Brass Plating Problems & Issues

A. Hi Samuel
Although too much cyanide can be a problem, the ASM Metals Handbook "Surface Cleaning, Finishing & Coating" ⇦ this on eBay, Amazon, AbeBooks [affil links] says that "a slight excess of cyanide is necessary ... to prevent the formation of insoluble zinc and copper salts on the anodes which will stop the flow of current".
Further, Bob Probert mage the suggestion to add cyanide to another plater experiencing anode polarization -- and he was found to be right. So rather than discussing the exact ratio you are using, I think the answer remains as Mr. Probert said: plate some panels in a Hull Cell and "start adding cyanide" :-)
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Hi Kiran. Sulfides, such as liver of sulfur ⇦ this on eBay or Amazon [affil links] , are used to darken brass.

If you've been satisfactorily doing brass plating for 40 years, but now the brass turns dark or black, you have to suspect sulfide contamination from new diesel equipment, trucks running at the loading dock, or some other change which has introduced a lot of sulfide into the area.

As far as deterring tarnish, the first step is probably a dip in a proprietary benzotriazole ⇦ this on eBay or Amazon [affil links] or similar solution, before the application of the lacquer. Some clear coats and brass lacquers like Incralac ⇦ this on eBay or Amazon [affil links] include benzotriazole in their formulation.

Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Hi Waseem.

Sorry to have to say this Waseem, but that plating is horrible. The supplier of that brass salt should be helping you to solve this problem.

Can you give us some additional details please? Are you an established brass plater and this problem suddenly popped up when you bought some new brass salt, or is this a new installation and you haven't done satisfactory brass plating yet?

Is the substrate plain steel? Is there copper plating under the brass plating or are you plating brass directly on the substrate? What is your pretreatment sequence? Do you know how long you plate and how thick the brass plating measures? Do you have a Hull Cell ⇦ learn moreA standard Hull Cell is a small plating cell, trapezoid-shaped from a top view, with a cathode test panel very close to the anode at one end and very far from it at the other, thus displaying the effect of plating across the whole range of current densities. It is sized at 267 ml for easy math when scaling up from test additions to the cell to additions to the plating tank. so that you can plate clean brass or steel panels and see how they come out?

Unfortunately, I think you are very far from successful plating :-(

Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Hi again.

The circumstances point towards the problem being defective plating salts, as you say ...

... but unless the photo is playing tricks on me, it looks like an area of no plating at all, and extremely thin very porous plating.

What you are calling a brown line, looks to me like no plating at all on the left bottom edge of the part, either due ro it being stripped, or not clean and remaining unplated.

Three things I can suggest besides replacing the brass plating bath would be:
• running a clean Hull Cell panel • scrubbing a few test parts with pumice before putting them through your plating cycle • pulling a few parts out after nickel plating and examining them.

Hopefully another brass plater will chime in with some insights. Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Is there a possibility that you are dragging in acid (which kills the cyanide) from your pretreatment?

A. Ferdinand,

I have been servicing and analyzing brass plating solutions for over 30 years. There are many possible reasons for high use of cyanide salts. Firstly, is the cyanide being broken down into sodium carbonate (analytical procedure available in many reference books)? If so, check the solution temperature and agitation. Either can accelerate the breakdown of the free sodium cyanide to form sodium carbonate and hydrogen gas. Another source of this problem is operation at high current densities where large amounts of hydrogen are evolved at the anode.

A. The temperature seems a bit high on the tank this would cause the cyanide to break down quicker than may be expected.

Is it possible to turn off the heating when not in use and then turn on in time for the tank to be ready for production?

"Analysis of Electroplating & Related Solutions"
by Langford & Parker

on Abebooks

or Amazon

(UTL on eBay)

(affil links)

A. Hi Sara,

Langford and Parker [on AbeBooks or eBay or Amazon affil links] , says 10 ml sample, 150 ml water and 2 ml of 10% KI. Titrate slowly to prevent premature end point. I believe that I used to titrate without the KI until the first turbidity, only then adding the KI. I don't remember if it was for cyanide analysis, but maybe it will improve reproducibility.

I don't remember having trouble with the analysis. What problems are you having?

Regards,

A. Sara,

I think cyanide analysis is always free cyanide, so if you add cyanide and make a analysis I expect that the results are lower than the value you added. This is because of the cyanide forming complexes. If you use always the exact same analysis method you should get values that are usable in the control of your baths.

Regards,

A. REF a book-not tried:
CuSO₄-40-55 G/L
ZnSO₄-35-55 G/L
ROCHELLE SALT ⇦ this on eBay or Amazon [affil links] 380-420 G/G
NaOH 80-100 G/L
T=45-50 °C,1-1.5 A/sqdm, good air agitation

OR
Na₆Cu(P₂0₇)-4G/L
Na₆Zn(P₂0₇)-12G/L
NaP₂O₇-11G/L
Na₂HPO₄-18G/L
T=40 °C/1.25-2A/sqdm

Good luck

A. Yes, but then you cannot freeze out the carbonates.

Ed. note: Robert is right that potassium carbonate will be soluble and not amenable to freezing out. For a detailed discussion of freezing, and carbonate removal from cyanide plating solutions, etc., please see thread 0473.

A. Dear Amish Gala,
Hi.
Firstly, for bright Brass, we usually use bright nickel as base coat and then a thin film of brass. This thin film can be achieved by low cyanide baths or Medium cyanide in short time, but the low cyanide is much better. As the thin film is too sensitive and active in electroplating polluted air and oxidizes soon, so you can seal it by using 20-30 gr/lit sodium or potassium dichromate in DIW with pH between 6 to 7. (I mean the pH of water). Deep in this solution for 5-10 seconds, rinse twice and let it dry. You won't see the blue parts at edges.
Good Luck

"Trouble in Your Tank: Handbook for Solving plating Problems"
by Larry Durney

on Amazon

(currently UTL
on AbeBooks & eBay)

(affil links)

A. Hi John. You've posted here over the years, and you are apparently an experienced brass plater who has been plating satisfactorily, rather than someone who has never done it before. As Durney notes, that means something has changed that you haven't accounted for yet. One possibility that occurs to me (why it's a problem is explained by Fred Mueller in thread 4620), is that maybe you started plating larger parts such that your anode to cathode ratio decreased and the anodes are therefore oxidizing?

Regards,

A. Try what Ted said first, of no help, then go into the Hull Cell and start adding cyanide.

A. Hi John,

What worked for me years ago, was mixing up the brass anodes with equal area of graphite anodes.

By physical observation I could see the evolution of O2 reduce and the anodes worked fine and didn't go passive. The metal content stayed level where I wanted.

All the best :)

"I understand that the redness is caused by a lack of ammonia and I have to control the pH between 10.10 to 10.30. Any suggestion?"

You already have the answer. Add a little ammonia and control the pH.

A. Yes that's nickel undercoat only because the cyanide content is almost double.

A. Hi Syed. It seems to me that the most important clue in your description is that you say you are adding zinc salt and having no increase in zinc content. Perhaps I'm misunderstanding you because that is simply not possible :-)

Either your analysis procedure does not work, or the salt which you are adding is not zinc salt. Has your supplier analyzed the bath? Have you plated any Hull Cell panels? Is it remotely possible that you are adding a nickel salt or some other salt when you think you are adding zinc?

Luck & Regards,

A. Hi SAMUEL. Nickel passivates quite quickly. Get some test parts from the nickel tank to the brass tank as quickly as you can consistent with proper rinsing and see if the adhesion problem goes away on that batch.

Luck & Regards,