Download or read book Lubricant Flow and De wetting at the Head Disk Interface of a Hard Disk Drive written by Alejandro Rodriguez Mendez and published by . This book was released on 2015 with total page 85 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this dissertation we investigate the lubricant behavior at the head-disk interface of a hard disk drive (HDD) by numerically simulating the formation of lubricant moguls on the disk and the accumulation of lubricant on the slider's air bearing surface (ABS). We use classical lubrication theory from continuum mechanics to model both the air bearing and the lubricant motion. The numerical simulations were compared to experimental tests of lubricant reflow on the disk after laser heating. A good agreement was found between experiments and numerical simulations. We investigate the effects of the slider's flying height, skew angle and ABS design on the lubricant flow and reflow. We describe the lubricant thickness profile and volume evolution on the slider's ABS and lateral walls. It was found that a smaller flying height contributes to a faster lubricant removal from the ABS due to the induced increase in the air shear stress. When the HDD is at rest, the lubricant accumulated on the deposit end flows back into the ABS driven by the action of disjoining pressure. It is found, for a particular slider design, that increasing the slider's radial position and thus changing its skew angle has the effect of enhancing the lubricant flow process due to a decrease in the slider's flying height. The lubricant migration process is significantly dependent on the ABS design. It is found that slider designs that accumulate most lubricant on a broader area on the deposit end and have larger values of air shear stress remove lubricant from the ABS at higher volume rates than those designs where accumulation is concentrated near the center of the deposit end and have smaller values of average shear stress. We simulate the flow and reflow processes of unstable lubricant films. We study the spreading of droplets with thickness larger than the critical de-wetting thickness. It is observed that, if surface tension is neglected from the governing equations, the disjoining pressure acts as a destabilizing force inducing an unrestrained growth of the film. The disjoining pressure breaks up the initial droplet into smaller ones which narrow down in width and increase in height. As the growth continues, the curvature of each droplet becomes sufficiently large to balance the disjoining pressure. The final state consists of a few isolated droplets connected by a uniform film. When we include the effect of air shear stress and air pressure gradient the initial droplet breaks up into smaller ones, which are then sheared downstream in the direction of the air shear stress. It was not possible to simulate the de-wetting behavior of the lubricant film on the entire slider domain, since it was found that surface tension is significant only at length scales several orders of magnitude smaller than the size of the slider. Finally we investigate the changes in magnetic spacing due to lubricant migration on the ABS and study the formation of lubricant clots on the disk surface known as "moguls". It is observed that the minimum magnetic spacing of a lubricant contaminated slider is significantly larger than that of a clean slider even after a relatively long time of flying the slider over the disk. This increase in spacing is detrimental for the read/write performance of the HDD. It is also observed that the air shear stress can generate lubricant moguls on the disk surface due to oscillations of the slider along the vertical, downtrack and offtrack directions.

Download or read book Experimental Investigations of Slider lubricant Interactions in Hard Disk Drives written by Sean N. Moseley and published by . This book was released on 2009 with total page 386 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Tribological Investigations of the Head disk Interface of Hard Disk Drives written by Qing Zhao and published by . This book was released on 1999 with total page 424 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Encyclopedia of Chemical Processing written by Sunggyu Lee and published by Taylor & Francis US. This book was released on 2006 with total page 682 pages. Available in PDF, EPUB and Kindle. Book excerpt: Collecting information of vital interest to chemical, polymer, mechanical, electrical, and civil engineers, as well as chemists and chemical researchers, this "Encyclopedia "supplies nearly 350 articles on current design, engineering, science, and manufacturing practices-offering expertly written articles on technologies at the forefront of the field to maximize and enhance the research and production phases of current and emerging chemical manufacturing practices and techniques.

