steam engine materials

[John Rudd]

Please pardon my ignorance....but is there any particular reason that brass is used as the fundamental material for building engines?

Is it because it is easy to work with?

Is it because of its physical properties compared to aluminium?

or something else?


Why can't I use Aluminium for the cylinder and another material (cast iron? ) for a piston?

 

[tel]

Well, some people do just that, but for the sliding surfaces (cylinder bores,slide valves, port faces etc) you really need something with good wear resistance. I use either bronze or cast iron for these applications. The other issue is rust, if you are running on steam you have to be meticulous with your oiling with ferrous materials.

Having said that, if you intend running on air, and for only shortish periods, you can use whatever you fancy.

 

[John Rudd]

Tel,

Thanks for that...I guess I missed the obvious corrosion issue with steam...

Brass it is then...

 

[rleete]

The most obvious reason is appearance.

Brass polishes up nicely, and even after a few years looks good. As time goes on, the patina it aquires is still attractive.

It is also one of the easiest materials to work with small machines. Use "free machining" brass, and you'll get decent results even before polishing.

 

[Metal Butcher]

Please pardon my ignorance....but is there any particular reason that brass is used as the fundamental material for building engines?

Is it because it is easy to work with?

Is it because of its physical properties compared to aluminium?

or something else?


Why can't I use Aluminum for the cylinder and another material (cast iron? ) for a piston?

Hi John. Using a combination of dissimilar metals is usually the best choice. Running say, an aluminum piston in an aluminum cylinder is best avoided due to a strong possibility of galling. A brass, cast iron, teflon, or Delrin (acetal) piston would a better choice. Cast iron and steel go well together as does brass and aluminum. Lining an aluminum cylinder with brass or bronze is also an option. A brass piston in a cast iron cylinder or visa versa seem to have the least friction followed by a brass piston in an aluminum cylinder. A Delrin piston in an aluminum cylinder is a good low friction choice.

Its a good idea to machine a piston to fit a more costly and time consuming cylinder.

When using aluminum as shaft (crank) bearing blocks I use bearing bronze or Oilite bushings. A spinning steel shaft will wear aluminum rapidly unless there is a substantial amount of support surface. Easily replaced bushings are very inexpensive.

Heres a cylinder lining choice:

http://www.use-enco.com/CGI/INPDFF?PMPAGE=1027&PARTPG=INLMK32

For crank and shaft bearing points:

http://www.use-enco.com/CGI/INPDFF?PMPAGE=1028&PARTPG=INLMK32

-MB

 

[steammodellR74]

I have found the using machining steel for the cylinders and even pistons works pretty well together. I advise using carbide tipped tools and coolant though. To help to extend the life of the parts, you want to make sure that the contact surfaces are as smooth as possible (cylinder bore and piston). Also, as far as the rust issue goes, as long as the parts are lubed well, rust should never be an issue when steaming. As for the crank shaft material, I suggest a steel shaft and either brass or bronze bearings or sealed roller bearings. The only thing with the roller bearings, you would have to make some sort of keepers to eliminate the cross travel.

 

[John Rudd]

Thanks for the replies guys...I guess the bottom line here is to stick with the materials as specified by the engine designer as he obviously knows better than I

Still a worthy question I thought...and after reading your answers something I ought to have known...

 

[Artie]

Hi John, like you, I am 'new' to this site. Please do ask whatever questions you have, it not only helps you but also myself and many others who had perhaps not thought to ask your particular question.

Its obvious from my limited time in here that these guys have a wealth of knowledge and certainly dont mind sharing that knowledge!

Personally Im in the middle of 'converting' and old set of plans to 'my' language (metric!) and before I begin making swarf Im sure to have many questions. Your question was pertinent to my project right now. Tah mate.

Rob

 

[tel]

Yep, the trick with aluminium is to use it for the bulk of the piece, and use real metal in the vital areas.

 

[John Rudd]

Continuing the thread....

What is the preferred material for a flywheel and why?

I'd guess the heavier the material the better because it has to do with kinetic energy?

Any reason not to use Aluminium?...I guess this harks back to my answer above?

 

[Tin Falcon]

John: For small demo display engines just about any material will work, if run on air.
PM Research sells several casing kits that are all aluminum, well mostly the castings are aluminum with some brass and steel rod to finish out the kit. I have engines built with Plexiglas/ Lucite Corian as well as aluminum.
People at shows frequently ask me about wear. Lucy my first see through engine has had quite a few hours running since summer of 2003 usually 2 shows a year probably about 14 hours on a two day show. No major cylinder wear steel piston in plastic cylinder. I do oil it.
As far as flywheel material I have used brass , Corian , Aluminum and cast iron.
I would say brass would be my first choice free machining brass is easy to machine looks good and has a density higher than steel.
Free machining steel would also work well especially if you plan on paint. several of my engine with a 1/4 ' bore have aluminum fly wheels and run on less than 10 psi of air pressure the aluminum flywheel is not a problem.
When I first started model building I worried much about the right material for the job. But experience has taught that the right material is often whatever is in your stock drawer/bin/rack. And remember with home built model engines if a part wears out or breaks because you picked the wrong stuff you have a machine shop make a new one only better. I have learned that plastic crank disks do not work for long so remade out of brass. here is my display

Also learn to scrounge and salvage. Most of my engines are built with stuff that others considered scrap.
Tin

 

[tel]

Also learn to scrounge and salvage. Most of my engines are built with stuff that others considered scrap.

And a hearty 'Hear Hear' to that.