Lubricant Retention Research Articles

Characterization of Surface Topographies Generated using Circular- and Cylindrical-Face EDT

Large area texturing using EDT is challenging due to surface damage resulted from inefficient discharges, such as arcs and short-circuits. Also, three-dimensional analyses of surface topography generated during electrical discharge texturing (EDT) are scarcely performed in the available literature. Therefore, in this work, two modes of EDT were developed for large area texturing based on the mode of electrode movement resulting in texture generation on work surfaces: circular-face EDT (CirEDT) and cylindrical-face EDT (CylEDT), and the generated surface topographies are characterized in terms of topography images, areal texture parameters, and scanning electron microscopy images. Parametric analyses are also performed to study the influences of the operating parameters, such as discharge current, pulse on-time, and peripheral velocity, on different areal texture parameters. Topography analyses reveal that these surfaces have a characteristic stochastic distribution of microstructures in shape, size, and location. Height parameter analyses reveal that CylEDT surfaces are twice positively skewed and have a higher kurtosis as compared to the CirEDT surfaces. Spatial parameter analyses reveal that both surfaces display dominance of isotropic nature and non-directional structures. CirEDT surfaces have higher lubricant retention capacity, but lesser wear volume available for running-in period as compared to CylEDT surfaces, as per volume parameter analyses. Discharge current and pulse on-time are identified as the significant parameters influencing the majority of the areal texture parameters analyzed. SEM analysis revealed that CylEDT results in a textured surface with sea-wave-like structures, whereas CirEDT results in a textured surface with lunar-craters-like structures.

Three-dimensional topography analysis of electrical discharge textured SS304 surfaces

• Present comprehensive three-dimensional topography analysis of EDT SS304 surfaces. • Peak count distribution of textured surface flattens as discharge energy increases. • Rough surfaces with taller, sharper, and less dense peaks at high discharge energy. • High discharge energy improves wetting and sealing properties of textured surface. • Running-in wear volume and lubricant retention capacity are also improved. In the current work, a comprehensive three-dimensional topography characterization of electrical discharge textured SS304 surfaces is performed under the following heads: quantitative representation, microstructures and their distributions, and surface functionality. Topography analysis reveals that peak count distribution tends to become flattened with their mean shifting to higher heights when discharge energy increases. Higher discharge energy generates rougher textured surfaces with taller and sharper, but less densely distributed peaks. These textured surfaces also show improvement in wetting and sealing properties, more running-in period wear volume, more surface area for load carrying, and improved lubricant retention capacity.

Mastering the Art of Cylinder Bore Honing

<div class="section abstract"><div class="htmlview paragraph">Honing is a stock removal process intended to perfect bore geometry and size by removing a minimal metal layer while generating a finish pattern to provide optimum lubricant retention. The hone process produces extremely tight tolerances in straightness, roundness, size, and surface finish of cylindrical bores. The material removal is effected by abrasive stones of suitable grit and grade that are expanded against the work surface of the cylinder bore under controlled pressure while being rotated and reciprocated at the same time. Combining these motions produces a characteristic crosshatch pattern with a dedicated surface roughness profile essential for the piston/bore tribology, which in its turn affects the engine performance. Multistep honing processes that combine rough honing with peak or plateau honing are increasingly used to produce state-of-the-art surface finishes without compromising productivity. The outcome of the honing process - not only in terms of the GD&T but also the tribology of the finished component - depends on a great number of parameters including the machine type, working conditions, tools, process fluid, and most importantly the operator experience. As the piston/bore tribology is concerned, mechanochemical processes offers significant advantages over conventional mechanical processes. Thus, the mechanochemical finishing of cylinder bores using the Triboconditioning® process allows one to reduce friction mean effective pressure of the piston/bore system by 5 to 15% at the same time significantly reducing piston ring wear, blowby and oil consumption.</div></div>

Femtosecond laser-induced sub-micron and multi-scale topographies for durable lubricant impregnated surfaces for food packaging applications

