Liquid Lubricants Research Articles

Tribological Behavior of Titanium Alloys during Friction against Ceramics

The article considers the issues of tribological properties of a titanium alloy when sliding without lubrication on zirconium ceramics. The coefficients of friction and wear resistance of friction pairs are investigated in relation to conditions in which it is impossible to use liquid lubricants. The statement about the possibility of normal operation of a pair of titanium - zirconium ceramics at a temperature of 150 ° C and more is substantiated. It is shown that the working capacity of a friction pair can be ensured by alphanizing the friction surface. Taking into account that titanium alloys are widely used in aircraft engine technology, special attention is paid to the coefficient of friction, because a high value can lead to failure of the friction unit. On the basis of the study, the application perspectiveness of zirconium ceramic materials for increasing the reliability and service life of friction units operating without lubrication at elevated temperatures in contact with a titanium alloy have been established.ds.

Ferromagnetic Lubricants in a Bearing with a Porous Coating of a Base Ring

Based on the flow equation of the ferromagnetic liquid lubricant for the “thin layer”, the continuity equation and the Darcy equation describing the flow of a lubricant in a porous body, the paper presents an accurate self-similar solution of the V-shaped sliding support with a porous coating of the base ring surface taking into account the rheological properties of the lubricant with ferromagnetic properties when the working gap is partially filled at the laminar flow mode. Analytical dependencies were obtained for the field of velocities and pressures in lubricating and porous layers. Besides, the main working characteristics of the studied friction pair are determined: bearing capacity and friction force. The paper provides the assessment of the influence of parameters characterizing ferromagnetic rheological properties, length of the loaded region of the Hartmann number and parameter characterizing the presence of electromagnetic field on the bearing capacity and friction force.

The Design and Evaluation of a High-Speed Jet Dispenser Driven by Single Piezoelectric Stack.

Droplet injection methods are widely used in the applications of microelectronic manufacturing, biological engineering, and 3-D printing. This work presents a new jet dispenser driven by a single piezoelectric stack that enables the capability of drop-on-demand patterning under a high working frequency (500 Hz). Due to the special designs of the jet dispenser, a broad range of liquids, whose viscosities span more than four orders of magnitude (21-665 320 cps), can be jetted. Moreover, a coupled Coulomb damping physical model is proposed, which includes an electromechanical and a dynamic model. Both the Coulomb and the fluid-solid damping are considered in the dynamic model. In order to validate the results obtained by using MATLAB/Simulink, the experiments were carried out. The injection performance of this jet dispenser has been tested by employing a self-made jetting platform. The minimum volume of a jetting droplet is about 14.4 nL with liquid wax. The error of volume uniformity among droplets does not exceed 8%, and the error of angle trajectory is about 0.17°. Furthermore, the versatility of the jet dispenser is demonstrated by printing liquid lubricant, food, glue, silver past, and a ceramic slurry in predefined patterns.

Bioinspired Fatty Acid Amide-Based Slippery Oleogels for Shear-Stable Lubrication.

Liquid‐repellent technology is an efficient means of energy‐saving and biofouling avoidance. However, liquid‐repellent surfaces suffer from inefficient lubricant retention under shear flow and fouling problem in marine environment. Here, the authors demonstrate a fatty acid amide (FAA)‐based oleogel for stable and sustainable lubrication in marine environment. The lubrication management of marine creatures is emulated in synthetic oleogels by incorporating solid (FAA) and liquid lubricants into the molecular meshes of polymeric networks, with the nature‐derived solid lubricant providing multifunctional synergistic effects with liquid oil molecules for slippery property and remarkable anti‐biofouling. The lubricant‐confining gel achieves shear‐stable lubricity with efficient oil management. The oleogel provides continued lubrication without biofouling for approximately 4 months in marine field tests. The gel design provides a new paradigm for sustainable and shear‐stable lubrication in marine environment.

