Electropolishing Parameters for Nickel Coating Replacement of Hard Disk Actuator Arm

Abstract

For hard disk drives (HDD), loose particles that are trapped between the head and disk during HDD operations can create damages to HDD. As a result, a nickel coating is used to minimize their loose particles. However, nickel is one of many carcinogenic metals known to be an environmental and occupational pollutant. Therefore, an electropolishing technique is proposed to replace a nickel coating process. To do experiments, a stainless steel actuator arm is set as an anode, a steel plate is set as a cathode, and a sulfuric acid is used as an electrolyte. With a design of experiment (DOE) technique, four parameters of the electropolishing technique which are an electrolyte concentration, an electrolyte temperature, a polishing time, and an electric intensity, are tested. The experiment result shows that the electrolyte concentration and electric intensity are not made any change for loose particles counts with liquid particle counter (LPC) testing whereas only two parameters which are the electrolyte temperature and polishing time play significant roles for LPC values. The lower LPC shows the smaller percentage of HDD failure. From these Box-Behnken DOE experiments, the optimal solution is 90 Celsius of the electrolyte temperature and 40 minutes of the polishing time. Although, the electrolyte concentration and electric intensity are not made any impact for LPC but they are set as a standard to be 0.2 mol/l and 0.25 A/cm2 consequently. With these parameters, the predicted LPC is only 442,106 counts/part. This LPC is still in an accepted level standard that will not cause failure to HDD. This means that the electropolishing technique initially can be used to replace a nickel coating process without loose particles.