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Problem in zinc plated components while aqueous washing

 

I am having a peculiar problem. If any body of you can solve it, I will be thankful.

I am having components made of various steels (EN1A etc.) which are heat treated, then zinc plated (8 to 15 microns thickness), then yellow passivated.

When I am cleaning these components in the Aqueous washing machine which I am having these components comes out with white rust / pit marks / passivation layer completely removed. The solution I am using is Blue gold at a concentration level of 3% and the rest pure DM water. The pH of the solution is 10.5.

The washing machine I am having is having 5 bar pressure cleaning, ultrasonic cleaning, rinsing with DM water, hot air drying, vacuum drying and air blowing.

Can anybody solve my problem?

Please suggest,

1. Whether pH >11 can solve my problem?

2. Whether any zinc alloy plating can solve my problem? (like zinc-nickel)

V S Magesh Valsala Kumar
- Chennai, Tamilnadu, India

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I hope someone tells me I'm wrong, but I don't think you can do any kind of effective cleaning without removing the chromate passivation film. And with the passivation film removed, the parts are going to white rust. Are you sure you have to clean them AFTER plating?

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

The chromate will not stand up to that pH and will fail, exposing the zinc. Zinc is an amphoteric metal and will dissolve in either acid or caustic solutions, thus pitting. Take a look at the precipitation of metals curve that you can get to somewhere near the bottom of the main page of this site.

James Watts
- Navarre, Florida

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The problem is the pH is too high try to get a cleaner nearer to pH 7. Zinc will react with alkali and it is being stripped by this cleaner.

Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England

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Dear Mr M.V.K ,

You're a lucky guy to have yr question answered in full in part by part by all of the above responses as each persons perspective is vital to your final outcome.

I know a guy selling a proprietary German make neutral Ph cleaner spray cleaner which will solve your problem , and I have seen Blue Gold being replaced with this cleaner at a spray cleaning installation in Bangalore but I am running the risk of sounding like a commercial for someone else, so I wish you luck in finding your own supplier with such a product.

good luck to you,

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

We have found that even with a ph of 9.5, (Nalco Texoclean 1704)The Zinc plating is damaged. We are, However using clear blue chromate dip. We have found that if we spray wash and do not immerse, The plating remains intact unless the chromate is not as thick as it should be.

Jim Dissette
hydraulics - Sarasota, Florida