Slider Material Research Articles

Sulfonated graphene improves the wear resistance of pantograph carbon slider materials under normal and wet conditions

Sulfonated graphene improves the wear resistance of pantograph carbon slider materials under normal and wet conditions

Sulfonated graphene improves the wear resistance of pantograph carbon slider materials under normal and wet conditions

AbstractA novel pantograph carbon slider (PCS-1) was designed and prepared via mold pressing, hot extrusion and sintering using sulfonated graphene (SG) as additive. The results show that PCS-1 demonstrates an obvious enhanced mechanical strength and wear performances than that of carbon slider in the absence of SG (PCS-0). For example, the current-carrying wear test indicates that the flexural strength of PCS-1 is 41.8% higher than that PCS-0 counterparts. The wear rate of PCS-1 reduces 51.0% and 50.0% in the wet and normal conditions, respectively. Moreover, the presence of SG, as reflected in scanning electron microscopy, polarizing microscope and white light interferometer, can markedly decrease the number of random cracks, increase the compactness of fracture surface and inhibit the electro-erosion of the slider materials, thus improving the mechanical strength and wear resistance significantly.

Experimental Investigation of Wear Effects on the Friction Coefficient of a Curved Surface Slider: Comparison of Small- and Full-Scale Tests

ABSTRACT The current practice to determine friction properties of sliding isolation systems is to perform displacement-controlled dynamic tests where the effects of several loading conditions with different amplitudes, loading velocities, and vertical forces are of concern. The number of cycles in these tests is generally three for most of the loading conditions assumed to be representative of seismic conditions. On the other hand, the isolator may undergo small-amplitude but large-cycles of service motions due to thermal deformations and accidental loads. In that case, the methodology requires to perform cyclic tests on small-scale samples of the slider material (not the isolator) considering very large accumulated sliding distances such as 1000 m for use in buildings, and 10,000 m for use in bridges. However, two unsettled issues are regarded: (i) the suitability of small-scale slider tests to estimate the characteristics of full-scale sliding isolation systems and (ii) the change in seismic performance of a sliding isolation system after it is subjected to a large amount of accumulated sliding distance. In the present study, both a full-scale double concave friction pendulum (DCFP) and small-scale sample composed of the slider of the DCFP are subjected to a total accumulated sliding distance of 1000 m. The corresponding variations in friction properties are comparatively presented, demonstrating that small-scale test results provide reasonable estimates for the friction properties of the tested full-scale DCFP. Moreover, the seismic response of the investigated DCFP remains almost the same regardless of the considered sliding distance.

Surface Chemical Aspects in Boundary Lubrication

Boundary lubricating behaviors were investigated from the viewpoint of surface chemistry based on our results. Boundary lubricating properties are closely related to the chemical structure of boundary lubricating films. TOF-SIMS (time of flight secondary mass spectroscopy) which has several advantages such as high sensitivity, high spatial resolution and high chemical resolution was applied to chemical analysis of boundary lubricating films. Degradation of lubricating films on hard disk media was investigated by TOF-SIMS and removal of the lubricant oil and chemical wear of slider materials was observed. It was found that the tribochemical degradation of the oil was catalyzed by the slider material such as Al2O3 and TiN. The degradation was suppressed when DLC and c-BN were used as a slider material. Thin layer of PTFE on tribo-material composed of PTFE-PEEK was characterized by TOF-SIMS after lubrication tests with a steel ring. It was found that the surface coverage of PTFE was decreased with increasing contact pressure from 6 to 27 MPa and welding occurred when the surface coverage was less than 20%. A tracer method with stable isotopes such as 2H(D), 13C and 18O was introduced for characterization of boundary layer formed from organic additives. Effectiveness of chemisorbed ethyl alcohol-d5 (CD3CD2OH) for lubrication of CrN with alcohol was confirmed by TOF-SIMS analysis. An important role of nascent surfaces on tribochemical reactions to form boundary layers was investigated. For the reaction of EP additives, an organic sulfide was more reactive on nascent steel surface than organic phosphates. It was found that decomposition of synthetic hydrocarbon oil was catalyzed by nascent surface of steel under the effect of frictional heat.

