Lubricant Supply Research Articles

An experimental investigation of grease lubricated EHD contact subjected to normal sinusoidally variable loading

Oil lubrication of the contacts between high-elastic modulus, non-conformal surfaces is well understood in fully-flooded, steady state conditions, when there is generous supply of lubricant in the inlet and the parameters that govern the film thickness or the friction force do not vary in time. Semi-analytical or full numerical formulas have been derived which can predict the lubricant film thickness in terms of the working parameters and the properties of the materials involved. In case of lubricating greases, their semi-solid nature given by the presence of a solid phase makes the prediction of the film thickness and thus the design of various systems difficult. The equations developed for oil lubricants can be used, using the properties of the base oil however it was found experimentally that the actual film thickness deviates strongly from theoretical values, for values of the entrainment speed above a certain critical value. Grease-lubricated contacts are very important because over 90% of the second most numerous machine components that is, the rolling element bearings are lubricated with greases. An added factor of uncertainty is the variable load on the contacts between the rolling elements and the raceways, due to on one hand the passage of the former through the loaded region of the bearing and on the other due to vibrations likely to be experienced by the bearing. In this paper film thickness measurements of grease lubricated EHD contacts subjected to harmonic load variation are reported for the first time. The experiments were carried in a test rig based on optical interferometry under both steady-state and variable loading conditions. It was found that severely starved contacts, which run under very thin films, show a degree of recovery of the film thickness towards fully flooded values, depending of the frequency of the variable load and the properties of the grease.

Enhanced lubricant replenishment by angled surface velocities in EHL contacts

Effective lubricant replenishment to the lubrication track is highly expected for the purpose of lubricating film formation. In this paper, a novel lubricant replenishment mechanism is investigated. It is found that when velocities of the two bounding surfaces are angled, the lubricant adjacent to the track is efficiently moved back, and the inlet oil reservoir is enhanced considerably. The patterns of the inlet reservoir vary with disc revolutions, entrainment velocities, included angles of the surface velocities as well as lubricant feeding amount. The inlet lubricant supply and film formations by the grease are compared to those by its base oil, and the differences are analyzed from a perspective of lubricant transportations.

Application of artificial neural networks to diagnostics of fluid-film bearing lubrication

The paper deals with the problem of monitoring the complicated hydromechanical system of a rotary machine with fluid-film bearings. The prospect of accurate recognition of changes in the lubrication system, which are expressed in the appearance of air bubbles in the lubricant, is investigated. The monitoring of the state is carried out by means of high-speed measurements of shaft vibrations, lubricant pressure supply and other parameters. Measurement data are transmitted for analysis to an artificial neural network to recognize the state of the system. The developed neural network has demonstrated high recognition accuracy of more than 98 %. Some recommendations on the measurement results processing and the neural network settings are represented in the paper.

Demand planning strategies for the control of energy flexible components of machine tools

The volatility of the energy market is increasing due to the renewable energies for electricity generation. As a result the adaptation of electricity consumption to electricity generation is gaining importance. Companies can make a significant contribution by controlling their production and thus their energy consumption. Machine tools have various components such as pumps and accumulators for cooling lubricant supply which are suitable to increase the energy flexibility of the machine. In order to be able to evaluate the energy flexibility potential of individual components, strategies from production planning and control (PPC) such as demand planning were examined. Selected strategies were adapted to control the components. With a simulation of the energy consumption of a machine tool, the PPC strategies were compared by determining the energy flexible part of the components energy consumption.

Методика управления процессом принудительной подачи смазки при работе шарошечного бурового долота с герметизированными маслонаполненными опорами

Методика управления процессом принудительной подачи смазки при работе шарошечного бурового долота с герметизированными маслонаполненными опорами

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.

