Search Results (229)

This study investigates the influence of the additive illite on the thermal, tribological, and energy efficiency characteristics of calcium grease (CG) at different concentrations (0.05 wt.%, 0.1 wt.%, 0.2 wt.%, 0.4 wt.%, 0.6 wt.%, and 0.8 wt.%). Thermo-gravimetric analysis under inert and oxidative atmospheres revealed that illite enhances thermal stability by increasing inorganic residue under N₂, but promotes oxidative degradation under O₂, limiting practical thermal use to around 400 °C. Grease with 0.1 wt.% illite (CGI2) performed well in tribological tests by reducing the coefficient of friction and wear scar diameter by 53% and 57%, respectively, compared to the base grease. Fleischer’s energy-based wear model showed that all grease samples operated within the mixed friction regime, and CGI2 exhibited a 93% higher apparent frictional energy density and a substantially lower wear intensity that was 47% lower than the base grease, indicating improved energy dissipation and wear resistance. All samples had the same weld load (1568 N), but CGI2 had a 21% higher load–wear index than the base grease in the extreme-pressure test, indicating better load-carrying capacity. In the energy consumption test, a 6% reduction in current consumption was observed in CGI2 in comparison with the base grease. Overall, illite at an optimal concentration significantly enhances lubrication performance, wear protection, and energy efficiency. Full article

Modern power transmission systems are required to meet increasingly stringent demands, including a wide range of transmission ratios, compact dimensions, high precision, energy efficiency, reliability, and thermal stability under dynamic operating conditions. Among the solutions that satisfy these requirements, cycloidal reducers are particularly prominent, with their application continuously expanding in industrial robotics, computer numerical control (CNC) machines, and military and transportation systems, as well as in the satellite industry. However, as with all mechanical power transmissions, friction in the contact zones of load-carrying elements in cycloidal reducers leads to power losses and an increase in operating temperature, which in turn results in a range of adverse effects. These undesirable phenomena strongly depend on lubrication conditions, namely on the type and properties of the applied lubricant. Although manufacturers’ catalogs provide general recommendations for lubricant selection, they do not address the fundamental tribological mechanisms in the most heavily loaded contact pairs. At the same time, the available scientific literature reveals a significant lack of systematic and experimentally validated studies examining the influence of lubricant type on the energetic and thermal performance of cycloidal reducers. To address this identified research gap, this study presents an analytical and experimental investigation of the effects of different lubricant types—primarily greases and mineral oils—on the thermal stability and efficiency of cycloidal reducers. The results demonstrate that grease lubrication provides lower total power losses and a more stable thermal operating regime compared to oil lubrication, while oil film thickness analyses indicate that the most unfavorable lubrication conditions occur in the contact between the eccentric bearing rollers and the outer raceway. These findings provide valuable guidelines for engineers involved in cycloidal reducer design and lubricant selection under specific operating conditions, as well as deeper insight into the lubricant behavior mechanisms within critical contact zones. Full article

Rubber materials undergo continuous wear in high-pressure seal applications. To address the risk of adhesive wear and consequent leakage of rubber seals operating under reciprocating sliding in high-pressure hydrogen storage and refueling systems, this study employed high-pressure hydrogen tribology testing. Ball-on-disk reciprocating tests were conducted using a 316L stainless-steel ball against silica-filled nitrile butadiene rubber (NBR), and the friction response and wear-morphology evolution were compared under ambient air, 1 MPa hydrogen (H₂), 50 MPa H₂, 50 MPa nitrogen (N₂), and grease-coated conditions. Under dry sliding, the coefficient of friction (COF) of NBR in air and hydrogen ranged from 1.34 to 1.44, whereas it decreased markedly to 0.942 in 50 MPa N₂. The wear volume under the four dry conditions was concentrated in the range of ~0.292–0.320 mm³. After grease coating, the steady-state COF in air and at 50 MPa H₂ dropped to 0.099 and 0.105, respectively, and the wear features changed from ridge-like wear patterns/tear pits to regular, smooth indentations with slight running marks. The results demonstrate that a lubricating film can effectively separate direct metal–rubber contact and suppress stick–slip, enabling a low-friction, low-wear, and highly stable interface in high-pressure hydrogen, and providing a practical engineering route for reliable operation of rubber seals in hydrogen service. Full article

