Lubricant Volume Research Articles

Tribological Behaviors of Cu/RGO/WS2 Composites in Air and Vacuum Environments

No single lubricant can provide effective lubrication in various environments. In this study, both graphene (RGO) and WS2 were added to the Cu matrix to prepare self-lubricating composites that can adapt to different environments. Three kinds of Cu-based composites containing different volume ratios of lubricants were fabricated by a hot-pressing method. The physical and mechanical properties of the composites were measured. The tribological behaviors of the composites were tested using a ring-on-disc wear tester in air and vacuum environments. Scanning electron microscopy, 3D laser scanning confocal microscopy, and X-ray photoelectron spectroscopy were used to characterize the worn surface of the composites. Monolayer RGO was prepared, and the ID/IG ratio of RGO was 0.85. The fabricated composites were mainly a mechanical mixture of Cu/RGO/WS2. The total volume of lubricant was constant in the composites, and the hardness increased and thermal conductivity decreased with increasing volume ratio of WS2 to RGO. In air, Cu-RGO exhibited the lowest friction coefficient and wear rate, and Cu-WS2 showed the highest. In a vacuum, Cu-WS2 demonstrated the lowest friction coefficient and wear rate, whereas Cu-RGO was worn through. RGO played the lead role in wear reduction and self-lubrication in air, whereas WS2 was dominant in a vacuum. Cu-RGO-WS2 had greater potential applications due to its low sensitivity to different environments.

Thickness of the Ice-Shedding Lubricant Layer in Equilibrium with an Underlying Cross-Linked Polymer Film

A thin lubricant oil layer in equilibrium with an underlying cross-linked polymer film is ideal for ice shedding and smudge repellency. While the oil film renders the desired repellency, the polymer layer bestows the mechanical strength and serves as a reservoir for the lubricant. Despite this knowledge, there have been no theoretical studies on factors that affect the equilibrium thickness hs of the lubricant layer. In this work, we treat the substrate-bound polymer as a rubber film that can only expand or contract along the vertical direction. The Flory–Rehner theory for treating the 1D swelling of a rubber by a solvent is then used to derive the system’s free energy, which is further used to construct the phase diagrams of such systems. From these phase diagrams and the known feed volume ratios between the lubricant and the polymer, we calculate hs and plot hs as a function of the Flory–Huggins parameter for the polymer and the lubricant, the cross-linking density of the polymer, and the molecular volume and amount of lubricant. Aside from using these plots for regulating hs and for justifying prior experimental observations, we also propose methods to tune the different variables to sustain the release of the lubricant until it is essentially exhausted. Additionally, we draw attention to possible measures that can be used to design thermoresponsive ice-shedding coatings that store the lubricant in the polymer matrix during the warm seasons to minimize lubricant loss but release the lubricant during winter to enable ice shedding. While the current theory involves approximations, the predicted trends will be of guidance value for designing and preparing robust and long-lasting ice-shedding coatings.

Effect of Air Bearing Pressure and Slider/Disk Contact on Lubricant Depletion Using Molecular Dynamics Simulation

Slider/disk contact, which will lead to lubricant depletion, is likely to occur due to the nano spacing between slider and disk. To understand the mechanism of lubricant depletion under contact, a molecular dynamics model is developed in this article. The effects of air bearing pressure, the contact force, and the disk velocity on the penetration depth of the slider and the depletion volume of lubricant is studied. The results show that higher contact force and smaller air bearing pressure cause deeper penetration depth, which leads to a larger amount of lubricant depletion. The effect of disk velocity on lubricant depletion can be neglected at a high contact force. In order to effectively reduce lubricant transfer and lubricant depletion, high air bearing pressure should be suggested and slider/disk contact should be avoided.