Reliability improvement of heavy machineries friction units

s. The demand for more sustainable agriculture promotes the need for friction parts and components with a high durability and better performance. Widely known that absence of the constant and smooth lubricant supply into the working system is the main cause of the decline in reliability. As a result, most of the time the machines work in conditions of a lubricant deficiency. Thus, the development and implementation of the direct adaptive control methods into the friction nodes could be of great importance. Moreover, this approach increases reliability and simplifies the industrial application of the similar systems.

Sliding energy of textured surfaces via pendular tests

PurposeSurface texturing can improve the tribological performance of contacting sliding surfaces under different contact and lubrication conditions, which has been proved both numerically and experimentally. This study aims to suggest a new methodology to evaluate the tribological behavior of textured surfaces using an adapted pendular scratch tester.Design/methodology/approachA Charpy-type tester was adapted to meet conditions that are relevant for sliding surfaces. The test rig was used to evaluate low carbon steel textured surfaces produced via maskless electrochemical texturing. The textures were composed of 100 pockets with an average diameter of 200 µm of and variable average depths (1.5, 3.5 and 7 µm). The tests were performed under dry and lubricated conditions for smooth and textured surfaces. The lubricated tests simulated a starved condition by applying a drop of lubricant.FindingsFor starved lubrication, surface texturing reduced the sliding energy when compared with smooth surfaces. This was attributed to the pocket’s ability to provide an additional supply of lubricant, as well as a reduced amount of plastic deformation around the pockets during sliding of the indenter. However, under dry sliding conditions, no significant effect of surface texturing was detected.Originality/valueA new evaluation methodology was proposed, using single-pass pendular sliding of a spherical indenter to measures the energy absorbed during sliding, which was referred to as sliding energy. The measurements are repeatable and can detect sliding energy differences between smooth and textured surfaces.

The Influence of Surface Texturing on the Frictional Behaviour in Starved Lubricated Parallel Sliding Contacts

Starvation occurs when the lubricated contact uses up the lubricant supply, and there is not enough lubricant in the contact to support the separation between solid surfaces. On the other hand, the use of textures on surfaces in lubricated contacts can result in a higher film thickness. In addition, a modification of the surface’s geometrical parameters can benefit the tribological behaviour of the contacts. In this article, for parallel sliding surfaces in starved lubricated conditions, the effect of surface texturing upon the coefficient of friction is investigated. It is shown that surface texturing may improve film formation under the conditions of starvation, and as a result, the frictional behaviour of the parallel sliding contact. Furthermore, the effect of starved lubrication on textured surfaces with different patterns in the presence of a cavitation effect, and its influence on frictional behaviour, is investigated. It is shown that surface texturing can reduce the coefficient of friction, and that under certain conditions, the texturing parameter could have an influence on the frictional behaviour of parallel sliding contacts in the starved lubrication regime.

Mechanochemical Reactions of Adsorbates at Tribological Interfaces: Tribopolymerizations of Allyl Alcohol Coadsorbed with Water on Silicon Oxide.

Mechanochemical reactions of adsorbed molecules at tribological interfaces can benefit or impede lubrication, depending on the type of reactions induced by the interfacial shear or friction. Shear-induced polymerization of oxidatively chemisorbed organic species can occur at tribological interfaces, and their products can mitigate the wear of the surface in the case of the intermittent cessation of the lubricant supply. In contrast, tribochemical reactions involving water molecules impinging from the ambient air could facilitate surface wear. In this study, we investigated how such processes are affected when a silicon oxide surface is exposed to the environment containing both water and polymerizable organic molecules. For the polymerizable organic moiety, allyl alcohol was chosen because it is known to have a good tribopolymerization activity and can compete with water for surface adsorption sites. The adsorbate composition can be divided into two regimes: water-rich and alcohol-rich. The tribopolymerization yield was found to be significantly enhanced, compared to the alcohol-only case, in both water-rich and alcohol-rich regimes. The coadsorbed water molecules appeared to be incorporated into the tribopolymerization product of allyl alcohol. The friction coefficient qualitatively correlated with the tribopolymerization yield. Surprisingly, a small degree of surface wear was observed in the alcohol-rich regime, although wear was completely suppressed in the water-rich regime and the alcohol-only condition. These results suggested that the wear prevention effect does not necessarily correlate with the tribopolymerization effects.

