Polymer block materials usually have good lubricating properties and their nano particles as lubricants are well anticipated. However, the preparation processes of polymer nanoparticles are ...complicated and their applications are confined. The evaluation of particles size and preparation process of polyvinylidene fluoride (PVDF) nanospheres are described. Reducing the number of PVDF chains when forming a crystal ball does often make the diameter smaller. The preparation process undergoes crystal nucleation, crystal growth and separation, to form nano particles. In this study, PVDF nanospheres were prepared under acetanilide (AA) solvent, which played an important role to separate and disperse PVDF nanospheres. Meanwhile, TGA, FT-IR, XRD and XPS characterizations revealed that AA was inside the PVDF nanospheres. In order to obtain pure PVDF nanoparticles, AA was washed by anhydrous ethanol. A strategy was proposed to promote the preparation method. Polymer nanoparticles were stably dispersed and their agglomeration was controlled. In the present work, a series of tribological tests were applied to evaluate the lubrication effect of PVDF nanoparticles. The results manifested that PVDF nanoparticles with low concentration possessed good lubricating property because of their film formation on the contact surface. The lubricating mechanism of PVDF nanoparticles was illuminated. The current study has potential applications in preparing polymer nanoparticles with good lubrication.
This paper reports a novel work on the synergetic effects of microscale surface texturing and lubricant friction modifier additive of molybdenum dialkyldithiophosphate (MoDDP) subject to both flooded ...and starved lubrication conditions. The experiments were performed on reciprocating ball-on-disk friction in GTL8 base oil with and without MoDDP. In the flooded lubrication condition, the test results demonstrated that the presence of the MoDDP additive contributed to lower friction coefficients and also more pronounced effect of surface textures on friction than in the case of the bare base oil. In the starved lubrication experiments, textured and texture-free surfaces in the oils with and without MoDDP additive were tested until an abrupt rising of friction coefficient was detected. The results showed that the magnitude of friction coefficient before terminating each test was the almost same for various tests, while the endurance time in different test conditions was significantly different. The textured surface exhibited longer endurance time than the texture-free surface, especially when the MoDDP additive was used. The mechanism of the synergetic effects of surface textures and MoDDP additive has been discussed based on the experimental observations in the following sections. This study provides a new idea for the application of surface texture in boundary lubrication when lubricant additive is contained in the lubricating oils.
Bubbly oil lubrication is a type of lubrication method. However, the lubrication model of the bubbly oil has not been thoroughly considered. This paper aims to investigate the modelling for bubbly ...oil lubrication considering the interfacial effect and thermal effect, and a theoretical model is established based on the theory of multiphase mixtures. The interfacial and thermal effects on the static characteristics of a thrust bearing are analyzed. A test rig for the thrust bearing is developed to measure the static characteristics of the bearing under bubbly oil lubrication. The results show that the bearing static characteristics, i.e. bearing temperature rise, film thickness, friction torque, and volume flow, increase with consideration of three interfacial effects; the bearing temperature rise increases but the film thickness, friction torque, and volume flow rate decrease with consideration of the three thermal effects; the thermal effect on the bearing static characteristics is greater than the interfacial effect.
The passivation of hydrogen atoms and the conformation of textured surfaces under oil-lubricated conditions are effective strategies to obtain amorphous carbon (a-C) films with extremely low ...friction. It is critical to understanding the influence mechanism of selective surface hydrogenation on the tribological behaviors of textured a-C film under oil-lubricated conditions. In particular, the interactions of hydrogen atoms and lubricants are confusing, which is enslaved to the
in situ
characterization technique. The reactive molecular dynamics (RMD) simulations were conducted to analyze the friction response of textured a-C films with selective hydrogenation surfaces under oil-lubricated conditions. The results indicate that the existence of hydrogen atoms on specific bump sites significantly decreases the friction coefficient (
μ
) of textured a-C film, which is highly dependent on the surface hydrogen content. The repulsion between hydrogen atoms and lubricant molecules prompts the formation of a dense lubricant film on the surface of the mating material. Interestingly, with the enhancement of the surface hydrogen content, the passivation of the friction interface and the repulsion between hydrogen atoms and lubricants play dominant roles in reducing the friction coefficient instead of hydrodynamic lubrication.
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This article describes the experimental bench simulating the operation of thrust bearings of the main circulation pump (MCP) of powerful power plants. The coolant moves in them at high speeds ...(5–10 m/s), at high pressure (up to 150 × 10
5
Pa) and temperatures up to 300°C. This entails the requirements for increased reliability of this unit. The bench was adapted for testing both when the bearing is lubricated with oil and when lubricated with water. The substitution of mineral oils with water became possible thanks to a comprehensive improvement of the bearing through the introduction of new antifriction materials and design solutions. The bench was also equipped with measuring systems for recording the moment of resistance to the rotation of the disk, the rotational speed of the disk, the angular velocity of the disk, and the temperature field near the working surfaces of the thrust bearings. The startup–rundown operating regime was programmed with a special software function. As a result of the studies, it was shown that simulating the main rundown stage on a test bench when a thrust bearing is operating in a water-filled volume cannot provide a comprehensive assessment of the performance of the main thrust bearing, since under operating conditions the lubrication process may be disrupted due to partial drainage of the bearing, leading to lubrication starvation, a sharp deterioration in heat dissipation, and damage. These phenomena must be carefully studied on real objects.
