External Lubrication Research Articles

The wear behavior and service life of Madar and Bauhinia Racemosa reinforced polyester hybrid composites for gear applications

Abstract In order to investigate the wear behavior and service life of Madar and Bauhinia Racemosa fibers reinforced polyester, the composite gears were fabricated with varying the fiber weight percentages of 5%, 10%, 15% and 20%. This paper examines the rolling and sliding of the composite gears running against nylon gear with a simplified method of analysing and understanding the wear rate and tooth damage. Tests were conducted without external lubrication over a range of loads using a gear test rig. The test results of composite gears are compared with unreinforced polyester gear (URPE). The extremely interesting investigation from the experimental work is the drastically different wear behavior when running composite gears against nylon gears, specifically the low wear rate when compared with URPE. It was found that the surface temperature was the primary factor affecting the wear rate and an initial relationship between gear surface temperature and load capacity.

Comparison Study on SU-8 and Its Composites

In this paper, SU-8 is an industrially useful photo resist polymer for micro-fabrication because of its unique UV sensitive curing property. It is also used as a structural material for micro-machines such as micro-electro mechanical systems (MEMS). However, it has poor tribological and mechanical properties which make SU-8 inferior to Si, the mainstay MEMS material today. In this paper, we report the fabrication of SU-8 nanocomposites which are self-lubricating and have better mechanical properties. The liquid lubricant i.e., perfluoropolyether (PFPE) and nanoparticles such as SiO₂, CNTs, and graphite were added into SU-8 for this purpose. These self-lubricating SU-8 + PFPE and SU-8 + PFPE + nanoparticle composites have shown a reduction in the initial coefficient of friction, increased wear life and the mechanical properties such as the elastic modulus and the hardness have increased. We have used perfluoropolyether (PFPE) as in-situ lubricant filler to SU-8. This composite material has shown highly superior friction and wear performance over pristine SU-8 and any such alternative material for this application. We have shown that the mechanical property can also be enhanced by this method if we utilize nano-particles for further reinforcement. This self-lubricating SU-8+PFPE composite can be used for the fabrication of MEMS applications requiring no external lubrication, and also these composites can find applications in many tribological components of traditional machines. The thickness of SU-8 and its composites coating is fabricated in the range ∼100–105 ±m. Further, SU-8 and its composites are characterized by a 3D optical profilometer, atomic force microscopy, scanning electron microscopy, a thermal gravimetric analyzer, a goniometer, a hardness tester, and an optical microscope. Under a tribology test performed at different normal loads of 2, 4, and 6 N and at a constant sliding speed of 0.28 m/s. The SU-8 composite reinforced with 10 wt.% h-BN and 20 wt.% PFPE demonstrated the best thermo-mechanical and tribological properties with a nano-textured surface of high hydrophobicity.

Thermal characteristics analysis and experimental study of the planetary roller screw mechanism

The thermal characteristics of the planetary roller screw mechanism (PRSM) under various working conditions are investigated both analytically and experimentally. Firstly, thermal boundary conditions including the thermal contact resistance, thermal constriction resistance, conductive and convective resistance are particularly characterized and formulated, based on the fractal theory and heat transfer theory. Secondly, a thermal model based on the thermal network method (TNM), is established to predict the PRSM temperature evolution. The thermal balance equation set is solved by considering the influence of lubricant viscosity drop and the change of heat generation. Thirdly, the main factors affecting the thermal characteristics of the PRSM system, such as the external load, screw speed, and lubricating grease, are discussed and analyzed. The correlation between the experimental data and the calculated values confirms the validity of the proposed thermal model for the transient thermal analysis. Results indicate that the external load, operating speed, and lubricant consistency have a significant influence on the temperature rise level, even leading to the thermal failure of the PRSM. This study provides an in-depth understanding of the thermal behavior and heat transfer mechanism of the PRSM, and thus can be applied to its design and development.

Wear Performance Analysis of Ni⁻Al₂O₃ Nanocomposite Coatings under Nonconventional Lubrication.

