Traditional Lubrication Research Articles

Recent Progress in Electrically Conductive and Thermally Conductive Lubricants: A Critical Review

Electrically as well as thermally conductive lubricants have drawn considerable attention and are an emerging research topic because they have unique advantages and advanced lubrication performance over traditional lubricants such as corrosion protection and efficient heat dissipation. For instance, some components of electric vehicles (EVs) such as bearings, seals, pads and gears require conductive lubricants to avoid premature failure and electromagnetic interference (EMI) problems due to induced shaft voltages and currents. This review provides a comprehensive overview of the recent developments in conductive lubricants. The review focuses on the important aspects to enhance the thermal and electrical conductivities as well as the tribological behavior (COF, and wear rate) of conductive solid, semisolid, and liquid lubricants. The lubricants that are electrically and thermally conductive with superior tribological performances have been identified through extensive literature review and presented in tabular form. This review summarizes the effect of various additives used to improve the conductive properties of the lubricants, such as polyalphaolefin oil, hydraulic oil, paraffin oil, and mineral oil. Furthermore, the review discusses the lubricating mechanism of conductive solid and liquid lubricants to facilitate a deeper understanding. Finally, the future perspectives and the research directions for conductive lubricants are also addressed.

ECOLOGY IN TRIBOLOGY: SELECTED PROBLEMS OFELIMINATING NATURAL OIL-BASED LUBRICANTS FROMMACHINE FRICTION COUPLES

The elimination of mineral oil-based lubricants from machines has multiple beneficial effects on the naturalenvironment. Firstly these lubricants are a direct threat to the environment in the event of leaks; secondly their elimination reduces the demand for crude oil from which they are obtained. In addition, in many cases,e.g. when replacing traditional lubricants with water, friction losses in the bearings can also be reduced due tothe lower viscosity of the water, which reduces the energy dissipation in machines.On the other hand, the introduction of self-lubricating materials or water-lubricated bearings causes problemsrelated to the need to adapt the design of machines and materials used to new operating conditions and changedproperties of the lubricants. In the paper, selected examples of problems related to the use of ecologicallubricants are discussed. The high cost of PEEK based polymers resulted in the emergence of cheapersubstitutes on the market; however, in the conducted research, the substitutes presented worse properties thanthose declared by their manufacturers.

Analysis of silica gel desiccant application in fuel storage tanks model to reduce palm oil-based biodiesel degradation

The need for a cleaner and more efficient engine arises as regulations on emissions become more stringent. besides increasing pollution and inefficiency concerns, manufacturing expenses are also on the upswing. As around 20% of all the energy used goes toward reducing friction, effective lubrication is a potential solution to the issues of efficiency, emissions, and engine wear. Several nanoparticles are being tried as potential performance-enhancing additions for engine oils. By sliding, polishing, rolling, and forming a third body, nanoparticles can improve liquid lubrication and lessen the contact between sliding surfaces. Because of its unusual characteristics, hexagonal boron nitride proven itself as a viable substitute for traditional inorganic solid lubricants. There has been a lot of study on how adding hBN nanoparticles to lubricating oil affects internal combustion engines. The impact of hBN as oil nano additions on engine fuel consumption, pollutants, and wear rate is the subject of this review study. Several studies show that hexagonal boron nitride, when added to engine oil, decreases the oil’s coefficient of friction (COF) and raises its thermal conductivity. From these improvements, lower fuel consumption, higher engine performance, lower exhaust gas emission, and prolonged moving parts wear rate are achieved for an internal combustion engine. This improvement will be beneficial to both operational and economic aspects.

