Pin Surface Research Articles

MoS2‐decorated talc hybrid for improving the tribological property of Nomex/PTFE fabric composites

AbstractProducing self‐lubricating fabric composites with excellent wear resistance and long service life is desired for their use in practical application, yet still challenging. Therefore, a novel nanoparticle of talc‐molybdenum sulfide (MoS2) hybrid nanosheets was synthesized via one‐step hydrothermal reaction in this work and incorporated into the Nomex/polytetrafluoroethylene (PTFE) self‐lubricating fabric composites. The spectroscopic and microscopic characterization demonstrated that the talc‐MoS2 nanosheets were successfully synthesized. The talc‐MoS2 nanosheets exhibit the obvious layered structure and covered with MoS2. The effect of talc‐MoS2 hybrid nanosheets on the tribological performance of fabric composites was systematically evaluated by tri‐pin on disk tribometer. The results show that the talc‐MoS2 nanosheets increased the thermal stability, thermal conductivity, tensile strength, and hardness of composite and was favorable for forming high‐quality transfer film on the surface of counterpart pin during the wear process owing to the cooperation effect of talc‐MoS2. The wear rate of talc‐MoS2‐reinforced composite was reduced by 30%–53% under different conditions compared with pure fabric composite.

Influence of Change in the Apparent Contact Area, Temperature and Vacuum on Tribo Response of Al6061 and EN8 Pair

Objective: Aluminium and its alloys components are used in aero and space industries where in many cases trioboloading prevails. In space application, in addition to triboloading, the components should also perform in the absence of atmosphere. In the present investigation, attempted has been made to simulate the field conditions in the laboratory by sliding Al6061 alloy pin of different diameters in a vacuum at different temperatures using a vertically configured pin-on-disc test rig. Method: The pin diameters were 2, 4, and 6mm and the testing temperatures were 373, 473, and 573K. The normal contact pressure was 0.625MPa and the sliding speed was 0.5ms-1 and both were constant throughout the experiment. The coefficient of friction was monitored using a PC and the worn pin surface was studied in scanning-electronmicroscope. Findings: The result showed that the coefficient of friction at sliding temperatures 373 and 473K was found to be dependent on apparent contact area i.e., pin diameters 2, 4, and 6mm. The coefficient of friction was found to be 3.27 and 2.69 for pin diameter 2mm at temperature 373 and 473K whereas the coefficient of friction was of the range 1.36 to 0.33 for the pin of diameter 4 and 6mm. The scanning-electron-microscopic study revealed uniform plastic deformation for pin diameter of 2mm and non-uniform plastic deformation accompanied with abrasion extrusion phenomenon for the pin of diameters 4 and 6mm. The coefficient of friction at sliding temperature 573K was found to be insensitive to the apparent contact area. The coefficient of friction was in the range of 1.24 to 2.30. The SEM study revealed a large scale of non-uniform plastic deformation accompanied by abrasion, tearing of ridges, extrusion of both ridges, and entrapped wear debris. Novelty: It is a generic study for understanding the response of aluminium for tribo loading which. Keywords: Pin on Disc (POD); Scanning Electron Microscope (SEM); High Temperature; Vacuum; Coefficient of Friction; Al6061 Aluminium Alloy 1

Localized droplet heating by hydrophobic pins: Influence of pin area and droplet size on heat transfer

Localized heating of hydrophobic droplet is considered and the effects of restricted area heating and droplet size on heat transfer are examined. Samples composing of vertical steel pins located in Perspex holders are designed and manufactured. Sample surfaces are hydrophobized via depositing treated silica nanoparticles by dip coating method. Hydrophobicity of pin and Perspex surfaces are evaluated simultaneously securing uniform wetting state over sample surface. Droplet is heated via pin while creating a localized heating effect on droplet fluid. The experiments are conducted obtaining flow structures in droplet liquid. Simulations are also performed predicting thermal state in droplet liquid during heating while adopting conditions of the experiments. It is found that hydrophobizing of samples results in uniform contact angle (150° ± 2°) over the entire surface having hysteresis of 6° ± 3°. Enlarging pin diameter and droplet size alter flow structures inside droplet; hence, center of circulating structures changes, which modify the ratio of convection over conduction currents at droplet liquid interface. Increasing pin diameter enhances the Nusselt and the Bond numbers, which becomes more apparent as droplet volume increases.

