Techniques to Reduce Friction in Bio-Based Lubricants

Abstract Cryogenic minimum quantity lubrication systems (MQL) combine the high cooling effect of cryogenic media and the resource-efficient lubricating effect of an MQL. However, for efficient use, the cooling and lubrication properties must be precisely matched to the respective application and the load case that occurs. This article presents a tribological approach that enables the quantification of the coefficient of friction and the thermal load in frictional contact. This has shown that the use of a cryogenic MQL can significantly reduce both friction and the temperatures that occur.

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Medical device with improved lubricity for minimally invasive procedures. The device features a substrate layer, an adhesive layer containing a hydrophilic copolymer with sulfobetaine and acidic groups, and a surface lubricious layer containing hyaluronic acid or a salt thereof and a hydrophilic copolymer with sulfobetaine and acidic groups. The lubricious layer exhibits enhanced lubricity and durability in aqueous environments, reducing friction and tissue damage during insertion and movement of the device.

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In mechanical systems, lubricants play a crucial role in minimizing friction, dissipating heat, and preventing wear. Additives, comprising both organic and inorganic compounds and typically constituting 0.1% to 30% of lubricant volume, are introduced to enhance lubricant performance. This study investigates the influence of various additives on lubricant behaviour and performance, encompassing antifoam agents, corrosion inhibitors, antioxidants, detergents, extreme pressure additives, pour-point depressants, and viscosity index improvers. Friction coefficients were meticulously measured using a pin-on-disk tribometer to assess the Tribological and physical properties of these additives. Surface analysis via SEM provided insights into wear characteristics influenced by the additives. The comprehensive tribological assessment reveals that the incorporation of additives consistently reduces friction and wear across different base oil types. This underscores the critical role of additives in improving lubricant properties, maintaining thermal stability, and forming protective films on su... Read More

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Dry lubricant composition for aqueous drilling fluids, comprising a spray-dried product of neutralized carboxylic acid terminated fatty amine condensate or neutralized modified tall oil, or a mixture thereof, that reduces coefficient of friction and improves lubricity of bentonite mud while enhancing ultimate viscosity and polymer hydration efficiency.

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Lubricants must exhibit good tribological behavior at low temperatures to ensure reliable startups in very cold regions. This study investigates the performance of lubricants, with a specific focus on their capacity for high-temperature lubrication and ensuring reliable low-temperature startup in engines. Experiments were conducted to assess the friction and wear characteristics of polydiethylsiloxane in conjunction with a Si3N4 ball and M50 (8Cr4Mo4V) steel across a temperature range of 80 C to 25 C. The results indicate that the coefficient of friction, as determined through friction and wear tests at various temperatures, remained below 0.1. As temperatures progressively decreased, the systems friction coefficient increased, and wear volumes recorded at 25 C and 60 C were 9749.513 m and 105.006 m, respectively, culminating in lubrication failure at 100 C. This failure is primarily attributed to the increased viscosity and decreased mobility of polydiethylsiloxane at extremely low temperatures. Additionally, the reduced temperature increases the strength of the quenche... Read More

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The initial friction stage between the contacting materials would generate a maximum shear force and an unstable fluctuating time, which had a negative effect on the entire frictional system, especially at low temperature conditions. In order to decrease the occurring shear force and fluctuating time on the onset of friction, two different lubricating oils were applied in this study to investigate the influence of lubricants viscosity on these friction behaviors. The frictional experiments were conducted between the steel ball and the 40CrMnMo, and special attention was paid to the relationship between maximum friction force, fluctuating time, frictional vibration and the initial lubricant temperature. The results showed that the friction force first increased to the maximum value and then experienced an oscillation damping period (fluctuating time) before it reached a stable state. And this fluctuating behavior caused corresponding vibrations on the initial contacting. However, compared to the high viscosity lubricating oil (HO), the low viscosity lubricating oil (LO) contributed t... Read More

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Organisms in nature have evolved a variety of surfaces with different tribological properties to adapt to the environment. By studying, understanding, and summarizing the friction and lubrication regulation phenomena of typical surfaces in nature, researchers have proposed various biomimetic friction regulation theories and methods to guide the development of new lubrication materials and lubrication systems. The design strategies for biomimetic friction/lubrication materials and systems mainly include the chemistry, surface structure, and mechanics. With the deepening understanding of the mechanism of biomimetic lubrication and the increasing application requirements, the design strategy of multi-strategy coupling has gradually become the center of attention for researchers. This paper focuses on the interfacial chemistry, surface structure, and surface mechanics of a single regulatory strategy and multi-strategy coupling approach. Based on the common biological friction regulation mechanism in nature, this paper reviews the research progress on biomimetic friction/lubrication mater... Read More