Hydrodynamic effect of technological lubrication and friction modes formation at sheet rolling

One of the main engineering industries is the processing of metals by pressure. Its purpose is the formation of products from metal blanks of simple forms. An important role in this case belongs to the technology of sheet rolling. The solution of issues related to the choice of optimal modes of sheet rolling is relevant for specialists in the field under consideration. The process of rolling metal products is special, since the contact stresses can exceed the deformation resistance of rolled metal by several times. The tasks of predicting the quality of products, taking into account the prevention of sheet metal continuity defects, as well as the study of technological operations reliability of rolling process are associated with the solution of industrial and scientific problems in this area. Domestic and foreign researchers have noted a significant influence of external friction in the deformation center on the technological parameters of rolling process and quality of the resulting metal products. It is known that rolling is impossible without external friction between metal and roll. The reduction of friction provides an opportunity to increase the economic indicators of sheet rolling, and the rolling production technology itself has significant opportunities for further improvement. Technology of sheet rolling in the conditions of hydrodynamic friction mode allows modeling of friction conditions in the deformation zone. Taking into account the hydrodynamic effect of lubrication allows us to assess the influence of technological factors on the conditions of contact friction during metal pressure treatment and to control the rolling process. Regularities of the flow of liquid Newtonian lubricant are investigated, taking into account features of the deformation zone geometry during sheet rolling. Pumping capacity of the lubricating wedge during rolling is determined, which allows us to explain the regularities of lubrication influence on friction conditions. As an example, the results of calculation of the lubricant pressure depending on the rolling speed are presented. The rolling speeds that provide a liquid friction mode are given. The obtained relations allow us to estimate the influence of contact friction on technological parameters of sheet rolling and can be used in technological calculations of this process

Gas–Liquid Slug Flow Studies in Microreactors: Effect of Nanoparticle Addition on Flow Pattern and Pressure Drop

Colloidal suspensions of nanoparticles (e.g., metals and oxides) have been considered as a promising working fluid in microreactors for achieving significant process intensification. Existing examples include their uses in microflow as catalysts for enhancing the reaction efficiency, or as additives to mix with the base fluid (i.e., to form the so-called nanofluids) for heat/mass transfer intensification. Thus, hydrodynamic characterization of such suspension flow in microreactors is of high importance for a rational design and operation of the system. In this work, experiments have been conducted to investigate the flow pattern and pressure drop characteristics under slug flow between N2 gas and colloidal suspensions in the presence of TiO2 or Al2O3 nanoparticles through polytetrafluoroethylene (PTFE) capillary microreactors. The base fluid consisted of water or its mixture with ethylene glycol. The slug flow pattern with nanoparticle addition was characterized by the presence of a lubricating liquid film around N2 bubbles, in contrast to the absence of liquid film in the case of N2-water slug flow. This shows that the addition of nanoparticles has changed the wall wetting property to be more hydrophilic. Furthermore, the measured pressure drop under N2-nanoparticle suspension slug flow is well described by the model of Kreutzer et al. (AIChE J 51(9):2428–2440, 2005) at the mixture Reynolds numbers ca. above 100 and is better predicted by the model of Warnier et al. (Microfluidics and Nanofluidics 8(1):33–45, 2010) at lower Reynolds numbers given a better consideration of the effect of film thickness and bubble velocity under such conditions in the latter model. Therefore, the employed nanoparticle suspension can be considered as a stable and pseudo single phase with proper fluid properties (e.g., viscosity and density) when it comes to the pressure drop estimation.

The effect of temperature on water desorption and oxide formation in MoS2 coatings and its impact on tribological properties

Molybdenum disulfide (MoS2) is used extensively in aerospace applications, where liquid lubricants are not suitable. MoS2 has excellent tribological properties in vacuum, however, further research is required to fully understand the mechanisms taking place when exposed to varying temperatures in ambient atmosphere due to storage and on-ground testing. MoS2 coatings were deposited on AISI 440C steel substrates, friction and wear tests were conducted at increasing temperatures, up to 75 °C, determining the effect of temperature on wear mechanisms in air. It was found that the detected surface oxides do not impact tribological properties in MoS2 at temperatures around 75 °C. The water molecules at room temperature hinder the alignment of MoS2 layers leaving some active edge sites exposed to contacting surfaces, leading to high friction and wear. Desorption of water molecules promote parallel alignment of layers, reducing shear strength, friction and wear.

