Pistons and Cylinders

[majorm]

I have read through quite a bit about various material types for pistons and cylinders but havent seen this brought up. Some of what I have read on various forums and from prototype steam engines say there are certain materials avaliable where you dont have to use a lubricant. I could maybe see a ptfe piston or cylinder wall if you could work out the expansion under heat (and cooling) but what other combinations are out there? This isnt limited to model engines either.

The Cyclone steam engine is one that specifically says it doesnt use a lubricant other than the water (superheated steam) its using to run. I always thought superheated steam was corrosive so the thought that it could be used as the lubricant throws up some questionmarks. I suppose a cylinder with a polished ceramic finish could last a while but then what kind of piston would you use?

I looked into cerakote finishes and they have a piston coat that is sopposed to help with lubricity. Then there are various moly coatings but I would think they would. There are other more industrial finishes like we have on tooling and guns. Some examples would be melonite or the diamond black finishes. So getting into this subject are they using a surface finish or a new material all together.

The thought of not having to use oil in a steam engine is a big deal so that caught my intrest. For a small model or even a larger engine thats useable not having to add in an olier and seperator would be helpful. So what do yall think?

 

[Brian Rupnow]

Grey cast iron is popular for cylinders and pistons in both steam and i.c. engines. This form of iron has a very high carbon content, so is to a great extent "self lubricating". Thats not to say that it doesn't need some lubrication.---but not nearly as much as many of the steels available, nor aluminum.

 

[Tin Falcon]

IIRC some stirling engines and ICS of Jan riddrers designs use glass cylinder and a graphite piston no lube.
Tin