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Abstract Applying a lubricant to the colonic mucosa and reducing the dynamic friction coefficient (DFC) between the endoscopic shaft and colonic mucosa may reduce colonoscopy invasiveness. However, the ideal lubricant viscosity remains unknown. Here, we developed a DFC measurement model integrating samples of colonic mucosa from forensic autopsy specimens into a simulated bowel bend and determined the low-friction lubricant viscosity that minimizes the DFC. Carboxymethyl cellulose, xanthan gum, hydroxyethyl cellulose, sodium alginate, and sodium polyacrylate aqueous solutions of various concentrations were used as lubricants. Low-friction lubricants minimized the load on the colonic mucosa during colonoscope insertion and reduced the total endoscopy insertion time. The highest correlation was between the DFC and the lubricant viscosity at a shear rate of 100 1/s. The lowest DFC was almost constant at approximately 0.09, irrespective of the chemical composition of the lubricant, and the low-friction lubricant viscosity (100 1/s) was 0.0310.086 (median: 0.059). The viscosities of conv... Read More

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Friction and lubrication are ubiquitous in all kinds of movements and play a vital role in the smooth operation of production machinery. Water is indispensable both in the lubrication systems of natural organisms and in hydration lubrication systems. There exists a high degree of similarity between these systems, which has driven the development of hydration lubrication from biomimetic to artificial manufacturing. In particular, significant advancements have been made in the understanding of the mechanisms of hydration lubrication over the past 30 years. This enhanced understanding has further stimulated the exploration of biomimetic inspiration from natural hydration lubrication systems, to develop novel artificial hydration lubrication systems that are cost-effective, easily transportable, and possess excellent capability. This review summarizes the recent experimental and theoretical advances in the understanding of hydration-lubrication processes. The entire paper is divided into three parts. Firstly, surface interactions relevant to hydration lubrication are discussed, encompass... Read More

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Conventional friction modifier MoDTC becomes ineffective at lower temperatures. This paper investigates the concept of "precipitation lubrication," where saturated fatty acid precipitation enhances load capacity and solid lubrication at contact points to overcome this issue. PAO8 with 4.2 % palmitic acid lubricant was prepared, precipitating below 35 C, reducing friction by approximately 14 % at 30 C for both boundary and mixed lubrication. In situ reflectance spectroscopy demonstrated palmitic acid forming a solid layer on the disk specimen, preventing direct contact between asperities and significantly reducing friction. These findings underscore the effectiveness of palmitic acid precipitation in enhancing lubrication performance at lower temperatures.

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Conventional friction modifier MoDTC becomes ineffective at lower temperatures. This paper investigates the concept of "precipitation lubrication," where saturated fatty acid precipitation enhances load-bearing capacity and solid lubrication at contact points to overcome this issue. PAO8 with 4.2 % palmitic acid lubricant was prepared, precipitating below 35 C, reducing friction by approximately 14 % at 30 C for both boundary and mixed lubrication. In situ reflectance spectroscopy demonstrated palmitic acid forming a solid layer on the disk specimen, preventing direct contact between asperities and significantly reducing friction. These findings underscore the effectiveness of palmitic acid precipitation in enhancing lubrication performance at lower temperatures.

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Minimizing the deformation caused by friction on surfaces enabled to maintain a stable friction force and coefficient of friction (COF), and valuable insights could be gained from studying bio-based lubrication systems. A natural polysaccharide was derived from fresh okras in order to enhance the lubricating efficiency of aqueous system. The lubricating performance and mechanism of okra polysaccharide were unveiled through the implementation of multiple wear tests between the steel and PA66. Particular attention was paid to the relationship between the deformation, friction force and COF. The results indicated that the surface fluctuated deformations caused comparable fluctuations in both the friction force and the COF. However, the inclusion of okra polysaccharide at a concentration of 2 wt% significantly diminished the amplitudes of friction force by decreasing surface deformations. As a result, almost 50% decrease in both COF and wear loss were observed. The lubricating mechanism of okra-polysaccharide lubricant could be described as the interaction between the hydrophilic groups ... Read More

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The evolution of lubricating oil containing additives under dynamic conditions is very significant, since its oil film structure, velocity distribution, and adsorption characteristic have an obvious impact on friction and wear. In this work, a boundary lubrication (BL) and elastohydrodynamic lubrication (EHL) models under sinusoidal load were carried out by nonequilibrium molecular dynamics (NEMD), using iron oxide as the substrate, hexadecane, and stearic acid molecules as lubricants. It was discovered that the friction in the BL regime is positively correlated with the degree of additive's solidification. The greater the solidification degree of additive layers, the less the interlacing between them, making the relative motion between them easier and reducing compression oscillation within them, thus diminishing friction in the BL regime. The degree of liquefaction of base oil and additive regions, as well as the velocity difference within their interlacing zones, are connected to the friction force in the EHL regime. At high frequencies as well as large amplitudes, the oil film ha... Read More

