 47%). Its plateau modulus is significantly higher, reflecting stronger network entanglement. However, Li + 0.1% nBN shows lower structural recovery (61.0%) than Li (65.8%) and Li + 0.1% mBN (67.2%) due to rigid particle–fiber junctions. Notably, Li + 0.1% mBN exhibits a unique frequency-dependent viscoelasticity: higher tanδ at low frequencies but lower tanδ at high frequencies relative to Li. Tribologically, Li + 0.1% nBN reduces friction coefficient by 35% and wear scar diameter by 12.7% compared with Li, outperforming Li + 0.1% mBN. XPS confirms a protective hybrid tribofilm (BN + organic nitrogen species + iron oxides) on the nano-BN lubricated surface. Particle size critically governs BN–fiber interactions and the resulting rheological and tribological performance. Full article

The recent motivation for sustainable lubrication has driven the development and advances of bio-based and potentially environmentally favorable alternatives to petroleum-based greases. Yet, their industrial adoption is largely hindered by the thickener weak network or inconsistency leading to grease unacceptable degradation under applied loads and operating temperatures in rotating machinery. This study investigates a novel grease formulated from 80% palm oil and a 20% complex thickener system from carnauba wax (CW) and glycerol monostearate (GMS). The effect of thickener composition on grease performance was investigated by testing their X-ray diffraction (XRD) spectra, Fourier transform infrared (FTIR) spectra, penetration level, oil separation percentage, viscosity, thermal properties, and tribological behavior. GMS-rich blends achieved up to 70% lower friction than lithium grease. However, they showed high wear rates and excessive oil separation ranging from 0.07% at room temperature for the 20% GMS blend to above 9% at 40 °C for softer formulations. The blend of 15% CW + 5% GMS showed only 0.113% and 3.145% oil bleed at room temperature and at 40 °C, respectively, with suitable consistency (NLGI 3) and acceptable dynamic viscosity rates. Regarding thermal behavior, CW-based samples revealed an enhanced melting point compared to GMS. For validation, investigations were conducted on rolling element bearings on a customized test setup operating at 1400 rpm under selected radial loads. The results demonstrate that CW/GMS bio-thickeners achieved lower vibration levels compared to the GMS thickener, approaching the performance of lithium grease. Full article

Pin–bushing bearings in heavy-duty construction machinery operating in severe industrial environments are susceptible to accelerated wear, grease degradation, and lubrication failure, yet application-specific guidance for lubricant selection and re-greasing intervals under such conditions remains limited. This study evaluates the combined effects of bushing material (hardened steel, cast bronze, and Cu–Sn alloy), grease type (three commercially used greases with viscosities of 120, 460, and 150 mm²/s at 40 °C), and lubrication interval (8, 12, and 24 h) on grease-condition indicators in a field-operating wheel loader used in slag handling, where surrounding slag temperatures may reach 700–800 °C. A Taguchi L9 orthogonal array was used to define nine experimental configurations, each applied for approximately one week under real operating conditions. Grease samples were characterised using the SKF grease analysis kit based on NLGI consistency grade, base oil release rate, and contamination particle count. All greases showed an increase in NLGI grade from 2 to 3–4 during service, indicating thickening and a possible risk of lubrication channel blockage. Oil release rates decreased by up to 60% in some configurations, indicating reduced base oil mobility during service. When the three grease-condition indicators were evaluated together by Grey Relational Analysis, the combination of steel bushing, type B grease (ISO VG 460, lithium complex with MoS₂), and a 12 h lubrication interval showed the most balanced overall response. These findings provide field-based guidance for grease selection and maintenance scheduling in pin–bushing systems operating under demanding service conditions. Full article