Electroless Ag films for ionic liquid lubricated electrical contact

Two kinds of plating solutions, i.e. a standard plating solution and a commercially available plating solution, are employed for the preparation of electroless Ag film. The commercially available plating solution enables fast film deposition within several minutes and is highly selective for deposition onto Cu substrate, and cost-effective (reusable solution, and much less Ag consumption) compared to the standard plating solution. Both electroless Ag films prepared have distinct microstructure, surface chemistry, and bulk chemistry. The film from standard plating solution is composed of nano-grains with an average grain size of 300 nm and homogeneity. The film prepared with commercially available plating solution is composed of equiaxed grains (140 nm in size), and ribbon fish-like grains (80 nm in size and 0.5-2 μm in length) and shows microstructural inhomogeneity. The tribological properties of these electroless Ag films in presence of flooded 1-methyl-3-octylimidazolium hexafluorophosphate are investigated on a reciprocating tribometer with a pin-on-disk configuration under electrical contact. The results demonstrate that both electroless Ag films show better tribological property than Cu-on-Cu contact. Due to their dissimilar microstructure the tribological properties of the two electroless Ag films are quite different. For the standard plated film, local adhesion and tear-up in an annular shape on pin result in many plate-like wear debris in the early stage of the sliding test. For commercially the plated film from a commercial solution, compact and thin tribo-film on the worn surfaces of pin and disk as well as little or no wear debris are observed. The microstructural effect also has an influence on the design of the tribo-interface.

Dry Sliding Wear Behavior of Magnesium Nanocomposites Using Response Surface Methodology

Abstract In this study, a pure magnesium material reinforced with 0.5, 1, 1.5, and 2 w% of CaO was prepared through disintegrated melt deposition technique (DMD process). Nanocomposites were investigated for their sliding wear behavior in dry condition at room temperature. The amount of CaO, load, sliding distance, and sliding velocity were selected as input design parameters at their five level in central composite design using minitab 18.1 statistical software. The influence of design parameters on wear loss is reported through the response surface methodology (RSM). Analysis of variance (ANOVA) was used to confirm the soundness of the developed regression equation. The results indicate the contribution of linear, quadratic, and interaction terms of design parameters on response. Three-dimensional response surface and two-dimensional contour plots indicate the interaction effect. The result shows that an increase in the sliding velocity contributes to a decrease in the wear loss of the composites because of the emergence of protective oxidative layer at the surfaces of the pins, which is confirmed through field emission scanning electron microscope and energy dispersive X-ray analysis analyses of the pin surfaces. Wear loss of the material decreased as the amount of CaO increased. The ANOVA analysis concluded that the sliding distance and load contribute significantly to wear loss of the composites, and their percentage of contribution is 64.02% and 3.69%.

Effect of in-service work hardening on the sliding wear resistance of a heavy haul rail in the gauge corner

This work evaluates the tribological behavior of three samples taken from a pearlitic steel rail with different hardness values (550, 450 and 370 HV0.1) due to the in-service work hardening effect. A pin-on-disc sliding wear test was selected to simulate the sliding wear conditions among the wheel flange and rail head corner and gauge face. The influence of the stress level was evaluated by varying the applied normal loads; the 50 and 500 N loads were associated with large and small radius curves, respectively. Pins were made from the rail samples, and the counter body (disc) used was H-13 steel (600 HV30). The mass loss was measured, and the coefficient of friction (COF) for each condition was calculated. Scanning electron microscopy (SEM) was carried out for microstructural characterization of the samples before and after the sliding wear test. The results showed a monotonic correlation between the superficial hardness and the sliding wear resistance under the low severity condition. The sample with the intermediate hardness (450 HV0.1) has the greatest sliding wear resistance under the low severity, 50 N condition, and under the high severity test condition (500 N). For the tests performed at 50 N, the wear facilitated crack propagation, and the preexisting cracks were removed from the pin (rail) interface. In contrast, for the tests performed with a 500 N load, the material removal rate did not overcome the crack propagation. In addition, the energy at the sliding interface was enough to promote a white etching layer (WEL), which reproduced the surface of the in-service rails, and the material removal was not sufficient to remove the cracks from the pin (rail) surface.

