Where theworld gathers for metal finishing
Q&As since 1989
-----
Passivation for Brass Plating
adv.:
Q. We do Brass plating (flash) on NICKEL PLATED Mild Steel components. The components are then Lacquered. But we see brown spots on the components after lacquering which goes on increasing day by day. Can you suggest us any anodic or good passivation to protect the golden colour of Brass plated component before lacquering.
D.Roy ChowdhuryMetal Finishing - KANPUR, U.P, India
2004
A. A photo would help, so we could see not only what the brown spots look like, but whether the components have spot welds, crimped areas, etc. Most brass plating is done from cyanide baths and this sounds like cyanide bleedout which can be fixed with better rinsing.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004
Thanks for your reply. The brass plated components are casted hence fine holes are present, but we rinse with plenty of water, even tried with hot water, neutralising with mild acid dips, dried it in oven before lacquering. But could not get result.
D.Roy Chowdhury [returning]- Kanpur, U.P. INDIA
2004
2004
A. We may have a semantics problem here because I don't consider cast parts to be 'mild steel'. In any event they get brown spots, and again, I think this is most likely cyanide bleedout. So I don't think you can fix it with lacquer, I think you need to stop the bleedout. It may be cost prohibitive to do as a matter of course, but I think you should get some test parts vaccuum impregnated to see if this stops the problem.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004
A. Mr D Roy Choudhry Hello,
This problem can be solved as follows
1) Pretreat: Soak. Cathodic. Anodic.Rinse 2 Times. Sulfuric activate.10 percent 30 secs.
2) Rinse .
3) Strike in a Woods Nickel strike for 2-4 minutes at 3-5 volts.
4)Rinse
5) Activate for 30 secs in Sulfuric acid 10%
6) Plate for 15 Minutes in Acid Copper at 25 ASF. 3-5 Volts.
7) Dragout and rinse twice
8) Plate 5-10 minutes of Nickel or as you are now doing.
9) dragout and rinse twice
10) Rinse in Brass Dragout First.
11) Brass Plate,
12) Dragout and 2 rinses
13) Hot 80 °C water Dip. De-Ionised. Change daily.
14) Dry.
15) Passivate in proprietary Brass passivation solution.
16) Rinse 2 times. Dry.
17) Wait for 24 Hours then lacquer with a PU spray lacquer.
The Woods strike followed by copper will "Put a Lid " ( Dhakkan) over the porosity.
Regards,
Asif Nurie [deceased]
- New Delhi, India
With deep regret we sadly advise that Asif passed away on Jan 24, 2016
A. Dear Mr Roy Chowdhary,
Use a good rinse aid, to neutralise the brass completely before lacquering. Follow that up with 20 gms per lit of Sodium Dichromate and rinse well. That should do it.
Khozem Vahaanwala
Saify Ind
Bengaluru, Karnataka, India
2004
June 22, 2009
A. DEAR Mr. CHAUDHARY,
AFTER DOING THE BRASS PLATING JUST FOLLOW THE PROCEDURE AND YOU WILL GET 100% RESULTS.
1) RINSE
2) RINSE
3) RINSE IN 5% OXALIC ACID SOLUTION, KEEP FOR 20-30 SEC.
4) RINSE
5) HOT WATER RINSE AT 80-90 °C
6) PASSIVATE IN 5 % POTASSIUM DI CHROMATE SOLN.AT 4-5 pH
7) RINSE
8) HOT AIR DRY
9) LACQUERING
- New Delhi
"Zipper: An Exploration in Novelty"
by Robert D. Friedel
on
AbeBooks
or
eBay or
Amazon
(affil links)
Q. Hello Mr. ALOK JAIN
We are having a similar case as yours. We produce small parts made out of 85Cu/15Zn subsequently flash plated with 70Cu/30Zn in order to attain desired colour.
Subsequently we lacquer the teeth in 2 different process phases (before and after making the complete zipper).
When we test the zipper in salt fog according to ASTM, after 96h the zipper is severely tarnished.
Prior to 1st lacquering. we use a benzotriazole passivating solution but it doesn't work.
We are no going to test with potassium dichromate hoping that salt fog test will be passed.
Do you have any other suggestions ?
- Varese, Lombardia, Italy
Q, A, or Comment on THIS thread -or- Start a NEW Thread