The effect of surface indentations on gouging in railguns

Hypervelocity gouging occurs in high speed sliding systems such as rocket sled test tracks, light gas guns, and electromagnetic railguns. Gouging takes the form of teardrop-shaped craters on the rail surface, and occurs above a threshold speed which is dependent on the slider and rail materials. In this study, gouging of aluminum railgun armatures on flat and indented copper rails was performed to examine the effect of macroscopic surface defects on gouge onset velocity and morphology. Both galling and gouge craters were shown to initiate at existing macroscopic and microscopic defects. Macroscopically flat rail surfaces provide no practical advantage over indented surfaces insofar as gouge onset velocity is concerned. However, the shape of the resulting gouge craters can be significantly affected.

Sliding wear behavior of plasma nitrided Austenitic Stainless Steel Type AISI 316LN in the temperature range from 25 to 400 °C at 10−4 bar

There is a research knowledge gap for the dry wear data of nitride treated Stainless Steel in high temperature and high vacuum environment. In order to fill this gap, plasma nitriding was done on austenitic Stainless Steel type AISI 316LN (316LN SS) and dry sliding wear tests have been conducted at 25°C, 200°C and 400°C in high vacuum of 1.6×10−4bar. The two different slider material (316LN SS and Colmonoy) and two different sliding speeds (0.0576m/s and 0.167m/s) have been used. The tribological parameters such as friction coefficient, wear mechanism and volume of metal loss have been evaluated. Scanning Electron Microscopy (SEM) was used to study the surface morphology of the worn pins and rings. Electronic balancing machine was used to record the mass of metal loss during wear tests. The 2D optical profilometer was used to measure the depth of the wear track. The Plasma Nitride treated 316LN SS rings (PN rings) exhibit excellent wear resistance against 316LN SS pin and Colmonoy pin at all temperatures. However, PN ring vs. Colmonoy pin Pair shows better wear resistance than PN ring vs. 316LN SS pin Pair at higher temperature.

Mechanical and tribological response of ABS polymer matrix filled with graphite powder

Thermoplastic-based polymer composites containing solid lubricant filler have been developed using a hot compression molding technique. The thermoplastic polymer is Acrylonitrile Butadiene Styrene (ABS) which is of great importance in applications such as bearing and slider material. The solid lubricant employed is graphite powder. Four mass ratios of the graphite particles in the ABS matrix were considered in the range of 0–7.5%. The mechanical properties of ABS composites were investigated using tensile test. The results show that the mechanical properties decrease significantly with the increase of graphite particles amount. Friction experiments were also conducted using a reciprocating tribometer recently developed in our laboratory. For each of the considered mass ratio, evolutions of the friction coefficient, the weight losses and the wear scar micrograph with respect to the number of sliding cycles were analyzed. Severe adhesive wear mechanism is activated for the ABS without graphite particles. Addition of graphite in ABS matrix exhibits lower friction coefficient and weight losses, whose values decrease as the weight fraction of graphite increases in the polymer matrix. Based on scanning electron microscopy (SEM) observations, the worn surface of the filled ABS composites reveals the development of a specific third body which reduces friction and wear. The best friction coefficient and weight loss were obtained with 7.5% in weight (7.5 wt%) of graphite.

