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Martin Hartl - One of the best experts on this subject based on the ideXlab platform.
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On the Temperature and Lubricant Film Thickness Distribution in EHL Contacts with Arbitrary Entrainment
Lubricants, 2018Co-Authors: Milan Omasta, Petr Sperka, Jakub Adam, Ivan Krupka, Martin HartlAbstract:An understanding of mechanisms which are responsible for elastohydrodynamic Lubricant Film formation under high sliding conditions is necessary to increase durability of machine parts. This work combines thin-Film colorimetric interferometry for Lubricant Film Thickness measurement and infrared microscopy for in-depth temperature mapping through the contact. The results describe the effect of operating conditions such as speed, slide-to-roll ratio, ambient temperature, and sliding direction on Lubricant Film Thickness and temperature distribution. Film Thickness data shows how much the Film shape is sensitive to operating conditions when thermal effects are significant, while the temperature profiles provides an explanation of this behavior.
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including the method of Lubricant Film Thickness measurement with the use of the monochromatic interferometry to the education of tribology
2016Co-Authors: David Kostal, I Křupka, Martin HartlAbstract:Measuring of distance as presented at the universities is usually limited to dimension down to microns. This orders of distance are sufficient for common engineer’s application. However dimension are a lot smaller when engineers deal with the tribology research. One of the most important progresses in the field of tribology in last century is without doubts the elastohydrodynamic lubrication (EHL). This lubrication regime can be found for example in rolling bearings or gears. Common Thickness of the Lubricant Film in the EHD contact is in order of tens or hundreds of nanometers. Optical method which enables measurements of such distances was developed by Gohar and Cameron in 1960s. This method is based on interference of monochromatic light and provides possibility of obtaining Lubricant Film Thickness from known wavelength of used light and its intensity in the lubricated contact. Students can create central Film Thickness prediction with use of the analytical formulae of the Hamrock and Dowson. This prediction is then confirmed by hands-on experiment in laboratory. Contact simulator with microscope and red light is used to record sequence of the interferograms. These interferograms are then processed in Matlab® software in order to obtain Film Thickness.
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Effect of shot peening on rolling contact fatigue and Lubricant Film Thickness within mixed lubricated non-conformal rolling/sliding contacts
Tribology International, 2011Co-Authors: Martin Vrbka, Petr Sperka, Ivan Křupka, Martin Hartl, Petr Svoboda, Tomáš Návrat, Jiři NohavaAbstract:Abstract The effect of shot peening on rolling contact fatigue (RCF) and Lubricant Film Thickness within non-conformal rolling/sliding contacts operated under mixed lubrication conditions was observed in this study. Rolling contact fatigue tests and Film Thickness measurements were carried out using specimens with modified surface topography by shot peening process using glass beads having diameter between 0.07 and 0.11 mm. It has been shown that the effect of shot peening on RCF has no positive effect even if shot peened surface of the roller exhibited somewhat higher hardness in contrast to the grounded surface. The reduction of RCF may be caused due to asperities interactions because after shot peening the surface roughness of the roller was increased. Film Thickness measurements confirmed that the contact is realized actually only between asperity peaks of shot peened ball and smooth disc. Conversely, no negative effect on RCF was observed when the shot peened surface of the roller was polished. The polish of asperity peaks causes the creation of lands and micro-cavities, which may be employed as Lubricant micro-reservoirs. From Film Thickness measurements it has been observed that Lubricant emitted by shallow micro-cavities can provide the local increase in lubrication Film Thickness, which thereby reduces asperities interactions. Similar results were obtained for start-up conditions where the squeeze Lubricant enlarges Film Thickness and reduces surface interactions. From the obtained results, it can be suggested that properly designed surface topography modification could help to increase the efficiency of lubrication Films leading to the enhancement of contact fatigue life of non-conformal mixed lubricated rolling/sliding contacts.
