Chrome plating tank contamination

A. Hi Ahmed. These days 'rubber' rarely means the product of a rubber tree, but usually means one of many varieties of artificial rubber. But yes, I believe that chromic acid is able to dissolve most of them, and will result in dissolved organic molecules that can mess up a chrome plating bath.

If you are sure that significant contamination with rubber is the problem, I doubt that anything practical can be done to fix it, and the solution will have to be dumped. But what problems are you experiencing, and what is the contamination level or evidence that rubber contamination is the problem?

Luck & Regards,

A. Iron contamination will cause hazy/cloudy deposit and lower the plating rate. Dummy at low CD can help to remove iron. However, bath dilution is recommended should iron content be too high.

A. Use porous pot technology. It also reduces the trivalent.

A. There is a chrome purification system called a porous pot you should research.

A. A porous pot is the key to reducing trivalent-copper and iron.
This product is excellent I have used them for years and works better than dummying.
Be sure to keep them running and fresh clean solution in them at least twice a week or more couldn't hurt just produces more waste. Be sure to block off before doing a reverse if using the same rectifier to plate with. The costs is around $1,100 U.S and are for tanks around 1,000 gallons. They make larger ones but are harder to get in and out of the tanks to check and clean. Just use a hand pump to change solution and take out once a month to clean and check plastisol coating. This is a very good investment.

A. Dear sir, there is an instrument called AAS ⇦ this on eBay or Amazon [affil links] . Analyse your bath for trivalent, copper, zinc, iron, etc. remaining in the bath in ppm. If they exceed some limit then there is a problem, otherwise no worry.
Thanks.

A. Mark,

I certainly wouldn't expect the iron at that level to be a concern. I would be rather more worried about a copper level measurable in g/l, I would normally expect that in the ppm range.

I would consider a dummy plate to reduce the copper levels if I was you.

Saying that, your problem still sounds like a surface cleaning problem or a sulphate:chromic acid imbalance.

A. An acquaintance of mine had done a good amount of research on metal contamination in the hard chrome bath. He was able to show that it was the total concentration of cationic metals (iron, trivalent chrome, copper, etc.) that was more important than having unique limits for the different metals individually. According to his study, you want the total contamination not exceed 7.5 g/L. In my own tests which extended his work, I found that limiting the total contamination to no more than 5.0 g/L was a better limit for quality assurance.

A. Hi Rupesh. When you say that the cathode is steel, may be assume that this tank is only used for hard chrome plating of steel components? (I've seen some small job shops use the same chrome plating tank for hard chrome on steel, and decorative copper-nickel-chrome plating of zinc diecastings).

If you can make your posting a bit less abstract you'll probably get more helpful answers. For example, how much zinc contamination? A one-time event or constantly? What tool or evidence are you using to determine that you have a zinc contamination problem? Thanks!

Regards,

A. I thought that hexavalent plus trivalent chrome had to equal total chrome in solution.

I think that your chloride is very high. Chloride is about 10 times stronger than sulphate as a catalyst. Unfortunately, it does not remain constant, so is bad.

If you can find one, a porous pot will do a wonderful job of removing trash ions and converting trivalent to hexavalent.

I used Hard Chrome Consultants in Cleveland, OH for mine. I think they went out of business a couple years after Clarence Sr. died.

There a few companies that sell this equipment as an outside of the tank set up, but they were extremely expensive.