Lubricant Particles Research Articles

Analytical Surface Energy Model of Fine Copper-Graphite Core-Shell Particles in Oil Lubricant

Analytical Surface Energy Model of Fine Copper-Graphite Core-Shell Particles in Oil Lubricant

Investigation of lubricant viscosity and third-particle contribution to contact behavior in dry and lubricated three-body contact conditions

The generation of third particles and change in viscosity lead to the gradual degradation of the performance of the machine interface. The generation of third particles may come from wear debris or environmental particles, which form a three-body contact system at the contact interface. The viscosity of the lubricant will also change with the long-term operation of the components. This paper uses a three-body lubrication model to study the influence and interaction of lubricant viscosity change and the presence of third particles on the contact characteristics, including the real contact area, the particle contact area ratio, the solid load percentage, the film thickness, and the evolution of the lubrication regime. The results show that when the interface is in a three-body mixed lubrication regime, the dimensionless total real contact area increases with the increase in particle size and density at the same lubricant viscosity, while the trend is the opposite in dry contact and boundary lubrication interfaces. When viscosity decreases, a three-body contact interface is more prone to entering boundary lubrication than a two-body contact interface, resulting in surface damage. Regardless of surface roughness, particle size, and dry or lubricated contact conditions, the turning point of the contact area (TPCA) phenomenon is usually when the ratio of particle size to surface roughness is 0.8–1.3. Under the same ratio of particle size to surface roughness, the critical load of the TPCA phenomenon increases with the increase in third-particle size and surface roughness, but decreases with the increase in lubricant viscosity and particle density.

Characterization and fractography of stir-cast ZA-27 composites reinforced with Zircon silicate and MoS2 solid lubricant particles

Zinc Aluminum alloy (ZA-27) is a primarily known alloy used in bearings. In this work the alloy is reinforced with Zircon silicate in varying amounts ranging from 1.5 wt% to 6 wt%, incrementally increasing by 1.5 wt%, along with 3 wt% Molybdenum di sulfide (MoS2) microparticles via a stir-casting process. Zircon silicate is prized for its increased hardness and thermal stability, and MoS2 provides remarkable wear resistance to the composite. The primary goal of this study is to investigate how Zircon silicate particles and MoS2 affect the strength and fracture behavior of the prepared composites. The current study shows a decrease in both load bearing and percentage elongation as the Zircon silicate concentration increases, owing to weaker MoS2 secondary particles inside the ZA-27 matrix. To provide a suitable explanation for crack development, the study also includes microstructure analysis, evaluation of porosity, microhardness, CTE evaluation, and the influence on the fracture mechanism of the ZA-27 composites.

Combining Carbon Nanoparticle Coatings and Laser Surface Texturing for Enhanced Lubricity Under High Loads

Developing new lubrication concepts greatly contributes to improving the energy efficiency of mechanical systems. Nanoparticles such as those based on carbon allotropes or 2D materials have received widespread attention due to their outstanding mechanical and tribological performance. However, these systems are limited by a short wear life. Combining nanoparticle coatings with laser surface texturing has been demonstrated to substantially improve their durability due to the reservoir effect which prevents immediate particle removal from the contact. In this study, we investigate the high-load (20 N) tribological performance of AISI 304 austenitic stainless-steel substrates, which are line-patterned by laser interference patterning and subsequently coated with different carbon nanoparticle coatings (carbon nanotubes, carbon onions, carbon nanohorns) against alumina and 100Cr6 counter bodies. In addition to that, benchmark testing is performed with conventional solid lubricant coatings (graphite, MoS2, WS2). Electrophoretic deposition is used as the main coating technique along with air spraying (for WS2). All coatings substantially improve friction compared to the purely laser-patterned reference. Among all coating materials, carbon nanotubes demonstrate superior lubricity and the longest wear life against 100Cr6 and alumina counter bodies. Detailed characterization of the resulting wear tracks by energy-dispersive X-ray spectroscopy, scanning electron microscopy, and confocal laser scanning microscopy provides insights into the friction mechanisms of the various solid lubricant particles. Further, material transfer is identified as an important aspect for effective and long-lasting lubrication.