Polyurea grease (PU) is widely used in the lubrication of heavy machinery, but it can still suffer from structural or performance degradation under extreme conditions such as high temperatures and heavy loads. This study successfully synthesized a hybrid polyurea grease (LiTFSI-PU) by incorporating lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into polyurea matrix. LiTFSI coordinates with the carbonyl groups (C=O) in the thickener molecules to form weakly Lewis acidic complex, thereby reinforcing the soap fiber network structure. As a result, LiTFSI-PU exhibits increased apparent viscosity under shear. The tribological properties of LiTFSI-PU were evaluated under both ambient and elevated temperature conditions. At a load of 200 N and 150 °C, the average coefficient of friction for the 3 wt% LiTFSI-PU formulation was 0.094, which is 32.3% lower than that of the baseline polyurea grease (PU), while the wear volume was reduced by 77.5%. XPS and FIB-STEM/EDS analyses confirmed that LiTFSI-PU forms a multicomponent protective film in situ during friction, which simultaneously shields the substrate and provides lubrication. The additive strategy proposed in this work offers novel insights for the development of high-performance lubricants suitable for extreme thermomechanical conditions. Full article

In this study, a green lubricating grease was prepared based on cellulose and epoxidized soybean oil (ESO). The cellulose extracted from the corn stover was functionalized using diphenylmethane diisocyanate (MDI), which enhances its compatibility and thickening ability in non-polar oil, and subsequently dispersed in ESO to form a stable gel-like bio-based grease. The functionalized surface of cellulose was characterized by FTIR, SEM, and XRD. And the rheological and tribological characteristics of the prepared bio-based grease were discussed. The superior lubricity and anti-wear properties of our bio-based grease are demonstrated by its lower friction and diminished wear relative to commercial lithium-based formulations. This work provides practical guidance for designing environmentally friendly grease for sustainable lubrication. Full article

(1) Background: Developing fully bio-based lubricating greases requires eco-friendly alternatives to conventional harmful components. This study highlights unmodified nanocellulose as an effective structuring agent in vegetable oils, enabling 100% bio-based formulations. (2) Methods: Three bio-based greases were formulated using 1.4 wt.% cellulose nanofibers (CNFs), derived from elm wood pulp through mechanical and chemical pretreatment, as thickening agents in castor oil. Their tribological performance was evaluated under varying temperatures and contact loads and compared to a reference lithium-based grease (LBG) containing 14 wt.% thickener, also formulated with castor oil. (3) Results: Among the CNFs, the unbleached variant (CNF-U) which retained the highest lignin content exhibited the highest coefficient of friction (COF), ranging from 0.09 to 0.14 across test conditions, along with a wear scar diameter of approximately 615 µm at 60 °C. Notable differences in shear stress sensitivity were observed between mechanically and chemically treated nanofibers. The TEMPO-oxidized nanofiber (CNF-TO) grease demonstrated outstanding lubrication stability across contact loads of 10–40 N and temperatures from 25 to 100 °C, maintaining COF values below 0.1—comparable to the reference LBG at 40 N load. Wear scar analysis confirmed that CNF-based greases significantly reduced wear relative to the lithium reference: CNF-B produced the smallest scar diameter (188 µm at 25 °C) while CNF-TO yielded the lowest at 60 °C (457 µm). (4) Conclusions: Nanofiber type and pretreatment significantly impact the tribological performance of CNF-based biogreases. TEMPO-oxidized CNFs provided stable lubrication under varied loads and temperatures, while all CNFs showed strong thermal adaptability, supporting their use in sustainable lubrication. Full article

