Steel Blacking

[yngndrw]

Hi,

I'm interested in the technique of blacking steel.

As far as I know, this involves putting steel into a bath of hot oil.

I'd like to know a few things about it:
1) If I had a machined mild steel part and I was to black it, would the part be warped in any way ?
2) Does the blacking process change the dimensions of the part ? I.e. Like how paint adds thickness to the surface.
3) Would this protect the part from rust ? What if it got a light scratch, how deep does this technique affect ?
4) What kind of temperature is required ?
5) Are there any other finishing techinques for mild steel to stop rust without adding thickness to or warping the part ?

Thanks,
-Andrew.

[teamtexas]

It sounds like the process of plating steel. I've done a little electric work in a few plating companys. Some of their parts where black when finished. I'm not sure what the plating material was. Cadium I think. I know this process does add thichness to the part, but I don't think warping was an issue. It was a very caustic process. My hand tools would rust by the end of the day just working in the plant.

Dan

[yngndrw]

The process I was thinking of didn't use electrolysis - I think I may have gotten the name wrong. I think it might be "Metal bluing", but I can't quite remember.

After some searching on Google, I found that one type of metal bluing seems to involve panting it with some liquid and gives this kind of result:
http://www.bayonetsonline.com/images/111_%20080.JPG

I don't know if that is just an artificial way of the oil treatment that I was talking about.

I found this link:
http://en.wikipedia.org/wiki/Bluing_(steel)
It seems to suggest that there's hot bluing (Using oil) or cold bluing (Using paint stuff). It also mentions that hot bluing uses electrolysis, which I want to avoid.

I want to stay away from caustic processes as much as possible.

Any suggestions ?

[Crevice Reamer]

I don't know about other steels, but 12L14 will blacken very nicely by heating to a bright red color and quenching in oil. I have never had any deformation from this process.

Size increase is miniscule. Part will still rust if not kept oiled. Blacking or bluing will scratch through. Only something tough like chrome plating will resist scratching.

CR.

[Geof]

I think the blueing is done on fire arms and it is a mild chemical that just slightly oxidizes the surface. You have probably seen when you slowly heat a piece of shiny steel it changes color through various browns and then blue before it gets red hot; the chemical solution kinda duplicates what is going on. You need to get hold of a gun enthusiast.

[yngndrw]

Thanks for your help guys. By the sounds of it this process won't help me because the part will still rust.

Any ideas on an easy way to stop rust without changing the size of the part ? (Scratch prevention is a plus, but not required.)

[Crevice Reamer]

Most forms of steel rust prevention other than plating, (Bluing, Parkerizing etc.) involve adding surface area for oil retention. Plating, paint and duracoat gun finishes involve adding to size. Even stainless steel can rust.

It's all a trade off.

CR.

[yngndrw]

Ah I see, I will have to think about what I need.

Thanks for your help.

[Geof]

Originally Posted by yngndrw ....Any ideas on an easy way to stop rust without changing the size of the part ? (Scratch prevention is a plus, but not required.)

Use stainless.

The thinnest coating I know about is electroless nickle. It does give reasonable rust prevention but only for mild conditions.

[yngndrw]

Well it's for a home-made CNC machine, the steel box-section frame will be welded together and then face milled to make all sides perfectly flat and parallel. (To compat the warping from welding.)

I've been told that stainless steel doesn't conduct heat very well, therefore would not machine very flat. For this reason, stainless steel is unfortunatly out of the question.

I've attached a picture of the frame if it helps. (Everyone on here likes pictures of CNC stuff.)

[Crevice Reamer]

Paint the frame and keep the ways oiled.

CR.

[Herbertkabi]

I wonder you have not just searched Google -> steel blacking -> readings for all day and night like Blacking iron and steel at room temperature ... or go to ebay and buy gun blue kit, for example this one http://cgi.ebay.com/Birchwood-Casey-...2em118Q2el1247
... many anothers you can find as well.
Interesting results I have got when small well-finished parts - just spry LOCTITE Activator on to part and heat on the electric range - you can see how it will change colour at bronze-brown to violet to blue ... dont remember was it 7471 or 7455 the best - but layer is ultrathin, resist and nice.
Regards,
Herbert