What is Involved in Electroless Nickel Plating?
Electroless nickel plating is an alternative to electroplating that doesn’t rely on an electric current. Both methods use a chemical bath; electroplating passes electricity through the bath and into the workpiece to accomplish the plating, while electroless plating relies on a chemical reaction. Electroplating deposits a layer of the plated material on the workpiece in non-uniform thicknesses, depending on the contours of the workpiece and the location of the anodes discharging the electric current into the plating solution. Electroless nickel plating deposits the nickel to a uniform thickness all over the workpiece, regardless of its geometry. In addition, electroless nickel plating can deposit the plate on non-conductive surfaces such as plastics, nylon or rubber, a distinct advantage over electroplating.
The first step in the electroless nickel plating process is the preparation of the workpiece; as with electroplating, the quality of the final job is dependent upon this preparation. The workpiece must be absolutely free of any contaminants or soils. Even the slight traces of oil left from human fingers will interfere with the plating process. The pretreatment of workpieces is accomplished by a series of washings with caustic compounds that will efficiently scour the surface. After each pretreatment bath, the workpiece is thoroughly rinsed with water to remove any residues of the chemical. The final step in the pretreatment process for conductive workpieces is an acid bath to remove any scaling; proprietary methods are used for the final pretreatment steps for non-conductive materials.
After pretreatment, the workpieces are immersed in a chemical bath containing nickel ions and a reducing agent, which prompts the formation of nickel deposits on the workpiece. Unlike electroplating, the nickel plate will layer workpieces uniformly, no matter how irregular its contours. Like electroplating, the electroless nickel plating process will faithfully follow the contours and imperfections in the workpiece’s surface. If there are scratches in the workpiece after pretreatment, the nickel plating will reproduce those scratches. Any designs, emblems or text engraved in the workpiece will likewise be perfectly reproduced in an electroless plating job, unlike electroplating, which is likely to leave the deeper portions of grooves and etches unplated.
Electroless plating does have some disadvantages as well, generally concerning the chemicals used both in pretreatment and the plating bath itself. Environmentally responsible waste treatment can add significant costs to the electroless plating process. In addition, while it’s not necessary to monitor an electric current and keep the bath heated and agitated, it is necessary to monitor the level of nickel ions in the bath and replenish them as they decline. Even so, electroless nickel plating compares very well with nickel electroplating, producing a bright, hard plate of uniform thickness whose hardness can be increased with appropriate heat treatments. It provides good protection against rust and corrosion, often better than electroplating because it’s less porous. Electroless nickel plating can even be used to restore old parts by adding thickness to them and then machining them to proper thickness.
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