Stirlingengineforum.com

Hello,

As stirlig engine builders without lathe or any other power tools we always search for solutions to replace the power piston. Gloves, balloons or bellows help us to get the engines running.
I have devised an easy way, how to make your own rubber bellow of any desired shape. This is easily possible with liquid latex (see attached picture) and some patience. I have used a short tube, some tape and some washers to construct the profile. Then I have wetted the profile with the liquid evenly. After one day I have removed the tube (do not use the adhesive side of the tape to connect to the tube, make the tape sliding on the tube, this allows you to remove each part individually), then the tape, and then I have removed the washers carefully. The result is a true rubber bellow, very flexible, very elastic, very stretchable.
Indeed my first try failed, I have attached a picture. The rubber seems to shrink a bit, leading to small gaps. So for the second bellow I have added 3 to 4 Layers in the critical places (wait 20..30 min until the rubber becomes black, then add the next layer), instead of only 2 layers. One single layer might be not sufficient, the rubber will become very thin with only 1 layer.
Of course this is not only applicable to rubber bellows for stirling engines. In fact you can make any rubber part of any desired shape, that you would need to make.
I really hope, that this will help you to make progress with your machines and would appreciate your opinions

with kind regards

Soeren

Interesting concept, nicely executed.. Whole lot of potential there, too.

Nicely done!

Just thinking.. You could perhaps use that woven mesh tubing 'sleeve' stuff as a structural base that would still hold some flexibility but also be pretty strong..

for reference, I mean this stuff


It'd probably need to be done in 'stages' of tension and compression to get that 'wave' effect you've got so nicely with the washers, though. Pull it tight on whatever your minimum radius is, tape off the sections you want to have the wider radius, cover the exposed areas in latex. Once it's dry, remove tape and compress it to flare those uncovered sections out, then paint them up as well, then give another final coat to bring it all together?


Whether it'd be worth the effort, I have no idea.

Soeren, interesting bit of engineering, and an interesting material. At one time I was involved with designing, and making molds for the manufacture of rubber goods for vintage cars, mainly Willys Jeeps. Each mold valued at well over $NZ1000, in these the rubber is hot vulcanised. Yours is a simple, and possibly cheaper way of making rubber things, maybe air seals on crankshafts for pressurised engines, so bellows may not be the only thing to be made with this sort of stuff. Ian S C

I truly liked your idea and moreover, the way you have implemented it. Great job man! Keep it up.
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rubber bellows

Soeren,
I was really into using bellows, but there seemed to be one big drawback. After some use the plastic (rubber ) gets hot and looses it elastic nature. I wonder if there is a plastic, easy to use, that doesn't get heat fatigue ? Your way of making the bellows is great.

I keep looking at the silicon rubber bakeware in the shops hoping that one day I will see a shape begging to become a rolling sock seal.

John, in some of the $2 type shops in Christchurch (NZ) there are some silicon bake ware products that could be made into diaphramns. Ian S C

Yes Ian, Briscoes have quite a few bits too also the big red shed but I have not seen anything that would lend itself to becoming a rolling sock except for muffin trays but they do seem to be quite stiff. I will keep looking!

Might get into town in the next day or so, I'll keep my eyes open. In Christchurch, and other parts of NZ, the firm that could probably be best to obtain suitable plastics is Mulford Engineering Plastics Ltd., 18 Sonter Rd., Wigram Park 8042. I have got some of the plastic, including Carbon impregnated Teflon from them, also the nylon screws that hold the top and bottom plates of my LTD motor together. Ian S C

Briscoes have rolled sheets of the stuff too, but I dont have an idea of how that could be used.

John

I was thinking more in the line of tubing. Ian S C

I have not seen any tubing and I dont know how a sheet material could be rolled into a tube without the seam being a problem.

Nor have I, what is needed is a tube of a truncated conical shape, so that it can be turned back in its self, I imagine it would be made on a mould, and it would be between 1 mm and 2mm thick, but I don't know how the heat proof silicon is formed. Ian S C

Some silicone cook-pans have tapered sides, but the ones I've seen have reinforcing corrugations that defeat the purpose. You can make a roll-sock from an inflatable ball. Some are very pliable but don’t stretch too badly, so the movement stays where you want instead of adding dead space. They could match up with bowls for different purposes. The balls I know of aren't silicone though. I like the thread's original premise of forming your own shapes, but with the added thermal range of silicone. Automotive RTV is kind of spendy for my usual trial and error error error process though; I wonder if the cheaper silicone caulking used in construction would work?
Here's a factory solution: http://www.controlair.com/downloads/air_cyl_spec.pdf
Bumpkin

Also worth looking at a PDF Fabricating with Silastic High Consistancy Silicon Rubber.
www.dowcorning.com/content/publishedlit/45-0111A-01-pdf