Blackening steel parts

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neksmerj

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This question has been bantered around many forums, still haven't seen what I call an easy and safe method, so I'll ask here.

Do you have a home made bluing recipe handed down from your grandfather?

I know reasonable results can be achieved by heating the part, then quenching in dirty oil.

Japanning is another time honored process, but tricky.

I think in industry they use a black phosphating process. Is this a form of plating, or a chemical dip process? In my opinion, the stuff you buy in a bottle, is not worth 2 bob.

Ken
 
Hi ken I use this process a lot blueing hands screws etc, for clocks. also the odd larger part.
the problem with heating in a flame is that it is hard to get the temperature even therfore the color varies.

The answer lies in useing Bluing salts thet melt at exactly the temp to provide the perfect blue.
the part is imersed in the salts until it changes color then quenched in water. then oiled
The first few times you use the salts the results may not be perfect as the salt bath needs "running in " so a few trials
help this ,
I get my salts from Meadows & Passmore ltd www.m-p.co.uk a very good company.

I hope this helps

Regards Brian

g
 
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I do the 'heat with a torch and quench in dirty oil' method. Comes out quite nicely. I find best results from very dirty dino oil (non-synthetic) and heating with a standard propane torch. It works best on parts that have been polished/brushed and then cleaned thoroughly. Heat until it starts to change color, and dunk in the oil. Repeat as required. I usually do it twice, just because.

It will magnify any dents, nicks or turning marks, so the finish must be uniform. I have successfully blackened parts for airsoft guns, real guns, model engines and even tools for the lathe/mill.

A little gun oil (or equivalent) will keep the part looking good for quite a while. It does not completely prevent rust, though.
 
Ken, the phosphate process is a chemical conversion. Both Zinc and Manganese are used in this process. They are used to deter corrosion and provide a bit of oil retention. The process is dreadfully simple. Hot soapy water (caustic soda, actually, back in the good ol days) tank, a rinse tank, a phosphate tank, another rinse tank, and an oil dip tank. Unless the part is so large it chills the phos tank, the entire process takes about 45 mins. The caustic and the phos tank are kept warm (about 160 f if I remember right). They give a nice dark gray or almost black coating. It makes an exellent undercoating like a primer for paint.

The same basic process is Parkerizing for firearms. I used to run tanks that were 5 x 5 x 16 feet. Lots of downhole motor driveshafts, mandrels and BOP's. 24 x 7 schedule. Come to think of it, I have a small drilling motor I need to set up a system for in the next few weeks.
 
You can also use Dicropan IM from Brownells. That is what I have used plenty of times.

1 Preheat the part in the oven to 250F or so. While that happens I start an Enamel pot of water boiling.
2 When both are up to temp I then swab the blueing compound until it will not take any more.
3 Next dunk in the boiling water for the time required.
4 Remove from pot and scrub/card with CLEAN steel wool.
5 Reapply the Dicropan and put back in the pot.
6 Repeat as many times as required to get the color you want.

The more coats the deeper the blue. When done heat to dry and oil down and leave over night.
 
Tony,

You make black phosphating sound easy. Is there any chance you could be more specific in terms of

1. Precisely which chemicals to use and the quantities?
2. What temperatures?
3. Method from start to finish.

The subject of blackening parts seems to have alluded all but the professionals.

It would be nice to get this process nailed.

Ken
 
Ken,
zinc or manganese phosphate is pretty easy. I'll work up some details of the process and post it. I am manufacturing an order for a customer that requires it, so at that time, I can do photos. The problem for commercial shops like me is accountability for hazwaste. It's not really that mush of a problem, but I am required to keep records. Small amounts of the required chemicals as would be used in a hobby shop are no problem.

Of course, I may think is it easy because I've done it.
 
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