Rolling Bearings are crucial components for induction motors and generators in electric vehicles (EVs), as their performance considerably influences the system’s operational reliability and safety. However, the commercial greases used for bearing lubrication in EV motors pose a detrimental impact on the environment. In addition, they are ineffective in mitigating the effect of electric discharges on rolling surfaces leading to premature bearing failures. This study investigates the viability of a developed eco-friendly grease from palm olein as the base oil and glycerol monostearate as the thickener, enhanced with conductive multi-walled carbon nanotubes (MWCNTs) for EV motor bearings prone to electrical currents. Chemical–physical, tribological, and electrical tests were conducted on the developed grease samples without and with MWCNTs at 1 wt.%, 2 wt.%. and 3 wt.% concentrations and results were compared to lithium and sodium greases. Palm grease samples demonstrated a lower EDM voltage range reaching 1.0–2.2 V in case of 3 wt.% MWCNTs blends, indicating better electrical conductivity and protecting the bearing surfaces from electric-related faults. These findings were further confirmed using vibrations measurement and SEM-EDX analysis of the electrically worn bearings. Bearings lubricated with palm grease blends exhibited lower vibration levels. Palm grease with 2 wt.% MWCNTs reduced vibration amplitudes by 28.4% (vertical) and 32.3% (horizontal). Analysis of bearing damaged surfaces revealed enhanced damaged surface morphology for MWCNT-enhanced palm grease as compared to surface lubricated by commercial greases. The results of this work indicate that the proposed bio-grease is a promising candidate for future application in the field of next-generation electric mobility systems. Full article

Deep groove ball bearings are important mechanical elements in the automotive and process industries, particularly in electric motors. One of the primary reasons for their failure is lubricant degradation due to stray shaft current. Thus, the present work exhibited the failure of bearings under simulated lubricated conditions similar to those of real time bearings failing in presence of stray electric current. The test was conducted using a full bearing test rig with an applied radial load, 496 N, an alternating current, 10 A, and a rotation of 2000 rpm for 24 h. The bearings (6206 series) were greased using two commercially available ester-polyalphaolefin oil-based greases with viscosity 46–54 cSt (Grease 1) and 32–35 cSt (Grease 2, also contained aromatic oil). The optical microscopic images of the bearing raceways after the tribo test indicated the superior performance of Grease 1 compared to Grease 2, with lesser formation of white etching areas, micro-pitting, spot welds, and fluting on the surfaces of the bearings. Additionally, 80% less vibrations were recorded during the test with Grease 1, indicating a stable lubricating film of Grease 1 during the test as compared to Grease 2. Furthermore, a higher extent of Grease 2 degradation during the tribo test was also confirmed using Fourier transform infrared spectroscopy. Statistical analysis (t-test) indicated the significant variation of the vibrations produced during the test with electrified conditions. The present work indicated that the composition of the greases plays a significant role in controlling the bearing failures. Full article

This study investigates the influence of hexagonal boron nitride (h-BN) particle size and concentration on the tribological performance of lithium and calcium greases. Formulations containing h-BN nanoparticles and microparticles at 1%, 3%, 5%, and 10% by weight were evaluated in ball-on-flat reciprocating tests under three load conditions. The tests were conducted using a steel ball and a steel plate. The most favorable results were obtained for greases with 3% h-BN, characterized by an average particle size of 130 nm and the highest nanoparticle content. In lithium grease, this formulation reduced friction by up to 9.7% and wear by up to 69.2% compared to the base grease. In calcium grease, the same additive concentration led to reductions of up to 18.2% in friction and 70.2% in wear. Tribological performance was significantly influenced by the type of base grease, which affected the dispersion of the additive and its ability to form protective surface layers. SEM/EDS analysis of the surfaces after testing revealed that the dominant lubrication mechanisms included shearing-sliding and surface-mending effects. This study confirms that h-BN—especially in nanoparticle form—is an effective additive for improving the performance of greases. Full article

Lithium is a strategic resource due to its use in rechargeable batteries for electric vehicles and electronic devices, driving high demand for extraction. This study analyzes the lithium supply chain in Mexico, focusing on both the extraction of lithium carbonate for export and the potential for producing lithium–ion batteries and lithium grease, considering their environmental impact. The proposed mixed integer linear programming (MILP) model, solved using the GAMS modeling environment, suggests that lithium extraction in Mexico is viable, with Sonora having the greatest extraction capacity. Three solutions were evaluated: Solution A maximizes profits (USD 317.19 M) but has high greenhouse gas (GHG) emissions (1,119,808 tons), Solution B balances profits (USD 186.98 M) with lower emissions (559,904 tons), and Solution C prioritizes emission reduction (44,792 tons) at the cost of lower profits (USD 48.20 M). Solution C implies a scenario with severe environmental restrictions, which indirectly leads to lower investment costs by avoiding the production of lithium grease and batteries. This study highlights the potential impact of tariffs on U.S. lithium exports, with a 25% tariff making exports economically unviable. This underscores the need for Mexico to diversify its export markets. Decision-makers can use this model to explore alternative strategies, reduce dependence on a single market, and optimize the economic and environmental sustainability of the lithium sector. 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