A Review on Bio-Lubricants as an Alternative Green Product:Tribological Performance, Mechanism, Challenges and Future Opportunities

Industries, especially those related to transportation, have relied extensively on petroleum products for lubrication, raising serious questions about the security of the world energy supply in the future. Observed that the end-products might be released back into the environment, posing major environmental risks. As a result, bio-based products have attracted increasing interest as prospective replacement to mineral-based type due to their important role in resolving the issues of pollution. With renewability and biodegradability as their greatest points, bio-based lubricants have been discovered to offer superior lubricating qualities to those of traditional mineral lubricants but currently have some undesirable qualities that need to be improved based on the literatures. Therefore, this research objective is to showcase the potential of bio-lubricants, both in terms of their environmental benefits and for technical applications, based on studies that have been published over the years. Review of the natural oil's molecular structures, physio-chemical characteristics, and lubricating ability is crucial for the creation and choice of lubricants. Owing to their accessibility in a wide range of characteristics, which are necessary for specific applications, bio-based lubricant is a possible replacement for a variety of applications, according to the primary findings. The results showed that sunflower oil improved in reducing friction and wear by 93.7% and 70.1%; and 77.7% and 74.1%, under TiO2 and SiO2 studied, against base lubricant values of 0.0511 and 11.2414 (mm3), respectively. However, to get beyond some of the restrictions such as poor low temperature and oxidative stability, adequate chemical modification is necessary in solving agglomeration challenges.

Environmentally Friendly Drilling Fluid Lubricant: A Review

The traditional drilling fluid lubricants are seriously polluted and have biologically lethal toxicity to the ecological environment. They cannot be used for a long time in the drilling site and lack thermal stability. So, the replacement of traditional lubricants with new environmentally friendly lubricants has become one of the important research directions of drilling fluid lubricants in recent years. In this Review, we highlight the state of the research for an environmentally friendly drilling fluid lubricant. Using bio-oil, synthetic esters, amides, and polyols as raw materials, the configuration mechanism, lubrication performance, and field construction status of environmentally friendly lubricants for drilling fluids in China and abroad were reviewed. After analyzing the potential of lubricants in various countries’ research, the development direction of environmentally friendly lubricants in the future is proposed, such as the modification of recycled vegetable oil, polysaccharides, alkyl glycosides, and nanometer material, for reference by relevant scholars.

Tuning the interfacial behavior of extreme pressure lubrication by stearic acid-modified TiO2 nanoparticles

The development of high-performance lubricants under extreme pressure (EP) is of great significance for reducing energy waste and protecting ecology in heavy industries such as aerospace, large machinery, and so on. Sulfurized isobutylene (SIB) has been explored as one of the most effective EP additives for oil-based lubricants and delivered promising friction-reducing performance. However, the excessive corrosion caused by SIB on the metal surface seriously reduces the instrument’s lifetime and hinders its extensive practical application. Herein, we develop stearic acid-modified TiO2 nanoparticles (SA-TiO2) as a lubricant additive to improve the EP lubrication performance of obtained composite lubricant (CL). During EP friction, the SA-TiO2 can tune the interfacial structure of tribopair and form a high-strength nano-ceramic film to improve tribological performance. Meanwhile, the SA-TiO2 can also compensate for the high wear caused by SIB, thus significantly enhancing the antiwear, friction reduction, and EP properties by 27%, 20%, and 25%, respectively, when compared with the traditional lubricant (TL) obtained by only SIB. Benefiting from the above synergistic effects, the CL can significantly lower the SIB contents while maintaining high EP performance (4900 N weld load). These findings demonstrate a promising eco-friendly lubricant and provide new insights into the mechanism study for EP lubrication.

Preparation and tribological properties of multi-layer graphene/silicon dioxide composites-based solid lubricant coatings at elevated temperatures.

The solid lubricating coatings have an important role in hot metal forming. However, traditional lubricants cannot be applied to the harsh working conditions. In this investigation, the novel solid lubricant coatings including multi-layer graphene (MLG)/silicon dioxide (SiO2) composites and sodium metaphosphate phosphate were prepared. The high-temperature tribological properties of the solid lubricant coatings were investigated by friction and wear tester. The experimental results showed that SiO2 nanoparticles were evenly grafted by sol-gel method on the surface of MLG, forming MLG/SiO2 composites. MLG/SiO2 composites presented excellent thermal stability at 800°C. In the range of 400-800°C, the average coefficients of friction (COFs) were decreased from 0.3936 to 0.3663, and then increased from 0.3663 to 0.4226. Based on the analysis of wear scar, the lubrication mechanisms of the solid lubricating coatings were proposed. The low interlayer shear of MLG and the ball bearing of SiO2 nanoparticles are the main reason for the reduction of COFs. In addition, the tribo-chemical reaction film formed on the frictional interface could protect the contact surfaces from severe damage. The findings would be beneficial for developing novel lubricants for hot metal forming process.