This article presents a wear study of Ni–Al2O3 nanocomposite coatings in comparison to uncoated steel contacts under reciprocating motion. A ball-on-flat type contact configuration has been used in this study in which a reciprocating flat steel sample has been used in a coated and uncoated state against a stationary steel ball under refrigerant lubrication. The next generation of environmentally friendly refrigerant HFE-7000 has been used itself as lubricant in this study without the influence of any external lubricant. The thermodynamic applications and performance of HFE-7000 is being studied worldwide, as it is replacing the previous generation of refrigerants. No work however has been previously performed to evaluate the wear performance of HFE-7000 using nanocomposite coatings. The wear scar developed on each of the flat and ball samples was studied using a Scanning Electron Microscope (SEM). The micrographs show that a combination of adhesive and abrasive wear occurs when using uncoated steel samples. Micro-delamination is observed in the case of Ni–Al2O3 nanocomposite coatings accompanied by adhesive and abrasive wear. Wear volume of the wear track was calculated using a White Light Interferometer. Energy-Dispersive X-ray Spectroscopic (EDS) analysis of the samples reveals fluorine and oxygen on the rubbing parts when tested using coated as well as uncoated samples. The formation of these fluorinated and oxygenated tribo-films helps to reduce wear and their formation is accelerated by increasing the refrigerant temperature. Ni–Al2O3 nanocomposite coatings show good wear performance at low and high loads in comparison to uncoated contacts. At intermediate loads the coated contacts resulted in increased wear, especially at low loads. This increase in wear is associated with the delamination of the coating and the slow formation of protective surface films under these testing conditions.

Creation of Oil-Filled Composites of Tribotechnical Purpose Based on Aromatic Polyamide Phenylone C-2

The authors of the paper suggested a recently developed technology of creating oil-filled composites based on aromatic polyamide Phenylone C-2. The depicted approach originates in the functional modification of the matrix base with nanomodified fillers and nanodimensional additives. The paper formulated the principles of absorption modification of mineral nanofiller for creating universal inhibitors of tribosystem or oleaginous polymer, more known as «maslyanit». It was demonstrated that the efficiency of polymer filling is enhanced by the joint application of the methods of preliminary solvent cleaning and dispersion of mineral particles to the nanodispersed state. The increase of the sorption capacity of natural and synthetic minerals was carried out by acid modification of minerals. A set of comparative tribological tests on a friction machine of Amsler II 5018 type according by a «finger-roller» scheme without external lubrication was carried out to evaluate the resistance of composite materials to abrasion at a constant specific pressure. It was found that the introduction of PFPE oil led to a significant decrease of the coefficient of friction practically in the entire loading range only in composites containing Aerosil. While the introduction of PMPS oil, in contrast, strengthened the antifriction effect of the samples, containing spinel and serpentine, in the load range of 209-720 N. The study of physical and mechanical properties of composites was carried out by NanoTest 600 complex. It was established that the samples with the addition of Arimid are characterized with the highest physical and mechanical properties. Besides, it as noted that the addition of PFPE and PMPS oils when creating oil-filled composites results in 20-25% decrease the microhardness and modulus of elasticity values. The carried out researches allowed concluding that the composite with that composition is most suitable for use in non-lubricated friction units.

Tribological characterisation of epoxy–graphene–liquid filler composite coatings on steel under base oil external lubrication

ABSTRACTIn our earlier study, epoxy-based composites with graphene (10 wt-%) and in situ liquid fillers (base oil SN150 or perfluoropolyether at 10 wt-%) were found to provide low friction and highly wear durable as thin coatings on the steel substrate in dry interfacial state. In this present work, we have tested this composite in the presence of an external lubricant (base oil SN150). The lowest coefficient of friction was recorded as 0.04 and the lowest specific wear rate was measured as 9.8 × 10−7 mm3 Nm−1 for the composites without any failure of the coating up to 200,000 sliding cycles. It is shown that such polymeric coatings can be an excellent boundary film in both dry and lubricated conditions for various bearings.

Die wall lubrication for UO2 pellets pressing: A case study

This paper investigates the tribological performance of different external lubricants on the die wall for UO2 powder pelletization without any admixed internal lubricant. Different lubricants and various ways of depositing lubricant on the die wall were investigated through different parameters during powder compaction and pellets characterization. We have thus compared depositing solid zinc stearate (StZn) lubricant by two ways (StZn powder pelletization vs. StZn spray). Results show that the tensile strength of green pellets (compacts before sintering process) is enhanced and surface defects are reduced when the lubricant is sprayed. Furthermore, the application of silicon oil on the die wall does not make it possible to manufacture UO2 pellets, which is probably due to its tribological inefficiency under pressing conditions considered in this work. By contrast, an industrial grease makes it possible to obtain green pellets with good properties and fewer surface defects. The lubrication mechanism changes from one lubricant to another and influences the pressing parameters (wall friction, friction index, ejection force, etc.) and the characteristics of the final UO2 green pellets. The ejection force seems to be more sensitive for the lubricants performance assessment in case where only external lubrication is used for nuclear powder compaction.