Tribological behaviour of surfaces with stepped wettability under limited lubricant supply

Abstract Using less lubricant is currently a trend in tribology design to address fuel economy and environment concerns. The present study was conducted to identify how an oleophilic lubrication track bounded by oleophobic areas achieves efficient lubrication under limited lubricant supply (LLS) conditions. Findings showed that the stepped wettability formed at the border of the oleophilic track can reduce the coefficient of friction and wear for steel ball-on-steel plate contact in a mixed lubrication regime, and the width of the oleophilic track plays an important role. Correspondingly, optical interferometry measurement showed that the stepped wettability can improve lubricant replenishment and increase the film thickness. The unbalanced interface from the stepped wettability enhances the replenishment of the lubricant on the contact track.

INVESTIGATION OF THE BEARING UNIT FOR PISTON HEAD OF CONNECTING ROD

The article investigates the bearing unit of the piston head of the connecting rod (PGSh) of 6DN 12/2x12 type diesel transport. The PGSh bearing assembly contains a two-row, non-standard needle bearing of a non-standard design. Needle bearings in the PGSh assembly are often used for the designs of high-speed small-sized two-stroke internal combustion engines. Bearing failures PGS appear as a result of wear of the working surfaces at significant speeds of rotation of the crankshaft and low loads. In order to increase durability, the production technology of its parts is improved, the quality of installation is improved and the heat sink is provided. A design, a complete analysis of the geometry and materials of which the basic elements are made is given. Distinctive features of the design are the installation of the sleeve in PGSh with a gap that provides the necessary mobility relative to the connecting rod, and rotation of the piston pin in working condition in the piston bosses. The operating temperatures of the loaded part of the raceway surface are provided only by a sufficient supply of lubricant. To lubricate the raceways and needle rollers in the bearing bush there are four radial holes. To increase productivity and reduce the cost of rounding off the sharp edges of the holes along the outer and inner surface of the sleeve, it is proposed to perform this procedure using the electrochemical method. To compare the fatigue strength of the sleeves manufactured by serial technology (manually) and using the method of electro-chemical processing, their accelerated durability tests were carried out, the results were analyzed. In the process of research, a design scheme for loading the sleeve was developed. For this purpose, a special device for fatigue tests has been manufactured. A mathematical model was compiled and the optimal choice of modes was analyzed. Studies have been carried out that make it possible to draw practically important conclusions about the fatigue strength in bending of experimental and serial bushings. It has been established that the electrochemical technology of processing the edges of the holes does not reduce the fatigue strength of steel ShKh15-Sh.

Vibration Study for a Subassembly – Part of Hydraulic Turbines

Abstract A common problem with hydraulic turbines is the rupture of turbine horizontal shaft in the area between the rotor and its bearing, caused by different stresses [1], as well as problems caused by excessive bearing wear, vibration caused by instability of lubricant film from bearings, lubrication supply interruption of hydrodynamic bearings, gripping, decrease of bearing stiffness due to fatigue of supporting structures. In addition, during operation, vibration appear depending on exciter forces or bearing type. In present paper we present an analysis of vibrations measured on a subassembly found at hydraulic turbines. For the experimental subassembly was used a straight-lined shaft, having variable cross-section, and a sliding type bearing. The tests were made for bearings of different dimensions and materials. Vibrations were measured on two axes for established case studies and results were compared.

