Process Plating

Plating is used for applying coatings for decoration or corrosion resistance. It general plating is suitable for thin coatings and most often not cost effective for thicker coatings.

The electroplating processes are carried out in an electrolytic cell. The cell contains a socalled electrolyte (an electrical conducting liquid) and two electrodes. The negative electrode (cathode) is the part to be coated and the positive (anode) is the coating metal. Under low-voltage current, ions in the electrolyte move towards the cathode and deposit on it.

Electroless plating enables metal coating of non-conductive materials, such as plastics, glasses and ceramics, but is also used for metals. Unlike electroplating, coatings usually have a very uniform distribution of thickness. The deposition is carried out in liquids (solutions), and is based on chemical reactions (mainly reductions), without an external source of electric current.

Vapour deposition is a class of processes used for coating metals, plastics, paper and glass with all kind of materials (plastics, metals, ceramics) for decorative purposes, wear and corrosion resistance. The coating layer is formed by condensation of metal vapour arising from molten metal, from high voltage discharge between electrodes (sputtering), or from chemical processes, like hydrogen reduction.

Danish Name Plettering, udfældning
Category Surface processes

Anodizing
processes
Anodizing & Hard-anodizing
Electro-
plating processes
Alloys plating (bronze/brass and others)
Chromium & Hard-chromium plating
Copper & Tin plating
Plating with Gold, silver and other precious metals
Zinc & Nickel plating
Electroless
plating
processes
Chemical metallisation
Chromating
Electroless nickel-plating
Phosphating
Interference colouring Interference colouring
Vapour
deposition
CVD - Chemical Vapour Deposition
PACVD - Plasma Assisted CVD
PVD - Physical Vapour Deposition
Vapour metalizing
Electro-forming Electroforming

References Arbeitsgemeinschaft - Galvanotechnik
Galvanisk Kompagni A/S
Galvaonline

BIV
Additional information

Coating thickness in electroplating depends on the current intensity. Irregular shapes and blind holes causes non uniform coatings. Hydrogen embrittlement of parts can be a problem.

Electroplating works similar to electroplating but much thicker layers are made so the surface layer becomes a part itself.

Electroless plating can be done using two different process principles. Autocatalythic-plating is used for nickel, copper and their alloys. For tin plating of copper and aluminium the ion exchange-plating (very thin coatings) is used.

All vapour processes involve treatment in a vacuum chamber. The equipment is big, heavy and expensive and requires maintenance. Limitations in the size of the objects to be coated is imposed by the capital expenditure.

Environmen- tal notes Especially old types of electrodeposition plants can give severe pollution problems, from waste water and soil pollution.
Photo Thomas Nissen (Computer graphics)
Copyright © 1996-2008 Torben Lenau
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