Model and Experimental Verification of the Dynamic Forced Performance of a Tightly Sealed Squeeze Film Damper Supplied With a Bubbly Mixture

Abstract Practice and experiments with squeeze film dampers (SFDs) sealed with piston rings (PRs) show the lubricant exits through the PR slit, i.e., the gap made by the PR abutted ends when installed, forced as a jet during the portion of a rotor whirl cycle generating a positive squeeze film pressure. In the other portion of a whirl cycle, a subambient dynamic pressure ingests air into the film that mixes with the lubricant to produce a bubbly mixture. To reduce persistent air ingestion, commercial air breathing engines utilizing PRSFDs demand of a sufficiently large lubricant supply pressure (Ps), and hence a larger flow rate that is proportional to the journal squeeze velocity (vs = amplitude r × frequency of motion ω). The stringent requirement clearly limits the applicability and usefulness of SFDs. This paper presents a computational physics model for a sealed-end SFD operating with a mixture and delivers predictions benchmarked against profuse laboratory test data. The model implements a Reynolds equation adapted for a homogeneous bubbly mixture, includes temporal fluid inertia effects, and uses physics-based inlet and outlet lubricant conditions through feed holes and PR slit, respectively. In the experiments for model validation, a SFD damper, 127 mm in diameter D, film land length L = 25.4 mm (L/D = 0.2), and radial clearance c = 0.371 mm, is supplied with an air in ISO VG2 oil bubbly mixture of known gas volume fraction (GVF), zero (pure oil) to 50% in steps of 10%. The mixture supply pressure varies from Ps = 2.06 bar-g (30 psig) to 6.20 bar-g (90 psig). Located in grooves at the top and bottom of the journal, a PR and an O-ring (OR) seal the film land. The OR does not allow any oil leakage or air ingestion; hence, the supplied mixture discharges through the PR slit into a vessel submerged within a large volume of lubricant. Dynamic load tests with a single frequency ω, varying from 10 Hz to 60 Hz, produce circular centered orbits (CCO) with amplitude r = 0.2c. The measurements record the exerted forces and journal motions and an analysis delivers force coefficients, damping and inertia, representative of the exerted frequency range. The model predicts the pressure field and evolution of the GVF within the film land and, in a simulated process replicating the experimental procedure, delivers representative force coefficients. For all Ps conditions, both predictions and tests show the SFD added mass coefficients significantly decrease as the inlet GVF (βs) increases. The experimentally derived damping coefficients do not show a significant change, except for tests with the largest concentration of air (βs = 0.5). The predicted damping differs by 10% with the test derived coefficient which does not readily decrease as the inlet GVF (βs) increases. The added mass coefficients, test and predicted, decrease with βs, both being impervious to the magnitude of supply pressure. The test PRSFD shows a quadrature stiffness due to the sliding friction between the PR being pushed against the journal. An increase in supply pressure exacerbates this unique stiffness that may impair the action of the squeeze film to dissipate mechanical energy. The comprehensive test results, first of their kind, demonstrate that accurate modeling of SFDs operating with air ingestion remains difficult as the flow process and the paths of its major components (air and liquid) are rather complex.

Determination of Optimum Working Parameters for Multiple Response Characteristics of Worm Gear Box

The reason for this task is to optimize the multiple response of single start worm gear using three working parameters to improve its performance. As the input torque and lubricant heating time are the most effective responses of worm gear box to reduce the no-load dependent losses, they are taken as the response parameters in this research. Taguchi Grey Relational Analysis (GRA) is the method used to determine the influence of type of lubricant, volume of lubricant and speed of worm gear on multiple responses (input torque & lubricant heating time) of worm gear. The specific test rig is developed based on direct torque measurement technique to measure the input torque and lubricant heating time of worm gear box. Experimental results have shown that the input torque and lubricant heating time can be improved effectively through Taguchi-Grey Relational Analysis. The result is validated using the Confirmation Test. ANOVA determines the important of parameters. It has been found that the type of lubricant and speed of worm gear are influential parameters for worm gear performance. By selecting these parameters, efficiency of the worm gearbox can be increased.

