Effects of Gas Composition,Humidity and Temperature on the Tribology of the Head/Disk Interface—Part II: Model and Analysis

A qualitative model for the effect of water condensation on the frictional behavior of unlubricated and lubricated carbon-overcoated disks is presented. The model suggests that for unlubricated disks adsorbed water acts as a lubricant, protecting the unlubricated disk surface from direct solid/solid contact and direct exposure to the environment. For lubricated disks, the interaction between adsorbed water and lubricant molecules seems to be responsible for the effect of humidity on the frictional behavior of lubricated disks. The effect of temperature on the frictional behavior of the head/disk interface is discussed in terms of surface energy, lubricant viscosity and mobility.     

Effects of diffusion on lubricant distribution under flying headon thin-film disks

Lubricants on thin-film disks have large effects on head–disk interface characteristics. They reduce head and disk wear while thick lubricant film increases friction force between them and lubricant transfer onto head surfaces. Therefore, we have to know the lubricant behavior in many cases. Lubricant depletion due to disk rotation has been studied very well. However, the effects of flying heads have not been understood systematically until now. We developed a simulation program to numerically calculate the change in lubricant thickness under a flying head on a thin-film magnetic disk. The program included the effects of centrifugal force, shear stress from the air due to disk rotation with a flying head, and the effect of lubricant diffusion. We first calculated a change in lubricant thickness under a flying head using previously published data without the effect of diffusion. Calculated results showed fairly good agreement with the published experimental data with very high peaks on both sides of the flying head rails. With the introduction of diffusion effects, these peaks became moderate and the calculated result agreed very well with the experimental data. The coefficient of diffusion obtained to best fit to the experimental data was close to that reported in a literature. We analyzed the effects of air shear stress patterns under flying head on the change in lubricant distribution. We found that the side shapes had large effect on the distribution. We also confirmed that our program could calculate lubricant depletion on rotating disks without a flying head.     

The effects of texture height and thickness of amorphous carbon nitride coating of a hard disk slider on the friction and wear of the slider against a disk

In order to minimize the stiction force caused by contact of the extremely smooth surfaces of head sliders and disks in hard disk drives, texture is usually applied on the disk surface. For future contact/near-contact recording, the stiction-induced high friction between slider and disk will become a problem. Texture on the slider/disk interface will still be an expected method to reduce friction. Recently, it was suggested to texture the slider surface. A protective coating is usually required on the textured slider surface to reduce wear of the texture. The results showed that texture on the slider surface was effective in reducing the friction between head sliders and disks. On the other hand, the texture and coating on the slider surface increase the spacing between the read/write element and the magnetic layer of the disk. The necessary and effective texture height and coating thickness are still not clear. In the present research, island-type textures with different heights (3–18 mn) were formed on slider surfaces by ion-beam etching. Amorphous carbon nitride (a-CN_x) coatings of different thicknesses (0–50 nm) were coated on the textured slider surfaces as a protective overcoat. The friction and wear properties of these sliders were evaluated by constant-speed drag tests against hard disks coated with diamond-like carbon (DLC). The results show that 2 nm texture on a slider surface is sufficient for low (0.3–0.5) and stable friction of the slider against the disk in a drag test, and coatings thicker than 5 nm show similar wear resistances of the texture on slider surfaces.     

仿生制动盘表面温度场与应力场的计算机模拟

根据天然生物与生俱有的高效散热原理,设计三种可抑制温升,从而预防磨损和疲劳的仿生车辆制动盘,并建立三维计算模型。借助于有限元分析软件ANSYS,研究比较这三种表面形态的仿生制动盘和常规制动盘在紧急制动工况下,温度场和应力场的大小及变化趋势。结果表明,仿生制动盘能够降低制动盘表面的温度梯度和应力集中,从而可减小由于循环应力而导致的热疲劳趋势,其降低幅度从大到小依次为具有网格状凹槽的仿生制动盘、具有放射状凹槽的仿生制动盘和具有环形凹槽的仿生制动盘。摩擦生热降低和散热性的提高是温度梯度下降的主要原因。该模拟研究为今后仿生制动盘的优化设计和试验研究提供了重要参考依据。     