Tribological analysis of automotive material under wet lubrication condition using diesel, biodiesel and their blend

Biodiesel made from vegetable oil can be considered the best alternative fuel for a partial or complete diesel replacement. Earlier studies on biodiesel and its blends have proven that biofuels in the existing engine can be favorable for partial eradication of diesel from C.I. engines. Therefore, this study investigates the tribological impact of various biodiesels and diesel and their optimum blend at normal room conditions. The tribological analysis is performed on a pin-on-disc tribometer. During the tests, the coefficient of friction, friction force and wear of pins (Aluminium, Copper and Iron) were examined; apart from this, weight & volume loss of the metal pins were also investigated. The pin surfaces were characterized by surface microscopic analysis. Fuel constituents and fatty acid content were analyzed by GC-MS and FT-IR tests to understand the cause of tribological wear better. Castor and Rapeseed biodiesel show the lowest weight of pin in comparison to diesel. The wear rate of metals with diesel shows extreme rises in wear as the sliding distance increase. The coefficient of friction, friction force of pins was found to be highest in diesel, followed by biodiesel and their blend in almost every case.

Wear characteristics of small ball-end fine diamond grinding pins dressed by on-machine electrical discharge

Small ball-end fine diamond grinding pins dressed by on-machine electrical discharge method are promising tools for ultra-precision grinding complex structural components of hard and brittle materials. Since the electrical discharge dressing can affect the grinding pin surface morphology, it is necessary to study the wear mechanism of the metal bonded fine diamond grinding pin dressed by electrical discharge. Electrical discharge dressing experiments and fused silica grinding experiments are conducted to investigate the relationship between grinding pin wear and the dressed grinding pin surface morphology, and analyze the influence of grinding pin wear on the grinding ratio G, surface roughness, and grinding force. The metal bond recast layer, the discharge crater around the diamond grit, and the diamond graphitization are the surface morphologies of the dressed grinding pin that affect the grinding pin wear. The wear modes of the grinding pin are micro-fracture, abrasion, metal bond wear, grit pull-out. Although metal bond wear accelerates the grinding pin wear, it is prone to improve the grinding pin self-sharpening. The grinding ratio, surface roughness, and grinding force variations with the fused silica sample removal volume further verify the analysis of the dressed grinding pin wear mechanism and the self-sharpening.

Characterization of wear and friction between tool steel and aluminum alloys in sheet forming at room temperature

This work investigates the coefficient of friction (COF) at room temperature between tool steel 1.2343 and aluminum alloys EN AW-5182, EN AW-6016 as-delivered (T4) and EN AW-6016 naturally aged (T4*) using a strip drawing tribometer. In order to simulate the contact conditions of industrial sheet metal forming processes, the surfaces of the steel pins and of the aluminum strips were maintained as-delivered, i.e., the pins were wire-cut from a hardened and ground plate and the strips were cut from electrical discharge textured (EDT) and dry-lubricated sheets. Two sliding velocities, 50 mm/s and 250 mm/s, and two nominal contact pressures, 10 N/mm2 and 20 N/mm2, were considered. The sliding distance on each strip was 0.5 m. Each pair of pins was utilized for testing 10 or 20 strips to study the influence of increasing the sliding distance on the COF. Before and after the tribological experiments, surface topographies of selected pins and strips were analyzed using 3D optical surface profilometry, optical microscopy and scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS). Strain hardening due to plastic surface deformation of the strips was investigated using an automated hardness tester. In general, an increasing trend of the COF was observed with increasing sliding distance. The mean COF obtained for each of the tests was in the range of 0.09−0.17; however, it was considerably higher if aluminum was transferred from the strip to the pins. Moreover, moist pin surfaces were identified to increase the COF, as the originally dry lubricant became pasty and sticky which promoted entrapment of abraded aluminum particles. Slightly higher strain hardening of alloy EN AW-5182 compared to alloy EN AW-6016 caused less flattening of the strip asperities and more severe wear of the pin surface.

