Re: Ancient Coins: How to Start a Collection?

On Sun, 30 Sep 2007 10:03:26 +1000, "Jeff R." <contact.me@xxxxxxx>
wrote:

----- Original Message -----
From: "Reid Goldsborough" <reidgoldsborough@xxxxxxxxx>
Newsgroups: rec.collecting.coins
Sent: Sunday, September 30, 2007 1:36 AM
Subject: Re: Ancient Coins: How to Start a Collection?


On Sat, 29 Sep 2007 13:50:32 +1000, "Jeff R." <contact.me@xxxxxxx>
wrote:

"How can you achieve plastic deformation of coin metal at room temperature
with a wire brush?"

It's NOT room temperature at the point of interaction!

If the temperature is raised by friction to a point *anywhere* near that
which will assist plastic deformation, then brass bristles will melt, nylon
bristles will char and burn and steel bristles will completely lose their
temper.

Any temp gain at the point of contact would be (would *have* to be) marginal
at best. "Room temperature" is probably still a reasonable description.

Reid - try to *think* about it. If the temp is so elevated, then the tools
would be destroyed.

Are you claiming that temperature rise (through friction) is germane to your
understanding of whizzing?

The coin is a big heatsink. Adequate spot-heating of the surface would
utterly destroy the wire in the brush, air-cooling effects notwithstanding.


... As explained to
you. But when this is pointed out to you, you say, "My point exactly."
LOL. And you wonder why.

As explained above. LOL as much as you like. Try, instead, to rationally
explain. Yes, I do wonder why you fail to see my oft-expressed point.


... AGAIN, your experiment is flawed and your
results irrelevant because ... I'm really not trying to insult you,
despite how this is inevitably going to sound ... you don't know what
you're doing. First, you can't do something as well the first time as
somebody who has done it a hundred times.

Reid, I'm not (in any way, shape or form) a professional numismatist nor an
accomplished whizzer. Only one poster here has dropped hints that he may
be.

I am, however, a metalworker who spends a large part of every working day in
a well-equipped metalworking workshop. I can cast and forge and cold-work
and solder and braze and weld and polish right up there with the best of
them. When I prepare metallurgical specimens for examination, I take raw,
cut surfaces and reduce them abrasively to a mirror finish which is so fine
that the scratches can no longer be detected - even with a 1000x oil
immersion objective on my metallurgical 'scope. I have polished glass
blanks to an accuracy better than small fractions of the wavelength of
visible light - again with no scratches detectable. (Don't ask about
sleeks.) Working such materials has been a large part of my profession for
over 30 years, and a satisfying hobby to boot. I've studied (*and* passed!)
metallurgy and physics and chemistry (amongst many others). Whist not being
a specialist in those fields, I have done and continue to do a darn sight
more with them than you have time to Google and read about.

.... Second, I'm not professional
whizzer, have never once in fact tried to whiz a coin, but in just
reading your experiment it was obvious to me that you're just coming
up on your own with what you're supposed to be doing, that you have no
knowledge of what whizzers actually do, that you haven't done your
homework. And then you've got the basic understanding of the physics
totally wrong,

Please be specific.
*Exactly* what have I claimed that is in error, physics-wise?

... talking about room temperature, ignoring what happens
at the point of contact, regardless of whether it's a planchet struck
or a coin whizzed.

The action of a die on a planchet is a *totally* different case, and I only
neglected to raise that as an issue because I didn't think that anyone would
be silly enough to claim any sort of similarity.

Do I need to explain the difference between a hardened and tempered tool
steel die, rigid and totally inflexible, mass approaching a kilogram (or
*far* surpassing 100kg if the intimately conjoined press ram is considered)
and a relatively soft, lightweight and certainly quite flexible wire from a
whizzing brush? I will if you like, but most folk here would get it without
a tedious explanation.

Please address the original question:
"How can you achieve plastic deformation of coin metal at room temperature
with a wire brush?"

If you like, you can delete the reference to "room temperature" if it makes
you uncomfortable, and substitute:

"How can a wire brush achieve plastic deformation of coin metal, whilst
operating at temperatures which would assist such deformation, without
self-destructing?"

or more simply:

"How can plastic deformation be achieved with a wire brush?"

or, for extra credit:

=======================================================
A wire brush achieves its effect through the action of:

(a) movement of metal on the subject surface
(b) abrasion
(c) years of experience of the professional operator
(d) voodoo
(e) hope and prayer

Check the _best_ alternative.
========================================================


Or, of course, you could just admit defeat and bow out of this thread, as
you have so many times before. A snide comment, a non sequitur or two, your
insidious <g>, then a "bye bye... I'm out'a here."

Anyone laying odds?

That's interesting, Jeff. I don't know anything about either physics,
metallurgy or whizzing, and I'm not about to make pronouncements about
any of those topics.

Anything I ask here is purely out of curiosity. If a brass brush in a
Dreml set at the highest speed is rotated on a coin's surface, each
wire is in contact with the coin's surface for a very brief period of
time. However, the coin's surface is in contact with *some* wires at
all times.

If so, is the rise in temperature of the coin's surface equaled by a
rise in temperature of the wires? In other words, can't the coin's
surface get hotter than any of the wires? Each wire, as it rotates,
cools (albeit minutely), doesn't it? But the coin's surface doesn't
cool.

The only whizzed coins I've seen have been US gold. That's the only
type of coin that I deal with. I got one back from ANACS marked
"Whizzed", but I'd have to go to the safety deposit box to find out
which one it is.

Is your premise that the whizzed gold that I have did not experience
any surface flow? Is the effect purely abrasion?

BTW, I would consider "abrasion" to be the removal of metal, not the
movement of metal. Metal that "moves" on a coin is redeposited on the
coin as it would with flow. Abrasion moves metal off of the coin.

In your quiz, I'll pick (d). Anyone who can successfully alter a gold
coin's surface without visibly (without the aid of magnification)
destroying the coin has some mojo and keeps his tools in a gris-gris.



--


Tony Cooper
Orlando, FL
.

Relevant Pages

  • Re: Ancient Coins: How to Start a Collection?
    ... It's NOT room temperature at the point of interaction! ... The coin is a big heatsink. ... utterly destroy the wire in the brush, ...
    (rec.collecting.coins)
  • Re: Ancient Coins: How to Start a Collection?
    ... kind of temperature that would be required to "soften" steel. ... our typical coin silver is alloyed with copper I searched for sterling ... a temperature increase to this level is not possible with a wire brush ...
    (rec.collecting.coins)
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