Tryin' something new

[Mr. Miagi!!!]

Hello everyone!

I'm a new member here (this is the first forum that I've ever actually wanted to post on) and I was wondering if I could run some material selection past you guys.

The first steam engine I built was made almost entirely of brass and cast iron. I wanted to try and build an engine, however, that requires very little maintenance and will last for a very long time. Preferably, I would to use corrosion resistant materials that last a long time. In addition, I wanted to try and avoid bronze and brass because its gettin' kind of expensive where I am. So, my proposition:

Cylinders: a single piece of 304 or 316 stainless with bored cylinders. As a result, the heads and boxes are also stainless steel

Pistons: also stainless

Rings: one of the places I'd use 660 bearing bronze. Coefficients between bronze and stainless are pretty similar. I want to reduce the wear on the pistons and cylinders and from what i understand stainless on stainless ain't a pretty combo.

Crankshaft: This ones tricky. I want to use stainless with 660 bronze for bearings and crankpin bearings. I guess the other option is 1144 stressproof, but I hear it corrodes pretty easily.

Structurals: All made of either 1018 or 12L14 (whichever is cheaper) and painted.


I dunno, I'm kind of a novice on material selection, but I want to experiment. The target for me is the longevity and functionality of the engine.

Thoughts or recommendations? I really would like to hear what you guys think because you are FAR more knowledgeable than I :bow:

 

[JorgensenSteam]

Welcome Mr. Miagi-

There have been some discussions on this forum about material for steam engines, and many have their preferences/favorites.

As I recall, aluminum cylinders tend to gaul and seize.
Aluminum pistons are ok when run on cast iron sleeves.

Cast iron rings are the norm, and gray cast iron rings run very well on a gray cast iron cyinder liner.
I have also used brass rings successfully on a mild steel and a cast iron cylinder successfully.

I use 416 stainless for piston rods due to its low corrosion under heat and high machinability.

I am not sure if stainless run on stainless will gaul/sieze.

The things I look at in metals are:
1. Machinability (if it is too hard, you can't machine it and it is not good for anything).
2. Strength, in tensile, yeild and sheer, PSI. (don't use a weak piece of material in a high stress situation).
3. Weldability/silver soldering/brazing (I sometimes like to weld/silver solder/braze parts together, and some metal will crack if welded).
4. Heat treatability (if you want to heat treat the metal, pay attention to this).
5. Hot and cold forming (sometimes I like to bend material into shapes, and some metals will just crack if you try this).
6. Corrosion resistance (corrosion resistance varies with stainless grades, and some stainless has a very low machinability, and cannot be welded).
7. Adonizable (some people like an adonized finish, but not all metals will accept this finish).

You have already mentioned thermal expansion, and that is also important.
I have heard that some use cold rolled steel for crankshafts, and just take into the account enough spare material to allow for the spring which will occur when you cut cold rolled steel.

Hope this helps.

Edit:
304 stainless has a high tensile strength, but only a 45% machinability, so it may be tough going. 316 stainless has an even lower machinability at 36%, but is also high strength. Both can be welded.
416 stainless has a machinability of 110%, but cannot be welded very well.

 

[kvom]

Since you mention thermal expansion, I am assuming you would run it on steam rather than air. If that's the case, I'd use cast iron for the cylinders and rings, with a steel piston. You'll want to run steam oil, and that will lubricate everything inside the bore, and you can paint the exterior. CI is much easier to machine than SS, and with CI for both rings and cylinder thermal expansion is a non-issue. The same applies to the steam chest, where I'd use bronze for the valves.

SS would be excellent for the piston rods and valve rods.

 

[Mr. Miagi!!!]

Awesome! But just out of curiosity, why is it that stainless on stainless is a no-no? just out of curiosity, all machining qualities and cost aside, what's the big downside? And how would you go against protecting the crank from corrosion?

 

[Leucetius]

As my prof always said: "Gleich und gleich das frisst sich gern" - (not literally "Never run parts of the same material on eachother".
Cast iron is a exception (as is Aluminium with Pb in it) as it's self lubricating (structure thing)