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- From johnmenc@optonline.net Thu May 20 08:47:28 2004
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From: johnmenc@optonline.net
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Subject: Re: HARMON MINT
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The hardness of this alloy is dependent on tin levels and influences=20=20
this alloy on how it should be worked.
Rob Retz's results looking at it from a working industrial hygenist=20
point-of-view we have the tin levels on the wood scrappings being 30=20
TIMES the level of the copper and 10.5 TIMES the level of the zinc=20
levels in this workhouse. This tin situation is not commonplace? Just=20
a thought JS. See below on how high or increasing tin concentrations=20
changes the alloy properties of these bronzes. Just a thought JS ...=20
I find Bob's finding minimally worth investigating...FURTHER?
Copper-Tin Alloys: The Bronzes
Abstract:=20
The important alloys of copper and tin from an industrial point of=20
view are the bronzes comprised within certain limits of tin content.=20
As in the case of the brasses, the addition of tin to copper results=20
in the formation of a series of solid solutions.
The addition of tin to copper results in the formation of a series of=20
solid solutions which, in accordance with usual practice, are=20
referred to in order of diminishing copper content as the =E1, =E2, =E3,=20
etc., constituents.=20=20
The important alloys of copper and tin from an industrial point of=20
view are the bronzes comprised within certain limits of tin content.=20
As in the case of the brasses, the addition of tin to cooper results=20
in the formation of a series of solid solutions. The constitutional=20
diagram of copper-tin alloys is very complex, but that part of it=20
which deals with alloys of industrial importance is reproduced in=20
Fig. 1.
http://www.key-to-metals.com/Article70.htm (go here for this diagram)
Figure 1. Constitutional Diagram of the Copper-Tin Alloys
The addition of tin to copper results in the formation of a series of=20
solid solutions which, in accordance with usual practice, are=20
referred to in order of diminishing copper content as the =E1, =E2, =E3,=20
etc., constituents. The diagram may be summarized as follows:
Percentage composition Constituent just below the freezing point=20=20
Constituent after slow cooling to 400=B0C=20=20
Copper Tin=20=20
100 to 87 0 to 13 =E1 =E1=20=20
87 to 86 13 to 14 =E1 + =E2 =E1=20=20
86 to 78 14 to 22 =E1 + =E2 =E1 + =E4=20=20
78 to 74 22 to 26 =E2=96>(=E1 + =E2) =E1 + =E4=20=20
Further changes on cooling from 400=B0C to room temperature are so=20
sluggish that they only occur in conditions very far removed from=20
actual practice.
The =E1 solution is the softest of the constituents; it may be rolled=20
or stamped cold, but it hardens under this treatment much more=20
rapidly decreases than =E1-brass.
The =E2 and a constituents do not exist in the alloy slowly cooled to=20
room temperature: this is due to successive changes occurring at 586=B0
C and 520=B0C whereby =E2 is resolved into =E1 +=E3 and =E3 into =E1 + =E4.
The =E4 constituent has the crystal structure of =E3-brass. It has a=20
narrow range of composition corresponding approximately to the=20
formula Cu3lSn8 and, like all intermetallic compounds, is extremely=20
hard and brittle. The =E4 -> (=E1 + =E5) change at 350=B0C does not occur i=
n=20
commercial practice, though alloys richer in tin may contain the a=20
constituent, which corresponds to Cu3Sn, and the =E7 solid solution,=20
which approximates to the composition CuSn.
95:5 Copper-Tin Alloy
On cooling from the liquid condition, the solid solution which first=20
forms contains only about 2 percent of tin. Thus the cast metal has a=20
cored structure and the coring is very marked because of the long=20
range between liquidus and solidus; but it may be eliminated by=20
diffusion on cooling more slowly or by annealing.
Any absorption of oxygen occurring during manufacture results in the=20
presence of SnO2 in the alloy, tending to make it brittle. A=20
deoxidizer such as zinc is therefore frequently added. The addition=20
of zinc, as in coinage bronze, causes no change in the microscopical=20
appearance of the homogeneous =E1 constituent. The zinc, however,=20
exerts its deoxidizing effect in the liquid, and slight hardening=20
effect on the solid solution. The structure of a bronze coin shows=20
marked deformation of the crystals. On annealing, recrystallization=20
takes place with subsequent crystal growth. Twinning is a=20
characteristic feature of the cold-worked and annealed alloy.
90:10 Copper-Tin Alloy
This is typical gun-metal, most varieties of which, however, contain=20
a deoxidizer, frequently zinc (e.g. Admiralty gun-metal, copper 88%,=20
tin 10%, zinc 2%). The structure of the cast material depends on the=20
rate of cooling, both through the range of solidification and below.
On account of the wide solidification range of the alloy and the slow=20
rate of tin diffusion, the apparent solubility limit of the =E1=20
solution is well below that shown in the diagram. The cast structure=20
is always definitely dendritic and if coring is pronounced, some =E2=20
solution may be formed at 798=B0C This interdendritic =E2, on cooling,=20
gives rise to the hard =E4 constituent. On the other hand, after slow=20
cooling or prolonged annealing, the homogeneous =E1 constituent may be=20
produced. A chill-cast gun-metal will therefore be very different in=20
structure and properties from one which has been annealed.
85:15 Copper-Tin Alloy
This chemical composition is typical for a number of bronzes used as=20
bearing metals, most of which, however, contain a little zinc as a=20
deoxidizer. It is also the approximate composition of bell metal.
