Hydrodynamic Lubrication Conditions Research Articles

Ply-ply friction behavior between unidirectional thermoplastic prepreg plies during thermoforming: Characterization and modeling

The ply-ply friction behavior of unidirectional carbon fiber reinforced polyphenylene sulfide (UD CF/PPS) prepreg in thermoforming was investigated through an improved pull-through testing system. The effects of temperature, normal force and slipping velocity were considered in testing. The results indicated the existence of three key mechanisms underlying slipping: namely the resin shear, fiber–fiber contact and fiber-resin interaction. A three-stage division of the experimental curve was proposed, and several factors were defined to establish a quantitative definition of the ply-ply friction behavior. The results showed that the influence of slipping velocity is particularly evident. Its post-yield stress (12.8 kPa), steady-state CoF (0.118) and residual stress (0.705 kPa) were the highest, exhibiting the largest changes of 957.9 %, 736.9 % and 47.2 %, respectively. This indicated the strong contribution of resin in ply-ply friction. In addition, the Stribeck analysis also suggested the dominance of hydrodynamic lubrication condition in slipping. Based on the experimental results, a simple phenomenological model was proposed based on experimental curves to accurately describe the effects of processing parameters. This work presents a comprehensive characterization of the ply-ply friction behavior of UD CF/PPS prepreg in thermoforming, providing a substantial experimental foundation for the subsequent simulation research.

Molten Salt Pump Journal-Bearings Dynamic Characteristics Under Hydrodynamic Lubrication Conditions

Abstract A reliable high-temperature molten salt pump is critical for the development of Fluoride-salt-cooled, High-temperature Reactors (FHRs). By supporting the rotating journal, the appropriate journal bearing can ensure that the high-temperature molten salt pump runs smoothly and efficiently in the high-temperature fluoride salt over a long period of time. However, many bearing candidates served well for only a short period and experienced several issues. Moreover, the alignment of the molten salt pump journal bearings is a key factor for the molten salt pump's long-term steady running. In the long-term operation, a misalignment in the journal bearing can result in vibrations and excessive wear on the bearing surface of the molten salt pump. The journal bearing dynamic characteristics can be used to accurately assess the journal misalignment. Therefore, it is necessary to investigate the detailed journal-bearing dynamic behavior under the high-temperature hydrodynamic fluoride salt lubrication conditions for FHR applications. In this study, a small amplitude vibration is superimposed on a steady-running journal bearing to simulate the molten salt operating conditions. A Fortran 90 code has been written for the journal-bearing dynamic behavior analysis. The code was verified using the numerical data reported in the literature. The code is then employed to predict the dynamic coefficients of high-temperature fluoride salt hydrodynamic lubricated journal-bearing with various Sommerfeld numbers. These journal-bearing dynamic coefficients can be used to provide guidelines in the design of molten salt pumps.

Multiple Drive Shaft Fractures in Lift Oil Pumps

Abstract Several high-pressure lift oil pump failures were reported from the field. These assemblies are used to inject lubrication oil into the sliding bearings of heavy rotating turbomachinery equipment, such as steam and gas turbine rotors, often weighing in excess of a hundred tons. This ensures that the rotor shaft “floats” on a lube oil film even at low rotational speeds, when hydro-dynamic lubrication conditions have not yet been fully established. A fractured spline shaft, which was the driven shaft of one of the failed pumps, was received from the client for the determination of the metallurgical root cause of failure. The subject spline shaft failed due to torsional overload. This cracked the hardened case and initiated high cycle fatigue (HCF) cracking as secondary damage. The main fatigue cracks were nucleated at overload fractures in the hardened case, in the fillet radii at the base of the teeth of the spline shaft. No evidence of any material defects that could have contributed to the failure or could even have been causative for it was found.

Predictions of Friction Coefficient in Hydrodynamic Journal Bearing Using Artificial Neural Networks

This paper explores the influence of the frequency of shaft sleeve rotation and radial load on a journal bearing made of tin-babbitt alloy (Tegotenax V840) under hydrodynamic lubrication conditions. An experimental test of the frictional behaviour of a radial plain bearing was performed on an originally developed device for testing rotating elements: radial and plain bearings. Using the back-propagation neural network, based on experimental data, artificial neural network models were developed to predict the dependence of the friction coefficient and bearing temperature in relation to the radial load and speed. Using experimental data of the measured friction coefficient with which the artificial neural network was trained, well-trained networks with a mean absolute percentage error on training and testing of 0.0054 % and 0.0085 %, respectively, were obtained. Thus, a well-trained neural network model can predict the friction coefficient depending on the radial load and the speed.