Study of the Conditions for the Formation of an Adsorption Lubrication Mode of Heavily Loaded Friction Couples with Modeling in a Laboratory Setup

Abstract—The mechanism of contact interaction of a heavily loaded friction pair in the presence of a lubricant at the contact is investigated. The results of tribological studies aimed at studying the influence of volumetric parameters of a lubricant at the time of friction and wear are presented. The adhesive ability of the lubricant was studied. It was concluded that the formation of a stable lubricant film is more influenced by the volume of lubricant supplied, which makes it possible to control the type of lubrication in contact and the amount of wear of samples under study. An explanation is proposed for the negative effect of the action of a lubricant supplied in large quantities.

Prediction and optimization of lubrication performance for a transfer case based on computational fluid dynamics

The lubrication performance and lubricant volume are of great significance in the design and operating processes for closed mechanical assemblies. A transfer case was taken as the research object, and simulations of flow fields under different working scenarios based on computational fluid dynamics and optimization of lubricant volume were performed. First, a model was proposed based on the volume of fluid method, and the model was validated when good agreement was achieved between simulation and experimental results. Next, the lubrication performances under different lubricant volumes and gear rotation speeds were predicted, and they showed that too much or too little volume of lubricant is undesirable and harmful. Consequently, the optimization of lubrication volume was designed by means of a response surface methodology, and an optimal lubricant volume was configured under a gear speed of 5260 rpm and immersion depth of 2.6 mm, accounting for 66.69% of the total volume.

Designing a Novel System for the Introduction of Lubricant in Control Cables for the Automotive Industry

The increasing competitiveness installed in the automotive industry implies continuous improvements in all fields of knowledge and action. Thus, it is very important to be aware of the wastes generate across all the productive and logistics operations. In this regard, and considering the production process of command cables for the automotive industry, it was detected that a significant volume of lubricant is wasted during the task of introducing grease into the spiral used in the command cables utilized to drive the doors, windows and brakes of motor vehicles. The industrial operation was carefully followed leading to identify the main causes of the wastes and a brainstorming was carried out allowing the discussion of new ideas on how to overcome the problem. A novel equipment was developed, being also cared all the logistics around the supplying task. The new solution developed, as well as the redefinition of the logistic process of supplying the lubricating grease to the production lines, made it possible to make the process more flexible for the admission of different grease packs, as well as a better utilization of the existing grease in the reservoirs, resulting in a cut of grease waste by more than 70%. It was also produced a prototype of the grease supply system, which allowed validate the previously developed system.

Characterisation of starved hydrodynamic lubricating films

Abstract Optimisation of lubricant supply to bearings has considerable benefits in terms of energy saving and smooth running. This paper presents a study on the hydrodynamic lubrication of sliding contact with various supplied lubricant quantities. Experiments were conducted with an optical slider-bearing test rig. Under limited lubricant supply (LLS), there exists a critical speed beyond which film thickness no longer increases with increasing speed due to starvation at the inlet. The critical speed significantly depends on lubricant quantity, as well as lubricant viscosity and load. Comparison between experimental and theoretical results indicates that the starved films have certain load-carrying capacity and viscous resistance. Under LLS, film thickness is a sensitive function of supply lubricant volume, but friction is not.

Effect of Helium-Induced Pressure and Temperature on Lubricant Transfer in Helium–Air-Filled Hard Disk Drives

A numerical model combined an air-bearing model with a molecular dynamics model is used to investigate lubricant transfer at the spacing between slider and disk in helium–air-filled drives. The physical properties of the helium–air gas mixtures are calculated with respect to the content of helium. Then, the pressure and temperature distributions induced by helium at the head/disk interface are obtained based on the air-bearing model. Furthermore, the obtained pressure and temperature are used as the inputs of the molecular dynamics model to study the mechanism of lubricant transfer. The results show that the lubricant volume transferred to the air-bearing surface increases with an increase in pressure and temperature. The volume of lubricant transfer decreases slightly as the helium volume in the gas mixture increases from 0% to 80%, after which, the transferred lubricant greatly decreases.