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effect of surface texturing on lubrication Film formation and rolling contact fatigue within mixed lubricated non conformal contacts
Meccanica, 2011Co-Authors: Martin Vrbka, O Samanek, Ivan Křupka, Miroslav Vaverka, Petr Svoboda, Martin HartlAbstract:The paper is focused on the influence of surface micro-cavities in non-conformal contact on tribological quantities, such as Lubricant Film Thickness, contact pressure and especially rolling contact fatigue (RCF). Both the possible negative and positive effects of surface texturing under mixed lubrication conditions are considered. The Lubricant Film Thickness was measured using optical test rig based on thin Film colorimetric interferometry, where the contact is realized between steel ball and glass disc. The experimental apparatus consisting of two discs loaded and running against roller specimen was used for measurement of RCF. Obtained results confirmed the key effect of micro-features depth on Film Thickness and RCF behavior under rolling/sliding conditions.
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Effect of surface texturing on lubrication Film formation and rolling contact fatigue within mixed lubricated non-conformal contacts
Meccanica, 2011Co-Authors: Martin Vrbka, O Samanek, Ivan Křupka, Miroslav Vaverka, Petr Svoboda, Martin HartlAbstract:The paper is focused on the influence of surface micro-cavities in non-conformal contact on tribological quantities, such as Lubricant Film Thickness, contact pressure and especially rolling contact fatigue (RCF). Both the possible negative and positive effects of surface texturing under mixed lubrication conditions are considered. The Lubricant Film Thickness was measured using optical test rig based on thin Film colorimetric interferometry, where the contact is realized between steel ball and glass disc. The experimental apparatus consisting of two discs loaded and running against roller specimen was used for measurement of RCF. Obtained results confirmed the key effect of micro-features depth on Film Thickness and RCF behavior under rolling/sliding conditions.
Jorge H O Seabra - One of the best experts on this subject based on the ideXlab platform.
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Two phosphonium cation-based ionic liquids used as Lubricant additive: Part I: Film Thickness and friction characteristics
Tribology International, 2017Co-Authors: A. Hernández Battez, Miguel Bartolome, Carlos M.c.g. Fernandes, Ramiro C. Martins, R. Gonzalez, Jorge H O SeabraAbstract:The Lubricant Film Thickness and friction properties of a mineral base oil and its mixtures with two phosphonium cation-based ionic liquids: [P66614][(iC8)2PO2] and [P66614][BEHP] at 0.5 and 1 wt% concentrations were studied under different slide-to-roll ratios (SRR) and temperatures in an EHD2 ball-on-disc test rig. All Lubricant samples showed similar Lubricant Film Thickness in full Film lubrication and behaved similarly in friction tests with polished discs at SRR of 5%, but the mixtures outperformed the neat base oil at SRR of 50%. The mixtures were also better in tests with rough discs. Tribological improvements with mixtures were achieved under mixed and boundary lubrication regimes. Real application such as rolling bearings will be presented in the second part of this work.
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Scuffing and Lubricant Film breakdown in FZG gears Part II. New PV scuffing criteria, Lubricant and temperature dependent
Wear, 1998Co-Authors: J. Castro, Jorge H O SeabraAbstract:The analysis of experimental and theoretical results, from constant temperature scuffing tests with FZG type A gears lubricated with base oils, show a good agreement between the scuffing loads and the scuffing Lubricant Film Thickness, meaning that a close relation exists between scuffing failure and Lubricant Film breakdown, for a base oil tested in the FZG rig. This relation is exploited, associating the classic PV scuffing criteria with the Lubricant Film Thickness in scuffing conditions. Correlating experimental and theoretical results, a more general PV scuffing criteria is developed which depends on the Lubricant properties and Lubricant temperature. The application of the new scuffing criteria to FZG-A/8.6/90 standard tests predicted the corresponding scuffing loads with excellent accuracy.
