thermally stable material needed (i think)

[RnDSolo]

ok, let me see if i can explain what im doing "simply" then we can go into detail..

i have an aluminum hole, the hole is 1.875" then there is an open gap, and about an inch down another identical hole.

basically, im "sleeving" these 2 holes. there will be a piston inside of this sleeve. (rings will compensate for expansion there) the sleeve ID is 1.775, so the sleeve is on .050 thick.

what im worried about, is cracking the "holes" when it heats up. its possible temps could get to 300-400F i need something stable.

I was thinking of using an MMC like 225xe or X-fine, but the piston will have no lube and will be moving at ridiculously high rpm. (sort of like a normal craftsman aircompressor but higher rpm)

so now I'm thinking about using ammco45. which is a bronze (or is it brass?) material used in cylinder head skulls in big $$ race engines. Its a self lubing material, and coupled with some PTFE coated rings for the piston, i think this might be the route to take, but then comes pressure concerns. Pressure in the sleeve will be 80-100psi, then as the piston is forced down, pressure will grow to around 240psi...BUT the part of this sleeve that has to contain this pressure is surrounded by the aluminum "hole"

ok, so now that piston...it will be moving at around 4500 up/down strokes per minute. stroke will be about .300" piston is made from MMC. still undecided on rings, but i was thinking it need something coated to deal with lack of lube

ok so now, if anyone can grasp all that..again, im looking for a material to use for the sleeve that will
1) hold the pressure
2)not expand to much and hurt the mounting points
3) keep the piston from seizing with no lube

i will post a drawing if needed. thanks ahead of time for the advice..

(and sorry for the long post)

oh 1 more thing...in order to give an air tight seal and make sure the sleeve doesnt come out, i was planning on using a cryo method to install the sleeve into the holes

 

[KENAT]

I'm not sure I follow everything you post but I think I see a possible issue.

The Aluminum will expand with temperature so the hole will tend to grow in dia.

If you use a relatively temp stable material for the actual sleeve then it will expand much less.

So depending on exact size and coefficients of expansion I can see that either your sleeve will no longer be a tight fit with the al or, the interference at ambient temperature may need to be fairly large with the problems inherent on that.

We use Invar for components sensitive to thermal expansion but I don't think that'll work for you.

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[RnDSolo]

thanks for the reply..ok, i guess i hadnt thuoght of it like that, so i need something that will expand relativly similar to the aluminum block, while still offering the other properties. ..

thanks that also led me to my next question of how tight i needed to make the piston/sleeve but i think i have that now.

 

[KENAT]

Well, if you play it that way of matching the sleeve to the block, then you also need to match the cylinder to the sleeve.

I'm not an automotive guy but it sounds like looking at what they and maybe other pneumatic pump folks use may be a good starting point.

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[RnDSolo]

Thank you for your help.