Showing papers on "Friction modifier published in 2019"

Mechano-chemical decomposition of organic friction modifiers with multiple reactive centres induces superlubricity of ta-C

Abstract: Superlubricity of tetrahedral amorphous carbon (ta-C) coatings under boundary lubrication with organic friction modifiers is important for industrial applications, but the underlying mechanisms remain elusive. Here, combined experiments and simulations unveil a universal tribochemical mechanism leading to superlubricity of ta-C/ta-C tribopairs. Pin-on-disc sliding experiments show that ultra- and superlow friction with negligible wear can be achieved by lubrication with unsaturated fatty acids or glycerol, but not with saturated fatty acids and hydrocarbons. Atomistic simulations reveal that, due to the simultaneous presence of two reactive centers (carboxylic group and C=C double bond), unsaturated fatty acids can concurrently chemisorb on both ta-C surfaces and bridge the tribogap. Sliding-induced mechanical strain triggers a cascade of molecular fragmentation reactions releasing passivating hydroxyl, keto, epoxy, hydrogen and olefinic groups. Similarly, glycerol’s three hydroxyl groups react simultaneously with both ta-C surfaces, causing the molecule’s complete mechano-chemical fragmentation and formation of aromatic passivation layers with superlow friction. The mechanism underlying the superlubricity of tetrahedral amorphous carbon coatings lubricated with organic friction modifiers is still under debate. Here the authors combine experiments and simulations to reveal that superlubricious layers form due the mechano-chemical decomposition of friction modifiers.

Friction Modifier Additives, Synergies and Antagonisms

Abstract: There is growing interest in reducing friction in lubricated machine components to thereby increase the energy efficiency of machines. One important way to minimise friction is to employ friction modifier additives to reduce friction in thin film boundary lubrication conditions. There are currently three main types of friction modifier additive, organic friction modifiers, oil soluble organomolybdenum friction modifiers and functionalised polymers. In common practice, a single such additive is generally employed in a formulated lubricant, but it is of interest to explore whether combinations of two friction modifier additives may prove beneficial. In this study, the performance of eight commercial friction modifier additives spanning all three main types was first measured in three quite different friction tests. The aim was to identify the contact conditions under which each additive was most effective. Additive solutions in both a base oil and a formulated engine oil were investigated. In general, functionalised polymers were most beneficial in sliding–rolling contacts, while oil soluble organomolybdenum friction modifiers worked best in severe, reciprocating sliding conditions. However, all friction modifier additive response was strongly affected by the other additives present in formulated engine oils. The friction performance of combinations of friction modifier additives was then explored. When two different friction modifiers additives were combined in solution, several possible outcomes were observed. The most common was for one of the additives to predominate, to give friction that was characteristic of that additive alone, while in some cases friction lay between the values produced by either additive on its own. In a few cases the additives behaved antagonistically so that the combination gave higher friction than either additive by itself. In a few cases true synergy was observed, where a combination of two additives produced lower friction in a given test that either individual component at the same overall concentration. Another, and possibly more important synergy could also occur, however, when a pair of FMs worked more effectively than either individual additive over the range of test conditions present in different friction tests. This study suggests that optimal combinations of FMs may provide a means of reducing boundary friction and thus increasing the efficiency of machines, especially if the latter contain a range of lubricated machine components that operate with different types of tribological contacts.

Adsorption of Stearic Acid at the Iron Oxide/Oil Interface: Theory, Experiments, and Modeling.

Abstract: Improved friction performance is an important objective of equipment manufacturers for meeting improved energy efficiency demands. The addition of friction-reducing additives, or friction modifiers (FMs), to lubricants is a key part of the strategy. The performance of these additives is related to their surface activity and their ability to form adsorbed layers on the metal surface. However, the extent of surface coverage (mass per unit area) required for effective friction reduction is currently unknown. In this article, we show that full coverage is not necessary for significant friction reduction. We first highlight various features of surface adsorption that can influence the surface coverage, packing, and free energy of adsorption of organic FMs on iron oxide surfaces. Using stearic acid in heptane and hexadecane as model lubricant formulations, we employ a combination of experiments and molecular dynamics (MD) simulations to show how the dimerization of acid molecules in the bulk solvent and the cry...

