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Rusting of zinc-electroplated hardware in contact with wood

I sub-contract the production of wooden products with pre-assembled zinc electro-plated hardware and am having problems with the goods arriving at their destination with the hardware having heavily rusted. I asked the factory to improve the corrosion resistance of the hardware with chromate passivation but the problem crops up time and again. Obviously, the quality of the finishing of the hardware is a big factor in the rate of corrosion of the fasteners but I suspect that the acetic acid ⇦this on eBay or Amazon [affil links] content of the wood and the acidic vapours given off by the glue used to assemble various wooden components could be driving the accelerated rate of corrosion as well. In addition, I have noticed that the problem occurs when the weather at the factory is either very cold or very humid, which means increased condensation inside the polybags. The goods are shipped by sea and the journey takes only about 3 weeks. The goods are packed in standard perforated polybags with silica gel packets to reduce the moisture content in the bags. They are then placed in cardboard cartons. I wonder if anyone has come across a similar situation and if so, whether a solution to the problem was found. I am currently considering using hot-dipped galvanized, nickel-chrome plated and even stainless steel hardware.

Sophie Li
Supply of wooden furniture - Shanghai, China
2005

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You've chosen the least expensive finish, and anything you do will drive the cost up. But a possible missing step is QA on the zinc plated hardware. Do you require salt spray testing? If so, how many hours?

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005

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Sophie,

I have seen this sort of problem before (albeit with Cadmium rather than with Zinc).

Ted is right, the only way to stop this is going to increase the unit price of your hardware.

The solution we used was first of all to use packaging other than wood if possible (eliminating the source of the corrosion should always be the first goal). If that was not possible we used a protective compound such as lanolin based oil to enhance corrosion resistance.

You may also want to consider the protective qualities of the VCI products (known as VpCI in the UK before anyone starts shouting about promoting corrosion).

Brian Terry
Aerospace - Yeovil, Somerset, UK
2005

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First of two simultaneous responses --

Thanks for the feedback. We requested a 24-hour salt spray test, which with hindsight, was too low. Regarding the advice not to use wood packaging, the product itself is made of wood, so this is not an option unfortunately! We'll be trying hot-dipped galvanised, nickel-chrome electroplated and Dacromet-plated hardware to see which one is the most suitable. I'd be interested to know if anyone has used Dacromet in an acetic acid ic environment - we don't know much about it but one of the finishing factories suggested its use. We'll also be asking for acetic acid salt spray testing - any recommendation on the minimum no. of hours that we should specify?

Sophie Li
- Shanghai, China
2005

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Second of two simultaneous responses --

Plain zinc plating is bound to corrode; look around for someone who can offer black zinc-iron alloy plating in your area. We are successfully sending parts overseas without rusting using this.

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

2005