In the spirit of educational threads: planchet preparation
nwcs
Posts: 13,386 ✭✭✭
I sometimes see people post pictures of suspected (or hoped for 
) error coins which are the result of planchet preparation. I thought, what the heck? why not post a little information about how planchets are prepared. There probably is little new here for those of you who have been in the hobby a while but I hope it can be interesting for those of you who may be new to collecting or are just simply curious about this part of the coin making process.
Basically, 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 flat metal sheet that was rolled to proper thickness
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. (One notable exception: the mint buys ready made cent planchets from Tennessee) 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 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.
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 not struck by any dies. 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 (laminations).
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.
) error coins which are the result of planchet preparation. I thought, what the heck? why not post a little information about how planchets are prepared. There probably is little new here for those of you who have been in the hobby a while but I hope it can be interesting for those of you who may be new to collecting or are just simply curious about this part of the coin making process.Basically, 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 flat metal sheet that was rolled to proper thickness
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. (One notable exception: the mint buys ready made cent planchets from Tennessee) 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 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.
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 not struck by any dies. 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 (laminations).
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.
0
Comments
Great post. I learned a few things. Thanks
cool thread man.....very cool
>What is the next stage?
The next stage would be the striking stage. I'll write up a little bit on that one later.
>How did they get the stars onto the $10 indian rim...was it kind of like a reeding process or was it part of the initial strike? Is it one of those things that polite people don't talk about?
As I recall, they used a segmented collar so that they would be "put on" during striking like reeds. In the days before closed collar striking, I believe the legends were placed on during the upsetting stage. But then again, they might have been polite in what they told us.
>How are the planchets burnished?
In the modern process there are baffles lining the dryer so that when the planchets are mixed around to dry, they get burnished during the process.