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Black Oxide Coating Thickness



A discussion started in 2004 and continuing through 2017 . . .

(1999)

Q. I am outsourcing some components from Taiwan, and they have a difficult time maintaining a consistent plating thickness using zinc/chromate on the steel parts. I would like to consider using black oxide, but need to know more about the capabilities of the process. Will it build up on sharp corners like the chromate? Can the thickness be held to a tolerance of +/- 0.0002"? What about color variation? Thanks,

Doug M [last name deleted for privacy by Editor]
- Radford, Virginia


(1999)

A. Hi Doug. Black oxide has virtually no thickness at all; it doesn't begin to approach 0.0002", so +/- 0.0002" tolerance is no problem. And it will not build up on the corners either. But it will offer almost no corrosion protection.

As for color variation, that should be no problem unless you outsource the parts to a shop in Taiwan which doesn't have a good QA system tightly controlling any variations smiley
It strikes me that the problem might be QA rather than inherent difficulties in zinc plating which you hope will be absent in black oxiding. Switching horses in midstream can be a poor idea, but especially if the horses haven't yet been broken :-)

Sorry for trying to be colorful in my answer, just trying to get across the idea that difficulties encountered in metal finishing aren't necessarily due to the technical limitations of the process -- but may simply be due to poor practice. Best of luck.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(1999)

A. Doug - Black oxide is a conversion coating, not a deposit type coating, so there is no dimensional change to the part and no potential for "build up". However, there is potential for color variation caused by inadequate cleaning before the black oxiding step. Complete removal of all soils and other oxides (rust, etc.) are critical to achieving un-mottled parts. Some black oxide products tolerate imperfect cleaning better than others - be sure to see samples of finished parts.

Dan Brewer
chemical process supplier - Gurnee, Illinois



(2004)

Q. We are considering use of Black Oxide coating for the first time. For our ultra-clean needs, we need to know just how thick the oxide is on carbon steel. This info. doesn't seem to be presented anywhere. Does the thickness depend on the specification used?

DARREL LEMON
AEROSPACE - BOULDER, Colorado, US


(2004)

A. DARREL

Black Oxide is not a deposit, it is a Chemical Oxidation of the Steel, making the surface turn Black. It has almost no thickness, or at least any value as such.

This is one of the reasons it is used in gun barrels, because it doesn't change the dimensions of the parts to be covered. Also, It's of no protective value if it's not finished with a wax or oil.

I hope this helps,

Carlos

Carlos Cielak
plating shop - Mexico City, DF, Mexico



To minimize searching and offer multiple viewpoints, we combined multiple threads into the dialog you're viewing. Please forgive any resultant repetition.



(2004)

Q. Does black oxide on steel add to the thickness of the part? If so how much.

Thanks,

Ray Paolini
Medical products - Orchard Park, New York


(2004)

A. Hi Ray. It's somewhere between undetectable and a couple of millionths of an inch.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2004)

A. I also agree with Ted Mooney

The black oxide coating is a very thin layer.

T.S.N. Sankara Narayanan
T.S.N. Sankara Narayanan
- Chennai, Tamilnadu, India



(2005)

Q. I need to plate spring steel parts. I have tried zinc plating with baking but it is making it brittle. Is black oxide plating a good solution. These parts are being used in fire panels. Will the parts last over a long period of time.

Neville
J. N. Wadia - Karachi, Pakistan


(2005)

A. I'm not familiar with 'fire panels', Neville, but black oxide offers no corrosion resistance beyond the oil that is used on it. Other options include dip-spin coating, autophoretic coatings, and mechanical plating. Hydrogen embrittlement can certainly come from zinc electroplating, but it can also come from an acid pickle or any cathodic process, and it can almost always be relieved if the parts are baked immediately after the processing.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



To minimize searching and offer multiple viewpoints, we combined multiple threads into the dialog you're viewing. Please forgive any resultant repetition.



September 24, 2008

Q. We recently just made some parts and sent them out to be black oxidized. Will this coating change the thickness of the part? Thanks.

