Formation Of Lubricating Film Research Articles

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.

Preparation of Al2O3/Ti(C,N)/ZrO2/CaF2@Al(OH)3 Ceramic Tools and Cutting Performance in Turning.

Aiming at the contradiction between the lubricating performance and mechanical performance of self-lubricating ceramic tools. CaF2@Al(OH)3 particles were prepared by the heterogeneous nucleation method. An Al2O3/Ti(C,N) ceramic tool with CaF2@Al2(OH)3 particles and ZrO2 whiskers was prepared by hot press sintering (frittage). The cutting performances and wear mechanisms of this ceramic tool were investigated. Compared with the Al2O3/Ti(C,N) ceramic tool, the Al2O3/Ti(C,N)/ZrO2/CaF2@Al(OH)3 ceramic tool had lower cutting temperatures and surface roughness. When the cutting speed was increased from 100 m/min to 300 m/min, a lot of CaF2 was smeared onto the surface of the ceramic tool, and the flank wear of the Al2O3/Ti(C,N)/ZrO2/CaF2@Al(OH)3 ceramic tool was reduced. The main wear mechanisms of the Al2O3/Ti(C,N)/ZrO2/CaF2@Al(OH)3 ceramic tool were adhesive wear and micro-chipping. The formation of solid lubricating film and the improvement of fracture toughness by adding ZrO2 whiskers and CaF2@Al(OH)3 were important factors for the Al2O3/Ti(C,N)/ZrO2/CaF2@Al(OH)3 ceramic tool to have better cutting performances.

Influence of the fatty acid profile on the lubricating film formation in micro-milling process on 7050-T7451 aluminum alloy

This work studies the technical performance of vegetable-based metalworking fluids as a more environment-friendly alternative for micro-milling on 7050-T7451 aluminum alloy. Micro-milling investigations were performed using two vegetable-based oils, two emulsions prepared with the same vegetable-based oil and a commercial emulsion for comparison. It was noted that the vegetable-based oils with high oleic fatty acid profile provide better lubrication films than mid-oleic fatty acid profiles. However, the wear of the cutting tools is slightly more pronounced when the high oleic oil was used. When these oils were used for the preparation of vegetable-based emulsions, the high oleic emulsion presents better lubricating potential and provides high surface quality than the mid-oleic emulsion. However, the wear of the cutting tool was similar. The vegetable-based metalworking fluids showed similar performance than the commercial reference. Therefore, the oil with high oleic fatty acid profiles presents good technical performance and can be used in vegetable-based metalworking fluids formulations.

Interactions of Ethanol with Friction Modifiers in Model Engine Lubricants

When employed as an engine fuel, ethanol can accumulate in the lubricant during use. Previous work has shown that ethanol contamination affects friction and elastohydrodynamic lubrication (EHL) film formation, and also the growth and stability of anti-wear tribofilms. The present work uses spacer-layer ultrathin interferometry and MTM tests to investigate how ethanol (both hydrated and anhydrous) interacts with friction modifiers in model lubricants. Small proportions (5 wt %) of ethanol were added to solutions of friction modifiers (one MoDTC and three organic friction modifiers) in a Group I base oil. For the three organic friction modifiers, the presence of ethanol promoted the formation of thick viscous boundary films so that very low friction coefficients were measured at low entrainment speeds. For the MoDTC additive, the presence of ethanol prevented the formation of a low friction film at low speeds at 70 °C, but this effect disappeared at 100 °C, probably due to ethanol evaporation.

Polydopamine-Assisted Immobilization of Chitosan Brushes on a Textured CoCrMo Alloy to Improve its Tribology and Biocompatibility.

Due to their bioinert and reliable tribological performance, cobalt chromium molybdenum (CoCrMo) alloys have been widely used for articular joint implant applications. However, friction and wear issues are still the main reasons for the failure of implants. As a result, the improvement of the tribological properties and biocompatibility of these alloys is still needed. Thus, surface modification is of great interest for implant manufacturers and for clinical applications. In this study, a strategy combining laser surface texturing and chitosan grafting (mussel inspired) was used to improve the tribological and biocompatible behaviors of CoCrMo. The microstructure and chemical composition were investigated by atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy, respectively. The tribological properties were discussed to determine their synergistic effects. To evaluate their biocompatibility, osteoblast cells were cocultured with the modified surface. The results show that there is a distinct synergistic effect between laser surface texturing and polymer brushes for improving tribological behaviors and biocompatibility. The prepared chitosan brushes on a textured surface are a strong mechanism for reducing friction force. The dimples took part in the hydrodynamic lubrication and acted as the container for replenishing the consumed lubricants. These brushes also promote the formation of a local lubricating film. The wear resistance of the chitosan brushes was immensely improved. Further, the worn process was observed, and the mechanism of destruction was demonstrated. Co-culturing with osteoblast cells showed that the texture and grafting have potential applications in enhancing the differentiation and orientation of osteoblast cells.

