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"Baked zinc plating vs. zinc without bake"

Current questions and answers:

February 12, 2021

In case Hex Bolts 10.9 (diameter 14 above) were zinc plated before but did not have baking process, can they be reworked to re-zinc with baking process? In case bolts were rejected due to lack of baking, can we send it back to re zinc with baking process? I would much appreciate your answer to clarify, thank you.

Best regards,

Jane Wong
- Las Cruces, New Mexico

February 2021

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,

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

February 8, 2021

Q. The electro zinc plated product has a bad appearance after baking. Non-baked product is no problem, but baked product is not glossy.

Ansan Kyeonggi
- South Korea

February 2021

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,

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

Previous closely related Q&A's, oldest first:

January 5, 2010

Q. I need to know what the differences with parts being plated zinc and baked and not baked. Is there a visual difference between these two plating styles?

Cathie Magub
Buyer - Phx, Arizona, USA

January 6, 2010

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.


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

January 8, 2010

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.

Kannan Boopathi
- Salem,Tami Nadu,India

Frosted zinc after baking

February 28, 2020

Q. When we are baking zinc plated parts a lot of times they are coming out of the oven frosted. What is causing this issue? Any help is appreciated!!

Matthew Gilberg
- fridley Minnesota

February 2020

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?


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

February 28, 2020

Q. To answer your question, we do chromate before baking. This is a hex yellow. I know this is not the correct way. It's my understanding that you can bake trichromates and sometimes we have frosting on those too. We bake our parts at 375°F and our ovens are calibrated on a regular basis.


Thanks for your time and input.

Matthew Gilberg [returning]
- fridley Minnesota

March 17, 2020

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 :)

Daniel Montañés
N. Ferraris S.A. - Cañuelas, Buenos Aires, Argentina

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