Zinc plating rusts in shipment by sea

A. When shipping overseas, your parts are exposed to moisture and salt. It's like "asking for trouble". Try placing Dry-Packs Moisture Absorbing Indicating Silica Gel Packets, inside the VCI bags.

A. Once upon a time, only cadmium was considered as a protective coating in marine environment.

Now cadmium is considered as a four letter word.

The only solution is to apply a sealer on top of the conversion coating.

A. Try packing after 36-48 hrs curing in an acid fume free atmosphere..

A. Products plated and passivated with trivalent chromate has to preferably hot air dried at a heat "not too hot to hold" i.e say up to 60 degrees +, Parts has to be handled with care with out allowing friction, and packed compulsorily only after 24 hrs- 36 hrs of curing.
It is advisable to use VCI packing material.
sulfur must have come from the corrugated boxes. even the glues has to be checked.
Regards

A. Hi, Mithun.

It isn't clear to me if you plated these parts in house or you bought them. Although 15 microns is a very substantial electroplating thickness, and much more resistant to red rust than 8 microns, I see two other immediate issues here:
First, if the parts do not adhere to the specifications, all bets are off because the process is out of control; trying to assign causality if you have a meandering, will-o-the-wisp, out-of-control process which specifies 15 microns but accepts 8 will prove hopeless. In this case you have to start with fixing whatever weaknesses allowed out of spec parts to get into the system.
Second, white rust is usually caused by ineffective passivation or wet storage. 8 microns of zinc is still substantial enough for reliable performance indoors for a while if the passivation was proper.

Still, "industrial conditions" is a tricky definition; if it is an acidic environment like most plating shops, you are going to get white rust.

Regards,

A. Hi Paul. I've always believed in buying plating processes from suppliers rather than doing in-house formulation. In this age of RoHS compatible trivalent chromating it is an absolute necessity to use such a proprietary process and to rely on the vendor's guidance for operating parameters.

In this case though, it looks like there was a good chance that the parts were stored wet and that this caused the problem. Again, though, zinc plated parts stored in an acidic environment (if that is the case) will rust quickly.

Is there an alternate explanation for the nice plating on one end of the connector and the bad plating on the other end, other than one end being down and wet? It sort of looks like a poorly plated part was crimped to a better plated part -- are the half shells plated before or after being joined?

Regards,

A. Hello Ted,

Both the rusted half & the nice half are two different components from different batches of plating. This could possibly mean the passivation has been improper for that particular batch.

When you mention the parts could have been stored wet, do you mean either
1. Storing of parts that have been improperly dried after passivation, or
2. Storing of parts in a moist atmosphere.

In the case of point 2, how much life do you think we would get with proper plating thickness and proper passivation

And can we ascertain the plating life by a 24 hr/ 48 hr salt spray testing?

Thanks for your feedback

Regards,

A. Mithun,
8 micron is okay but 8-12 is fine...it means the minimum should be 8 microns. There are trivalent passivations available with reputed supply houses which can give up to 250 hrs WR and can enhance to 350 White Rust (repeat, WR)
The main parameters:
1. Passivation bath should preferably be made in DM water
2. pH of the passivation bath should be monitored and followed as per supplier TDS
3. regular replenishment has to be maintained
4. Dip timings are say up to one minute as against 4-5 seconds in Hex passivation. So if the operator is not educated, he will go back to his "old style"
5. Discarding pattern has to be fixed (Main enemies are Iron & Zinc contaminations) - again ref: TDS
6. A hot water final rinse and hot air drying is recommended.
7. hot- "too hot to hold"
8. items should not be handled till 24 hours minimum before packing - Curing - 24 hrs minimum
9. follow VC packing if sent thru sea.
Finally the plating bath should be maintained well ... means if contaminated then also you will not get results.

You may find reputed supply house around your city; Chennai will be near.

A. Hello Mr. Kumar,

Please add more details of the issue:
- Photographs?
- Zinc thickness? (if you have any data)
- Conversion coating? (hex chrome, tri chrome, blue or yellow)
- The corrugated box was wet or dry?
- Your warehouse is in a coastal zone? (to know what are the conditions)
- Has this happened before?

With this data we may be able to help you!

Regards,