[TheForge] Rebound and Work

[Jonathan Nedbor]

Mike,
I remember seeing some old advertising for some brand of cast anvil that 
addressed the rebound issue. Their copy stressed that the cast anvil with 
minimum rebound allowed for more of the force from the hammer blow to 
penetrate the metal being worked on, thusly producing more "work". They 
contrasted this with a forged anvil with good rebound and claimed their cast 
anvil, for this reason was far superior.

Food for thought or just plain old advertising sleight of hand? If you can 
convince 'em, confuse 'em.

Jonathan


----- Original Message ----- 
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To: <theforge at mailman.qth.net>
Sent: Saturday, November 05, 2005 4:01 AM
Subject: TheForge Digest, Vol 22, Issue 14


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>   1. Re: uri hammer (Mike Spencer)
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> ----------------------------------------------------------------------
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> Message: 1
> Date: Sat, 5 Nov 2005 00:46:34 -0400
> From: mspencer at tallships.ca (Mike Spencer)
> Subject: [TheForge] Re: uri hammer
> To: theforge at mailman.qth.net
> Message-ID: <200511050446.jA54kYs13470 at bogus.nodomain.nowhere>
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>
>> Hmm.  Looking at the web page, I wonder if you ever figured
>> out the energy imparted to the hot iron by the hammer head?
>
> Well, I have a little trouble with the computations. [1]  But as a
> first approximation, the kinetic energy of the hammer head is:
>
>    1/2 X mass-of-hammer X velocity-of-hammer X velocity-of-hammer
>
>    1/2 m v^2
>
> If the hammer head stops dead with no rebound, then there's zero
> kinetic energy so all the kinetic energy of the hammer must have been
> converted into work in deforming the the iron and is eventually
> dissipated internally as heat.  If there's rebound, that kinetic energy
> has to be subtracted from the original KE to get how much went into
> the iron.
>
> Rebound is hard to measure with a hand hammer.  And the above ignores
> all the other possible variables such as energy absorbed by the anvil
> and stump/stand, energy dissipated as sound, etc.
>
> Those pics on the web page were done with hot iron.  We did some
> others with a piece of lead and with a piece of cold steel at faster
> frame rate.  I haven't gone over those carefully but intuitively,
> there was less rebound with the lead and, of course, a great deal with
> cold iron.
>
> Thinking about this stuff is for the winter when the shop is cold, the
> snow deep and the house warm.  Maybe this winter.  I finally found
> some manuals for Maple V and mean to play with it when the weather is
> nasty.
>
>
> - Mike
>
> [1] "...a little trouble with the computations."  Tedious and OT.  I
>    don't have trouble with the usual, textbook, frictionless billiard
>    ball or ballistic pendulum examples of conservation of momentum.
>    But in the case of hammering on an anvil, I can't quite figure out
>    how to do the computations when the "system" consists (1) a hammer
>    of mass m and velocity v colliding with (2) the earth of mass
>    5.9736e24 kg and velocity 0, of which latter a little piece (the
>    hot iron) is (almost) completely inelastic.  I need to put my feet
>    up, read some hard stuff (hard for me, anyhow) and scribble,
>    scribble, scribble.
>
> -- 
> Michael Spencer                  Nova Scotia, Canada       .~.
>                                                           /V\
> mspencer at tallships.ca                                     /( )\
> http://home.tallships.ca/mspencer/                        ^^-^^
>
> -- 
>
>
>
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> End of TheForge Digest, Vol 22, Issue 14
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