Study On The Migration Characteristics Of The Lubricant At The Head-disk Interface In The Helium-air Mixture

In order to meet the requirements of data storage,helium-filled hard disk drive has been developed and utilized as an efficient and reliable large capacity storage carrier.Using helium instead of air in sealed device can effectively reduce vibration of disk,reduce wind resistance loss,meanwhile,it can significantly decrease the temperature of the hard disk drive.However,with the increase of areal density of hard disk drives,the flying height between slider and disk has been reduced to several nanometers,and the phenomenon of lubricant migration on disk surface is becoming more and more serious with small gap.Lubricant migration and depletion may lead to change of dynamic characteristics of slider,and contact or collision between slider and disk happened eventually,which is damaging to the reading and writing units of head and destroying lubrication layer.However,the mechanism of lubricant distribution and migration in air-helium gas mixtures are not clear.In this case,it is necessary to investigate the mechanism of lubricant migration and depletion in air-helium mixtures.It is very important and useful for high areal density of recordings.Therefore,by establishing aerodynamic model of slider disk interface in air-helium mixtures,the influences of mixture gas density,viscosity and mean free path acting on the air bearing force and air shear force were studied.The magnitude and distribution of air bearing pressure and air shear force at HDI were obtained as well.Besides,the effects of flying height,pitch and roll degree,operating parameters of disk and environmental factors like temperature variation on air bearing force and air shear force were analyzed.Afterwards,by coupling aerodynamics model with molecular dynamics model of lubricant migration between head and disk,a calculation method of lubricant migration was developed.The migration mechanism of lubricant under the effects of air bearing pressure,air shear force and Van der Waals force was analyzed.The influence of helium fraction on the migration of lubricant in air-helium mixtures was investigated.The influence mechanism of air-helium mixtures properties(density,viscosity,mean free path,etc.)on the migration of lubricant was revealed.The effect of slider flying height,the initial disk speed and initial boundary pressure at HDI on lubricant migration and its redistribution status were discussed.The main factors affecting lubricant migration and distribution,such as the relationship between air bearing pressure and shear force,were explained.The optimal combination of operating parameters was obtained to suppress lubricant migration.At last,the contact MD model between head and disk was established in air-helium gas mixtures.The influences on the penetration depth and the amounts of the lubrication depletion in the contact state were analyzed,through change the pressure distribution and operation parameters.The lubricant depletion volume affected by normal forces was studied.The effects of head structure and configuration parameters on the amount of lubricant depletion were investigated as well.This thesis revealed the microscopic phenomenon and mechanism of lubricant molecules migration process at HDI,and analyzed the amounts of lubricant molecules depletion when the slider and disk contact occurs,which further explains the redistribution of lubricant on the disk and slider surface.Based on those factors affecting the lubricant migration in the air-helium mixtures,an effective method for suppressing the migration of lubricant was obtained and the reliability and stability of HDD was improved.The conclusions of this thesis supply a reference for the design of slider surface structure.On the other hand,it will provide theoretical and technical supports for high capacity,fast access as well as safe and reliable development of HDD.