Friction and Wear Properties of Copper/Carbon/Rice Bran Ceramics Composite under Water-Lubricated Condition

In this paper, friction and wear properties of a copper/carbon/rice bran ceramics (Cu/C/RBC) composite under water-lubricated conditions were investigated experimentally. The mass fractions of copper, carbon and the RB ceramics particulates were 60, 35 and 5 mass%, respectively. The mean diameter of the RB ceramics particulate was 4.9 μm. Friction tests were conducted with a pin-on-disk friction apparatus under water-lubricated conditions. The Cu/C/RBC composite and a copper/carbon (Cu/C) composite were used as disk specimens. The Cu/C composite is a conventional pantograph slider material in Japan. A copper alloy was used as a pin specimen, which was used to simulate a contact wire. The friction coefficients for the Cu/C/RBC composite were lower and more stable than those for the Cu/C composite. The Cu/C/RBC composite showed superior friction and wear properties such as 70.0% reduction in friction coefficient, 86.1% reduction in the specific wear rate of the composite disk and 99.1% reduction in that of the copper-alloy pin compared with the Cu/C composite.

An asperity-based fractional coverage model for transfer films on a tribological surface

An asperity-based fractional coverage (AFC) model has been developed for studying the process of lubricant film transfer on a real surface. A solid/powder lubricant film is transferred to a test disk surface by intentionally shearing a compacted pellet against the rotating disk surface. A slider pad simultaneously riding on the disk can be lubricated or starved during a competition process where the pellet deposits film as the slider depletes it. The tribological behavior of this film transfer process is modeled at the asperity scale to get an understanding of the macro-scale transient and steady-state friction. The AFC model was developed for this study by extending the range of applicability of its predecessor, the control volume fractional coverage (CVFC) model, to a real tribosurface. Topography data for the tribosurface was obtained from an atomic force microscope (AFM) image of the tungsten carbide (WC) test disk. The model predicts the wear rate of the pellet, pellet/disk and pad/disk friction coefficients, and lubricant thickness as a function of the pellet load, slider pad load, disk speed, and material properties.

Physics of ice friction

Although the study of friction has a long history, ice friction has only been investigated during the last century. The basic physical concepts underlying the different friction regimes, such as boundary, mixed, and hydrodynamic friction are also relevant to ice friction. However, these friction regimes must be described with respect to the thickness of the lubricating liquidlike layer on ice. In this review the state of knowledge on the physics of ice friction is discussed. Surface melting theories are introduced. These theories attempt to explain the existence and nature of the liquidlike surface layer on ice at any temperature and without any load applied. Pressure melting, as the long-time explanation for the ease of ice friction, is discussed, together with the prevailing theory of frictional heating. The various laboratory setups for ice friction measurements are presented as well as their advantages and disadvantages. The individual influence of the different parameters on the coefficient of ice friction is discussed; these include the effects of temperature, sliding velocity, normal force exerted by the sliding object, the contact area between ice and slider, relative humidity, and also properties of the slider material such as surface roughness, surface structure, wettability, and thermal conductivity. Finally, the most important ice friction models based on the frictional heating theory are briefly introduced and research directions on the subject of ice friction are discussed.

Interferometry Measurement of Lubricating Films in Slider-On-Disc Contacts

Interferometry proves to be an efficient way to measure thin lubricant film thickness. However, there are very few reports on the film thickness measurement of conformal lubricated contacts using optical interferometry due to experimental difficulties. In this article, a custom-built test apparatus is introduced, in which a lubricated conformal contact is made between a stationary fixed-incline slider and a moving transparent disc. With a flexible holder, the slider can be positioned in such a way that a specified inclination with respect to the flat disc plane can be obtained. When the disc rotates and the slider is loaded against it, lubricating films are generated. The minimum film thickness h m at the exit can be determined by interference intensity changes. Measurement error correction in the film thickness was discussed. Case experiments were carried out using the new test apparatus. The credibility of the measurement system is validated by good correlation between the experiments and the theoretical results. The applicability is demonstrated by the film thickness measurement under different inclinations, loads, velocities, lubricants and slider materials. Amongst those case experiments, it is highlighted that the influences of solid/liquid interface properties on the lubrication behaviours can be clearly identified in terms of film thickness.

