Lubricant Particles Research Articles

Removal of magnetite particles and lubricant contamination from viscous oil by High-Gradient Magnetic Separation technique

This article presents investigations on the removal of particles from viscous lubricant oil by High-Gradient Magnetic Separation (HGMS). The study deals with the removal of magnetite particles (Fe3O4) and solid lubricant contamination from a mineral oil. The lubricant contamination particles are extracted from a used wind power plant (WPP) gear oil filter. Both particle systems are characterised regarding their particle size distribution, solid density and magnetisation. The WPP particles are analysed in terms of their chemical composition by Energy-Dispersive X-ray Spectroscopy (SEM-EDX) and Inductively-Coupled Plasma Optical Emission Spectroscopy (ICP-OES). In order to predict the separation efficiency of different matrices a theoretical approach is used. The theoretical calculation are also compared to experimental data. The experiments focus primary on the separation efficiency and grade efficiency of different matrix geometries. The concentration of the feed suspension is low (3mg/l), hence an laser particle counter is best suited for the online characterisation of the separation efficiency. In case of a single-stage arrangement, the removal of magnetite particles from lubricant oil showed that it is more successfully done with the fine matrix than with the coarse matrix. Using a multi-stage separation chamber, the removal is improved significantly compared to the single-stage processes. The investigation of magnetic separation of WPP particles was carried out with a multi-stage arrangement. Comparing the obtained separation efficiencies showed that the removal of WPP particles is not as good as that of magnetite particles. Nevertheless, the experiment showed that it is possible to separate solid lubrication contamination from an industrial gear oil to a high amount. The chemical analysis by ICP-OES of the WPP particles before and after HGMS treatment resolves that magnetically induced hetero-agglomeration occurs and that the agglomerated particles are captured on the HGMS wire mesh. The results of the experiments are compared to theoretical calculations. Their values are qualitatively in good agreement. Deviations are due to magnetic induced agglomeration, which involves particle growth and reduced magnetic susceptibility. Nevertheless, the calculation is a reliable tool in order to predict the separation efficiency and is used for the enhancement of the matrix geometry and stage number.

Effect of precursor content and sintering temperature on the scuffing resistance of sintered self lubricating steel

Abstract The production of self lubrication composites containing second phase particles incorporated into the volume of the material appears to be a promising solution. A new processing route to obtaining a homogeneous dispersion of discrete solid lubricant particles in the volume of sintered steels produced by metal injection molding (MIM) was recently presented. This new route was achieved by in situ formation of graphite nodules due to the dissociation of precursor (SiC particles) mixed with the metallic matrix powders during the feedstock preparation. Nodules of graphite (size ≤20 μm) presenting a nanostructured stacking of graphite foils a few nanometers thick were obtained. The thermal debinding, as well as the sintering, was performed in a single thermal cycle using a Plasma Assisted Debinding and Sintering (PADS) process. In this work, we present and discuss the effect of precursor content and sintering temperature on the scuffing resistance of plasma assisted debinded and sintered self lubricating steel produced by metal injection mould technique. Three different temperatures (1100, 1150 and 1200 °C) and six different SiC contents (0–5%) were analyzed. Increasing the precursor content and, as a consequence, the number of graphite nodules, produced a clear increase in scuffing resistance for all analyzed sintering temperatures. Friction coefficient was little affected by the sintering temperature. However, the scuffing resistance was greatly increased (5×) for the lower sintering temperature (1100 °C).

Lubricant ash particles in diesel engine exhaust. Literature review and modelling study

Reducing particulate emissions from diesel engines has been a concern in recent decades. The increasing use of diesel particulate filters (DPFs) has highlighted the importance of predicting ash emissions from lubricant, since ash accumulates in DPFs. Ash accumulation will increase the pressure drop across the filter, and thereby also the fuel consumption, eventually necessitating filter cleaning or replacement. This paper examines the ash transfer rate, calculated as accumulated ash divided by calculated ash consumption (oil consumption times oil ash content). Three times 500 hours of ash accumulation testing was performed on a Scania heavy-duty diesel engine; in addition, the relevant literature was reviewed. The main results of the study are: (a) the main contributor to ash particulate emissions is lubricant ash; (b) the oil ash transfer rate was found to be oil specific; testing indicated transfer rates of 38–59 per cent; (c) the slight increase in ash transfer rate when reducing the engine load indicated that the load might be dependent on the oil ash transfer rate, although the effect was clearly lower than that of the changing oil.

