Surface Lubrication Research Articles

High density Fe-based soft magnetic composites with nice magnetic properties prepared by warm compaction

The influences of compacting temperature (Tc), molding pressure (Pm), contents of lubricant (Cl) and binder (Cb) on the compacted density (ρc) and its comprehensive soft magnetic properties for the FeSiCr soft magnetic composites (SMCs) fabricated by warm compaction were systematically studied. Appropriate increase of Tc is beneficial to improve the surface lubrication effect of magnetic powders during the forming process of SMCs, thus giving rise to the increase of ρc and the decrease of porosity fraction for the SMCs. Under this situation, the resistance of domain rotation and domain wall displacement in the SMCs during magnetization process is reduced, which is finally in favor of the improvement of SMCs’s soft magnetic properties. The results of loss separation show that the Ph value plays a dominant role in the variation trend of Pcv value for the FeSiCr-SMCs in the test frequency range of 20–200 KHz, wherein the ratio of Ph/Pcv is large than 81 %. Under the optimized process parameters of Tc= 110 ℃, Pm= 600 MPa, Cl= 1.5 wt. % and Cb = 2.5 wt. %, the ρc of FeSiCr-SMCs increases by 8.14 % to 6.38 kg/m3, and the SMCs exhibit better comprehensive soft magnetic properties compared with those at Tc = 25 ℃. Hereinto, μe increases by 19.89 % to 45.8 @ 100 kHz, Pcv decreases by 26.11 % to 495.8 kW/m3@f= 100 kHz, Bm= 50mT, and μe % reached 85.5 % at H = 8000 A/m. These results indicated that the warm compaction process is one of the effective ways to further promote Fe-based SMCs to meet the development requirements of high-frequency, miniaturization and high-power of electronic equipment.

Sustainable Drag Reduction of Fatty Acid Amide‐Based Oleogel Surface Under High‐Speed Shear Flows

AbstractNepenthes alata‐inspired micro/nano‐textured lubricant‐infused surface (LIS) has shown strong potential in the fields of drag reduction (DR), anti‐biofouling, and self‐cleaning. However, its surface‐slippery property is largely degraded under turbulent shear flow conditions due to the loss of the impregnated oil. This condition inhibits its practical applications to marine vehicles. The mucus‐impregnated tissue systems of marine creatures are primarily based on fatty acid amides (FAAs), such as erucamide or oleamide, which have been commercially utilized as solid‐slip additives. A stable lubricant interface of erucamide‐PDMS composite (EPC) oleogel is formed by cross‐linking erucamide with PDMS gel network prior to infusion of silicon oil. In this study, the surface stability and lubricant retention of EPC are investigated in consideration of DR applications. The fabricated EPC‐oleogel surface exhibits shear stable DR under harsh conditions, such as high pressure, temperature, and shear flow conditions. The surface shows a shear stable DR performance of about 14% even up to a high‐speed flow of 12 ms−1, corresponding to friction Reynolds number (Reτ) of approximately 5000. The superior lubrication stability of FAA‐oleogel at the flow conditions of cruising ships ensures its strong potential for sustainable fuel economy of marine vehicles.

Numerical and Experimental Study of Elastohydrodynamic Grease Lubrication of Surfaces with Longitudinal and Transverse Pattern

The interaction of non-Newtonian grease with patterned surfaces was considered as a promising approach to find an effective method for reducing friction and wear in rolling contacts. Longitudinal and transverse patterns can retain the lubricant in the contact area and prevent it from escaping under high loads. In this paper, a model has been developed for grease elastohydrodynamic lubrication of surfaces with different patterns to estimate the lubrication parameters such as lubricant film thickness, pressure distribution, and viscous friction. Then several experimental tests are rolled out for different loads, velocities, and surface patterns. Because the friction model estimates only viscous friction, a correlation is recommended for considering the friction due to asperity interaction. This relation is based on average lubricant film thickness results which are calculated from the model. The calculated friction and experimental results have a good agreement. According to the experimental tests, transverse, longitudinal, and isotropic pattern had a lower friction coefficient, respectively. While the isotropic viscous friction coefficient estimated by the model is lower than others. Higher loads and lower velocities cause a higher friction coefficient in all surface patterns.

