The Minting Process: Planchet Preparation

[nwcs]

The Minting Process: Planchet Preparation

 

In this little exposé of the minting process, I'll explain how metal is taken from strips and turned into planchets ready to be struck into coins. After I explain the process, I'll go into some of the errors that can occur in the process. Before I get started, I need to define a few terms:

 

1. Blanks. Blanks are the discs of metal punched out of a strip

2. Planchets. Planchets are blanks that have a rim added to them

3. Annealing. Annealing is the process of heating metal to soften it

4. Quenching. Quenching refers to a process of cooling blanks after annealing

 

From strip to blank

Most of the metal that the Mint uses comes from outside contractors. The metal typically arrives in sheet form that is rolled up. The sheets are roughly 1300 feet long and weigh between 1,100 and 7,000 pounds. Each lot that comes in is assayed to ensure that the metal composition is correct. This is usually done by clipping a portion of the metal sheet and melting it into constituent parts. The sheets are already the correct thickness for blanking (that is, they have already been rolled and pressed by the contractor before it arrives at the mint, which leaves open the possibility that the thickness can sometimes vary from mint specifications, which results in a thin or thick coin after striking)

 

First, the coil of metal is fed into a blanking press. This is a large cookie cutter that takes in the metal and punches out blanks, then draws more metal to punch out of. The blanks are then carried off to another process I'll describe in a moment. The metal that wasn't punched out is called a webbing and it is chopped up and recycled.

 

From blank to planchet

After the blanks are produced, they are conveyed over to an annealing furnace. This furnace softens the metal and heats it to around 1700 degrees. Then the blanks are slowly quenched and cleaned using soap chips and okite (a brightener). This makes the blanks have a brighter appearance. Usually this process takes around 1 to 1.5 hours depending upon the metal and denomination size.

 

After being cleaned, the blanks are then dried and burnished to a high luster to prevent water spots and to smooth the coin surfaces (which are quite rough after annealing/quenching). It is the bit of roughness left on the blank that you see when a coin isn't struck with enough force to remove it. This can be misidentified as wear.

 

Then the blanks are fed down a path to the upset mill. The upset mill is a machine that has a stationary outside part with a V shaped indentation and an inner spinning disc with a V shaped indentation. The spacing between these two is designed to give the blank a squeeze as it passes through the mill, which gives the blank a rim. The upset mill squeezes a blank by 10 thousandths of an inch. At this point, the blank is now considered a planchet and is then fed down to the striking chamber. If the planchet is destined to be a cent, it is at this point that the copper coating is put onto it.

 

Errors

As with any complex process, there are always errors that take place. The vast majority of these are found at the mint and the resulting coin errors are destroyed. However, sometimes the coins escape the mint. I'll now describe a few of the planchet oriented errors.

 

Unstruck Planchets

Type 1: These are blanks that have no rim and somehow did not pass through the upset mill. These are not as easy to fake as many people think.

Type 2: These are planchets with an upset rim but with no design. These will have no reeding or any lettering on the rim as these elements are only put on during striking.

 

Alloy Mix Planchets

All our circulating coinage is an alloy of various metals. Most of the time these metals behave and mix well, but sometimes they do not mix well. If there are trace elements of other metals in the alloy, the trace elements can create different effects on coins. Many early wheat cents had improper alloy mixing and have irregular streaks and a roughened surface. This improper mixing can also lead to planchets splitting apart or parts of them splitting off.

 

Melting Error Planchets

There are many types of defective planchets. They can have cracks or holes in them or look outright fake. These errors occur in a manner similar to the alloy mix problem.

 

Gas bubble planchet: gases that were trapped during the melting of the metal can produce bubbles on the coin surface

Improperly annealed planchet: If a blank wasn't annealed, or annealed correctly, the resulting planchet will be very hard and not strike up well

Weld area planchet: Sometimes different coin coils are welded together when fed into the blanking process. Sometimes blanks are punched from where the weld took place and leave a rather interesting looking planchet

 

Sometimes when the coil of metal is not advanced correctly into the blanking press, blanks are punched that are irregularly shaped. This can lead to clipped planchets of varying sizes and degrees. Most of these problem coins are caught after the striking process, but not always. Also, parts of the webbing that should have been chopped up and recycled gets through and gets struck as well.

 

Other problems can be found at this stage. For example, pieces of metal can be rolled into the coil of metal at the contractor's site and then get struck into coins. The rollers on the blanking press could etch lines into the coil that blanks are produced from and be evident on the coins after they are struck.

 

So there you have it. A brief explanation of the planchet preparation process and some of the errors that can occur from it.

[nwcs]

Someone on the other boards asked me what my source was. It is derived from "The Modern Minting Process" by James Wiles, Ph.D. Copyright 1997 by the ANA.

