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Difference between Mechanical and Electro Plating ingredients

Hello all,

I am in the Product Development department for an industrial fastenings distributor called TFC Plc based here in the UK. Part of my job is to make sure that the parts we supply conform to the European Union ELV (IMDS) and now RoHS legislations, which leads me to why I am here. I have no training or specific background in metal finishing, so I am picking it up as I go along, I'm afraid you will have to excuse my serious lack of knowledge!

My first question (no doubt one of many) is this:

Are there any particular chemical differences between mechanical zinc plating & chromating (such as Mechanical Zinc & Yellow) and Electro Zinc plating and chromating (electro zinc & yellow)?

All I seem to be able to find on searching the net is that the colour is a duller finish with mechanical, but is generally a thicker plating so provides better corrosion resistance (which I could figure out easily enough anyway). Many thanks for any help!

Martin Cross
TFC Plc - Fastening Solutions - South East, East Sussex, United Kingdom
2004

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The simplest way to answer this question is to say that electroplating of zinc is done by dissolving suitable zinc containing salts in water and passing an electric current through the resultant liquid. The zinc is deposited on the -ve side (cathode). Generally this technique will give reasonably good coverage and with a good degree of thickness control. The deposit can be made bright or dull just by adding (or not) special chemicals to the bath. Mechanical coating does not involve solutions, but a variety of materials ranging from high velocity zinc "shot" through to molten zinc. These processes are cheaper and easier to do than zinc electroplating, but offer much less control. The different techniques will produce either dull or bright zinc. Using a chromate coating on the zinc will offer corrosion protection to the zinc layer. I hope this gives you the required explanation without getting technical.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2004