Shape optimization of hydrodynamic textured surfaces for enhancing load-carrying capacity based on level set method

In order to maximize the load-carrying capacity (LCC) of the textured surfaces, the level set method is introduced to conduct the shape optimization of surface textures under the cavitating hydrodynamic lubrication condition. The optimized surface texture shapes are evolved by the Hamilton-Jacobi equation based on the shape derivative obtained by the shape sensitivity analysis. In the optimization procedure, the velocity regularization method and the re-initial equations are applied to make sure a smooth evolution process. The optimization method is validated by two slider bearing optimization problems. Then the optimal surface texture shapes of a textured surface and a parallel thrust bearing are analyzed. The results show that the optimization method is stable and the optimal geometries are the chevron-type shapes.

Elastohydrodynamic lubrication characteristics of surface-textured slipper bearing in an axial piston pump

This paper aimed to reveal elastohydrodynamic lubrication characteristics for surface-textured slipper bearing of axial piston pump. The proposed model was established including slipper-tilting motion and surface deformation. Further, a numerical simulation was conducted under hydrodynamic and elastohydrodyamic lubrication conditions. Numerical solutions were obtained under this lubrication conditions in terms of the film pressure, film thicknesses, and bearing stiffness. The simulation results reveal that the film pressure in EHD solution increases slightly with the growth of the area density within the range of 10–30% and then tends to remain stable. When the area density of dimple is set to 38%, the dimensionless stiffness of oil film shows the highest value. If the dimple depth is set to 0.8 μm, there exists the maximum dimensionless stiffness of oil film in EHD solution when the optimum dimple depth-to-diameter ratio is set to 0.22.

Elastic hydrodynamic lubrication analysis for a sine movable tooth drive

The sine movable tooth drive has small radial dimension such that the heat, caused by friction, becomes an important factor in deciding its load-carrying ability. It is important to determine the amount of tooth lubrication in order to reduce the heat caused by the friction. This study provides equations for the meshing performance and provides the forces for the sine movable tooth drive. Using these equations, the minimum oil film thickness for the drive system is investigated. Results show that the minimum film thickness between the movable tooth and input shaft or shell changes periodically along the input shaft rotation angle. A large movable tooth radius and a movable tooth rotation radius could increase the film thickness between the movable tooth and the input shaft or the shell. In addition, a large speed ratio could increase the film thickness between the movable tooth and the input shaft, but this would also decrease the film thickness between the movable tooth and the shell. A large sine amplitude could increase the film thickness between the movable tooth and the input shaft, but this does not change the film thickness between the movable tooth and the shell. Under normal operation speeds, the hydrodynamic lubrication condition occurs between the movable tooth and the input shaft, and the partial membrane hydrodynamic state occurs between the movable tooth and the shell.

Optimization of groove texture profile to improve hydrodynamic lubrication performance: Theory and experiments

It is well known that groove texture with a careful design can be used to enhance the load-carrying capacity of oil film under the conditions of hydrodynamic lubrication. In this study, a general parametric model was developed, and agenetic algorithm-sequential quadratic programming hybrid method was adopted to obtain the global-optimum profile of the groove texture. The optimized profiles at different rotating speeds are all chevrons. The numerical analysis results verified the effect of the optimization. In addition to the numerical optimization, experiments were conducted to validate the superiority of the optimized results.The experimental results show that the optimized groove texture can efficiently reduce the coefficient of friction (COF) and the temperature rise of the specimen. In particular, the optimized groove textures can achieve stable ultra-low COF values (COF < 0.01) under certain conditions.

A study and comparison of frictional losses in free-piston engine and crankshaft engines

Friction work in free-piston engines is expected to be lower than in crankshaft engines due to the elimination of the crank mechanism. In this paper, friction mechanisms were reviewed and compared between a free-piston and crankshaft engine of similar size. The main friction mechanisms were identified to be the piston assembly including piston rings and piston skirt, valve train system, the crank and bearing system for the CSE, and the linear electric generator for the FPE. The frictional loss of each friction mechanism was estimated and discussed. A Stribeck diagram was used to simulate the piston ring friction during hydrodynamic lubrication, mixed lubrication, and boundary condition. It is found that the FPE doesn’t show advantage on piston ring friction force over the CSE, and the frictional loss from the piston ring is even higher. While the elimination of the crankshaft system reduces the frictional loss of the FPE, and the total friction loss of the FPE is nearly half of the CSE.

ANALYSIS OF THE LOAD-CARRYING CAPACITY OF A HYDRODYNAMIC WATER-LUBRICATED BEARING IN A HYDROELECTRIC POWER PLANT

The paper presents an analysis of the load-carrying capacity of a historic hydrodynamic water-lubricated radial bearing of an unconventional segment design installed in the Braniewo Hydroelectric Power Plant. The aim of the calculations was to determine whether the bearing operates in the conditions of hydrodynamic or mixed lubrication, as well as to establish the optimal geometry of the axial grooves allowing for the highest load-carrying capacity. Computer simulations were performed using proprietary ARTbear software developed at Machine Design and Vehicles Department of Gdańsk University of Technology. The calculation results led to the creation of the technical documentation of the bearing’s modernization serving to increase its lifespan and reliability.