高密度光盘径向动态特性测量方法研究

分析了现有光盘径向动态特性测量方法的特点，深入研究了一种适用于高密度光盘径向动态特性的基于过道波形信号连续测量方法及其具体实现。比较了该方法与国际标准推荐的测量方法的测量精度，结果表明该方法精度更高，更能适应未来高密度光盘的测试要求。     

含有非线性摩擦阻尼的失谐叶盘系统受迫响应研究

基于谐波平衡法,提出一种可用于分析含有非线性摩擦阻尼叶盘振动响应的多谐波法,对含有非线性干摩擦阻尼的失谐叶盘系统的受迫响应进行仿真计算.研究失谐叶盘系统在不同的耦合强度、失谐程度、粘性阻尼系数、干摩擦强度等系统参数影响下的受迫响应特性.同时对叶片的非线性干摩擦阻尼的散乱失谐和刚度失谐的耦合影响进行研究,总结含有非线性干摩擦阻尼的失谐叶盘系统的受迫响应规律.     

Development of flying type head/slider for optical recording technology

Flying-type sliders with the integration of optical components were developed for Near-Field Recording (NFR) and Far-Field Recording (FFR) technologies. The key design issue was the integration of the optical components with the slider. Due to the size of the lenses mounted on it, the slider had to be relatively large, corresponding to the size of a micro-slider. Also, the non-uniform distribution of the slider body density was incorporated in the design. As for the optical disk substrate, a plastic material such as polycarbonate was investigated because of its manufacturing convenience and cost effectiveness. The flying and tribological performance of the prototype optical sliders on various media were assessed. The results showed that the tribological characteristics of the slider/disk interface were sensitive to several factors including the properties of the disk. Adequate flying characteristics of the optical sliders on glass (NFR) and plastic (FFR) disks could be attained by optimizing these parameters.     

Experimental and analytical studies of dynamic friction at the head/disk interface

Friction is an important parameter that critically impacts the tribological performance of a head/disk interface. The head/disk interface with laser zone texture affords a model system for the study of dynamic friction by virtue of its precisely-controlled contact geometry. By using two types of head sliders, i.e. the conventional slider and the padded slider, and a matrix of hard disks with a wide range of laser zone texture parameters, head/disk contacts involving a small number as well as a large number of bumps are realized. A rich variety of dynamic friction behaviors are observed with respect to bump height and bump density variations. To shed new light on the nature of HDI dynamic friction, an analytical model that treats both the deformational and the adhesive friction components on equal footings is formulated. It is shown that, based on the model analysis, the friction is deformation-dominated for HDIs involving a small number of contacting bumps and adhesion-dominated for HDIs involving a large number of contacting bumps. In the former case the friction decreases with bump density, whereas in the latter the friction increases with bump density.     

Liquid Nanodroplets on Thin Film Magnetic Recording Disks©

As magnetic recording slider size and flying height evolve to smaller dimensions, previously insignificant levels of contamination begin to play a role in slider media tribology. This article describes a new type of contamination. Liquid nanodroplets on disks originate with electrostatic deposition of hygroscopic ultrafine particles, also referred to as cloud condensation nuclei (CCN). On lubricated disks, the CCN equilibrate with atmospheric moisture and become partially overcoated with disk lubricant, which acts as a fluorocarbon surfactant. Dark-field microscopy measured deposition rates of 0.001 to 0.006 #/mm ² /sec on initially clean disks exposed to ambient air in nonconductive cassettes. Tapping mode atomic force microscopy determined that the sites were deformable nanodroplets 70 to 300 nm in diameter and up to 150 nm high. From AFM profiles, the contact angle of the spherical capped nanodroplets with the disk was between 40 and 90 degrees. Nanodroplet contamination is characterized, and its effect on friction, acoustic emission, and slider smears is demonstrated. A surface chemical thermodynamic model is developed and employed to estimate that the average initial dry nucleus diameter is 110 nm. The estimated size range and composition of the initial nuclei are consistent with those well known in the atmospheric sciences. Nanodroplets were absent from disks that were stored in a CCN-free environment, and the deposition rate was reduced 10× by air ionizer or conductive cassette.     