Variations in the friction coefficients of tablet lubricants and relationship to their physicochemical properties.

A previously described modified annular shear cell (MASC) has been used to measure the friction coefficients of some powdered tablet lubricants on a steel surface. Commonly used lubricants, as well as others belonging to the stearate group, differed in their friction coefficients at equivalent sample sizes and in the degree of their ability to reduce friction with increasing amounts when evaluated by the apparatus. In all comparisons, magnesium stearate had the lowest friction coefficient. Divalent salts of stearic acid appeared to be better than the other lubricants tested, and among themselves differed only in the extent of their ability to decrease friction. The lubricants also differed in their physical and chemical properties. On evaluation by stepwise regression analysis, such physical properties as projected surface area of lubricant particles, Martin's diameter and bulk density accounted for most of the variation in friction coefficients of the lubricants rather than moisture content or melting point. It could therefore be suggested that particle size and/or surface area parameters be incorporated in product specifications to ensure reproducible functionality.

Influence of nano-level variation of solid lubricant particle size in the machining of AISI 1040 steel

Significant advances have been made in understanding the behaviour of engineering materials when machining at higher cutting conditions from practical and theoretical standpoints. Nano-integrated manufacturing is a subject of immense interest for various sustainable engineered systems. Metal removal processes involves generation of high cutting forces and temperatures. Usage of proper lubricant is an important aspect to reduce forces and temperatures and as a whole to improve total cutting phenomena. The present investigation analyses a green, petroleum-free lubricant that is produced by mixing two environmentally benign components – canola oil and nano crystalline boric acid. To study the influence of variation of nano-level boric acid particle size and its weight percentage on the performance of proposed green particulate fluid lubricant (GPFL), various turning tests were conducted on AISI 1040 steel using tungsten carbide inserts. Variations in cutting forces, tool temperatures and surface roughness are studied. The experimental results reveal that increase of cutting forces as well as the tool temperatures with the decrease in the boric acid particle size. The surface quality of the machined surface is reduced as the solid lubricant particle size is reduced in the nano-level.

Formation of Low-Friction Particle/Polymer Composite Tribofilms by Tribopolymerization

Inorganic fullerene-like (IF) solid lubricant particles based on MoS2 or WS2 have recently gained attention in various tribological applications, for instance incorporated in coatings, porous materials, greases and dispersed in oils. However, their effect in oil can be limited often due to inadequate penetration into the contact zone. Meanwhile, tribopolymerization of monomer additives in oil have proven to be efficient to reduce wear, but without significantly reducing the friction. This investigation combines these two lubrication techniques in order to form particle/polymer composite tribofilms, aimed to give low friction and wear in high-pressure sliding contacts. A cyclic amine, caprolactam, was used as the monomer together with IF as well as normal 2H WS2 particles. Zn-DTP was used as a reference antiwear additive and poly-alfa-olefin (PAO) was used as the base oil. Reciprocal ball-on-flat sliding test results found that monomer plus particles reduced the friction by 10–50%, depending on sliding speed and type of particles, compared with particles or monomer alone. And the scattering between different tests was also considerably lower. The wear rate was also substantially reduced to a level similar to that of Zn-DTP. The particle/polymer composite tribofilms were generally much larger than the actual contact area and its thickness varied from below a few nanometres in the contact centre to several micrometers in the outer parts. Consequently, the reduced friction is believed to come from two effects: one being a trapping of particles in the contact zone, which reduces the boundary friction level; and the other a shift in lubrication regime towards EHD-lubrication due to reduced contact pressures accompanied with the formation of the composite tribofilm.