Branched polyethyleneimine modified carbon nanoparticles as the effective additives of water lubrication

Branched polyethyleneimine (PEI) modified carbon nanoparticles (CNPs-PEI) with an average particle size of 20.1 nm were facile synthesized by hydrothermal treatment of citric acid and PEI. The PEI and oxygen-containing groups on CNPs-PEI endowed them with excellent dispersion stability in water. The tribological properties of CNPs-PEI as the water-based additives were evaluated under the four-ball mode, steel/steel contact and fixed load of 40 N by varying additive concentration. Amazingly, adding only 0.15 wt% of CNPs-PEI made the mean friction coefficient and wear volume of base liquid reduced by 53.4% and 94.9%, respectively, reflecting that the CNPs-PEI could be an effective additive of water lubrication. The wear scar surface analyses indicated that CNPs-PEI as additives promoted the formation of boundary lubrication films on the rubbing surfaces by mending and depositing effects, directly accounting for the distinguished friction-reducing, antiwear and oxidation resistance properties of CNPs-PEI.

Performance evaluation of graphene oxide nanosheet water coolants in the grinding of semiconductor substrates

The use of coolants is normally required in the grinding of most of the engineering materials as it can significantly affect the ground surface quality and machining efficiency. Presently, in manufacturing industries, water or water emulsion is often used, but water has low viscosity and lubricity, which cannot provide sufficient lubrication, and the use and discharge of waste emulsion coolants is of environmental concern. In this study, water based coolants containing graphene oxide (GO) were developed to replace water or water emulsion, which is environmentally friendly. The lubrication characteristics of the GO coolants was investigated, and their grinding performance was systematically evaluated in terms of grinding force, force ratio and ground surface/subsurface damage. The experimental results showed that the GO coolants would significantly improve the lubrication with a much lower friction coefficient compared with water and emulsion coolants. The use of a 0.1 wt% GO coolant substantially reduced the tangential grinding force, and improved the surface quality in the grinding of Si and GaAs substrates. The improved grinding performance was attributed to the formation of a dynamic lubricating film of GO at the wheel-substrate interface.

Effect of boron-nitrogen modified soybean oil additive on biodegradability, anti-oxidation property, and lubricity of rapeseed oil

Two novel boron-nitrogen modified soybean oil additives with different length of chain structures (abbreviated as BNS1 and BNS2) were synthesized. The thermal stability of BNS1 and BNS2 was evaluated by thermo-gravimetric analysis. The effect of the as-synthesized additives on the biodegradability, anti-oxidation property, and lubricity in rapeseed oil was evaluated by respective standard method. Moreover, the morphology and tribochemical characteristics of the worn surfaces were examined by scanning electron microscope assembled with energy dispersive spectrometer. The results indicated that BNS1 and BNS2 both possess good thermal stability; BNS1 slightly impairs the biodegradability of rapeseed oil, but BNS2 facilitates the biodegradability of rapeseed oil. BNS1 and BNS2 could improve the anti-wear and friction-reducing performance of the rapeseed oil, but BNS1 exhibited better anti-wear ability as compared to that of BNS2, BNS2 exhibited better anti-wear ability in reducing friction coefficients as compared to that of BNS1. The enhanced anti-wear and friction-reducing abilities of rapeseed oil were ascribed to the formation of a composite boundary lubrication film due to the strong adsorption of BNS1 or BNS2 and rapeseed oil onto the lubricated surfaces and their tribochemical reactions with metal surfaces. BNS1 and BNS2 could both facilitate the anti-oxidation properties of the rapeseed oil.

Study of the Conditions for the Formation of an Adsorption Lubrication Mode of Heavily Loaded Friction Couples with Modeling in a Laboratory Setup

Abstract—The mechanism of contact interaction of a heavily loaded friction pair in the presence of a lubricant at the contact is investigated. The results of tribological studies aimed at studying the influence of volumetric parameters of a lubricant at the time of friction and wear are presented. The adhesive ability of the lubricant was studied. It was concluded that the formation of a stable lubricant film is more influenced by the volume of lubricant supplied, which makes it possible to control the type of lubrication in contact and the amount of wear of samples under study. An explanation is proposed for the negative effect of the action of a lubricant supplied in large quantities.

Wetting Behavior and Tribological Properties of Polymer Brushes on Laser-Textured Surface.