Download or read book Lubricant Additives written by Leslie R. Rudnick and published by CRC Press. This book was released on 2017-07-12 with total page 708 pages. Available in PDF, EPUB and Kindle. Book excerpt: This indispensable book describes lubricant additives, their synthesis, chemistry, and mode of action. All important areas of application are covered, detailing which lubricants are needed for a particular application. Laboratory and field performance data for each application is provided and the design of cost-effective, environmentally friendly technologies is fully explored. This edition includes new chapters on chlorohydrocarbons, foaming chemistry and physics, antifoams for nonaqueous lubricants, hydrogenated styrene–diene viscosity modifiers, alkylated aromatics, and the impact of REACh and GHS on the lubricant industry.

Download or read book Some Tribological Aspects of the Hard Disk Drive Head Disk Interface for Quasi Contact Conditions written by YUNG-KAN CHEN and published by . This book was released on 2015 with total page 125 pages. Available in PDF, EPUB and Kindle. Book excerpt: The magnetic recording hard disk drive has been one of the most important storage strategies since 1956. Among all storage solutions, hard disk drives possess the unrivaled advantageous combination of storage capacity, speed, reliability and cost over optical strategies and flash memory. Unlike other storage solutions, hard disk drives utilize a mechanical interface to perform the magnetic read/write process, and therefore its success relies heavily on the stability of the head-disk interface (HDI) which is composed of a magnetic transducer carried by an air bearing slider, an air gap of a few nanometers thick, and a disk surface coated with multiple layers of molecularly-thin films. This dissertation addresses the physics of the interface in terms of contact detection, lubricant modulation and wear. Contact detection serves as one of the core requirements in HDI reliability. The writing process demands a strict spacing control, and its accuracy is based on a proper choice of a contact reference from slider dynamics and therefore the heads’ signal. While functioning in a real drive the only feedback signal comes from sensors neighboring the read-write transducer, and a high speed head-disk contact is associated with complex structural responses inherent in an air-bearing/suspension/lubricant system that may not be well explained solely by magnetic signals. Other than studying the slider-disk interaction at a strong interplay stage, this dissertation tackles the contact detection by performing component-level experimental and simulation studies focusing on the dynamics of air-bearing sliders at disk proximity. The slider dynamics detected using laser Doppler vibrometry indicates that a typical head-disk contact can be defined early as in-plane motions of the slider, which is followed by vertical motions at a more engaged contact. This finding confirms and is in parallel with one of the detection schemes used in commercial drives by magnetic signals. Lubricated disk surfaces play an important role in contact characteristics. As the nature of contact involves two mating surfaces, the modulation of disk lubricant films should be investigated to further understand the head-disk contact in addition to the slider dynamics. In this dissertation, the lubricant modulation is studied under various contact conditions with reference to slider dynamics. It is found that lubricant modulation can be directly associated with the slider’s dynamics in a location specific way, and its evolution is likely to affect the slider’s stable back-off fly-height as the contact is retracted. In addition to modulations at contact proximities, the lubricant response to passive flying and continuous contacting conditions are also addressed for different lubricant types and thicknesses. By integrating the observations from slider dynamics and lubricant modulations, we can establish an insightful understanding towards the transition from flying to the onset of contact. Head wear is also a concern when an erroneous contact detection occurs or imperfections from disk surface exists. Typically a protective diamond-like carbon (DLC) layer of thickness 1-2 nm is coated over the area of the reader/writer shields, and this film loss poses a threat to long term reliability. In this dissertation, in-situ methods of monitoring head wear is proposed in two ways. One method is to evaluate the touchdown power variations as a measure of spacing increase by DLC wear, which was verified by using Auger Electron Spectroscopy, and the other method studies the temperature contact sensor response to gauge mechanical wear. The later possesses the advantage of detecting wear without going into actual contact, but it may be affected by the location difference between the touchdown sensor and wear area.

Download or read book Fundamentals of Fluid Film Lubrication written by Bernard J. Hamrock and published by CRC Press. This book was released on 2004-03-15 with total page 794 pages. Available in PDF, EPUB and Kindle. Book excerpt: Specifically focusing on fluid film, hydrodynamic, and elastohydrodynamic lubrication, this edition studies the most important principles of fluid film lubrication for the correct design of bearings, gears, and rolling operations, and for the prevention of friction and wear in engineering designs. It explains various theories, procedures, and equations for improved solutions to machining challenges. Providing more than 1120 display equations and an introductory section in each chapter, Fundamentals of Fluid Film Lubrication, Second Edition facilitates the analysis of any machine element that uses fluid film lubrication and strengthens understanding of critical design concepts.

