I have 32 years exprience in machining metals of all kinds but nothing in machining plastics. Can the body of a low temp engine be glued up from layers of plexiglass which have been rough bored and turned. Then machined as a unit ? Can anything else be used for the body such a PVC or does that absorb the heat which would be used by the engine itself. Thanks Peteski
Plexiglass body for low temperature engine
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Tin Falcon
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Pete:
By low temperature engine I assume you mean a LTD Stirling Engine? You may want to take a look at the Corian thread in the Q & A section.
http://www.homemodelengine.freeforums4u.com/viewtopic.php?t=650&mforum=homemodelengine
I feel quite humbled by the engine this artist built. IIRC he used black pvc pipe for the displacer cylinder. The original LTD stirrings were mostly developed by a PHD in Engineering in a college Lab funded by NASA. The displacer cylinder machined from a solid block of lucite.
This guy knocks one out at home with scrounged bits and pieces and virtually no machine tools.
So this running engine proves there is flexibilities in material. The great thing about the plexi is you can see the displacer piston moving. I have started one of these engines and the displacer cylinder is gray pvc. I machined the center thinner to reduce heat transfer. The key for cylinder material is something that is reasonably strong,stable and low heat transfer(Good insulator) You could probably make one out of oak or cherry with glued up scraps using a similar technique as is uses in making banjo heads. I think it would look and work great as long as the wood was sealed with a nice finish. You could probably make it octagon or even square as long as the cylinder was kept from turning and therefore rubbing.
To answer your question"
Ok you got me curious.I had to research. the thermal conductivity of PVC is .9 Btu in./ft. 2. hr.F somewhat less conductive than Lucite @ 1.45 Btu in./ft. 2. hr.F wood is about the same as PVC depending on species and moisture content.
for more info on plastics check out
http://www.boedeker.com/mtable.htm
(edited for accuracy I was looking at different charts with different units of measure almost whoops)
Tin
By low temperature engine I assume you mean a LTD Stirling Engine? You may want to take a look at the Corian thread in the Q & A section.
http://www.homemodelengine.freeforums4u.com/viewtopic.php?t=650&mforum=homemodelengine
I feel quite humbled by the engine this artist built. IIRC he used black pvc pipe for the displacer cylinder. The original LTD stirrings were mostly developed by a PHD in Engineering in a college Lab funded by NASA. The displacer cylinder machined from a solid block of lucite.
This guy knocks one out at home with scrounged bits and pieces and virtually no machine tools.
So this running engine proves there is flexibilities in material. The great thing about the plexi is you can see the displacer piston moving. I have started one of these engines and the displacer cylinder is gray pvc. I machined the center thinner to reduce heat transfer. The key for cylinder material is something that is reasonably strong,stable and low heat transfer(Good insulator) You could probably make one out of oak or cherry with glued up scraps using a similar technique as is uses in making banjo heads. I think it would look and work great as long as the wood was sealed with a nice finish. You could probably make it octagon or even square as long as the cylinder was kept from turning and therefore rubbing.
To answer your question"
I think the idea is you want a cylinder material that does not tranfer the heat from one plate to another. So therefore low thermal conductivity. Yes PVC will work actually better.
Ok you got me curious.I had to research. the thermal conductivity of PVC is .9 Btu in./ft. 2. hr.F somewhat less conductive than Lucite @ 1.45 Btu in./ft. 2. hr.F wood is about the same as PVC depending on species and moisture content.
for more info on plastics check out
http://www.boedeker.com/mtable.htm
(edited for accuracy I was looking at different charts with different units of measure almost whoops)
Tin
mklotz
Well-Known Member
Here's a Ringbom Stirling I built using PVC drain pipe for the displacer chamber and styrofoam for the displacer.
Runs nicely. The PVC is tapped to accept the 2-56 screws that secure the hot and cold plates.
Assuming rational choices of materials, LTD Stirling performance is more dependent on sealing and friction minimization than it is heat transfer. Since the pressures involved are so miniscule, I use Vaseline to seal the displacement chamber/end plate interface.
Runs nicely. The PVC is tapped to accept the 2-56 screws that secure the hot and cold plates.
Assuming rational choices of materials, LTD Stirling performance is more dependent on sealing and friction minimization than it is heat transfer. Since the pressures involved are so miniscule, I use Vaseline to seal the displacement chamber/end plate interface.
jagwinn
Active Member
Polycarbonate. Known here as 'metal you can see through'.
I have bent it in a brake, and drilled and tapped it to make see through guards on the machines here.
I have bent it in a brake, and drilled and tapped it to make see through guards on the machines here.
I know this is an old thread; but I just started checking this site over.
If you are using Plexiglas, or other brand of acrylic sheet, you can build up a thicker piece by layering. I have built up some plates over 1" thick from 1/4" sheet by wetting the surface with acetone and clamping together. I would leave them clamped overnight to be sure it's cured; but the resulting seam will be invisible.
I have some pieces that I put together this way 4-5 years ago that show no signs of deterioration or willingness to part company.
I have no idea if this will work on polycarbonate though.
Kevin
If you are using Plexiglas, or other brand of acrylic sheet, you can build up a thicker piece by layering. I have built up some plates over 1" thick from 1/4" sheet by wetting the surface with acetone and clamping together. I would leave them clamped overnight to be sure it's cured; but the resulting seam will be invisible.
I have some pieces that I put together this way 4-5 years ago that show no signs of deterioration or willingness to part company.
I have no idea if this will work on polycarbonate though.
Kevin
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