Ramp load/unload friction dependence on temperature, velocity and ramp material

Abstract

A simple tool was developed to evaluate ramp/tab friction during dynamic ramp load/unloads on component level test stands for hard-disk drives. By extracting key attributes of each load/unload time-varying friction cycle, multiple valuable engineering studies were performed. A screening test of candidate ramp materials revealed a strong correlation between friction and wear, with acetal homopolymer and aliphatic polyketone being the most attractive choices. The rate of change of friction with temperature can significantly vary between materials. Data are also presented on friction versus load/unload cycles (showing the onset of wear), load velocity and tab roughness. With knowledge of extreme friction values on each section of the load ramp (slope, top, detent), their influence on actuator torque during load and unload can be calculated and included in tolerance analyses. It is shown that friction can play a significant role in multi-disk drives.

Analysis of slip characteristics between dimple and flexure in hard disk drives

“…Ramp contact events were not related to On the other hand, the in case cycles over 6 K, wear particles were generated. Generally, an increase of contact events generates an increase in the friction coefficient and friction force (Hiller et al 2001;Suk and Gillis 2000). These results indicated that it was likely to create wear particles and contact events only affect friction coefficient and wear.…”

“…Down-track slip distance also increased, but the rate of increase was slight because the ramp contact was in the off-track direction. Based on the material, an increase of velocity on a frictional surface causes an increase of coefficient of friction (Hiller et al 2001). However, it is possible to ignore the effect of change in the friction coefficient because the increment of the coefficient was from 0.02 to 0.05 and friction coefficient converged as the emergency parking velocity increased.…”

Ramp wear and debris from load/unload lift-tab roughness

“…7. For large roughness values, initial "effective friction" [2] on the ramp angle was often high and required a "wearing in period" before stabilizing. It had minimum effect on ramp top friction.…”

“…Zero is best." Substantial efforts have been made at selecting ramp material for properties of friction [2], moldability, mechanical stability and, to a lesser degree, wear and debris generation. There is a plethora of polymer ramp materials to choose from, but only one material for the suspension lift-tab: stainless steel.…”