Adhesion of viscous liquids on packaging surfaces could lead to wastage, an increase of recycling costs, and even customers' dissatisfaction in applications related to food, cosmetics and agrochemical industries. Lubricant-impregnated surfaces (LIS) gained much attention recently over other surface functionalisation technologies due to their non-sticking response to highly viscous liquids. This work reports an investigation into anti-adhesive properties of LIS, with an emphasis on their durability. It provides an insight into the rationale design of LIS topographies in order to maximise their lubricant retention in potential food packaging applications. Femtosecond laser processing and hot embossing were employed to produce two types of topographies for LIS on stainless steel, polypropylene and polystyrene surfaces. The first type was single-scale sub-micron laser induced periodic surface structures (LIPSS), while the second one was multi-scale (MS) structures with both micron and sub-micron features. Droplet shedding characteristics of such LIPSS-LIS and MS-LIS substrates with water, milk and honey were examined under vibration and shear. The critical sliding angles at which liquid droplets attained motion on LIS were observed to be less than 32° for all investigated liquids. However, the LIPSS-LIS substrates retained their functionality even after subjecting them to severe vibration, while the MS-LIS substrates partially lost their anti-adhesive characteristics. At the same time, the MS-LIS substrates exhibited premature pinning of droplets as compared to LIPSS-LIS substrates, under shear forces. Both vibration- and shear-induced loss of lubricant impacted the MS-LIS functionality.

Parametric optimization of the generation of the porous layer for lubrication in tube drawing process

For severe metal deformation processes such as metal drawing operations, the use of porous lubricant carrier layer on metal surfaces has been proposed in recent literature for better lubricant retention and effectiveness under extreme conditions. The porous layer may be generated by different methods and the method chosen in this study involves electroplating a thin layer of an alloy of tin and zinc on the parent metal and subsequent selective etching of zinc. The aim of this study is to optimize parameters for specific application of the new technique in steel tube drawing operation using Taguchi's experimental design procedures. Experiments are designed based on three controllable factors namely electric current density, process time and Sn-Zn composition by weight in electrolyte at three levels. L9 orthogonal array is used for this study. The regression models have been constructed for drawing force and surface roughness along with verification of the model fit using (R2) values and analysis of variance (ANOVA). The optimal values for parameters have been identified using signal to noise (S/N) ratio. All the calculations are obtained by using Minitab software. The optimal levels for: current density (I) is 1 A/cm2; for plating time (T) is 12 min and; Sn:Zn composition is 1:6. This study may pave the way for industrial adoption of the new technique of using porous layer in tube drawing operations to bring out the associated benefits of doing away with the conventional lubrication systems that have proven environmental hazards.

Efficacy of surface microtexturing in enhancing the tribological performance of polymeric surfaces under starved lubricated conditions

The efficacy of microtexturing on the tribological performance of Aromatic Thermosetting CoPolyester (ATSP) and Ultra High Molecular Weight Polyethylene (UHMWPE) were investigated under oil-lubricated starved conditions. Nominal contact pressures of 5.02 and 10.04 MPa were applied over a range of sliding velocities, 0.008–2.278 m/s. Static and kinetic coefficients of friction (COF) for untextured and textured surfaces were obtained and compared. Reduction in the average kinetic COF up to 29% for microtextured ATSP and 25% for microtextured UHMWPE were obtained. Static COF did not exhibit a notable change as a result of microtexturing. The core void volume was identified as a reliable indicator of the wear intensity of the dimples and consequently lubricant retention capacity for texturing. While both microtextured polymers illustrated reduction in the kinetic COF, only ATSP showed mechanical integrity for applications that experience high contact load under starved conditions. Microtextured UHMWPE experienced mechanical failure due to fluid pressure build up in the dimples under high load tests.