Influence of normal load, electric current and sliding speed on tribological performance of electrical contact interface

The purpose of this study is to investigate the effect of normal load, electric current and sliding speed on tribological performance of electrical contact interface. Sliding electrical contact tests of H65 material are carried out by using a customized ball-on-flat tribometer. Results show that with the increase of normal load, both the friction coefficient and contact voltage drop show a downward trend. Too low or too high load will not cause the generation of friction-induce vibration (FIV). Although increasing the normal load appropriately can improve the wear behavior of the interface, it will intensify wear if the normal load is overly high. Larger electric current will increase the friction coefficient, contact voltage drop and surface temperature, but reduce the contact resistance. A certain value of electric current will cause the generation of FIV. Larger electric current will destroy the surface lubricating film of interface and intensify wear. With the increase of sliding speed, the friction coefficient firstly increases and then decreases, while the contact voltage drop shows the opposite trend. Strong FIV will be generated at a certain value of sliding speed. Larger sliding speed will cause the formation of a dense film layer, which plays a good lubrication effect.

Influence of variable thermal conductivity and diffusion coefficients in the flow of Jeffrey fluid past a lubricated surface with homogeneous-heterogeneous reactions: A finite-difference approximations

The key function of lubricants is to reduce the friction, wear, and heat between the parts that are in contact with each other. The main applications of the lubricants are to control temperature, and reduction in wear and corrosion of the machinery. Keeping in mind the importance of lubrication and its applications in varied machines. The goal of this research is to inspect the heat transmission impact in the magnetohydrodynamic flow of Jeffrey liquid near a stagnation point through a lubricated surface. Lubrication is accomplished by a shear-thinning liquid. The velocity, continuity, and shear stress, amalgamated with power-law fluids, are used to develop interfacial conditions. The exclusivity of the anticipated model is the inclusion of variable thermal conductivity and diffusion coefficients in the existence of homogeneous-heterogeneous reactions. Using the Keller–Box finite-difference approximation approach, the numerical results are accomplished. The outcomes are portrayed and tabulated in the form of diagrams and tables, respectively. It is witnessed that a greater magnetic field affects the fluid flow velocity and the drag force coefficient. Moreover, it is also inferred that the heat transfer rate dwindled for the greater thermal conductivity parameter. Authentication of the presented model is also part of this investigation.

Proper matching of lubricants and modifiers: Another key factor for durable anti-icing performance of lubricated surfaces

Slippery liquid-infused porous surfaces (SLIPSs) with anti-icing properties are challenged by the lubricant loss. Many strategies (such as structure optimization, lubricant improvement) are used to retain the lubricant in the porous structure. However, the matching of modifier and lubricant is rarely studied, which is another key factor for durable anti-icing performance of lubricated surfaces. Herein, proper matching of different lubricants and modifiers were investigated. Perfluoropolyether oil (PFPE) and silicone oil (SO) are chosen as lubricants. Linear alkane (OTS) and fluorinated alkane (FAS) are chosen as modifiers. A series of SLIPSs were prepared by infusing lubricants into unmodified and modified anodized aluminum oxide (AAO) surfaces. The suitable matches (OTS with SO, FAS with PFPE) make the prepared SLIPS have high water mobility and enable high affinity between the lubricant and modified AAO surface. The former contributes to improving the anti-icing performance in the simulated glaze icing test, and the latter is beneficial to improving the durability during the icing/deicing cycles. This work provides useful information to determine the suitable pairs of lubricant-modifier for durable anti-icing lubricated surfaces.

