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Is there such thing as chromate cure time?


Q. We have two large automated plating lines for tubing, many of these tubes are bent after plating. We do have some color lost on the bends, my question , is there a cure time for chromates, will cure time help?

Thank you ,

Paul Ellingson
plating shop - Wahpeton, North Dakota, United States


A. I'm not aware of published test results on this, but it is at least urban legend that chromates should be allowed to cure for 24 hours.

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


A. The specification ASTM B117 [affil link] requires that a chromate coating be aged for 24-48 hours prior to salt fog testing. The reason is classical. The Gel film that we call a chromate conversion coating will lose some water by evaporation. This tightens the film and makes it a bit more scuff and scratch resistant (and more stable for the start of corrosion testing).

There is no definitive age of the film. I suggest that you experiment with the chromate that you are using, and confer with your vendor from which you purchase your chromate.

Keep in mind, that some of the thicker films (green and black) can appear to powder when the tubing is bent. This might have its roots in the operating parameters of the particular chromate that you are using. When trouble strikes with a chromate, most of the problems center upon the pH, Concentration, or Temperature of the bath. Again, your vendor can be your most valuable asset in this case.

ed budman eb sig
Ed Budman [dec]
- Pennsylvania
With deep sadness we advise that our good friend Ed passed away Nov. 24, 2018

July 18, 2014

Q. Can you please point me to the section of B117 that specifies 24-48 hours for the chromate cure? I have looked through it a couple times and am not finding it. I'm reviewing B117-03.

Thanks - Joel

Joel Smith
- Zeeland, Michigan, USA

July 21, 2014

A. Take a look at ASTM B201-80 [affil link] (Standard Practice for Testing Chromate Coatings...), section 5.1. ASTM B117 [affil link] really just describes how to run the salt spray (fog) test in general, and not with respect to a specific coating.

Tom Rochester
CTO - Jackson, Michigan, USA
Plating Systems & Technologies, Inc.
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July 21, 2014

A. Hi Joel,

You are correct that ASTM B117 [affil link] doesn't state any curing time, but MIL-DTL-5541 [affil link or DLA] Para 4.4.1 states the parts should be dried for 24 hours at 60-100 °F before testing.

Brian Terry
Aerospace - Yeovil, Somerset, UK

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