"Sintered" Another questionable term in numismatics.
RogerB
Posts: 8,852 ✭✭✭✭✭
While some gather background on the terms "wire edge" and "wire rim," here's one that is both modern and completely wrong. Yep, not a suggestion of accuracy.
This ersatz term is "sintered" or "sinter."
First, no U.S. coin has ever been made from sintered metal. None. Zero. No U.S. coin has ever been intentionally sintered. None. Zero. No U.S. Mint has equipment to sinter metal or coins or even a lunch time panini !
The Philadelphia Mint made a few Martha Washington test pieces on compressed and sintered powdered titanium planchets provided by Gould, Inc. in 1976. They have bright, slightly granular surfaces. That is the limit.
Background --
Some metals are very difficult to work using conventional melting technology. (A few details will be in the forthcoming Inco private pattern article.) By converting the metal to a fine powder, then compressing the powder, and then heating it to a temperature below its melting point (sintering), the metal can be formed and later machined into useful shapes. This includes coin planchets.
This is the ONLY coin making aspect related to sintering. Since there are no U.S. coins made from powdered metal, no U.S. coins are or ever were made that used sintering. (Some Canadian coins were made from powdered nickel. This was sintered in thick sheet or bar/billet form then cold rolled.
Confusion likely occurred because some had noticed a few coins that had been subjected to excess heat after manufacture. This produced was is commonly called "fire scale" on copper, but is more generally known as surface oxidation or "burn." It's a defect - nothing more. You can make your own by putting coin in a yellow-gas flame (too much oxygen) or low in a campfilre but away from the 'Smores. 
Comments
I have what I believe is a so-called sintered planchet (or improperly annealed) on a Sac $ but it is a dark starburst pattern, not a uniform dark color that covers the entire coin. Has anyone ever seen one like that? I know it is original as I pulled it out of a roll of new $ coins from the mint.
I will try to dig it out for a photo op.
Are you trying to bring numismatics and actual metallurgy into the same conversation?
Danger, danger!
Using the term "sintering" incorrectly is probably one of the lesser offences.
I like lamination errors ......
I have a Sac proof that looks something like that - assumed it was a finger smudge...
so what you are saying is that the Mint has never procured any planchets made from powdered metal by an outside supplier??
That is a mechanical error , label is supposed to say sinister. You can tell by the positioning of the infant that that particular Sacajawea is left handed
Roger,
I agree with you and know that specific words communicate something specific, As to this term, from what I've seen, the interior of these coins is normal so the darkening is caused by some outside factor that has nothing to do with the atomic arrangement of the metal.
As it was explained to me, during the entire minting process metal waste products in the form of flakes, dust, and particles are produced. These can and do contaminate "stuff" and can produce a dark color like an oxidation on the surface of a coin. I'm sure that both HEAT and CHEMICALS can also cause the discoloration of metal at the Mint.
Perhaps struck on a discolored planchet or stained coin may describe the effect we see better but Who Cares?
Lots of numismatists come along and give neat names to things. Ever hear terms like "spider-web," "mud-cracked," "EM?" The important thing to me is that the error guys know what a "sintered planchet" is when they see it.
PS These coins came in original rolls from the mint, interspersed with normal pieces. Against my better judgement, I just put some EZest on the rim of one of mine and the discoloration came off. Mine was not as dark as the one imaged above. I'll need to get a really dark on to try the same. If I recall, the dark ones do not change much.
Interesting that some of the slabs have "sintered" in the description. Shows you what can happen when things are left to the pros without question.
"A dog breaks your heart only one time and that is when they pass on". Unknown
Interesting !!!
"make (a powdered material) coalesce into a solid or porous mass by heating it (and usually also compressing it) without liquefaction. https://en.wikipedia.org/wiki/Sintering
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Are you sure "sintered" is not the same as "centered"? "That baby sure is "sintered" in that plastic holder"!! or "No doubt it is a proof coin; just look at that cameo "sinter". OK - I am outa here'
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Are you sure "sintered" is not the same as "centered"? "That baby sure is "sintered" in that plastic holder"!! or "No doubt it is a proof coin; just look at that cameo "sinter". OK - I am outa here'
With 3D printing of powdered metal in a binder, sintering (correctly used) may become a more common term. But not for coins (yet?)
