Cylinder Material for an Alpha Stirling

[keys]

I'm considering the use of aluminum for the hot cylinder on a alpha Stirling engine. I plan on using graphite for the piston. Does anyone see a problem with using an aluminum cylinder? I noticed many of you seem to use stainless on your hot caps for gammas. I just happen to have plenty of aluminum round and no steel that is suitable in size. I'm not apposed to ordering different material if aluminum is going to be a bad idea.

 

[keys]

A friend of mine called and offered me some 2.5 inch round steel stock. He said it's shaft steel, not mild steel. Anyone know what shaft steel is or could be?

 

[keys]

I'm surprised no one has chimed in. Did I post to the wrong site? Perhaps I will try turning the hot cylinder out of a piece of sharp cheddar.

 

[mu38&Bg#]

I'm not familiar with stirlings. Stainless is probably used to avoid corrosion from the heat of the flame. Steel also has very slow heat transfer properties compared to aluminum. Heat transfer (or possibly lack there of) is what makes the stirling work, but I'm not familiar with which materials are beneficial where.

Shaft steel, I would guess, is something like 4140 or 4340.

 

[b.lindsey]

Keys,

All that I have seen or built use stainless for the hot end...it transfers enough energy to heat the enclosed air but is sufficiently non conductive thermally such that the thin wall where it necks down keeps much of the heat from transferring to the frame or hot cap mount, etc. I am assuming you are using the graphite piston on the power cylinder side and not the hot cap where the displacer doesn't contact the inside of the hot cap but merely pushes the heated air from one end to the other....or have I got my alphas and gammas confused. I have used aluminum on a Duclos designed flame licker but there you need the thermal conductivity of the cylinder to draw the heat FROM the air and cool it. It does stand up to the alcohol flame well enough, but I wouldn't subject it to anything hotter. At least with stainless you know it will last and can stand hotter flames if needed.

Bill

Edit: Should have checked before writing...the alpha does have two pistons in contact with the cylinder walls. You should be fine with the graphite piston there but I would still use stainless for the hot end if for no other reason than longevity and certainty that it will hold up.

 

[keys]

Thanks for the reply guys. It sounds like I should avoid the "shaft steel" because it will probably corrode quickly being heated all the time. Looks like I better order some SS. Does anyone have a recommendation for a Stainless alloy that turns well on a mini lathe?

 

[Metal Butcher]

Thanks for the reply guys. It sounds like I should avoid the "shaft steel" because it will probably corrode quickly being heated all the time. Looks like I better order some SS. Does anyone have a recommendation for a Stainless alloy that turns well on a mini lathe?

I don't have a specific recommendation, but this source may have whatever you deem appropriate. They offer a good selection of stainless steel.

http://www.onlinemetals.com/

-MB

 

[b.lindsey]

I usually use type 316...its generally easy to find and for stainless, it machines as well or better than most of the common types.