Improved Dynamic Viscosity of Lubricating Oil Under Shear

Lubricant composition with reduced oil leakage, oil scattering, and improved pore permeability for applications like impregnated bearings and machine tool lubricants. The composition contains a lubricant base oil and particles with a thickener. The particles behave like a non-Newtonian fluid with low viscosity at low shear stress and high viscosity at high shear stress. This provides the benefits of reduced oil leakage and scattering while also reducing stirring resistance during operation compared to conventional lubricants. The particle size, thickener ratio, and base oil viscosity are optimized for this behavior.

Source

Lubricant composition for industrial gearboxes, particularly windmill gearboxes, comprising at least 30% polyalphaolefin base oil with a kinematic viscosity of ≤5 cSt at 100°C and at least 5% ethylene-propylene copolymer with a kinematic viscosity of 200-5000 cSt at 100°C. The composition provides improved oxidation stability and energy efficiency for high-stress gear applications.

Source

Viscosity modifier for lubricating oil and hydraulic fluid composition. The viscosity modifier comprises an ethylene-α-olefin copolymer with specific characteristics, including an ethylene molar content rate of 40-60 mol%, a rotational viscosity of 1,000-5,000 mPa·s at 150°C, and a Hasen Chromaticity of 30 or lower. The copolymer is produced using a specific catalyst system and process conditions. The viscosity modifier is used in a hydraulic fluid composition that contains a lubricating oil base oil and has a kinematic viscosity at 40°C of 28-170 mm2/s.

Source

Abstract External excitations and unbalanced rotor forces can increase vibration amplitudes and may also cause the breakdown of continuous liquid lubricant film in hydrodynamic journal bearings. The perfect isolation of the journal-bearing system from these undesirable forces and excitations are difficult. However, recent studies suggest that by utilizing advanced manufacturing techniques, smart coating materials, and highly efficient synthetic lubricants; one can improve the reliability of hydrodynamic lubricant film under such critical operating conditions. In the present study, authors observed the influence of micro-scale textures, low surface energy coatings with slip boundary condition, and pseudoplastic lubricants on the stability margin of hydrodynamic journal bearings. To perform this investigation, the unsteady thermo-hydrodynamic Reynolds equation with considering Elrod cavitation algorithm has been solved. Further, to observe variation in stability margin as compared to conventional bearings, the various dynamic characteristics such as stiffness and damping coefficients, ... Read More

Source

Grease is used as a lubricant in a wide range of fields, including bearings, because it reduces friction, prevents harmful wear of components, protects against rust and corrosion, and acts as a seal to prevent the invasion of dirt and water. Although most of the research on grease has focused on the environment inside the bearing, there has been little research on the fundamental lubrication mechanism of grease. It is known that thickeners, which keep a complex three-dimensional structure in the grease, have a significant effect on the shear characteristics of grease, and it is assumed that this is due to the orientation of the thickener structure in the shear direction. In this study, the apparent viscosity of grease in a micro-order gap was measured using our original viscometer and compared with the apparent viscosity measured with a submillimeter-order gap rheometer because grease may show different rheological properties compared to conventional measurements. In addition, the dynamic response of viscous resistance that appeared when each grease was subjected to a change in the s... Read More

Source

Lubrication theory is adapted to incorporate the large normal stresses that occur for order-one Deborah numbers, $De$ , the ratio of the relaxation time to the residence time. Comparing with the pressure drop for a Newtonian viscous fluid with a viscosity equal to that of an Oldroyd-B fluid in steady simple shear, we find numerically a reduced pressure drop through a contraction and an increased pressure drop through an expansion, both changing linearly with $De$ at high $De$ . For a constriction, there is a smaller pressure drop that plateaus at high $De$ . For a contraction, much of the change in pressure drop occurs in the stress relaxation in a long exit channel. An asymptotic analysis for high $De$ , based on the idea that normal stresses are stretched by an accelerating flow in proportion to the square of the velocity, reveals that the large linear changes in pressure drop are due to higher normal stresses pulling the fluid through the narrowest gap. A secondary cause of the reduction is that the elastic shear stresses do not have time to build up to their steady-state equilibr... Read More

Source

Due to the low viscosity of water, water-lubricated bearings are susceptible to significant wear and noise in demanding operating conditions. It has been demonstrated that a small quantity of secondary lubricating medium can improve the lubrication performance of water-lubricated contact surfaces and achieve the purpose of temporary risk aversion. As a further step, the feasibility of the proposed idea is experimentally validated on a water-lubricated bearing test bench. A numerical model that couples the NS equation and the VOF model is then developed to investigate the behavior of the flow field lubricated by pure water and water with a small quantity of the secondary lubricating medium. This model provides the predictions of important quantities such as the load-carrying capacity, the secondary lubricating medium volume fraction and the contact pressure under different lubricated conditions. The results show that the secondary lubricating medium can enter into the contact region and improve the lubrication performance of water-lubricated bearings, especially at lower shaft rotati... Read More