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Author: 3rd Edition of the SampleSlabs book, https://sampleslabs.info/
I'm not clear on what you are asserting, so I'll try to break down what I believe to be your argument.
We know that planchets made through a sintering process exist.
A planchet is not in and of itself a coin.
A final product, a coin, has never been itself sinetered directly, with the aspects of what makes a coin NOT be just a planchet (i.e. a raised or incuse design).
Therefore, a coin does not exist that has been sintered?
And FWIW, I can print a coin on a Markforged Metal X 3D printer. Binderized metal powder is extruded, layer by layer, until the design is completed, somewhat oversized to the specs of the final product. The "green" part is first chemically debinderized, then introduced into a sintering oven, where it regains roughly 99.7% of the original base metals' properties, and shrinks within tolerance. Voila, a sintered coin.
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Which begs the question that if a raw planchet is sent through the minting process and escapes being minted (thus retaining the qualities of being a planchet) and is released accidentally into circulation with all of the other "business strikes", is it a coin?
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I don't think we ever satisfactorily decided what they called the first three sinters.
Upon further review, I should not undertake to speak to issues like this so close to happy hour.
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Gosh, going back to my early young years working in the “Preforming” department in a Carbide facility we “machined” ingots (pressed, porous powered carbide alloyed with other metals and wax where it looked and machined like messy/dirty graphite). We made whatever the customer wanted - carbide film cutters for the movie industry, oil drilling wizzers, carbide bearings, speciality pieces. Once we completed the rough product form, it was then “sintered” (heated) in a vacuum chamber, cooled and moved on to the fabrication department for grinding or EDM or other machining. The lab later tested it’s “Rockwell hardness”.
Something like that.....
Enjoyed numismatic conversations with Eric P. Newman, Dave Akers, Jules Reiver, David Davis, Russ Logan, John McCloskey, Kirk Gorman, W. David Perkins...
RE: "We know that planchets made through a sintering process exist."
This is incorrect. The U.S. Mint has never had equipment or the need to sinter powdered metals. Cold or hot rolled metals are not "sintered."
Use of the term "sintered" for ANY U.S. coin is false and entirely defective. Application to U.S. coinage implies that something occurred which did not, and never did, happen.
Whoever applied "sintered" to any U.s. coin did not know what they were doing. There was likely no intention to mislead, just ignorance and a neat sounding word.
I agree @RogerB , and since I have a background that includes some metallurgy, I always wondered why this term was applied to coins with a discolored surface. I thought then, and still do, that the term was applied in the mistaken belief that 'sintered' meant 'heated'...and thus the darkened surface. Sintered metals do have applications elsewhere.... just a bit of research will show usage. This is a clear case of misapplied terminology.. though I am not sure it can be corrected at this late stage since it is even on labels. Cheers, RickO
There is no "Sinter Klaus" in Numismatics!
I've used that term (apparently incorrectly!) for at
least a few decades, both in my own description
of coins, and for PCGS.
Since Roger told me, about a year or more ago, that
the term wasn't correct, I've stopped using 'Sintered'
in the description for PCGS, and my own raw coins.
Since then, I only use the term 'mis-annealed planchet'
So what do I do with all my PCGS Sintered Planchet Slabs .......... LOL !!!!!!
Unless one saw the supply chain procurement records for what was eventually delivered to the Mint as raw stock, one wouldn't know for certain whether the raw stock had been fabricated through a sintering process. Other than that your point is well taken. Anyone want to buy a 3D printed, truly sintered coin?
Check out my current listings: https://ebay.com/sch/khunt/m.html?_ipg=200&_sop=12&_rdc=1
so the argument is a little clearer now. though a coin may have been struck from a sintered planchet a grading service shouldn't call it sintered, it can only be called that if it is struck and then sintered? that seems sort of like splitting hairs.
What is actually happening to these coins? I am not a metallurgist.