Immediately after solidification the alloy consists of the =E1 and =E2=20
constituents. If rapidly cooled, these are preserved. If slowly=20
cooled, the =E2 (or =E3) is completely broken down below 520=B0C into a=20
complex =E1 + =E4. The =E1 + =E2 structure is being replaced by =E1 + (=E1 =
+ =E4)=20
complex in the slowly cooled alloy. This accounts for the fact that=20
sand castings of this alloy are much harder than chill castings. It=20
also provides the basis of heat treatment method, applied in the one=20
case to bells and in the other to bearing metals.
--- In colonial-coins@yahoogroups.com, johnmenc@o... wrote:
> I am still not very comfortable with this high? tin situation. Will=20
> investigate a bit further ... mixing well and way above average are=20
> two different scenarios such as the the proper lead content in cast=20
> counterfeits which in general has very little leeway for a proper=20
> cast coin to be formed properly. Your definition of impurities in=20
the=20
> ingot stock is exactly my point with this high tin ... how much is=20
NO=20
> GOOD...to be continued.=20
>=20
>=20
>=20
> --- In colonial-coins@yahoogroups.com, johnmenc@o... wrote:
> > I remember several years ago reading a metallurgical article on=20
> trace=20
> > element fluctuations based on re-working the copper such as you=20
> > indicate: Previously struck planchets that have been well=20
annealed=20
> > prior to
> > > restriking generally show almost no details of the undertype. I=20
> > will see if I can track this article down and post here and=20
> SCIENTECH=20
> > eSIG. Thanks again for the clarification/update.
> >=20=20
> >=20
> >=20
> > --- In colonial-coins@yahoogroups.com, JCSpilman=20
<JCSpilman1@C...>=20
> > wrote:
> > > NEW TOPIC - Harmon Mint
> > >=20
> > > John - - et al
> > >=20
> > > In general - copper laminations are usually the result of poor
> > > rolling techniques plus impurities within the ingot stock
> > > remaining from inadequate smelting and alloying. Annealing=20
has
> > > nothing to do with it but only results in a very hard planchet
> > > that is difficult to strike up fully in a single press stroke.
> > > Work hardened previously struck coins that are restruck without
> > > additional annealing are the best example of that problem.
> > > Previously struck planchets that have been well annealed prior=20
to
> > > restriking generally show almost no details of the undertype.
> > > Both tin and zinc alloy well with copper and seldom affect
> > > hardness until the proportions reach a level that the end=20
product
> > > becomes brass or bronze.
> > >=20
> > > Jim/CNLF
> > >=20
> > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D
> > >=20
> > >=20
> > > johnmenc@o... wrote:
> > >=20
> > > > Unquestionably a well run coin club ... small in numbers ...
> > > > but
> > > > focused and hard working. I remember hearing about his Vermont
> > > > Vacationing article and the high tin found in the wood samples
> > > > he
> > > > took at Harmon's Mint. There was some speculation that the=20
high
> > > > tin
> > > > found may be a contributing factor? as to why Vermonts always
> > > > come so
> > > > poorly annealed (i.e.,lamination marks virtually found in=20
every
> > > >
> > > > example). This is a noteworthy find and I will see if I can=20
add
> > > > to it
> > > > from future/past readings. A poor alloy mix such as high tin=20
in
> > > > the
> > > > copper alloy composition would explain this phenomenon.
> > > >
> > > > R.T. anything from your database of hand held XRF post=20
analyses
> > > > with
> > > > Vermonts??? This may have already been discussed??? I believe
> > > > Rob's
> > > > 1994 speculations were confirmed???
> > > >
> > > >
> > > > --- In colonial-coins@yahoogroups.com, Steve Frank
> > > > <taxi_steve929@y...> wrote:
> > > > >
> > > >=20
> >=20
http://www.pdxcoinclub.org/OnSiteLinks/02_25_2003_PressRelease.html
> > > >
> > > > >
> > > > > http://www.pdxcoinclub.org/
> > > > >
> > > > > Ray,
> > > > > I took the liberty of lightening the photo a bit and=20
resizing
> > > > it
> > > > for anyone who may want to keep it on there hard drive. I=20
also
> > > > added
> > > > a couple of links above for those who may find it difficult
> > > > getting
> > > > around the net who might want to see Rob receiving the Past
> > > > Presidents medal from his coin club, and also a nice link to
> > > > his coin
> > > > club....there is a double struck Fugio shown...I would assume
> > > > it was
> > > > his, but he may have gotten a pic from someone here...I don't
> > > > know.
> > > > Seems like a very varied group.
> > > > >
> > > > > Steve
> > > > >
> > > > > Ray Williams <njraywms@o...> wrote:
> > > > > Hi All,
> > > > > The pictures are a little blurry, but I wanted to=20
reshare
> > > > these
> > > > pictures
> > > > > with you all.
> > > > > Ray
> > > > >
> > > > >
> > > > >
> > > > > ---------------------------------
> > > > > Do you Yahoo!?
> > > > > Yahoo! Domains - Claim yours for only $14.70/year
> > > >
> > > >
> > > > --------------------------------------------------------------
-
> > > > Yahoo! Groups Links
> > > >
> > > > * To visit your group on the web, go to:
> > > > http://groups.yahoo.com/group/colonial-coins/
> > > >
> > > > * To unsubscribe from this group, send an email to:
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> > > >
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