Friction Modifiers Research Articles

Effectiveness of glycerol-monooleate in high-performance polymer tribo-systems

High performance polymers possessing superior mechanical properties may replace metal components and improve machine efficiency. Successful replacement, however, relies on the compatibility of these polymers with current engineering systems, including lubricants and their additives. This study examines the compatibility of two high performance polymers, polyetheretherketone (PEEK) and polyamide-imide (PAI), with glycerol monooleate (GMO), an organic friction modifier (OFM) commonly used in steel-steel rubbing contacts. Friction tests were conducted with a ball-on-disc geometry in reciprocating motion at 100 °C in polyalphaolefin (PAO) base oil. GMO reduces friction in polymer-steel and polymer-polymer contacts. When steel is involved, the use of GMO and oleic acid (OA) give similar friction coefficients. Since OA is believed to be a hydrolyzed product of GMO in steel-steel contacts, our results show that the interaction of OA with steel controls friction in polymer-steel contacts when GMO is the additive. Results from FTIR and Raman spectroscopies show that steel surfaces contain little to no polymeric materials, nor iron oxides after rubbing against polymers in GMO- and OA-containing PAO. This supports OFM layers are formed on steel surfaces. These OFM layers prevent polymer transfer layer formation and possibly protect steel surfaces from oxidation. Our results show that using OFM that interacts strongly with steel can, contrary to dry friction, eliminate the need of polymeric transfer film on steel for achieving low friction in polymer-steel contacts.

Corrosion Characteristics of Rolling Oil on the Rolled Copper Foil.

Static corrosion experiments were carried out to investigate the corrosion of each kind of component in the rolling oil on the rolled copper foil. The surface morphology and chemical composition of corrosion products were detected by a digital camera, scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS). The results showed that the maximum corrosion rate of rolled copper foil in the base stock and friction modifiers (butyl stearate and dodecanol) was close to zero, while that of rolled copper foil in the N-containing borate, phosphate and the fully formulated rolling oil were 0.17, 1.12 and 0.78 mm/a, respectively. The color of rolled copper foil changing from pink into purple-black when corroded in the N-containing borate. The composition of it was mainly CuO and Cu2O with some N-containing borate adsorbed on it. However, the color and composition of the corroded copper foil in the phosphate were similar to that of the original copper foil. It was complicated for the corroded copper foil in the fully formulated rolling oil, which showed characteristics both in the N-containing borate and in the phosphate according to different positions. It indicated that there might be little corrosion for the base stock and friction modifiers on the rolled copper foil. It might mainly be extreme pressure additives (N-containing borate and phosphate) that caused the corrosion of rolled copper foil. There might be competition between N-containing borate and phosphate for the corrosion of rolled copper foil in the fully formulated rolling oil, resulting in a lower corrosion rate compared with that in the phosphate.

Optimization of Tribotechnical Characteristics of Wheel–Rail Friction Modifiers

Optimization of Tribotechnical Characteristics of Wheel–Rail Friction Modifiers

The challenges and benefits of using carbon nano-tubes as friction modifier lubricant additives

The engine oils used in automotive industry are one of the most widely used consumable entities. There has been an ever increasing demand to improve the performance of engine oil lubricants. For that purpose, performance enhancing additives have been added to engine oil lubricants since past few decades. Subsequently, there is an ever increasing need to show the contribution lubricant additives make towards the automotive industry, the consumer and the impact on the environment. Such additives encompass applications for lubrication of passenger car (diesel and gasoline engine) lubricants, truck, coach and bus diesel engine lubricants, heavy duty engine oil etc. The document demonstrates the contribution made by lubricant additives in these applications to the consumer, industry and the environment, through their ability to optimise desirable lubricant properties while suppressing unwanted ones. New additives are under development to improve wear and tear properties of engine components, fuel efficiency and to reduce carbon emissions from cars and commercial vehicles by reducing friction. To prolong the lifetime and maintain the efficiency of exhaust car emission reduction devices, the modern engine oils must contain low sulphated ash, phosphorus and sulfur. This thesis describes the impact of adding lubricant additives on the visco-elastic and thermo-physical properties of engine oils. In this paper the benefits and challenges of Carbon Nanotubes as Lubricant additives has been discussed in detail.