I thought I heard these coins cooked too long in the annealing process and another metal (like copper) got transferred to the surface. (I may be totally wrong on this, just what I thought I heard)
Can someone with knowledge of the science of metals please explain why my coins looked the way they do.
back in the 70's and 80's when I was getting started as a Tool and Die maker we used a lot of CPM M-4 tool steel. my recollection is that it didn't look any different than standard bar stock either before or after machining and heat treatment.
After reading all of this....one can KIND OF see where the use of the term sintering came from.
If during annealing, a foreign substance attaches itself, and "becomes one" with the planchet, you could say, it was sintered to it. The heating without melting component is there....But the pressure component would be missing....
Now, that's not the actual definition of sintering that we have read here, as an intentional process to create a solid metal. But the term might have a colloquial use in the metallurgy business for contamination that takes place during a heating process(?)
All that being said, I agree that the term sintering gives the wrong impression, but don't know what better term might be used. Contaminated planchet? Discolored planchet?
Older mind documents refer to "burned" coins and "fire scale" on copper. The coins are clearly damaged in some odd way, and by something not part of usual production. Otherwise there would be lots of them. It almost is certainly a post manufacture source, also. Did anyone ask the Philadelphia Mint folks about this?
RE: "so the argument is a little clearer now. though a coin may have been struck from a sintered planchet a grading service shouldn't call it sintered, it can only be called that if it is struck and then sintered? that seems sort of like splitting hairs."
Nope. No US coins were ever struck on a sintered planchet. Thus, they cannot exist.
The Gould samples were made on planchets composed of compressed powder, sintered, then stamped.
Real "sintering" is performed in an oxygen-free furnace. Otherwise the metal simply oxidizes, gets ugly and useless.
While I would never disagree with the great RogerB, as Mongo just pawn in game of life:
I have had Sintering operations for years, and it is NOT powered metal, but a post etch aluminum final die to package interface process, brief synopsis as follows:
.1µm backside aluminum deposition/sinter
a. Prime wafers using HMDS
b: Spin OGG825 photoresist
c. Hard bake wafers for 30 minutes at 120 °C.
d. Short BOE etch to remove backside oxide.
c. Load wafers into sputter tool
d. Sputter aluminum at 1 kW, 15 cm/min, 10 mTorr.
e. Strip resist in oxygen plasma
f. Sinter at 400 °C in forming gas
This is critical for silicon detectors with low reverse bias currents with dopant ions to 20 – 100 keV . The aluminum is not reflowed, but there is a crystalline structure alignment.
There is also Direct Sintered aluminum nitride which is used in applications requiring high thermal conductivity and electrical resistivity with extreme temperature fluctuation, like high-intensity discharge lighting, but I am not familiar with the process, other than it has been reviewed by some of my staff.
Yes, you are correct. However, those are specialized uses of the technology.
I was referring only to Gould and other companies that used it for planchet preparation from powdered metals. Gould also made a few aluminum pieces from powdered metals.
The point is that no sintering technology was ever used at any US mint for any purpose. Therefore there could never be any sintered planchets or coins.
I will agree and add to RogerB:
Real "sintering" is performed in an oxygen-free furnace. Otherwise the metal simply oxidizes, gets ugly and useless.
From what I remember, (I could have this process partially backwards) sintering at the carbide facility was done at high heat to fuse cobalt, then again heated under a vacuum for a specific timeframe. Naturally, the dimensions changed slightly.
Enjoyed numismatic conversations with Eric P. Newman, Dave Akers, Jules Reiver, David Davis, Russ Logan, John McCloskey, Kirk Gorman, W. David Perkins...
Ignore this post as I didn't read the complete thread before posting.
The US Mint does not strike coins on sintered planchets.
Not quite. A coin made OUTSIDE the US Mint by a private manufacturer may be struck on such a planchet. Our coins are not.
There are many good technical articles and papers on the general process of sintering, along with others on specific uses.
A big advantage of powdered metal technology is the ability to create composite materials from materials that cannot normally be combined. See the articles for details.
Also, my research article on Gould, Inc. private pattern pieces has a section discussing Gould's approach including diagrams. It will, I hope, be helpful to collectors.
Forgot to mention that the three metals pictured are: titanium, copper and nickel. All pure or nearly so.
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