Design of Robust Lubricant-Infused Surfaces for Anti-Corrosion.

A lubricant-infused surface such as an oil-impregnated porous surface has great potentials for various applications due to its omniphobicity. However, the drainage and depletion of the lubricant liquid oil remain practical concerns for real applications. Here, we investigate the effect of a specially designed bottle-shaped nanopore of anodic aluminum oxide, which has a smaller pore diameter in the upper region than the lower one, on the oil retentivity and anti-corrosion efficacy. The effects of the viscosity and volatility of the lubricant oil were further investigated for synergy. Results show that the bottle-shaped pore helps to stably immobilize the lubricant oil in the nanostructure and significantly enhances the robustness and anti-corrosion efficacy, compared to the conventional cylindrical pores with straight walls as well as the hybrid one featured with additional pillar structures. Moreover, the enlarged oil capacity in the bottle-shaped pore allows the oil to cover the underlying metallic surface effectively at cracks, enhancing the damage tolerance with a unique self-healing capability. The oil with a higher viscosity further enhances the benefits so that the bottle-shaped pore impregnated with a higher-viscosity oil shows greater anti-corrosion efficacy. It suggests that the combination of the geometric features of nanopores and the fluid properties of lubricant liquid can lead to a maximized longevity and anti-corrosion efficacy of the liquid-infused surfaces for real applications.

Investigation of material strength and oil compressibility on the hydrostatic pressure build-up in metal forming lubricants

Friction in sheet metal forming is largely governed by the flattening of surface asperities. Liquid lubricants can reduce flattening and friction by filling the surface valleys and carry a substantial amount of the pressure. Experimental and numerical work is presented for investigating the influence of the compressibility of the lubricant and the material strength on the deformation of a simple cylinder with an enlarged surface pocket filled with oil. Results show that deformation is not sensitive to differences in compressibility of typical lubrication oils under hydrostatic pressure conditions. This was observed independent of the material strength.

Simultaneous effect of CaF2 and TiC on tribological properties of ZTA ceramics for high temperature application

Liquid lubrication poses risk to environment; it can vaporize under high temperature or vacuum. Solid lubricant has the potential to replace liquid lubricants due to better stability at severe working environment. This work has been focused to improve tribological properties of zirconia toughened alumina (ZTA) by adding an optimized 4 wt% of CaF2 as a solid lubricant. Since CaF2 is softer material it degrades the mechanical properties of ZTA. To make a balance between the mechanical and the tribological properties, a comparatively harder material TiC is added simultaneously by 10 wt%. All the ceramic composites have been consolidated by hot press sintering at 1500 °C with 30 mins holding time under uni-axial pressing of 50 MPa. Four samples: ZTA, ZTA_CaF2, ZTA_TiC and ZTA_TiC_CaF2 were prepared through the same route. The relative density of the sample (ZTA_CaF2_TiC) achieved was 96.4%. The hardness and fracture toughness has been measured as ∼15GPa and ∼5 MPa m1/2 respectively for the hybrid ceramic composite which is better than ZTA_CaF2 ceramic composite. The tribological characteristics have been evaluated using high temperature tribo-meter with a ball on disc arrangement at 600 °C in vacuum condition. The COF of the ZTA_CaF2 has also been improved by ̴ 39 % compared to the main composite due to the self-lubricating film formation on wear track. A considerable improvement as ∼24.5% in coefficient of friction (COF) and ∼40% in specific wear rate has been found in hybrid ceramic composite as compared to the ZTA ceramic. Thus, it can be used for developing self-lubricating components used in high temperature application.

Ultrahigh Performance Triboelectric Nanogenerator Enabled by Charge Transmission in Interfacial Lubrication and Potential Decentralization Design.