Proteins are generally characterized by three-dimensional structures that are well suited for their specific function. It is much less accepted that a particular flexibility or plasticity of a protein is essential for performing its function. The latter plasticity encompasses the stochastic motions of small protein sidechains on the picosecond timescale that serve as “lubricating grease”, allowing slower functionally relevant conformational changes. Some remarkable examples of potential correlations between protein dynamics and function were observed for pigment–protein complexes in photosynthesis. For example, electron transfer and protein plasticity are concurrently suppressed in Photosystem II upon decreases in temperature or hydration, thus suggesting a prominent functional role of protein dynamics. An unusual dynamics–function correlation was observed for the major light-harvesting complex II, where the dynamics of charged protein residues affect the pigment absorption frequencies in photosynthetic light-harvesting. Generally, proteins exhibit a wide variety of motions on multiple time and length scales. However, there is an approach to characterize the plasticity of a protein as a single effective force constant that permits a straightforward comparison between different protein systems. Within this review, we determine the latter effective force constant for three photosynthetic proteins in different functional and organizational states. The force constant values determined appear to be rather different for each protein and are consistent with the requirements imposed by the various functions. These findings highlight the individual character of a protein’s flexibility and the role(s) it is playing for the specific function. Full article

The study systematizes the current state of knowledge on the morphological diversity of dispersed-phase particles in the most widely used lubricating greases, encompassing their shape, size, surface structure, and overall geometry. The extensive discussion of the diversity of grease thickener particles is supplemented with their microscopic images. Particular emphasis is placed on the influence of thickener particle morphology, the degree of their aggregation, and interparticle interactions on the rheological, mechanical, and tribological properties of grease formulations. The paper reviews recent advances in investigations of grease microstructure, with special emphasis on imaging techniques—ranging from dark-field imaging, through scanning electron microscopy, to atomic force microscopy—together with a discussion of their advantages and limitations in the assessment of particle morphology. A significant part of the work is devoted to rheological studies, which enable an indirect evaluation of the structural state of grease by analyzing its response to shear and deformation, thereby allowing inferences to be drawn about the micro- and mesostructure of lubricating greases. The historical development of rheological research on lubricating greases is also presented—from simple flow models, through the introduction of the concepts of viscoelasticity and structural rheology, to modern experimental and modeling approaches—highlighting the close relationships between rheological properties and thickener structure, manufacturing processes, composition, and in-service behavior of lubricating greases, particularly in tribological applications. It is indicated that contemporary studies confirm the feasibility of tailoring the microstructure of grease thickeners to specific lubrication conditions, as their characteristics fundamentally determine the rheological and tribological properties of the entire system. Full article

Sulfonate greases, which have excellent performance characteristics—high dropping point, good mechanical and structural stability, water resistance, high thermal oxidation stability, and good anticorrosive properties—are widely used in various industries. The greases are exposed to water during operation: moisture in the environment, water-based coolants, operation in the presence of water vapor, etc. Water can affect the properties of the greases during operation. The subject of the study was a commercial complex grease thickened with overbased calcium sulfonate, with a water additive in amounts ranging from 1% to 50% by weight. This paper presents two standardized methods for testing the thermal oxidation stability of lubricants—according to ASTM D942 and ASTM D8206, in standard programs, and with an extension of oxidation duration to 100 h and a temperature increase to 100 °C. The aim of the study was to investigate how the addition of water affected the thermal oxidation stability of this grease. The presentation concludes with an analysis of FTIR differential spectra. The tests showed that as the water content in the grease samples increased, its resistance to oxidation decreased. Water also caused a change in the consistency of the grease at a concentration of just 1% by weight. Mechanical stress affected the thermal oxidation stability of the grease tested. Each method presented separate mechanisms of oxidation initiation, including different sample quantities during the test, the presence of water in the classic method, and different contact with oxygen as a catalyst for this reaction. The work provided a comprehensive presentation of the possibilities for testing the thermal oxidation resistance of greases and a detailed comparison of the two methods. Full article