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Abstract Most studies of liquid lubricants were carried out at temperatures below 200 C. However, the service temperature of lubricants for aerospace and aeroengine has reached above 300 C. In order to investigate the friction mechanism and provide data for high temperature lubrication, the friction and wear properties of chlorophenyl silicone oil (CPSO)-lubricated M50 steel and Si 3 N 4 friction pairs were investigated herein. Ball-on-disk experimental results show that the lubrication performance of CPSO varies significantly with temperature. Below 150 C, coefficient of friction (COF) remains at 0.130.15 after the short running-in stage (600 s), while the COF in the running-in stage is 0.20.3. At 200 C and above, the running-in time is much longer (1,200 s), and the initial instantaneous maximum COF can reach 0.5. Under this condition, the COF gradually decreases and finally stabilizes at around 0.160.17 afterwards. This phenomenon is mainly due to the different thickness of boundary adsorption film. More importantly, the wear rate of M50 steel increases significantly with t... Read More

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The development of environmentally friendly and cost-effective lubricating materials to reduce friction and wear at macroscale is crucial for reducing fuel consumption and exhaust emissions, thereby enhancing sustainability. Deep eutectic...

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The non-renewability and and non-biodegradability of petroleum based lubricants as well as the environmental impacts their waste contributes to the environment has caused the search for a substitute for precursor of lubricant formulation. The food security issue has caused major concerns on how vegetable oil could replace petroleum based product lubricants. This paper reports the feasibility studies of kinematic viscosity, friction and wear properties of treated used cooking palm oil as precursor for development of new bio-lubricant. The treated used cooking palm oil displayed a comparable value of kinematic viscosity of 43.6cSt, coefficient of friction of 0.126 and 122m which is almost similar to the value of fresh cooking palm oil. Treated used cooking palm oil is seen to be a suitable candidate for precursor of bio-lubricant formulation, However, some additives may need to be added as to increase the tribological properties for treated used cooking oil to be used as a bio-lubricant.

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A method for creating low-friction surfaces on medical devices by incorporating oligofluorinated additives into the base polymer composition. The additives, known as surface-modifying macromolecules (SMMs), are admixed with the base polymer to form a surface with reduced coefficient of friction. The SMMs can be combined with a variety of base polymers, including polyurethanes, silicones, and polyamides, to create medical devices such as catheters, guidewires, and stents with improved lubricity. The method eliminates the need for separate coatings or liners, reducing the risk of delamination and particulate generation.

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Silicone-free, lipid/liposome-based lubricant for medical devices that eliminates particle shedding and immunogenicity risks associated with traditional silicone lubricants. The lubricant comprises liposomes with cationic lipids that break down into lamellar structures upon heat treatment, forming a stable, non-silicone coating on device surfaces. The lubricant is applied through conventional coating methods followed by thermal treatment, and can be used in place of traditional silicone lubricants in medical devices such as syringes and implants.

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Biocompatible and degradable slippery surfaces (SLIPS) and liquid-infused surfaces (LIS) that utilize lubricating liquids or emulsions to prevent fouling by microorganisms and other substances. The surfaces comprise a porous matrix of degradable polymers, such as poly(lactic-co-glycolic acid) (PLGA), that is infused with a lubricating liquid or emulsion, including vegetable oils and other biocompatible oils. The surfaces exhibit improved biocompatibility and degradability compared to conventional SLIPS and LIS, and can be fabricated using techniques such as electrospinning and solution blow spinning.

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Many laboratory tribology test machines are available for evaluating the effect of different lubricants and different operating conditions on friction. For the Mini Traction Machine (MTM) there is much published data that shows how the measured friction coefficient varies with operating conditions and lubricant type. Fully formulated lubricants containing the anti-wear additive ZDDP have often been found to have a significantly higher friction coefficient, which persists to higher speeds, compared to base oils (lubricants with no additives). Recent work has found that the surface roughness of ZDDP tribo-films can evolve to become significantly higher than that of the surfaces they are deposited on. When the measured friction coefficients of lubricants tested in the MTM machine are suitably normalized and plotted against the ratio (which is equal to the oil film thickness separating the moving surfaces divided by the combined surface roughness) then the curves for various different lubricants lie on a master curve which enables reliable friction estimates to be made for lubricated... Read More