Download or read book Numerical Simulation of the Lubrication of the Head disk Interface Using a Non Newtonian Fluid written by Frank A. De Bruyne and published by . This book was released on 1992 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Tribochemistry of the Decomposition Mechanisms of Perfluoropolyether Lubricants at the Head disk Interface of Hard Disk Drives in UHV written by Chao-Yuan Chen and published by . This book was released on 1999 with total page 328 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Frontiers of Magnetic Hard Disk Drive Tribology and Technology written by and published by . This book was released on 2003 with total page 122 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Study of the Head Disk Interface in Heat Assisted Magnetic Recording Energy and Mass Transfer in Nanoscale written by Haoyu Wu and published by . This book was released on 2018 with total page 114 pages. Available in PDF, EPUB and Kindle. Book excerpt: The hard disk drive (HDD) is still the dominant technology in digital data storage due to its cost efficiency and long term reliability compared with other forms of data storage devices. The HDDs are widely used in personal computing, gaming devices, cloud services, data centers, surveillance, etc. Because the superparamagnetic limit of perpendicular magnetic recording (PMR) has been reached at the data density of about 1 Tb/in^2 , heat assisted magnetic recording (HAMR) is being pursued and is expected to help increase the areal density to over 10 Tb/in^2 in HDDs in order to fulfill the future worldwide data storage demands. In HAMR, the magnetic media is heated locally (~50nm x 50nm) and momentarily (~10ns) to its Curie temperature (~750K) by a laser beam. The laser beam is generated by a laser diode (LD) and focused by a near field transducer (NFT). But the energy and mass transfer at high temperature from the laser heating can cause potential reliability issues. The design temperature of the NFT is much lower than the media’s Curie temperature. However, the distance between the NFT and the media is less than 10nm. As a result, the heat can flow back from the media to the NFT, which is called the back-heating effect. This can cause undesired additional temperature increase on the NFT, shortening its lifetime. Additionally, depletion, evaporation and degradation can happen on the lubricant and the carbon overcoat (COC) layer of the media. The material can transfer from the media to the head at high temperature and cause solid contamination on the head, adversely affecting its reliability. Since the laser heating in HAMR happens at nanoscale spatially and temporally, it is difficult to measure experimentally. In this dissertation, a comprehensive experimental stage, called the Computer Mechanics Laboratory (CML)-HAMR stage, was built to study different aspects of HAMR systems, including the heat and mass transfer in the head-disk interface during laser heating. The CML-HAMR stage includes an optical module, a spinstand module and a signal generation/acquisition module. And it can emulate the HAMR scenario. The head’s temperature was measured during the laser heating using the stage and heads with an embedded contact sensor (ECS). It was estimated, based on a linear extrapolation, that the ECS temperature rise is 139K, 132K, 127K and 122K when the disk is heated to the Curie temperature (~750K) and the head-disk clearance is 0nm, 1nm, 2nm and 3nm, respectively. The heating effect of the ECS was also studied and a related heat transfer experiment was performed. The normalized ECS self heating temperature rise, an indicator of the heat transfer in the head-disk interface (HDI), was measured. It was concluded that the heat transfer coefficient across the HDI strongly depends on the width of the gap size, especially when the gap size is smaller than 1nm. The head disk interaction during the laser heating was studied using a waveguide head, i.e., a HAMR head without the NFT. It showed that the laser heating can cause head surface protrusion. This lowers the fly-height (FH) and results in early touchdown (TD). It was shown that the ratio of touchdown power (TDP) change to the laser current is 0.3mW/mA. The dynamics of the head also changes during the laser heating. It was found that the magnitude of the 1st-pitch-mode vibration on the head increases over time both in short term and long term. The accumulation of material transferred to the head was also investigated. It was found that the solid contamination caused by the laser heating forms in the center of the waveguide. The round-shaped contamination formed on the head surface after laser heating. Finally the disk lubricant reflow after laser heating was studied. In the experiment, a beam of free space laser shines on the rotating disk at different laser powers, disk rotating speeds and repetitions. Then the disk was examined by an optical surface analyzer (OSA). It was found that 80% of the displaced lubricant recovers within 20 minutes. A simulation was also performed. The experiments and the simulation are in good agreement.