In this work, we produced a new polyurea (PU)-based thickener based on serine derivatives (ethanolamine or L-Serine ethyl ester) and 1,5 pentamethylene diisocyanate (PDI), using castor oil as base oil and methylene diphenyl diisocyanate (MDI) as a reference. Polymerization was carried out in a planetary ball mill at room temperature for 75 min. The polymerization degree of the PU thickener was examined via ¹H NMR, which ranged between 1.8 and 14.6 repeating units after the extraction of the base oil. Rheological analysis showed gel formation for ten out of twelve samples, which was strongly dependent on the polymerization degree and thickener amount. The decomposition temperature of the MDI-based PU greases was consistently roughly 20 °C higher than that of PDI-based systems. The lubricants were further evaluated through rheology experiments before and after the gels underwent an annealing process at 100 °C for 1 h (amplitude and frequency test), indicating a strong increase in the storage modulus G’, whereas the yield point γ_F remained constant or decreased. Full article

Continuous advancements in application technology aimed at higher efficiency and power density place ever-increasing demands on mechanical components and construction elements—and, consequently, on the lubricating greases employed. This is particularly true for rolling bearings, where greases are exposed to high mechanical loads and wide temperature ranges. A current example can be found in the bearings of hybrid vehicle powertrains, which are subjected to extreme thermal and mechanical stress due to engine downsizing, high rotational speeds, and radiant heat from the combustion engine. A collaborative project between the Competence Center for Tribology (KTM) at Mannheim University of Applied Sciences and the OWI Science for Fuels gGmbH (OWI), affiliated with RWTH Aachen University, demonstrated that the loss of lubricating performance—which ultimately leads to bearing failure—is directly linked to changes in the thickener structure. Various degradation processes reduce yield stress and viscosity, thereby eliminating the typical grease characteristics. Mechanical, thermal, oxidative, and catalytic processes all play decisive roles. This paper presents analytical methods that enable these individual influencing factors to be investigated and evaluated independently. These approaches can significantly reduce the need for time-consuming and costly laboratory tests in grease development and qualification. Full article

The temperature rise of drive motor bearings in new energy vehicles is a critical factor affecting their reliability and lifespan, with grease performance and driving conditions being the primary determinants of this rise. Addressing the lack of research on how different grease types affect the temperature rise of drive motor bearings under operational conditions, this study utilizes a high-temperature, high-speed testing machine for drive motor bearings in new energy vehicles. It conducts a comparative analysis of the temperature rise in bearings lubricated with four different types of grease under three typical driving conditions: emergency start–stop, smooth driving, and high-speed driving. Results show that the temperature rise varied from 25.1 °C to 50.3 °C under rapid speed change, 22.7 °C to 40.2 °C at fixed speed, and that grease No.3 achieved the lowest temperature rise and the highest limiting speed (23,000 rpm). These results provide quantitative evidence for selecting grease and optimizing bearing design. Full article

As a key medium in industry, lubricating oil plays a significant role in reducing friction, cooling sealing and transmitting power, which directly affects equipment life and energy efficiency. Traditional mineral-based lubricating oils rely on non-renewable petroleum, and they have high energy consumption and poor biodegradability (<30%) during the production process. They can easily cause lasting pollution after leakage and have a high carbon footprint throughout their life cycle, making it difficult to meet the “double carbon” goal. Bio-based lubricating oil uses renewable resources such as cottonseed oil and waste grease as raw materials. This material offers three significant advantages: sustainable sourcing, environmental friendliness, and adjustable performance. Its biodegradation rate is over 80%, and it reduces carbon emissions by 50–90%. Moreover, we can control its properties through processes like hydrogenation, isomerization, and transesterification to ensure it complies with ISO 6743 and other relevant standards. However, natural oils and fats have regular molecular structure, high freezing point (usually > −10 °C), and easy precipitation of wax crystals at low temperature, which restricts their industrial application. In recent years, a series of modification studies have been carried out around “pour point depression-viscosity preservation”. Catalytic isomerization can reduce the freezing point to −42 °C while maintaining a high viscosity index. Epoxidation–ring-opening modification introduces branched chains or ether bonds, taking into account low-temperature fluidity and oxidation stability. The deep dewaxing-isomerization dewaxing process improves the base oil yield, and the freezing point drops by 30 °C. The synergistic addition of polymer pour point depressant and nanomaterials can further reduce the freezing point by 10–15 °C and improve the cryogenic pumping performance. The life cycle assessment shows that using the “zero crude oil” route of waste oil and green hydrogen, the carbon emission per ton of lubricating oil is only 0.32 t, and the cost gradually approaches the level of imported synthetic esters. In the future, with the help of biorefinery integration, enzyme catalytic modification and AI molecular design, it is expected to realize high-performance, low-cost, near-zero-carbon lubrication solutions and promote the green transformation of industry. Full article