This study investigates the effectiveness of micron- and nano-sized molybdenum disulfide (MoS₂) particles as additives in lithium (Li) grease under electrified conditions. By systematically applying electric current and high temperatures as experimental parameters, we evaluated the frictional and wear performance of the grease formulations. Our results showed that micron MoS₂ (M-MoS₂) particles outperform their nano counterparts in reducing friction in the range of room temperature to 40 °C. Meanwhile, at 80 °C, nano-sized MoS₂ (N-MoS₂) particles provide better surface protection. The superior performance of M-MoS₂ is attributed to their particle size, which improves the ability to form a more stable and robust lubricating film under the given electrical conditions. In terms of wear, both MoS₂-added greases showed substantial improvements, with a 93% reduction in wear at 40 °C and an 85% at 80 °C under an applied 3 A current. Surface characterization revealed that M-MoS₂ resulted in a smoother surface with less severe pitting and melted pools compared to the base grease. EDX analysis showed the existence of oxygen, molybdenum, and sulfur in M-MoS₂, indicating the presence and stability of MoS₂ on the wear track. These findings suggest that MoS₂ additives have great potential for improving the efficiency and durability of lubricants in electrically and thermally demanding applications. Full article

The electrified environments encountered in electric vehicles (EVs) in terms of parasitic currents present significant challenges for the performance of EV bearings and their lubricants. This study investigates the effectiveness of various concentrations (0.1 wt.%, 0.2 wt.%, 0.3 wt.%, and 0.4 wt.%) of multi-walled carbon nanotubes (MWCNT) and alumina (Al₂O₃) as two different nanoparticles incorporated into lithium grease, specifically focusing on their ability to mitigate the bearing surface damage caused by varying magnitudes of bearing DC discharges. A specialized test rig was developed to evaluate the electrical discharge characteristics, vibration response, and extent of surface wear on bearings lubricated with both lithium grease without additives and when infused with each nano-additive. Microscopic examination was employed to qualitatively and quantitatively evaluate the surface degradation of each test bearing. The results of this study demonstrate that the addition of nano-additives into the lubricating grease of bearings subjected to electrical loads resulted in a reduction in electric discharge voltage thresholds and levels. This reflected on the mitigation of surface damage in terms of surface roughness and vibration amplitudes by up to 70.67% and 65.19% in the case of MWCNTs. In contrast, alumina nanoparticles yielded a reduction in vibration amplitude and surface wear by 44.89% and 37.5%, respectively. Full article

This study synthesized a nanocomposite composed of silver nanoparticles and boron nitride (Ag/BN nanocomposite) by depositing Ag nanoparticles on BN surfaces. The chemical composition, structure, micromorphology, and tribological properties of the Ag/BN nanocomposite were investigated using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and a high-speed reciprocating tribometer. Under a 10 N load, 30 min test duration, 50 mm/s sliding speed, and 2 wt% additive concentration, lithium-based grease (LBG) containing Ag/BN nanocomposite exhibited the lowest average friction coefficient of 0.33 and a wear rate of 1.08 × 10⁻¹⁴ m³/(N × m), representing reductions of 35.2% and 41.6%, respectively, compared to pure LBG. A further analysis of the friction mechanism was conducted using 3D laser scanning microscopy, scanning electron microscopy (SEM), and XPS. The results indicate that the Ag/BN nanocomposite effectively reduced friction and wear on the friction pair surfaces through repair mechanisms, the formation of lubricating films, and micro-bearing effects. Full article