| Porous chromium plating is used in the automobile parts industry for plating engine cylinders or cylinder liners, and piston rings. Porous chromium plating with oil retaining characteristics makes the automobile parts more corrosion-and wear-resistant. The mast conventional process for porous chromium plating is electrochemical etching after chromiumplating. The present study was undertaken to investigate effects of bath composition, plating temperature ancnd ent density on the type of porous plating achieved, surface condition, current efficiency, hardness and crack size. The change of porosity ratio was also examined with regard to etching and honing. Major results obtained can be summarized as follows: 1. The current efficiency decreased with a rise of bath temperature and sulfate ratio but decreased with a rise of current density. 2. The crack size increased with a rise of bath temperature and sulfate ratio but slightly decreased with a rise of current density. 3. The optimum conditions for obtaining pit-type, intermediate-type and channel-type porousplating were the current density of 50 A/d㎡ at 50℃, the current density of 50∼60 A/d㎡ at 55℃ and the current density of 60 A/d㎡ at 60℃, respectively. 4. A fluosilicate self-regulating solution for porous chromium plating that is stable and is of high current efficiency was developed by controlling the solubility of sodium fluosilicate. When this plating solution was used, pit-type and intermediate-type porousplating were obtained at 50℃ and 60℃, respectively. 5. The etching process after chromium plating had to he adjusted, depending on plating thickness, honing thickness and type of porous plating. |
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