51043

250 micron Nickel Deposit With High ductility and Low hardness(175HV)  

January 23, 2009

We want to deposit 250 microns of Nickel from Nickel sulphamate bath with high ductility & hardness should be around 175HV.We are using Brass mendrel which is flash plated from Wood's Nickel bath & further passivated with 3% Sodium Dichromate Sol. We need to detach 250 microns electroformed Nickel from the mandrel prepared above.
Kindly Help.

Suresh Bhardwaj
Plating shop employee - Punjab, India

I would be tempted to use a Sulfamate strike vs a Woods Strike since you are going to passivate it. You might even consider a short bake at low temp to passivate it before the chromate step. Whether you can separate the electroform will be difficult on some parts that do not get adequately passivated. You might need to use a thermal step to get the release without damaging the product. Try several scrap forms before you bet the company on a contract.

James Watts
- FL

Personally I would use a stainless steel mandrel that is passivated in 5% sodium dichromate solution for about 2 minutes. This eliminates the problem of nickel plating the brass and it is just s easy to machine as brass.

Sodium dichromate is not very nice to handle as it is hexavalent chromium, so it is perhaps better to avoid it. In the case of passivating the stainless steel, you can use 5-10% permanganate solution, which is much safer.

As for a nickel passivation to allow the electroform to be detached from the mandrel, why don't you use sodium metabisulphite (ca 150-200g/l) for about 15 minutes? This gives a nice blackish passive film that is quite robust.

If you insist on your brass mandrel, I would certainly use a nickel sulphamate flash, not Woods nickel - it is easier to use and more compatible with your overall process

Trevor Crichton R&D practical scientist - UK

I have SS 316 one sided mirror polished mandrel for electroforming nickel from nickel sulphatamate bath. I want to know which is the best practice suited to DETACHED/ REMOVE safely the electroform from the mandrel
the electroform thickness is 50 microns
regards

Hiren Sanghavi
plating shop employee - Bombay, Miaaharsatra, India