Tribology! - ok - lubricating blanks at the US Mint
MsMorrisine
Posts: 36,066 ✭✭✭✭✭
It is written:
http://nist-takingmeasure.blogs.govdelivery.com/make-mint-using-measurement-science/
Pay, and you can be blinded with science:
http://www.tandfonline.com/doi/figure/10.1080/10402004.2013.797530?scroll=top&needAccess=true
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I worked with some tribologists when I was at General Motors - mostly wheel bearings and internal engine components.
They are an interesting breed.
“In matters of style, swim with the current; in matters of principle, stand like a rock." - Thomas Jefferson
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Very interesting post MsMorrisine. I just reposted your thread on another thread that is currently very contentious; "The Sun and the blue-toned rooster". The use of lubricants in the minting process is a possible explanation of toning in IHC proof coins that exhibit many shades of color, including blue. Some believe this toning was coin doctored and some believe this coloring is due to environmental causes. I have posited that die lubrication could be a potential cause for the toning of proof IHC's whereas MS IHC's do not seem to exhibit this toning, possibly to difference in the die lubricant.
Please vist us there as your input might be significant.
OINK
Check "From Mint to Mint" for more information on lubrication of planchets.It was and remains normal practice.
That first article is the total of my knowledge!
It is quite amazing they are down to single molecule thickness lube and a non-STD process then BOOM die life goes up 300% instead of finishing earlier.
It's called "From Mine to Mint" , but don't tell the author !
A very good book !
R.I.P. Bear
Yeah -- I won't tell him.
Fascinating!
If you look at U.S. Mint sets from 1968 to well into the 1970's, you will see that the copper-nickel coins are typically discolored from the oil that the mint employees used to spray on the bins of blanks. Then at some point (I forget when) the discoloration stops but the coins look kind of beat up.
In 1981 I was accompanying a group of ANA Summer Seminar students on a tour of the Denver Mint. We were downstairs in the area where they were packaging the Denver coins (and S-mint SBA dollars) in the plastic sleeves. I wandered into the next room and found a small cement mixer and a stack of 100-pound(?) bags of dried crushed corncobs. I casually asked our guide what this was for, and he said that the coins came down from the production floor covered with oil, so they would dump each bag in the cement mixer, add a few scoops of the dried crushed corncobs, and tumble the coins until the oil was removed.
I published this information and, no doubt by sheer coincidence, the Mint suspended making Mint Sets for two years.
TD
From the Tribology thread on this forum CaptHenway posted:
If you look at U.S. Mint sets from 1968 to well into the 1970's, you will see that the copper-nickel coins are typically discolored from the oil that the mint employees used to spray on the bins of blanks. Then at some point (I forget when) the discoloration stops but the coins look kind of beat up.
"In 1981 I was accompanying a group of ANA Summer Seminar students on a tour of the Denver Mint. We were downstairs in the area where they were packaging the Denver coins (and S-mint SBA dollars) in the plastic sleeves. I wandered into the next room and found a small cement mixer and a stack of 100-pound(?) bags of dried crushed corncobs. I casually asked our guide what this was for, and he said that the coins came down from the production floor covered with oil, so they would dump each bag in the cement mixer, add a few scoops of the dried crushed corncobs, and tumble the coins until the oil was removed.
I published this information and, no doubt by sheer coincidence, the Mint suspended making Mint Sets for two years.
TD"
It appears that the Mint has always used lubricants in the process of minting coins, probably because it makes the dies last 3x longer. And then at one time they were removing the residual on the coins by tumbling them in a "cement mixer" with crushed corn cobs to remove the residual oil. Certainly they would not tumble proof coins in a cement mixer, but how do they remove the residual oil from proofs? Maybe with acetone?
Fascinating.
OINK
I suppose it depends upon what they are striking. For silver eagles [at least back in 2011] the purpose of the lubricant was to facilitate feeding of the blanks into the dies. It doesn't appear that it was removed after the coins were struck. IIRC from other sources, the useful life of a die is around 100,000 coins.
https://youtube.com/watch?v=86WEutE1RCE
@BAJJERFAN..." For silver eagles [at least back in 2011] the purpose of the lubricant was to facilitate feeding of the blanks into the dies."
I wonder if that had/has anything to do with the milk spot issue??? Cheers, RickO
I don't believe so since the spots are most likely silver chloride. The PCGS sniffer might be able to detect the presence of a foreign substance. One could also wash a bunch of coins with hexane and collect the washings and strip/evaporate the hexane off and evaluate the residue. Or check the Mint's purchase records to see what lube/s they're buying.
@BAJJERFAN ....And yet, no seems to have done this....Cheers, RickO
imo. the lubes/grease etc used over various periods have both contributed to and prevented color and/or toning in general.
if you look a LOT of toned morgans especially, but some barber, seated etc, colorful toning will abound until it hits big brown patches of what i presume is mint grease to prevent flans from sticking to dies and it may be multipurpose grease. it could be partially due to the "thickness/amount" of those particular coins, where as the grease that would obviously then "stick" to the obv/rev dies would slowly wear off and perhaps once it was thinned out enough, would permit colorful toning.
i wonder if anyone has tried this removing grease/lube/haze from copper on morgans with ms70 or similar chems to see what is under the brown stuff w/o losing the existing color toning. there are plenty of minor toners to test something like this on, although i'm sure its already been done.
.
I have just finished reading Tony Ying's three papers in Tribology Transactions. They are well-written, and convincing. He provided clear FT-Infrared spectroscopy evidence for his work, which dealt with copper surfaces in the minting process. Using a trial-and-error approach, he took a common surfactant, [N(CH3)2(C10H21)2]+, and studied two derivatives, one using bicarbonate [HCO3-] and another using the benzotriazole anion. He used these to extend die life by first coating tons of the planchets with thin films of these surfactants. The infrared spectra clearly showed that chemical bonding between the nitrogen in the ammonium group occurred with the copper surface, and that coatings thicker than monolayers could be produced. These thicker coatings quickly deposited surfactant on the dies themselves, as black-looking deposits (probably decomposition products, due to heat). Hence, the finished products emerged from the Mint press used with a layer of surfactant already on them.
RMR: 'Wer, wenn ich schriee, hörte mich denn aus der Engel Ordnungen?'
CJ: 'No one!' [Ain't no angels in the coin biz]
Interesting. Maybe not germane to this discussion, but years ago I used to soak photographic prints (gelatin silver) in a benzotriazole solution which imparted a slightly blue, "cold" look to them. Nice for scenes of ice and snow.