Dispersion effect and auto-reconditioning performance of nanometer WS2 particles in green lubricant

This paper reported on dispersion effect and dispersing techniques of nanometer WS2 particles in the green lubricant concocted by us. And it also researched on auto-reconditioning performance of nanometer WS2 particles to the abrasive surfaces of steel ball from four-ball tribology test and piston ring from engine lubrication test. The treated and untreated nanometer WS2 particles were analysed by infrared spectrum. And the elementary component and interior elementary distribution of abrasive surface repaired by nanometer WS2 particles were analysed by multifunction electron spectrometer. The results showed that the combinative method of ultrasonic dispersion, mechanical agitation and surface modification could improve the dispersion uniformity and stability of nanometer WS2 particles in the green lubricant effectively. And the optimal ratio of the mass between surface modifier and nanometer WS2 particles was 1: 2.5, the optimal treating time was 5 h. And IR analysis indicated that surface modifier could react with hydroxide radicals on surfaces of WS2 particles and modify the surfaces, and the long lipophilic groups on surfaces of nanometer WS2 particles could stretch in oil adequately and form steric hindrance layers between particles which prevented particles from conglomerating and depositing. In addition, tribological tests and surface analysis indicated that there were WS2 adsorption film and reaction film on abrasive surfaces during the tribological tests, which could fill and level up the furrows on abrasive surfaces. As a result, the abrasive surfaces were repaired effectively by nanometer WS2 particles.

Effects of Some Solid Lubricants Suspended in Oil Toward Controlling the Wear Performance of a Cast Iron

The present investigation deals with the examination of the sliding wear response of a gray cast iron in oil lubricated condition over a range of applied pressure. The composition of the oil lubricant was changed by adding 5.26 wt % solid lubricant particles. The solid lubricants used were graphite, talc, MoS2, and lead. The observed wear response of the samples has been substantiated through the characteristics of wear surfaces, subsurface regions, and debris particles and discussed in terms of specific response of different microconstituents, such as ferrite, pearlite, and graphite present therein. Operating wear mechanisms were assessed through the observed features of wear surfaces, subsurface regions, and debris. The wear rate increased with applied pressure. The slope of the wear rate versus pressure plots was low up to a critical pressure. This was followed by a sudden rise in the slope at higher pressures irrespective of the test environment. The frictional heating was affected by pressure in a manner practically identical to that of the wear rate. The presence of graphite, MoS2, and lead in the oil led to a substantial decrease in the wear rate and severity of frictional heating. The oil plus lead lubricant mixture was observed to offer best results in terms of reduced wear rate and lower frictional heating. This was followed by the ones containing graphite and MoS2 while talc caused the wear performance of the samples to deteriorate over that of the bare oil. However, the severity of frictional heating decreased in general in the oil containing solid lubricant particles. Seizure brought about high frictional heating and wear rate.

On the role of copper in brake friction materials

Copper is a major ingredient in friction materials used for automotive braking. The purpose of this study was to find out how copper contributes to good brake performance properties in addition to providing good thermal conductivity. Microstructural investigations of copper chips at the surfaces of brake pads revealed a zone of severe plastic deformation which provides high hardness, but there is also evidence of recrystallized copper nano-particles which are incorporated into friction layers as soft ingredient once detached from the pad surface. Thus copper seems to play a dual role, firstly as reinforcing element of the brake pad providing primary contact sites, and secondly as solid lubricant by contributing to the formation of a layer of granular material providing velocity accommodation between the rotating disc and fixed pad. Confirmation for this hypothesis was obtained by modelling contact sites on the nanometre scale with the method of movable cellular automata. Results show both, the similarity of steel fibres and copper macro-particles in respect to providing primary contact sites, as well as similar sliding behaviours of friction layers containing either copper or graphite as soft inclusions. Furthermore, it is shown that not only material properties, but also the concentration of solid lubricant particles in the friction layers, determine conditions for friction force stabilization and smooth sliding behaviour.

Influence of talc concentration in oil lubricant on the wear response of a bronze journal bearing

This study pertains to the examination of the effects of dispersing talc particles in an oil lubricant towards controlling the sliding wear characteristics of a journal bearing (bush) fabricated using a leaded-tin bronze. Influence of the content of the suspended mass in the oil and applied load on the wear behavior was also investigated. Properties evaluated were wear loss, frictional heating and friction coefficient. Addition of talc particles to the oil lubricant decreased the wear loss, frictional heating and friction coefficient while the applied load produced a reverse effect. Further, increasing content of talc up to 3–5% led to a decrease in the observed properties; the trend reversed at higher concentrations of the suspended mass in the oil. The increasing test duration caused the frictional heating and friction coefficient to increase at a high rate initially. The rate of increase lowered down at longer test durations. The observed wear behavior of the samples has been substantiated through the characteristics of wear surfaces and subsurface regions. The latter also enabled to understand the operating wear mechanisms.