Two – Arm, Randomized, Open Labeled, Comparative, Prospective Clinical Study to Assess the Efficacy of Amalaki Ghrita Aashchyotana versus Hydroxypropyl Methylcellulose Eye Ointment in Dry Eye Syndrome with special reference to Shushkaakshipaka

Background: Increased computer work hours, reduced blinking and effect of light rays and radiation lead to raised number of cases of dry eye. Amalaki Ghrita Aashchyotana can be useful in the management of dry eye. Objectives: to compare the clinical efficacy of Amalaki Ghrita Aashchyotana with Hydroxypropyl Methylcellulose (HPMC) eye ointment as a surface lubricant in dry eye syndrome with special reference to Shushkaakshipaka. Methods: In an open labeled, comparative, randomized, prospective clinical study, 60 patients of Dry eye syndrome were randomly selected randomly and categorized into 2 groups, each comprising 30 patients each. Patients in trial group were given Amalaki Ghrita Aashchyotana while patients in the control group were given local application of HPMC eye ointment for consecutive 90 days. Patients were assessed on various clinical parameters before and after the treatment. The data generated through clinical study was subjected to appropriate statistical tests. Results: On treatment of Amalaki Ghrita Aashchyotana in trial group and HPMC eye ointment in control group for 90 days showed significant difference in all objectives as well as subjective parameters on intra-group comparison. The statistically insignificant inter-group comparison shows that both the treatments were equivalent. No adverse events during or after the completion of study in any of the groups. Conclusion: Amalaki Ghrita Aashchyotana is equally efficient as HPMC eye ointment in Dry eye syndrome and has more advantage over HPMC ointment, as it also can help to improve visual acuity.

Comparison of graphene as an oil additive with conventional automotive additives for the lubrication of steel and DLC-coated surfaces

The present work is focused on comparing the tribological behaviour of graphene platelets and commercially available automotive additive package, combined with glyceryl isostearate (GIS) as a friction modifier. The investigation was performed with steel/steel and DLC/DLC contacts, at 25 °C and 100 °C, in all lubrication regimes and by considering the running-in effect. Under all the investigated conditions the graphene platelets provided the lowest friction in the ML and BL regimes. This is the result of forming graphene-based tribofilms which, unlike for the other tested lubricants, is relatively insensitive to temperature, tribochemical activation and the conditions before or after the running-in. By combined the use of graphene platelets and conventional additives some interactions in their tribological behaviour were also observed.

Droplet detachment force and its relation to Young-Dupre adhesion.

Droplets adhere to surfaces due to their surface tension γ and understanding the vertical force Fd required to detach the droplet is key to many technologies (e.g., inkjet printing, optimal paint formulations). Here, we predicted Fd on different surfaces by numerically solving the Young-Laplace equation. Our numerical results are consistent with previously reported results for a wide range of experimental conditions: droplets subjected to surface vs. body forces with |Fd| ranging from nano- to milli-newtons, droplet radii R ranging from tens of microns to several millimetres, and for various surfaces (micro-/nano-structured superhydrophobic vs. lubricated surfaces). Finally, we derive an analytic solution for Fd on highly hydrophobic surfaces and further show that for receding contact angle θr > 140°, the normalized Fd/πR is equivalent to the Young-Dupre work of adhesion γ(1 + cos θr).

Numerical and experimental investigation of static wetting morphologies of aqueous drops on lubricated slippery surfaces using a quasi-static approach.

The static wetting behavior of drops on surfaces with thin lubricating films is very different compared to solid surfaces. Due to the slow dynamics of the wetting ridge, it is challenging to predict the apparent contact angles of such drops. It is hypothesized that for a sinking drop on a lubricated surface, quasi-static wetting morphology can be numerically computed from the knowledge of interfacial energies, lubricant thickness, and drop volume. In this study, we use Surface Evolver to numerically compute the static wetting morphology for the four-phase system using a quasi-static approach with a sinking time similar to the early-intermediate times, and the results agree well with the corresponding experiments. We find that the apparent contact angles depend significantly on the lubricant thickness and substrate wettability compared to other parameters.