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Scuffing and Lubricant Film breakdown in FZG gears. Part I. Analytical and experimental approach
Wear, 1998Co-Authors: J. Castro, Jorge H O SeabraAbstract:This paper presents the influence of the base oil viscosity and of the pitch line velocity on the scuffing load of a spur gear. Standard FZG A/8.6/90 tests, and constant temperature tests for several pitch line velocities, were performed, for three mineral paraffinic base oils, with different viscosities. These tests were complemented by the analytical evaluation of the most important operating parameters, such as the oil bath temperature and viscosity, the Lubricant Film Thickness and the contact temperature along the gear contact path, for each load stage considered. The analysis of experimental and theoretical results shows a good correlation between the scuffing loads and scuffing temperatures and the Lubricant Film Thickness, suggesting that a close relation exists between scuffing failure and Lubricant Film breakdown, for a base oil tested in the FZG rig.
Bruce W Drinkwater - One of the best experts on this subject based on the ideXlab platform.
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Auto-calibration of ultrasonic Lubricant-Film Thickness measurements
Measurement Science and Technology, 2008Co-Authors: Tom Reddyhoff, Rob Dwyer-joyce, Jie Zhang, Bruce W DrinkwaterAbstract:The measurement of oil Film Thickness in a lubricated component is essential information for performance monitoring and design. It is well established that such measurements can be made ultrasonically if the Lubricant Film is modelled as a collection of small springs. The ultrasonic method requires that component faces are separated and a reference reflection recorded in order to obtain a reflection coefficient value from which Film Thickness is calculated. The novel and practically useful approach put forward in this paper and validated experimentally allows reflection coefficient measurement without the requirement for a reference. This involves simultaneously measuring the amplitude and phase of an ultrasonic pulse reflected from a layer. Provided that the acoustic properties of the substrate are known, the theoretical relationship between the two can be fitted to the data in order to yield reflection coefficient amplitude and phase for an infinitely thick layer. This is equivalent to measuring a reference signal directly, but importantly does not require the materials to be separated. The further valuable aspect of this approach, which is demonstrated experimentally, is its ability to be used as a self-calibrating routine, inherently compensating for temperature effects. This is due to the relationship between the amplitude and phase being unaffected by changes in temperature which cause unwanted changes to the incident pulse. Finally, error analysis is performed showing how the accuracy of the results can be optimized. A finding of particular significance is the strong dependence of the accuracy of the technique on the amplitude of reflection coefficient input data used. This places some limitations on the applicability of the technique.
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Acoustic measurement of Lubricant-Film Thickness distribution in ball bearings
The Journal of the Acoustical Society of America, 2006Co-Authors: Jie Zhang, Bruce W Drinkwater, Rob Dwyer-joyceAbstract:An oil-Film Thickness monitoring system capable of providing an early warning of lubrication failure in rolling element bearings has been developed. The system is used to measure the Lubricant-Film Thickness in a conventional deep groove ball bearing (shaft diameter 80mm, ball diameter 12.7mm). The measurement system comprises a 50MHz broadband ultrasonic focused transducer mounted on the static outer raceway of the bearing. Typically the Lubricant-Films in rolling element bearings are between 0.1–1.0μm in Thickness and so are significantly smaller than the ultrasonic wavelength. A quasistatic spring model is used to calculate oil-Film Thickness from the measured reflection coefficient data. An accurate triggering system has been developed to enable multiple reflection coefficient measurements to be made as the contact ellipse sweeps over the measurement location. Experiments are described in which the loading conditions and rotational speed are varied. Lubricant-Film Thickness distributions measured ultr...
