19th century die cracks/ effect of annealing and hardening
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CoinMiner1
Posts: 166 ✭
Howdy,
Someone asked me this interesting question - would be interested in your thoughts on the matter:
Is it possible that a19th century reverse die with a crack could have the crack reduced in size via annealing and subsequent hardening ? Such a closing of the crack would be expected under the laws of Thermodynamics, but such a reduction in crack size would be temporary and would quickly reopen once coin striking was resumed.
tia
Someone asked me this interesting question - would be interested in your thoughts on the matter:
Is it possible that a19th century reverse die with a crack could have the crack reduced in size via annealing and subsequent hardening ? Such a closing of the crack would be expected under the laws of Thermodynamics, but such a reduction in crack size would be temporary and would quickly reopen once coin striking was resumed.
tia
www.CoinMine.com
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Comments
die striking many coins well AFTER the
die has been prepared for use.
I believe your premise is incorrect.
If a die develops a crack during use, and the crack is identified by the mint workers, is there anything the mint could do to extend the life of the die....such as annealing and hardening?
My guess is that any heat treatment probably wouldn't be effective, and might itself worsen the crack as opposed to "healing" it....even temporarily. It might also distort the devices on the die, making them mushy? (Just thinking out loud).
but I don't believe the Mint would take a die with a crack
on it, and anneal it again, to be put back into use.
And I agree that to do so would increase the chance that
the die-crack would expand, and possibly make it much worse.
Sorry if I mis-read the OP's question.
solution to a minor crack would be to lap it out
and see if it was still usable. This may have
resulted in a diminished appearance of detail.
Others may have a better answer, but have not
heard of the OP's fix.
R.I.P. Bear
It's my understanding that at that time their
solution to a minor crack would be to lap it out
and see if it was still usable. This may have
resulted in a diminished appearance of detail.
Others may have a better answer, but have not
heard of the OP's fix.
This happened. I was once studying some 1882 and 1882-O dollars that I thought were overdates, and I had several pieces from one die pair in different die states. One had light die cracks in an intermediate die state, that disappeared in the late die state after the die was rebasined.
Die Cracks are usually the result of the
die striking many coins well AFTER the
die has been prepared for use.
I believe your premise is incorrect.
Court is adjourned.
One had light die cracks in an intermediate die state, that disappeared in the late die state after the die was rebasined.
ty.
re-working of dies is something intense vammers know about, intimately. some of the techniques. trials are/were staggering.
when the die prep process isnt done properly (or simply doesnt hold up) and/or the stock/dies dont receive the processes/creation well, all kind of crazy stuff starts to happen, nearly from coin 1. often seen in cuds that happen in big chunks, nearly instantly instead of the normal and neat progressions.
of course die set-up and extreme pressure/clashing can exacerbate minor defects during the hub/die creation processes.
these things can be seen in dmpl & pl, often.
got a few cool disc. coins from improper basining, annealing, hardening, reworking etc.
the early and late years are notorious for such things.
im sure you already know this but liked your confirmation that minor cracks have various processes in a probable futile attempt to increase quality and die life.
phew. im done.
.
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Is it possible that a19th century reverse die with a crack could have the crack reduced in size via annealing and subsequent hardening ? Such a closing of the crack would be expected under the laws of Thermodynamics, but such a reduction in crack size would be temporary and would quickly reopen once coin striking was resumed.
No. In fact, the die would likely crack even more, and possibly shatter. Both annealing and hardening are heat treatments. Annealing requires that the die be raised to the "critical temperature - around 1400 - 1500 F for 1% carbon steel - and then allowing the die to slowly cool. For hardening, the die would be heated to about the same temp and then rapidly quenched by plunging into water.
Both of these heat treatments involve thermal expansion and contraction of the steel, with the rapid cooling of hardening being obviously much more so. Significant cracks would thus expand quite rapidly.
BTW, many of the arcing cracks thru the tops/bases of letter and points of stars seen on early state 19th cen. coins are "hardening" or "quench" cracks caused by the rapid contraction of the steel, with the sharp vertices of the letters and stars serving as "stress risers." They can also appear quite early in striking as the stress induced by striking along with the residual stress from hardening exceeds the fatigue strength.
Edited to add: There are many excellent metallurgical references available on the web. Just google.
Any crack minor enough to be polished out was probably not even noticed as the coins left the press. I'll bet there was another reason the die was removed (clash?) and fixed and in the process the minor break was removed. IMO, it is useless to try to repair a really cracked die. Evidence for this exists in all the coins with heavy die breaks/shattered dies/retained cuds that continued to be used!
Although this was in December 1794, chief engraver Robert Scot explained the "precariousness" of the die hardening process in his report to Congress, just recently published in its entirety. Excerpt:
"Before a Die to strike money can be made, the previous step is to engrave an Original one first. The execution of that of the head of the Cent will take four or five days, and if is hardened with success, a Hubb is struck out of it (that is an impression in steel) but if otherways, which is not unfrequent; is to begin de novo. The Original Die being compleat, and the Hubb struck; by failure in hardening it, it becomes useless immediately, or very soon so."...and..."From the same source of uncertain decision whereby the time of executing the Dies cannot be ascertained, arises the same difficulty in determining how long they will last. Namely, the precariousness and uncertainty of hardening and tempering the Dies, whereby they are often lost without striking a single Coin;"
Processes and materials improved in the nineteenth century (and in 1795), but Scot's description of the difficulties in the hardening processes (done by the coiner/asst, not the engraver) was still a problem.
Scot included "tempering" in his report. Tempering reduces the brittleness of a hardened die, and increases the toughness. It is done after hardening, by heating the die, but not to the same level of annealing/hardening (probably 400-600F). I can tell you from my day job, that the heat treating of metal in industry is still an imperfect science.