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Pulse form for Nickel Cobalt electroforming
adv.
2006
Dear people, I'm working in a small company and trying to find a way to produce electroformed holograms to press on to silver coins.
(0.925 Sterling, 70-80 Hv. diameter 38 mm). The installation I have is a 75 liter bath, fully heat controlled with a carbon filtering system, filtering the bath continuously. Inco 'S' rounds as anode material.
The electrolyte I use is a 600 gr/L nickel sulfamate, Co 6 gr/L, 40 gr/L H3BO3, 150 cc wetting agent. pH 4.0, temp 60 °C, no other additives.
The rectifier I have can produce wave trains 100-1100 Hz, duty rate
10-90% and then reverse the pulse to - (minus) and produce the same trains with setting at choice.
The time of each cycle train can be changed between 0.1 sec and 60 sec.in length.
Please can anyone help me and suggest a starting point to set my rectifier? and or any other suggestions? (how many A/dm3?)etc. to obtain a as stress free as possible layer of 0.8 mm and approx.
450-500 Hv. in hardness.
Thanks in advance and all have a merry Christmas and a Happy and healthy new year.
Best Regards,
Patrick Onelcoin technology - Amsterdam, The Netherlands
2006
A. Patrick,
I appreciate you want to get hard nickel, but why use cobalt? Nickel-cobalt baths are quite hard to control because cobalt deposits preferentially to nickel and with only 1% cobalt relative to nickel, you are walking a tough path. If the hardness you need is only 450-500Hv, try using a conventional sulphamate nickel bath with about 1.6-2 g/l sodium saccharin. This will give you the required hardness and the deposit should be slightly compressive or stress free. There is also no need for pulsed plating.
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
Q. Thanks Trevor for your quick response,
I will try your 'recipe' in the beginning of next year (sounds far away!) and update you on the results.
The requested hardness is really the minimum I need to obtain a nice flat impression, even on very soft silver. Thanks a lot for the help and I will try this with flat DC and start with 8A dm2.
Do I need any other additives in the sulphamate bath? or is a standard plain bath ok for this purpose?
Thanks a lot for your help and have a good and healthy new year!
Best Regards, Patrick
- Amsterdam NL
2006
2007
A. Patrick, you don't need anything complicated, but I suggest you use a nickel bath produced by a reputable supply house. The addition of wetting agents and brighteners can interfere with the stress of deposits, so some supplier, such as Macdermid, Scloetter and Schering have other proprietary additives that help minimise these effects. The systems are not expensive and work very well. In the long run it is probably cheaper to buy in a system than to develop it yourself. The important thing is to use a sodium saccharin based bath!
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
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