High Temp Epoxy Piston Rings????

[GoVertical]

Greetings, I am starting a project using a 2 cylinder V air compressor to try to convert it to Alpha Stirling. I found some links were small projects created there own pistons using high temp epoxy.  Using their idea, I am going to try to replace the piston rings with high temp epoxy and add a dry lubricant between the high temp epoxy rings  Hopefully this will give a good seal and reduce friction.  Has anyone tried this before? Best regards

[bj]

   I guess it partly depends on how high a temp you intend to run at.  For what it's worth, big recip's use carbon filled teflon for ring
material.  It's fairly long life, but temp is critical.  It would be interesting to see how the Epoxy stands up.
   Regardless, good luck with it.

[cmmguy]

Why not ceramic?

[Basil]

Why not use the rings in it and run it with freon.

[freejuice]

I use to use a powder mixed with a heavy oil to rifle barrrels with a carbide button.

I dont know what kind of dry lube you have in mind, but check out Dow Cornings  " Moly Z Coat" its a moly powder which is similiar in texture and look to graphite, but dont let that fool you...it is one heck of a lube, which works well, even under tremendous pressures...probably overkill for a stirling... but you wont have any wear!
 All the best,
 Gavin

[GoVertical]

Greetings, this is a first attempt and I am sure it will be a learning experience.  I like the Freon idea.
One of my biggest concerns is I read that hot O2 can mix with the oil and explode and one death has been recorded.  I plan on adding a pressure release valve  the top of the cylinder on the hot side. How does Freon react in a heated closed system?  I do not know anything about ceramics and I think I can not buy it at the local hardware store.  I plan on removing the heat fins on the hot cylinder using the lathe.  Then add a stainless steel scrubbing pad inside the hot cylinder at the top to increase the hot surface area inside the cylinder.  I also plan to add aluminum shaving inside the regenerator, again to increase the surface area.
Thanks for all the ideas this should keep busy for awhile. Thanks again and best regards.   

[GoVertical]

I dont know what kind of dry lube you have in mind, but check out Dow Cornings  " Moly Z Coat" its a moly powder which is similiar in texture and look to graphite, but dont let that fool you...it is one heck of a lube, which works well, even under tremendous pressures...probably overkill for a stirling... but you wont have any wear!
 All the best,
 Gavin

Greetings, thanks for the heads up.  I was reading that the US AIR Force stopped using Graphite because it promotes corrosion on aluminum. I plan on proceeding using the stock piston rings and if that proofs to have to much friction I will try the high temp epoxy with dry lubricate idea. Thanks again and best regards.

[BigBreaker]

Compressed air pressure vessels are not rated to the same pressure when hot.  Especially aluminum yields much sooner when hot.  Steel less so but it is still weaker.  In a stirling the materials problem is the high pressure and the high temperature on the hot side.  Be careful!

Personally, I would start with a steel scuba tank.  The steel they typically use is similar to what is used in high pressure boilers, chrome moly.  At room temperature they are rated to 2500+ PSI.  At 400 or 500C I don't know but it's going to be way better than a compressor tank.

If you don't want your stirling to explode, don't run it with O2 in the working gas.  Nitrogen and hydrogen are cheap and safe, helium is safe and expensive.  Draw a hard vacuum in your stirling first, then add the working gas.  Low concentrations of oxygen prevent explosions, so you don't need to be too mental about the vacuum but don't use regular air, that's 20% oxygen!

Hydrogen is an excellent working gas and cheap.  The only issue with hydrogen is progressive embrittlement.  Helium is a close second and is perfect other than cost being totally inert.  Nitrogen is a distant third from a performance perspective but cheap and effectively inert.

[joestue]

hydrogen is going to be a mess, there is a reason sandia labs uses helium in their Stirling engines. considering the fact that hydrogen has like half the viscosity and 3 times the thermal capacity of helium, you would think it would be worth using... not the case. (they do use it to cool motors and generators btw)

i suppose a close alternative is methane, or a light molecule freon. those heavy ones that condense at -40C or higher may also breakdown at high temps (what temperature are you planning on running this at?) propane should not breakdown below 700K, or it will do so very slowly.