Adsorption Behavior and Nanotribology of Amine-Based Friction Modifiers on Steel Surfaces

Abstract: This work describes the effect of the adsorption behavior of fatty amine-based organic friction modifiers on their tribological performance. The adsorption of four different fatty amines with a var...

Surface Reaction Films from Amine-Based Organic Friction Modifiers and Their Influence on Surface Fatigue and Friction

Abstract: Surface reactive additives are crucial in the lubrication of surfaces experiencing cyclic contact. The combination of additives in the lubricant, on the material surface and the complex tribo-contact conditions hinders the design of additive packages which can simultaneously protect steel surfaces from wear and fatigue. Amine-based Organic Friction Modifiers (OFMs) influence the tribological performance of steel surfaces. This study investigates the tribochemical impact of three amine-based OFMs in combination with Zinc DialkylDithioPhosphate (ZDDP) on tribological performance, particularly surface fatigue, for steel surfaces in severe rolling–sliding contacts. The thickness of reaction films was tracked throughout experiments and the chemistry of reaction films was examined using X-ray Photoelectron Spectroscopy (XPS). Results highlight the impact of the OFM polar moiety on tribological performance and its influence on chemical composition of tribo-reaction films and their formation kinetics. The combination of selected OFMs with ZDDP reduces frictional forces and can mitigate surface fatigue under certain conditions.

Ethoxylated Amine Friction Modifiers and ZDDP

Abstract: The influence of a series of Ethomeens (ethoxylated alkylamine organic friction modifiers) on the durability and friction of tribofilms formed by a commercial blend of primary and secondary ZDDP in sliding/rolling contact has been studied. When pre-formed ZDDP tribofilms are rubbed in Ethomeen solution, boundary friction is reduced and some of the ZDDP film is removed. Ethomeens having just two ethoxy groups give lower boundary friction on ZDDP than those with 15 ethoxy groups, but result in much greater removal of the tribofilm itself. Based on XANES analysis, the film removed by both types of Ethomeen consists primarily of nanocrystalline orthophosphate. The level of boundary friction and its dependence on sliding speed, coupled with the dimensions of the molecules, suggests that the Ethomeens with two ethoxy groups may form quite closely packed vertical monolayers on ZDDP tribofilm surfaces, but that those with fifteen ethoxy groups cannot be close packed; yet they still reduce boundary friction significantly. The study shows that selection of an appropriate aminic friction modifier for use with ZDDP is a balance between its ability to reduce friction and its potentially harmful effect on a ZDDP tribofilm.

Production and characterization of brake pad developed from coconut shell reinforcement material using central composite design

Abstract: In this work, locally sourced non-hazardous materials were used to produce brake pad using grey relational analysis (GRA) and experimental design via central composite design. Raw materials selected for production include coconut shell, epoxy resin (binder), graphite (friction modifier) and aluminum oxide (abrasive). Twenty-seven samples were produced separately using coconut shell as reinforcement material by varying process parameters. Formulation of the brake pads samples was done using rule of mixture and a weight percent of 52% reinforcement material, 35% binder, 8% abrasive and 5% friction modifier were used for the production. Grey relational analysis (GRA) shows that optimal process performance can be obtained using molding pressure, molding temperature, curing time and heat treatment time of 14 MPa, 140 °C, 8 min and 5 h, respectively. Optimized sample was produced using the optimal set of process parameters obtained from GRA and compared with commercially available sample produced by Ibeto Group. The experimental results showed that the performance of the optimized coconut shell-reinforced brake pad compared satisfactorily with commercially available samples and capable of producing less brake noise and vibration during application. Analysis of variance shows that curing time with a contribution of 30.38% and 31.40% have the most significant effect on the hardness and ultimate tensile strength of the coconut shell-reinforced friction material, respectively, while heat treatment time with a contribution of 46.3% and 24.23% have the most significant effect on the wear rate and friction coefficient of coconut shell-reinforced brake pad, respectively. The effects of all the factors on the properties of the friction materials are significant since their p values are greater than 0.010 (1%).