Experimental Study of Laser Texturing Processes on the Lubricant Retention of Carbide (WC-Co) Surfaces

Machining process usually involves relevant wear effects on the cutting tool, producing undesirable surface features on the work-pieces. Lubricants and cooling fluids are used with the aim to minimize the wear phenomena as well as high temperatures produced during the cutting processes. However, the use of these fluids may have an adverse environmental impact. For this reason, the reduction of quantity of cutting fluids used in the machining process is a requirement in order to improve the performance and sustainability of the process. For this purpose, this work proposes an increase of the lubricant retention ability for cutting tools based on surface modification. In this research, micro-geometrical features of Carbide (WC-Co) surfaces have been modified by laser texturing techniques. A wide range of roughness topographies had been developed by changing the laser irradiation parameters of energy density of pulse (Ed) and scanning speed of the beam (Vs). Different geometries of the textured tracks (single spots, linear tracks, circular tracks) also were studied. Moreover, through specific roughness features conducted by texturing process, the retention ability of cutting fluids was modified. It was evaluated by the contact angle between liquid and solid phases. This modification allowed to increase the self-lubricant effect of the WC-Co surface. This methodology has been validated on carbide tools under lubricated machining processes. Wear effects on the cutting tool were reduced and the surface finish of the machined parts was remained at least in the same ranges as non-modified tools.

Self-competing and Coupled Effect of Laser-Engraved Counterface Groove Depth and Density on Wear of Alumina PTFE

Polymeric solid lubricants rely on the deposition of a debris-formed transfer film on the usually metallic counterface to reduce wear and friction. Debris retention at the sliding surface is determined by the interactions between debris and roughness asperities which are complex functions of debris size and roughness profile. Recent works found pre-existing, sandpaper-lapped counterface roughness grooves perpendicular to the sliding direction could significantly improve debris retention and reduce the wear rate of an alumina PTFE solid lubricant by 70%. In this paper, we aimed to test the independent effects of roughness groove depth and density on debris retention and wear performance of a well-studied alumina PTFE solid lubricant using laser-textured counterfaces with independently varied groove depth and interval. All grooves in this study were engraved perpendicular to the sliding direction. The results suggested both groove depth and interval have self-competing effect on wear due to the in situ grounding and roughness alignment of the counterface topography during sliding and may compete or cooperate with each other in determining solid lubricant wear. A new surface directionality parameter was defined to quantify the in situ counterface roughness alignment which increased proportionally with increased composite wear volume at low-wear transition. A conceptual framework was proposed to illustrate the relations between counterface texture, transient wear volume, surface directionality and counterface abrasion.

Development of novel cutting tool with a micro-hole pattern on PCD insert in machining of titanium alloy

The development of a novel cutting tool that had a micro-hole pattern on their rake and flank face of cutting tool surface has found wider potential in the field of manufacturing. Micro-hole pattern features on a tool rake face help in controlling the tribological characteristics of the cutting tool. Micro-holes with the different number of holes orientation, diameter and depth were fabricated using the advanced application of the electrical discharge super drilling machine with the view to assist lubricant penetration and retention. A comparative study has been conducted between micro-hole patterned Polycrystalline Diamond (PCD) cutting insert and the commercially available PCD cutting insert. The effect of micro-hole pattern on the machining of Titanium alloy (Ti-6Al-4 V) is investigated with the application of the Minimum Quantity Lubrication (MQL) method in turning operation. Vibration signals were captured in feed force direction and measured using the tri-axial accelerometer. The cutting temperature, tool-wear, and chip-morphology were measured with an infrared thermometer and Scanning Electron Microscope (SEM). It was found that micro-hole textured inserts reduced the friction on the rake face resulting in the decrease of vibration up to 30–50%. The cutting temperature, tool wear and surface roughness were reduced to 30%, 50% and 40%, respectively. The conical and helical chips were produced in micro pool lubrication system. The friction coefficient can be minimized at the tool-chip interface by using liquid lubrication method. There is no unfavourable effect on the performance of cutting tools having holes on the cutting tool surface. All these parameters led to the improvement in the tool life.