Effects of Oil Palm Empty Fruit Bunch and Magnesium Oxide Volume Fraction on Mechanical Characteristics of Railway Brake Block Composite Material

Railway brake block is one of the most important components of the braking system of a railway vehicle. Materials for railway brake blocks are commonly made from metal or composite. The metallic brake blocks have some disadvantages that are heavy, low wear-resistant and has potential in generating a spark. While the composite brake blocks do not have those disadvantages. Natural fiber from oil palm empty fruit bunches as the waste from the production of palm oil can be used as a composite constituent. This composite brake blocks made from oil palm empty fruit bunches as reinforcement, phenol resin as matrix, and alumina, magnesium oxide and iron powder as a friction modifier. Density, hardness, coefficient of friction, compressive strength and flexural strength tests were carried out to determine the mechanical characteristic of the composite railway brake block material. The railway brake block test results consist of the density of 1.96 g/cm3, the hardness of 57.6 HRB, coefficient of friction of 0.43, the compressive strength of 37.1 MPa, and flexural strength of 33 MPa. There are three samples of volume fraction combination with 20% of oil palm empty fruit bunch in sample 1, 15% oil palm empty fruit bunch in sample 2 and 10% oil palm empty fruit bunch in sample 3. Percentage of MgO is adjusted to compensate the volume fraction of oil palm empty fruit bunch in the sample. Sample test results show that composite with volume fraction 10% of oil palm empty fruit bunch, phenolic resin of 30%, Al2O3 of 25%, MgO of 20%, iron powder of 15% has better mechanical properties for the alternative composite railway brake block material as compared to the other two.

Contribution of Lubricant Additives to Ash Generation on a Close-Coupled GPF

<div class="section abstract"><div class="htmlview paragraph">In order to meet the particulate emission targets (6 x 10<sup>11</sup> #/km), some gasoline direct injection (GDI) engines might require the use of particulate filters (GPF). The lifetime of wall-flow filters is influenced by the composition of the engine lubricant due to its potential to contribute to the ash accumulation in the GPF.</div><div class="htmlview paragraph">Due to space constraints and to facilitate trapping and soot regeneration, a large number of GPFs will be in closed-coupled configuration. A study was carried out on an endurance test with a radio labelling method and conventional mass gain measurement to evaluate this GPF configuration, and verify the impact of metallic additives contained in the lubricant such as magnesium (Mg) and calcium (Ca) based detergent, a zinc (Zn) based anti-wear, and a molybdenum (Mo) based friction modifier.</div><div class="htmlview paragraph">Two oils were evaluated, with two levels (0.85%-1.1%) of SAPS (Sulphated Ash, Phosphorus and Sulphur). In total, 4.5kg of oil were consumed for a global mass gain of the TWC and the GPF of 30g. The test methodology allowed to determine the laws of evolution of the GPF ash loading for each element monitored (Ca, Mg, Zn, Mo), based on the content of the element in the oil and oil consumption. This, in order to facilitate oil formulation and GPF sizing. This study also demonstrate that the main contributor is the detergent, far beyond Mo and Zn. The post-mortem ashes analysis showed that the lubricant is not the only contributor to the ashes, wear elements and fuel impurities are also involved.</div></div>

Influence of structural factors on the tribological performance of organic friction modifiers

The influence of structural factors on the lubrication performance of organic friction modifiers (OFMs) formulated in Group V (polyol ester oil) base oil was studied using a ball-on-disk tribometer. The results show that OFMs can mitigate friction under heavy loads, low sliding speeds, and high temperatures. These conditions are commonly encountered in internal-combustion engines between cylinder liners and piston rings. The reduction in friction is ascribed to the boundary lubrication film containing the OFM. The chemical composition analysis of the metal disk surface using energy dispersive X-ray spectroscopy (EDS) confirmed the presence of a protective film of OFM on the wear track, albeit inconsistently deposited. Although the adsorption of the OFM on the metal surface was observed to be dependent on the chemical reactivity of the functional groups, levels of unsaturation, and hydrocarbon chain length of the OFM, the frictional performance was not always directly correlated with the surface coverage and tribofilm thickness. This implies that the friction reduction mechanism can involve other localized processes at the interface between the metal surface and lubricant oil. The occasional variation in friction observed for these OFMs can be attributed to the stability and durability of the boundary film formed during the rubbing phase.

Efficiency of Application of Friction Modifiers in Internal Combustion Engines According to the Operational Tests Results

The efficiency of using of mineral engine oil modifier to restore compression of the cylinder–piston group of internal combustion engines is investigated. According to the results of full-scale tests of four different automobiles operating in an urban environment, the effect of increasing the compression of the cylinders to 20%, compared with the original, and reducing the pressure difference between them up to four times, was determinated. The effect reached a stable value after a run of 2000–4000 km and remained until the end of the experiment (10 000 km). It was found that when implementing the recommended procedure for flushing the engine before using oil with a friction modifier (FM), complete engine failure can occur. According to preliminary data the probability of this event is 20–30%.

