Metal Finishing Guide Book


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Table XX. Wood's Nickel Strike Bath Composition Component Nickel chloride Concentration 30-34 oz/gal (225-255 g/L) Hydrochloric acid, 22[deg]Be 10-12% v/v Nickel anodes Sulfur free Electrolytic Nickel The purpose is the same as the copper strike, protect and seal the zincate film, preparing the part for reception of additional deposits. (See Table XIX.) The bath is operated at the same current density as Watts nickel barrel and rack plating solutions. Time is just sufficient to cover the zincate. Bath pH should be maintained at 4.4 to 4.6 to minimize attack of solution on the zincate. Proprietary wetting agent and zinc tolerant Class I brightener (carrier) are normally added. Routine low current density (LCD) dummying at 5 to 10 A/ft2 is recommended to plate out zinc contaminant. Where possible, live entry into any of the described strike baths is recommended. This can be accomplished by using an auxiliary cable, while parts are in transit "live" to the strike bath. Plating begins as soon as the parts contact the solution, significantly minimizing attack on the zincate. Alkaline Electroless Nickel The benefit of this bath is total, even nickel thickness of all exposed surfaces since this is an immersion process. The zincate itself is catalytic toward the electroless nickel solution. For a 10-min immersion the deposit thickness may range from 20 to 30 millionths of an inch, at 110°F (43°C). Bath pH is 8.5 to 10.0. Low Carbon Steels (e.g., stampings and extrusions) Standard soak clean, electroclean, and acid dip, as described in process bath descriptions. High Carbon Steels (e.g., springs, fasteners, lock parts) Classified as above 0.35% carbon. Base metal has higher smutting tendency. Preferred acid dip consists of 25 to 40% v/v hydrochloric acid with additions of a pickle aid and wetting agent. The pickle aid minimizes attack on the base metal, greatly reducing tendency for hydrogen embrittlement. Stress due to hydrogen embrittlement can be relieved by baking at 350 to 400°F (177-204°C) for to 3 hours. Cast Iron Standard alkaline soak clean, followed by alternate hot and cold rinsing to push solutions out of pores. Anodically electroclean in alkaline descaler. Parts exiting the electrocleaner should have a uniform light yellow cast. Dip in 15 Table XXI. Wood's Nickel Strike Operating Parameters Operating Parameter Temperature Anodic Treatment Cathodic Treatment Range 75-90°F (24-32°C) 10-20 A/ft2, 1-2 min (optional) 40-120 A/ft2, 2-3 min 151

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