When I was testing the pressure gauge from last week's post, I noticed that one of the accessories that I made for Pressure Maker II, namely the base plate with a 1/4'' BSP female connection for testing pressure sensors, started to "grow" tiny rust spots in several places. I made this plate from an old cylinder rod (the most hydraulic-technician-accessible stock in the world) and since I didn't give it proper rust protection, it began oxidizing with time.
I love making stuff from old CK45 cylinder rods. First, since we repair cylinders, I have access to a virtually unlimited supply of damaged rods and left-overs, and second - the steel is strong and yet easily machinable, which makes them the best choice for making base plates, fittings, adapters, custom knobs and levers, and whatever else your imagination may compel you to make.
But the problem with parts machined from carbon steel is, of course, the rust. And since this opportunity is, kind of, presenting itself, I want to show you a way of protecting steel parts from oxidation which I like a lot, and which I, hands down, prefer to any paint, because it not only prevents rust but also gives the parts a beautiful finish. If you haven't guessed already - I am talking about bluing.
I know that the bluing of steel (i.e. - the formation of a thin oxide layer on the surface) is old news, and there are many ways to do it. So, what I want to show you today is the way that has been working for me for a long time. It is simple, it does not require any chemicals or expensive equipment, it works great for relatively small parts, and I like it very much.
The type of bluing I will be showing is thermal bluing. It is a very basic process that consists of three steps - preparation, heating, and dousing in oil.
The preparation is, basically, finishing the surfaces and degreasing. The surface finish makes a lot of difference. Roughly finished parts will also blue, but polished parts will look better, and with the CK45 steel - polished surfaces can really gain that beautiful blue color, while roughly finished patches tend to stay more brown-ish or purple-ish in appearance, which is beautiful too, in my opinion, but in general - the better the surface polish, the cooler the part will look in the end. So, make'em shine anyway you can!
The degreasing is also very important. I like washing parts with hot soapy water and then drying them with compressed air, but if a part is small, a thorough douse with a brake-clean spray does the job as well. I actually had more steel parts to rust-proof besides that base-plate I just showed you (a knife sharpener that I made, if you need to know) so this will indeed be a good show-and-tell:
Now, let me show you my very sophisticated "bluing gear". It consists of a cheap electric hot plate (bought it at a Chinese corner shop for €8), a tin filled with used oil, tools to manage and move hot steel parts, and an (optional) cover to make a hot-box for bigger parts:
I'll leave the safety issues to your imagination, but I would strongly suggest using gloves and considering what may happen if you add enough heat to mineral oil, and also preparing rags for very likely oil spills (which, by the way, can case you to slip and do damage to your precious self in most unimaginable ways).
And... that's it. You're all set for bluing. Now you crank your hot plate to the max, put the parts on top of it, and watch the magic happen. As the steel heats up, the surface oxide layer grows thicker, and when the height of the layer is "right", the light that reflects from its surface starts interfering with the light that's reflecting from the surface beneath it, giving birth to those beautiful colors. You basically wait till a part reaches the color you like, then you take it off the heat and "drown" it in mineral oil. There's an urban legend that says you should let the parts sit in oil for several hours. I don't know if it makes that much of a difference. but I still do it when I can.
It is important not to "overdo" the parts, though, because when the oxide layer becomes too thick, the beautiful coloring is gone, and you are left with a dull grayish finish. It's not bad in the sense that it is still a passivated surface, but it will lose that "gun" touch, which I, personally, love!
Different carbon steels will react differently, and the time it takes for the colors to appear varies greatly for parts of different sizes - so if you have multiple parts to blue - it'll be almost like flipping burgers. Here you can see me feeding the parts to the "grill" and replacing them as they get "done":
And here are some before and after shots. I especially like the fact that since all this is done manually, the finish is quite uneven, I don't know why, but it appeals to me greatly:
Small parts are usually pretty fast to blue, but with larger parts, it may take a while. There are two ways you can do them. You can either cover them with the "hot box" and leave them be for several hours, occasionally checking on them, or you can greatly speed the process up with a torch. The only problem with the torch is the fact that it heats steel so fast that you can easily shoot past the colors into the dull gray finish.
The resulting layer is quite durable, especially if you occasionally "treat" it with an oiled cloth, but it is not eternal - especially if it is a part that's rubbed all the time, But then again - isn't' t it the same with any other type of surface protection?
So, next time you make something out of a piece of cylinder rod - give the "redneck heat bluing" a try and see if you like the result!