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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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Zinc electroplating with yellow passivation is dull
Current questions:
January 25, 2021Q. Hi Ted who is father of finishing academy on internet and other family members.
We have a cyanide zinc electroplating bath including:
Zn+2 : 25 g/L
CN: 62 g/L
NaOH: 60 g/L
V: 9V, A: 1800 amperes, t: 10 min
Freshly added brightener and purifier.
Cr+6 in the yellow passivation bath: 13 g/L
pH: 1,7
I have been trying to figure out that why big medias have dull yellow appearance while small ones not have. I can show that with pics.
- Ankara, Turkey
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Ed. note: Yes, please e-mail pics to mooney@finishing.com for posting here.
Trivalent yellow zinc plating dull finish on CRCA surface
Q. We are plating CRCA sheet zinc plating trivalent yellow in rack plating bath few components are giving dull finishes even after replating no changes found. I want to know the proper root cause and solution. Please help me in this regard.
- Bangalore Karnataka India
January 29, 2021
⇩ Related postings, oldest first ⇩
Q. Dear gentlemen,
We are facing a lot of problems when we apply zinc electroplating on carbon steel components. components are forged and buffed before zinc electroplating. After zinc electroplating our vendor applies yellow passivation @ 2-3 micron. But after a couple of hours ( 72 hours ) we found finishing is very dull; and due to this we found quality query from our customer. so in this case what we have to do ? is there any process which we have to amend during plating or after plating.
Need your help to sort it out.
buyer - Ahmedabad, Gujarat, India
July 9, 2009
July 17, 2009
A. Mr Prajapati
You did not provide much detail so one can only provide educated guesswork as follows.
The possible causes are.
Poor Post Passivate rinsing
Poor Drying Practice in which damp parts are packed because someone is in a BIG hurry....?Who could that person be.
Poor Rinsing and Neutralisation of caustic in the NITRIC dip after alkaline zinc BEFORE passivate. This is the activation stage in Dilute 1 to 1.5% Nitric before the passivate when the zinc is plated out of an Alkaline caustic based bath Zincate bath called Alkaline Zinc.
Caustic carry over is a definite cause of los of yellow shade in the Yellow passivate.
You need to audit and control the plating and Post plating line carefully.
Asif Nurie [deceased]
- New Delhi, India
With deep regret we sadly advise that Asif passed away on Jan 24, 2016
July 24, 2009
A. Poor Post rinsing could one of the reason
Beside please check the fallowing
1 check the iron contents in plating solution and avoid the roughness in plating
2 Reduce the brightening agent
3 use water soluble base brighteners
4 increase the nitric ions in pre-passivation tank
5 Dry the components properly
- Delhi, India
February 20, 2021
A. Prajapati,
After alkaline zinc plate rinse then dip in 0.5% nitric acid for 10-20 seconds then rinse and hot dryer ,if you yellow chromate passivation , make sure yellow chromate pH and concentration within limit.
Popatbhai B. Patel
electroplating consultant - Roseville, Michigan
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