Metallurgy of Steam Engines

[FKreider]

Hello All,

I will hopefully soon start on my first live steam locomotive build. I have been reading some old copies of Model Engineer and I am looking at a couple of LBSC's "beginner" locomotives for my first build.

While looking at some of the available castings I was wondering about the cost effectiveness of using bar stock vs. castings. I started researching various metals and quickly discovered that I have a lot to learn about the different alloys available.

So my question is: are certain metals best used for model steam locomotives and others that should be avoided? Also should particular parts always be made of of certain metals?

If plans call for brass castings for cylinders, horn blocks and axle boxes, is there any reason why I could not make these parts from scratch from cast iron bar stock? I see some aluminum castings for the larger scale engines, is there any reason why aluminum is not used more in the construction of steam engines?

[NP317]

Certain metals work best as bearing surfaces.
Others resist corrosion in the sometimes severe environments of steam engines.
Some metals are easier to machine. Some are better heat conductors.
Some metals are very strong, and others can be heat treated for additional strength.
Some metals weld better than others; some not at all.
Locomotives like lots of weight to increase tractive effort, so aluminum is not an optimum material to use, despite the easy machinability of certain alloys.
As a result, each part has optimum materials it should be made from. This is the history that has produced preferences for materials we use.

If you wish to learn excellent methods for constructing steam locomotives without castings, purchase yourself copies of Kozo Hirioko's books on building the Shay, Heisler, Climax, and/or 0-4-0. These are often referred to as the "Kozo University." I studied his books before beginning construction of my locomotives and they helped me immeasurably.
Even though he builds in 3/4" scale, 3.5" gauge, his techniques are first class for use on all scales.
My thoughts.
~RN

[SteveM]

Here's a repeat of a post I made a few years ago. One of the things to take away is not to use aluminum on anything that needs to slide against anything.

Here's the original post:

In Joe Nelson's book there was a chart showing different metal to metal contacts and which were good bearing surfaces and which were not.

Aluminum pretty much sucked with everything, while cast iron was great and bronze was a close second, IIRC.

Aluminum tends to gall easily.

Gunmetal is red brass (a type of bronze):
https://en.wikipedia.org/wiki/Gunmetal

LBSC recommends it on may parts, particularly cylinders.

Steve

[FKreider]

I was thinking aluminum would be most suitable for non moving part components for example; smoke box, smoke box door and stack. Is there a reason aluminum would not be suitable for these components?

From what I can tell class 40 cast iron bar stock can be purchased pretty affordably in comparison with brass/bronze and/or castings.

"Red Brass" seems hard to find however maybe I am looking in the wrong places...It does appear that C360 brass is easily obtained but is suitable for our purposes?

Also aluminum bronze seems to be readily available as well, not sure how it's wear resistance is...

[rkcarguy]

There is a lot to be found online generally about metals and how they react with each other. I have found some stuff out the hard way as well. I made a spacer/thrust bearing out of Teflon that was riding against an aluminum side plate for example, and the Teflon ate it's way well into the side of the aluminum.

[RET]

Hi rkcarguy,

Teflon is a soft plastic so what probably happened is that dirt got embedded in the Teflon and wore the aluminum away. This happens also with metals; abrasive dirt gets embedded in the softer metal and that wears away the harder one which is not what you would expect to happen. As the parts get harder, more force is required, but the wear mechanism is still the same.

There are certain combinations of metals that are good: bronze on steel and cast iron on cast iron, but there are others to be avoided, like aluminum on aluminum and stainless on stainless. In these instances, the tendency is for them to gall and seize. Just try making two aluminum parts that are a close threaded fit, tighten them up with a wrench and then try to get them part. You might be able to do it once or twice, but unless you use something like NeverSeez you will get to the point where it is impossible to get them apart. Stainless does the same thing, but it takes longer to happen. Oh yes, chrome on chrome also does the same thing.

As mentioned before, with a locomotive, you need weight on the drivers, so while it may be easy to machine, aluminum is too light to be a good choice.

Generally speaking, except for cast iron, assemblies of dissimilar metals usually work best together. Cast iron is the only metal I know in which sliding surfaces can be assembled with no play at all and the assembly will work indefinitely. It also tends to dampen vibration and to a degree is self lubricating. That's why machine tools are made from it.

Over the years you learn things and some of it sticks. Hope this helps.

Richard Trounce.

[FLSTEAM]

You don't want to use aluminum for the smoke box or door. Ask little engines....Mike had a little 0-4-0 at Largo several years ago hooked up to a big train which it pulled with no problem except one...the big load and hot fire melted the smoke box door.

John B.

[NP317]

My Allen Ten Wheeler "kit" arrived with aluminum castings for the smokebox top, bottom, and front door.
It interesting to see the melted petticoat portion of the upper smokebox casting on a restoration project being shared here.

Also, note that Allen Models of Nevada now offers cast iron replacements for these same castings.
You gain strength, rigidity, and weight.
A good trend.
~RN

[Rich_Carlstedt]

A number of years ago, and I believe it was here on Chaski, there was a discussion about smoke boxes and materials.
Temperatures were measured on various locomotives and some were in the 700+ (F) range and others only 550 degrees.
I do not remember if this was also related to coal, oil, or propane fired locos.
Obviously if you have a 70+ smoke box, aluminum is not a choice.

A number of factors besides design or fuel affect this temperature
We know that 100 PSI steam has a temperature of 350 ~ degrees ( Brain fart) so how does the temp get so high.
Draft speed, fire tube diameter and soot on the tube surfaces all affect the ultimate temp as well as how hard the engine is working.

Rich

[Bill Shields]

heat comes from combustion of coal and inefficient transfer of the gas temperature to the boiler / water...so smokebox inside temps are always higher than steam temp.

[Joe Tanski]

Why not take a look at the 3/4 scale Raritan a very basic easy to build 2-4-0 steam locomotive
If you would like a free catalog just send me a self addressed stamped envelope
Tanski model Engineering
8927 Notre Dame Dr
Eden ,NY 14057

All castings in stock ,and construction updated book ,

[Bill Shields]

absolutely the best place to start..a solid proven design that doesn't require a home mortgage or 3 decades to build.