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Fungus/White rust on Zinc Plated Square Nuts

2004

We found fungus formation on steel square nuts of M 6 size with zinc plating with blue passivation having 10 microns plating thickness. Fungus formation observed after @60 days of plating in our store dept. where nuts were stored in polythene bags. Because of the fungus some of the nuts had sticked to each other in the quantity of 6 to 8 nos.but not all.

One more input I wish to give; to avoid internal thread missing problem we necklace square nuts in galvanised wire & store in necklace form only. Quantity per necklace & bag is 3000 Nos. Fungus quantity is @ 25 to 30 No.s per bag. Can anybody tell us the root cause?

Regards,

Dhananjay Shedbale
carburetors manufacturer - Pune, Maharashtra, India

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2004

Mr Shedbale, here is what may have occured:

1) The components were not fully dried when packed.
2) The Polyethylene bag is actually a transparent PVC bag with some traces of chloride from manufacture. Chloride can corrode zinc.
3) The Plating Post treatment was not done correctly.
4) There was moisture in the storage area which entered the bag. Did you seal the bag during monsoons or damp weather when humidity is high ?

Check these aspects. In future store in Real polyethylene bags. To check, take a little deionised water. Check its pH is 6-7. Rinse a sample bag from inside and re check the pH. The pH must remain unchanged. If it is acidic I guess you known what to do.

Regards,

Asif Nurie [deceased]
- New Delhi, India
With deep regret we sadly advise that Asif passed away on Jan 24, 2016

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Dear Sir,

In my opinion pretreatment and contamination in Zinc plating baths will lead to white rust formation apart from the contaminated passivating dips.

Shankara Narayanan N
- Bangalore, Karnataka, India
2004