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Abstract: We have an increasing global need for bio lubricants that are safe for human and environmental use, easily biodegradable, and non-polluting. The friction and wear qualities of cotton seed blended lubricant as well as castor blended lubricant are compared and contrasted in this research using a Pin on disc wear testing Tribometer. In this research, we will look at the study's results and analyse their significance. Blended lubricants were created by combining cotton seed & castor based biodiesel with the basic lubricant SAE20W40 at volumetric ratios of 5, 10, 15, & 20%. Cotton seed and castor blended bio lubricants were tested for friction and wear at sliding velocities of 2.5 metres per second while subjected to weights of 50 N, 100 N, and 150 N. Wear might be slowed by as much as 15 percent by mixing in cotton seed biodiesel with the base oil, as has been shown. When this threshold is passed, wear increases at an ever-increasing pace. Castor oil blended lubricant performed best in wear tests when coupled with a base lubricant at a 5 and 10 percent castor oil blende... Read More

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Lubricants with a functional water portion have demonstrated a drastic reduction in friction under elastohydrodynamic lubrication conditions. With water-containing polyalkylene glycols, superlubricity with coefficients of friction <0.01 have been measured in model and gear contacts. In addition to the low friction, their calorimetric properties make them particularly interesting for application in electrified vehicles because the liquid can simultaneously serve as lubricant for the gearbox and coolant for the electric motors and the power electronics. In this study, the influence of water content between 8 wt% and 40 wt% of water-soluble polyalkylene glycols on friction and film thickness in elastohydrodynamically lubricated rolling-sliding contacts such as in gears and bearings is investigated. A polyalphaolefine oil is used as a reference. Friction has been measured on a ball-on-disk tribometer and film thickness on an optical tribometer. For a water content of 40 wt%, superlubricity with coefficients of friction down to 0.004 are found. The decrease in friction is up to 95%... Read More

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This paper presents new non solved, scientific research directions and their applications in contemporary non-conventional lubrication problems of the bio-surfaces domain. Here are described new research scientific trends and research problem solutions of hydrodynamic lubrication for living tissue, human skin and human cartilage joints surfaces. At first in introduction is described the state of the art, a new purpose of anticipate research and the bio-tribology connections with other scientific domains are documented. The bio-tribology is a new scientific domain where the bio-properties of living, mutually cooperating bio-materials have an important influence on joint human functioning and on the consequences of obtained bio-tribology effects. Using experimental and numerical methods, the main result is focused on the influence of the bio-sweat dynamic viscosity variations across the film thickness on the load carrying capacity of the lubricated human skin and limbs.

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Abstract The use of lubricants is commonplace when drilling with water-based drilling fluids. They are less frequently applied when drilling with non-aqueous fluids, as the oil-based drilling fluid is thought to impart a high lubricity. With increased reach of the wells, lubricants are also applied in non-aqueous fluids (NAF) to reduce torque and drag at high angle, for extended reach and horizontal wells to improve drilling efficiency. However, the performance of these lubricants in NAF at extended periods of elevated temperature at downhole conditions is often inconsistent, thought to be hampered by ineffective metal binding and hydrolytic instability of the lubricant molecule. This requires frequent re-dosing and therefore higher cost to maintain performance. In order to identify a better-performing lubricant, it was necessary to better understand the fundamentals of lubrication in a drilling fluid. For example, what portion of the well contributes most to torque and drag? What is the frictional regime that dominates the lubricity between a drill pipe and its contact points? Looki... Read More

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Lubrication is necessary to minimise the frictional impact created during the running of a vehicle since it increases wear and friction among the parts in contact. Wear and friction shorten the component's life, decrease its dependability, and raise maintenance costs. The current study uses a tribo tester to examine the friction and wear properties of rapeseed biodiesel at fixed parameters. The investigated lubricants included B0 (diesel), B100 (biodiesel), and four distinct blends of biodiesel: B15, B30, B45, and B60. Analysis was done for one hour at ambient temperature with a standard load of 140 N at a speed of 1000 rpm. The outcome showed that as the concentration of biodiesel augmented, friction and wear scar get reduced. The aluminium pin wear in B100 appeared 16% less than that in diesel. Also, the presence of esters and fatty acids during Fourier transform infrared analysis of biodiesel contributes more to its possibilities as a lubricant.

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A lubricating coating for medical devices that combines a base layer with a lubricating layer to reduce friction and bacterial adhesion. The base layer can be a ferroelectric material, oil gel, hydrogel, silica gel, or solar cell material, while the lubricating layer is formed by applying a lubricating liquid directly to the device surface or base layer. The coating enables long-lasting lubricity and antibacterial properties, improving biocompatibility and reducing tissue damage during medical procedures.

