Piston material

[rpbidgood]

Hi,
I'm building a 45mm gauge De winton. I have made the cylinders out of brass and would like to know if phosphor bronze is a suitable material for the pistons. My searches have suggested a number of combinations, but I can't find this particular one. I would like to use bronze simply because I have some suitable bar stock in the workshop. I will post some photos of my progress later.

 

[Brian Rupnow]

If anything, you want the piston to wear out before the cylinder wears out. It's a lot cheaper to replace a piston. If your cylinders are brass, I would go with an aluminum piston. Don't make the piston and cylinder from the same material or you run the risk of galling.-Which screws up both piston and cylinder. (unless you are using grey cast iron for both piston and cylinder. Grey cast iron has a lot of "free graphite" in its metallurgical make up and is somewhat self lubricating) Another factor is the weight of the moving parts. It is always better to have the piston from a lighter material, to cut down on the inertial loading the con rod will see.

 

[rklopp]

I tried a phosphor bronze piston/crosshead on brass cylinders/crosshead guides on my Cracker, and it was a bad friction pair, starting to gall almost immediately. I changed to 303 stainless steel piston/crosshead, and it has been great ever since.

 

[deeferdog]

I have just finished a 76 mm bronze piston running in an aluminium cylinder and it seems OK. Thermal expansion of Al is greater than copper so it should be fine at operating temperatures, (steam). I use a good bit of hope when I build a model as I generally make do with what I have lying around if possible.