Wednesday, October 11, 2017

Electroless Nickel Plating

Electroless Nickel Plating, what is that? Electroless plating is an auto catalytic chemical technique used to deposit a layer of nickel phosphorous or nickel boron alloy on a solid work piece, such as metal or plastic. On this process is no need additional electric current because the electric charge is merging from the substance itself. The principle of work of this process is the present of reducing agent, for example hypophospite react with metal ions to deposit metal.

Electroless nickel plating often use in various type of parts to protect against wear and corrosion. Uniform deposit of nickel useful for hydraulic cylinders, worm feeds, gears, bellows, shafts, chain belts and other close filling components.

Nickel plating on subject can be doing in two kind of process, using electroplating method and can do by electroless nickel plating. For electroless nickel plating or coating then be classified in accordance with the thermal treatment applied:

  • Class 1 = no subsequent heat treatment: A bake for hydrogen belittlement relief is not considered a heat treatment.
  • Class 2 = using heat treated to obtain required hardness: this can be applied to all metals not affected by heating up to 260° C or above.
  • Class 3 = by non heat-treatable, and use beryllium alloys to improve adhesion nickel plating deposit.
  • Class 4 = heat-treatable, use aluminum alloy and heat applied to improve adhesion nickel deposit.

Quality of Plating Thickness

Beside divide into the class on the process do, electroless nickel plating also divide into the grade of coating thickness. There are three thickness class:
  • Grade A = 0.127 mm
  • Grade B = 0.254 mm
  • Grade C = 0.381 mm

Hard Electroless Nickel Plating

If use alloy with low phosphorous, plating utilizes a unique bath providing coating hardness up to 60 Rockwell. This result can be similar with hard crome Hard, with the advantage of a uniform thickness inside complex configurations, as well as outside. Low contain of phosporous have excellent result and resistance to corrosive and high pH chemicals.

The quality of electroless nickel plating may not stronger as using Nickel electroplating, but electroless nickel plating will improves the quality of components. Tight manufacturing tolerance can be achieved as the electroles nickel is deposited evenly on the surface of the parts. It can be also used to improve the surface of a component so that it is back within the specific tolerance, and provide a surface that allows post finishes to be carried out effectively produce bright surface coating.

Some example product of Electroless Nickel Plating as on the picture below:

Electroless nickel plating
Electroless plating product

Reaction on Electroless Nickel Bath

Electroless nickel bath contain of nickel ions, reducing agent, complexant, neutralizer, buffer, stabilizer and brighteners.

The reation on bath as follows:

1) NiSO4 + H2O → Ni2+ + SO42 - + H2O
2) NaH2PO2 + H2O → Na+ + H2PO2- + H2O
3) Ni2+ + H2PO2- + H2O → Ni + H2PO3- + 2H+
4) H2PO2- + H2O → H2PO3- + H2 (by catalist)

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