Performance of inert particles as lubricant additives compared to fully formulated industrial forming oils in sheet metal forming

The increasingly restrictive legislation on the use of hazardous chemicals in lubricant formulation necessitates the use of less hazardous lubricant additives in the sheet metal forming industry. The tribological performance of calcium carbonate (CaCO3) as a green lubricant additive was evaluated in comparison to commercially available forming lubricants used in industry, some of which contain hazardous chemicals such as chlorinated paraffins to enable their function. The lubricants were tested by four-ball wear testing, four-ball weld load testing, and bending-under-tension. The ease of cleaning of surfaces formed with the different lubricants was evaluated by methods used in industry and the viscosity was evaluated using standard methods. The CaCO3 mixtures showed a better performance than commercial lubricants in four-ball wear testing, worse performance in four-ball weld load testing, worse cleanability, and a similar development of drawing force in bending-under-tension over 1000 consecutive strokes. When added to fully formed commercial lubricants, the particles degrade the performance of the lubricant in resisting adhesive wear but improve its capacity for resisting abrasive wear. Surfaces of formed parts after bending-under-tension testing with CaCO3 mixtures were scratched, while parts formed using commercial lubricants showed less scratching. The effect of including particles in a commercial lubricant depended on the application, either degrading it or improving it. It is therefore clear that the use of solid particles as lubricant additives should be constrained to selected applications where abrasive wear is a dominant wear mechanism.

Effect of particle size on the dispersion behavior of magnesium stearate blended with microcrystalline cellulose

The majority of tablets manufactured contain lubricants to reduce friction during ejection. However, especially for plastically deforming materials, e.g., microcrystalline cellulose (MCC), the internal addition of lubricants is known to reduce tablet tensile strength. This reduction is caused by the surface coverage by lubricant particles, the extent of which depends on both process and formulation parameters. Previously published models to predict the lubrication effect on mechanical strength do not account for changes in the excipient particle size. In this study, the impact of both lubricant concentration and mixing time on the tensile strength of tablets consisting of three different grades of MCC and four grades of magnesium stearate (MgSt) was evaluated. By taking into account the particle size of the applied excipients, a unifying relationship between the theoretically estimated surface coverage and compactibility reduction was identified. Evaluating the dispersion kinetics of MgSt as a function of time reveals a substantial impact of the initial surface coverage on the dispersion rate, while the minimal tensile strength was found to be comparable for the majority of formulations. In summary, the presented work extends the knowledge of lubricant dispersion and facilitates the reduction of necessary experiments during the development of new tablet formulations.

Effect of nano-graphene as an additive for the improved rolling contact fatigue life of through hardened AISI 4140 alloy steel

The Rolling Contact Fatigue (RCF) behaviour of through-hardened AISI 4140 samples under formulated lubricant with nano-graphene additives were investigated. Results showed that the reference oil added with 1% (wt.) of nano-graphene particles has significantly improved life by 6 folds. The increased RCF performance is attributed to the efficient action of graphene nano particle which improves the antiwear and pitting resistance of contact pairs. Moreover, spectroscopy and microscopy analyses indicated that graphene particles are adsorbed on the contact surface and delay the surface pit formation. Adding nano-graphene particles in the reference lubricant is an effective way to improve the RCF life under thin oil having low lubricant viscosity and also for the samples having lesser surface hardness such as through- hardened compared to induction-hardened samples.

