Date: Sun, 28 Jul 2002 12:15:11 +0100
Reply-To: Clive Smith <clive.harman-smith@NTLWORLD.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Clive Smith <clive.harman-smith@NTLWORLD.COM>
Subject: Re: Just wondering (solutionising dural for bending)
Content-Type: text/plain; charset="iso-8859-1"
>I tried to modify a stock slider for rear installation but could not get
the
corners bent w/o breaking the aluminum. I will try to get some done
professionally at a later date.
If its near pure alumnium, then it shouldn't crack unless you're bending
technique is not very good -a big hammer & a sharp former.
If it cracked or broke I expect it was duralumin alloy of some kind (and
their are many).
Here's what to do to bend a sheet of duralumin nicely without cracking to
create a component that is as strong and stiffer than the original.
Required - a heating flame large enough to get the whole sheet up to 515 C,
I used to use an oxy-acetylene torch with say an 8 or 10 jet, but a decent
sized propane/butane torch can do the same. Set the oxy/acetylene flame so
its slightly carburising.
1) Put the pre-cut to size sheet on some firebricks or asbestos that will
spread the heat and not concentrate it (i.e. not in the vice!)
2) Have a bowl or tank of water (about 40 - 50 F) large enough to easily
drop the component into and quench it quickly and some tongs to move it
around and pick it up easily.
3) Have some safety matches available; that is a match made of quality
boxwood, they're usually fairly whitish with a good finish ('Ship' brand are
perfect if you have them there) - strike a few to burn off the phosphorous.
4) Start heating the whole component by continually playing the flame
systemically along and across it, don't stop moving the torch for a moment.
If its large or you don't have high heat source, place some more insulation
around it, say some bricks around the sides to make a small furnace. When
you think its getting pretty hot start wiping the clean end of match (not
the end you ignited) across the surface of the ally - if it just atrats to
make a char mark (like a small thin bitumen coloured trace) then it getting
near 500 C. Keep heating evenly an generally until almost any area you wipe
the match end across makes line, but the wood shouldn't burn or smoulder -
too hot. Watch out, ally melts at not much more - 550 ish I think - so
practice getting this right - its not that difficult - the match should
'just' be making a consistent trace - that is 515 C ish, good enough.
5)While still playing the flame grab the component with the tongs at one
corner and immediately drop in quenching tank.
6) When cool you have succesfully 'solutionised' the duralumin - it will be
soft as a baby's bum (nearly) - nominal gauges (16 - 30) certainly will take
a 2T radius bend without cracking. Thicker gauges might require a bend
radius (inside) of 2.5 - 3T (T is the thickness). It will start to age
harden straight away, the hotter ambient conditions speeding this process.
Can refrigerate to delay this process.
7) If you're a perfectionist and want a nice looking job, make up bend bar
with a calculated radius of say 2 or 2.5T. Put a pencil line 2T from where
you want the bend to start and eyeball this flush with top of bend bar as
you clamp it all up in vice or your workmate (great British invention that
it is :-)
Once bent nicely, leave to age harden for a day or accelerate with warmth,
the bending proces itself will re-harden it to an extent. It will get so
stiff you can't bend it again easily, or it will crack if you try.
We'll thank one of Mr Zeppelin's metallurgists for that one, but although it
sounds a right pain, it is in fact very quick and simple to do and well
worth it to get a strong, stiff, good-looking durable component - in fact
once you get down to about 14 or 12 gauge you can't usually bend it without
solutionising it first anyway. Commercially (aviation industry), use large
tanks of sodium held at 515C to heat soak dural sheets and baskets of dural
rivets before forming.
Clive
'88 Syncro Transporter
----- Original Message -----
From: "Ben T" <BenTbtstr8@AOL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Sunday, July 28, 2002 9:14 AM
Subject: Re: Just wondering
> Mark,
>
> Stan the wildman from TX installed a PVC pipe as a scoop up front for
added
> venting. Why not cut a whole in the rear side window glass and do
something
> similar. Valves for large diameter PVC pipe is available. That way you can
> open and close the. If you can't get holes done on glass, get Plexiglas
> installed on one side. You can even get creative and put small reverse
NACA
> ducts so as not to disturb the airflow much and still have an efficient
vent.
>
> I tried to modify a stock slider for rear installation but could not get
the
> corners bent w/o breaking the aluminum. I will try to get some done
> professionally at a later date.
>
> BenT
> <A
HREF="http://hometown.aol.com/bentbtstr8/myhomepage/index.html">Vanagon
> Cafe</A>
