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Stirring/agitation in hard chrome plating bath?
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Does a hard chrome bath need stirring while plating or isn't it allowed? Does the stirring have effects on the plated layer?
andy daan- Germany
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Suppose you like your coffee very sweet, Andy. You might put 3 spoonfuls of sugar into it. If you put in still more, say 6 spoonfuls, the coffee can only dissolve some of it, the balance will sink to the bottom of your cup as a syrupy sludge. But if you now drink some of that coffee, and top up your cup, your refill will be just as sweet as the original without any further addition of sugar because that syrup at the bottom will go into solution to maintain the sweetness at the maximum sugar concentration that coffee can sustain.
Traditional chrome-sulfuric plating baths required a 100 to 1 ratio of chromic acid to sulfuric acid, and some people felt that it was laborious to maintain this ratio. So they invented a "self-regulating" fluoride bath where excess catalyst would settle at the bottom of the tank.
As catalyst is consumed, these precipitated salts go back into solution to keep the catalyst in balance. Stirring the tank can be very helpful towards that. Regards,
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 Ted Mooney, P.E. finishing.com Brick, New Jersey |
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I like Ted's description about coffee. When you use a SRHS bath you must stirring the bath for 5 minutes before you start plating. I has seeing when using stirring when I plated hard chromium inside a diameter the deposit goes faster with using a stirring it is approximately 23 % deposit rate. Because the content of trivalent chrome never builds up in the inside diameter you get a change of solution there. But when you plate a out side the chromium deposit goes first to the outstanding portion of the part, because the diffusion layer will be less.
Regards,
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Anders Sundman surface finishing engineer Sweden |
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Tom Pullizzi reminded me that the solubility of these regulating salts is temperature dependent and, since the bottom of the tank can get cold, stirring is essential to get them back into solution.
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 Ted Mooney, P.E. finishing.com Brick, New Jersey |
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Most hard chrome plating solutions should be agitated during the plating process. Dried compressed air is the best method to introduce agitation. Several benefits are to be had including maintaining electroplating solution temperature. Regards.
Stephen C. Ward- Canada
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Dear All,
I think,it's important to know that stirring during the electroplating may effects on the layer with two ways:
1-It can effect on the the roughness of the layer, because enter the Fe,Cu& some metal particle to the layer. Generally,there are some of them such as a deposit in the bottom of bath.
2-It may effects on the brightness of layer and lose it.
It's more happened on the old solution and base of sulfuric acid.
It can't hard to prevent of this problems, dependent on the condition of your solution.
Rgds;
- Karaj , Iran
October 16, 2008
Is it true that vigorous stirring affects the work of the fume suppressant used to reduce the surface tension?
Chris Sigalas- Athens, Greece