Bio-bearings: Numerical Model of the Solid Lubricant in the Leg Joints of Insects

The proposed model describes the behavior of the lubricant particles at the interface between two surfaces for a group of cylindrical semi-solid lubricant fragments observed in a real beetle leg joint. It is shown that the lubricant particles may maintain a gap between joint surfaces at load. At the regular shear motion, such randomly oriented particles are reorienting perpendicular to the shear and function as a rolling bearing: the system demonstrates the lowest energy loss and lowest friction. At an increased load, the friction non-linearly increases, because of an increase of the particles’ eccentricity. Finally, at some load, the particle rotation stops, friction switches from the rolling to the sliding regime and increases significantly.

Investigation of Dispersion Kinetics of Particulate Lubricants and their Effect on the Mechanical Strength of MCC Tablets

IntroductionTablets are commonly produced by internally adding particulate lubricants, which are known to possibly lower the mechanical strength of tablets. This reduction is caused by the coverage of matrix forming components by lubricant particles, resulting in decreased interparticulate interactions. The known incompatibilities with some active compounds of the predominantly used lubricant, magnesium stearate, call for the in-depth characterization of alternative lubricants.PurposeInvestigation of the dispersion behavior of five commonly applied pharmaceutical lubricants by mathematically modeling the dispersion kinetics for short and extended mixing times.MethodsThe dispersion behavior of five different pharmaceutical lubricants were examined by systematically varying lubricant concentration and mixing time of binary formulations and evaluating the kinetic of tensile strength reduction by theoretically estimating the surface coverage based on particle sizes.ResultsFor short mixing times, a unifying relationship between compactibility reduction and theoretical surface coverage was identified. Subsequently, for extended mixing times, distinct differences in the shear strength and dispersion kinetics of the investigated lubricants were found.ConclusionsThe lubricant particle size controls the tensile strength reduction if short mixing times are applied. For extended mixing times, the investigated lubricants can be divided into two groups in terms of dispersion kinetics. Possible underlying reasons are discussed in detail in order to enhance the general understanding of lubricant dispersions in tablet formulations.

Optimization Numerically for Five-Pad Tilting-Pad Journal Bearings Design Based on Particle Swarm

The design of five-pad tilting-pad journal bearings (TPJB) is complicated because of the uncertainty of design parameters that greatly affects the performance of TPJB. In this study, the numerical lubrication model is established to predict the performance of TPJB. Furthermore, a new optimal method combining the lubrication model and particle swarm method with a comprehensive target is brought out, which can obtain the optimal design parameters correctly and rapidly compared with the enumeration method. The performance of TPJB is better after optimization, especially the when the temperature and frictional coefficient decreased by about 31.1% and 35.8%, respectively. Moreover, different application scenarios of TPJB need different weight factor combinations in the comprehensive target, which is valuable for different design requirements.

ДОСЛІДЖЕННЯ ЕФЕКТИВНОСТІ ТЕПЛООБМІННОГО ПРОЦЕСУ В ОХОЛОДЖУВАЧІ ТУРБІННОГО МАСТИЛА МО-2 В ЗАЛЕЖНОСТІ ВІД СХЕМИ РОЗТАШУВАННЯ ТРУБОК У ТРУБНИХ ҐРАТАХ

Effective cooling of the turbine oil is important for the reliability and optimal operation of the turbogenerator. The oil is used for lubrication and cooling of the support and radial bearings of the turbine, bearings of the generator and reducer, gears and splined rollers. It is also used as a hydraulic fluid in the hydraulic turbine start-up system. For reliable and safe operation of the system, it is necessary to maintain the correct temperature of the lubricant. Research is aimed at studying the influence of the layout of the heat exchange tubes in the tube grids on the cooling efficiency of the TP-22 turbine oil. With the help of the SolidWorks software complex, a geometric model of the MO-2 turbine oil cooler was created with three schemes for the placement of heat exchange tubes in tube grids: corridor, radial and checkerboard. Adhering to the parameters of the technical characteristics of this cooler, the nominal parameters of temperatures and consumption of coolants (cooling water and turbine lubricant TP-22) were chosen. The result of the calculations were the temperature fields of the coolants and the trajectories of the movement of lubricant particles in the intertube space of the cooler. When creating a geometric model and further research, the main technical characteristics of the shell-and-tube horizontal cooler MO2 were adopted, namely: the temperature of the turbine oil at the inlet is 45°С, the nominal flow rate of the oil is 3.1 m3/h, the temperature of the water at the inlet is 20°С, the nominal flow rate water - 15 m3/h. The conducted computer modeling made it possible to investigate the influence of the layout of the heat exchange tubes in the tube grids on the cooling efficiency of the turbine lubricant in the MO-2 shell-and-tube cooler. It was shown that the most effective, among the studied schemes, is the checkerboard arrangement of heat exchange tubes in tube grids. This scheme makes it possible to reduce the consumption of cooling water, relative to the nominal one, which will allow the use of water pumps of lower power.

