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Contact Material for Hard Chrome Plating Jig

We use copper bars as jigs for hard chrome plating. tips are bolted on this bar. entire bar is coated with vinyl plastisol and the contact portion of the tip is scrapped off the coating to expose the metallic part. These tips are in contact with the jobs. Each tip handles about 600 amps of current. The observation is that the contact surface gets attacked by the chromic acid and gets tarnished. this increases the contact resistance and the subsequent heating damages the plastisol. once the chromic acid reaches the copper base, it causes irreparable damage to the jig. we have tried steel, stainless steel, Hastelloy, titanium tips but without success. Is there a better material for tip that would be a good conductor of electricity and yet stand the actions of chromic acid. we use both fluoride based as well as fluoride free chemistries for plating.

Nikhil Kulkarni
Chemist - Mumbai, India
2007

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If your tip were copper, the tip would have to be 2/3 inch diameter to carry that load. You need at least 2 tips or you will have a serious voltage drop across the part (which you fail to explain size or material).
I would use an aluminum bolt, 1 inch diameter and tape the bolt/rack after racking. It will give you the required contact pressure and is expendable If you desire longer life out of the bolt, have it lead or solder plated. If you start with it a bit long, you can always cut a bit of the tip off and reuse it numerous times.

James Watts
- Navarre, Florida
2007

The tips that we presently use are either copper of dia. 1.25 inch with a 5 mm SS plate where the actual job is clamped, or plain mild steel. Using bare copper causes the tip material to dissolve. the length of the tip is about 1 inch.

Nikhil Kulkarni
- Mumbai, India
2007

SS is a terrible conductor of electricity. Could you use an aluminum tip in place of it? You would need to lightly sand the tip before each use. Can you send a picture of the tip before racking and after racking? It would be a lot of help for suggestions.

James Watts
- Navarre, Florida
2007

Simply you should use Lead tin anodes.

Kuldeep Singh
- Pantnagar, Uttrakhand, India
2007