Amplification of stick-slip events through lubricated contacts in consolidated granular media

The influence of lubricated contacts on the stick-slip behavior of a granular system is investigated. Samples of cylindrical shape made of glass spheres confined at a constant pressure and subjected to gradual deformation along their main axis are considered. Under constant axial deformation, the granular compact exhibits a regular stick-slip regime, in which gradual stress loading (stick) is followed by rapid relaxation events or failure (slip). The amplitude of stress drops (slips) and their recurrence time are investigated as a function of the amount of lubricant fluid. In the absence of lubricant, stress drops are very frequent but their amplitude is relatively small. However, the addition of a minute volume of lubricant into the granular packing, increases both the amplitude of stress drops and their recurrence time, following a saturating exponential loading curve with the lubricant volume. We show that the typical volume at which saturation occurs corresponds to the amount of fluid required to completely cover the surface of the spheres, with the thickness of the coat corresponding to the size of the asperities. These results support the idea that, to a certain extent, adding lubricant reduces sliding friction, as well as synchronously mobilizes a set of contacts.

Influence of Surface Design on the Solid Lubricity of Carbon Nanotubes-Coated Steel Surfaces

Topographically designed surfaces are able to store solid lubricants, preventing their removal out of the tribological contact and thus significantly prolonging the lubrication lifetime of a surface. The present study provides a systematic evaluation of the influence of surface structure design on the solid lubrication effect of multi-walled carbon nanotubes (MWCNT) coated steel surfaces. For this purpose, direct laser writing using a femtosecond pulsed laser system is deployed to create surface structures, which are subsequently coated with MWCNT by electrophoretic deposition. The structural depth or aspect ratio of the structures and thus the lubricant storage volume of the solid lubricant is varied. The frictional behavior of the surfaces is recorded using a ball-on-disk tribometer and the surfaces are thoroughly characterized by complementary characterization techniques. Efficient lubrication is achieved for all MWCNT-coated surfaces. However, and in contrast to what would be expected, it is shown that deeper structures with larger lubricant storage volume do not lead to an extended lubrication lifetime and behave almost equally to the coated unstructured surfaces. This can be attributed, among other things, to differences in the final surface roughness of the structures and the slope steepness of the structures, which prevent efficient lubricant supply into the contact.

Liquid Superlubricity of Polyethylene Glycol Aqueous Solution Achieved with Boric Acid Additive.

Boric acid is a weak acid and has been used as a lubrication additive because of its special structure. In this study, we report that boric acid could achieve a robust superlubricity (μ < 0.01) as an additive in polyethylene glycol (PEG) aqueous solution at the Si3N4/SiO2 interfaces. The superlow and steady friction coefficient of approximately 0.004-0.006 could be achieved with boric acid under neutral conditions (pH of approximately 6.4), which is different from the acidic conditions leading to superlubricity. The influence of various factors, including boric acid concentration, sliding speed, applied load, PEG molecular weight, and the volume of lubricant on the superlubricity, were investigated. The results reveal that the PEG aqueous solution with the boric acid additive could achieve superlubricity under a wide range of conditions. The surface composition analysis shows that the synergy effect between boric acid and PEG provides sufficient H+ ions to realize the running-in process. Moreover, a composite tribochemical film composed of silica and ammonia-containing compounds were formed on the ball surface, contributing to the superlubricity. The film thickness calculation shows that superlubricity was achieved in a mixed lubrication region, and therefore, the superlubricity state was dominated by both the composite tribochemical film formed via the tribochemical reaction on the contact surfaces and the hydrodynamic lubricating film between the contact surfaces. Such a liquid superlubricity achieved under neutral conditions is of importance for both scientific understanding and engineering applications.

