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How to increase Chrome plating hardness

April 23, 2010

Q. We are using a horizontal plating system to plate gravure printing cylinders with chrome. Our required hardness is > 700 HV, but we cannot get above 550 HV.

We are plating condition
-temperature of 50-55 °C
-Rectifier current of 12 V and 35 A/dm2
-Chromic Acid - 250 g/l
-sulfuric Acid - 2.7 g/l
-CH10 5 cc/l for catalyst
-CH20 300 cc/Chromic 1 Kg for catalyst
For chemical analysis for contamination is 6.6 gm/l

Please guide me to solve this problem

BJ Keyanon
- Bankok, Thailand

A. Since you are using proprietary catalysts, they are the only ones that can help you. The rest looks fairly good, but I would personally use a 90 - 100 : 1 chrome/sulfuric ratio vs the 110 ratio.
12 volts is very high, I might try to slowly move the anodes closer to the cathode which will reduce the heat and allow you to use less voltage for the same amperage.

Your impurities looks high.

James Watts
- Navarre, Florida
April 26, 2010

A. Hi,

Is the chrome deposit bright? How did you test the HV?

Try to get to a lower temperature and lower the sulfuric ratio to the chrome in your case it should be 2,-2,5 ml/l.

Is the contamination from trivalent chrome? if it so you should electrolyse using a small cathode in the chrome solution over 24 hour day

The another agent you use for catalyst " supplier " did I don't know how they work in chrome solution, then I don't know anything about them.

Regards

Anders Sundman
4th Generation Surface Engineering
Consultant - Arvika,
Sweden
April 27, 2010

A. Did you use hard copper underlayer before hard chrome?
So, please check you hard copper hardness as well, otherwise you will get wrong reading, or you have to use Knoop hardness tester (diamond drop) instead of normal hardness testes for Hard chrome on Steel.

Tony Chandra
- Jakarta, Indonesia
May 15, 2010

Hello all,

Tony, what has the hard copper (max. hardness 230HV) to do with a hardness measurement of the chrome on 6 microns and above.

Sawadi keyanon,

send in a sample of your chrome to your provider and have a check on contaminants (anionic, cationic). Also I did not see how high was trivalent chrome. What anodes are in use and how much is the effective anode area vs your biggest cylinder to be produced?

Regards,

Dominik Michalek
- Mexico City, Mexico
May 17, 2010

Reliable hardness measurements are best taken with a micro hardness machine and indentation parallel to the chrome surface, not perpendicular. This is done over cut samples. If it is not possible, the perpendicular indentation depth should not exceed 1/5 of the chrome thickness, otherwise the reading is influenced by the hardness of the substrate.

Guillermo Marrufo
Monterrey, NL, Mexico
May 17, 2010

A. I think the best method to test the hardness of chromium deposits is micro Vicker hardness.

Talib A. Jasim
Academic - Baghdad, Iraq
January 11, 2019

Q. I am working in a company where nickel printing plates are chrome plated, but the hardness of chrome is approx. 250 to 280 HV only which should be around 750 HV. The chrome bath is HARD chrome bath. Concentration ratio of chromic acid with sulfuric acid is 100 : 1. The nickel plates is having hardness of 200 HV. Please suggest me the changes to be done or otherwise any addition agent is required to increase the hardness.
Waiting for your values answer please.

With regards

Satish Kankarej
- Nasik, Maharashtra, India
October 10, 2012

A. Looking at Properties of Electrodeposited Metals and Alloys by Safranek, your hardness has to be a measuring problem.
There are very very few combinations of plating that get that low. The other way is to heat treat it above 650 °C.

James Watts
- Navarre, Florida
October 11, 2012

A. Hi,

How thick is the chrome deposition and which method are you using to determine the hardness of your chrome layer?

If you're too thin with your chrome then most likely you will measure the substrate below the chrome.

Dominik Michalek
- Melbourne, VIC, Australia
October 13, 2012

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