Triboelectric nanogenerator (TENG) is a promising strategy for harvesting low frequency mechanical energy. However, the bottlenecks of limited electric output by air/dielectric breakdown and poor durability by material abrasion seriously restrict its further improvement. Herein, we propose a liquid lubrication promoted sliding mode TENG to address both issues. Liquid lubrication greatly reduces interface material abrasion, and its high breakdown strength and charge transmission effect further enhance device charge density. Besides, the potential decentralization design by the voltage balance bar effectively suppresses the dielectric breakdown. In this way, the average power density up to 87.26 W·m−2·Hz−1, energy conversion efficiency of 48%, and retention output of 90% after 500,000 operation cycles are achieved, which is the highest average power density and durability currently. Finally, a cell phone is charged to turn on by a palm-sized TENG device at 2 Hz within 25 s. This work has a significance for the commercialization of TENG-based self-powered systems.

Solid lubricant materials for high temperature application: A review

Understanding the nature of the frictional behaviour of sliding contacts at high temperatures is of fundamental importance, which ultimately leads to material loss. Modern applications require proper lubrication to improve the life of the components used in extreme environment. Liquid lubricants in contacting surfaces are still in wide use, but the same has a constraint to work in extreme conditions i.e. in high temperature environment. So, currently, worldwide research is going on towards development of innovative solid lubricants for use in various such conditions. In current context, the review article provides a brief overview of current research in this area. This article concentrates on four different types of solid lubricants mostly used in high temperature tribological application on the basis of their crystal structures and compositions viz. Layered Structure Solid Lubricants, Soft Metals Solid Lubricants, Oxides Solid Lubricants and Fluorides Solid Lubricants. The review highlights the operating range of these solid lubricants and limitations of their usage. The application of those solid lubricants as coating (such as, monolithic, multiphase and self-adaptive coating) or composite (such as metallic, intermetallic and ceramic matrix) has also been discussed. This review will make a path way for researchers towards further application specific development of the solid-lubricating materials and their future evolution.

Effect of Electric Field on Friction Properties in Eco-friendly Lubricants

In the future, eco-friendly type and circular type machines are expected to appear and play an active role in our daily lives. These machines will require unconventional design guidelines. One example is the use of biodegradable liquid lubricants. On the other side, in recent years, active friction control methods have been actively developed. One example is the use of external electric fields. In this study, a new friction control method was developed by combining biodegradable liquid lubricants, and the application of an external electric field. We used propylene glycol as a liquid lubricant and conducted friction tests between SUJ2 balls and acrylic resin while applying an electric field. As a result, it was observed that the external electric field lowered the friction coefficient during sliding. In addition, as a result of changing the pH of the liquid, it was observed that the friction reduction effect during the application of an electric field increased as the pH was reduced and the liquid became more acidic.

Environmental Impacts of Geomaterials Exploitation in the Republic of Congo

Geomaterials are extracted everywhere in Congo, generally without environmental and social impact studies. The objective of this study was to assess their exploitation and the associated environmental consequences. Data were collected through interviews and field surveys. A total of 163 quarry sites (17% industrial and 83% artisanal) were studied, with an annual production of nearly 52 million tons. The activity is carried out either in the open air or in water. Three types of materials are exploited: soft (65%), hard (35%) and smooth (0.1%). The activity is mainly centered around urban agglomerations, and sand and gravel are the most prized geomaterials, regardless of the type of exploitation. The geomaterials exploited come either from primary rocks (granite and quartzite) or from the products of their dismantling (accumulations of gravel, sandstone, recent sands or laterites). The various mining processes use, from extraction to finishing, incoming flows in the form of consumable materials (oils, greases, tires, etc.), in the form of energy (fuel, electricity, etc.), and in the form of water, in the form of energy (hydrocarbons, engines or explosives), water and outflows in the form of solid (abandoned gravel heaps), atmospheric (dust, gas, vapors) and liquid (lubricants, fuels, water for washing materials) discharges that induce various pollutions that affect all the compartments of the environment (physical environment, biodiversity, health and human well-being). The impacts of artisanal mining are mostly medium and minor, with only 18% of major impacts, in contrast to industrial mining, which generates 55% of major impacts and appears to be the most degrading for the environment. Despite of the legislative and regulatory texts, the exploitation sites are abandoned without any rehabilitation, which impacts the environment for a long time. To impulse a sustainable management of the activity, proposals have been made.