Effect of specimen orientation and heat treatment on electroless Ni-PTFE-MoS2 composite coatings

In this study, the effects of simultaneous co-deposition of polytetrafluoroethylene (PTFE) and MoS2 particles on tribological properties of electroless nickel (EN) coating were studied. The influences of specimen orientation and heat treatment on EN-PTFE-MoS2 composite coatings were also investigated. Scanning electron microscopy was used to study the morphology of coatings and the distributions of the lubricant particles in the deposits. Chemical analyses of coatings were done by electron dispersive spectrometry. The phases of the coatings were identified by X-ray diffraction utilizing CuKα radiation. Wear and friction properties of the coatings were also determined by pin-on-disk wear tester. The wear investigations showed that the EN-PTFE-MoS2 composite coating performs better than EN-PTFE and EN-MoS2 coatings in terms of friction coefficient and wear resistance. PTFE and MoS2 contents of the EN-PTFE-MoS2 coating were increased by changing the specimen orientation from vertical to horizontal configuration, which leads to enhancement in tribological properties of the coating. After heat treatment, the wear rate of EN matrix composite coating decreased with corresponding change in phase structure.

Stokes' cradle: normal three-body collisions between wetted particles

In this work, a combination of experiments and theory is used to investigate three-body normal collisions between solid particles with a liquid coating (i.e. ‘wetted’ particles). Experiments are carried out using a Stokes' cradle, an apparatus inspired by the Newton's cradle desktop toy except with wetted particles. Unlike previous work on two-body systems, which may either agglomerate or rebound upon collision, four outcomes are possible in three-body systems: fully agglomerated, Newton's cradle (striker and target particle it strikes agglomerate), reverse Newton's cradle (targets agglomerate while striker separates) and fully separated. Post-collisional velocities are measured over a range of parameters. For all experiments, as the impact velocity increases, the progression of outcomes observed is fully agglomerated, reverse Newton's cradle and fully separated. Notably, as the viscosity of the oil increases, experiments reveal a decrease in the critical Stokes number (the Stokes number that demarcates a transition from agglomeration to separation) for both sets of adjacent particles. A scaling theory is developed based on lubrication forces and particle deformation and elasticity. Unlike previous work for two-particle systems, two pieces of physics are found to be critical in the prediction of a regime map that is consistent with experiments: (i) an additional resistance upon rebound of the target particles due to the pre-existing liquid bridge between them (which has no counterpart in two-particle collisions), and (ii) the addition of a rebound criterion due to glass transition of the liquid layer at high pressure between colliding particles.

Studies on the Behaviour of the Green Particulate Fluid Lubricant in Its Nano Regime when Machining AISI 1040 Steel

Significant advances, both practical and theoretical, have been made in understanding the behaviour of engineering materials when machining at higher cutting conditions. Nano-integrated manufacturing is a subject of immense interest for various sustainable engineered systems. Metal removal processes involve the generation of high cutting forces and temperatures. The use of proper lubricant to reduce forces and temperatures and to improve total cutting phenomena overall is an important aspect. The present investigation analysed a green, petroleum-free lubricant that is produced by mixing two environmentally benign components, canola oil and nano-crystalline boric acid. To study the influence of variation of nano-level boric acid particle size and its weight percentage on the performance of the proposed green particulate fluid lubricant, various turning tests were conducted on AISI 1040 steel using tungsten carbide inserts. Variations in cutting forces, tool temperatures and surface roughness were studied. The experimental results revealed that both cutting forces and tool temperatures increased as the boric acid particle size decreased. The surface quality of the machined surface was reduced as the solid lubricant particle size was reduced to the nano-level. Interestingly, reductions in both cutting force and tool temperature were observed as the boric acid weight percentage decreased, tending towards the pure canola oil-based machining results. The surface quality of the machined surface was also improved as the volume fraction of boric acid was decreased.

