Surface Finishing - The Hong Kong Polytechnic University

Surface FinishingThe main component of the ultrasonic clean device is transducer. It can convertelectrical energy to ultrasonic vibration (frequency is above 20,000 cycles persecond).The type of the transducer is piezoelectric or magnetostrictive made of nickel orits alloys or electrostrictive made of lead zirconate or barium titanate and othertype such as polarised ceramic.2.2.3 Electrolytic alkaline cleanIt is more rapid and reliable way for cleaning the surface than soak alkaline clean.In the electrolytic alkaline clean the articles are made cathodic or anodic, thegases are liberated at the surface of the article and would cause mechanicalagitation and scrubbing action to dislodge soil and contaminants on the surface.Anodic reaction:Cathodic reaction:4(OH) (-4e - ) 2H 2 O +O 2 ↑4H + (+4e - ) 2H 2 ↑Anoderod+Cathoderod-Anoderod+O2Stainless Steel Anode2H2WorkpieceFigure 1-Electrolytic cleanCathodic cleaning would evolve twice as much volume of hydrogen as theoxygen at the anode side at a given current density, so the cathodic cleaning ismore effective degreasing process than the anodic cleaning.Positive charged ions such as Cu +2 , Zn +2 , Fe +2 could be deposited and formed ametallic smut at the cathode. So, different solution should be applied when thenon-ferrous metals are to be cleaned.Hydrogen gases evolved at the cathode may penetrate into the steel or otherferrous metals.Certain ferrous metals may be susceptible to hydrogen embrittlement. For thisreason, an anodic cleaning cycle is usually applied after cathodic cleaning or,uses anodic cleaning alone in order to avoid embrittlement of the ferrous metal.Page 4IC Professional Training