A STUDY ON OPERATIONAL PROPERTIES OF ANTI-WEAR ADDITIVES FOR MOTOR LUBRICATING OILS DEPENDING ON THEIR PROCESSING AND SEDIMENTATION

The article presents studies on the dependence of sedimentation resistance of the anti-wear additive solid component for marine diesel trunk-type internal combustion engines on the technological conditions of its manufacturing. A friction modifier, molybdenum diselenide, which has optimal anti-wear properties, was selected as a solid component. The authors consider the process of sedimentation of a given substance, stabilized in the volume of an additive solution with unsaturated acids, at different times of rotary stirring, and under the influence of subsequent treatment of the prepared solution with ultrasound. The mass of the solution solid component is studied as irretrievably precipitated over various periods of storage time of the additive solutions, subjected to rotary stirring and additional ultrasonic treatment. The recommended storage time of the considered anti-wear additive with a 10% content of molybdenum diselenide has been established.

Sticky but Slick: Reducing Friction Using Associative and Nonassociative Polymer Lubricant Additives

Sustaining the current trend toward lower viscosity lubricants requires the development of improved friction modifier additives to compensate for the increased prevalence of boundary lubrication. I...

Surface Wear Anisotropy in AlSi10Mg Alloy Sample Fabricated by Selective Laser Melting: Effect of Hatch Style, Scan Rotation and Use of Fresh and Recycled Powder

AbstractAdditive manufacturing (AM) has witnessed substantial growth in recent years due to its excellent manufacturing capabilities and innovative production methodologies. However, the mechanical suitability aspect in terms of material wear has not received much attention yet and needs rigorous assessment. This study investigates the wear anisotropy in an AlSi10Mg alloy sample fabricated by selective laser melting (SLM) technique. Different scanning strategies encompassing the island and the continuous scanning patterns were used in sample manufacturing. The effects of the scanning vector orientation, design pattern, and the island pattern size on the mechanical wear and wear anisotropy have been analyzed in detail. The study also focused upon a comparative investigation of the wear properties at the top and the side surfaces to understand the wear anisotropy in different directions. The samples are fabricated both by the fresh and the recycled powder and the role of powder state is described. The ball-on-disk test is performed to simulate the similar contact applications for marine/automotive components such as bearings. Bearing steel balls are used as a standard sliding counterpart material to investigate the wear properties. The wear microstructure is analyzed by scanning electron microscopy. Overall, the island strategy with 2 mm hatch style and 45 deg scan rotation have achieved better wear resistance and friction coefficient compared with the continuous hatch style. The wear behavior is found to be anisotropic. The Raman spectra validate the presence of silicon and carbon particles on the wear track, which have a significant effect on the tribological properties. The type of particles present in the sliding zone characterizes different wear stages. Wear mechanism is described by considering four parameters, namely, scan pattern, scan vector rotation, type of powder, and the wear measurement direction. Results show that the surface wear rate of samples made by the fresh powder is lower than the recycled powder. However, samples of the recycled powder have friction modifier characteristics. The best wear rate and friction coefficient values are obtained with the island strategy (2 mm hatch, 45 deg scan rotation) in the side plane and are 3.76 × 10−6 mm3/N m, 0.0781, respectively.

MoS2 tribofilm distribution from low viscosity lubricants and its effect on friction

The current study analyses the friction performance of low viscosity fully-formulated oils containing the Molybdenum Dialkyl Dithiocarbamate (MoDTC) friction modifier at different concentrations. The MoDTC friction modifier is known to produce MoS2 sheets in the tribocontact providing a low coefficient of friction under boundary lubrication conditions. However, there is a little knowledge around the quantitative relationship between the concentration of MoDTC in the oil and MoS2 amount and distribution in the contact. The study uses Raman spectroscopy mapping capability to characterise the tribofilm formed from different chemistry lubricants and under different tribological conditions as defined by the lambda ratio. After qualitative and quantitative chemical surface characterisation a discussion is presented to highlight some important aspects to relate the formed MoS2 sheets, their spatial distribution in tribofilms and the subsequent tribological performance.

Understanding Adsorption Behaviors of Organic Friction Modifiers on Hydroxylated SiO2 (001) Surfaces: Effects of Molecular Polarity and Temperature.

