2006 SAE 20th Anniversary - Burnished Planchet?

Preface this with the fact that I am a jewelry maker. I KNOW what it means
to "burnish" metal and how it is done.

So, uh, what is the mint doing burnishing planchets? It work-hardens the
metal. Why would they want to work-harden the metal before striking?

What, exactly, are they thinking they are saying when they say "burnishing"
the planchets? Is this a coin term that bears not resemblence to the "real"
term?

Thanks in advance for any comments.

Jonathan_ATC

"Jonathan_ATC" wrote in message
ink.net...
Preface this with the fact that I am a jewelry maker. I KNOW what it
means
to "burnish" metal and how it is done.

So, uh, what is the mint doing burnishing planchets? It work-hardens the
metal. Why would they want to work-harden the metal before striking?

What, exactly, are they thinking they are saying when they say
"burnishing"
the planchets? Is this a coin term that bears not resemblence to the
"real"
term?

Thanks in advance for any comments.

Jonathan_ATC

The way I understand it--could be wrong you know me lol--but anyhow the
satin finish mint set coins are also said to be 'burnished'. What they do
with those is just sand blast some chrome dies. Also with coins minted at
West Point they don't care about how many dies they use up because they
replace them after 5,000 coins--at least 5,000. Each machine there gets more
TLC than any other mint facility. Each technician is specially trained so
that the QC is exceptional. They also have a more rigorous inspection regime
at West Point. They also strike coins more times than any place else--as
many times as they think they need to get hit to produce superior coins.

"bri" wrote in message
nk.net...

"Jonathan_ATC" wrote in message
ink.net...
Preface this with the fact that I am a jewelry maker. I KNOW what it
means
to "burnish" metal and how it is done.

So, uh, what is the mint doing burnishing planchets? It work-hardens
the
metal. Why would they want to work-harden the metal before striking?

What, exactly, are they thinking they are saying when they say
"burnishing"
the planchets? Is this a coin term that bears not resemblence to the
"real"
term?

Thanks in advance for any comments.

Jonathan_ATC

The way I understand it--could be wrong you know me lol--but anyhow the
satin finish mint set coins are also said to be 'burnished'. What they do
with those is just sand blast some chrome dies. Also with coins minted at
West Point they don't care about how many dies they use up because they
replace them after 5,000 coins--at least 5,000. Each machine there gets
more
TLC than any other mint facility. Each technician is specially trained so
that the QC is exceptional. They also have a more rigorous inspection
regime
at West Point. They also strike coins more times than any place else--as
many times as they think they need to get hit to produce superior coins.

They also hand feed those in one by one. They could also be talking about
the reverse proof dies--they'll just sand blast the fields of chome dies
instead of the recesses like they would on a normal proof coin.
Actually it's at MOST 5,000 coins before they swap die pairs out. I hear
they'll swap them out as soon as they can within reason. Then those dies
that aren't total trash might get recyled to another mint facility to strike
many more coins that don't have to be of the highest quality. They'll just
fill in the MM.

Once Upon A Time Jonathan_ATC wrote:

Preface this with the fact that I am a jewelry maker. I KNOW what it means
to "burnish" metal and how it is done.

So, uh, what is the mint doing burnishing planchets? It work-hardens the
metal. Why would they want to work-harden the metal before striking?

What, exactly, are they thinking they are saying when they say "burnishing"
the planchets? Is this a coin term that bears not resemblence to the "real"
term?

Thanks in advance for any comments.

What does "work-harden" mean?


**
Captain Infinity

"Captain Infinity" wrote in message
...
Once Upon A Time Jonathan_ATC wrote:

Preface this with the fact that I am a jewelry maker. I KNOW what it
means
to "burnish" metal and how it is done.

So, uh, what is the mint doing burnishing planchets? It work-hardens the
metal. Why would they want to work-harden the metal before striking?

What, exactly, are they thinking they are saying when they say
"burnishing"
the planchets? Is this a coin term that bears not resemblence to the
"real"
term?

Thanks in advance for any comments.

What does "work-harden" mean?


**
Captain Infinity

Work-harden means that when you "work" metal, it gets hard. Think of a
paper clip. If you bend it back and forth, finally it breaks. If you are
hammering out a bowl made of copper, it gets harder and harder and you have
to anneal it to soften the metal again or you'll crack the bowl. If the
paper clip were not work-hardened, they would not work as a paper clip. Raw
wire used to make the paper clip is burnished in order to make it hard and
inflexible. If you annealed a paper clip, bring it to cherry red and quench
it in water, it becomes so soft you could bend it several times back and
forth before it hardened up in the bend and broke.

When I picture them "burnishing" a coin planchet, I get the image that they
are, for no known reason, making it harder and the dies would not make as
good of a strike.

Can someone tell me where they got the information that these coins would be
burnished? I don't see it on the US Mint site.

Thanks!

Jonathan_ATC

Jonathan_ATC wrote:

Can someone tell me where they got the information that these coins would be
burnished? I don't see it on the US Mint site.

It's in the press release in the "pressroom" at the Mint web site.

In this case I believe the definition of the word burnish is "polish or
make smooth, generally by rubbing". I don't really believe they are
burnishing the planchets to the point where the physical properties of
the metal would be affected.