A low temperature nano-lubrication method for enhancing machinability in ultra-precision grinding of binderless tungsten carbide (WC)

This paper presents a low temperature nano-lubrication method, using a vortex tube to generate a low temperature grinding environment for increasing heat transfer with a mixture of nanoparticles as a nano-lubricant for reducing friction in ultra-precision grinding of tungsten carbide. The results show the method significantly reduces wheel deterioration and improves workpiece surface integrity. The arithmetical mean height (Sa) and maximum height (Sz) were reduced by 50.8% and 65.3% respectively, with wheel deterioration 57.8% lower than traditional minimum quantity lubrication. These results were obtained by optimized low temperature gas at −20 °C and MoS2/Fe3O4 nano-lubricant with mix-ratio 1:2.

Observation of enhanced nanoscale creep flow of crystalline metals enabled by controlling surface wettability

Understanding and controlling interface friction are central to many science and engineering applications. However, frictional sliding is closely related to adhesion, surface roughness, surface chemistry, mechanical deformation of contact solids, which poses the major challenge to experimental studying and theoretical modeling of friction. Here, by exploiting the recent developed thermomechanical nanomolding technique, we present a simple strategy to decouple the interplay between surface chemistry, plastic deformation, and interface friction by monitoring the nanoscale creep flow of metals in nanochannels. We show that superhydrophobic nanochannels outperforming hydrophilic nanochannels can be up to orders of magnitude in terms of creep flow rate. The comparative experimental study on pressure and temperature dependent nanomolding efficiency uncovers that the enhanced creep flow rate originates from diffusion-based deformation mechanism as well as the superhydrophobic surface induced boundary slip. Moreover, our results reveal that there exists a temperature-dependent critical pressure below which the traditional lubrication methods to reduce friction will break down. Our findings not only provide insights into the understanding of mechanical deformation and nanotribology, but also show a general and practical technique for studying the fundamental processes of frictional motion. Finally, we anticipate that the increased molding efficiency could facilitate the application of nanoimprinting/nanomolding.

Comparative life cycle analysis of environmental and machining performance under sustainable lubrication techniques

One of the issues confronting manufacturers is the requirement for establishing sustainable production methods, which poise between economic feasibility and ecological preservation. Alternative sustainable cutting fluid methods must be developed since the traditional lubricants employed in machining operations are unsustainable from the environmental impact point of view. The balance between energy-production demand and quality-productivity is required for sustainable production. In this respect, this research studies the tool life, machining efficiency, energy consumption, and carbon emission under dry, flood machining, and minimum quantity lubrication machining. This study comprises two parts: evaluation of machining characteristics in terms of tool life, machining efficiency, energy consumption, and carbon emission, and the life cycle assessment (LCA) of inventories used during machining experimentation. The outcomes of this novel work revealed an increase of 42% and 61% in tool life at a cutting speed of 185 ​m/min under flood and MQL media than dry machining. At a cutting speed of 185 ​m/min in three different lubricating conditions, the percentage increase in the efficiency was 31%, and 28% for dry, flood, and MQL machining. In MQL machining, due to more uniform lubrication than flood machining, energy usage decreases by 38%, 32%, and 27% at the rate of metal removal of 93.67, 131.68, and 152.36 ​mm3/min. Also, A decrease in CO2 emissions of 16%, 21%, and 18% was attained in MQL machining than flood machining at 185, 215, and 245m/min cutting speeds. Furthermore, this also compares life cycle inventory analysis in dry, flood, and minimum quantity lubrication. Gate-to-gate approach methodology adopted for LCA analysis of system boundaries and functional unit to examine the environmental impression through ReCipe 2016, Endpoint (H) methodology. Sustainable assessment through life cycle analysis determined that dry and mist machining are more sustainable than wet machining.

