Tube in Tube Bending

fine sand.

fine sand is also good. It may be btter as it will not squeeze out and allow the tube to flatten. You can also use a tight steel coil that fits the tube. Bend it and remove the coil

Not familiar with bendable double walled pipes.

If the wax is intended to keep the spacing constant between the walls even fine sand might not be suited.

You may have to experiment a bit.

Frozen water.

I recommend fine sand taking into consideration that the gap between the double wall is enough for filling. Fine sand will not squeeze out, where wax will not prevent squeezing out.

Unless something different has come up in the last couple of years, sand or other fine media was the method used in production of double walled automotive catalytic converter pipe bending.

Dear Sir,

I would like to know who are all working on" pipe bending by rotary draw type " methods and studying the encountering problems like spring back, stretching, elongation, etc. and how to analytically and virtually calculate them

Regards

Another possibility is to use a low melting point alloy. You can cast the alloy in place when the tube is straight then drop the bent tube into hot water to melt the alloy out. The alloy is completely re-useable & should be dense enough and malleable enough to allow the tube bend.

I've used this in the past when machining thin walled components to stop them distorting & 'ringing' when in the lathe. After some initial outlay the running cost was negligible.

As Aurizon said: a spring, or, as Nigh said low melting point alloy:-

http://www.mcp-group.com/alloys/lmpa_tube.html

Or, an off the wall suggestion: cornflour and water mixture. It will take a long time to "run" out of the gap but may do the job.

What wall thickness is ID of outer tube? What is OD of inside tube? What material is each tube made out of? What application after forming? What length of parts? These questions will help me suggest approach. Sometimes the final use will rule out certain materials. If I were in my shop trying to do this and the parts were shorter than a tig welding wire and the gap between the parts allowed me to position three filler rods 120 deg. apart and keep them in place during the bend. I would slip that assembly into my diacro tube bender and give it a shot. Pull the wires after bending or leave them there?

Large Copper coax (3" and 4" outer tube) used on cell Phone towers has a nylon spacer spiraling around the inner conductor. After the bend is made you can pull it out of the end unwinding it as you go. I used to do this to scrap excess copper when the job was completed.

You could do the same thing with rope. Wrap it around the center tube (The tighter the bend radius, the more wraps per foot.) Perform your bend. Pull the rope out of the end.

yes, sand can be used

Our system replaces all current methods of Double wall tube in tube bending.It is quicker,safer and easier, requires no melting filling or post bend removal of material.Can be used any metal tube bending application.Significantly reduces manufacturing time and cost.

You can veiw further information and installations and inquire at www.wolfbend.com

or contact me through CR4.

Steve Wolf