Film building in circular EHL contact lubricated by oil droplet groups

AbstractNumerical calculations have been conducted to study elastohydrodynamic lubrication (EHL) with lubricant in the form of droplet groups, which was aimed to simulate air‐oil lubrication. Two types of lubricant droplet distributions, ie, 1 row of droplets along the centreline of the contact or 2 rows of droplets on each side of the centreline, were adopted. The results showed that continuous EHL film could be obtained in spite that discontinuous lubricant droplets were supplied, which is attributed to the squeeze spread and rejoining of the droplets at the inlet. The total effective lubrication time for full film lubrication has a linear correlation with the number of the droplets, and there exists an optimum droplet spacing distance for continuous full film lubrication. For a constant volume of lubricant, calculations indicated that for most efficient lubrication, there is a trade‐off between the droplet size and the number of droplets divided.

Effect of topical application of 2% lidocaine gel on corneal sensitivity of clinically normal equine eyes

ObjectiveTo assess the degree and duration of corneal anaesthesia provided by topical application of a non-ophthalmic 2% lidocaine gel in horses. Study designExperimental, ‘blinded’, randomized prospective study. AnimalsTwelve adult horses without relevant ocular abnormalities. MethodsBaseline corneal touch threshold (CTT) measurements were obtained bilaterally by use of a Cochet–Bonnet aesthesiometer just prior to topical treatment. A volume of 0.2mL of 2% lidocaine gel was administered in one randomly selected eye and the same volume of a viscous lubricant in the other eye to serve as control. The CTT value was measured on both eyes 5, 10, 20, 30, 45, 60, 75 and 90 minutes after drug application. The potential for local adverse effects following lidocaine gel application was also evaluated. ResultsMean CTT baseline measurements were not significantly different (p>0.05) between the control eyes (3.41±0.56cm) and those subsequently treated with the lidocaine gel (3.50±0.64cm). In control eyes, no significant changes in corneal sensitivity (p>0.05) occurred over time during the study period. By contrast, a marked reduction in corneal sensitivity was observed after lidocaine application, with mean CTT values significantly lower (p<0.001) than those of the control eyes from 5 to 75 minutes. A steady-state maximal corneal anaesthesia was present from 10 to 45 minutes after lidocaine gel application with mean CTT values ranging from 0.21 to 0.45cm. Corneal epithelial irregularities were detected in three lidocaine-treated eyes, but spontaneous resolution occurred within 24hours. Conclusions and clinical relevanceDeep and sustained corneal anaesthesia is achieved after application of 2% lidocaine gel to the equine eye, with minimal changes in the corneal epithelium. It might be useful for minor ophthalmic surgeries performed in the standing sedated horse.

Influence of analyzed lubricant volumes on the amount and characteristics of generated wear particles from three different types of polyethylene liner materials.

The articulating components of artificial joints consist mainly of metals, ceramics, or polymers. Resulting abrasive wear particles can promote osteolysis and aseptic loosening of the endo-prosthetic implants. Ultra-high-molecular-weight-polyethylene is the material used most for bearing couples in total hip replacement. In the present study, three types of polyethylene (PE) liners varying in material composition, i.e., (1) conventional PE (C-PE), (2) sequentially cross-linked PE (SX-PE), (3) cross-linked PE blended with vitamin E (EX-PE) articulating with two types of femoral heads were used. After ultrasound treatment of each simulator lubricant, different concentrations (0.1/0.25/0.5/1.0 mL) were taken and dissolved in hydrochloric acid (37%) in a similar manner. The aim was to analyze the characteristics of wear particles generated in a hip simulator, with respect to different volumes of the lubricant. Within the scope of particle analysis, distinct alterations for particle characteristics were determined in the lubricant volumes and types of PE material used. A significant decrease in particle number for SX-PE liners, compared to the C-PE inserts and even more for EX-PE inserts, was detected at each lubricant volume. Particle morphologies varied depending on PE material. Alterations in particle size and other morphologic parameters between the four tested volumes, could be proven for each PE type. In general, particle sizes and parameters (e.g., length and width) increased with increasing serum volumes. In conclusion, the chosen volume of the simulator lubricant used for particle analysis has a crucial influence on detected particle number, size distribution, and morphologic parameters. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1299-1306, 2018.