High-Temperature Wear Properties of 35Ni15Cr Fe-Based Self-Lubricating Die Materials

Hot forging dies play an important role in metallurgy, automotive, aerospace and weapons industries. However, due to the high temperature and high pressure of hot forging die and the working environment of cyclic load, the friction and wear performance of hot forging die is poor and the service life is low. The use of traditional lubricants can prolong the life of the mold, but it will cause environmental pollution, harm to workers’ health and other problems. In this paper, 35Ni15Cr Fe-based self-lubricating die material was prepared by high energy ball milling and vacuum sintering. The wear properties of the materials were studied under ball-to-disc wear conditions at 600 °C. The results show that when CaF2 content is 8 wt%, the friction coefficient and wear rate of the material are the lowest, which are 0.3 and 0.9166 × 10−5 mm2 min−1, respectively. When the load increases, the friction coefficient first increases and then decreases, but the wear rate continues to increase. The wear mechanism mainly includes abrasive wear, adhesive wear, oxidation wear and fatigue wear. The friction reduction mechanism is that CaF2 is precipitated from the self-lubricating mold material and Fe and Ni are oxidized to the boss on the wear surface. The broken boss and lubricant form a lubricating film and accumulate into a glaze layer. The material can be used in high temperature forging environment without additional lubricant.

Mill condition monitoring based on instantaneous identification of specific force coefficients under variable cutting conditions

Following the necessity of increased performance and availability requirements for manufacturing systems, research is becoming more and more attracted by monitoring solutions for cutting tools. In this paper, a robust unsupervised strategy for milling tool wear monitoring under variable process parameters and lubrication conditions is presented. The proposed method is completely unsupervised, thus not requiring any kind of training procedure, and is validated on different machine tools. The solution is based upon the online estimation of specific force coefficients (SFC) from instantaneous cutting forces in high-feed milling of Ti6Al4V workpiece. This avoids the need for continuously variable feed per tooth during cutting tests, necessitated for the application of reference literature approach. For this purpose, a novel high-feed mill mechanistic model was conceived and developed. Five run-to-failures were performed in different lubrication conditions – cryogenic and traditional lubrication – with different cutting speeds (50 m/min, 70 m/min and 125 m/min) on two different machine tools. Principal Component Regression was introduced in order to deal with the variability of the estimated coefficients. Self-starting tabular cusum control charts were implemented and demonstrated high accuracy and reliability in the prediction of notch wear phenomena as well as chipping of tool cutting edges for all the cases considered. The solution detected an out-of-control conditions ranging from 166μm to 499μm of maximum flank wear for the analysed tests. The mean prediction error with respect to the 600μm threshold is of −45% with a peak of −72%, whereas reference literature algorithms reach −57% and −66%, respectively. A sensitivity analysis of control chart threshold was performed with reference to the maximum flank wear at the detection point. In a supervised scenario, the threshold can be increased to obtain a less conservative approach: for instance, a mean prediction error of −41% was reached by doubling the threshold.

Performance of oil-soluble ionic liquids as novel lubricant additives

Two new oil-soluble ionic liquids (ILs) with the same anion but different cations, N88816-Doss (N/S) and P88816-Doss (P/S), have been synthesized in this study. Three traditional lubrication additives, T321, T204, and T306, were added to PAO10 at specified ratios; five lubricants based on PAO10 were prepared. The effect of differences in the molecular structure between the two new ILs and traditional lubricant additives was systematically studied in terms of their tribological properties. The results demonstrated that N/S significantly improved the physicochemical and frictional properties of PAO10. When N/S was added to PAO10, the friction coefficient was reduced by approximately 50 %, while the wear volume was reduced by approximately one order of magnitude. The lubrication mechanism was validated by scanning electron microscopy, energy dispersion spectrometry, and X-ray photoelectron spectrometry. The results revealed that when N/S is used as a lubricant additive, a chemically reactive film containing the active elements N and S is formed between the steel/steel friction pair. This film plays an important role in reducing friction and wear during the friction process.

