Copper Tube.

[Bo’sunParticipant @bosun58570]

Getting it straight?

[Bo’sunParticipant @bosun58570]

Good morning,

I've just bought some 4mm O/D copper tube, and as expected, it came in a coil. Albeit a little tighter than I would have liked.

Are there any tips for straightening it out, other than patience? I don't expect to get it arrow straight by any means, but somewhat better than it is would be nice.

[Former MemberParticipant @formermember12892]

[This posting has been removed]

[JasonBModerator @jasonb]

Rolling between a flat surface and a board about 4" wide in your hand works fairly well. Remember and straightening will start to work harden the copper so best to anneal before you start to bend it.

[Bo’sunParticipant @bosun58570]

Thanks for that, annealing will have to done a section at a time. The final aim is to produce a close fitting cooling coil, so the piece needs to be reasonably long to start with.

[PaulGParticipant @paulg46657]

Don't know about this size but there are small hand tools to do this by pulling through rollers. Sold by brake pipe suppliers but I may have seen them elsewhere – "Repair Shop" perhaps.

[egaParticipant @ega]

Tubal Cain dealt with this in WPS28.

[not done it yetParticipant @notdoneityet]

Posted by Bo'sun on 08/12/2020 11:37:41:

Thanks for that, annealing will have to done a section at a time. The final aim is to produce a close fitting cooling coil, so the piece needs to be reasonably long to start with.

Are you annealing it with a fag lighter?🙂 Getting it straight, by rolling between flat surfaces, might have limits to length, but any decent gas torch should enable you to steadily progress from one end to the other.

[EmgeeParticipant @emgee]

Posted by PaulG on 08/12/2020 11:43:27:

Don't know about this size but there are small hand tools to do this by pulling through rollers. Sold by brake pipe suppliers but I may have seen them elsewhere – "Repair Shop" perhaps.

This works on MICC (mineral insulated copper covered) cables.

Emgee

[Former MemberParticipant @formermember12892]

[This posting has been removed]

[Bo’sunParticipant @bosun58570]

So that I can wind a close/tight fitting coil around a cylinder giving good conduct.

[Bo’sunParticipant @bosun58570]

I'm hoping that annealing will reduce "spring back", further helping me to get a close fit. I have considered using a heat conducting compound if need be. Any comments on using such a material appreciated.

Just in case you're wondering. I'm experimenting with a water cooling coil around the "cool" end of a Stirling Engine transfer cylinder.

[Bo’sunParticipant @bosun58570]

Posted by ega on 08/12/2020 12:42:33:

Tubal Cain dealt with this in WPS28.

Hi ega, do you have a link? That reference doesn't yield anything.

[Jeff DaymanParticipant @jeffdayman43397]

Hi Bo'sun, by using a pipe applied to the hot end, you introduce a barrier to heat conduction at the interface of the pipe to the hot end part. Every such barrier will seriously reduce heat transfer from a hot item to a cooler item. If you can fit a water jacket around the hot end and transfer heat directly from the hot end to the cooling media the heat transfer will be far better. This method is used in the majority of liquid cooled IC engines in the world, for good reason. Only mentioning it as food for thought, and may save some cost and time straightening copper pipe.

[JasonBModerator @jasonb]

Jeff, not sure why anyone would want to put a cooling jacket or coils around the hot end of a stirling engine as you heat the hot end and it's the temp differential between hot and cold ends that makes them run so heat the hot end and cool the cold end either with fins for air cooling or jacket coils for water cooling.

Materials are also selected to reduce heat transfer not encourage it

Edited By JasonB on 08/12/2020 16:18:58

[Bo’sunParticipant @bosun58570]

I'm no expert, but I wondered the same.

[old martParticipant @oldmart]

Posted by Bo'sun on 08/12/2020 15:15:43:

I'm hoping that annealing will reduce "spring back", further helping me to get a close fit. I have considered using a heat conducting compound if need be. Any comments on using such a material appreciated.

Just in case you're wondering. I'm experimenting with a water cooling coil around the "cool" end of a Stirling Engine transfer cylinder.

COOL,not Hot end, he said.

[duncan webster 1Participant @duncanwebster1]

Posted by Bo'sun on 08/12/2020 15:15:43:

… I have considered using a heat conducting compound if need be. Any comments on using such a material appreciated.

…

Devcon used to be the stuff, the one loaded with aluminium -powder. Soft solder would be better I think. However as others have said a proper water jacket would be a lot better. If you're pumping the water then arrange the flow to be tangential in at one end and tangential out at the other, then it sort of spirals round and you don't get any dead spots

Edited By duncan webster on 08/12/2020 21:35:15

Edited By duncan webster on 08/12/2020 21:35:52

[John BaronParticipant @johnbaron31275]

Hi Guys,

In the old days before I retired, I used to straighten 50 foot lengths of 6 mm copper tube for making coils by stretching the tube. It was anchored at one end to a steel peg and stretched by pulling it with a four foot lever at the other. The very slight reduction in diameter didn't matter at 144 Mhz.

[Tim StevensParticipant @timstevens64731]

Another way to straighten tube (or wire, etc) is to unwind as much as you can, fit one end in the vice, and pull the other. As you do this you will feel the metal 'give' as you get past the springiness. That should be enough – at the cost, of course, of 2cm at each end.

If you don't feel the 'give' it may be that the tensile strength is more than you can pull. Annealing will help – but this can be counter-productive if you need elasticity – eg when making a coil spring.

Oh, look, John Baron has just beaten me to it.

And you will improve conductivity between tube and cylinder with solder – soft or (even better) hard.

Cheers, Tim

[egaParticipant @ega]

Posted by Bo'sun on 08/12/2020 15:27:13:

Posted by ega on 08/12/2020 12:42:33:

Tubal Cain dealt with this in WPS28.

Hi ega, do you have a link? That reference doesn't yield anything.

WPS28 = Workshop Practice Series no 28 which is entitled Simple Workshop Devices.

You may feel you already have enough advice but I could send further information if you PM your email.

The book is one of the better in the series.

[Jeff DaymanParticipant @jeffdayman43397]

Sorry re my brain fade / typo hot end vs cold end, of course OP did mention cold end was where he was working. I still think a water jacket where you want to transfer heat will be much more efficient than coils wound around. I agree with others who suggested soldering the coils or using heat transfer compounds would help if coil must be used, but a jacket and liquid or gaseous cooling media is a better method to move heat.

[not done it yetParticipant @notdoneityet]

Just as a suggestion….

One can buy flat copper tube for radiators, etc. Don’t know whether it could be bent in a tight curve without collapsing or how to do it if it could (maybe fill it with Wood’s metal or something equivalent/suitable?).

[Bo’sunParticipant @bosun58570]

Thanks Jeff,

Yes, a water jacket would be a better idea, but for expediency and simplicity, and after all it is an experiment, I'll give the water coils a try and see how we go.

[Neil WyattModerator @neilwyatt]

An experimental idea could be using a CPU cooler with a water pump or heat pipes.

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