Stirlingengineforum.com

Hello all!
If I want to join copper plumbing pipe to tin can for
making of power piston, what is the neatest, and
easiest method that you might be able to reccomend.
Any soldering tips would be much appreciated.
Regards, Peter

Welcome to the forum Peter.

I find that if one wants a good neat solder one needs to make sure that both surfaces are clean. "Tin" each surface by applying heat, I prefer a torch, and when hot apply flux or use acid core solder so that a thin layer of both surfaces are covered independently with a very thin layer of solder before attempting to join them. When both surfaces are good and "tinned" position them as they will need to be. Reapply the heat and SPARINGLY add more solder. Work the heat around the joint and allow the solder to flow from cold toward the point more warm. I find that "waving" the torch in the direction toward the unjoined surfaces so that the solder melts and flows works best. I'm sure there is a you tube video "how to". You might try that. if my instructions are confusing.

R

I would recomend that if you must use non ferrous metal for a piston (or a cylinder), use brass if possible, it has a lower co-efficiwent of friction, and is generally more accurate as far as round etc.The only metal that can be worked against it own type is cast iron,ie., CI piston and cylinder. With brass a steel or cast iron cylinder would be best. I don't recomend aluminium, it tends to stick.
If copper is all you can get, use a steel cylinder for best results, and if you can make / obtain a leather cup seal to fit on top of the piston, you will get away with a quite loose fitting piston (don't get too wobbly)
Ian S C

Sorry if I appear a bit fussy, but friction is the biggest killer of Stirling engines, and the power piston is a big point of friction, you'v just got to reduce it as much as possible. I'm proberbly preaching to the converted, but it may help someone.

The thing to remember about solder is that it has very little structural strength. When using it to join two metal surfaces you will have a strong joint if the flat surfaces are sitting flush against each other. Solder will not fill a large gap. So the best tip I can give you is to make sure your parts fit together well before soldering.

Thanks all for the helpful replies.
@Theropod - I'll have a go as you say, I have a small Dremel gas powered tool that I hope will do the trick. Those seem like good hints, I will 'tin' the joint first
this sounds very logical - I'll practice a bit first too.

Once again - thanks

I assume the tin forms the crown of the piston, if so place it on something heat proof, place the copper tube on top, heat it until the solder melts, hold it down with a bit of stick so that when the solder cools, it sits square, and seals right round the joint. If you use plumbers solder it will give a little more strength at working temperature than electrical cored solder wire, the stuff used for car radiators is even better. I believe that tin / lead solder is, or is going to be hard, if not impossible to get in some parts of the world, so it might be an idea to grab what you can. Ian S C

Thanks everyone for this assistance, just in case it isn't clear I don't mean to make the piston itself,
I mean to solder the tube the piston travels inside to the can in which the displacer moves.

regards Peter

Peter wrote:Thanks everyone for this assistance, just in case it isn't clear I don't mean to make the piston itself,
I mean to solder the tube the piston travels inside to the can in which the displacer moves.

regards Peter

I got that the first time through Peter. One thing that might help after you have both surfaces tinned is to affix the cylinder copper tube to the displacer body with a length of soft wire. Wrap the wire around the displacer and the end of the copper tube opposite the displacer and twist it until the two are firmly joined. Sort of a throw any clamp. This should leave a gap along the sides so you can snip the wire later. This way you can turn the whole affair this way and that and things won't fall apart. I've found that keeping the two parts rigid until the solder cools helps a bunch. I also suggest you put a small radius on the copper pipe/tube so the profile matches the displacer side curve as snugly as possible. This will help keep solder from seeping between the two parts. If you're real careful you can build up the solder into a pretty good thickness and really beef up the joint. If you really want this stout you could cut some narrow "straps" of copper from excess tubing and bend them so they fit the tube and the displacer. I wouldn't worry about this too much though as the solder, if done right, will be plenty strong enough to do the job.

The only other advice I can offer is to maybe practice on joining steel to copper with scrap before beginning with your polished tube/power cylinder. Remember that the steel and copper with heat at different rates. The steel displacer will take more heat before the solder flows than will the copper. You'll see this effect when you do the tinning.

I'd consider adding a cooling tank to the top of the displacer, making sure your displacer rod gland extends above the top of this tank. I just used red silicone to affix mine, but I wished I'd soldered it as it was slightly flexible and I didn't like that. If I build another tin can walking beam I'm gonna solder that cooling tank in place. You can paint over solder, if you clean it up good before, but silicone sealer refuses to take any paint. If I wanted to contain the fire box, should you want to add one, I'd braze that since solder might melt there.

You'll find we're glad to help any way we can. Don't be afraid to ask. The only stupid question is the one you don't ask!

R

Theropod -
that all looks like great advice - I shall let you know how I get on. I'll definately do a few practice pieces first.
Many thanks again
Peter

With most cans, the inside has a coating on it to protect the food in the can from the bare metal,you must remove this before soldering, sometimes it's transparent, other times its white (maybe other colour)paint. Ian S C

Peter wrote:Hello all!
If I want to join copper plumbing pipe to tin can for
making of power piston, what is the neatest, and
easiest method that you might be able to reccomend.
Any soldering tips would be much appreciated.
Regards, Peter

As you see in the former responses, soldering and prep is a pain. Clear dry Epoxy fits the neat and easy here. You may want to go to auto supply or hardware store for a grommet to help support the power cyl. into the displacer cyl.

i would say use JB stick weld and you will be impresses. since the heat will not be directly on the JB you should be fine. its like a puddy and you kneed it and mould it then it drys in 3-5 min. i like it because i had to do what you did (only it was a pvc elbow to an aluminum can) and its been banged on and it hadent budged at all

Well, I feel that learning the skill of soldering is a worthy goal in and of itself. I also feel that solder will withstand a higher temperature for a longer time than will just about any epoxy. If one wishes to use silver solder, or brazing, the joint will be nearly as strong as a weld and withstand more than enough heat as we employ in these high temperature engines before failing.

R

Following are some tips to join copper plumbing pipe to tin. Hope these will help you bit.

> Cut the tube end squarely.
> Ream the tube end.
> Clean the tube end.
> Clean a fitting socket.
> Applying flux with the flux brush.
> Apply flux to the fitting socket.
> Assemble tube and fitting.
> Apply heat to entire circumference of the copper tube.
> Apply heat to fitting socket.
> Feed solder to the joint.
> Remove excess solder & flux.

Once again thanks all for tips. I definately want to use solder, as Theropod2 says the skill in itself is worthy of
mastering, I bought a teapot in a junk shop made from tin can and copper pipe, it is an object of real beauty
and the soldering looks like the work of a jeweller! I'd be more than proud if any model of mine could look like that!
thanks Martinnman for the working check list.

regards all. Peter