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Topic ClosedBending 2inch 16g ERW tube

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Basil View Drop Down
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Direct Link To This Post Topic: Bending 2inch 16g ERW tube
    Posted: 30/November/2009 at 12:51
I'm trying to bend the above tube but it buckles on the inside face of the bend.  I'm using a pro-tools bender and the spec says that 2inch x .095 is the thinnest 4130 tube it will bend so I must be on or near the limit unless I buy a very expensive mandrel bender.

Does anyone have any tips?  Annealing, filling with sand (didn't help) filling with anything else, giving up? 
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Direct Link To This Post Posted: 30/November/2009 at 18:22
what is the centre line bend radius which you are trying to achieve?
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Direct Link To This Post Posted: 30/November/2009 at 22:13
7 inches
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Direct Link To This Post Posted: 30/November/2009 at 22:33
Shouldn't be an issue at 7" (greater than 3 x diameter)
Sand must be really hard packed and sealed at either end to work properly.
How are you aligning the weld of the tube. Along the neutral axis of the bend?
Warming it should also help.
I assume that it's a hydraulic machine? so slow and steady bending.
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Direct Link To This Post Posted: 01/December/2009 at 08:37
Tried annealing without using sand and it made it worse.  Sand alone made it slightly better but not acceptable.  Will try sand and heat.
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Direct Link To This Post Posted: 01/December/2009 at 08:41
Presumably one solution would be to use aluminium since the wall thickness would be greater for the same strength.  Shame my aluminium welding is much dodgier than steel.
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Direct Link To This Post Posted: 01/December/2009 at 13:04
Beg, borrow or buy a ball mandrel.
for example
One must be available for 2" 16swg as it's a pretty common size.
It's a lot messier than sand, but I have seen the ends of a tube welded up and the inside filled with hydraulic oil under pressure.
With the information I have infront of me (I'm not in my office) the elongation of ERW is 12%. CFS3BK (The old CDS2 tubing) is 22%.
4130 is 17% (apparantly)
T45 would be upwards of 20% (I suspect)
Maybe you should choose some CFS tubing to do the job. It should be fairly available in that size. I've also had it bent to a 6"CLR without buckling on the inside many times.
Hope that helps.
MBG
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