Contact Problem for a Viscoelastic Half-Space and a Rough Rigid Cylinder under the Conditions of Hydrodynamic Lubrication

A model has been proposed for use in studying the combined effect of the roughness of a rigid punch and the viscous properties of a base separated by a thin lubricant layer exerted on the characteristics of contact interactions and the sliding friction force. The problem of the motion of a thin a lubricant layer between a fixed rigid cylinder with a regular relief, as well as the surface of a moving viscoelastic half-space, the rheological properties of which are described by an integral operator with an exponential creep kernel, has been considered. The pressure and thickness of the lubricating layer, as well as the deformation component of the frictional force depending on the sliding velocity, have been analyzed. A comparison of the results of solutions of contact problems for viscoelastic and elastic rough bodies in the presence of a lubricant has been presented.

Evaluation of Lubricating Properties of Diesel Based Fuels Micro Emulsified With Glycerin

The mineral diesel oil sold in Brazil, due to environmental reasons; presents sulfur concentration of 10 ppm, which causes a deficiency of lubricity, since sulfur is one of the chemical species that gives a good lubricating characteristic. Poor lubricity affects performance and causes failure of engine parts. This study aimed to evaluate the use of glycerin as an antiwear additive by means of tribological tests of the mineral diesel S10 B7 and 10 formulations of diesel based fuels, micro emulsified with 0% (distilled water), 7.5% and 15% of glycerin solution. The formulations were subjected to lubricity tests on HFRR (Hight Frequency Reciprocating Rig) under hydrodynamic lubrication conditions, according to the ASTM D-6079 standard. The results showed that the increased concentration of glycerin added to diesel S10 B7 contributes to improved lubricity and wear reduction

Static Characteristics of Journal Bearings With Square Dimples

Surface texturing is a technique for improving frictional and hydrodynamic performances of journal bearings because microtextures can serve as reservoirs for oil or traps for debris and may also generate hydrodynamic pressure. Over the past two decades, many researchers have experimentally demonstrated that texturing of various tribological elements can reduce friction force and wear, contributing to improvement of lubrication performance. Some numerical studies have examined the hydrodynamic lubrication conditions and reported that surface texturing affects the static characteristics of journal bearings, such as their load carrying capacity and friction torque. However, the validity of these numerical models has not been confirmed because of a lack of experimental studies. This study proposes a numerical model that includes both inertial effects and energy loss at the edges of dimples on the surface of a journal bearing in order to investigate the bearing's static characteristics. Experimental verification of journal bearings is also conducted with a uniform square-dimple pattern on their full-bearing surface. The results obtained by the model agree well with those of experiment, confirming the model's validity. These results show that under the same operating conditions, textured bearings yield a higher eccentricity ratio and lower attitude angle than the conventional ones with a smooth surface. This tendency becomes more marked for high Reynolds number operating conditions and for textured bearings with a large number of dimples.

Multiple-support shafts with journal bearings: A simulation and evaluation of their performance

As the most common example of multiple-support shafts, the crankshaft of a multicylinder internal combustion engine (ICE) resting on the supports with journal bearings operating in steady-state regimes under the conditions of hydrodynamic lubrication has been considered. It has been taken into account that the supports can be deformed elastically causing a bending of the shaft, the deviation of shaft journals, and the change in the working conditions of the bearings up to the occurrence of the regime of mixed lubrication. Methods of estimating the performance of the tribosystem have been described.

The comprehensive effect of surface texture and roughness under hydrodynamic and mixed lubrication conditions

A theoretical study is carried out to investigate the comprehensive effect of the machined roughness and fabricated textures, by solving the average Reynolds equation coupled with a mass-conservative cavitation algorithm and taking into account asperity contact. We analyzed the influence of surface roughness, which is represented by the combined root-mean-square roughness σ and surface pattern parameter γ on the optimum texture parameters including the dimple depth-over-diameter ratio and area density under hydrodynamic and mixed lubrication conditions. The results show that the effect of surface roughness on load-carrying capacity can be ignored under hydrodynamic lubrication condition. Furthermore, the optimum texture parameters under hydrodynamic lubrication condition and the optimum dimple depth-over-diameter ratio under mixed lubrication condition are determined at minimized friction coefficient, which can be taken as the same for smooth-textured surface and rough-textured surface. The corresponding minimum friction coefficient increases with increasing σ and γ, and decreasing dimple area density under mixed lubrication condition.