Ice friction: the effect of thermal conductivity

AbstractThe effect of thermal conductivity on ice friction is studied systematically for different metallic slider materials over a wide range of temperatures, and sliding velocities. By thermally insulating the slider with fiberglass, the isolated effect of thermal conductivity on ice friction is investigated. A decrease of the friction coefficient in the boundary friction regime and an earlier onset of the mixed friction regime in terms of sliding velocity are found. Furthermore, the dependence of the ice friction coefficient on sliding velocity is compared for different sliding materials. It is found that the influence and importance of thermal conductivity decreases with increasing sliding velocity.

Optimization of micro-thermal actuator for flying height control

In this paper, a three dimensional finite element model of an entire thermal flying height control slider (TFC) with a detailed read/write transducer structure is created. We used the model to perform a thermal-structural coupled field analysis in order to investigate the transient thermal and protrusion response of the TFC slider. Parameter studies are conducted to identify the dominant parameters to reduce the response time of the heat transfer and thermal protrusion of the actuator. The simulation results show that increasing the heat transfer on the air bearing surface (ABS), reducing the distance from the heater to the ABS, reducing the thickness of alumina of the slider body and replacing the slider materials with Si/SiO2 can reduce the response time of the heat transfer and thermal protrusion around the actuator. But the effects of the input power and modifying the thermal properties of the shield materials are very small.

Selective Transfer Phenomenon in Copper-Steel Tribological Systems

The paper deals with possibility of selective transfer phenomenon generation in couples consisting of materials of railway traction trolley wire and of pantograph slider material. Some examinations are described concerning tribological characteristics evaluation of above couples. The most characteristic condition of selective transfer phenomenon (known also under the name of “Garkunov effect”) is generation of specific protective metallic layer on friction surfaces of both frictionally cooperating elements that minimize wear and friction resistance. Obtained results led to the conclusion that the selective transfer phenomenon was generated in the model friction pairs examined in the frames of presented work. The magnitude of this phenomenon depended on minimal differences in quantities of additives and impurities in copper.

Friction and Wear Properties of Copper/Carbon/RB Ceramics Composite under Electrical Current

Friction and wear properties of the copper/carbon/RB ceramics (Cu/C/RBC) composite were investigated under electrical current with and without arc-discharge. The weight fraction and the mean diameter of RB ceramics powder were 5 wt% and 4.9 μm, respectively, in the Cu/C/RBC composite. Friction tests were conducted with the block-on-ring friction apparatus. The Cu/C/RBC and the copper/carbon (Cu/C) composite, the conventional pantograph slider material of a railway current collector, were used as block specimens. Under electrical current without arc-discharge, the Cu/C/RBC composite showed 98% reduction in the specific wear rate of the block specimen, 23% reduction in that of the ring specimen, and 75% reduction in the friction coefficient over the conventional Cu/C composite. Under electrical current with arc-discharge, the Cu/C/RBC composite showed the wear resistance to arc-discharge equivalent to the conventional Cu/C composite.

Slider Optical Constant Distribution, $n$ and $k$ Correlation, and FH Measurement Accuracy

The slider material is a composition of alumina (Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) and titanium carbide (TiC) with a big difference in the optical constants. The random grain size, shape, and composition of TiC make the effective optical constant of slider air bearing surface (ABS) in the size of test spot vary largely. The spot-by-spot scanning of optical constant over slider ABS by ellipsometer indicates that the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> correlate each other linearly. As the commercia flying height (FH) testers use the averaged <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> value to calculate FH, there is a concern of FH testing error if the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> value at the testing spot derivates from the average value. This work discovered that the FH testing error is mainly determined by the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> correlation rather than the absolute value of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> dispersion. The laser phase detection method improves the repeatability of FH testing significantly, but the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> correlation is the key to estimate the accuracy of FH measurement.