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Calibration of the ultrasonic Lubricant-Film Thickness measurement technique
Measurement Science and Technology, 2005Co-Authors: Jie Zhang, Bruce W Drinkwater, Rob Dwyer-joyceAbstract:This paper describes an experimental apparatus and procedure for the calibration of the ultrasonic Lubricant-Film Thickness measurement technique. It also presents a study of the accuracy of the technique. The calibration apparatus is demonstrated on a three layer steel–mineral oil–steel system. This was chosen to be representative of a typical bearing system which is the industrial application of the technique. In such bearing systems the Lubricant-Film Thickness typically ranges from 0.1 to 100 µm. The calibration apparatus uses a high precision piezoelectric displacement translator to controllably displace one of the steel surfaces relative to the other and hence alter the Lubricant-Film Thickness by a known amount. Through-Thickness resonant frequency measurements are then used to accurately measure a thick Lubricant Film (h > 10 µm). These resonant frequency measurements form the starting point of the calibration. The displacement translator is then used to reduce the Lubricant-Film Thickness into the, more practically interesting, low micron range. In this range the amplitude of the measured reflection coefficient is used via a spring interface model to calculate the Lubricant-Film Thickness. Issues of ultrasonic beam alignment and frequency of operation are discussed. A detailed study of the effect of reflection-coefficient errors on the resultant Thickness measurement is presented. Practical guidelines for use of the calibration are then defined and calibration is demonstrated experimentally over the range 0.5–1.3 µm.
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The on-line measurement of Lubricant Film Thickness for condition monitoring
Insight: Non-Destructive Testing and Condition Monitoring, 2004Co-Authors: Bruce W Drinkwater, Rob Dwyer-joyceAbstract:The ultrasonic reflectivity of a Lubricant layer between two solid bodies depends on the ultrasonic frequency, the acoustic properties of the liquid and solid, and the layer Thickness. In this paper, ultrasonic reflectivity measurements are used as a method for determining the Thickness of lubricating Films in bearing systems. An ultrasonic transducer is positioned on the outside of a bearing shell such that the wave is focused on the Lubricant Film layer. The transducer is used to both emit and receive wideband ultrasonic pulses. For a particular Lubricant Film the reflected pulse is processed to give a reflection coefficient spectrum. The Lubricant Film Thickness is then obtained from either the layer stiffness or the resonant frequency. The method has been validated using fluid wedges at ambient pressure between flat and curved surfaces. Experiments on the elastohydrodynamic Film formed between a ball sliding on a flat were performed. Film Thickness values in the range 50-500 nm were recorded which agreed well with theoretical Film formation predictions. Similar measurements have been made on the oil Film between the balls and outer raceway of a deep groove ball bearing.
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On‐Line Measurement of Lubricant Film Thickness Using Ultrasonic Reflection Coefficients
AIP Conference Proceedings, 2004Co-Authors: Bruce W Drinkwater, Rob Dwyer-joyce, P. HarperAbstract:The ultrasonic reflectivity of a Lubricant layer between two solid bodies depends on the ultrasonic frequency, the acoustic properties of the liquid and solid, and the layer Thickness. In this paper, ultrasonic reflectivity measurements are used as a method for determining the Thickness of lubricating Films in bearing systems. An ultrasonic transducer is positioned on the outside of a bearing shell such that the wave is focused on the Lubricant Film layer. For a particular Lubricant Film the reflected pulse is processed to give a reflection coefficient spectrum. The Lubricant Film Thickness is then obtained from either the layer stiffness or the resonant frequency. The method has been validated using static fluid wedges and the elastohydrodynamic Film formed between a ball sliding on a flat. Film Thickness values in the range 50–500 nm were recorded which agreed well with theoretical Film formation predictions.
Atsunobu Mori - One of the best experts on this subject based on the ideXlab platform.