Ben Knight
engineer - Birmingham, Alabama


September 24, 2008

A. No, Ben, it won't. The thickness is measured in millionths of an inch rather than thousandths or ten thousandths.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


April 27, 2011

Q. If there is no build-up how robust is the plating with regards to wear? My company is finding some parts look good at the beginning of the line and the coating wears off by the time it gets to the end of the line. This is just by handling and it's not excessive. Is there a test that can be done?
Thanks,
Bob

Robert Trottier
- Chester, New Hampshire, USA


April 27, 2011

A. Hi, Robert.

Black oxiding imparts color but not much else. The parts are oiled or waxed after the black oxide, and this is what gives some very minimal wear resistance and corrosion resistance. Still, if the coating is coming off, it may be a selenium-based cold blackening process rather than a true hot black oxide. These room temperature processes tend to be smuttier than real black oxide.

Firearms are often hot black oxided and, although it is not a robust finish, it doesn't come off quickly in that application. Many people have rifles that are decades old, as long as they are lovingly maintained.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



June 19, 2014 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. How can we check if black oxide is okay or not?
Can we measure black oxide thickness by using DFT meter??
if not which instrument can we use to check black oxide thickness?

Please clarify me...

Asha G
Quality engineer - Pune, Maharashtra


June 2014

A. Hi Asha. Black oxide has virtually no thickness, but to my knowledge there is no need and no practical way to measure the thickness. The only QA measure I'm aware of is visual. But if you apply a specific post treatment oil or wax or clearcoat, the finish can survive a short salt spray test, and you can require passing that test as a QA requirement. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


June 21, 2014

Hi Asha,

In my experience I don't know regarding thickness of black oxide coating. I think thickness is not applicable.

Applicable two qualitative tests for black oxide coating are:

1. Oxalic acid spot test
2. Smut test.
One more Environmental test (salt spray test)

Regards,

Surya Narayana
Process Engineer - Tumkur , karnataka , INDIA.


June 2014

thumbs up signThanks Surya. It looks like the Oxalic acid spot test and smut test are included in AMS2485 [link by ed. to spec at TechStreet] and MIL-DTL-13924 [link is to free spec at Defense Logistics Agency / dla.mil] . The salt spray test only applies to type 3XX stainless steels, not carbon steel.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



July 31, 2015 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear seniors,
After blackening on steel metal how many microns dimension layer forms, or no dimension change after the process?

hemanth_kumar
Hemanth kumar
- Karnataka, india


July 2015

A. Hi Hemanth. We appended your inquiry to a thread which answers it: no significant dimensional change.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


August 4, 2015

thumbs up signThank you sir. I got solution to my problem from your reply.

hemanth_kumar
Hemanth kumar [returning]
- Karnataka, india



Black Oxide Smut Test

March 30, 2017

Q. Hello ,
I am come from Shanghai China , I have a problem about the standard of MIL-DTL-13924 [link is to free spec at Defense Logistics Agency / dla.mil] rev. D 18 March 1999, I don't know what is the SMUT TEST; I'm looking forward to have experts give me some professional explanation, thank you !

4.4 Test procedures.
4.4.1 Smut test. The test shall be made prior to application of corrosion preventive compound or after vapor degreasing. Each black oxide coated piece shall be inspected visually under strong light to assure a satisfactory appearance. Each sample shall also be wiped with a clean white cloth for indications of smut (see 3.7).
A slight amount of smut which is inherent in the process is acceptable for all classes of coatings and shall not be cause for rejection.

Ariven Chen
technical company - Shanghai , China


April 17, 2017

A. Hi Ariven,

Abnormal black oxide growing will easily cause smut formation affect reliability such as potential short between fine traces on printed wiring board if any smut particles fall off and stick between.

There's 2 easy ways to detect smut formation. One is use cotton bug to wipe black oxide coating gently to observe how significant darkish smut particles left on cotton bug. The other way is to immerse black oxide coated article into ultrasonic bath with DI water to observe how significant darkish smut particle escape from article and spread into DI water.

Regards,
David


David Shiu
- Singapore

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