Molecular dynamics simulations are used to investigate the physisorption of organic friction modifiers (OFMs) lubricated by 1-decene trimer (PAO4) representing a base oil and confined between hydroxylated SiO2 (001) surfaces. The results indicate that OFM molecules form dense, tendentiously vertical monolayer films at low temperature but loose adsorption layers at high temperature, particularly for R-NH2 with weaker molecular polarity. The structural information is quantitatively clarified by mass density profiles, radial distribution function, and probability distributions of an end-to-end distance at a perpendicular-to-surface direction. The movement performance of lubricant, reflected by the thickness of the organic part and radius of gyration of PAO4 molecules, strongly depends on temperature. The adsorption amount of OFM molecules decreases dramatically with lowering OFM polarity and increasing temperature above the critical desorption temperatures of about 320, 373, and 453 K for amine (R-NH2), alcohol (R-OH), and acid (R-COOH), respectively. The interaction energies of the OFM-surface decrease continuously for the R-NH2 system with temperature and decrease rapidly as temperature exceeds a critical value for both R-OH and R-COOH systems. The single-molecule geometry optimization validates the significant role of the electrostatic and hydrogen-bond attractions in molecular adsorption. Therefore, the OFMs with stronger polarity (like R-COOH) present stronger adsorption and better temperature resistance. The findings in this work are of particular value and provide a guideline in designing and engineering novel OFM additives for extreme lubrication conditions.

Formation mechanisms of zinc, molybdenum, sulfur and phosphorus containing reaction layers on a diamond‐like carbon (DLC) coating

AbstractDiamond‐like carbon (DLC) coatings are nowadays successfully applied on industrial components like pistons, piston rings and bearings in lubricated tribological contacts due to friction and wear reducing effects. In contradiction thereto, todays lubricants and additives are designed for tribological steel/steel contacts, whereby the knowledge on tribochemical layer formation on steel surfaces is comprehensive in contrast to the physical‐chemical interactions between diamond‐like carbon coatings, lubricants and additives. Therefore the formation mechanisms of zinc, molybdenum, sulfur and phosphorus containing reaction layers on a zirconium modified diamond‐like carbon coating a‐C : H : Zr (ZrCg) in lubricated tribological contacts were analyzed by means of pin‐on‐disc (PoD) tribometer by varying the distances from s = 200 m–3,000 m under boundary and mixed friction conditions at T = 90 °C and a contact pressure p = 1,300 MPa regarding the application of diamond‐like carbon coatings on gears. The base lubricant poly‐alpha‐olefin (PAO) was formulated using the anti‐wear (AW) and extreme pressure (EP) additive zinc dialkyldithiophosphate (ZnDTP) and the friction modifier (FM) additive molybdenum dialkyldithiophosphate (MoDTP). The chemical composition of the tribochemical reaction layers by means of and Raman spectroscopy and x‐ray photoelectron spectroscopy (XPS) as well as for the thickness differ significantly by varying the additivation.

Tribological Properties of Friction Materials Developed from Non- Asbestos Materials using Response Surface Methodology

Over many years, asbestos has been used as reinforcement material in the production of brake pads production but it has lost favour due to its carcinogenic nature, as a result, there is need to investigate other possible substitute which can offer similar tribological properties as the carcinogenic material (asbestos). Several works has been carried out using different reinforcement material with the aim of finding a possible replacement for asbestos. In this work, Rule of mixture (ROM) was ustlised for sample formulation and the tribological properties of natural based material (coconut shell and seashell) were investigated using experimental design (response surface methodology) and multi-response optimisation technique (Grey relational analysis). The multi-response performance of the formulated brake pads samples was compared with a commercial brake pad sample. The research findings revealed that sample can be produced using 52% reinforcement, 35% binder, 8% abrasive and 5% friction modifier while the Grey relational analysis (GRA) showed that optimum multi-response performance of the developed coconut shell based sample can be achieved using MP, MT and CT and HTT of 12MPa, 100 oC, 6mins and 2hrs respectively while that of the developed seashell based brake pad can be achieved using MP, MT and CT and HTT of 10MPa, 160 oC, 12mins and 2hrs respectively. Also, the Analysis of variance (ANOVA) results show a percentage error of less than 5% indicating minima noise effect. In addition, the optimized coconut shell-based brake pads falls within the category of class H (µ >0.55) type of brake pads while seashell based sample falls within the class G (µ: 0.45-0.55) type of brake pads. It therefore concluded that the use of coconut shell can serve as a better substitute for asbestos-based brake pads.

Effect of organic friction modifiers on lubrication of PEEK-steel contact

The rapid adoption of the advantageous PEEK/steel pairing in many tribological applications has prompted intense research to optimize its lubrication. Thus, the role of organic friction modifiers (OFMs) in improving the lubrication of PEEK-steel contacts has been studied and their mechanism explained. Their effect on friction and wear depends on the type of contact motion (i.e. sliding or sliding-rolling) and the steel surface roughness. N-oleoyl sarcosine had a significant effect on tribological properties due to its ability to absorb strongly on both materials, inhibit the formation of PEEK transfer films on steel and thus exert either a positive or negative effect depending on the test conditions.

