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Anyone heard of a process of converting Hex chrome to Tri chrome plating

Hi all,

I came across a guy from a plating shop and he told me a process I never heard before: To comply with RoHs directive, he use normal hexavalent chrome plating process. Upon completion, he dip the plated parts in a chemical solvent and all hexavalent chrome converted to trivalent chrome. The parts pass SGS test perfectly. Does anyone hear such a process? Does anyone know what's the chemical he uses for the process?

Sam Chen
Buyer - Shenzhen, Guangdong, China
May 9, 2008

simultaneous replies

I somehow think that procedure is not allowed by RoHS. If it is, any reducing agent will work. Hot sugar water will do a good job with about a 5 min dip.

James Watts
- Navarre, Florida
May 9, 2008

May 11, 2008

Hello Sam,

When you state that you are doing Hexavalent Chrome plating , we assume this is done over Nickel . This is referred to as Nickel Chrome decorative plating.

The process of Hexavalent Chrome Plating using DC current deposits the METAL called Chrome on the surface of the part from a colution of Chromic acid in solution.

Being a metal it does not come under the Hexavalent or Trivalent category. In fact the METAL chrome is not a subject under RoHs, BUT the bath used to coat the Chrome is definitely subject to RoHs.

Your friend is simply rinsing the parts well in PLAIN CLEAN WATER and neutralising the parts in a Chrome neutraliser which is sold as a proprietary material by the Chemistry suppliers , OR you could use Sodium Metabilsulfite @ say 50 Grams per liter.

The " solvent " is simply water. The neutraliser removes any HEX chrome from the parts througn a chemical reaction.

BUT you need to know that if a buyer specifies a Trivalent Chrome Bath you need to conform to that instruction and not go running after these shortcuts because the buyer is smart these days. Stay with Trivalent Chrome bath. Or instal one...


Asif Nurie [deceased]
- New Delhi, India
With deep regret we sadly advise that Asif passed away on Jan 24, 2016

May 19, 2008

You may find letter 19341 beneficial. Yes, Asif is right. Decorative Chromium plating from a conventional Hexavalent chromium bath, the chromium is deposited as chromium metal which has a valency of zero. It is neither Hexavalent or trivalent. Usually, if the article is properly rinsed after conventional chromium plating, some residue Hex chromium may be present. I have checked these by sending to laboratory test using ICP-MS, the result ...less than 5 ppm.
Subsequent to RoHS Directive 2002/95/EC, there was an amendment on 18 August 2005, Amendment 2005/618/EC, which states :
'A maximum concentration value of 0.1% by weight in homogeneous materials for lead, mercury, hexavalent chromium,PBB,PBDE and 0.01% by weight for cadmium shall be tolerated.'
This means for hexavalent chromium, a maximum concentration of 1000 ppm is tolerated.RoHS Directive 2002/95/EC does not mention plating process or conversion coating process.In my humble opinion, any components/parts for electrical/electronic industry, tested by approved laboratories that do not exceed the tolerated limits is RoHS compliant.
However, be aware that there are multi national companies which have their own regulations for hexavalent chromium and a host of other heavy metals.Their regulations are much stricter compared to RoHS. As an example, SS00259.Hexavalent chromium is classified as level 1 and has been ban effective January 1,2005.It states 'Residues on the surface of screws,steel sheets,etc, that are processed with plating or conversion coating.'
Therefore, one may be RoHS compliant but not SS00259 compliant.

SK Cheah
- Penang, Malaysia

thumbs up signThanks James, Asif and SK!
Thank you all for clarification. Actually I'm a customer who from time to time source these plate shop. Now I understand my friend's trick.

Sam Chen
- Shenzhen, Guangdong, China
May 21, 2008

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