Correlating and evaluating the functionality-related properties with surface texture parameters and specific characteristics of machined components

Machining-process-induced surface texture plays an indispensable role in determining surface integrity and final functional performance of the machined components. Although there are already many existing standard parameters for quantitatively characterizing the machined surface, accurately describing and effectively correlating the 3D surface texture parameters and specific characteristics with the relevant functional performances in practice, are still not well solved. The inadequacy of using 2D single-valued surface profile parameters and the non-ubiquity of using 3D areal surface texture parameters in industry are the main obstacles. The research reported in this paper addressed this issue by proposing a practical means which makes use of both 3D surface texture parameters and statistical functions for surface geometrical characterization and functional correlation and evaluation. To better investigate the influence of machining-induced surface texture and its characterization on the functionality-related performance of machined surfaces, Ni-based superalloy GH4169, a typical difficult-to-machine material widely used in aircraft industry, was selected for the machining experiment. Two kinds of mechanically-processed surfaces, one ground and the other turned, both having an identical value of 3D arithmetic mean deviation (Sa), were quantitatively characterized and analyzed using 2D and 3D surface texture parameters. Considering that the measured 3D surface texture is of random nature, the corresponding functionality-related performances were also investigated with statistical functions, e.g. power spectral density (PSD) and auto-covariance (ACV). Correlation between the 3D surface texture parameters or statistical functions with the corresponding functional performance, e.g. contact, running-in wear and lubricant retention, were then established. This study emphasized on the effectiveness and veracity of the 3D surface texture parameters and statistical functions in characterizing and evaluating machined-surface performance along with the traditional 2D parameters. It is especially suitable for machining materials whose functionality-related properties are machining-process-sensitive and surface-texture-dependent.

Modeling of oil retention in microchannel type evaporators and its effects on refrigerant heat transfer

This paper presents a new model for lubricant retention in microchannel type evaporators and shows a comparison between experimental and simulation results using refrigerants R134a and R410A and synthetic polyolester (POE) mixtures. Two different microchannel geometries were considered: a single and a double slab heat exchanger. The model predictions of the heat transfer capacities were within ± 10% with respect to the experimental data. The pressure drops were estimated with an error that ranged from ± 20% to ± 50%. Oil retention was predicted both locally and for the entire heat exchanger. The negative effect of oil on the performance of heat exchangers differs with oil concentrations and most of the lubricant was retained in the superheated region of the evaporator and in the outlet header. The predicted oil retention volume was within ± 60% and the simulation results suggested that the geometry details inside the headers have significant effects on the amount of oil retained.

An investigation on surface functional parameters in ultrasonic-assisted grinding of soft steel

In engineering applications, many surfaces are manufactured with some specific functional properties such as bearing, sealing, and lubricant retention capabilities. In order to figure out the characteristics of surfaces ground by ultrasonic-assisted grinding, surface bearing index Sbi and core fluid retention index Sci were adopted in this study to investigate the effects of grinding velocity and ultrasonic vibration amplitude on the bearing and fluid retention properties of ground surfaces. Results indicated that the surface bearing index Sbi and core fluid retention index Sci of ultrasonic-assisted grinding (UAG) were larger than those of common grinding (CG) under the same condition. The surface bearing index Sbi decreased with the increase of grinding velocity and increased with the increase of the ultrasonic vibration amplitude, while the core fluid retention index Sci increased with both the grinding velocity and ultrasonic vibration amplitude. Ultrasonic-assisted grinding mechanisms were further explored to interpret these trends. The oscillation in the axial direction generates more overlaps, resulting in relatively flat-top surface. The oscillation in the radial direction generates more intermittent concave, thereby increasing the space for fluid.