Oil and its derivatives affect marine ecosystems due to pollution. Analytical methods for detecting oils and greases in saline water can identify oil-derived pollutants in seas and oceans, supporting the preservation and recovery of water quality. This study describes a methodology based on Raman spectroscopy to quantify oil in saline water. Specific seriate volumes of synthetic lubricating oil (SLO) and diesel fuel oil (DFO) were added to a beaker containing 1000 mL of saline water. A magnetic stirrer was used to create vortex, where the added oil dispersed uniformly over the surface and created a thin film. Raman spectra of the surface’s film were obtained by a spectrometer (830 nm, 350 mW) at a fixed position with reference to the beaker border, in triplicate. Two spectral models were developed; one based on the intensity of the peak at ~1400–1500 cm⁻¹ and another based on partial least squares regression (PLSR). Both spectral models enabled the quantification of SLO and DFO at concentrations ranging from 25.6 to 307 mg/L, and from 16.8 to 205 mg/L, respectively, with correlation coefficients as high as r = 0.99. The results highlight the potential of using Raman spectroscopy for analyzing oil in environmental water samples. Full article

The cage shape plays a critical role in controlling lubricant distribution and replenishment and enhancing lubrication performance within rolling bearings. This study investigates the effect of four tailored cage shapes on lubricant migration and frictional characteristics at both Ball-Cage (B-C) and Ball-Disc (B-D) contacts. Utilizing a bearing cage friction and lubrication test rig (BCFL), adapted from an optical elastohydrodynamic lubrication (EHL) apparatus, the variation in grease films and friction forces was examined under varying entrainment speeds, grease properties, and grease quantities. Cage-induced lubricant redistribution on the ball surface, replenishment at the B-D contact, and the formation mechanism of thicker film thickness were recognized. The influence of cage design for four distinct shapes on mechanisms enhancing grease lubrication efficiency and friction reduction was examined. The findings provide critical insights for designing next-generation self-aligning cage structures with improved lubrication performance and reduced friction force. Full article

Environmental contamination critically affects the durability and performance of lubricants in machine components. Over long operating periods, particles and water ingress through degraded seals accelerate grease degradation and deteriorate tribological behavior. This study evaluates the effects of SiO₂ particle concentration and water contamination, alone and in combination, on the performance of calcium-based grease in bearing steel contacts. Friction coefficients, grease temperatures, wear, pitting, and vibration signals were analyzed. The results show that an increase in particle concentration raised both friction and temperature, leading to more severe wear and pitting. The addition of 0.6 wt% water reduced fluctuations in friction and temperature, but when combined with high particle concentrations, it significantly worsened wear and pitting. The vibration-based energy ratio correlated strongly with pitting evolution, highlighting its potential as a sensitive parameter for monitoring surface fatigue. These findings provide insights into lubricant degradation under contaminated conditions and offer guidance for improving the reliability of lubricated systems. Full article

The failure behavior of steel wire ropes under heavy load conditions is a complex system involving the interaction of mechanical damage, lubrication status, and detection technology. Despite numerous studies, the existing literature seriously lacks a systematic framework to correlate the structural integrity and deformation behavior of gel-like grease and its central role in suppressing the critical failure modes (wear, fatigue, corrosion) of steel wire ropes. This review aims to fill this critical knowledge gap. By critically synthesizing existing studies, this paper explains for the first time how the microstructural evolution and rheological behavior of gel-like grease can ultimately determine the macroscopic failure process and life of steel wire ropes by influencing the interfacial tribological processes. We further demonstrate, based on the understanding of the above mechanism, how to optimize the detection strategy and design high-performance gel-like greases for specific working conditions. Ultimately, this work not only provides a unified perspective for understanding the system reliability of steel wire ropes but also lays a solid theoretical foundation for the future development of intelligent mechanism-based lubrication and predictive maintenance technologies. 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