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Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Chrome Bath Help: Chrome to Acid Ratio
Quickstart:
The first successful chrome plating solution was chromic acid and sulfuric acid at a 100:1 ratio. Since that time some people have adopted fluoride catalysts or MSA catalysts. If this is new or confusing to you, you might want to start with thread 35184 "FAQ: Chrome Plating Catalysts".
Q. Good morning, I just redid a 5300 lt tank with 27% chromic acid for hard chrome plating. I put CHROMIC ACID SOLUTION 37% 500 g/l Kg. 1250 for 3750 lt. then I added 2000 lt of distilled water to bring it to the level. now how much 96% sulfuric acid do I need to get it going? A chemist told me 8.5 lt while another told me 4.5 lt. Can someone help me understand who is right? thanks
marco- torino italy
October 7, 2024
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A. Hi Marco.
The rule of thumb for conventional Sergeant's chrome plating baths is 100:1 ratio of chromic acid to sulfuric acid (or sulfate -- the molecular weight of sulfate is so close to sulfuric acid that it doesn't really matter much).
I don't quite understand the numbers you are giving us, but if you are saying the chrome or chromic acid is 27% (270 g/l of chromic acid), that would be reasonably conventional ... and it would call for a target of 2.7 g/l of sulfuric acid (or sulfate). We have several threads about this, so search the site for "chromic sulfuric ratio".
But a general approach in stuff like this is to test stuff in the lab and scale up rather than working from theory on 5300 liters of chemical. Why did you "redo" a 5300 liter tank instead of just making adjustments by the way? Thanks.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
⇩ Related postings, oldest first ⇩
Q. I have a Baumé of 28 at room temp. Is this right? Does sulfuric acid raise or lower the Baumé
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
June 10, 2008
|
RECOMMENDED CHROME PLATING BOOKS
for Shops, Specifiers, & Engineers
"Chromium Plating" A. Hey there, - Mexico City, Mexico A. Baumé 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 sulphate 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. - Navarre, Florida A. Brian, - Great Neck, New York |
Q. 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
A. 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
A. 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 sulphate is 100:1
Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])
A. 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
Hi, Sandry. That is very interesting; I have never heard of sulphate ratios even half that high!
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. 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 Baumé
reading, is the temperature of the bath when the reading is taken very critical?
Thank you very much.
- Cavite, Philippines
June 9, 2009
A. Hi
It's not quite dimensionless, but if you go by mass rather than volume it is -- it's grams to grams or ounces to ounces, etc.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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