Modeling of material removal rate considering the chemical mechanical effects of lubricant, oxidant, and abrasive particles for aluminum chemical mechanical polishing at low pressure

Lubricants are widely used for aluminum (Al) chemical mechanical polishing (CMP) to eliminate surface scratch damage. Understanding of the fundamental of CMP material removal mechanisms including lubrication is crucial to offer insights into the control and optimization of the polishing process. This paper proposes a novel material removal rate (MRR) model based upon molecular-scaled removal mechanism, micro-contact force equilibrium theory, chemical reaction kinetics and diffusion effects, with further considering the lubricant effect on the removal rate at low polishing pressure. Moreover, the presented model also clarifies the nonlinear dependence of removal rate on lubricant concentration, oxidizer concentration, and abrasive concentration. The model prediction results could provide qualitative insights into the influence of lubricant concentration, oxidizer concentration, and abrasive concentration on MRR, thus providing theoretical foundation and support for delineating the Al-CMP process at low pressure. Finally, it is found that the theoretical predictions possess qualitative agreement with the experimental results.

The Theory of the Surface Wettability Angle in the Formation of an Oil Film in Internal Combustion Piston Engines.

In internal combustion piston engines, the formation of an oil film is completely different from that seen in industrial machines. The molecular adhesion force at the interface between the surface coating of engine parts and the lubricating oil determines the load-carrying capacity and the ability to form a lubricated film. The geometry of the lubricating wedge between the surfaces of the piston rings and the cylinder wall is created by the thickness of the oil film and the height of the ring's coverage with lubricating oil. This condition is affected by many of the parameters that characterize the engine's operation and the physical and chemical parameters of the coatings used for the cooperating pairs. For lubricant particles that reach energies that are higher than the potential energy barrier regarding adhesive attraction at the interface, slippage occurs. Therefore, the value of the contact angle of the liquid on the surface of the coating depends on the value of the intermolecular force of attraction. According to the current author, there is a strong relationship between the contact angle and the lubrication effect. The paper shows that the surface potential energy barrier is a function of the contact angle and contact angle hysteresis (CAH). The innovation of the current work consists in examining the contact angle and CAH under the conditions of thin layers of lubricating oil, in cooperation with hydrophilic and hydrophobic coatings. The thickness of the lubricant film was measured under various speed and load conditions, using optical interferometry. The study shows that CAH is a better interfacial parameter for correlation with the effect of hydrodynamic lubrication. This paper presents the mathematical relationships relating to a piston engine, various coatings, and lubricants.