Contact Force and Frictional Heating due to “Large” Particles in the Head Disk Interface

Particles in the head disk interface may cause large contact forces acting on the slider as well as thermal asperities in the read/write signal. This is especially true for the close spacing required for 1Tbit∕in.2. In this paper, a three-body contact model is employed to study the effects of a particle entrapped between a slider and a disk. A criterion for determining a particle’s movement pattern is proposed. The study of particles in the head disk interface shows that large particles are likely to slide between the slider and disk interface, and the particles going through the trailing pad of an air bearing slider cause severe contact forces on the slider and generate large heat sources. The frictional heating study shows that the temperature around the magnetoresistive head increases to about 5°C for a single 200nm particle passing through the trailing pad of the slider. The effects of the particle size, disk material, and friction coefficient are also studied. It is found that the disk and slider materials and the frictional coefficient between the materials largely affect the contact force acting on the slider by an entrapped particle as well as the temperature rise at its contact region. It is also found that the friction coefficient largely affects a particle’s movement pattern in the head disk interface.

INVESTIGATION ON EVALUATION METHOD OF SLIP RESISTANCE OF BUILDING ELEMENTS AND MEMBERS WITH HANDS FROM THE VIEW POINT OF POSTURE KEEPING

The purpose of this study is to present the evaluation method of contact resistance between hands and building elements from the view point of safety. In this repot, we firstly carried out sensory test, to make the evaluation scales of posture keeping in slipperiness with hands. Next, we developed the slip meter that could measure the slip resistance of plane samples. Then, coefficients of slip resistance of the plane samples by various slider materials, shapes, vertical loads and pull speeds are searched with the slip meter. Also, the relations are investigated between slip resistance and evaluation scales of posture keeping in slipperiness. As a result, we presented main points of measurement method of slip resistance of building elements and members with hands.

Friction and Wear Properties of Copper/Carbon/RB Ceramics Composite Materials under Dry Condition

In order to realize reducing wear of both overhead wires and pantograph sliders, the authors have developed new composite materials for pantograph sliders by using hard porous carbon materials “RB ceramics”. The new composite materials were developed by sintering compounds of copper, carbon and the RB ceramics particles. Friction and wear properties of these copper/carbon/RB ceramics composite materials (Cu/C/RBC composites) sliding against a copper alloy pin under dry condition were investigated. The friction coefficient for the Cu/C/RBC composites was lower and more stable than that for the conventional pantograph slider material, Cu/C composite. The friction coefficient for the Cu/C/RBC composites was about 1/2 ∼ 3/5 of that for the Cu/C composite. The specific wear rate of the Cu/C/RBC composites was extremely lower than that of the Cu/C composite. The specific wear rate of the Cu/C/RBC composites was decreased with a decrease of the weight fraction and the mean particle size of the RB ceramics particles. The specific wear rate of the Cu/C/RBC composites was about 1/220 ∼ 1/70 of that of the conventional Cu/C composite. Furthermore, the specific wear rate of a copper alloy pin sliding against the Cu/C/RBC composites is about 1/1700 ∼ 1/150 of that sliding against the conventional Cu/C composite.

On dry sliding friction and wear behavior of PPESK filled with PTFE and graphite

Novel poly(phthalazinone ether sulfone ketone) (PPESK) resins have become of great interest in applications such as bearing and slider materials. In this paper, dry sliding wear of polytetrafluoroethylene (PTFE) and graphite-filled PPESK composites against polished steel counterparts were investigated on a block-on-ring apparatus at the same sliding velocities and different loads. The results indicated that the addition of 5–25 wt% PTFE and 5–30 wt% graphite contribute to an obvious improvement of tribological performance of PPESK at room temperature. Worn surfaces were investigated using a scanning electron microscope (SEM). As a result, the friction coefficient and wear rate of the PPESK composites decreased gradually with addition of fillers. A moderately low friction coefficient and specific wear rate were reached when the filler contents were above 20 wt%. The mechanical properties of PPESK composites were also investigated. The tensile and impact strength of PPESK composites decrease slightly as the addition of fillers contents were below 15 wt%.