Surface Finishing - The Hong Kong Polytechnic University

Surface Finishing10.5 SafetyElectrical hazardsAs the voltage used in electrophoresis tends to be higher, care must be takenduring manual handling. Interlocking switches, warning devices and fast actingoverload devices and leakage breakers are to be installed.FumesAdequate ventilation should be provided to ensure that all toxic fumes arereadily extracted. Tank additions may include ammonium hydroxide, amine, andsolvent, the vapour generated are harmful if inhaled.Fire riskThe electrophoresic tank depending on the system may contain inflammablematerials.11. Electroless Nickel DepositionElectroless nickel deposition (EN) is used to deposit nickel without the use of anelectric current. Electroless nickel-phosphorus coating consists of an alloy ofnickel and phosphorus. The process relies on the presence of a reducing agent,for example hydrated sodium hypophosphite (NaPO 2 H 2·H 2 O) which reacts withthe metal ions to deposit metal. The alloys with different percentage ofphosphorus, ranging from 2-5 (low phosphorus) to up to 11-16 (highphosphorus) are possible. The metallurgical properties of alloys depend on thepercentage of phosphorus.EN has several advantages versus electroplating. Free from flux-density andpower supply issues, it provides an even deposit regardless of workpiecegeometry, and with the proper pre-plate catalyst, can deposit on non-conductivesurfaces.Advantages include:1. Does not use electrical power.2. Even coating on parts surface can be achieved.3. The process can plate recesses and blind holes with stable thickness.4. High wear resistance and excellent corrosion resistance5. Easily soldered with a highly active acid flex6. Matte, Semi Bright or Bright finishes can be obtained.Disadvantages include:Page 40IC Professional Training