Improving properties of h-BN/GH4169 self-lubricating composites prepared using nickel coated h-BN powders

ABSTRACT The service conditions of high temperature and heavy load of aero-engine require high-temperature self-lubricating composites with high strength, low wear and long life. Hence, the high-level objective of this study is to regulate the interface between the substrate and hexagonal boron nitride (h-BN) lubricant in GH4169 nickel-based high-temperature self-lubricating composites to improve the interfacial bonding strength and the overall performance. Electroless plating method was adopted to coat nickel on h-BN, and the dense high-temperature self-lubricating composites were fabricated through hot-pressing sintering. The effects of nickel coating on h-BN on the microstructure, mechanical properties and high-temperature tribological behaviors of composites were analyzed in detail, and the lubrication mechanism was also elucidated. The results illustrate the Ni@h-BN/GH4169 composites with addition of chemically modified lubricant particles have excellent mechanical properties and lubrication and wear reduction properties, compared to h-BN/GH4169 composites. This is mainly due to the introduction of nickel coating contributed to the distribution uniformity of h-BN in the matrix, and the wettability between h-BN and the substrate together with interfacial bonding strength were enhanced as well. This work provides an insight to overcome the challenges facing the technology when using GH4169 nickel-based self-lubricating composites in manufacturing of mechanical components in aerospace.

Comparative study of nano fluid lubricant in face milling through DFA approach

Material research in industry is a prominent part of their investigation as the customer’s demand kept changing according to their requirement. To process a hard material is always a stimulating charge for the industry. One of such hard material EN31 has been kept under consideration here in this work. The idea in the standing work is to improvise the deduction rate of material and to observe the power consumption rate. These two responses have been focussed under controlled machining environment with or without Nano fluid particles. Thus a comparative analysis provided the significance by exploiting the Nano particles in lubricant along with least amount of lubrication. As there are two output responses, a multi response optimization technique has to be adopted. Hence the multi response system desirability functional analysis (DFA) has been practiced. Depth of cut (DC) analysed as the best affecting input for both environment situations. The experimental array was created using the Taguchi approach. A total of eighteen number of try-outs were executed and on comparing it has been found that no big difference seen in material removal rate (MR) whereas power consumption (PC)gets lower on using Nano fluid particles in minimum quantity lubrication (MQL). For instance, in seventeenth experiment, PC reduced from 965 to 740 W and MR only increases from 420 to 435 mm3/min.

Water-based lubricant containing protic ionic liquids and talc lubricant particles: Wear and corrosion analysis

Water-based lubricants have been used in different industrial applications in recent years. However, studies evaluating the tribological and electrochemical effects of lubricants with Protic Ionic Liquid (PIL) and talc particles (TC) as additives on SAE 1010 and SAE 1045 steels are still scarce in the literature, which is the objective of this work. Samples extracted from steel sheets were investigated in the normalized (SAE 1010) and quenched-tempered (SAE 1045) conditions. Wear tests in a ball-on-plate type tribometer and corrosion tests using potentiondynamic polarization curves were performed in the presence of different lubricant solutions (PIL 3% + DI water, commercial lubricant 3% + DI water, with and without talc particle additions 0.05 and 0.1 wt%). Analyses of viscosity, pH, wettability, and particle size distribution were conduted on the lubricant and talc samples. Wear and corrosion surfaces were analyzed by SEM/EDS, and Raman techniques. The results showed that the tribofilm formed from the interaction between PIL lubricants and steel substrates decreased the wear due to the increase of lubricity of these lubricants. When the PIL and the commercial lubricants are compared, PIL additives presented higher performance, despite the talc addition. The influence of talc on the corrosion of steel is associated with the differential aeration effect, mitigated by adding the PIL.

Particle Scale Insights into a KG-Pharma RoTab Tablet Press Feed-Frame System Using the Discrete Element Method (DEM) Modeling