Interactions between Friction Modifiers and Dispersants in Lubricants: The Case of Glycerol Monooleate and Polyisobutylsuccinimide-Polyamine.

Abstract: The structural and frictional properties of 10 wt % solutions of the amphiphilic molecules glycerol monooleate (GMO) and polyisobutylsuccinimide-polyamine (PIBSA-PAM) in squalane are studied using molecular dynamics simulations in bulk and under confinement between iron oxide surfaces GMO is a friction modifier, PIBSA-PAM is a dispersant, and squalane is a good model for typical base oils A range of liquid compositions and applied pressures is explored, and the formation and stability of reverse micelles are determined under quiescent and shear conditions Micellization is observed mainly in systems with a high GMO content, but PIBSA-PAM may also form small aggregates on its own In the confined systems under both static and shear conditions, some surfactant molecules adsorb onto the surfaces, with the rest of the molecules forming micelles or aggregates Shearing the liquid layer under high pressure causes almost all of the micelles and aggregates to break, except in systems with around 75 wt % GMO and 25 wt % PIBSA-PAM The presence of micelles and adsorbed surfactants is found to be correlated with a low kinetic friction coefficient, and hence, there is an optimum composition range for friction reduction This work highlights the importance of cooperative interactions between lubricant additives

A comparison of friction modifier performance using two laboratory test scales

Abstract: This paper describes two methods, carried out at two different test scales, for assessing the friction modifier performance. Study A used the wear data from a full-scale rig test at the voestalpine...

Improving Heavy Duty Vehicles Fuel Consumption with Density and Friction Modifier

Abstract: With the increasing role of electro mobility it is predictable that for heavy duty sector it would not be able to replace the traditional engines. There are several researches to develop alternative propulsion solutions but in short term the efficiency improvement of diesels both in engine and fuel side is a must. In this research paper the main influencers of diesel fuel composition on combustion is investigated based on literature overview. Our research is focusing as most important parameters the density and friction. Different sample fuels were prepared to show how these parameters influencing fuel consumption in engine bench measurements. Our results showed that both with density and modification of friction are tools to improve fuel.

Friction and normal forces of model friction modifier additives in simulations of boundary lubrication

Abstract: Interaction forces between solid surfaces are often mitigated by adsorbed molecules that control normal and friction forces at nanoscale separations. Molecular dynamics simulations were con...

Interactions of Ethanol with Friction Modifiers in Model Engine Lubricants

Abstract: 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.

Effects of top-of-rail friction modifiers on the friction, wear and cracks of railway rails

Abstract: The railway is an economical and environmentally friendly mode of transport for long distances and heavy loads. The demands on the operators are increasing with increased competition in the market, ...

Tribological Behavior of Nano-ZrO2 Reinforced PTFE-PPS Composites

Abstract: Polytetrafluoroethylene (PTFE) is a commonly used seal material for oil-free engine that is well known for its excellent tribological properties. In this work, the nano-ZrO2 particles were used as the friction modifiers to improve the friction and wear performance of PTFE-PPS composites. The friction and wear characteristics of PTFE/PPS-nano-ZrO2 composites were investigated by a block-on-ring tester under dry friction sliding condition. The worn surfaces, counterpart transfer films and wear debris were studied by scanning electron microscopy and X-ray photoelectron spectroscopy. It was found that the increase of nano-ZrO2 content could effectively reduce the coefficient of friction and enhance the anti-wear ability of PTFE-PPS composites. Especially, the best tribological properties of the composites were obtained when the particle content of nano-ZrO2 was 10 vol%, the anti-wear performance of composite is 195 times better than that of the unfilled PTFE-PPS composite. Under different conditions, the coefficient of friction of PTFE/PPS-nano-ZrO2 composites was more affected by the applied load while the wear rate was more affected by the sliding velocity.