Tribological performance of biomedical grade UHMWPE/nano-Al2O3/Vitamin-C hybrid composite for cartilage replacements

This paper presents the fabrication of UHMWPE/nano-Al2O3/Vitamin-C hybrid composites suitable for use as artificial cartilages in total joint prosthesis. Three composite variations were fabricated using the hot press technique, keeping the Vitamin C weight percentage constant at 2% and varying Al2O3 weight percentage by 0.5%, 1% and 2% respectively. Al2O3 was used as an anti-wear additive in UHMWPE and Vitamin C was used as an anti-oxidant. The fabricated composite pins were subjected to wear tests against Ti6Al4V alloy under dry sliding and human serum lubrication. It was observed that the 2 wt% Al2O3 filled UHMWPE showed better wear performance than the other composites and that human serum adheres to the surface of the composite pins upon sliding. This leads to the formation of a film which results in better wear resistance of the composite pins under human serum lubrication than dry sliding.

Reusable support for additive manufacturing

Abstract Additive manufacturing (AM) processes such as material extrusion and vat photopolymerization all require supports to print parts with overhang features. These additional supports using the same or different materials are a waste of materials since they need to be removed after the three-dimensional (3D) printing process and cannot be reused. The printing of supports is also time-consuming for the nozzle-based material extrusion processes. A new type of reusable support has been developed to address the support-related challenges in AM. The main idea is to use a set of dynamically controlled metal pins as a programmable building platform. In the layer fabrication, the metal pins will move up one-layer thickness after the printing of each layer. Also, each metal pin will automatically stop at a specified height that is determined by a combination of metal tubes, magnetic discs, and magnetic rings. Additional supports can be 3D-printed on the top surface of the metal pins, while the amount of the supports is dramatically reduced. After the printing process, the metal rods can be separated from the part and reset for the next printing job. A prototype system has been constructed to demonstrate the reusable support principle. The layout optimization and toolpath generation algorithms for the reusable support are also presented. The experimental results of several test cases show an average of nearly 40% saving on the printing time and material with increased reliability and robustness. The reusable support provides a support generation strategy that could be beneficial to other AM processes such as stereolithography and selective laser melting.

Eksperimentalna analiza zavarivanja trenjem korišćenjem ravnih igala kod AA2024-T3 limova

In friction stir welding, lesser tool life restricts the usage of non-circular pin in friction stir welding tool eventhough it delivers comparatively better weld joints than circular pin. Process peak temperature during the process affects the shear strength of the flowing material around the tool pin. Maintaining the process peak temperature as low as possible improves the properties in heat affected zone but on the other hand it increases the stress on the tool pin.Especially on the usage of non-circular pin, the pin surface experiences uneven stress distribution and causes premature tool failure. In this paper, optimum thermal environment through proper selection of process parameters and dwell period with respect to the pin geometry are analysed. A comparative analysis is also made to understand the impact of increase in flat surfaces in the pin surface on weld quality in the view of developing a suitable thermal environment that can improve tool life without compromising joint strength. Apart from this, optimum dwell period for the chosen tool pin geometry is analysed based on the empirical softening temperature of the material.

Ornaments of daily usage can be a source of microbial contamination and a causative agent of diseases

Hand hygiene is the most simple and effective way to prevent infection. Contaminated hand and related ornaments act as a vector of transmitting diseases. The main goal of this study was to find out whether personal accessories of different categories of working women are responsible for foodborne illness or contagious diseases. For this purpose, six categories of individuals were chosen, and five types of ornaments were taken from each individual. Total thirty swab samples were taken from the surface of bangles, nose pins, ear rings, finger rings and chains. Conventional culture techniques and biochemical tests were performed to determine the presence and identification of the pathogenic microorganisms. Total viable bacteria was present in all those samples but the presence of specific microorganisms were not found in all of those samples. Moderate growth of Staphylococcus spp. was found in finger rings and ear rings of the home makers and presence of Escherichia coli was detected in 16% of these samples as an indicator of fecal contamination. In the light of these results, it is essential to maintain proper hand hygiene and sanitation practice as some ornaments could be the significant source of pathogenic microorganisms. Food handlers and health care workers should abide by the rules and regulations of personal hygiene.
 Stamford Journal of Microbiology, Vol.10 (1) 2020: 5-8