Download or read book Synthetics Mineral Oils and Bio Based Lubricants written by Leslie R. Rudnick and published by CRC Press. This book was released on 2020-01-29 with total page 1195 pages. Available in PDF, EPUB and Kindle. Book excerpt: Highlighting the major economic and industrial changes in the lubrication industry since the first edition, Synthetics, Mineral Oils, and Bio-Based Lubricants: Chemistry and Technology, Third Edition highlights the major economic and industrial changes in the lubrication industry and outlines the state of the art in each major lubricant application area. Chapters cover the use of lubricant fluids, growth or decline of market areas and applications, potential new applications, production capacities, and regulatory issues, including biodegradability, toxicity, and food production equipment lubrication. The highly-anticipated third edition features new and updated chapters including those on automatic and continuously variable transmission fluids, fluids for food-grade applications, oil-soluble polyalkylene glycols, functional bio-based lubricant base stocks, farnesene-derived polyolefins, estolides, bio-based lubricants from soybean oil, and trends in construction equipment lubrication. Features include: Contains an index of terms, acronyms, and analytical testing methods. Presents the latest conventions for describing upgraded mineral oil base fluids. Considers all the major lubrication areas: engine oils, industrial lubricants, food-grade applications, greases, and space-age applications Includes individual chapters on lubricant applications—such as environmentally friendly, disk drive, and magnetizable fluids—for major market areas around the globe. In a single, unique volume, Synthetics, Mineral Oils, and Bio-Based Lubricants: Chemistry and Technology, Third Edition offers property and performance information of fluids, theoretical and practical background to their current applications, and strong indicators for global market trends that will influence the industry for years to come.

Download or read book Frontiers of Magnetic Hard Disk Drive Tribology and Technology written by Andreas A. Polycarpou and published by . This book was released on 2003 with total page 150 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Tribological Performance of the Head Disk Interface in Perpendicular Magnetic Recording and Heat Assisted Magnetic Recording written by Tan Duy Trinh and published by . This book was released on 2019 with total page 185 pages. Available in PDF, EPUB and Kindle. Book excerpt: International Data Corporation (IDC) estimates that hard disk drives will still be the main storage device for storing digital data in the next 10 years, holding approximately 80% of the data inside data centers. To increase the areal density of hard disk drives, the mechanical spacing between the head and disk surface has decreased to approximately 1nm. At such a small spacing, tribology of the head-disk interface, including head-disk contacts, wear, material buildup, and lubricant transfer, become increasingly more important for the reliability of hard disk drives. In addition to small spacing, heat-assisted magnetic recording (HAMR) technology aims to deliver higher areal density recording by heating up the media surface to a few hundred Celsius degrees, facilitating the writing process. High temperature at the head and disk surfaces cause serious reliability issues for the head-disk interface (HDI). Therefore, understanding of the main factors that affect the reliability of the head-disk interface is an essential task. In this dissertation, the effect of bias voltage and helium environment on the tribological performance of the head-disk interface is investigated. To do this, we first simulated the flying characteristics of the slider as a function of bias voltage in air and helium environment. Thereafter, an experimental study was performed using custom built tester located inside a sealed environmental chamber to study the effect of air and helium on wear and lubricant redistribution at the head-disk interface during load-unload. We investigated the effect of bias voltage and relative humidity on wear, material buildup, and nano-corrosion on the slider surface. Finally, we have studied laser current and laser optical power in heat-assisted magnetic recording as a function of operating radius, head-disk clearance, media design, and their effects on the life-time of the head-disk interface. The results of this dissertation provide guidance for the effect of bias voltage, relative humidity, and helium environment on wear, material buildup, corrosion, and lubricant transfer at the head-disk interface. More importantly, our experimental study in heat-assisted magnetic recording leads to a better understanding of the main factors that cause failure of the HAMR head-disk interface. Our results are important for the improvement of the tribological performance and reliability of perpendicular magnetic recording (PMR) and heat-assisted magnetic recording (HAMR) head-disk interface.