I really can't see the point of doing this pre-strike. You'd gave to
think that the striking pressure they use would obliterate the effects
of any pre-strike "polishing or smoothing".

This really isn't anuthing new for the Mint....the 5,000 Sac dollars
the Mint used to pay sculptor Glenna Goodacre supposedly received some
type of burnishing. I also believe Sacs in one of the Coin and Currency
Sets may have been slabbed as "burnished"

As a matter of fact, if I remember correctly, I believe the company
that provides Sac planchets to the Mint "burnishes" them....probably
just to shine them up for striking.

Coin blanks used in collector quality coins are cut from sheets of
silver which have been cast, rolled, and rolled several times again.
The blanks are burnished with a water, chemical agent and tiny steel
beads or corncob grit in rotating tanks...or other similar equipment
designed for higher volumes. Then the blanks are annealed in a furnace
to further smooth out the surface.


Jonathan_ATC wrote:
Preface this with the fact that I am a jewelry maker. I KNOW what it means
to "burnish" metal and how it is done.

So, uh, what is the mint doing burnishing planchets? It work-hardens the
metal. Why would they want to work-harden the metal before striking?

What, exactly, are they thinking they are saying when they say "burnishing"
the planchets? Is this a coin term that bears not resemblence to the "real"
term?

Thanks in advance for any comments.

Jonathan_ATC

Blanks which arent carefully prepared can show surface defects even
after strike.


Phil DeMayo wrote:
Jonathan_ATC wrote:

Can someone tell me where they got the information that these coins would be
burnished? I don't see it on the US Mint site.

It's in the press release in the "pressroom" at the Mint web site.

In this case I believe the definition of the word burnish is "polish or
make smooth, generally by rubbing". I don't really believe they are
burnishing the planchets to the point where the physical properties of
the metal would be affected.

I really can't see the point of doing this pre-strike. You'd gave to
think that the striking pressure they use would obliterate the effects
of any pre-strike "polishing or smoothing".

This really isn't anuthing new for the Mint....the 5,000 Sac dollars
the Mint used to pay sculptor Glenna Goodacre supposedly received some
type of burnishing. I also believe Sacs in one of the Coin and Currency
Sets may have been slabbed as "burnished"

As a matter of fact, if I remember correctly, I believe the company
that provides Sac planchets to the Mint "burnishes" them....probably
just to shine them up for striking.

Bad blanks can also wear a die down improperly.

Burnishing coin blanks is soley done for cleaning and polishing.
Burnishing will remove marks on the blanks from the strip rolling,
blanking, and rimming processes, as well as removing any remaining oils
or solutions used on the blanks during those processes.
There are several types of burnishing procedures that can be used. At
the SF mint they use "high energy" centrifugal disc (CD) finishing
machines. These machines have a rotating disc in the bottom of a
"rubberized" bowl / tub. As the disc spins the coin blanks are pushed
up the side walls of the bowl which is designed to cause the blanks
fall back on to the spinning disc. Add burnishing media (typically some
sort of steel shot) and burnishing compound (typically some sort of
mild acidic / abrasive solution) and stir for several min. and you get
bright blanks without work hardening. The blanks and media are removed
from the bowl and seperated over a riddling screen with the media going
back into the bowl. These machines are made by Spaleck, you can see
them here;
http://www.spaleck.biz/seiten/produk...eschluessel=en

Another method is vibratory burnishing. Coin blanks are fed into a
large bowl that has a trough around the outer circumference that is
loaded with burnishing media that is vibrating. There are settings
within the bowl that causes the vibrating action to move the blanks
around the trough as well the amount of "tumbling" within the trough.
Add the burnishing compound to the mix and develop a process time and
again you will get bright blanks with out any work hardening. The
blanks and media are rinsed and discharged uover a riddling screen with
the media falling back into the bowl. Roto-finish is one manufacturer
of this equipment and you can see one of these bowls here;
http://www.roto-finish.com/equip/Rot...on_diagram.htm

The third type of burnishing process is a rotary barrel or rotary
drum. This type of machine is designes for continous feeding where as
the previous machines are designed for batch feeding. These machines
have a large internal like a front load washing machine at home. The
drum can be anywhere fron 4' - 12' in diameter. Inside some drums there
is a helical ridge that moves the blanks and media through the bowl.
Other bowls are angled so the blanks and media move towards the exit.
At a certain length down the drum there are holes that allow the media
to fall out and be recycled back to the start while the blanks are
removed from the drum. I saw several of these in operation at the
Japanese mint in Osaka. Continential Equipment makes this type of
machine and you can see it here;
http://www.continentalequipment.com/drum.htm

Once the blanks exit the burnishing process they need to be dried.
There are 2 main options typically used. First is a vibratory bowl with
a heated drying media, typically crushed corn cob or rice hulls. This
type is normally a batch type process. The other is again a vibratory
bowl but with a high flow of very hot air. The rotary drum machines can
be made with drying sections, but I do not know of anybody in the
minging trade useing one.
By selecting different machines, burnishing media, compounds and
process times a virtual smorgasbord of finishes can be had, or
duplicated from one system to another.

Sean Moffatt
Operations Manager
Hoffman Mint, Inc.