Badania wpływu różnych typów powłok na zużycie elementów pompy wtryskowej

The geometric structure of mating surfaces has a crucial influence on the friction and resulting wear processes. This is particularly important in the case of injection pumps, where ensuring appropriate surface quality and tightness in a long-term operation process is extremely important in order to maintain nominal operating parameters. It is extremely important during variable pump operation conditions, start-up and shutdown, when there is a significant deterioration of cooperative conditions resulting from insufficient lubrication of the mating surfaces. The contact pressures on the mating surfaces are increasing and they are in contact with each, causing significant wear and high movement resistance. The technology of the application of special coatings is used in industrial scenarios for the deposition of thin layers to modify the surface layer in order to improve tribological properties, increase abrasive wear resistance, and improve the visual quality of the surface. The authors compared the current possibilities of the technique (ceramic coatings) with the commonly known methods for strengthening the cooperative surface (phosphating). As part of the work, several potentially applicable types of protective coatings were tested.

IMPROVING METHODS FOR MONITORING BEARING UNITS OF ELECTRIC MOTORS IN REVERSE WATER SUPPLY SYSTEMS OF NUCLEAR POWER PLANTS

Ensuring the reliability and safety of nuclear power plants is an urgent task for the Ukrainian energy industry. Permanent circulation of mineral turbine oil is necessary for lubrication of friction surfaces in bearing units of electric motors of water pumping units in cooling systems. Monitoring its condition can indicate the presence of equipment defects under the influence of various factors. Increasing the reliability of oil-filled equipment of nuclear power plants can be achieved by determining the content of dissolved gases in turbine oils; additives “Ionol”; mechanical impurities with the determination of their type. The content of dissolved gases and additives “Ionol” in turbine oils was determined by gas chromatography methods. For turbine oil and a mixture of “water in turbine oil” the physico-chemical and thermophysical properties were investigated – density; flash point; kinematic viscosity; acid number; the content of mechanical impurities, water, additives “Ionol”. The dependences of the concentrations of dissolved gases in turbine oil and the “water in turbine oil” mixture on temperature, as well as the nature of the effect of acoustic cavitation on the kinematic viscosity of the oil and the generation of dissolved gases, have been studied. The aim of the work is to increase the reliability of power equipment of nuclear power plants by improving the control of the physicochemical and thermophysical properties of mineral turbine oil of the brand “Tp-30” of the circulation system for supplying bearing oils with electric motor units of water pumping units of reverse water supply of nuclear power plants.

Slippery quartz surfaces for anti‐fouling optical windows

AbstractThe surface of camera‐based medical devices is easily smeared by blood and fog during the surgical procedure, causing visual field loss and bringing great distress to both doctors and patients. In this article, a slippery liquid‐infused porous surface (SLIPS) on a quartz window surface that can repel various liquids, especially blood droplets is reported. A femtosecond laser pulse train was used to create periodic microhole structures on the silica surface. The subsequent low surface energy treatment and lubricant infusion led to the successful preparation of a slippery surface. Such blood‐repellent windows exhibited high transparency, great antifogging, and antibacterial properties. In addition, the slippery ability of the as‐prepared surface exhibited outstanding stability since the surface could withstand harsh treatments/environments, such as repeated pipette scratches and immersion in different pH solutions. The as‐prepared millimeter‐sized quartz samples with SLIPS were attached to the endoscope lens as a protective coating and could maintain high visibility after repeated immersion in blood. We believe that the coating developed in this study will provide inspiration for the design of next‐generation endoscopes or other camera‐guided devices that will resist fouling, keep clear vision, and reduce operation time, thus offering great potential applications in lesion diagnosis and therapy.

Macroscale superlubricity induced by film-forming polymer brush-grafted colloidal additives

HypothesisModifying surfaces with concentrated polymer brushes (CPBs) is an effective way to reduce friction of tribo-pairs lubricated with liquids. We investigate the hypothesis that colloids grafted with CPBs (hybrid colloids) can deposit onto tribo-substrates by varying the solvent quality with respect to the polymer, in order to obtain ultra-low coefficients of friction (CoFs), so-called superlubricity. ExperimentsHybrid colloids are synthesized and characterized, and a dynamic light scattering compares their swellings in aqueous solutions of glycerol or polyethylene glycol. A mini-traction machine with viscoelastic tribo-pairs is used for lubrication experiments. Adsorption of colloids and film structures are tested using a quartz crystal microbalance and an atomic force microscope. FindingsThe solvent controls whether hybrid colloids spontaneously adsorb to the substrate under quiescent conditions or require contact forces to enable (tribo-)deposition. In both cases, the friction in the boundary-mixed lubrication regimes is lower upon increasing the degree of swelling of CPBs and upon increasing coverage of deposited colloids. The greatest lubrication enhancement and surface coverage occur for the spontaneously adsorbed colloids, with ultra-low CoFs of order 10-3 over a large range of speeds. The results demonstrate the potential for hybrid colloids to be used as solvent dispersible “friction modifier additives”.