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Abstract Lubricated contact processes are studied using classical molecular dynamics simulations for determining the entire range of the Stribeck curve. Therefore, the lateral movement of two solid bodies at different gap height are studied. In each simulation, a rigid asperity is moved at constant height above a flat iron surface in a lubricating fluid. Both methane and decane are considered as lubricants. The three main lubrication regimes of the Stribeck curve and their transition regions are covered by the study: Boundary lubrication (significant elastic and plastic deformation of the substrate), mixed lubrication (adsorbed fluid layer dominates the process), and hydrodynamic lubrication (shear flow is set up between the surface and the asperity). We find the formation of a tribofilm in which lubricant molecules are immersed into the metal surfacenot only in the case of scratching, but also for boundary lubrication and mixed lubrication. The formation of a tribofilm is found to have important consequences for the contact process. Moreover, the two fluids are found to show distin... Read More

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The development of effective bio lubricants with anti-friction and wear properties is gaining recognition due to their ecofriendly nature and good lubrications in mitigating challenges associated with friction and wear on tribo-components during lubrication. In this research, rapeseed oil served as the base lubricant, and the high frequency reciprocating rig was utilized to examine the responsiveness of the multiwall carbon nanotubes (MWCNTs) and Eichhornia crassipes carboxylmethyl cellulose (EC-CMC) polymer additives. To determine the constituents and strength of the formulations, the samples were characterized using scanning electron microscope, Energy-dispersive X-ray, Fourier transform infrared spectroscopy, Raman, and X-ray photoelectron spectroscopy. The tribological test was conducted in terms of synergistic tendency, load carrying capacity, friction and wear reduction as well as tribo-film nature. The investigation came to the following conclusions: Depending on the operating conditions, all nanoparticle suspensions showed decreases in friction and wear relative to the base o... Read More

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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, respec... Read More

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Herein, we present a generalized close-formed model of the friction coefficient between fractal surfaces in mixed lubrication. A mathematical transformation from asperity area to oil film thickness is conducted, which changes the fractal methods traditional basis of the area distribution to establish an analytical fractal model of oil film thickness. A dynamic film thickness model with external load under the determination of the surface roughness is further proposed. Based on the fractal-based oil film thickness, the contact force for each part is solved under the external normal force, and decoupling is achieved presented by contact ratio. Through the contact ratio, the constitutive model of friction coefficient is elucidated. The effects of fractal parameters and important working parameters on friction coefficient are then analyzed, and comparison with experimental data is conducted. This work provides a general analytical expression for friction coefficient in mixed lubrication with explicit form and wide applications.

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Lubricants predominantly used to reduce friction and gain smooth functioning of a vehicle. Biodegradable lubricants are perceived to be alternative to mineral oil lubricants because of their properties and biodegradability. This review paper discusses the effect of biodegradable lubrication in term of emission performance, wear, friction and viscosity effect to the internal combustion engine using multiple types of biodegradable lubrications. Bench wear test was conducted using Yamaha, ET 950 to carry out the effect of the biolubricant in spark ignition (SI) engine. The bench test was conducted under several conditions: pressure, 3.0 MPa; sliding speed, 0.20 m/s; sliding stroke, 80 mm; room temperature, >25C. The second experiment were conducted with 100 percentage SAE 40, palm oil and palm oil (14%) + castor oil (86%) blend as its crankcase lubricant using four stroke compression ignition (CI) engine.A thermocouple was used to measure the parameters temperature every 5 minutesinterval with the engine operating for an hour under no load, 2.5 kg, 5 kg, and 7 kg load condition. Th... Read More

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Abstract The tribological and vibration behaviors of a lubricated system are often studied separately. However, in recent years, the combination of tribology and mechanical vibration significantly contributes in analyzing and solving many practical problems. The main objective of this study is to establish empirical equations that describe friction-vibration interactions under dynamic (sliding) lubricated contacts. The effects of operating conditions on the tribological and vibration behaviors of lubricating oils having different viscosities were experimentally investigated using a four-ball wear test machine. The results indicated that the vibration velocity tends to increase with the sliding velocity. With a lower combination of ratio of the vibration velocity to the sliding velocity and the specific film thickness, lower friction coefficients were observed in the boundary and mixed lubrication regimes. The mean wear scar diameters exhibited positive correlations with the amplitudes of vibration accelerations. The empirical equations provide basic information for the prediction of... Read More