Source

Abstract The reduction of frictional power losses in power transmitting gears takes a crucial role in the design of energy- and resource-efficient drivetrains. Water-containing lubricants like glycerol and polyalkylene glycols have shown great potential in achieving friction within the superlubricity regime with coefficients of friction lower than 0.01 under elastohydrodynamic lubrication. Additionally, a bio-based production of the base stocks can lead to the development of green lubricants. However, one challenge associated with the application of water-containing lubricants to gearboxes is the evaporation of water and its impact on the lubricant properties. In this study, the influence of water evaporation on elastohydrodynamic friction and film thickness was investigated for three water-containing polyalkylene glycols. Two nominal water contents of 20 wt% and 40 wt% and two viscosities were considered. The results show that the friction increases continuously with higher evaporated water content, while the overall friction level remains low in nearly water-free states. A similar ... Read More

Source

This study explores the influence of fluid viscoelasticity in soft lubrication, in which elastohydrodynamic lubrication (EHL) plays an important role. Our findings reveal that introducing polymers can significantly reduce the friction coefficient, particularly for high Deborah numbers, i.e., the ratio between the polymer relaxation time and the flow residence time, due mainly to an increased minimum film height. This augmented film thickness reduces the Newtonian pressure contributions, lowering friction. The study highlights the non-linear relationship between Deborah numbers, load, and viscoelasticity effects, as well as the complex interplay between these factors in the Pipkin space analysis. These insights provide a comprehensive understanding of the fluid viscoelasticity in soft lubricated contacts.

Source

As countries prioritize climate change concerns, promoting the use of new environmentally friendly working fluids has become a common goal for the industry. In thermal systems, lubricants come into contact with these working fluids and directly affect their utilization efficiency. Therefore, investigating the effect of lubricant mixing on the physical properties of process media is essential to promote the adoption of new environmentally friendly working fluids. This paper categorizes and organizes recent research literature on working fluids and lubricants. It was aimed to comprehend the effect of lubricants on the operating characteristics of working fluids. By comparing the research methods and experimental equipment utilized in previous studies, this work analyzes the variation of basic physical properties, including miscibility, solubility, viscosity, and gas-liquid phase equilibrium. In addition, the effects of lubricant mixing in terms of heat exchange characteristics, additives, and material compatibility are also summarized. These findings provide a reference for achieving o... Read More

Source

ABSTRACT Lubricants play a crucial role in reducing friction and wear between surfaces in relative motion. Engine oil, as a lubricant, is specifically designed to minimize friction and wear between the moving parts of different equipment and machinery. Engine oil blending serves the purpose of adjusting the variety of lubricants available to meet specific performance requirements. Through blending, it is possible to tailor the characteristics of the lubricating oil, such as viscosity, stability, and additive content, to optimize its effectiveness in reducing friction, protecting engine components, and enhancing overall equipment performance. By customizing lubricant formulations through blending, manufacturers can address the diverse lubrication needs of modern engines and machinery, ensuring smooth operation, longevity, and efficiency.To enhance the quality of the lubricant and achieve the desired high-performance multi-grade engine oil, a systematic approach was followed. The process began with testing the specific gravity of the oil using a hydrometer and thermometer to ensure acc... Read More

Source

In this work, we propose a functionalised bi-viscous lubrication model to study the material properties of concentrated non-Brownian suspensions and explore the possible confinement-induced non-Newtonian effects of the lubricant in the rheological response of this type of suspensions. From tribological studies, it is well-known that even macroscopically Newtonian liquids under strong confinement might exhibit properties which deviate significantly from their bulk behaviour. When two surfaces separated by an extremely small gap (still large compared to the molecular size) are sheared, strong shear-thinning of the lubricant viscosity at low shear-rates is observed, in spite of its Newtonian-like bulk response. This is connected to a significant increase of the zero-shear-rate viscosity under extreme confinement. We start from an effective lubrication algorithm recently proposed and develop a new gap-size-dependent interparticle bi-viscous lubrication model, able to capture qualitatively the main phenomenology of confined lubricants. We solve the lubrication interaction between particle... Read More

Source

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

Source

Abstract The rheological properties of lubricating greases are determined by the viscosity of the base oil, the interaction between base oil and thickener, and the interaction between thickener particles. The contribution of the oilthickener interactions to the viscosity is well known, but the contribution of the thickenerthickener interactions has not yet been studied by employing theoretical or computational frameworks. In this paper, we use coarse-grained molecular dynamics to simulate a fibrous microstructure, and we show that the experimentally observed viscoelastic/plastic behaviour can be well reproduced. A parametric study shows that the apparent viscosity increases with increasing fibre length, fibre stiffness and thickener concentration. This is as expected, showing that this modelling approach is useful to study effects on grease rheology that are not accessible experimentally, such as impact of fibre entanglement or agglomeration.

