Tricks to Minimize Friction

[jaskiewiczm]

Hello,

In order to get a Stirling engine running as smoothly as possible, are there any tricks that one could apply with respect to friction? A quick Google check brought me back dry lubricants that one could apply. Are those worth anything? I figure that if you run your engine for a while eventually it would rub off. I'm curious to see what the community thinks.

Thanks,

mj

[fullofhotair]

I think I remember people using graphite pistons and pistons embedded with graphite.magnetic bearings would reduce friction.Precision machining where there is no wabble.Expansion and contraction of different metals or other substances should make a difference but I dont know anything about that.

[Ian S C]

For displacer glands, I'v used Carbon impregnated Teflon bushes on quite a few motors, also cast iron and bronze. Where possible I use ball races on all the bearings, except the little end of con rods, these are bushed with bronze. The only exception is where the big end is split, these bearings have a bronze bush fitted.
I try to use cast iron pistons, in either cast iron (best), or steel cylinder. I would use Graphite if I could get it. I try to keep the weight of the moving parts to a minimum, ie., the power piston, and the displacer. Ian S C

[Coogrrr]

I am curious if there is a "balance" item here as well. I know that the stirling typically has a 90 degree offset so a second setup 180 degrees to balance the first cylinder set would allow the whole engine to be balanced evenly right? Now this doesn't answer friction directly but there are losses due to balancing even on other engines. Then I think the next step is to use what Ian said stick to metals that are inherently slippery like bronze etc and avoid powders and liquids that can build up or wear off.

What are the thoughts on balance?

Coog

[theropod2]

I am curious if there is a "balance" item here as well. I know that the stirling typically has a 90 degree offset so a second setup 180 degrees to balance the first cylinder set would allow the whole engine to be balanced evenly right? Now this doesn't answer friction directly but there are losses due to balancing even on other engines. Then I think the next step is to use what Ian said stick to metals that are inherently slippery like bronze etc and avoid powders and liquids that can build up or wear off.

What are the thoughts on balance?

Coog

Coog,

Friction first. Stirlings hate friction. Balance isn't as much an issue until rpms are high and there is cyclic loading putting undue pressure on the bearing surfaces. Getting into that much power will involve some balancing before the engine is running. I would think the technology used by watch makers could be adapted to our uses. Superhard shafts tapered to fit matching "jewels" . I think I've mentioned that glass beads might be used like that before.

R

[Ian S C]

Last weekend I saw an old Stirling Engine, it had been a demonstration engine a North Island(NZ) university (it's proberbly over 100yrs old), its a BETA type with a bore of about 2 1/2", and a power stroke of about 1", it has a single crank pin and is coupled up with bell cranks, these bell cranks are supported each side by bolts with tapered ends, in tapered holes (see Coog's entry), the crankshaft is actually on top of the cylinder. I'll eventually get a photo to my gallery(don't hold your breath). It was made by Paul Lockmann, its also got ZEITZ on it. We ran it for a couple of hours, until the cold end warmed up too much for it to run, it has water cooling, but we did'nt use it.
Balance, I'v tried counter weights, no great advantage on my motors, they vibrate quite badly until they reach working speed, then settle down, and when you turn the gas off they reach a point on the slow down where they vibrate again. But if the engine is bought down in revs under load, its OK. Some of my motors have counter weights because I turn the crankout of solid bar, so I cut away each side of the crank pin, and leave the semicircle opposite the pin, it's all for show really. Ian S C

[Geoff V]

If any body on the Forun thinks imbalance in an engine is inconsequential then please try the following test.

Take a reasonable mass, say a house brick, shake it hard for 10mins (if you can, I can't) then tell me again that it doesn't consume any power.

GeoffV

[Ian S C]

Agreed. Ian S C