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Lubricants predominantly used to reduce friction and gain smooth functioning of a vehicle. Biodegradable lubricants are perceived to be alternative to mineral oil lubricants because of their properties and biodegradability. This review paper discusses the effect of biodegradable lubrication in term of emission performance, wear, friction and viscosity effect to the internal combustion engine using multiple types of biodegradable lubrications. Bench wear test was conducted using Yamaha, ET 950 to carry out the effect of the biolubricant in spark ignition (SI) engine. The bench test was conducted under several conditions: pressure, 3.0 MPa; sliding speed, 0.20 m/s; sliding stroke, 80 mm; room temperature, >25C. The second experiment were conducted with 100 percentage SAE 40, palm oil and palm oil (14%) + castor oil (86%) blend as its crankcase lubricant using four stroke compression ignition (CI) engine. A thermocouple was used to measure the parameters temperature every 5 minutes interval with the engine operating for an hour under no load, 2.5 kg, 5 kg, and 7 kg load condition. T... Read More

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The main topic of this paper refers to the numerous relations between the decrements of the dynamic viscosity of non-Newtonian bio-liquid lubricated human joints on the one hand and, on the other hand, with consequences resulting from various diseases such as low fitness and low skills of human limbs, joint unfitness, large wear of cooperating cartilage bio-surfaces. Additionally, this paper indicates the pharmacology methods performed in vivo to enhance the bio-liquid lubricant dynamic viscosity. After numerous experimental measurements, it directly follows that the collagen fibre, hyaluronate acid particle, power hydrogen ion concentration pH in lubricating bio-liquid and absorbability features of lubricated bio-surface have a direct and indirect significant influence on the bio-liquid dynamic viscosity values variations with interfacial energy distribution across the film thickness. The results presented in this paper are confirmed based on experimental measurements and analytical, numerical solutions of the load-carrying capacity, friction coefficient and bio-liquid dynamic varia... Read More

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Modified glycoproteins, including lubricin and mucins, with tunable glycosylation patterns for diverse applications. The glycoproteins feature contiguously repeated sequences flanked by native protein segments, enabling controlled glycosylation and lubrication properties. The modified glycoproteins can be used as anti-adhesives, lubricants, and therapeutic agents for conditions such as joint sepsis, wound healing, and ocular diseases.

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The molecular arrangement in the lubricating film will affect the friction coefficient. When using liquid crystal as a lubricant, various methods can be tried to adjust the arrangement of the liquid crystal molecules to actively control the lubrication effect. In this study, 5CB with a clearing point of 35C was used as a lubricant. By changing the temperature, the lubricating molecules in the contact area were switched between an ordered liquid crystal state and a disordered liquid state, and a friction coefficient that changed synchronously with the temperature was obtained. It provides new ideas for active control of lubrication in the fields of smart bearings and emergency braking.

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With the increasing awareness and concerns towards the detrimental impact of mineral-oil-based lubricants, a step forward is crucial to replace them with benign environment-friendly lubricants. Bio-lubricants, due to their intrinsic lubricant properties attributed to the presence of long chain fatty acids, have an immense potential to be utilised as green lubricants and could be promising substitutes for the mineral oil-based lubricants. In this work, the performance evaluation of three bio-lubricants (Cottonseed, Karanja, and Jatropha oils) is carried out by applying in strip drawing and deep drawing experiments. The strip draw tests are conducted to determine the coefficient of friction, whereas the effectiveness of the bio-lubricants in the deep drawing are examined evaluating the drawability, thinning, drawing load and surface finish. The obtained results are compared with a mineral-oil-based lubricant and a water soluble paste. All the three bio-lubricants are found to perform well in comparison to mineral-oil-based lubricant in terms of resulting friction coefficient, drawabili... Read More

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The friction characteristics of the lubricated rough surfaces are of great significance for the lubrication design of mechanical structures. To study the behaviour of friction coefficient in the rolling-sliding coexisting line contact rough surfaces under mixed lubrication regime, the Kogut-Etsion elastic-plastic model and the Carreau rheological model are utilized to describe the dry rough contact and the non-Newtonian characteristics of the lubricant film, respectively. A mixed lubrication model for predicting friction coefficient is proposed based on the load-sharing concept at which the normal load is shared by the lubricant film and the asperity component. The effects of normal load, surface roughness and lubricant inlet viscosity on hydrodynamic scaling factor, film thickness parameter and the coefficient of friction were analyzed. The dimensionless predictive expression for the critical sliding velocity is derived by nonlinear regression. The research results provide theoretical guidance for the lubrication design and optimization of mechanical structures.

