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Ask for the prevention of the cracking in the electroforming object

2005

I have using electroforming making a hollow screw like thread bar. Would you please give me some idea why the object have crack when I bend. Also, when I using the microscope to see the thread bar.There are thicker on the tip of the screw and the crack is from thicker part.

The conditions: Nickel sulphamate: 501 g/l
Boric Acid : 45 g/l
Volume of the bath: 5 L
Wetting Sodium dodecylsulphate (SDS) 0.2 g/l
Saccharin : 3 g/l
Temperature : 57 °C
pH : 4.2
Anode : platinum coated titanium mesh (insoluble anode)

Can you have any suggestion on the about conditions can improve the brittleness of the thread bar.

F.Y.CHAN
HKPC - H.K.

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I am not surprised that you are having problems. Sulfamate nickel is a wonderful material because it can be tweaked to give virtually zero internal stress. Now, your bath has a very high amount of saccharine which produces considerable compressive stress. Then you compound the problem by using an insoluble anode which breaks down the sulfamate radical and one of the breakdown products will produce a great amount of compressive stress.
solution: dump your bath, use SD rounds or SD pellets in a titanium anode basket that is bagged and eliminate or greatly reduce your saccharine. Use a spiral contractometer to track your stress on at least a monthly basis. Stress tabs are a poor mans method of checking, but only give relative answers.

James Watts
- Navarre, Florida
2005

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I agree with James, you are using much too much saccharin. I suspect you want as harder deposit as possible, so you have loaded the bath with saccharin; this has caused a very high compressive stress in the deposit and you don't want that in electroforming. I suggest you drop the saccharin down to less than 1 g/l; if you want a hard deposit, try adding cobalt. Trying to remove saccharin form the bath will be a difficult problem; it will come out with carbon treatment, but it is probably easier to remake the bath. I would also suggest you drop your pH to about 3.8-4.1 and keep it on the lower side; this is only a slight modification, but it can affect your stress. Furthermore, I would strongly recommend you use S-nickel rounds and not an inert anode. The inert anode will oxidise the saccharin and this can have very unpredictable effects on it. You do not need to use chloride if you use S-nickel. You do not say what your cathodic current density is, but I would suggest you do not exceed 35 ASF; I know your bath is heavily loaded so it should take higher cd's, but it is not worth the hassle trying to electroform at a higher rate at the expense of quality. Good luck.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2005