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Bending 10mm copper tube

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Sulaiman

Sun Oct 25 2009, 12:14PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I guess that 10mm tube with 30 to 50 mm od winding will have significant inter-turn capacitance and 'proximity-effect' will be as significant as 'skin'effect' (which is why I assume you're using tubing) as a pfn.
You'd probably achieve better results with smaller diameter tubing.

To save on weight could you;
- wind the pfn coil on a plastic tube
- slip a larger tube over the winding
- encapsulate the space between the tubes

P.S. Coils made of tubing should have both ends free and a clear bore,
This allows later use as a condenser for distilation use.
Just an idea.

uzzors2k

Sun Oct 25 2009, 01:10PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

I simply used table salt when winding a new induction heater coil. It has the benefit of being cheap and easily dissolved, so you don't need to worry about it getting stuck in the pipe. Both ends of the pipe were clamped shut with a vice prior to bending, and the salt was packed sufficiently simply by tapping the pipe on the cement floor of my garage. Here's a coil with 10mm copper pipe and 5cm inner diameter.

Proud Mary

Sun Oct 25 2009, 01:23PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Sulaiman wrote ...

I guess that 10mm tube with 30 to 50 mm od winding will have significant inter-turn capacitance and 'proximity-effect' will be as significant as 'skin'effect' (which is why I assume you're using tubing) as a pfn.
You'd probably achieve better results with smaller diameter tubing.

To save on weight could you;
- wind the pfn coil on a plastic tube
- slip a larger tube over the winding
- encapsulate the space between the tubes

Thank you, Sulaiman, for your excellent insights.

The inducters concnerned are but a few uH - and my idea in using the 10mm tube was to keep R as low as possible, as very high currents are to be iniated by a thyratron into a lo-Z load at the end of the line.

Thanks also Eirik, for your demonstration of how it can be done!

Bored Chemist

Sun Oct 25 2009, 05:23PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

I like the ide of using table salt rather than sand as a packing because it's easy to remove; but why bother? Are you planning to run cooling water through the tube?

Fabio

Sun Oct 25 2009, 06:42PM

Registered Member #122 Joined: Fri Feb 10 2006, 12:55PM
Location: Milano Italy
Posts: 148

metal spring,
Removed while creating a continuous bend.

I used this system few years ago to make a coil with a 16mm copper tube; the overall result was great but a lot of work was required; the last two turns was the hardest to make because the tube bending spring became too loose and finally totally useless: a coil bending spring cannot make more than 10 turns!

http://4hv.org/e107_plugins/forum/forum_viewtopic.php?24548.post

EDIT:
Since this was his application i selected a refrigerating anealed copper tube of course!

Ciao!
Fabio.

Z28Fistergod

Mon Oct 26 2009, 01:48AM

Registered Member #2040 Joined: Fri Mar 20 2009, 10:13PM
Location: Fairfax VA
Posts: 180

What about starting with a 30mm (Or whatever your closest standard size is over there) straight piece and cutting a spiral along the length of it.

IamSmooth

Mon Oct 26 2009, 12:44PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

Bored Chemist wrote ...

I like the ide of using table salt rather than sand as a packing because it's easy to remove; but why bother? Are you planning to run cooling water through the tube?

Harry,

The play sand is just fine, clean sand. It is used on playgrounds, but any sand will do. The sand comes out easily. I simply connected on end to an air compressor and blew the sand out in two seconds. Salt or sand would be fine.

Proud Mary

Mon Oct 26 2009, 12:53PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Thank you all, gentlmen!

Nik

Mon Oct 26 2009, 01:59PM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

Sand tends to get stuck when you do tight bends, it will jam up and be really hard to remove. I use salt because you can dissolve it out with hot water. To make sure its packed well I also vibrate it with an off center weight in a drill.

TwoSpoons

Wed Oct 28 2009, 01:36AM

Registered Member #1621 Joined: Tue Aug 05 2008, 05:26AM
Location:
Posts: 19

Anneal the copper first, by heating to red heat. It becomes much softer and easier to bend smoothly, as bending work hardens the copper as you go.

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