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Effects of ultra-thin liquid Lubricant Films on contact slider dynamics in hard-disk drives
Tribology International, 2007Co-Authors: Norio Tagawa, Yoshiaki Tashiro, Atsunobu MoriAbstract:Abstract This paper describes the effects of ultra-thin liquid Lubricant Films on contact slider dynamics in hard-disk drives. In the experiments, the contact slider dynamics as well as ultra-thin liquid Lubricants behavior are investigated using three types of Lubricants, which have different end-groups and molecular weight as a function of Lubricant Film Thickness. The dynamics of a contact slider is mainly monitored using acoustic emission (AE). The disks are also examined with a scanning micro-ellipsometer before and after contact slider experiments. It is found that the Lubricant Film Thickness instability occurs as a result of slider–disk contacts, when the Lubricant Film Thickness is thicker than one monolayer. Their unstable Lubricant behavior depends on the chemical structure of functional end-groups and molecular weight. In addition, it is also found that the AE RMS values, which indicate the contact slider dynamics, are almost same, independent of the end-groups and molecular weight for the Lubricants, when the Lubricant Film Thickness is approximately one monolayer. The molecular weight, however, affects the contact slider dynamics, when the Lubricant Film Thickness is less than one monolayer. In other words, the AE RMS values increase remarkably as the molecular weight for the Lubricant increases. When the Lubricant Film Thickness is more than one monolayer, the AE RMS values decrease because of the effect of mobile Lubricant layer, while the Lubricant instability affects the contact slider dynamics. Therefore, it may be concluded that the Lubricant Film Thickness should be designed to be approximately one monolayer Thickness region in order to achieve contact recording for future head–disk interface.
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effects of molecularly thin liquid Lubricant Films on slider hysteresis behavior in hard disk drives
Journal of Tribology-transactions of The Asme, 2006Co-Authors: Norio Tagawa, Atsunobu Mori, Ken SenoueAbstract:In order to achieve a magnetic recording density of 1 Tb/in 2 , the spacing is expected to be less than 2-3 nm. However, a critical issue in achieving such an ultralow spacing is the dynamic instability of the head disk interface (HDI). That is, the experimentally observed hysteresis of fly sliders. The phenomenon of slider hysteresis has two features: slider touchdown and slider takeoff The goal of this research is to experimentally clarify the effects of the Lubricant bonded ratio as well as the Lubricant Film Thickness on slider hysteresis behavior in detail. It also aims to determine the contributing factors. In this study, the difference in the touchdown and takeoff velocities was monitored by varying the Lubricant bonded ratio and Lubricant Film Thickness of the disks. Furthermore, the correlation between the observed phenomenon and the variation in the experimental parameters was investigated. The results showed that the touchdown velocities were almost independent of the Lubricant bonded ratio, while the takeoff velocities were greater for a Lubricant with a higher bonded ratio. These results were obtained for a constant Lubricant Film Thickness of around one monolayer. Therefore, the slider hysteresis was greater for a Lubricant with a higher bonded ratio. With regard to the effect of Lubricant Film Thickness, it was observed that the touchdown and takeoff velocities were greater for thinner Lubricants. These results for the effect of Lubricant Film Thickness are very similar to those obtained by Ambekar, Gupta, and Bogy (2005, ASME J. Tribal., 127(3), pp. 530-536). However, the slider hysteresis was greater for thicker Lubricants. Considering these experimental results as well as the experimental data for the effect of the surface roughness of a disk on the slider hysteresis obtained by (Tani et al. (2006, J. Appl. Phys. , 99(8), pp. 08N104-1-08N104-3), it was suggested that the variation in the touchdown velocity is due to a variation in the intermolecular forces. Furthermore, it was suggested that the variation in the takeoff velocity is caused by a variation in the friction forces between the slider and disk surface. This occurs because the takeoff velocity was greater for a Lubricant with a higher bonded ratio or a thinner Lubricant, which only has a small fraction of free mobile Lubricant. The results predicted by the simulations are consistent with those observed experimentally. In addition, a design guideline for next-generation HDI, with small touchdown and takeoff velocities, resulting in small slider hysteresis, is discussed in detail in this paper.