Lubricant, Mucus, and Other Contaminant Materials as a Potential Source of Interpretation Errors in ThinPrep Cervical Cytology

To investigate the possibility of the occurrence of errors in the interpretation of cervical smears in the presence of lubricant, mucus and other contaminant particles in ThinPrep (TP) technique (Cytyc Corp., Boxborough, MA) liquid-based cervical cytology. Four thousands sixty-eight TP cervical smears were reviewed over a 12-month period. Those cases that initially had caused interpretation errors in which lubricant, mucus, and other contaminant materials were confused with infectious agents or epithelial abnormalities among the primary screening cytotechnologists and pathologists were selected for our study. These cases were retrieved from the cytology unit's registered logbook. The possibility of these detected lubricant, mucus, and other contaminant materials in these cases to cause misinterpretation for randomly selected pathologists and cytotechnologists who were blinded for the study was further investigated. Three cytotechnologists and 2 pathologists were independently asked to give their opinions on each case without their prior knowledge of the selected cases. Only 15 cases out of 4068 were found to cause interpretation errors. Five different contaminant patterns were detected. The main potential misinterpretations included secondary diagnosis that is confused mainly with infectious agents. However, other contaminants were even misinterpreted as high-grade squamous epithelial abnormalities. This study illustrates the potential of lubricant, mucus, and foreign body contaminant materials to cause interpretation errors in TP cervical cytology. Although liquid-based preparation reduces the obscuring effect of these materials, the unusual appearance of some of these particles in TP cervical smears not only can mimic infectious microorganisms, but also squamous dyskaryosis. This can lead to serious interpretation errors for the inexperienced cytotechnologists and pathologists, which subsequently can have an effect on the women's management.

Influence of Suspended Talc Particles in Oil And Nature of Material Microconstituents on Sliding Wear Characteristics of Cast Iron and Zinc-based Alloy

This investigation pertains to some observations on the sliding wear behaviour of a zincbased alloy and grey cast iron as influenced by the content of talc particles suspend in SAE40 oil lubricant. Tribological parameters evaluated using a pin-on-disc machine were wear rate, frictional heating and friction coefficient. The study suggests that the presence of suspended talc particles in the oil lubricant brought about improved wear response of the samples. However, the degree of improvement was strongly dependent on the talc content and even adverse effect of talc addition beyond a limit was noted. The observed wear response of the samples has been eXplained in terms of characteristics like compatibility, lubricating and cracking tendency of various microconstituents of the specimen materials and formation and stability of lubricant film during sliding. Characteristic features of wear surfaces, subsurface regions and debris particles enabled to further substantiate the wear response of the samples.

A Trial of FGM Bearings with Solid Lubricant

It is difficult to use an ordinary plain bearing under a high load or at a high friction speed because lubricant oil is pushed out from the friction surface or deterioration of the lubricant oil is caused by heat of friction. A solid lubricant, MoS2, is promising in such condition. When the lubricant is dispersed in a matrix, the solid lubricant is always supplied from the matrix. Such a composite bearing needs a back metal to maintain its shape. The heat of friction may cause a crack between the bearing and the back metal due to thermal stress. A bearing with low coefficient of friction is necessary to decrease the heat of friction, and an FGM structure is also promising to decrease the stress. The aim of this experiment is to fabricate and to examine friction properties of the composites. Cu was plated on the lubricant particles by electroless deposition. The lubricant volume fraction (hereafter Vf) was up to Vf 30 %. The Cu plated lubricant particles were hot-pressed to form a composite at 873 K under 30 MPa in a vacuum. Friction properties of the composites were determined by using a ball-on-disk type testing machine. The test was performed in the air without oil at room temperature. The solid lubricant in the composites was effective to decrease the coefficients of friction under a high load when the Vf was higher than 20 %.