Potassium titanate powder, method for producing same, friction modifier, resin composition, friction material, and friction member

Abstract: Provided is a potassium titanate powder capable of imparting exceptional friction characteristics when used in a friction material while avoiding safety and health concerns. The powder is a powder configured from columnar potassium titanate particles having an average long diameter of 30 [mu]m or greater, an average short diameter of 10 [mu]m or greater, and an aspect ratio of 1.5 or greater, andis characterized in that the columnar potassium titanate particles are represented by the compositional formula K2TinO (in the formula, n is equal to 5.5-6.5).

Friction and Adsorption Properties of Oleic Acid-Based Gemini Amphiphile at Silica/Ester Oil Interfaces.

Abstract: We characterized the friction and adsorption properties of an oleic acid-based gemini amphiphile having two carboxylic acid headgroups. We employed silica as a solid material, and diethyl sebacate and bis (2-ethylhexyl) sebacate as polar ester oils. Oleic acid and stearic acid were used as comparative amphiphilic materials. These amphiphiles were soluble in the ester oils, and the solubility of the gemini amphiphile was lower than that of the other two amphiphiles. Quartz crystal microbalance with dissipation monitoring measurements suggested that the gemini amphiphile had greater adsorption capability than the two comparative amphiphiles. The greater adsorption density of the gemini amphiphile resulted in the formation of a rigid interfacial film, as suggested by the normal force curves obtained by atomic force microscopy (AFM). We assessed the friction property of these systems using a ball-on-plate-type friction analyzer and by friction-mode AFM (friction force curve). These measurements confirmed that the gemini amphiphile had a smaller kinetic friction coefficient than that of the other two amphiphiles. These results suggest the potential of the gemini amphiphile as a friction modifier in polar oils.

Tribological study of polyol ester-based biolubricants and the effect of molybdenum sulphide as lubricant additives / Nurul Adzlin Zainal

Abstract: The possible scarcity of oil and gas resources in the future (whether in quantity or areas of availability) is a major concern throughout the world. For this reason, governments all over the world are working on reducing their dependence on imported energy resources. Alternative energy resources such as bioethanol, biodiesel and biomass have gained prominence over the years in order to substitute petroleum-derived products. Biolubricants have also gained importance as alternatives to conventional petroleum-based lubricants in various applications, especially in the automotive industry. Biolubricants (also known as bio-based lubricants) are appealing alternatives for mineral-based lubricants because of their biodegradability and good lubricity. Owing to the advantages of biolubricants, the study was conducted to investigate the physicochemical properties and wear preventive characteristics of polyol ester-based biolubricants, namely, neopentyl glycol (NPG), trimethylolpropane (TMP), and pentaerythritol (PE) ester-based biolubricants. In addition, different concentrations of surface-capped molybdenum sulphide (known as friction modifier additive) were blended into the polyol ester-based biolubricants to study the effect of additive on the friction and wear properties. A four-ball wear tester is used to investigate the tribological properties (coefficient of friction and wear scar diameter) of the biolubricants in accordance with ASTM standard test methods, and the results are compared with those for paraffin oil and commercial lubricant. In general, the tribological performance of biolubricants is comparable to that for paraffin oil, and therefore, these polyol ester-based biolubricants are potential alternatives to replace mineral-based lubricants. Besides that, the addition of molybdenum sulphide improves the friction and wear properties of the polyol ester-based biolubricants.

Friction pad for brake clutch device, and production method thereof

Abstract: The invention provides a friction pad for a brake clutch device. The friction pad for the brake clutch device is produced from, by weight, 40-45 parts of xylene-modified phenolic resin, 15-20 parts of nitrile butadiene rubber powder, 10-16 parts of a reinforcing fiber, 18-30 parts of a solvent, 5-8 parts of a curing agent, 8-20 parts of a friction modifier, 10-14 parts of a wear-resistant filler, 2-5 parts of a mold release agent and 1-4 parts of pigment. The finished friction pad for the brake clutch device, produced by using the above special wear-resistant and high temperature-resistant formula, is improved from the composition and the production method, and strong combination greatly improves the comprehensive performances, including thermal stability, wear resistance, strength, hardness, high temperature resistance, scouring resistance and corrosion resistance, of the friction pad, so the friction pad has a long service life when used in the brake clutch device.