Experimental study of oil retention in microchannel type evaporators of air-source heat pump systems

In air-source heat pump systems, lubricant is often used with refrigerant compressors and, a small portion of oil, which is inevitably discharged by the compressor, circulates with the refrigerant across the systems components. Oil tends to accumulate in heat exchangers, increasing the pressure losses and reducing the heat transfer capacity. In addition to energy efficiency degradation, safe and reliable operations of the compressors can be compromised by unknown amounts of oil retained in the heat exchangers.In the present paper, the lubricant retention in two microchannel type evaporators for residential air heat pump systems was measured and the oil effects on evaporator heat transfer capacity and refrigerant-side pressure drop were investigated. Refrigerant R410A was investigated with polyolester lubricant that had a viscosity grade of 32. Saturation temperature was controlled from 0.5 °C and up to 9 °C and the impact of the degree of refrigerant vapor superheat at the evaporator outlet on the oil retention in the heat exchanger was significant. At high oil concentration, 13% of the internal volume of the evaporators was occupied by lubricant that was either retained or in circulation with the refrigerant inside the evaporators. When oil concentration was below 1 wt.%, which is typical in today's systems, the retained oil was about 10% of the internal volume, pressure losses increased up to 25% and the heat transfer capacity was reduced by 4%.

Anti-spreading behavior of 1,3-diketone lubricating oil on steel surfaces

Abstract For many precision devices with limited amount of lubricants, the retention of lubricating oil between solid surfaces is of great significance for the lubrication reliability in the long-term operation. In this study, the spreading behavior of a synthetic 1,3-diketone lubricant (1-(4-ethyl phenyl) nonane-1,3-dione) 02/06 on steel surfaces was investigated. By measuring the surface tension of oil and the surface energy of steel, the spreading parameter of 02/06 was determined, which was much smaller than the reference oils with similar viscosity. Rotary friction test shows that 02/06 was positioned at the contact region in the presence of a strong centrifugal force and performed a stable ultralow friction. Moreover, the addition of 02/06 into the reference oils also improved the lubricant retention.

Effect of crystal size on the tribological behavior of manganese phosphate coatings under lubricated sliding

In this study, the wear and friction behavior of manganese phosphate coatings with different crystal sizes were investigated. Crystal size was controlled modifying the chemical composition of the phosphating bath, particularly the concentration of the activator which modifies the number of nuclei for crystal growth. Activator concentration range used for this work varied from 0 to 0.7 g/L, and crystal size was measured using image analysis software on scanning electron microscopy photographs. Available volume for lubricant retention was determined measuring the phosphated surface with a 3D optical profilometer. At the same time, lubricated wear tests were carried out using a ring-on-block configuration at low speeds (23 mm/s) and high loads (14,500 N). Wear behavior was determined as the sliding distance to failure, which was noticed through signs of removal of the phosphate along with the increase of coefficient of friction. It was found that there is a competition between the availability of volume to hold the lubricant, which increases with the crystal size, and the surface coverage, which diminishes as the crystal size grows. Optimal results were obtained for an activator concentration of 0.3 g/L, which meant an average crystal size of 16 µm.

In-situ observation of lubricant flow on laser textured die surface in sheet metal forming

Abstract In the present study, to observe the contact interface during sheet metal forming process, in-situ observation system using transparent silica glass dies and high speed recording camera was developed. To correlate the dimensional parameters of micro-textured structures and tribological properties during the forming operation, in-situ observation during ironing process of stainless steel sheet with a thickness of 0.1 mm was performed. Tribological behavior was compared between the different dimple structures under different contact state. Dimple structure arrays with diameters of 10, 50, 100 µm were achieved by using femto-/pico-second laser processing. As results, the textured die with dimple diameters of 10 and 50 µm showed the lubricant flow transferred from one to the other dimple structures, in which hydrodynamic pressure seems to generate inside the dimples, while that of 100 µm indicated the less supply of lubricant. However, for the textured die with a dimple diameter of 10 µm demonstrated higher ironing force than that of 50 µm, due to the coverage of dimple structures by generated wear debris during the forming process. Based on these experimental findings between different contact states, the principle in generation of hydrodynamic pressure, the function of micro-trap for wear debris and the micro-reservoirs effect for lubricant retention depending on the size of dimple structures were discussed by correlating with the in-situ observation results.