Atomically Dispersed Dopants for Stabilizing Ceria Surface Area

Ceria is known to be a very good catalyst as well as a support for oxygen transfer (oxidation) as well as for hydrogen transfer (hydrogenation and dehydrogenation) reactions. Many of these reactions occur at high temperatures where ceria is known to sinter, leading to loss of surface area. The thermal stability of ceria can be improved by the addition of dopants, but the location of the dopant atoms and the mechanisms by which ceria stabilization occurs are poorly understood. We show here that dopants located on the surface of ceria are remarkably effective at stabilizing ceria surface area. Keeping metal loading constant at 0.88 mol%, we found that surface area of the ceria aged at 800 °C in air for 5 h ranged from 45 m2/g to 2 m2/g. Strongly bound dopants in atomically dispersed form help to pin surface sites and lower the mobility of ceria.

Effect of velocity and temperature on the dry sliding behavior of a SiC-Graphite composite against WC-CoCr and WC-FeCrAlY HVOF coatings

Dry sliding tests on pin on disc testing equipment were conducted on a new and developing SiC-graphite composite material, for racing applications, against WC-CoCr and WC-FeCrAlY HVOF coated discs. The coated discs were paired with the composite material to observe the friction coefficient and wear behavior at elevated testing conditions for potential applications in high intensity aerospace and train braking systems. The testing conditions included one constant contact pressure of 0.5 MPa, two sliding velocities of 1.57 and 7 m/s, and two working temperatures at room temperature (RT) and 300 °C (HT). The COF and pin wear increased with increase in velocity at RT conditions. Conversely, the COF and pin wear decreased with increase in velocity at HT testing conditions. For both the testing conditions, tests with WC-FeCrAlY coated disc provided for higher COF and wear compared to the tests with WC-CoCr coated disc. The friction layers on the worn pin surfaces were made by elements originating from the pin and also transferred from the disc and their extension increased with increase in velocity and testing temperatures. The disc surfaces were characterized by mild abrasive wear, in particular at HT and high sliding speed. A basic analysis on contact temperature was conducted to understand the mechanism of formation of friction layer for various testing systems. For RT testing conditions, due to low contact temperature, pin wear as well as uncompact friction layer were observed. However, as the contact temperature increased for HT tests accompanied by high velocity, a well compact friction layer with reduced COF and wear were noted.

Повышение долговечности переводников бурильных колонн электромеханической обработкой

Increasing the durability of drill pipe subs is a pressing problem, a solution to which will improve the efficiency of oil and gas companies when drilling wells. Outer diameter wear, tears on the end surfaces of couplings and the end surfaces of pins, as well as blemishes on external and internal conical rotary-shouldered connections are the most typical defects of the subs. A study and comparative bench tests of the 5135 steel subs with the Z-117 screw were conducted. Testing of the subs with hardening of the work surface by electromechanical processing was done in comparison with the base technology (hardening and high tempering) and carbonitriding. The drill pipe subs were manufactured and hardened by OOO Alexandrovsky Drilling Equipment Plant on the 1М63 machine modernized for electromechanical processing. The comparative bench tests of the drill pipe subs were conducted by OOO Kovrovsky Drilling Equipment Plant on the coupling makeup machine MC-4 by screwing on / unscrewing threaded connections, taking into account the Russian Federation standards and recommendations of the American Petroleum Institute API 7. Electromechanical processing, being one of the method of hardening by a concentrated flow of electric energy of industrial frequency, builds up a gradient layer with the hardness of 52–56 HRC on the surface of the drill pipe subs. The results of the screwing on / unscrewing tests of threaded connections with a toot-joint thread demonstrated high efficiency of carbonitriding and electromechanical processing (500 and more cycles) as a method of increasing hardness of the work surfaces and low efficiency of the current bulk heat treatment (up to 47–66 cycles).