Download or read book Study of Perfluoropolyether Lubricant Transfer and Hydrocarbon Contamination at the Head Disk Interface written by Young Woo Seo and published by . This book was released on 2017 with total page 251 pages. Available in PDF, EPUB and Kindle. Book excerpt: To achieve an areal density of 1 terabit per square inch (1 Tb/in2) in hard disk drives, the mechanical spacing between the flying slider and the rotating disk has decreased to approximately 1 nm. With this decrease in spacing, the head-disk interface has become increasingly more susceptible to slider-disk contacts, wear, and lubricant transfer from the disk to the slider. Contamination at the head-disk interface can cause "flying stiction", flying instability, and read/write errors, leading ultimately to failure of the disk drive. It is essential to understand perfluoropolyether lubricant transfer and hydrocarbon contamination at the head-disk interface to improve the tribological performance and the reliability of hard disk drives. In this dissertation, perfluoropolyether lubricant transfer and lubricant fragmentation at the head-disk interface are investigated numerically as a function of temperature, local pressure change, and disk velocity. Molecular dynamics is used to study the effect of laser pulse peak power, pulse duration, and repetition rate on lubricant depletion. Hydrocarbon contamination at the head-disk interface is modeled experimentally by assuming a three-step mechanism for hydrocarbon contamination, consisting of evaporation, transfer, and condensation. In addition, a numerical investigation of hydrocarbon contamination at the head-disk interface is performed using molecular dynamics simulations. The results of this dissertation provide guidance in the design of perfluoropolyether and hydrocarbon lubricants to improve the tribological performance and reliability of the head-disk interface in hard disk drives.

Download or read book Tribological Study of Contact Interfaces in Hard Disk Drives written by Youyi Fu and published by . This book was released on 2016 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt: To achieve an areal density of 1 terabits per square inch (1.55 gigabits/mm2) in hard disk drives, the size of magnetic grains in hard disks has been reduced to approximately 7 nm and the spacing between the magnetic head and the disk has been minimized to 1 to 2 nm. At a spacing on the order of 1 to 2 nm between the head and the disk, it is likely that contacts between the magnetic head and the disk occur during reading and writing, causing erasure of data or even failure of the head/disk interface. Wear particles can be generated as a consequence of contacts between slider and disk, and if particles enter the head/disk interface, catastrophic failure of the head/disk interface can occur. To reduce the generation of wear particles and avoid failure of the head/disk interface, it is important to investigate how the tribological performance of all contact interfaces in hard disk drives can be improved. In this dissertation, the tribological performance of the most important contact interfaces in a hard disk drive are investigated with a focus on the generation of wear particles and lubricant migration. First, fretting wear is investigated to study the effect of a diamond-like carbon (DLC) overcoat on wear of the dimple/gimbal interface. A numerical simulation model based on finite element analysis was developed to explain the experimental results. Then, lubricant migration on the air bearing surface and its effect on the head medium spacing (HMS) was investigated as a function of temperature, slider position, and "parking time" of the slider on the ramp. Thereafter, the thermal response of a thermal sensor during contact with asperities on the disk surface was analyzed. The effects of experimental and environmental conditions on the resistance change of the sensor were studied. Finally, experimental and numerical investigations were performed to analyze contact between the suspension lift tab and the ramp in hard disk drives. The voice coil motor current was used to characterize the change of the friction force and the generation of wear debris at the lift tab/ramp interface during load/unload testing. Numerical simulations were performed to analyze how to reduce contact stress between the lift-tab and the ramp. The results of this dissertation will be helpful in improving the tribological performance of hard disk drives.

Download or read book Nano structured Lubricant Film in Head disk Interface written by Haigang Chen and published by . This book was released on 2007 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: