[TheForge] warped 1" plate table

Sun Sep 1 10:28:00 2002

        Peter,  I've never really had luck heat shrinking plate of
substantial size as I dont' have the means to get it all hot enough.
        At the Boston ship yard years ago I watched an 8 hour shift turn a
huge 4" plate red for 18" wide and four feet long with four huge
rosebuds........then one fellow up on a staging platform hit the piece with
a four inch fire hose to make it curve up for the hull bend on an ice
breaker.........worked well as the entire sheet across the section was hot
for 18" wide.......this allowed one side to cool rapidly and the other to
stretch as it was not cooling anywheres near as fast as the hose side.  It
was neat to watch, but they said the whole thickness had to be heated to
make this work.
        I've always ended up getting puckering and little results as you
have found as I corilate it to the welding of cast that isn't preheated
enough......the weld looks fine till you see it cool and crack........so the
heat differentiation is splitting the weld.   Another way to look at it is
the working with a power hammer that isn't big enough for the job and you
skate the skin around the core.........so your affecting and puting tension
on one side of one surface.....but not enough to stretch the other side.
        I find heat shrinking works on tubing machine fences that warp when
you weld them up and small structural shapes like pipe, rod and angle, but
to expect accurate results on heavy plate......one would need some awesome
heat for an extended period of time.
        So you ask - what do I do for bent plate...........I usually do it
like in a hydrualic press where you put to risers to hold your part and push
to a kiss block.  My method has been to load rock onto a boom truck and run
over it with the corners blocked and the center comes down to the ground and
it acts as the kiss block - (just on a grander scale).   I've had results
with this method in up to 3/4 & 1" plate ..............but if your dealing
with HY 80, 100, T1 etc......your dreaming, you won't get enough rock on the
truck to move the dam thing,  The quench and tempered plates are really
springy - thus used for frames and cranes and submarine hulls.
        If this plate has been used as a highway plate it has literally been
"rolled" to the warp and it will take some serious weight to change the
memory that has been created in the grain of the plate.
        A loaded 10 wheeler of sand or crushed rock works well for
straightening if someone is running by you with loads during the day - you
may offer him a few bucks to do a drive by .......so to speak.  Start with
small blocks and work up.......nothing worse than going to far and having to
correct that.  You should do well as you have the 8 and 9 foot demensions
for leverage against the blocks so the weight should yield some results with
the correct size blocks.
        Of course a huge press brake at a ship or steel yard will
work........but those boys usually don't work cheap
        If you do find other answers or methods - let me know, I always like
to learn on how to improve my methods.

Ralph


----- Original Message -----
From: "Peter Fels and Phoebe Palmer" <[email protected]>
To: <[email protected]>
Sent: Sunday, September 01, 2002 1:03 AM
Subject: [TheForge] warped 1" plate table


> I'm in over my head again and wish to beg some of you-all's expertese.
> This 1"x8'x9' plate is warped and while I've been able to
> herd  the  warpage around, I've been unable to get it flat.
> It is up on house jacks in the work yard and presently has a gentle
> diagonal crease about 3' long  so the thing is high on 2 corners.
> The theory I had was that by spot heating and quenching, it would shrink a
> little at that spot and that if a line was heated and quenched,it would
> shrink along  the length of that line.
> What seems to be happening instead is that the spot heated area bulges and
> only partially returns to flat when quenched and that the heated line
seems
> to  cause a folding  along the line that draws the sides up perpendicular
> to the heated line.
> So the theory is wrong.
> Would someone be so kind as to explain this  and how to control it and fix
> the problem..or where to find the info?....thanks...Pete F
>
>
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