Characterisation and full-scale production testing of multifunctional surfaces for deep drawing applications

Full-scale deep drawing tests using tools featuring multifunctional surfaces are carried out in a production environment. Multifunctional tools display regularly spaced, transversal grooves for lubricant retention obtained by hard-turning, separated by smooth bearing plateaus realized by robot assisted polishing. Advanced methods are employed to characterise the tools’ surface topographies, detecting the surface features and analysing them separately according to their specific function. Four different multifunctional dies as well as two un-textured references are selected for testing. The tests are run using a non-hazardous, environmentally friendly lubricant, and the forming forces are constantly recorded. Multifunctional dies exhibit very good performances, with no galling occurrence and punch forces generally lower than the two references.

Development of low-cost deformation-based micro surface texturing system for friction reduction

Surface texturing as a means for enhancing tribological properties of mechanical components has been under intensive investigation over the last two decades. Many methods have been proposed to create surface texture of various patterns and geometries. However, among all these methods, deformation-based micro-surface texturing is least studied. It has many advantages over other methods that could lead to immediate industry application, including high productivity, high geometry fidelity and low cost. In the current work, a simple but effective incremental micro embossing system based on a commercially available press has been developed to create micro surface textures of various shapes and depths with accuracy up to 5 μm. The friction coefficients of the textured surfaces have been tested at different loadings and speeds with various lubricants to demonstrate their friction reduction capability. It has been observed that at high speed conditions, the friction reduction is achieved by the hydrodynamic lift. Interestingly, at the low speed conditions, the micro-surface texture is still capable of reducing the friction, thanks to its lubricant retention and debris entrapment capability. A micro surface textured mechanical face seal demonstrator has been built to further evaluate the micro surface texture created by incremental embossing method. A reduction of 20% in torque friction has been consistently achieved, which is on a par with that of the laser surface texturing method.

Development of a form rolling micro surface texturing system for friction reduction application in the shaft component

Surface texture is one of the most promising methods to achieve friction reduction in the mechanical components, and it has been rapidly developed in the last decade. The friction reduction mechanism of regularly patterned surface texture is widely considered to be lubricant retention and debris entrapment. There are many ways to manufacture micro surface texture, among which deformed-based micro-surface texturing is the least studied. However, it has many unique advantages that cannot be surpassed by the rest, such as high production efficiency, fine geometrical fidelity and smooth surface finishing. Therefore, this study aims at developing a deformation-based low-cost micro form-rolling machine to create micro surface texture on the cylindrical component. A new demonstrator for examining the friction reduction efficiency of the micro surface texture has also been built and tested. Results show that the shaft with micro surface texture is able to reach a maximum of 48.1% friction reduction at rotation speed 400 r/min with lubricant SAE30 compared to the non-textured workpiece with the same condition.

Experimental analysis and modeling of lubricant effects in microchannel evaporators working with low global warming potential refrigerants

In any vapor compression system, lubricant is needed to guarantee safe and reliable compressor operation. Indeed, most compressor mechanical failures are generally due to improper oil management, such as, lack of proper lubrication inside the compressor. Since in the usual operating condition of the system a small portion of oil circulates with the refrigerant through the system components, it can be retained inside the heat exchangers leading to oil missing from the compressor. In present article, the lubricant retention characteristics of two microchannel type evaporators for residential air conditioning systems and the oil detrimental effects on evaporator capacity and refrigerant-side pressure drop were investigated. The working fluids used in this study were R410A, as reference refrigerant, and low global warming potential refrigerants R32, R1234yf, and R454B, a new low global warming potential mixture candidate to replace R410A, whereas the lubricant was VG 32 Polyolester oil. The effects of oil mass fractions and degree of superheat were experimentally investigated considering working conditions typically found in air conditioning systems. Finally, the experimental results of the present article provided data that were used to develop and validate a semi-empirical model for microchannel evaporator simulation able to account for the oil presence. The developed model was summarized in the current article and the results were compared with the experimental ones in term of oil retention, capacity, and refrigerant-side pressure drop.