Bubbles in capillaries: Relaxing traditional assumptions

<h2>Abstract</h2> The dynamics of long gas bubbles and thin liquid films in confined channels is a classical problem in fluid mechanics and has been studied extensively under the assumptions of two-dimensional (Hele-Shaw cells or axisymmetric tubes) geometries, very viscous flows, negligible inertial and gravitational effects, and isothermal conditions. However, recent engineering applications such as microfluidics, where channels present angular cross-sections, or two-phase cooling via microchannel flow boiling, where low-viscosity fluids are utilised, require relaxation of these assumptions to deliver robust design principles. This work presents new insights into bubbles and thin films dynamics that emerge when studying this flow in unconventional settings. When bubbles propagate in noncircular capillaries, liquid films are much thinner than what observed in pipes and cross-stream film drainage induces a monotonic film thinning towards the bubble rear. Inertial forces cause the appearance of undulations at the bubble rear, which are described well by augmenting the traditional lubrication theory. Gravitational forces are impactful already when the Bond number is much smaller than unity, despite Bo<1 being a popular criterion to disregard the impact of gravity. Finally, these insights are exploited to explain heat transfer trends emerging from numerical simulations of flow boiling in microchannels for thermal management applications.

Potential application of graphene nanoplatelets as a high temperature lubricant for hot rolling

Graphene has been shown to be a promising solid lubricant to reduce friction and wear of the sliding counterparts, and currently is reported to only function below 600 °C. In this study, its potential as a lubricant above 600 °C was studied using a ball-on-disc tribo-meter and a rolling mill. Friction results suggest that a reduction up to 50% can be obtained with graphene nanoplatelets (GnP) under lubricated conditions between 600–700 °C when compared with dry tests. and this friction reduction can last more than 3 min. At 800 and 900 °C, the friction reduction is stable for 70 and 40 s, respectively, which indicates that GnP can potentially provide an effective lubrication for hot metal forming processes. Hot rolling experiments on steel strips indicate that GnP reduces the rolling force by 11%, 7.4%, and 6.9% at 795, 890, and 960 °C, respectively. These friction reductions are attributed to the easily sheared GnP between the rubbing interfaces. A temperature higher than 600 °C will lead to the gasification of the residual graphene on the strip surface, which is believed to reduce the black contamination from traditional graphite lubricant.

Insights into the tribological behavior of choline chloride—urea and choline chloride—thiourea deep eutectic solvents

Deep eutectic solvents (DESs) have been considered as novel and economic alternatives to traditional lubricants because of their similar physicochemical performance. In this study, choline chloride (ChCl) DESs were successfully synthesized via hydrogen-bonding networks of urea and thiourea as the hydrogen bond donors (HBDs). The as-synthesized ChCl-urea and ChCl-thiourea DESs had excellent thermal stability and displayed good lubrication between steel/steel tribo-pairs. The friction coefficient and wear rate of ChCl-thiourea DES were 50.1% and 80.6%, respectively, lower than those of ChCl-urea DES for GCr15/45 steel tribo-pairs. However, for GCr15/Q45 steel, ChCl-urea DES decreased the wear rate by 85.0% in comparison to ChCl-thiourea DES. Under ChCl-thiourea DES lubrication, the tribo-chemical reaction film composed of FeS formed at the interfaces and contributed to low friction and wear. However, under high von Mises stress, the film could not be stably retained and serious wear was obtained through direct contact of friction pairs. This illustrated that the evolution of the tribo-chemical reaction film was responsible for the anti-friction and anti-wear properties of the DESs.