Measurements of viscosity profile in elastohydrodynamic lubrication film using fluorescence method under various contact pressure conditions

This paper describes rheological properties of hydrodynamic and elastohydrodynamic lubrication (EHL) film under various contact pressure conditions using the fluorescence measurement method. In this measurement method, the viscosity and the information about the state of the lubricant (liquid or solid) can be obtained via the analysis of fluorescence spectrum of a pyrene excimer emission. Previous research revealed that the intensity of excimer emission decreased with increasing of viscosity. In addition, the intensity ratio between the excimer peak and lubricant 5P4E fluorescence peak was introduced for the analysis, and the ratio decreased with increasing viscosity of lubricant. In this study, the viscosity profile obtained from the relationship between the intensity ratio and viscosity showed that the state of lubricant in the lubrication film corresponded almost exactly to the lubrication regime proposed in previous researches. It is concluded that the viscosity measurement technique proposed in this study is useful method for practical uses in hydrodynamic and elastohydrodynamic conditions, while in the high viscosity range, the measured viscosity varies widely due to the variation of intensity ratio.

Hybrid method of stainless steel machining by Ti-Al-N coated tool in electrical discharge ionised gas

This work proposes a hybrid machining method of stainless steel cutting using a carbide tool coated with a multilayer coating in an activated gas medium. The multilayer coating is based on the TiCN+Al2O3+TiN coating. No lubrication is applied during the machining process when the activated gas medium is used. The new method can be used for machining hard-to-cut materials. It compensates for the effects of commonly used hydrocarbon oil-based lubrication by the activated gas medium. This novel method is compared with normal lubricated cutting and with dry machining. In this work, the gas medium is compressed air ionized by a series of discharges. It is shown that the activated gas medium is penetrating more into the cutting zone than liquid coolants. This medium has a strong influence on the interaction processes between the cutting tool and the machined material, which is very noticeable when machining parts made of heat-resistant materials. The technology helps to increase tool life up to 50% in a wide range of cutting parameters. It is seen that tool lifetime is increased significantly in the investigated range of cutting speed from 40 m/min to 100 m/min. The improvement is caused by a reduction of friction in the cutting zone. The friction is reduced by the formation of thin anti-friction films, such as AlN, Al2O3 on both tool and workpiece surfaces. The friction coefficient is reduced from 0.5...0.6 to 0.15...0.2. In addition, the absence of liquid lubricants results in a more environmentally friendly and energy-efficient cutting process.

Compositionally Driven Viscometric Behaviors of Poly (Alkyl Methacrylates) in Lubricating Oils

Viscosity index (VI) and shear stability index (SSI) are standard methods used in the lubricant industry to determine temperature-viscosity dependency and resistance to product degradation, respectively. A variety of oil-soluble polymers, including poly(alkyl methacrylates) (PAMAs) are routinely used to control these properties in fully-formulated liquid lubricants. In this report, we use reversible addition-fragmentation chain transfer (RAFT) polymerization to precisely target identical degrees of polymerization in a family of PAMAs with varying lauryl, hexyl, butyl, ethyl, and methyl groups. Then, expanding on previous methodology reported in the literature, we establish structure property relationships for these PAMAs, specifically looking at how intrinsic viscosity [η] and Martin interaction parameters KM relate to VI and SSI characteristics. While the intrinsic viscosity [η] is associated with the volume of macromolecules at infinite dilution, the parameter KM reflects the hydrodynamic interactions of polymer chains at actual polymer concentrations in lubricating oils. In this paper, we show that the dependence of VI on the non-dimensional concentration c/c* (or c[η]) can be presented in a form of master curve with shift factors proportional to KM that decreases with increasing size of alkyl groups. This finding implies that even in the dilute regime, the coil-expansion theory used to explain the effect of macromolecules on VI should be complemented with the idea of hydrodynamic interactions between polymer molecules that can be controlled by the choice of alkyl chains in the family of PAMAs.