In the pharmaceutical industry, tablets are a common dosage form. As part of the manufacturing process, powder in a tablet press passes through a feeding system called the feed-frame before reaching the die cavity. Under different manufacturing conditions (e.g., paddle speed, turret speed), issues such as segregation of powder blend components, over lubrication, and drug particle attrition often occur in the tablet press feed-frame, which affect the final drug product quality. Therefore, developing a particle-scale understanding of powder behavior in a feed-frame is essential. This paper used the discrete element method (DEM) to study powder flow in the feed-frame of a kg-pharma RoTab tablet press. Simulation results show that an increase in paddle speed has less effect on tablet mass than turret speed and that an increase in turret speed reduces tablet mass and increases variability in the tablet mass. The effect of paddle speed and turret speed on the API content in the tablet is small, but large paddle speeds exacerbate the segregation of powder blend components in the feed frame, increase particle traveled distance, particle shear work, and torque on the paddle wheel, thereby increasing particle over lubrication and attrition. However, the increase in paddle speed reduces the mean residence time of drug particles and prevents over lubrication at low turret speeds. Increasing the turret speed reduces tablet mass, particle shear work, paddle torque, and mean residence time. Although increasing turret speed can effectively prevent particle attrition and over lubrication, short residence times are not conducive to mixing excipients and API components, leading to higher tablet mass variability. This study not only gives us a particle-level insight into the process but can also be used to inform and optimize the design of experimental studies.

Understanding of the tribological behaviors of magnetic lubrication particle under magnetic field

Focusing on the way to regulate friction and wear, the synergistic effect of magnetic lubrication particles and applying an external magnetic field shows considerable application potential. However, different reports on the role of magnetic fields on tribological properties was still and lacked of reliable explanations. This study mainly focused on the effect of rubbing pairs material on the tribological behaviors of magnetic lubrication particle under magnetic field. Through a combination of experiments and simulations, the influence of different rubbing pairs on the tribological behaviors of magnetic lubrication particles under a magnetic field was analyzed, and then providing a reasonable explanation of the effect of the magnetic field in a macroscopic perspective.

Flow of lubricated granular material on an inclined plane

We have studied the gravity driven flow of spherical shaped, millimetric sized granular material coated with aspherical, micron-sized, near frictionless lubricant particles. Experiments were performed on an inclined plane using two different sized particles for varying concentrations of the lubricant. The particle volumetric flow rate exhibits a non-monotonic behavior with increasing lubricant concentration. It shows an increase at lower lubricant concentration followed by a decrease at higher lubricant concentration. The lubricant particles adhere to the granular particle surface thereby reducing the inter-particle friction. However, presence of lubricant particles at higher concentration damps out inter-particle collision thereby reducing the interparticle momentum transfer. Non-monotonicity in the observed behavior is then conjectured to arise due to competing effects of inter-particle friction and inter-particle collision. The present work and the overall observed behavior therein provides a simple experimental system to characterize the effects of added lubricant material in pharmaceutical and other relevant industrial applications.

Chemically bonded PA‐PTFE‐oil compounds by reactive processing: Chemical, thermal, morphological, and mechanical analysis

AbstractIn this research, the novel materials based on polyamide (PA), polytetrafluoroethylene (PTFE), and olefinic oil molecules are produced as a solid lubricant in metal‐plastic sliding contacts or sacrificial elements in metal–metal sliding contacts. For these applications, high durability of the compound material combined with low wear is required for long‐term use under high friction and mechanical loads. Earlier studies of IPF have shown that chemical bonding between the polymer matrix and the solid lubricant is mandatory to meet these requirements. For this purpose, the compounds are fabricated by a novel two‐step reactive processing procedure based on radiation‐modified PTFE, which exhibits reactive‐functional groups (COOH) and persistent perfluoroalkyl‐(peroxy)‐radicals (COO·). The PA‐PTFE‐oil‐cb compound materials (cb: chemically bonded) are analyzed by differential scanning calorimetry (DSC) concerning breaking down behavior and Fourier‐transform infrared spectroscopy with regards to the chemical covalent bonding state between the three components. Results of scanning electron microscopy investigations in correlation with DSC show that chemical bonding between PA and PTFE‐oil‐cb leads to a homogeneous distribution of solid lubricant particles in the three various PA matrices. Due to the chemical coupling, the compounds offer almost comparable or improved mechanical properties in the case of toughness compared to non‐modified PA.