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"How to test hard chrome without copper sulphate"

Current question:

July 19, 2021

Q. Sir,
We have been into the HCP of plastic extrusion die parts for the last 17 years. We have been using copper sulphate for checking the hard chrome plated surface where we cannot physically measure the thickness. Our customer requirement for HCP thickness is 10 to 40 microns. We have observed that repeated use of highly concentrated copper sulphate weakens the coating, and keeping the solution on the surface turns the HCP surface copper coloured. i.e., it erodes the coating. Not only does it erode the coating, it produces porosity in base material (which is ferrous steel -- EN8, EN19, etc).
Do we have any effective non-destructive test other than copper sulphate test, sir?

Plating shop Incharge - Vapi-India

Closely related historical postings, oldest first:

August 5, 2019

Q. This is Sabir, Sr. Manager-Production/Kaizen, manufacturing Shock Absorbers/Struts for vehicles/motor cycles.
I am having a problem regarding Test of Hard Chrome Plating on SS Rods.
We are using Copper Sulfate (CuSO4) to apply on the plated surface. If the plating is insufficient, it removed away and substrate become naked with color of Copper (reddish shade) on the portion from where plating is wiped off on the rod.
However this process has become dangerous environmentally since ECHA List of SVHC under REACH Regulation has categorized "Copper Sulfate" in list of Banned Material due to its Carcinogenic and Teratogenic effects on humans.

Please suggest some other way as Alternate solution to this efficient but dangerous process of Hard Chrome Plating Test by use of CuSO4 solution in water.

Syed Sabir / Ali
Agriauto Industries, manufacturing Shock Absorbers/Struts for vehicles/motor cycles. - Karachi,Sind,Pakistan

"Hard Chromium Plating"
by Robert K. Guffie
from Abe Books

(affil. link)
see our review

August 2019

A. Hi cousin Syed. I hate to laugh at a question, but the irony can't possibly escape any reader that copper sulfate -- a chemical which is poured into drinking water reservoirs palette load after palette load, which is sprayed on crops around the world from airplanes, which countless millions of households pour down their toilets by the bucket to deter roots -- is a tool you are forbidden to use a medicine dropper full of to keep huge vats of hot, fuming, concentrated, toxic, carcinogenic, hexavalent chromium working correctly :-)

Several of our readers keep a close eye on REACH and similar standards and may be able to suggest whether your concern is real or a misunderstanding, and offer advise on alternatives if it is real.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

simultaneous August 16, 2019

A. Hi Syed,

I can confirm that copper sulphate has been registered under the REACH regulations. This does not mean that it is harmful, only that it is used in the European Union in quantities greater than 1 tonne per annum.

Copper sulphate is not listed on the Candidate list of Substances of Very High Concern (SVHC), nor is it included in Annex XIV for sunsetting and potential authorisation for use. It is also not listed in Annex XVII, restricting its use.

Are you getting the copper sulphate confused with chromium trioxide (chromic acid)? This is a SVHC and is listed on Annex XIV, with a sunset date of 21st September 2017, with various authorisations granted or in the process of approval. As Ted has said, this is a really nasty chemical, being toxic, carcinogenic, mutagenic, toxic for reproduction, sensitising and dangerous for the environment, to list but a few of its properties.

Brian Terry
Aerospace - Yeovil, Somerset, UK

August 18, 2019

Q. Hi, thanks for the response. Yes we are fighting against Chrome III considering it of the same notorious qualities. Our customers have also of the same opinion -- eliminate CrIII (CrVI).
Regarding CuSO4, Info card depicts the hazardous/dangerous characteristics of this substance as majority of data submitters express, though not listed on ANNEX XIV or ANEEX XVI, or authorization list, yet I think. Anyway, is there any other method which can check the plating adhesion quality of chrome VI in a matter of seconds.

Syed Sabir Ali [returning]
Agriauto Industries Limited, Shock Absorber manufacturing for vehicles/motor cycles - Karachi,Sind,Pakistan

August 21, 2019

A. Hi Syed,

Not certain where you have got your information from, but under the current Classification, Labeling and Packaging for Supply (CLP) regulations, the EU adaptation of the Global Harmonised System of labeling (GHS), copper sulphate is classified as harmful if swallowed, irritating to eyes and dangerous for the aquatic environment. With a classification like this it is very unlikely to progress to the Candidate list of REACH, so will not make Annex XIV, nor is it likely to be restricted under Annex XVII.

However, as for other tests for adhesion, have you considered plating a test piece alongside you work and carrying out a bend test on it? The material of the test piece should be chemically similar to the material being plated. After plating, bend the test piece over a mandrel to 180 degrees and look for flaking on the bent area.

Depending on thickness of plating and your base material (needs to be a low alloy steel), you may consider a potassium ferricyanide test. Potassium ferricyanide will turn blue with the underlying steel. It is a test often used to determine whether there is porosity in a coating.

Brian Terry
Aerospace - Yeovil, Somerset, UK

August 23, 2019

thumbs up sign  Following is the link from where I read and got alarmed about Copper Sulfate hazards:

At least I have removed the substance from uncontrolled use; and secondly the operator is restricted from using it to check Plating Quality on Line side Quality Gate station until CuSO4 replacement is available for production use in Plating check .

Thanks for the alternate solution. I will study/check/make trial for result confirmation to meet our purpose. However, ECHA doesn't seem to have much data about this chemical as mentioned in "Infoard" on below link:

Anyway deeply grateful for your time, response and concern to my worry.

Syed Sabir Ali [returning]
Agriauto Industries Limited, Shock Absorber manufacturing for vehicles/motor cycles - Karachi,Sind, Pakistan

August 27, 2019

A. Hi Syed,

What you've seen is the accumulated self-classification of copper sulphate. Not all manufacturers/importers classify it the same, however it does have a Classification and Labeling (C&L) classification, which is the official EU designation:
for copper sulphate pentahydrate and the anhydrous version.

Brian Terry
Aerospace - Yeovil, Somerset, UK

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