Evaluation of thermal stability of ultra-precision water-lubricated spindle

Minimizing spindle thermal deformation is of key importance for reaching high machining accuracy. In this study, the thermal stability of a spindle with water-lubricated hydrostatic bearings was investigated via simulation with experimental data for defining boundary conditions for the simulations. The simulation study was divided into two separate tasks. In the first stage, the temperature distribution in the water flowing through spindle bearings was determined using commercial FEM flow simulation software. The experimentally obtained temperatures of lubricant and spindle surfaces were used as boundary conditions for a finite volume problem that introduced the temperature distribution of the spindle body and water flowing around the spindle. Then, a thermal analysis of the spindle was performed using the temperature field obtained in the first stage to investigate thermal deformation of the spindle. Temperatures at specific parts of the spindle derived from the temperature distribution were used as boundary conditions for analysis in the second stage. The results were used to investigate the influence of spindle thermal deformation on the positioning accuracy of the end surface of the spindle rotor. The pattern of gap variations in journal and thrust bearings due to the thermal deformation of bearing surfaces was established. The thermal stability of a spindle under the influence of an external temperature field was evaluated using the bearing load capacity and stiffness as indicators. The bearing load capacity and stiffness were defined based on the pressure distribution on the bearing surfaces with consideration of the non-uniformity of the bearing gap due to thermal deformation. A separate study was conducted to investigate the effect of changing viscosity of increasing the temperature of lubricating fluid on bearing performance. Furthermore, the resulting displacement of the spindle rotor end, which directly affects machining error, is also discussed.

Atomization Characteristics of Special-Design Pneumatic Two-Fluid Nozzles for Helicopter Main Reducers: A Numerical and Experimental Investigation

Oil mist lubrication can be utilized as an emergency lubrication system in the main reducer of a helicopter. A special-design pneumatic two-fluid nozzle is the crucial system component for atomizing lubricant oil, so exploring the atomization characteristics of the nozzle has a significance on effectively improving oil mist lubrication performance. A CFD (computational fluid dynamics) model with a DPM (discrete phase model) technique and a specialized atomization test system were set up to both numerically and experimentally investigate the nozzle’s atomization characteristics. For the atomization properties of the nozzle, the impacts of air pressure, gas–liquid pressure ratio, lubricant oil flow rate, and lubricant oil property factors, including viscosity and surface tension, were investigated. Combining the experimental and the numerical findings reveals that an increasing air pressure and gas–liquid pressure ratio contribute to the atomization effect of the nozzle, especially the air pressure. In addition, a higher lubricant oil flow rate is slightly unfavorable for atomization, but a rise in viscosity and surface tension prevents the atomization of the lubrication oil.

Flow of a concentrated emulsion with surfactant through a periodic porous medium

High-resolution, long-time three-dimensional simulations are presented for slow, pressure-driven flow of a periodic emulsion of deformable drops through a dense, simple cubic array of solid spheres (one drop and one particle per periodic cell). The drops, covered with insoluble, non-diffusive surfactant, are large compared with pores, and they squeeze with high resistance, very closely coating the solids to overcome surface tension and lubrication effects. The solid volume fraction is 50 %, the emulsion concentration $c_{em}$ in the pore space is 36 % or 50 %, the drop-to-medium viscosity ratio $\lambda$ is 0.25 to 4. The contamination measure $\beta \leq 0.1$ keeps the linear surfactant model (assumed in most of the work) physically relevant. The boundary-integral solution requires extreme resolutions (tens of thousands of boundary elements per surface) achieved by multipole acceleration with special desingularizations, combined with flow-biased surfactant transport algorithms for numerical stability. The time-periodic regime is typically attained after a few squeezing cycles; the motion period is used in the extrapolation scheme to evaluate critical capillary numbers $Ca_{crit}$ demarcating squeezing from trapping. Due to Marangoni stresses, even light ( $\beta =0.05$ ) to moderate ( $\beta =0.1$ ) contaminations significantly reduce the average drop-phase migration velocity (up to 2.8 times, compared with clean drops), especially at small $\lambda =0.25$ . In contrast, $Ca_{crit}$ is weakly sensitive to contamination and levels off completely at $\beta =0.05$ . At $\lambda =0.25$ and $c_{em}=0.36$ , the average drop-phase velocities are much different for lightly and moderately contaminated emulsions, except for near-critical squeezing when they become the same. Nonlinear surfactant models (Langmuir, Frumkin) are used to validate the linear model.