[GDJMSP]

One comment - the planchets for the cent are delivered to the Mint pre-manufactured & the copper is electroplated onto the zinc planchets. This is done by a company named Alltrista Zinc Products of Greenville Tenn. which used to be called Ball Corporation ( that company that made all those glass canning jars ).

 

They manufacture all of the US & Canada's cent blanks, as well as for several other countries. They produce over 85,000,000 of them per day.

[PQSeated]

That made for excellent reading, NWCS. When the coins are struck, are they still hot? Also, the reeded edges, are they created by a reeded collar? Thanks for the great post. I enjoyed it.

[nwcs]

True, and I knew that TN produced ready made planchets for the mint. I chose not to mention it specifically because it could get confusing from talking about the mint and the contractors. And the process is still the same, but the location it takes place is different. Thanks for pointing it out, though, for clarification.

 

BTW, I haven't made a pilgrimage up to Greenville yet. They're only about 2 hours from me.

 

Neil

[Oldtrader3]

The only thing that I would add is that: Planchets are pickled (passivated) in dilute sulphuric acid prior to the Oakite wash. This operation stabilizes the surface molecules after the rolling and blanking operations then the Oakite neutralizes any small amount of residual acid still on the coin surfaces. This operation is done to deactivate surface molecules that become more "active" (prone to oxidation) after being worked by the prior operations.

 

Good description. Thanks for posting it.

[nwcs]

>That made for excellent reading, NWCS. When the coins are struck, are they still hot? Also, the reeded edges, are they created by a reeded collar? Thanks for the great post. I enjoyed it.

 

They are generally still a bit warm when they get struck. Mostly to aid in bringing up the design but they have been cooled quite a bit by the time they get to the striking chamber, though.

 

Yes, the reeds come from the collar when it gets struck. The upset mill only raises a rim which makes the coins more stackable as well as helping to extend the life of the coin by protecting the coin's design. When the coin get struck, the planchet heats up and flows where the dies allow it to flow, which is outwards into the retaining collar and upwards/downwards into the die surfaces.

 

Incidentally, this also causes the metal to change its structure a bit near the edge devices and causes the "shadow" effect on some of the devices that toning doesn't always adhere to. From what I understand, this is due to how the atoms realign after being partially melted, moved, and cooled.

 

I'm glad you enjoyed the post. I'm liking the discussions of real things here on this board!

 

Neil

[GP_]

very informative posts! thank you!!

[jtryka]

Great post! I learned a lot from it. It did prompt a question though, how does the mint test and refine the process for different types of alloys? And how has it changed over time? Everyone likes to point out that coins today have a much lower relief than earlier coins, and most including myself assume it was largely due to the change from silver to base metals. But I find that theory somewhat lacking, as many of the early clad coins had wonderful strike characteristics, like quarters from the late 60s and early 70s. And it doesn't explain the differences in strike on nickels, as they have remained the same composition.

 

Thanks for the post, keep it up! I am looking forward to the next installment.

[nwcs]

I'm glad you enjoyed it!. I can answer a few of those...

 

The change to low relief actually happened in 1994/95 when the mint changed their process for hubbing a design from the galvano. A galvano is really a cutsie term derived from the process of creating the master relief from which the master hub is created. A galvanic process was used on a plaster model of the coin design to electroplate it with metal. Then using the janvier transfer mechanism, the galvano's relief was reduced to the appropriate size. Usually the relief was quite full and the master hub would require several impressions into the master die in order to bring in all the detail. This is one of those ways that a doubled die can be created.

 

In the mid 90s, the mint switched to using a single impression from the master hub into the master die which eliminated the doubled die problem and means that the relief has to be a bit lower. Incidentally, mint galvanoes are not metal coated anymore. So when these dies strike the coins today, it creates a different look than in the past. Which is why modern coins not only have uglier looks, but the finish of the coin has some subtle differences from the past.

 

As for the assaying part, I only have a general understanding of how that works. From what I understand, they heat it up to separate the constituent elements and then skim off each metal. Then weigh it according to what it should weigh. Someone who works with metals more would give a much better explanation. The only interesting thing I learned how to count was radioactivity in samples back in college.

 

Neil

[PQSeated]

I think it would be wonderful if you did an early minting process post also. Then we can see the differences between minting coins then and now.

[nwcs]

From what I understand, there has not been a great deal of change since the mid to late 1800s (except in speed and durability). I have a little bit of literature/reference on earlier types of presses. Mostly from the hammered coinage and some screwpress coinage period. But I'll see if I can find out some more. But generally I found myself more drawn to roughly the 1860s and up and ancient coinage so I will do some research on ancient coinage preparation. Would be interesting. I have a book on ancient technology that is waiting on my reading list. May also have some info.

 

Neil