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Abstract Nine organic compounds were utilized as model lubricants to investigate the impact of functional groups on tribological performances. Nonanoic Acid with carboxyl showed the best lubrication properties, and fluid film and tribofilm were coexistent in its friction test, bringing a low friction coefficient and wear rate. In addition, the lubricant with low friction coefficient corresponded to high adsorption energy in density functional theory (DFT) calculations. And the lubricant forming adsorption film with large surface energy displayed small wear rate in friction test. Moreover, adsorption energies positively correlated surface energies. Based on the experimental results, the action mechanism of functional groups on tribological properties of lubricants was proposed. Various functional groups make lubricant molecules show different adsorption energies and surface energies. Lubricant molecules with high adsorption energy are more likely to adsorb on substrates and form a vertical monolayer, which can maintain a regular molecular brush structure during friction and bring a lo... Read More

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Abstract At present, more and more diseases are associated with the lubrication dysfunction, which requires a systematic study of the complex lubrication behavior of tissues and organs in human body. Natural biomacromolecular lubricants are essential for maintaining ultra-low coefficients of friction between sliding biological interfaces. However, when the surface lubrication performance of tissues or organs destroys heavily, it will bring friction/shear damage for sliding contact interfaces. Therefore, the application of exogenous biological lubricating materials to improve the lubrication situation of damaged tissue or organ interfaces has attracted extensive attention of researchers. In this review, based on a simple summary of lubrication mechanism at sliding biological interface, we systematically introduce the research progress of several kinds of representatively biolubrication materials, including eye drops, tissue anti-adhesion agents, joint lubricants, and medical device lubricants. Meanwhile, the lubrication mechanism and individual advantage and shortcoming for each of th... Read More

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A new experimental approach is proposed to investigate the friction behaviour and highlight the relationship with the tribofilm formation. It is based on the accumulation of several free dynamic responses of a single-degree-of-freedom damped oscillating system on the same sliding surfaces. By analysing the decreasing amplitude of the damped free dynamic responses and their associated energy decays, it is not only possible to describe the evolution of the tribological behaviour, but also to accurately identify velocity-dependent and velocity-independent friction contributions as the gradually formation of tribofilm. To demonstrate the relevance of this original technique, two tribosystems were studied, each lubricated with either base oil or formulated one, and by comparing the results with those obtained by a conventional linear tribometer.

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The problem of high friction and high torque is one of the most troublesome problems for engineers in extended reach wells and long horizontal wells. Generally, the friction coefficient of oil-based drilling fluid is around 0.08, while the friction coefficient of water-based drilling fluid exceeds 0.2, which is much higher than that of oil-based drilling fluid. With the increasingly stringent environmental regulations, water-based drilling fluids have gradually become a better choice than oil-based drilling fluids. Therefore, lubricants become a key treatment agent for reducing the friction coefficient of water-based drilling fluids. Although there have been many related studies, there is a lack of comprehensive reviews on environmentally friendly water-based drilling fluid lubricants. In general, water-based drilling fluid lubricants can be mainly divided into solid lubricants, ester-based lubricants, alcohol-based lubricants, and nano-based lubricants. Vegetable oil ester-based lubricants, biodiesel lubricants, and dispersible nano-lubricants are all promising environmentally frien... Read More

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Boundary lubrication state may dominate the friction pairs operating under severe conditions, yet its mechanism is not clearly understood and related numerical models are still lacking. A boundary lubrication model considering zinc dialkyldithiophosphate (ZDDP) tribofilms, which impact friction and wear performances, was developed in this study. A series of reciprocating experiments were conducted to verify this model and also to investigate the effects of the tribofilm on friction and wear under various temperatures and loads. Moreover, the experimental data were employed to modify the tribofilm removal equation, which enabled the present boundary lubrication model to be applied under a wide range of loads. The results showed that the friction force and wear depth both decline with the increasing lubricant temperature due to thicker tribofilms formed. As the load becomes heavier, the wear depth keeps increasing, while the tribofilm thickness first increases then decreases.

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The presented study dealt with the experimental analysis of friction and lubrication mechanism observed with fluorescent microscopy in total knee replacement represented by CoCrMo wheel and PMMA plate. Model synovial fluid with marked constituents was used as test lubricant. The experiments investigated three main parameters. Slide-roll-ratio (SRR) showed the greatest influence on lubrication film formation. Friction coefficient was mostly influenced by axial load; its increase led to a decrease in friction. Relative speed was manifested for SRR 1.25 and higher where its increase caused a decrease in friction. The complex experiment showed a development of friction coefficient and lubrication film along the whole gait cycle. The results of this experiment correspond with the initial results concerning the influences of parameters.

