Baked zinc plating vs. zinc without bake

A. Hi Jane. Sorry, bad news. It is not possible to salvage high strength bolts which were not baked immediately after plating because the presence of the hydrogen does permanent damage (embrittlement). There should be a plating spec and a baking spec (or a plating spec which incorporates baking specs) for the bolts ... and it probably gives you a very short time frame (maybe 15 minutes, maybe 2 hours) to get them from the plating line to the oven.

Luck & Regards,

A. Hi Ansan. Please introduce your situation so we can best help. Do you work in the plating shop or do you buy this product or what? What is it that you are plating or having plated? What enters into your decision to bake or not bake it? What are the plating and baking specs?

As a wild guess, you are buying parts, some of which are hardened steel and require baking for hydrogen embrittlement relief, and they are being baked after chromate conversion coating whereas they should be baked before that step.

Luck & Regards,

A. Hi, Cathie. I don't think you would be able to see the difference. The baking is not for appearance, nor corrosion resistance, nor any other property of the zinc coating actually. Rather, the plating process causes hydrogen embrittlement of hardened steel, and the baking is to drive out the hydrogen. Soft steel does not need or get baking, and hardened steel requires it.

Regards,

A. Hi Cathie,
If the base material strength(before plating ) is more than 1000 Mpa we need to do the Baking after zinc plating
and before passivation.

For both (soft and Hard) material we will do only the passivation as a final process.i I think we are not able to see any difference. may be the passivation bath maintenance will be different while doing the two different parts.

Zinc plating is mainly for Corrosion resistance. this is not for 100 % appearance process.

If you want a Better appearance part. you need to go for powder or paint or any organic coating.

A. Hi Matthew. A picture is worth a thousand words -- please send a good one to mooney@finishing.com for posting here. But if by frosted you mean like a window pane, with a crystal pattern to the zinc, like you'd see on a galvanized garbage can, it sounds like your hydrogen de-embrittlement oven is way too hot.

You don't chromate before baking, do you?

Regards,

A. Hello Matthew,

We bake trivalent chromates without not so much discoloration nor brightness decrease, and we check post bake corrosion resistance regularly.

I would say that dullness you experience post bake could occur by:
- High (peak) temperature
- Too much bake time
- High organics in your zinc bath (often with low adhesion/peeling)
- High temperature in your zinc bath (often with low adhesion/peeling)
- Low chromate thickness / low zinc thickness
- Organic contamination in chromate

We bake our products for two hours at 375 °F immediately after chromating, but if some part shall be baked for more than four hours, you must re plate and chromate post bake, because chromate dehydrates too much in a long bake.

Hope it helps! Best of lucks :)