Source

This study proposes a mathematical expression for the high-viscosity surface layer generated by the confinement of a lubricant film, which is evident in engine oil with a metallic detergent additive. The characteristics of a microtapered pad bearing lubricated by a confined high-viscosity film were clarified by solving a modified Reynolds equation for the confined high-viscosity lubricant film. The load capacity began to increase compared with that in the bulk viscosity case when the trailing gap decreased from twice the saturated high-viscosity layer thickness. The maximum value of the friction coefficient at the trailing gap near the layer thickness becomes remarkable compared with the case of the adsorbed high-viscosity layer model. Assuming that the increased effective viscosity caused by the confinement of the lubricant film is due to an adsorbed high-viscosity layer, the load capacity is significantly overestimated when the trailing gap is greater than the saturated high-viscosity layer thickness. Next, a mathematical expression of the synthetic viscosity of a lubricant with a ... Read More

Source

This paper presents a novel analytical solution for journal-bearing viscoelastic lubrication using the perturbation method. The nonlinear Giesekus model was used for the constitutive equations to study the effects of fluid elasticity, shear-thinning viscometric functions, and strain-hardening elongational viscosity of viscoelastic lubrication. The investigation focuses on the impact of characteristic parameters such as mobility factor, eccentricity ratio, and Weissenberg number on the fluid film pressure distribution, load capacity, and shear stress. Although distinguishing between the normal stress differences and extensional viscosity in mixed viscoelastic flows is complicated, we investigated the role and contribution of these two factors. By increasing the elasticity of the fluid, the portion of both mentioned parameters increases consequently. Furthermore, analyses and comparisons show the contributions of the first normal stress and elongational viscosity to the load capacity of the bearing through the stress ratio and flow type parameter for the first time. The research findin... Read More

Source

To reduce the lubrication failure of water-lubricated bearings under short-term harsh conditions, preliminary experiments have shown that temporarily supplying a small amount of lubricating oil into a bearing as a secondary lubricant can improve the load capacity of the water film therein. However, the physical flow and diffusion state of this secondary lubricant (oil) in water are unclear. Therefore, a mixed lubrication model and a volume-of-fluid model are incorporated to study the diffusion behavior of a small amount of lubricating oil in a water-lubricated bearing. The results show that there is a backflow effect in the local area inside the bearing, where the fluid velocity is in the opposite direction to the linear velocity of the shaft. This backflow effect intensifies with increasing eccentricity ratio, which enlarges the oil-free zone in the middle part of the bearing. In the convergence area at the water inlet end of the bearing, the water supply pressure and backflow effect prevent the lubricating oil from escaping. Increasing the shaft speed has a positive effect on the d... Read More

Source

Grease composition for lubricating applications like gears that provides stable grease supply and retention. The grease has a base oil of polyalphaolefin (PAO) and a soap thickener. It has a viscosity transition stress of 300 Pa or more at 25°C to penetrate contact areas, but less than 40 Pa at 100°C to prevent grease migration. Shear viscosities at 25°C and 100°C are also optimized to balance grease supply and retention.

Source

The field of EHL (elastohydrodynamic lubrication) may be the only one in science in which a model for shear-dependent viscosity would be evaluated by means other than viscometer measurements [...]

Source

We present an experimental investigation into the influence of oil viscosity on gear churning losses in splash lubricated transmission systems. The inertia rundown method was used to perform tests on a single gear within a cylindrical housing with several oils of different viscosities at several immersion depths. A complex and non-monotonic relationship between churning torque and viscosity was observed which was highly influenced by the rotational speed, with higher viscosity oils resulting in lower churning torque at higher speeds in some cases. This was attributed to a reduction in effective immersion depth due to oil being centrifugally distributed around the casing by the rotating gear, an effect that was observed to be more pronounced with higher viscosity oils. An effective immersion depth parameter, dependent on the rotational speed of the gear and the lubricant viscosity, was defined to account for this phenomenon. Gear churning losses could be better predicted using an existing empirical model when this parameter was used instead of the nominal immersion depth as is usually... Read More

Source