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Abstract Intelligent lubricating materials can control the coefficient of friction between interfaces in response to external stimuli. Considering that mechanical transmission parts are mostly used in oilbased lubrication environments, the lubrication performance and electrical regulation mechanism of polyolefin50 (PAO50), a lubricating oil, containing 1octyl3methylimidazolium hexafluorophosphate ([OMIm]PF 6 ), an ionic liquid (IL), are investigated in this study. Friction tests on a universal microtribometer under current stimulation show that ionic lubricating oil has an excellent lubrication performance and electrical responsiveness. By changing the current strength, ion content, and the load, the reasons behind the change in the coefficient of friction are investigated. Ion aggregation results in an increase in the viscosity of the lubricating oil film, which leads to an increase in the coefficient of friction. Moreover, the realtime resistance value of the oil film is obtained through a selfbuilt voltage acquisition device. The mechanism of the electronic control of f... Read More

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Abstract Lubrication is a procedure that involves the use of a chemical called lubricant to reduce wear on surfaces that are in relative motion with each other. It aids in the transmission of pressure created between opposing surfaces. Lubricants serve as anti-friction agents. They allow for flat-level operations by retaining superior machine functionality and reducing the likelihood of recurring breakdowns. In today's world, the price of crude oil is rising in tandem with the depletion of reservoirs (oil). As a result, protecting a pollution-free environment is a major responsibility. The focus of current research is on creating and using an ecologically friendly lubricant made from renewable resources. This paper discusses the preparation, characteristics, characterization advantages, and uses of vegetable oil-based non-edible lubricants. Chemical changes are required since vegetable oil-based lubricants have lower thermal and oxidative stability. The article explores the required chemical modification approaches for improving the properties of bio-lubricants. The characterization ... Read More

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Globally, bio-lubricants are getting attention as these are sustainable, environment friendly, having good lubricity and can easily be extracted from vegetable oils. This study focused on the formulation of TMP based bio-lubricant from renewable cotton seed oil and measuring of its tribological characteristics to evaluate its potential for replacing petroleum-based lubricants. Coefficient of friction and wear for cylinder liner-piston ring combination was measured on HFRR and four-ball. SEM, EDX and surface morphology also described the wear nature and their surface roughness. SAE-40 was studied as a reference commercial lubricant for comparison purposes. It is concluded that pure cotton bio lubricant (CBL-100) gives good lubricity with low COF but higher wear than SAE-40. So, cotton bio lubricant with suitable anti-wear additives package has great potential to be used in global lubricant market instead of mineral based lubricants.

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The formation of tribofilm by lubricant additives plays an important role in improving the performance of boundary lubrication. In previous studies, it has been discussed that the frictional force due to adhesion can be expressed as a product of the real contact area and the shear strength of the contact junction. Therefore, to evaluate the friction mechanism dominated by the tribofilm in detail, it is important to divide and identify the effects of the shear strength and real contact area. However, there are few studies that have verified the relationship between shear strength and macro friction coefficient with experimental data. In this study, nanofrictional property and real contact area of tribofilm was investigated using nanoindentation equipment and contact analysis. The results show that the shear strength of base material and tribofilms are correlated with the macro friction coefficients. In addition, the friction coefficients are calculated by applying the shear strength to the basic friction equation. The result shows that the friction coefficients calculated from the bas... Read More

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A method for manufacturing a medical instrument with enhanced lubricating properties, comprising applying a solution containing a block copolymer, a choline derivative, and a solvent onto a base layer of the instrument. The block copolymer forms a lubricating layer that exhibits improved durability and lubricity, particularly in aqueous environments, while the choline derivative promotes cross-linking of the block copolymer without increasing the solution's viscosity. The lubricating layer can be formed on a variety of medical instruments, including catheters, guide wires, and indwelling needles, to enhance their maneuverability and reduce tissue damage.

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Abstract The boundary lubrication mode is usually implemented in conditions of low sliding speeds and high loads. The formation of strong boundary lubricating films under this friction mode determines the operability and durability of the friction units. It is believed that the formation of surface boundary films during friction includes the stages of the lubricant oxidation, and the aldol condensation reaction of oxidized molecules. As a result, high-molecular substances called friction polymers are formed. The paper studies the formation of surface films in the presence of substances with different reactivity in the aldol condensation and Claisen condensation reactions. Sunflower oil, bis (2-ethylhexyl) sebacate (DEHS), triisodecyl benzene-1,2,4-tricarboxylate (TC) were used as lubricants. It is shown by ATR IR-spectroscopy of that the common thing for the studied oils is that the C=O and C-O groups participate in the formation of boundary films in these oils. The addition of substances, active in aldol condensation reactions, into lubricants does not accelerate the formation of ... Read More

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