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Behavior of ultrathin liquid Lubricant Films for contact sliders in hard disk drives
Tribology Letters, 2005Co-Authors: Naoyuki Tagawa, Atsunobu MoriAbstract:In this paper, we describe the behavior of ultrathin liquid Lubricant Films for contact sliders in hard disk drives. In the experiments, the ultrathin liquid Lubricant Film behavior is investigated using Zdol and cyclotriphosphazene-terminated PFPE Lubricant which have different end groups as a function of Lubricant Film Thickness. The disks are examined with a scanning microellipsometer before and after contact slider experiments. It is found that the Lubricant Film Thickness profiles almost do not change, when the Lubricant Film Thickness is less than one monolayer. It can also be observed that Lubricant Film Thickness instability due to dewetting occurs as a result of slider-disk contacts for the tested Lubricants and the Films undergo spontaneous redistributions, resulting in significantly nonuniform Film Thickness profiles, when the Lubricant Film Thickness is thicker than one monolayer. In addition, it is found that the observed behavior of ultrathin liquid Lubricant Films for cyclotriphosphazine-terminated PFPE Lubricant contrasts markedly with that for Zdol. The difference between cyclotriphosphazene-terminated PFPE Lubricant and Zdol is only the functional end group. Therefore, it may be concluded that their unstable Lubricant behavior depends on the chemical structure of functional end groups.
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Behavior of ultrathin liquid Lubricant Films for contact sliders in hard disk drives
Tribology Letters, 2005Co-Authors: Naoyuki Tagawa, Atsunobu MoriAbstract:In this paper, we describe the behavior of ultrathin liquid Lubricant Films for contact sliders in hard disk drives. In the experiments, the ultrathin liquid Lubricant Film behavior is investigated using Zdol and cyclotriphosphazene-terminated PFPE Lubricant which have different end groups as a function of Lubricant Film Thickness. The disks are examined with a scanning microellipsometer before and after contact slider experiments. It is found that the Lubricant Film Thickness profiles almost do not change, when the Lubricant Film Thickness is less than one monolayer. It can also be observed that Lubricant Film Thickness instability due to dewetting occurs as a result of slider-disk contacts for the tested Lubricants and the Films undergo spontaneous redistributions, resulting in significantly nonuniform Film Thickness profiles, when the Lubricant Film Thickness is thicker than one monolayer. In addition, it is found that the observed behavior of ultrathin liquid Lubricant Films for cyclotriphosphazine-terminated PFPE Lubricant contrasts markedly with that for Zdol. The difference between cyclotriphosphazene-terminated PFPE Lubricant and Zdol is only the functional end group. Therefore, it may be concluded that their unstable Lubricant behavior depends on the chemical structure of functional end groups.
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effect of ultra thin liquid Lubricant Films on dynamics of nano spacing flying head sliders in hard disk drives
Journal of Tribology-transactions of The Asme, 2004Co-Authors: Norio Tagawa, Noritaka Yoshioka, Atsunobu MoriAbstract:This paper describes the effect of ultra-thin liquid Lubricant Films on air bearing dynamics and flyability of nano-spacing flying head sliders in hard disk drives. The dynamics of a slider was monitored using Acoustic Emission (AE) and Laser Doppler Vibrometer (LDV). The disks with Lubricant on one half of disk surface thicker than the other half as well as with uniform Thickness Lubricant were used to investigate the interactions between the slider and Lubricant Film experimentally. As a result, it was found that the flying height at which the slider-Lubricant contact occurs depends on the Lubricant Film Thickness and it increases as the Lubricant Film Thickness increases. Its flying height is also dependent on the mobile Lubricant Film Thickness under the condition that the total Lubricant Film Thicknesses are the same and the Lubricant bonded ratios are different. It increases as the mobile Lubricant Film Thickness increases. The slider-Lubricant contact flying height based on the theory for capillary waves is in good agreement with the experimental results. Regard to air bearing dynamics due to the slider-Lubricant interactions, it also depends on the mobile Lubricant Thickness as well as the total Lubricant Film Thickness. However, we should carry out more experimental and theoretical studies in order to confirm and verify these experimental results. In addition, the effect of nonuniform Lubricant Film Thickness on head/disk interface dynamics has been studied. It was found that the Lubricant Film Thickness nonuniformity caused by the slider-Lubricant interactions could be observed.
Norio Tagawa - One of the best experts on this subject based on the ideXlab platform.
