Where the
world gathers for metal finishing
Q&As since 1989


-----

Parting problem

2006

I will appreciate any suggestion regarding the problem we are having with our newly constituted nickel sulphate bath [watts].We are plating heavy nickel deposits [.9mm]plate for banknote printing.The problem we are having is non separation of the grown plate.The growth seems to be hard, smooth but impossible to separate from alto plate or mandrel.
We have tested bath composition and found it to be within spec.
We have carried out plating
Also we diluted the bath but the problem still persists.
Our old bath is not having this problem.
Any idea on how to solve this problem is highly welcomed

Thanks
R C Otika

Mr Romanus C Otika
printing and minting plc - Victoria Island, Lagos, Nigeria

---

2006

Very interesting situation, Romanus, because the nickel plating is supposed to adhere to the substrates it is plated onto. The method to allow separation is usually to passivate the substrate with a material like sodium dichromate and then plate it normally.

Because your old bath produces non-adherent plating, I would suspect that it has chromium contamination that you have come to rely on. I guess :-)

Strange!

Regards,

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

---

First of two simultaneous responses --

How are you precleaning and passivating your mandrels? Is there anything different in your new plating line?

Guillermo Marrufo
Monterrey, NL, Mexico
2006

---

Second of two simultaneous responses --

I am not sure what you are doing. I presume you are electroforming a plate using a (negative) master mother plate and then growing positive daughters from it. To do this, you need to passivate the master mother plate; the actual passivation material depends on what the mother is made form; if it is nickel or stainless steel, I would suggest dipping in a strong solution (180-250g/l) sodium metabisulphite for about 10 minutes. This will give you a good separating layer. You may also want to consider using a dichromate or permanaganate dip. However, if you are growing the plate directly and do not want it to separate, then I do not know how you are getting your printing pattern....perhaps I just missing the point!

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2006