A reduced order model based on sector mistuning for the dynamic analysis of mistuned bladed disks

In this paper, a pre-existing reduction technique suitable for the analysis of mistuned bladed disk dynamics, the Component Mode Mistuning technique (CMM), originally developed exclusively for the use of blade frequency mistuning pattern, is extended in order to allow for the introduction of a sector frequency mistuning pattern. If either mistuning is not confined to the blades (i.e. blades-to-disk interface mistuning), or the blades can not be removed from the bladed disk (i.e. integral bladed disks), sector mistuning rather than blade mistuning is a more suitable choice to perturb the tuned system. As a consequence, the extension of the original technique is referred as Integral Mode Mistuning (IMM). After a theory review of the original technique, the modifications leading to the IMM are described. Finally, the proposed IMM technique is validated in terms of both modal parameters estimation and forced response calculation, by means of a dummy bladed disk developed at Politecnico di Torino.     

Elastic–plastic deformations of rotating variable thickness annular disks with free, pressurized and radially constrained boundary conditions

Analytical solutions for the elastic–plastic stress distribution in rotating variable thickness annular disks are obtained under plane stress assumption. The analysis is based on Tresca's yield criterion, its associated flow rule and linear strain hardening material behavior. The thickness of the disk is assumed to vary in parabolic form in radial direction which leads to hypergeometric differential equations for the solution. It is shown that, depending on the boundary conditions used, the plastic core may contain one, two or three different plastic regions governed by different mathematical forms of the yield criterion. The expansion of these plastic regions with increasing angular velocity is obtained together with the distributions of stress, displacement and plastic strain. It is also shown mathematically that in the limiting case the variable thickness disk solution reduces to the solution of rotating uniform thickness disk.     

用于蓝宝石光盘的数字化数据存储

为了解决长时数据存储的难题,开展了以数字格式在蓝宝石光盘表面写入数据的研究工作。根据艾林方程,分析了利用常用无机材料进行数据存储的数据失效时间。描述了在蓝宝石材料为基底的光盘上以数字格式记录数据的基本工艺流程,重点介绍了用于蓝宝石光盘的离子束刻蚀系统。实验结果显示,蓝宝石光盘表面刻蚀的信息坑宽度为0.6μm,深度为0.2μm,磁道节距为1.6μm,符合ISO/IEC 10149:1995规定的CD-ROM格式数据存储要求,表明采用本文提出的方法实现蓝宝石光盘的数字化数据存储是可行的。此外,这种基本工艺流程不仅适用于蓝宝石光盘,同样适用于其它以高度稳定的材料(如石英玻璃)作为基底的光盘。     

Study on the cyclotriphosphazene film on magnetic head surface

Stable lubrication is very important to the slider/disk interface with the increasing demand on the life of computer hard disk drive (HDD). The inert lubricant perfluoropolyether (PFPE) on the surface of magnetic hard disk is still prone to be catalyzed to decomposition by the slider material Al₂O₃. The properties of a partial fluorinated hexaphenoxy cyclotriphosphazene, X-1P, are investigated and its function to reduce the catalytic decomposition of PFPE is discussed. The results of contact start–stop (CSS) tester indicate that the thermal stability of the lubricant was greatly improved in the presence of X-1P, and its film thickness has a great influence on the lubrication properties of the HDD.     