Анализ вибраций опор качения механизмов машин

The article analyzes the vibrations of rolling bearings and their influence on the operation of bearings. An increase in the speed of operation and a boost in power and forces cause an increase in the intensity of vibration fields. The impact of vibrations leads to a change in the characteristics of the contacting surfaces, an increase in friction at the joints and heating of the conjugations. The article describes the factors disturbing vibrations in the joints of machine parts. Ways to reduce vibrations are formulated, including as a result of the use of various lubricants. The analysis of the operability of the rolling bearings of the machine components before and after the use of repair and recovery compounds in lubricants is carried out. The use of repair and restoration compounds based on mineral additives and its addition to the lubricant makes it possible to evaluate the effectiveness of repair and restoration compounds on the processes of friction and wear in rolling bearings. The use of liquid lubricants with mineral additives with a particle dispersion of up to 10 microns during lubrication makes it possible to reduce the noise level and significantly reduce the vibration level in the rolling bearings of machine mechanisms.

Probing the Tribochemical Impact on Wear Rate Dynamics of Hydrogenated Amorphous Carbon via Raman-Based Profilometry.

Solid-liquid lubricating systems have received significant attention as a promising way for energy saving and emission control. For deeply understanding their tribological behaviors, it is necessary to study interaction mechanisms between solid and liquid lubricants from the tribochemical viewpoint, as tribofilms formed by tribochemical products on contact surfaces critically affect the whole tribological process. Continually or periodically monitoring tribofilm formation and evolution can contribute significantly to clarifying its dominating role in tribological behavior under boundary lubrication. However, detecting tribofilms in situ remains a big challenge for conventional surface analytical approaches, mainly due to their limitations in accessing tribofilms or low signal intensities of thin tribofilms. In this study, highly sensitive Raman-based profilometry with in situ potential has been developed for detecting molybdenum dialkyldithiocarbamate (MoDTC)-derived tribofilms and exploring their effect on a-C:H wear over time. The optical properties of tribochemical products formed on the coating surface in different wear stages could result in extra attenuation of Raman signal intensities in the form of measurement deviations in wear depth. By monitoring the deviations, key information of tribofilm compositions was obtained and a two-stage wear progression mechanism was proposed for the first time to clarify the detrimental effect of MoDTC-derived tribofilms on a-C:H wear by combining detailed structure and composition analyses.

Operational control of the parameters of liquid fuels and lubricants with impurities

The possibilities of operational control of the parameters of liquid fuels and lubricants with impurities using the resonator method of microwave dielectrometry are considered. Preliminary studies of liquid fuels and lubricants (gasolines, diesel fuels, kerosene, oils) showed that the values ​​of the real and imaginary components of the complex dielectric constant of the listed fuels and lubricants are in the operating range of the resonator microwave dielectrometer.
 The high resolution of the microwave resonator method determines the prospects of using this method for analyzing the complex dielectric constant of mixtures of fuels and lubricants with various impurities, including water, alcohols, benzene, etc.
 For a mixture of gasoline with benzene, it was experimentally established that with a small addition of benzene (no more than 15%), an increase in the real component of the complex dielectric constant of the mixture is observed, and with a benzene content exceeding 15%, an increase in both components of the complex dielectric constant of the mixture takes place.
 The process has also been installed, but the NHF dielectrometer has made it possible to identify the transformer in real time due to the presence of water in the amount of 14, 28 and 56 grams per ton of oil. The research results indicate that the microwave dielectrometry method can be considered promising for monitoring the quality of transformer oil both during the filling process and for monitoring its quality during the operation of high-voltage transformers.
 The results of the initial stage of research on alcohol gasolines have not yet revealed the predominant effect of the alcohol additive on the location of the experimental points on the complex plane. This circumstance is most likely due to the fact that alcohol gasolines with a close octane number can have a significantly different chemical composition.