Friction-reducing and anti-wear properties of 3D hierarchical porous graphene/multi-walled carbon nanotube in castor oil under severe condition: Experimental investigation and mechanism study

Traditional lubricants fail to meet the trend of green development. Consequently, eco-friendly hybrid nano lubricants are synthesized by incorporating 0.5 wt% 3D hierarchical porous graphene (3D HPG) and 0.7 wt% multi-walled carbon nanotubes (MWCNT) nanoparticles to castor oil. The performances of nano lubricants are determined by linear reciprocating wear test, and the obtained wear marks on steel balls and plates are evaluated by depth-of-field microscopy, scanning electron microscopy, energy dispersive spectrometer and Raman spectroscopy. The results of steel balls and steel plates wear analyses are highly consistent. Characterization results for steel plates show that the 3D HPG: MWCNT (0.5:0.7) achieves a reduction in friction coefficient and wear volume up to 26% and 48% at low speed and heavy load conditions (4 Hz - 20 N, 2.7 GPa), respectively. The mechanism of friction-reducing and anti-wear at low speed and heavy load is that 3D HPG is torn into 2D graphene nanosheets due to its easy shear performance, which forms a 2D graphene nanosheets/MWCNT/2D graphene nanosheets sandwich structure to be further involved in lubrication. This rolled bearing-like synergistic effect can further reduce friction and wear. All in all, the environmentally friendly nano lubricants consisting of 3D HPG/MWCNT hybrid nanoparticles and castor oil have sufficient potential for application in the field of heavy machine parts.

High-performance lubricants in powder compaction: An overview of their benefits

In powder metallurgy, compaction is a key step of the process which determines important properties of the parts produced (e.g., density, part weight, surface finish). It follows that compaction must be efficient, stable, and repetitive. Traditional powder metallurgy lubricants include EBS wax, which has been used for decades. New research has uncovered much better products which offer several benefits, including a better lubrication performance. This enables powder mixes to offer comparable ejection performance at lower loading levels. In turn, the performance of the process is improved, due to a more stable die fill and higher apparent density. For parts producers, these benefits can generate additional value through a better quality, a more stable operation and a reduction of scrap rates, which more than compensates the higher costs of these new materials.

A short review on cooling process using compressed cold air by vortex tube in machining

In machining hard surfaces the biggest challenge is the removal of heat produced during the machining operation and the lubrication required to reduce the frictional force at the machining zone. The present paper is divided into three sections. The first section describes the introduction concepts of heat removal along with different environmental conscious machining methods. The second section discusses about the compressed air cooling method by Ranque-Hilsch vortex tube and the popular theories related to the energy separation method in vortex tube. Finally, the third section discusses about various applications of compressed air-cooling method in machining with various materials along with different machining processes and comparison with other cooling methods. This paper concludes that the separation of fluid into cold and hot in vortex tube is due to several effects simultaneously and not a single theory is able to explain it completely. Cold air-cooling system is more environment friendly, decreases the cutting force, increases the tool life, increases the surface finish, eases the chip evacuation process, nonhazardous to operator and it has the ability to replace the traditional lubrication system and a more research is needed in this direction so that the device can be adopted in practical use in industry.

Gas film lubrication method on rotation shaft seal based on contact design

PurposeWear failure happens frequently in rubber seal of high-speed rotating shaft because of the dry friction. Some traditional lubrication methods are not effective because of the restrictions on the relative high speed, temperature and others. This paper aims to present a new method of lubrication with gas film for the rotation shaft seal based on the contact design.Design/methodology/approachTo obtain the generation condition of gas film and good effect of lubrication in the contact gap between the shaft and its seal, a series of micro-spiral grooves are designed on the contact surface of rubber seal so as to obtain a continuous dynamic pressure difference.FindingsThe result is that the distribution of the gas film in the micro-gap is continuous under the design of the spiral grooves and the contact with eccentricity because of the deformation of rubber seal, which is verified through the simulation calculation and experiment test. It is confirmed that the lubrication method with gas film through designing micro-spiral grooves on the contact surface is effective, and can achieve self-adaptive air lubrication for the high-speed shaft under the premise of the reliable sealing.Originality/valueThe method of gas film lubrication is realized through designing a microstructure of spiral grooves on the rubber surface to change the contact status, which can form a mechanism of adaptive lubrication to reduce the dry friction automatically in the contact gap. For the cross-scale difference between the rubber seal and gas film, a new modeling method is presented by building the mapping relation for the split blocks and repairing technique with integrated computer engineering and manufacturing, to reduce the possibility of nonconvergence and improve the efficiency and accuracy of calculation.