Heat Transfer Analysis And Experimental Investigation On Head Flying Characteristics In The Head Disk Interface

Magnetic hard disk drive(HDD)is widely used for its big capacity,high speed and safety performance.To achieve a higher magnetic recording density for HDDs,the spacing(flying height,FH)between head/slider and disk has decreased to several nanometers.In such an extreme narrow spacing,a rough surface of slider and/or disk would lead to wear,friction,read/write element magnetic degradation,collision in head/disk interfaces(HDIs)for magnetic material devices,as a result,the pressure distribution,and heat transfer,and head flying characteristics will be affected.Above all,the investigations of pressure distribution,and heat transfer,and head flying characteristics in HDIs are more important.This paper includes the heat transfer analysis and experimental investigation on head flying characteristics in the HDI.As the spacing between the head/slider and disk decreases to the order of a few nanometers,the gas dynamics cannot be described from the continuum transport theory directly,and the gaseous rarefaction effects must be taken into account in this case.The pressure distribution and heat transfer in the presence of a void on the slider surface in HDIs for magnetic material devices is solved based on a linearized flow rate(LFR)model of Reynolds equation in this paper.The numerical research ideas are as follows: 1)The pressure distribution in the air bearing with a void on the slider is first calculated based on LFR model of Reynolds equation.2)Then,the temperature distribution is calculated by solving the energy equation.3)The heat flux in the air bearing is determined based on the temperature distribution by Flour's law.The effects of environment variables(ambient pressure,boundary temperature)and internal variables(disk velocity,void size,pitch angle)are investigated based on LFR model in this paper,and the results can be summarized as follows: The internal variables such as disk velocity/void size /pitch angle has a similar effect on pressure distribution and heat transfer,while the environment variables such as ambient pressure/boundary temperature has a different effect on the pressure distribution and heat transfer.Thermal flying control(TFC)sliders have recently been implemented to increase recording density in magnetic HDDs,and the flying height between slider and disk continuously decreases to 1-2 nanometers.The spacing between the head/slider and disk can be decreased due to the presence of thermal protrusion which produced by heating the heater in TFC slider.The flying characteristics of the magnetic HDDs can be affected by the ambient pressure and disk velocity.In this paper,an experiment to identify the main factors contributing to the dynamic stability of air bearing slider in the HDIs is introduced.A special experimental set-up is introduced to investigate the ambient pressure and disk velocity effects on touch-down and take-off of air bearing slider in HDIs by using an HDF(Head Disk Flyability)Tester.The acoustic emission(AE)signal is used to detect the contacts between the slider and the disk to determine the critical disk velocity for the slider's touch-down and take-off in different given ambient pressure.The AE signal is used to determine the critical ambient pressure for the slider's touch-down and take-off in different given disk velocity.Correlation is established between the observed phenomena and the variation in the experimental parameters.Experimental results show that the disk velocity of take-off decreases generally with the increase of the ambient pressure,while the disk velocity of touch-down almost keeps constant within the measured range of the ambient pressure.The ambient pressure for slider to touch down and take off decreases with the increase of the disk velocity.Sliders with different ABS design have different velocity hysteresis and pressure hysteresis in the same flying environmental condition,which indicate that there are different intermolecular force acting on the sliders in proximity.