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Depletion of Monolayer Liquid Lubricant Films Induced by Laser Heating in Thermally Assisted Magnetic Recording
ASME STLE 2011 Joint Tribology Conference, 2011Co-Authors: Norio Tagawa, Takao Miki, H. TaniAbstract:In this study, the Lubricant depletion caused by laser heating was investigated for Lubricant Films with Thicknesses greater than and less than one monolayer. The conventional Lubricants Zdol2000 and Ztetrao12000 were used. It was found that the critical temperature at which Lubricants start to deplete by laser heating strongly depends on the Lubricant Film Thickness. To analyze the Lubricant depletion mechanism, we carried out temperature programmed desorption (TPD) spectroscopy on the tested Lubricant Films. It was found that the Lubricant depletion characteristics induced by laser heating could be explained using the experimental TPD spectroscopy results for the tested Lubricant Films. It was also found that the depletion mechanism involved the desorption or decomposition of the Lubricant molecules that interacted with the diamond-like carbon thin Films when the Lubricant Film Thickness was less than one monolayer.Copyright © 2011 by ASME
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Study on Lubricant Depletion Induced by Laser Heating in Thermally Assisted Magnetic Recording Systems: Effect of Lubricant Thickness
ASME STLE 2009 International Joint Tribology Conference, 2009Co-Authors: Norio Tagawa, Hideki Andoh, H. TaniAbstract:In this study, fundamental research on Lubricant depletion due to laser heating in thermally assisted magnetic recording was conducted. In particular, the effect of Lubricant Film Thickness on Lubricant depletion was investigated. The conventional Lubricant Zdol2000 was used. As a result, it was found that the Lubricant depletion characteristics due to laser heating depend largely on the Lubricant Film Thickness. In addition, it was suggested that the Lubricant depletion mechanism involves the evaporation of the mobile Lubricant molecules, when the maximum attained temperature is not very high. Another suggested Lubricant depletion mechanism involves the thermocapillary stress effect induced by the disk surface temperature gradient resulting from the non-uniformity of the laser spot intensity distribution.Copyright © 2009 by ASME
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Effects of ultra-thin liquid Lubricant Films on contact slider dynamics in hard-disk drives
Tribology International, 2007Co-Authors: Norio Tagawa, Yoshiaki Tashiro, Atsunobu MoriAbstract:Abstract This paper describes the effects of ultra-thin liquid Lubricant Films on contact slider dynamics in hard-disk drives. In the experiments, the contact slider dynamics as well as ultra-thin liquid Lubricants behavior are investigated using three types of Lubricants, which have different end-groups and molecular weight as a function of Lubricant Film Thickness. The dynamics of a contact slider is mainly monitored using acoustic emission (AE). The disks are also examined with a scanning micro-ellipsometer before and after contact slider experiments. It is found that the Lubricant Film Thickness instability occurs as a result of slider–disk contacts, when the Lubricant Film Thickness is thicker than one monolayer. Their unstable Lubricant behavior depends on the chemical structure of functional end-groups and molecular weight. In addition, it is also found that the AE RMS values, which indicate the contact slider dynamics, are almost same, independent of the end-groups and molecular weight for the Lubricants, when the Lubricant Film Thickness is approximately one monolayer. The molecular weight, however, affects the contact slider dynamics, when the Lubricant Film Thickness is less than one monolayer. In other words, the AE RMS values increase remarkably as the molecular weight for the Lubricant increases. When the Lubricant Film Thickness is more than one monolayer, the AE RMS values decrease because of the effect of mobile Lubricant layer, while the Lubricant instability affects the contact slider dynamics. Therefore, it may be concluded that the Lubricant Film Thickness should be designed to be approximately one monolayer Thickness region in order to achieve contact recording for future head–disk interface.
