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Chrome Bath Help: Chrome to Acid Ratio
June 10, 2008
I have a Baume of 28 at room temp. Is this right? Does sulfuric acid raise or lower the Baume reading.
My chrome is depositing gray. I'm new and have the books coming but I'm excited to see it work.
Please be gentle with me, I want to learn.
new operator - Arkansas
First of three simultaneous responses -- June 12, 2008
Hey there,
well, with 28°Bé you have approx. 345 g/l CrO3 containing in your bath. If you are using a conventional chrome plating bath, than the ratio between sulfuric acid and chromic acid should be max.
1% (3.4 g/l Sulfuric acid). Remember, sulfuric acid is your primary catalyst for your chrome process. On the market some other additives available which increases hardness, appearance, throwing power and efficiency.
You have described a grey deposit, so you should check at least your sulfuric acid content via centrifugal method and adjust if necessary.
The density of the electrolyte can also be influenced by metallic contaminations.
Regards,
- Mexico City, Mexico
Second of three simultaneous responses -- June 12, 2008
Baume is a poor estimate of the condition of the chrome bath. For good and consistent results,you need to do a titration for the chrome and analyze the sulfate with a precipitation and centrifuge method which is quick easy and reliable. Kocour makes an hand powered centrifuge that is OK, if you maintain a constant and correct RPM.
Baume measures everything and it all contributes to a higher reading. Chrome, acid, trash and etc.
- Navarre, Florida
Third of three simultaneous responses -- June 12, 2008
Brian,
First I should have thought you would have read the book before starting. Second, I hope you are an industrial user who is knowledgeable in the handling of these hazardous materials and in the disposal thereof. If not STOP NOW. You may be getting yourself ready for a lot of time spent in litigation over waste, storage, use and safety regulations.
The correct ratio of chrome to sulfate (not acid, but the sulfuric acid contributes the majority of the sulfate) depends on whether you are running a non proprietary or a proprietary bath. The proprietary bath with have technical data which will tell you what ratio is suited for that chemistry.
The Baume (Be) is giving you an idea of the total dissolved solids in the bath. By using a chart, an estimate of the amount of chromium or chromic acid can be arrived at. One then determines the sulfate by analysis and calculates the ratio and makes additions accordingly.
- Great Neck, New York
June 16, 2008
Brian,hello.
Sorry, I got more questions than answers. Apart from chromic acid and sulfuric acid content,
1. What is the operating temperature?
2. What is the current density applied ?
3. What is the plating time?
4. Hard Chrome/Decorative chrome?
5. Substrate ? Chrome applied over Nickel?
- Penang, Malaysia
June 16, 2008
SK,
They are all interdependent for a quality coating. Personally, I would buy two of the recommended books from amazon or whoever has used books in your country. Read them cover to cover before you spend a single rupee on anything else. There is a massive amount of information and sorting it all out is not simple as every plater has a tweak or two on one of the two or three main process methods.
Chrome plating is as much an art as a science, so consider working for a chrome plater for a year before jumping into the business.
- Navarre, Florida
June 27, 2008
Chromium used for decorative purposes is 0.16-0.2 microns. At higher thickness the chromium will crack severely. gold is relatively soft so the cracking may be visible at 0.5 microns. I guess this is a decorative application not practiced in the US to my knowledge. The optimum chromium to sulfate is 100:1
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Don Baudrand Don Baudrand, Consultant  Poulsbo, Washington |
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March 28, 2009
Sometimes you'll need more Sulfuric Acid as catalyst. When I start with metal finishing I had the same issue "gray chrome". I tested many ratios and today I rather to use 5:100 instead the most common 1:100.
Sandry Seibert- Campinas, SP, Brazil
opt
March , 2009
Hi, Sandry. That is very interesting; I have never heard of sulfate ratios even half that high!
Regards,
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 Ted Mooney, P.E. finishing.com Brick, New Jersey |
June 9, 2009
Hi,
When talking about ratio, are we talking about moles? or grams? or other units? or since it's ratio it's dimensionless?
On the Baume reading, is the temperature of the bath when the reading is taken very critical?
Thank you very much.
- Cavite, Philippines