The importance of the amount/thickness of die wall lubricant for UO2 pellets pressing

External lubrication is often used to complete compaction process of powder materials. The main goal of this method is generally to reduce the amount of admixed internal lubricant (Zinc stearate powder) within the raw material. The application of external lubricants enhances the density uniformity and the mechanical strength of the resulting compacts. This study investigates the effects of the external lubricant amount for UO2 powder compaction and the properties of the corresponding green pellets (corresponding to the compacts before sintering) without any admixed lubricant in the raw powder in order to evaluate the feasibility of this route in the case of nuclear powder. Results show that there is a quantity or number of layers from which the external lubricant applied on the die wall becomes detrimental to the friction index and the ejection force measured during the pressing cycle. The quality (surface defects, mechanical strength) of the green pellets can also be affected by the amount of lubricant. Thus the quantity and the thickness of the die wall lubricant must be optimized in order to assure an efficient mixed lubrication mode corresponding to the better lubrication mode in our study case.

Tribological Characterization of Centrifugally Cast Graphite Cast Iron under Dry and Wet conditions

The study is concerned with wear behaviour of centrifugally cast flake graphite iron, spheroidal graphite iron and compacted graphite iron in both dry and wet conditions. The test was conducted according to the ASTM G99 standards, to investigate the wear behaviour in dry and wet conditions by keeping time and sliding speed as constants but for varying loads. The graphite iron classified as flake graphite cast iron, spheroidal graphite cast iron, and compacted graphite cast iron depending upon the shape and distribution of graphite particles in the metal matrix. The variations of the co-efficient of friction and wear rate were experimentally measured. From the experimental results, the following things became clear. Initially the co-efficient of friction varies and later it converges to a certain value because of the debris, the debris grows and comes between the pin and disc surfaces. From the result it is clear that SGI has the highest wear in both dry and wet conditions. The graphite acts as an inherent lubricant for cast iron automatically coming in between the pin and disc surface and along with external lubrication it was found to decrease the co-efficient of friction by 10 times.

Design and analysis of plastic gears in rack and pinion steering system for formula supra car

Plastic gears have positioned themselves as serious alternatives to traditional metal gears in a wide variety of applications. The use of plastic gears has expanded from low power, precision motion transmission into more demanding power transmission applications. In an automobile, the steering system is one of the most important systems which used to control the direction and stability of a vehicle. In order to have an efficient steering system, one should consider the material and properties of gears used in rack and pinion. Using plastic gears in a vehicle’s steering system has many advantages over the current traditional use of metallic gears. High performance plastics like, glass fiber reinforced nylon 66 have less weight, resistance to corrosion, noiseless running, lower coefficient of friction and ability to run without external lubrication. Moreover, plastic gears can be cut like their metal counterparts and machined for high precision with close tolerances. In formula supra vehicles, weight, simplicity and accuracy of systems have prime importance. These requirements make plastic gearing the ideal option in its systems. An effort is made in this paper for analyzing the possibility to rebuild the steering system of a formula supra car using plastic gears keeping contact stresses and bending stresses in considerations. As a conclusion the use of high strength engineering plastics in the steering system of a formula supra vehicle will make the system lighter and more efficient than traditionally used metallic gears.

Roll Compaction/Dry Granulation of Dibasic Calcium Phosphate Anhydrous—Does the Morphology of the Raw Material Influence the Tabletability of Dry Granules?

The influence of raw material particle morphology on the tabletabilty of dry granules was investigated. Therefore, dibasic calcium phosphate anhydrous was used as a model material. One milled grade, 2 agglomerated grades with different porosities, and a functionalized structure, that is, an agglomerate formed by very small primary particles, were included. Particle size, density, and specific surface area of raw materials were measured. The starting materials and 2 fractions of dry granules were compressed to tablets. The tabletability of granules was compared to that of the powders and the influence of specific compaction force, granule size, and lubrication on tablet tensile strength was evaluated. All materials showed a loss in tabletability induced by a previous compaction step but to a varying extent. Only in case of the functionalized calcium phosphate morphology, this effect depended on the specific compaction force. In contrast to the other materials, the tabletability of functionalized calcium phosphate was influenced by the granule size. This effect was not related to an overlubrication as internal and external lubrication resulted in similar tensile strengths. A clear influence of the particle morphology on tablet strength was demonstrated by the study. The functionalized structure showed aspects of a more plastic deformation behavior. The functionalized dibasic calcium phosphate and the more porous agglomerate performed as potential filler/binder in the field of roll compaction/dry granulation.