A high‐gain cavity‐backed slot antenna using a perfect magnetic conductor ground plane and multilayered superstrates

AbstractThis article presents a high gain cavity‐backed slot antenna using a perfect magnetic conductor (PMC) ground plane and multilayered superstrates. A textured surface of periodic pins is applied to realize a high impedance surface (HIS), which simulates a PMC ground plane. The main advantage of using this structure is to suppress the surface wave propagation, improve the input impedance matching, increase the bandwidth, control the side‐lobe levels, and also provide higher gain. Moreover, the multilayered superstrates has been used to enhance the antenna gain. The simulations and measurements for the S‐parameter, gain, and radiation patterns of the antenna are presented. The proposed cavity‐backed slot antenna offers a maximum gain of 18 dBi and an impedance bandwidth of 16.5% at 11.5 GHz.

Study on traces left on a mechanical lock picked by a 3D printed key in toolmarks examination

The three-dimensional (3D) printed key is a key that can be manufactured from its virtual model by means of a 3D printer. This research focuses on the picking feasibilities and traces that can be observed and exploited from a forensic point of view after the picking of such type of keys.In this paper, 40 printed keys were manufactured using three different polymer materials (white resin, white nylon powder and black ABS). All the experiments were carried out under controlled conditions to allow the collections of data and traces produced by the picking. Of the 40 prints, only 38 picked the locks and the total picking ratio was 95 percent, meaning that a 3D printed key using polymer materials can be used to pick a lock. Elements of lock – pins and keyways – appeared to carry polymer materials (flakes or pieces) transferred from the prints during picking process. Additional, characteristic marks of a 3D printed key on the surface of pins was identical to those of an original key, but not similar to those of other picking tools. Indeed, this method could not create more marks on the bits of an original key while striations were left by the picking method using a duplicated key. Besides, FT-IR was a useful method of analyzing the type of polymer material used.When receiving original keys and a lock suspected to be picked in a crime scene, the toolmark examiners can quickly determine whether or not the lock was picked by a 3D printed key based on the examination results of these traces.

The role of scorching treatment on the wear and emission behavior of friction materials with and without copper

The present work aims at investigating the correlations between friction, wear and particle matter emission in copper-containing and copper-free automotive friction materials with particular emphasis on the effect of the scorching treatment. The tribological tests have been conducted using pin-on-disc laboratory equipment, and the airborne particles were measured in terms of number and mass. The results indicate that the number concentration of the airborne particles correlates well with friction coefficient, whereas their mass correlates better with the system wear rate. In addition, the copper-free material displayed a lower friction and wear and lower emissions than the copper-full. For this material, scorching was also found to reduce the friction coefficient, wear rate and emissions with respect to the pristine un-scorched condition, whereas no similar effects were found for the copper-full material. The results are discussed considering the characteristics and relevant role of the friction layers forming onto the pin surface.

Enhancing tribological characteristics of PEEK by using PTFE composite as a sacrificial tribofilm-generating part in a novel dual-pins-on-disk tribometer

In this work, polytetrafluoroethylene (PTFE)/bronze composite debris particles with strong tribofilm-forming abilities and slippery characteristics were released into a traditional pure poly-ether-ether-ketone (PEEK)-steel wear system to improve the tribological properties of PEEK. Wear tests were performed at room temperature under dry sliding conditions using a double-pin friction and wear test apparatus. The unfilled PEEK pins were allowed to slide against the steel counterparts with a fixed contact pressure of 4.0 MPa and speed of 0.8 m/s. Different amounts of PTFE/bronze debris particles were released onto the polymer/steel interface by introducing independent PTFE/bronze pins under different contact pressures (0.2–6.0 MPa) in the tribosystem. Results showed that the friction level and wear resistance of unfilled PEEK remarkably improved through releasing the PTFE composite debris onto the wear track. Under the test conditions used in this study, the friction coefficient and wear rate of unfilled PEEK decreased with the increasing contact pressure of the PTFE composite, but the wear rate of the PTFE composite increased. When compared to unfilled PEEK pins working alone, the optimal friction coefficient of PEEK was reduced from 0.45 to below 0.10, and its wear rate was reduced by approximately three orders of magnitude. Analyses of the worn surfaces revealed that the reduction in the friction and wear could be attributed to the formation of the ‘‘transfer film’’ on the counterpart steel surface and the ‘‘secondary transfer film’’ on the unfilled worn PEEK pin surface, both triggered by the PTFE composite debris. The wear mechanism of PEEK then transformed to sliding between the transfer and secondary transfer films, thereby preventing direct contact between the PEEK and steel countersurface.