The Lubricity Analysis of Cutting Fluid Emulsions

The new generation of cutting fluids should have some characteristics, such as low toxicity and biodegradability. A bio-cutting fluid emulsion are an excellent option because they present those properties, as well as good mechanical performance. The present study aims to investigate the lubricity of O/W emulsions (cutting fluid emulsion), varying the concentration of anionic surfactant (1%, 2.5% and 5%) and epoxidized oil (5%, 10%, 15%, 20% e 25%). A sunflower oil was chemically modified by epoxidation reaction, then its viscosity, iodine and oxirane index, density, and acidity were characterized. The performances of the emulsions were evaluated using a tribometer HFRR (High Frequency Reciprocating Rig), under hydrodynamic lubrication conditions. The ball wear scars were analyzed using an optical microscopy. The results showed that a low concentration of surfactant promote friction and wear reduction. Based on the tribological performance, the emulsions with 5% and 10% of epoxidized oil are more suitable.

Observation of the Behavior of a New Reducting Additive under the Elasto Hydrodynamic Lubrication Condition

Observation of the Behavior of a New Reducting Additive under the Elasto Hydrodynamic Lubrication Condition

Surface crack propagation and morphology in cutting tools

Purpose – The purpose of this paper is to investigate the driving mechanisms for crack propagation regarding the related microstructures. Cracks in white etching layers have been found at the surface of submerged steel blades subjected to frictional sliding conditions. Design/methodology/approach – In-situ monitoring revealed a fluctuation between mixed lubrication and hydrodynamic lubrication conditions. One lamella including a crack tip was prepared for transmission electron microscopy (TEM) using focused ion beam milling. Transmission electron microscope analysis was performed with the aim to understand the characteristics of the crack propagation, especially considering the influence of the microstructural configuration (grain refinement, carbides, martensite and ferrite grains). Findings – The investigations have shown a grain-refined plastically deformed layer (friction martensite with grain sizes of &lt; 100 nm) which influences the propagation direction of cracks introduced at the frictionally stressed surface. Thereby, the crack propagation is dominantly parallel to the margin of the grain-refined martensitic layer at the surface and the base material. Cracks were split into side cracks what mostly appears at present carbides. In this case, the crack propagation might strike through the carbide or separate it from the matrix due to the mechanical misfit. Originality/value – For obtaining the results of this paper, a very special preparation of tribologically stressed samples was performed. Accordingly, specific findings of the crack propagation behavior under such conditions were achieved and are documented in the presented work. Moreover, the described crack propagation process is a combination of several mechanisms which occur in very limited region underneath the surface and are investigated by high-resolution TEM.

The Analysis of the High Speed Wire Drawing Process of High Carbon Steel Wires Under Hydrodynamic Lubrication Conditions

Abstract In this work the analysis of the wire drawing process in hydrodynamic dies has been done. The drawing process of φ5.5 mm wire rod to the final wire of φ1.7 mm was conducted in 12 passes, in drawing speed range of 5-25 m/s. For final wires of φ1.7 mm the investigation of topography of wire surface, the amount of lubricant on the wire surface and the pressure of lubricant in hydrodynamic dies were determined. Additionally, in the work selected mechanical properties of the wires have been estimated. It has been shown that in the drawing process under hydrodynamic lubrication by drawing speed of 25 m/s the phenomena of uncontrolled formation of the surface and the diameter of the wire appears, and in the process the compressive stresses eliminating cracks on the wire surface occur, causing further smoothing. The wires drawn hydrodynamically in speed of 25 m/s, besides clearly worse properties compared to the wires drawn hydrodynamically at speeds in the range of 5 to 20 m/s, also exhibit large dimensional variations.

수직형 저널 베어링의 유량특성에 대한 그루브 형상의 영향

Abstract As journal bearing has a sliding motion between the shaft and bearing with lubricating oil, it produces ahydrodynamic lubrication condition. Journal bearing can receive a large force because it takes a distributed load at the large friction face. As the oil groove or oil hole is made in the journal bearing surface for the journal bearingsmoothly working under a hydrodynamic lubrication condition, sufficient lubricating oil is supplied through the clearance of journal bearing. The performance of the journal bearing is changed according to the shapes, sizes andpositions of an oil groove. In this paper, the flow rate according to the oil groove shapes (triangle, semicircle and rectangle) among the various oil supply conditions was measured. The shape that discharges the highest flow rate was observed and the groove shape of optimal performance for the journal bearing was determined. The results showed that the flow rate increases with decreasing operating temperature, the influence of temperature on the flow rate decreased with increasing rotational speed, and flow rate in the triangular groove shape was greater than in othershapes.