Tribological Properties of Aluminium Alloy Composites Reinforced with Multi-Layer Graphene—The Influence of Spark Plasma Texturing Process

Self-lubricating composites are designed to obtain materials that reduce energy consumption, improve heat dissipation between moving bodies, and eliminate the need for external lubricants. The use of a solid lubricant in bulk composite material always involves a significant reduction in its mechanical properties, which is usually not an optimal solution. The growing interest in multilayer graphene (MLG), characterised by interesting properties as a component of composites, encouraged the authors to use it as an alternative solid lubricant in aluminium matrix composites instead of graphite. Aluminium alloy 6061 matrix composite reinforced with 2–15 vol % of MLG were synthesised by the spark plasma sintering process (SPS) and its modification, spark plasma texturing (SPT), involving deformation of the pre-sintered body in a larger diameter matrix. It was found that the application of the SPT method improves the density and hardness of the composites, resulting in improved tribological properties, particularly in the higher load regime.

Considerations regarding the volume fraction influence on the wear behavior of the fiber reinforced composite systems

This paper contains an analysis of the factors that have an influence on the tribological characteristics of the composite material sintered with metal matrix reinforced with carbon fibers. These composites are used generally if it’s needed the wear resistant materials, whereas these composites have high specific strength in conjunction with a good corrosion resistance at low densities and some self-lubricating properties. Through the knowledge of the better tribological properties of the materials and their behavior to wear, can be generated by dry and the wet friction. Thus, where necessary the use of high temperature resistant material with low friction between the elements, carbon fiber composite materials are very suitable because they have: mechanical strength and good ductility, melting temperature on the higher values, higher electrical and thermal conductivity, lower wear speed and lower friction forces. For this purpose, this paper also contains an experimental program based on the evidence of formaldehyde resin made from fiber reinforced Cu-carbon with the aim to specifically determine the volume of fibers fraction for the consolidation of the composite material. In order to determine the friction coefficient and the wear rates of the various fiber reinforced polymer mixtures of carbon have been used special devices with needle-type with steel disc. These tests were conducted in the atmosphere at the room temperature without external lubrication study taking into consideration the sliding different speeds with constant loading task.

Effect of the External Lubrication Method for a Rotary Tablet Press on the Adhesion of the Film Coating Layer.

External lubrication is a useful method which reduces the adhesion of powder to punches and dies by spraying lubricants during the tableting process. However, no information is available on whether the tablets prepared using an external lubrication system can be applicable for a film coating process. In this study, we evaluated the adhesion force of the film coating layer to the surface of tablets prepared using an external lubrication method, compared with those prepared using internal lubrication method. We also evaluated wettability, roughness and lubricant distribution state on the tablet surface before film coating, and investigated the relationship between peeling of the film coating layer and these tablet surface properties. Increasing lubrication through the external lubrication method decreased wettability of the tablet surface. However, no change was observed in the adhesion force of the film coating layer. On the other hand, increasing lubrication through the internal lubrication method, decreased both wettability of the tablet surface and the adhesion force of the film coating layer. The magnesium stearate distribution state on the tablet surface was assessed using an X-ray fluorescent analyzer and lubricant agglomerates were observed in the case of the internal lubrication method. However, the lubricant was uniformly dispersed in the external lubrication samples. These results indicate that the distribution state of the lubricant affects the adhesion force of the film coating layer, and external lubrication maintained sufficient lubricity and adhesion force of the film coating layer with a small amount of lubricant.

The structure properties and tribological behavior of the ionic liquid–polyimide composite films under high-vacuum environment

Ionic liquid (IL) can be used as external or internal lubricant. The tribological performance of polyimide (PI)–steel contact surface driven by IL lubricant was investigated using a ball-on-disk tribometer in high-vacuum environment. The experimental results indicated that IL as the external lubricant could obviously decrease the friction coefficient of PI from 0.41 to 0.01 and corrode the surface of steel ball. As internal lubricant, some IL/PI composite films were prepared, and the structure properties and tribological behavior were investigated. IL can be uniformly dispersed in the polymer and could make film surface more hydrophilic along with the increasing content of IL in PI. The IL/PI composite film with 1% content of IL has the lowest friction coefficient and causes the least damage against the steel ball.