Study on the Quantitative Evaluation of the Surface Force Using a Scanning Probe Microscope

There are two types of friction modifiers (FMs) used as lubricant additives: Reaction film FMs (RF-FMs) and adsorption film FMs (AF-FMs). While RF-FMs provide good performance in severe conditions, AF-FMs excel in mild conditions. This empirical evidence leads us to combine these two FMs to cover broader conditions. However, the effects of their combination are highly complicated due to the interaction between these FMs. If the interaction force of AF-FMs with various materials can be evaluated, it would help us to improve tribological performances of lubricants. Although atomic force microscopy seems suitable for this application, we found some obstacles, such as fluid resistance, electrostatic force, and laser positioning of the cantilever, to achieve proper measurements of the adsorption force. In this study, the adsorption force between the polar group and the surface was directly measured in oil with a 1 µm silica probe modified with CH3 or COOH. This paper proposed how to eliminate errors included in the adsorption force measurement using AFM and a calibration method for obtaining an accurate adsorption force of the polar group, and a test of normality of the measured data was conducted by 400 measurements. As a result, it was shown that approximately 100 tests were needed to obtain an accurate adsorption force in this study.

Investigation on Tribology Behaviors of Oil-soluble Nano-Cu Lubricating Additive for Aluminum Alloy ZL101

Oil-soluble Nano-Cu lubricating additive was prepared and its tribology behaviors as lubricant additive in SJ 15W/40 heavy duty gear oil used for aluminum alloy material ZL101 were investigated on an end-face friction and wear tester apparatus. SEM and EDS techniques were used to characterize the morphology, compositions and chemical states of the worn surface. The results indicate that the oil-soluble Nano-Cu additive have excellent friction-reducing properties and 0.6wt.% addition exhibited the best friction behavior. An appropriate applied load and rotating speed can improve the tribology properties obviously. The combination of SEM-EDS analysis reveals that by addition of Cu nanoparticles, a tribo-film containing Cu nanoparticles was formed and helped improving the wear and friction properties. The results demonstrate that Cu nanoparticles are potential friction modifier when used in ZL101.

Interactions between organic friction modifier additives

The interactions of different additives in engine oils can create synergistic or antagonistic effects. This paper studies how mixing different organic friction modifier additives affects friction reducing properties of lubricants in the boundary lubrication regime. Amines of different degree of saturation were mixed with either glycerol monooleate (GMO) or oleic acid in hexadecane. The model lubricants thus formed were characterised with Fourier-transform infrared spectroscopy. Friction tests in reciprocating motion using ball-on-disc steel-steel contacts were conducted to examine the tribological performance of these lubricants. Worn surfaces were examined using X-ray photoelectron spectroscopy. Oleic acid and oleylamine, a primary amine, were found to form a partial ionic liquid, providing synergistic friction reduction. This positive interaction reduces with increasing degree of saturation of the amine. No synergistic effect was observed between GMO and oleylamine, suggesting that GMO does not hydrolyse into a carboxylic acid within a rubbing contact in the presence of amine.

Alkyl-Ethylene Amines as Effective Organic Friction Modifiers for the Boundary Lubrication Regime.

With the pursuit of fuel economy in the automotive industry, recently low-viscosity lubricant technology has been widely improved. The present work has systematically discussed a series of sulfur- and phosphorus-free organic friction modifiers (FMs)-alkyl-ethylene amines-by alkyl substitution from ethylene amines with various nitrogen-atom numbers and molecular configurations. Herein, the pin-on-flat reciprocation friction tests have exhibited that the addition of the novel alkyl-ethylene amines into base oil led to significant reductions in the friction coefficient (up to 23%). Further investigations of tribological properties at elevated temperatures demonstrated that the increased number of nitrogen atoms and the regular linear atomic arrangement contributed to an improvement of friction reduction (up to 66%) compared to the neat base oil. Notably, results of water contact angle measurement and infrared spectroscopy (IR) have provided favorable evidence that the novel FMs have adsorbed on the metal surface leading to the formation of a tribofilm, whereby the tribofilm prevented the sliding surfaces from direct asperity contact and markedly improved the tribological performance, as seen from the composition analysis of the worn surfaces by an energy-dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), and confocal Raman spectroscopy. Therefore, the present work can provide a practical reference for molecular structure design through investigation of structure-performance relations of lubricant additives.