A Computational Study of Contact Mechanics between Magnetic Recording Heads and Thin-Film Disks

The tribological phenomena between magnetic head sliders and thin-film disks are studied during rest, during start-up and shutdown, and during regular operation using numerical simulations. A theoretical model of stiction is first derived based on the surface tension of liquid and capillary condensation. Next, a hybrid method of FEM and BEM is developed in order to carry out high-precision microscopic contact stress analysis of a disk covered by multilayer thin films. An impact simulator based on FEM is then presented which considers the air lubricant film to be an elastic spring system determined from the solution of a compressible Reynolds equation, ft is found, that these simulators can be used to effectively study the tribology of slider/disk interactions and that the results can be used to establish qualitative design criteria for slider/disk mechanisms.     

Roughness effects on head–disk interface durability and reliability

This paper deals with the tribological reliability and durability issues in modern magnetic recording hard disk drives, where the slider flies at typically less than 10 nm. Specifically, we investigate the effect of disk surface roughness on the above performance characteristics. The durability of the interface is investigated using low-pressure on-track tests. The drive-level reliability data are presented to confirm general conclusions reached from the component-level testing. Component-level slider–disk clearance measurements are also used to better understand how the roughness affects both durability and reliability. Finally, we discuss possible explanations for the experimentally observed relationships.     

检测二齿差摆线轮时公法线长度的计算和确定方法

首先提出了二齿差摆线轮公法线的存在条件,并提出了一种新的方法来计算公法线检测时的接触位置参数和长度,确定了最小跨齿数就是最佳跨齿数,并考虑了等距、移距、转角修形对公法线测量的影响,根据本文理论编制计算机软件可以准确地计算出各种跨齿数下公法线长度及检测位置。     

Approximate solution of limit angular speed for externally loaded rotating solid disk

The present work proposes a numerical method to investigate the stress and deformation states of rotating disks using variational method taking the radial displacement field as unknown variable. Assuming a series approximation following Galerkin's principle, the solution of the governing partial differential equation is obtained. The analysis is carried out for various disk geometries and the effect of geometry and loading parameters on the stress and deformation states is investigated. Limit angular speed of the disks is also calculated for various system parameters and reported in dimensionless form. The results are validated with those of other researchers for appropriate values of the system parameters and very good agreement is observed. It is observed that the present methodology is quite robust, stable and realistic and the documented tables and curves may be used by the practicing engineers as design monograms.     

Molecular tribology of disk drives

A good molecular level understanding of the tribological properties of the materials at the slider-disk interface is essential to the future development of disk drive technology. This paper provides a short overview of the molecular tribology of disk drives related to the selection of lubricant materials for the slider-disk interface. Besides providing criteria for lubricant selection, this paper briefly discusses our current understanding of stiction and friction forces, lubricant degradation, lubricant mobility, spin-off, and lubricant transfer to sliders. This revised version was published online in June 2006 with corrections to the Cover Date.     

磁头磁盘系统动特性参数及系统稳定性分析

对硬盘系统的动特性进行了数值仿真，其中磁头结构为IBM3370，润滑模型中引入了二阶泊松流因子，保证建模精度。利用摄动法建立了气体润滑的静态方程，并给出了数值解。讨论了最小膜厚度、磁盘转速和磁头倾角对空气膜刚度系数、阻尼系数以及对系统稳定性的影响。结果表明，通过最小膜厚度、磁盘转速和磁头倾角的优化可以改善硬盘的设计。其中磁头倾角的优化可以同时满足硬盘高刚度和高稳定性的要求。     

Air Bearing Simulation for Bit Patterned Media

Patterned media are being considered as a promising approach for achieving storage densities beyond 1 Tb/in² on hard disks. Patterned media reduce cross talk of adjacent bits and improve thermal stability of the media. In this investigation, the flying characteristics of femto-type sliders over bit patterned media (BPM) are investigated. The discrete bits of the disk are modeled as isolated conical protrusions on the disk surface.