Process Oriented Choice of Lubricant Pressure and Volume Flow to Increase Machining Process Efficiency

In machining processes, the choice of a suitable pressure and thus volume flow of lubricant supply in drilling is rather performed with respect to process stability than energy efficiency leading to energetically inefficient processes.In this paper, results regarding the cooling and resource efficiency of lubricant supply in a drilling process of TiAl6V4 are presented. The main principle is to calculate the evacuated heat energy from the cutting zone based on a calorimetrical approach. The pressure as well as the lubricant supply channel diameter have been varied. For these efficiency calculations, the cutting energy, the heat energy evacuated by the lubricant as well as the hydraulic energy were considered. The wear development as well as the chip evacuation were additionally investigated. Based on these investigations, it is shown that high pressure and volume flow lead to reduced tool wear, but not necessarily increase energy efficiency.

Parametric analysis of mixed lubrication characteristics in work zone of strip rolling

A theoretical model for mixed lubrication with more accurate contact length has been developed based on the average volume flow model and asperity flattening model, and the lubricant volume flow rate and outlet speed ratio are determined by integrating differential equations based on rolling parameters. The lubrication characteristics at the roll−strip interface with different surface roughness, rolling speed, reduction and lubricant viscosity are analyzed respectively. Additionally, the average volume flow rates of lubricant under different rolling conditions are calculated and used to explain the change rule of lubrication characteristics. The developed scheme is able to determine the total pressure, lubricant pressure, film thickness and real contact area at any point within the work zone. The prediction and analysis of mixed lubrication characteristics at the interface is meaningful to better control the surface quality and optimize the rolling process.

A Hydrostatic Bearing Test System for Measuring Bearing Load Using Magnetic-Fluid Lubricants.

This paper conducts a study on the design of a hydrostatic bearing test system. It involves the determination of viscous properties of magnetic-fluid lubricants. The load of a hydrostatic thrust bearing using a water-based magnetite nanofluid of varying volume flow rate is measured under an applied external induction field via the test system. Results reveal that the presence of nanoparticles in a carrier liquid would cause an enhanced bearing load. Such an effect could be further magnified by increasing the lubricant volume flow rate or the external induction field strength.

Overcoming Extended-Reach Challenges for Annular Fracturing

Summary More operators are seeing the production benefits of targeted, horizontal annular fracturing. The most-active method of annular fracturing in the US involves ported sleeves installed with the completion and activated by means of an isolation packer. Initial operations were in lateral lengths of 2,000 to 3,000 ft; however, current operations are planned for accessing lateral lengths up to 10,000 ft. Increasing lateral length results in the traditional access challenges faced by all coiled-tubing operations. The traditional method of lubricant use is the primary option because of its simplicity. The second method is to use fluid-hammer tools (FHTs). These are industry standard for improving efficiency in composite-plug milling operations, but their use in genuine extended-reach operations is not as broad. This paper briefly covers historical ported-annular-fracturing operations and the various methods of achieving increased lateral reach. Results from four wells that have a lateral reach of 7,200 to 10,277 ft are detailed in the paper. The balance of the paper details operational results and optimization from several extended-reach wells. Detailed lateral-reach modeling was performed before all operations. This permitted the determination of the number of expected stages that would require the use of lubricant in the fracture-treatment flush. Given that residual lubricant in the completion is removed by the erosion effects of the proppant in the fracture treatment, each stage would require an additional fluid flush. This gives an opportunity to modify the lubricant concentration, type, and volume in the flush. Before using FHTs for setting the isolation packer, laboratory testing was performed to ensure the bottomhole-assembly-system compatibility. The lubricant testing and initial field results were reported previously (Livescu and Craig 2014; Livescu et al. 2014a, 2014b). This paper provides operators with sufficient case histories of the planned use of an advanced lubricant in genuine extended-reach wells in real-life situations. This knowledge can improve operator confidence in drilling longer laterals for predictable access for annular-fracturing operations.