Significance of Buongiorno’s model on viscoelastic MHD flow over a heated lubricated surface subject to Joule heating

Lubrication theory has attained attention lately due to its practical applications, such as the formation of thin films, adhesives, and lubrication of components of machines. Jeffrey’s nanofluid flow over the stagnation region past a power-law lubricated surface is presented in this study. Buongiorno’s model is employed to scrutinize the effects of thermophoresis and Brownian motion phenomena with constant wall and prescribed surface temperature (PST) and effects of heat source/sink, chemical reaction, and Joule heating. Due to the continuity of shear stress of fluid-lubricant and velocity at the interface, interfacial conditions are generated. By similarity conversions, ordinary differential equations are obtained and their solutions are computed numerically. For power-law index equaling [Formula: see text], local similarity solutions are calculated by adopting a finite difference scheme, viz. bvp4c in MATLAB. The energy profiles for constant and prescribed temperatures are monitored. The effects of pertinent parameters on the flow, thermal, and mass distributions are scrutinized and illustrated in graphs. Flow field decreases significantly by raising slip parameter as the aptitude of power-law lubricant to improve the velocity of the bulk fluid. The numerical comparison of wall stress and Nusselt number is also presented. The slip and Jeffrey’s material parameters raise the numerical outcomes of the wall shear stress. In addition, increment in Prandtl number enhances the numerical value of the Nusselt number; however, it reduces for relaxation-to-retardation times ratio.

Full and Hybrid Multiscale Lubrication Modeling

The numerical solution for the lubrication of parallel rough surfaces cannot be obtained using the well-known flow factors of Patir and Cheng. Nor can it be determined using homogenization techniques. Is there an alternative, besides a purely long-term deterministic way of solving the problem? The present paper aims at proposing a multiscale approach in order to reduce the computing time, specific to deterministic resolutions, while maintaining good accuracy. The configuration is a parallel rough surface slider, with imposed hydrodynamic operating conditions. The domain consists of independent macro-elements, on which the Reynolds equation is solved. Then, the macro-element boundaries are adjusted to ensure global mass conservation. In its hybrid version, the algorithm replaces some well-chosen macro-elements by simple linear finite elements. The results clearly show the potential of our method. Because the lubrication of each macro-element can be processed independently, the multicore architecture of the processor is exploited. Even if the performance depends on the ratio roughness/height, the computing time is half than for the classical deterministic method, with a few percent errors. The work concludes with some recommendations on the configurations for which the multiscale method is best suited, such as surfaces with short correlation lengths.

Roughness and humidity effects on contact, friction, and contact plasticity revealed by micromechanical testing and analysis

Understanding the effects of surface roughness, surface lubrication, and environmental conditions on inter-particle contact mechanics is important for a broad range of applications of granular materials. In this paper, a new micromechanical testing apparatus was developed and used to characterize smooth and rough soda lime glass particles in carefully controlled dry, humid, and lubricated environments during normal compression and shearing. From surface profilometry measurements and digital image correlation, we observed a humidity independent correlation between hysteresis, contact plasticity, and surface roughness in normal compression tests. From analysis of shear test data, we observed an increase in friction with increasing surface roughness, contact hold times, and water lubrication. Our work highlights roughness and environmental effects on contact and friction of silicate materials.