Frictional heating effect on thermal protrusion in head disk interface

The frictional heating effect on the clearance loss in the reader and writer elements of hard disk drive was investigated by conducting a coupled simulation between the air bearing dynamics and the head thermal-mechanics using a frictional heating model. The frictional heating power was obtained through experimentation. In this experiment, the frictional heating power was quantified based on the giant magneto-resistance, which varies with the frictional heating, and the frictional heating induced temperature rise was 15 °C. By matching it with the simulated relationship between the temperature rise and frictional heating power, we found that the frictional heating power was about 3 mW. The simulation results at this power indicated when a touchdown (TD) occurs on the wrap-around shield (WAS), the frictional heating can cause a larger additional protrusion on the writer element, which overestimates the reader topography loss to 0.32 nm, and when the TD point is on leading pole (LP), the frictional heating can cause a larger additional protrusion on the reader element, which underestimates the reader topography loss to 0.2 nm. However, the amount of protrusion caused by frictional heating in the reader and writer elements when TD point in on the WAS and LP is almost the same at only a small difference of 0.052 nm. Finally, we analyzed the frictional heating effect on the clearance in the reader and writer elements. The clearance in the pullback state is not equal to the spacing caused by the TFC pullback power, but the sum of the clearance change caused by the TFC pullback power and the clearance change caused by the frictional heating power, and the clearance change in the reader and writer elements caused by frictional heating are different. Therefore, it is very important to account for the frictional heating effect when designing the reader/writer clearance.