Polymer brush layers can act as effective lubricants owing to their low friction and good controllability. However, their application to the field of tribology is limited by their poor wear resistance. This study proposes a strategy combining grafting and surface texturing to extend the service life of polymer brushes. Surface microstructure and chemical composition were measured through scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Water contact angles were measured to evaluate the surface wettability of the grafted silicon-based surface texture. Results showed the distinct synergistic effect between polymer brushes and laser surface texturing (LST). The prepared polymer brushes on textured surface can be a powerful mechanism for friction reduction properties, which benefit from their strong hydration effect on the lubrication liquid and promote the formation of a local lubricating film. Moreover, the wear life of polymer brushes can be immensely extended, as micro-dimples on the textured surface can effectively protect the polymer brushes. This study presents a method to enhance the load-bearing capacity and wear resistance of the grafted surface of polymer brushes.

Friction reduction and viscosity modification of cellulose nanocrystals as biolubricant additives in polyalphaolefin oil

With the increasing requirement of environmental protection, the development of lubricating materials with non-toxicity and good biodegradability becomes more and more significant. As the novel green nanomaterial derived from natural cellulose, cellulose nanocrystals (CNCs) in the present work were prepared from native cotton and added into polyalphaolefin (PAO) base oil as the lubricant additive. To improve the compatibility of CNCs with PAO, the surface of CNCs were grafted by stearoyl chains, which entangled with polyolefin chains and led to a good dispersibility and stability of the colloidal solution. This hybrid oil with the elevated viscosity improved the formation of lubricant film in the boundary lubrication regime. Combining with the mending effect of CNC particles on the surface roughness and scars, both the friction and the wear were dramatically reduced. Specifically, the introduction of 2 wt% modified nanocrystals (mCNC) in PAO base oil reduced the coefficient of friction (COF) by 30%. The results of this study suggest that cellulose nanocrystal is a promising ecofriendly and effective lubricant additive.

Superlubricity in EHL Contacts with Water-Containing Gear Fluids

Fluid friction in elastohydrodynamically lubricated (EHL) contacts depends strongly on the lubricant considered. Synthetic oils can have significantly lower fluid friction than mineral oils. Water-containing fluids have the potential to significantly reduce fluid friction further. The aim of this study is to investigate the film formation and frictional behavior of highly-loaded EHL contacts with water-containing fluids. Comparisons are made with mineral and polyalphaolefin oils. Measurements at an optical EHL tribometer show good lubricant film formation of the considered water-containing gear fluids. Measurements at a twin-disk test rig show coefficients of friction smaller than 0.01, which is referred to as superlubricity, for all considered operating conditions.

Improved biodegradability and tribological performances of mineral lubricating oil by two synthetic nitrogenous heterocyclic additives

Purpose This paper aims to understand the influences of tris (2-hydroxyethyl) isocyanurate oleate and oleic acid tris (2-hydroxyethyl) isocyanurate phosphate ester on biodegradability and tribological performances of mineral lubricating oil. Design/methodology/approach Tris (2-hydroxyethyl) isocyanurate oleate and oleic acid tris (2-hydroxyethyl) isocyanurate phosphate ester were prepared and characterized by Fourier transform infrared spectrometer. The biodegradability and tribological properties of neat oil and its formulations were studied on a tester for fast evaluating biodegradability of lubricants and a four-ball tester, respectively. The worn surfaces were investigated by scanning electron microscope and X-ray photoelectron spectroscope. Findings Tris (2-hydroxyethyl) isocyanurate oleate and oleic acid tris (2-hydroxyethyl) isocyanurate phosphate ester both improved markedly the biodegradability, the anti-wear properties, friction-reducing properties and extreme pressure properties of base oil. The effect of oleic acid tris (2-hydroxyethyl) isocyanurate phosphate ester was better than tris (2-hydroxyethyl) isocyanurate oleate. The improvement of tribological performances was mainly ascribed to the formation of a complicated boundary lubrication film of tris (2-hydroxyethyl) isocyanurate oleate and oleic acid tris (2-hydroxyethyl) isocyanurate phosphate ester on the friction surfaces. Originality/value This paper has indicated that tris (2-hydroxyethyl) isocyanurate oleate and oleic acid tris (2-hydroxyethyl) isocyanurate phosphate ester effectively improve the biodegradability and tribological performances of mineral lubricating oil. Promoting biodegradation of mineral lubricant by additives is very significant for the development of petroleum-based biodegradable lubricants. These two additives not merely improve the tribological performances; more importantly, they improve the ecological performances.