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effects of molecularly thin liquid Lubricant Films on slider hysteresis behavior in hard disk drives
Journal of Tribology-transactions of The Asme, 2006Co-Authors: Norio Tagawa, Atsunobu Mori, Ken SenoueAbstract:In order to achieve a magnetic recording density of 1 Tb/in 2 , the spacing is expected to be less than 2-3 nm. However, a critical issue in achieving such an ultralow spacing is the dynamic instability of the head disk interface (HDI). That is, the experimentally observed hysteresis of fly sliders. The phenomenon of slider hysteresis has two features: slider touchdown and slider takeoff The goal of this research is to experimentally clarify the effects of the Lubricant bonded ratio as well as the Lubricant Film Thickness on slider hysteresis behavior in detail. It also aims to determine the contributing factors. In this study, the difference in the touchdown and takeoff velocities was monitored by varying the Lubricant bonded ratio and Lubricant Film Thickness of the disks. Furthermore, the correlation between the observed phenomenon and the variation in the experimental parameters was investigated. The results showed that the touchdown velocities were almost independent of the Lubricant bonded ratio, while the takeoff velocities were greater for a Lubricant with a higher bonded ratio. These results were obtained for a constant Lubricant Film Thickness of around one monolayer. Therefore, the slider hysteresis was greater for a Lubricant with a higher bonded ratio. With regard to the effect of Lubricant Film Thickness, it was observed that the touchdown and takeoff velocities were greater for thinner Lubricants. These results for the effect of Lubricant Film Thickness are very similar to those obtained by Ambekar, Gupta, and Bogy (2005, ASME J. Tribal., 127(3), pp. 530-536). However, the slider hysteresis was greater for thicker Lubricants. Considering these experimental results as well as the experimental data for the effect of the surface roughness of a disk on the slider hysteresis obtained by (Tani et al. (2006, J. Appl. Phys. , 99(8), pp. 08N104-1-08N104-3), it was suggested that the variation in the touchdown velocity is due to a variation in the intermolecular forces. Furthermore, it was suggested that the variation in the takeoff velocity is caused by a variation in the friction forces between the slider and disk surface. This occurs because the takeoff velocity was greater for a Lubricant with a higher bonded ratio or a thinner Lubricant, which only has a small fraction of free mobile Lubricant. The results predicted by the simulations are consistent with those observed experimentally. In addition, a design guideline for next-generation HDI, with small touchdown and takeoff velocities, resulting in small slider hysteresis, is discussed in detail in this paper.
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effect of ultra thin liquid Lubricant Films on dynamics of nano spacing flying head sliders in hard disk drives
Journal of Tribology-transactions of The Asme, 2004Co-Authors: Norio Tagawa, Noritaka Yoshioka, Atsunobu MoriAbstract:This paper describes the effect of ultra-thin liquid Lubricant Films on air bearing dynamics and flyability of nano-spacing flying head sliders in hard disk drives. The dynamics of a slider was monitored using Acoustic Emission (AE) and Laser Doppler Vibrometer (LDV). The disks with Lubricant on one half of disk surface thicker than the other half as well as with uniform Thickness Lubricant were used to investigate the interactions between the slider and Lubricant Film experimentally. As a result, it was found that the flying height at which the slider-Lubricant contact occurs depends on the Lubricant Film Thickness and it increases as the Lubricant Film Thickness increases. Its flying height is also dependent on the mobile Lubricant Film Thickness under the condition that the total Lubricant Film Thicknesses are the same and the Lubricant bonded ratios are different. It increases as the mobile Lubricant Film Thickness increases. The slider-Lubricant contact flying height based on the theory for capillary waves is in good agreement with the experimental results. Regard to air bearing dynamics due to the slider-Lubricant interactions, it also depends on the mobile Lubricant Thickness as well as the total Lubricant Film Thickness. However, we should carry out more experimental and theoretical studies in order to confirm and verify these experimental results. In addition, the effect of nonuniform Lubricant Film Thickness on head/disk interface dynamics has been studied. It was found that the Lubricant Film Thickness nonuniformity caused by the slider-Lubricant interactions could be observed.