M50 Matrix Sintered with Nanoscale Solid Lubricants Shows Enhanced Self-lubricating Properties Under Dry Sliding at Different Temperatures

Self-lubricating materials have attracted enormous interest from manufacturers and researchers around the world recently to enhance the durability and lifespan of mechanical components. Hence, the high-level objective of this study is to provide insight into how TiO2 and graphene (G) nanomaterials (NMs) could contribute toward enhancing replenishment of the self-lubricating layer on the worn surface of M50 matrix to maintain a supply of solid lubricant. Frictional samples were fabricated by spark plasma sintering (SPS), then their tribological properties against Si3N4 balls were evaluated using a pin-on-disk tribometer at various temperatures. The wear mechanisms of the rubbing surfaces were also elucidated using electron probe microanalysis (EPMA), field-emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS), three-dimensional (3D) surface profilometry, and X-ray photoelectron spectrometry (XPS). The results of the tribotests indicated that M50 manufactured with TiO2 and TiO2/G hybrid NMs presented excellent antifriction/wear properties at temperatures of 25–450 °C, in comparison with the reference material (M50 steel). This is mainly because of the nanoscale solid lubricant added into the M50 microstructure. The results highlight a novel self-lubricating technology for M50 steel sintered with NMs for use in manufacturing of mechanical components for aerospace and automobile engines.

Influence of positive texturing on friction and wear properties of piston ring-cylinder liner tribo pair under lubricated conditions

Purpose In an internal combustion engine, piston ring-cylinder liner tribo pair is one among the most critical rubbing pairs. Most of the energy produced by an internal combustion engine is dissipated as frictional losses of which major portion is contributed by the piston ring-cylinder liner tribo pair. Hence, proper design of tribological parameters of piston ring-cylinder liner pair is essential and can effectively reduce the friction and wear, thereby improving the tribological performance of the engine. This paper aims to use surface texturing, an effective and feasible method, to improve the tribological performance of piston ring-cylinder liner tribo pair. Design/methodology/approach In this paper, influence of positive texturing (protruding) on friction reduction and wear resistance of piston ring surfaces was studied. The square-shaped positive textures were fabricated on piston ring surface by chemical etching method, and the experiments were conducted with textured piston ring surfaces against un-textured cylinder liner surface on pin-on-disc apparatus by continuous supply of lubricant at the inlet of contact zone. The parameters varied in this study are area density and normal load at a constant sliding speed. A comparison was made between the tribological properties of textured and un-textured piston ring surfaces. Findings From the experimental results, the tribological performance of the textured piston ring-cylinder liner tribo pair was significantly improved over a un-textured tribo pair. A maximum friction reduction of 67.6 per cent and wear resistance of 81.6 per cent were observed with textured ring surfaces as compared to un-textured ring surfaces. Originality/value This experimental study is helpful for better understanding of the potency of positive texturing on friction reduction and wear resistance of piston ring-cylinder liner tribo pair under lubricated sliding conditions.

Effect of Oil Supply Pressure on the Force Coefficients of a Squeeze Film Damper Sealed With Piston Rings

Squeeze film dampers (SFDs) aid to both reduce rotor dynamic displacements and to increase system stability. Dampers sealed with piston rings (PR), common in aircraft engines, are proven to boost damping generation, reduce lubricant flow demand, and prevent air ingestion. This paper presents the estimation of force coefficients in a short length SFD, PR sealed, and supplied with a light lubricant at two feed pressures, Pin-1 ∼ 0.69 barg and Pin-2 ∼ 2.76 barg, i.e., low and high. Two pairs of PRs are installed in the test SFD, one set has flow conductance CS1 = 0.56 LPM/bar, whereas the other pair has CS2 = 0.89 LPM/bar. The second set leaks more as it has a larger slit gap. Dynamic load tests show that both dampers, having seal flow conductances differing by 60%, produce damping and added mass coefficients of similar magnitude, differing by at most 20%. Other experiments quantify the effect of lubricant supply pressure, Pin-1 and Pin-2, on the dynamic film pressure and force coefficients of the PR-SFD. The damper configuration with CS1 and operating with the high Pin-2 shows ∼20% more damping and added mass coefficients compared with test results for the damper supplied with Pin-1. Film pressure measurements show that the air ingestion and oil vapor cavitation coexist for operation at the low Pin-1. Computational predictions accounting for the feed holes in the physical model agree with the experimental coefficients. On the other hand, predictions from classical formulas for an idealized damper geometry, fully sealed at its ends, largely overpredict the measured force coefficients.