Development of devices for self-injection: using tribological analysis to optimize injection force

This article describes the use of analytical models and physical measurements to characterize and optimize the tribological behavior of pen injectors for self-administration of biopharmaceuticals. One of the main performance attributes of this kind of device is its efficiency in transmitting the external force applied by the user on to the cartridge inside the pen in order to effectuate an injection. This injection force characteristic is heavily influenced by the frictional properties of the polymeric materials employed in the mechanism. Standard friction tests are available for characterizing candidate materials, but they use geometries and conditions far removed from the actual situation inside a pen injector and thus do not always generate relevant data. A new test procedure, allowing the direct measurement of the coefficient of friction between two key parts of a pen injector mechanism using real parts under simulated use conditions, is presented. In addition to the absolute level of friction, the test method provides information on expected evolution of friction over lifetime as well as on expected consistency between individual devices. Paired with an analytical model of the pen mechanism, the frictional data allow the expected overall injection system force efficiency to be estimated. The test method and analytical model are applied to a range of polymer combinations with different kinds of lubrication. It is found that material combinations used without lubrication generally have unsatisfactory performance, that the use of silicone-based internal lubricating additives improves performance, and that the best results can be achieved with external silicone-based lubricants. Polytetrafluoroethylene-based internal lubrication and external lubrication are also evaluated but found to provide only limited benefits unless used in combination with silicone.

New Graphene/Ionic Liquid Nanolubricants

In this work, we have prepared new graphene/ionic liquid dispersions by adding a 0.1wt.% proportion of 1-2 layers graphene (G1) or 1-10 layers graphene (G2) to the ionic liquid 1-octyl-3-methylimidazolium tetrafluoroborate (IL). The new dispersions (IL+G1) and (IL+G2) have been used as external lubricants in polymer-steel and ceramic-steel contacts. For AISI 316L stainless steel/epoxy resin, the order of friction reduction is (IL+G2)>IL>(IL+G1). The wear reducing order is the same, as abrasive wear takes place for (IL+G1), while G2 prevents any degree of surface damage on both materials, even the very mild wear observed for neat IL. The poor performance of G1 is related to the formation of abrasive graphene-IL aggregates. The (IL+G2) dispersion also shows superior friction reducing and anti-wear behavior under more severe contact conditions, for AISI316L against sapphire.

Tribological Properties Study on Polyamide with Incorporated Lubrication

The polyamides have more engineering applications. Because it has better tribological properties. But in the case of filled polyamides does not has beneficial effect on the friction by using mineral oil as external lubricant. Itappears that the glass fibers came out on the rubbing surfaces and decreased the effectiveness of the lubricants. To reduce the above mentioned contradiction few vegetable oil used as lubricants. In this experimentation deals and gives the solution for tribological properties of filled polyamides incorporated with vegetable oil and mixed vegetable oil in equal proportion. It seems that vegetable oils were increased the effectiveness of filled polyamides surfaces.

Impact of process parameters on Mg–St content and tablet surface wettability in the external lubrication method for a rotary tablet press

External lubrication is a new alternative used in compression processes of the pharmaceutical industry to minimize the negative effect of lubricant and to resolve sticking problems. This method can also prevent the deterioration of tablet properties; e.g., reduced tensile strength and a retarded rate of drug dissolution. The current study prepared tablets using the external lubrication method with varying potential critical process parameters and clarified the process of external lubrication via statistical analysis. In accordance with past results, tablets prepared using the external lubrication method had better tablet properties (higher hardness and more rapid disintegration) than those prepared using the internal lubrication method. Quantitative analyses of the magnesium stearate content and contact angle showed that the wettability of the tablet surface increased with the magnesium stearate content. Analysis of variance showed that all potential critical parameters are influential for the magnesium stearate content, but not for the disintegration of tablets. In addition, predictions of the magnesium stearate content and disintegration time of tablets made using a model equation correlated well with observed values. The external lubrication method can thus be applied by identifying the critical process parameters in the compression process during the development and manufacture of pharmaceutical products.

Influences of graphite reinforcement on the tribological properties of self-lubricating aluminum matrix composites for green tribology, sustainability, and energy efficiency—a review

Aluminum/graphite (Al/Gr) composites have been used as self-lubricating materials due to the superior lubricating effect of graphite during sliding. This paper summarizes various tribological aspects of self-lubricating aluminum composites. The influence of various factors such as (a) material factors, graphite size and volume fraction, and (b) mechanical factors, applied load and sliding speed on the tribological properties of self-lubricating aluminum composites, is discussed. Furthermore, the tribological properties of self-lubricating composites as a function of these parameters and the active wear mechanism involved in various systems are discussed. Bringing self-lubricating composites into different operating systems is a solution to reduce the use of external toxic petroleum-based lubricants in sliding contacts in a way to help the environment and reduce energy dissipation in industrial components for strategies toward sustainability and energy efficiency.