In tandem hot strip rolling mills, different friction between the rolls and the strip material on the upper and lower strip surface can occur due to asymmetric surface temperatures or different ...conditions of oil lubrication. To capture these effects, this paper presents a hydrodynamic roll gap model with asymmetric friction. Based on similarities between the rolled material and viscous fluids, fluid mechanics theory is used to derive this model. Due to the nature of this model, the influence of the rolling speed is inherently taken into account, which allows an accurate prediction of the rolling force and the forward slip. As an analytic solution for the hydrodynamic roll gap model is available, it is well suited for online applications in rolling plants. For validation of the proposed model, an experiment with asymmetric work roll roughness was performed. A specimen of steel strip with copper pins inserted was repeatedly rolled to visualize the material flow inside the roll gap for multiple passes. The resulting deformed copper pins were cut out of the strip and show good agreement with the deformation profiles calculated by the developed model.
Theoretical analyses of the kinematics of a single-nut double-cycle ball screw are made in the present study. An adjustment in the preload can be achieved by generating an offset
λ
on the center ...pitch of two ball tracks. The critical load, which is very slightly higher than the preload, becomes the border of two axial load subregions. The contact kinematics for the axial load applied in each of these two load subregions are analyzed for these two ball tracks. Several parameters pertinent to the frictional forces formed at the ball–nut contact areas and the mechanical efficiency of a ball screw can thus be derived for these two axial load subregions. The theoretical frictional forces and thus the resulting mechanical efficiencies obtained by considering the oil lubrication are compared with that without oil lubrication. Experimental results of mechanical efficiency were also obtained from the performance tests of a ball screw; they show the behavior varying with an axial load quite similar to that exhibited in the theoretical solutions. The gaps in mechanical efficiency formed in a ball screw without oil lubrication are greatly reduced when considering the oil lubrication. This feature is consistent with the experimental results.
The objective of the research work was to study the potential of commercial ceramics such as Al
2O
3, Al
2O
3–ZrO
2 and SiC in pairing with steel 100Cr6 and laser-assisted deterministic ...microtexturing of the flat functional surfaces as design element for fast running friction systems, such as multiple disc clutches, under unidirectional oil lubricated sliding. A more fundamental part of the study was oriented towards understanding of the effect of microtexturing on mechanisms at mixed or boundary lubrication and development of lubricating oil film in the contact area. Experiments were carried out with pellet/disc geometry at relatively low velocities ≤0.3
m/s and normal loads ≤10
N using a model test with an attached microscope for in situ observation of the contact area. In the second part, friction behaviour of the different ceramic materials with and without microtexturing was characterised using a friction test rig at sliding velocities up to 10
m/s and normal loads ≤60
N under more practical-oriented conditions. Results showed that frictional behaviour was significantly influenced by the ceramic material and features of microtexturing, e.g. dimples, channels, width, depth and area coverage fraction. Improved understanding of operating mechanisms and design rules of microtexturing for controlling friction coefficient at practical sliding systems was obtained from a descriptive model.
As rolling bearings are widely used in various machines, there is a strong need to detect any problems as early as possible. Although vibration analysis is commonly used in the diagnosis of rolling ...bearings, it is possible that the failure of such bearings might be detected earlier by an acoustic emission (AE) technique. Methods for detecting potential fatigue damage in a thrust ball bearing by AE signal analysis and by vibration analysis were compared. For the AE signal analysis, the maximum amplitude and the frequency spectrum were used to detect and identify fatigue damage in the bearing. Features of AE signals detected when a defect was artificially formed on the raceway surface of a bearing by using a Vickers hardness tester were also examined. The AE technique detected initial cracks due to fatigue damage earlier than the vibration technique. Additionally, AE signals were always detected during bearing fatigue tests, but the AE signals detected during the running-in process, crack initiation, crack propagation, and flaking all contained different frequency components. Furthermore, the correlation map between the frequency spectra of AE signals and deformation and fracture phenomena (friction and wear modes) was updated by adding the new findings of this study.
The novel proposal of Wang’s triboelectric nanogenerator (TENG) has inspired extensive efforts to explore energy harvesting devices from the living environment for the upcoming low-carbon society. ...The inevitable friction and wear problems of the tribolayer materials become one of the biggest obstacles for attaining high-performance TENGs. To achieve super-low friction electrification of the TENGs, the tribological and electrical behaviors of the sliding-mode TENGs based on polytetrafluoroethylene (PTFE) films and metallic balls under both dry friction and liquid lubrication conditions were investigated by using a customized testing platform with a ball-on-flat configuration. Most interestingly, a super-low friction coefficient of 0.008 was achieved under graphene-doped silicone oil lubrication. The corresponding wear rate of the PTFE film was drastically decreased to 8.19 × 10−5 mm3/Nm. Simultaneously, the output short-circuit current and open-circuit voltage were enhanced by 6.8 times and 3.0 times, respectively, compared to the dry friction condition. The outstanding triboelectrical performances of the PTFE film when sliding against a steel ball are attributed to the synergistic lubricating effects of the silicone oil and the graphene nanosheets. The current research provides valuable insights into achieving the macro-scale superlubricity of the TENGs in practical industrial applications.
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