Subject: RE: baidarka R: "unbending" aluminum tubes
From: LEW PLUMMER (jayhawk@sos.net)
Date: Sat Feb 17 2001 - 16:04:43 EST
Unbending tubing, or any metal is not recommended it severely reduces
fatigue life and strength. When you bend tubing the material on the outside
of the bend is stretched, in tubing this reduces the wall thickness. When
straightened the wall in the area of the bend will not return to its
original thickness (usually it ripples and buckles). The stronger
un-stretched material along the inside of the bend neutral axis causes the
ripples and buckling on the outside of the straightened bend. The net result
will be a weaker tube. It's weaker because the wall thickness is less and
the material grain boundaries have been disturbed reducing fatigue life.
Heating the tube will affect material temper making it soft in most cases;
this is called annealing. This is especially true with aluminum, depending
on how the aluminum is alloyed. Some aluminum alloys are aged or
artificially aged to increase its strength. For example 6061 T6 aluminum is
not a good material to "work" so it is typically ordered in the softer T4
form so it can accommodate a tighter bend radius. Then, when the forming is
complete, increasing the material temperature (around 700deg f, if I
remember correctly) over time artificially ages it; bring it up to T6
strength.
Really makes you appreciate some of the properties of wood; it is what it is
and it floats too. Also, salt water doesn't rapidly accelerate its return
to its natural state if it isn't unprotected.
Regards, Lew Plummer
-----Original Message-----
From: owner-baidarka@lists.intelenet.net
[mailto:owner-baidarka@lists.intelenet.net]On Behalf Of Stefano Moretti
Sent: Saturday, February 17, 2001 10:28 AM
To: baidarka@lists.intelenet.net
Subject: baidarka R: "unbending" aluminum tubes
Heating helps the aluminum from fracture from "crude " bending. I lack the
technical term in english, but some metals when bnt become "crude" and brake
(copper, brass..). I found out that heating with a torch pushes the limit of
fracture quite a bit.
I do not use any tool to bend. Pouring sand into the tube and a vise +
larger tube to use as a leverage is my method (but I do not build aluminum
frame baidarkas)
Stefano
----- Original Message -----
From: Douglas and Leticia <huftdecruz@earthlink.net>
To: <baidarka@lists.intelenet.net>
Sent: Saturday, February 17, 2001 6:30 AM
Subject: Re: baidarka "unbending" aluminum tubes
> on 2/16/01 6:50 PM, Chris Burkhart at baidarkas@home.com wrote:
>
> > Hi Doug,
> >
> > True, you can't undo extreme bends in the aluminum tube. However, Mr.
> >
> > I also found that it was less messy to smear the vaseline into the
Holsclaw
> > Tubing bender instead of the tubing itself.
> >
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