Characterization and frictional behavior of nanostructured Ni–W–MoS 2 composite coatings

Ni–W–MoS 2 composite coatings were obtained by pulse plating from a Ni–W electrolyte containing suspended MoS 2 particles. The coating composition, morphology, crystalline structure, microhardness and frictional behavior were studied as a function of MoS 2 concentration. The results obtained in this study indicate that co-deposited lubricant particles strongly influenced the composite Ni–W coating properties. It was found that increasing co-deposited MoS 2 diminished tungsten content in the coating and consequently increased the average grain size. Ni–W nanostructured coatings with high MoS 2 content have a porous sponge-like structure, high surface roughness and irregular frictional behavior. However, the friction coefficient of Ni–W coatings is reduced to half its value with low MoS 2 content.

Lubricated Sliding Wear Behavior of a Cast Iron: Effect of Graphite and/or Talc Fraction in Oil

The effects of suspended solid lubricant (graphite and/or talc) particles in oil on the sliding wear response of a cast iron have been studied in this investigation. The role played by the changing concentration of the talc and graphite particles added to the oil separately as well as in combination toward controlling the wear behavior of the cast iron has also been analyzed. The investigation strongly suggests beneficial effects of the solid lubricant particles suspended in lubricating oil in terms of decreasing wear rate, frictional heating, and friction coefficient. Interestingly, increasing concentration of the suspended lubricant particles in oil led to reduction in the mentioned properties initially followed by the attainment of the minimum at a specific concentration of the solid lubricants. At still higher concentrations, the trend reversed in the case of wear rate and friction coefficient while it remained unaffected as far as the influence on frictional heating is concerned. Formation of stable lubricating film/layer was noted to be responsible for the improved wear performance of the samples while rupture of the lubricant film led to deterioration in wear behavior.

Exploration of the size, shape and abundance of UHMWPE wear particles using atomic force microscopy

Atomic force microscopy is proposed and explored as a technique for the characterisation of ultra-high molecular weight polyethylene (UHMWPE) wear particles from knee prostheses. This new approach may be an alternative to other techniques such as filtration and scanning electron microscopy. Atomic force microscopy can measure the size and geometry of polyethylene wear particles extracted from the joint lubricant with a precision on the nanometre-scale. This can further the understanding of wear processes at this length-scale. However, information about the absolute and the fractionated abundances of the particles in the lubricant is lost, since the particles precipitate non-uniformly on substrates suitable for atomic force microscopy. It is demonstrated that conventional filtration of polyethylene particles can cause similar non-uniform precipitation on a filter medium. This result gives support to the view that uniformity across a substrate or filter medium needs to be established in detail and quantitatively using an appropriate experimental protocol so that abundance distributions may be obtained reliably.

Sliding wear behaviour of a cast iron as affected by test environment and applied load

PurposeThe purpose of this paper is to understand the sliding wear response of a cast iron as influenced by applied load and changing concentration of solid lubricant (graphite) particles in oil lubricant, and operating material removal mechanisms in different sets of experimental conditions.Design/methodology/approachThe sliding wear response of a grey cast iron has been examined as a function of test environment and load. Properties evaluated were wear rate, friction coefficient and frictional heating. The wear behaviour of the samples has been substantiated through the characteristics of their wear surfaces, subsurface regions and debris particles.FindingsThe wear rate and frictional heating increased with load while friction coefficient was affected in an opposite manner. The presence of oil lubricant led to a substantial improvement in wear response (in terms of decreasing wear rate, friction coefficient and frictional heating) while the presence of graphite particles in the oil lubricant proved to be still better. A critical content of graphite in the oil lubricant becomes most effective towards improving the wear response of the samples. Formation of dark patches on the wear surface, substantial subsurface deformation and fine debris led to improved wear response.Research limitations/implicationsThe study enables one to understand the wear behaviour of a cast iron as influenced by the changing concentration of solid lubricant (graphite) particles in the oil lubricant. It also enables one to understand the operating material removal mechanisms responsible for the observed wear characteristics of the samples under varying test conditions. The investigation helps one to see that only a critical concentration of the solid lubricant particles in oil can lead to the best wear performance of materials.Originality/valueFrom a practical standpoint, the observations made here gain importance from the fact that solid lubricants are added frequently in oil in engineering applications but it becomes imperative to understand that only a critical concentration can lead to the best wear behaviour of materials.