Oil Blacking / Oil Blackening

[Machina]

I've tried searching for this but "oil" and "black" are common terms with nothing coming up for what I'm after. if there's an existing thread, or I'm in the wrong forum, please let me know.

In the office I'm working in there has been a lot of discussion on what can be done to prevent corrosion on parts that have some precision surfaces. For example a steel shaft which has bearings mounted on it. Where the bearings fit must be dimensionally accurate but we don't want corrosion. Usually these machines are in industrial environments but it's not always possible to keep them oiled (access sometimes a problem).

Someone suggested oil blacking (or oil blackening). Whilst I've found all sorts of "do it yourself" tips for this on the internet I've not found any clear description. Of particular concern are what effects this might have on material properties, part dimensions and surfacer finishes.

Most commercial offerings seem to be along the lines of chemical blacking, which one of my colleagues has had bad experiences with.
I'd appreciate it if someone could let me know where I might find more definitive information.

 

[TomDOT]

If you can keep salts and moisture away, an initial oiling will slow or prevent corrosion for a very long time.

There are a variety of flavors of phosphate treatment which darken/blacken the steel and provide additional corrosion protection - perhaps that's what they are thinking of.

 

[TVP]

One product that differs from chemical blackening and phosphating is called coat forming oils or coat forming quench oils. A deep black layer is produced by quenching into these oils. Here is a link to one vendor's product:

http://www.nippon-grease.co.jp/en/products/heat/h05.html

 

[Machina]

In this particular case the machine will be in an environment that'll see quite wide temperature changes. It's in an unheated building in the UK and, with winter approaching, condensation is an issue. Also it's a 'demonstrator' so has to look good.

Other than that I'd be happy to keep it clean and occasionally wiped down with oil, but it's not my decision. I just have to sort out the solution, whilst appreciating the help, of course!

The quenching oil sounds similar to what's been described to me, and to what I found on the internet. I just can't find a 'professional' description of the process, and the effects (good and bad).

I'm not a fan of phosphating, maybe I should be. I always associate that with black fasteners that seem to go rusty shortly after being installed.

My own searches showed up things like:
"Black finishes are a good preservative for some tools" from

http://www.practicalmachinist.com/vb/general-archive/oil-blackening-rust-protection-84713/

Similar at:

http://www.woodworkforums.com/f65/question-regarding-oil-blackening-147417/

"...oil bluing is pretty much a usefull tool for small machine parts..." from

http://www.milsurps.com/showthread.php?t=32570

"When I took blacksmithing class they said any hydrocarbon would work with the heat/oil method. It is the
cast-iron skillet seasoning method." from

http://www.practicalmachinist.com/vb/general-archive/oil-blackening-rust-protection-84713/

"I found a hammer I made back in high school some 20 years ago at my parents house a few months back and it I gave an oil black finish and consider it just has sat on a shelf for the last 10 to 15 years and it has hardly any rust..." from

http://www.homemodelenginemachinist.com/f26/how-do-you-blacken-steel-oil-3341/

 

[TVP]

Take a look at these links. The first two are for black oxide products, while the last one is for a pre-phosphate dip that creates a deep black finish after zinc phosphate. You definitely need to review phosphate technology, as it is substantially more corrosion resistant than black oxide.

http://www.birchwoodcasey.com/metal/iron.html

http://heatbath.com/metal-finishing-products/black-oxide-finishing/black-oxide-for-ferrous-metals/

http://heatbath.com/metal-finishing-products/phosphate-coatings/black-phosphate-coatings-pre-dips/

 

[PersonalProfile]

*May* be of interest:

http://en.wikipedia.org/wiki/Bluing_(steel)

Regards,
Lyle

 

[Machina]

I'd had a look at bluing and was wondering if that was what people were thinking of. And it sounds like the suppliers who understand the term 'oil black' are interpreting it as black oxide and then oiled.

The description being :
clean & de-grease parts
into hot salt solution (approx. 100degC)
into oil

From what I've learnt here and elsewhere I'd rather use a different process (such as phosphating and oiling, or just oil and care) but unfortunately I've been over-ridden on most parts.

Thanks for everyone's help.