An Experimental Study on Film Thickness in a Rolling Bearing for Fresh and Mechanically Aged Lubricating Greases

The lubricating film formation of greases has been widely studied using single contact ball-on-disc configurations. However, other than for oil, the film formation with grease is governed by starvation, which in a full bearing is clearly different from that of the single contact. In this paper, film thickness measurements for various greases in a shielded deep groove ball bearing will be presented. The results were obtained using an in-house-made film thickness measurement rig based on the ‘electric capacitance method’. It will be shown that the film thickness may deviate from the theoretical elastohydrodynamic film thickness calculated from the base oil and that the film thickness is not constant in time. It will also be shown that the film thickness for longer times is not only determined by the classical properties such as oil viscosity and grease bleed but also by shear degradation of its microstructure.

Effect of ultrasonic vibration on tribological behavior of carbon-carbon composite

Abstract The demand of carbon/carbon composite material is continuously growing in many fields. However, difficulties are easily faced during wear process such as micro crack, fiber breakage and delamination. This study attempts to improve friction behavior of carbon/carbon composite material by using of ultrasonic vibration. Based on experimental results, it is raveled that ultrasonic vibration provides more excellent tribological properties. Obvious reduction in friction force and surface damages is obtained with ultrasonic vibration. Moreover, ultrasonic vibration also produces small size particles, which is more effective in lubrication film formation. In addition, due to reduced friction force and excellent heat dissipation, lower friction temperature is achieved. Finally, it appears that ultrasonic vibration is beneficial to improve friction behavior of carbon/carbon composite materials.

A systematic review on correlation between biochemical and mechanical processes of lubricant film formation in joint replacement of the last 10 years

AbstractThis study provides a systematic review of the synovial and simulated body fluid research for the last 10 years (2006 to 2016). In particular, biochemical and mechanical properties of synovial fluid after joint replacement are focused, namely, the chemical composition of the formed lubricating film and structural changes of the associated proteins under mechanical loading. In summary, the formation of the film depends on pH, viscosity, and concentration of the solution, static, sliding, and rolling conditions and other factors related to the joint replacement. However, chemical changes of the synovial fluid proteins after the joint replacement are rarely addressed and require further attention. To this end, we provide a preliminary study of selected proteins within the synovial fluid using Raman spectroscopy. We conclude that chemical analysis together with the analysis of mechanical and biological properties of the synovial fluid after total joint replacement will help in comprehension of the process.

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.

Observation of lubrication mechanisms in knee replacement: A pilot study

The present study introduces a unique experimental approach for in situ observation of lubricant film formation in knee joint replacements. A knee joint simulator was designed and equipped with optical module based on fluorescent optical method for film thickness observation. The contact between the femoral knee metal implant and real-shaped polymer insert mimicking actual contact nature is observed. The shape of the polymer insert was fabricated with respect to the shape of original polyethylene insert to ensure corresponding contact conformity. Simple solutions of albumin and γ-globulin proteins as well as its mixture were used while the film thickness was studied as a function of time considering simplified flexion/extension motion with variable load over the cycle. Adequate fluorescent markers were employed enabling to observe one particular protein during each measurement. The results showed a clear importance of the interaction of proteins since the mixtures showed different results compared to simple solutions. Especially considering albumin protein, its behaviour was substantially affected by adding γ-globulin. Moreover, a satisfactory compliance with previous findings related to hip joint lubrication in terms of the behaviour of both proteins was found. Finally, the motivation for future experimental work is highlighted.

Effect of Boron Compounds on Lubricating Film Formation

Effect of Boron Compounds on Lubricating Film Formation

Tribological investigation of Si3N4-hBN on HXLPE bearing couple: Effects of sliding velocity and contact load

In present study, the effects of sliding velocity and contact load on the tribological properties of silicon nitride based bearing couples were investigated via the pin-on-plate tests. Pure Si3N4 and its composite (20 vol% hBN content) pins were sliding against highly cross-linked polyethylene (HXLPE) discs under simulated body fluid lubrication. Moreover, the solid lubrication film forming mechanism was investigated via worn surface characterization.For Si3N4–20 vol% hBN/HXLPE bearing couple, friction coefficients and wear rates were decreased with increasing of the contact load or sliding velocity (p-values < 0.001). Two-way ANONA analysis show that these two factors are significantly correlated (p-value = 0.011). Abrasion of the polymer disc is the main wear mechanism. Interfacial lubrication is achieved via the formation of a solid lubrication film on the ceramic pin. It contains H3BO3, SiO2·nH2O, Mg(OH)2, and HXLPE wear debris (-CH2CH2-)n. In comparison, the effects of contact load and velocity on the tribological performance of Si3N4/HXLPE bearing couple are similar to that of Si3N4–20 vol% hBN/HXLPE bearing couple. However, poor quality solid lubrication films (e.g. discontinuity, rough, and uneven appearances) were observed, this may cause by the lack of hBN compound to promote the formation of H3BO3.