Effect of microhole-textures filled with graphite on tribological properties of WC/TiC/Co carbide tools

To expand the industrial application of cemented carbide, micro-EDM was utilized to machine microhole-textures on the carbide surface; graphite powder was burnished into the textured microholes. The tribological properties of the microhole-textured tool combined with graphite were investigated and compared with the conventional one by carrying out reciprocating sliding friction tests and dry machining tests. Results exhibited that the microhole-textured tool combined with graphite possessed a much lower friction coefficient than that of the conventional one in sliding tests. The cutting forces, average friction coefficient at the tool–chip interface, and rake face wear of the textured tool were reduced, and the workpiece surface quality was also slightly improved. The worn regions of carbide specimen were examined and studied, and the possible effect mechanisms for the enhancement of friction and wear properties mainly consisted of the formation of uneven graphite film by friction extrusion, reduction of actual contact length, entrapment of wear debris and supply of graphite lubricant.

Effect of Over Rolling Frequency on the Film Formation in Grease Lubricated EHD Contacts under Starved Conditions

The service life of rolling bearings is significantly affected by the lubricating film formation in elastohydrodynamic (EHD) contacts. Grease lubricated EHD contacts show a film thickness decay from a characteristic rotational speed, which is referred to as starvation. Thus, the film thickness of grease lubricated contacts differs from that of oil lubricated contacts. However, the base oil properties under fully flooded conditions are commonly assumed to estimate the operating lifetime of grease lubricated bearings, which are usually not fully flooded. Hence, this assumption results in an overestimation of the film thickness for rotational speeds in the range of starvation, which can lead to uncertainties in the bearing design. At high rotational speeds, i.e., high over rolling frequencies, starvation is likely to occur, due to insufficient lubricant supply by replenishment behind the rolling element. Therefore, the focus of this contribution is to investigate the effect of over rolling frequency, and thus replenishment time, on the lubricating film formation in starved, grease lubricated EHD contacts. The film thickness measurements were performed on a ball-on-disc tribometer, which was extended by adding a second ball specimen in front of the measuring ball. By varying the angular distance between the two contacts, the lubricant displacement can be controlled, such that the effect of replenishment time on the film formation can be determined. These investigations should help to establish an advanced understanding of the mechanisms of grease lubrication, and encourage future work with a focus on developing a method to predict the film formation in grease lubricated EHD contacts.

Modelling of the Process of the Friction Couple Contacting and Examining the Conditions of Forming an Adsorbating Monolayer on the Friction Surface Regarding the Use of a Lubricant Material

The processes of friction and wear heavily depend on the structural formation of a block, the choice of the wear-resistant substances and effective lubricant material s for them, as well as the operational conditions for the machinery. The contacting of two elastic solids, under high (p_cp>200 MPa) normal contact and shear pressure, regarding the presence of a lubricant material in the place of contact is of our special interest. Nowadays one of the most common and effective ways of achieving reliability and a longer life cycle of the contacting machine elements and machines is the use of a lubricant material. In the course of developing new lubricant material and anti-friction substances and examining the properties of the existing materials one should pay special attention to the tribological trial plants to specify the requirements and recommendations for the producers of the substances regarding the technology of their future use. That’s why, the laboratory experiments, aimed at a detailed research of the influence of the lubricant material supply on the change of the parameters at the friction contact are timely. The current paper explores the influence of modes of the lubricant material supply on the change of the triboloical parameters of the friction couple contact and its durability with the help of the method of physical modelling of the contact of a heavily loaded friction couple. It also studies the conditions of forming a resistant coating on the friction surfaces that prevents from the abrasive wear of their surface layers.

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.