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Heat work hardening copper wire


#1

Hi Everyone,

A quick question for someone with niche abouta prototype
I just made. It is a fine hand fabricated chain of pure (drad soft)
copper wire. I welded all of the links with my tiny pulse arc
welder.(#1 tip 55 v). I tried tumbling it when it wasn’t as long as
it is now & there were some links I had to repair. It was just a bit
to softand the links vary in size (1/2" to 5/16" d) so it is not a
dense design.

I have used my oven to work harden very delicate silver & gold
pieces that would not fare well shot tumbled or hammered. My
thinking is to work harden & then tumble it in fine walnut shells
for finishing. Does anyone know the F temperature and time needed to
work harden ? Or have an alternate idea?

Eventually if it pencils out I want to make this in finer metals.

Thanks,
Eileen


#2

I have long been of there belief that you can’t harden copper any
way but by work hardening. I may be mistaken. I have successfully
harden copper to a small extent Ina tumbler. But it has been very
aggressive tumbling with large course media. (I have been tempted to
try it in a cement mixer with round gravel, not kidding)

Good luck with this. I’ll follow this thread.

Don Meixner


#3

Hi Eileen,

I work a lot I mean an extreme amount in copper. First forget
tumbling with walnut bits. Get some stainless steel shot. The mixed
variety.

After hundreds of thousands of copper ornaments I will say it again
get the stainless steel shot. Temperature unless you have it really
clean can cause small bits of the oils from your hands to turn a
funky brown. It may only be in the crevices but you will know. Second
you have to avoid the tangling that can happen to chance. I get the
biggest flyffiest pipe cleaners and thread it through my chain, using
my flat nose pliers to twist it and flatten the twisted end back on
itself. It helps to keep the chain from kinking and tangling. And
here is another bit that most won’t agree with me on. Put your chains
in the tumbler and forget about timing it.

Unless you have left it there for half a day. a few hours you would
be surprised how much it will improve copper things. silver and gold
never do that. Copper is a beast unto itself.

Now for the chain breaking, I would want to see the breaks. It may
not be the tumbler, but the welding you are doing. I use the high
copper bearing solder from Rio. I again after hundreds of thousands
of ornaments have found ways to deal with and copper. In fact when I
travel I just use a goliath sized hand held plumbers butane torch. It
is rare that something does break, but when i inspect it, I can see I
didn’t spend enough time letting the solder flow properly. I do make
mistakes, but I learn from them.

I use to heat harden the copper when I would polish up plates for
photographic needs. I don’t do that any longer.

Aggie sweltering in Florida this summer.


#4

Eileen,

Does anyone know the F temperature and time needed to work harden ?
Or have an alternate idea? 

None of the pure metals can be hardened via heating. Not pure gold,
nor pure silver, nor pure copper, and many more.

The heat treatment is not actually work hardening. work hardening
happens because the crystals that make up the structure of the metal
become distorted, and over time, additional distortion becomes harder
to do because the boundries between crystals are less able to be
distorted than the crystals themselves, and with work hardening,
those boundaries become stretched. They then resist additional
distortion.

With heat treatments, what generally has to happen is that the metal
consists of two or more elements (metals or other), and with heating,
one or more of those metals becomes segregated into separate
crystals, or another structural change happens that makes the result
more resistant to distorting the crystals. With both silver/copper,
and gold/copper, it works because copper is not actually all that
soluable in the other two, so with heating, the original crystals of
mixed metals separates out into discrete copper crystals along the
boundaries between gold or silver crystals. That makes those crystals
and their boundaries much more locked in shape and takes much more
force to then distort those crystals, thus they become hardened.

Because your copper does not have a convenient added componant which
can come out of solution or otherwise change structure with heat, you
cannot heat harden it.

As I noted, actual work hardening requires that the metal crystals
actually distort and stretch. That is difficult to achieve with
simple tumbling because the depth to which that distortion can happen
without actually also distoring the shape of the finished work, is
minimal. So tumbling may compact the surface slightly, making it a
little harder, but the overall wire won’t harden that much.

At this point, with the chain finished, you won’t really be able to
harden the wire much.

There is one method that occurs to me though, but it’s considerably
more involved. By the very nature of the process, an electroformed
copper deposit comes out of the electroforming/electroplating bath
already quite hard, because the process produces a chaotic mix of
small crystals rather than a uniform even structure. So if you were
to put a fairly heavy copper electroplated or electroformed deposit
on the chain, that would effectively increase the hardness of the
chain. electroforming and electroplating are essentially the same,
except electroplating isn’t as thick. Also, if your plating bath is
the type that produces a bright shiny deposit, it will be harder than
the simpler dull plating.

But as you can guess, putting on a thick enough electroformed layer
on your chain is more than a simple process in terms of needing other
equipment.

A better approach, before you make the next one of these chains,
would be to start with hardened wire. Pulse arc welding the links
will give you a small annealed/soft area at each weld, but it will be
small, not enough to affect the overall hardness of the chain. You
could harden the copper wire by buying it hard already, or by work
hardening it. You can do that by starting with heavier wire, and
drawing it down with a drawplate. You’d have to reduce the diameter
of the wire by about 50 percent to get a good workably hard wire,
though lesser reductions will help too, just by less. Even just
putting one end in a vise, the other in pliars and giving it a good
sturdy pull to slightly stretch it will harden it a little. But just
a little, though it’s enough to notice. The other way, if your wire
is already the right diameter, is to twist it. Put one end in a vise,
the other in the chuck of your flex shaft or an electric drill, pull
it straight with just a little tension, and let the drill twist it.
You’ll see a faint twist striation pattern on the wire so you can see
how much it’s twisted.

It will take more than just a little twisting to get it reasonably
hard, but this doesn’t much change the shape of the wire outside of
that surface texture it will form. Either way, once the wire is
hardened, then make your chain, and with this, is should then be hard
enough to resist the steel shot tumbling which will nicely clean up
that faint twist pattern if you wish.

One final option is to use an alloy of copper that CAN be heat
treated. There is such an alloy, called Beryllium copper. It’s made
for use in manufacturing springs. The down side of this is that it
can be toxic to work with. I don’t recommend this route for jewelry
if it will be in contact with skin.

Back again to the subject of heat hardening (or as it’s more
properly called, age hardening or precipitation hardening). Not all
alloys of even two or more metals will do this. It requires that, on
heating, one or more of the alloy componants seperate out from the
others. Usually, this requires that it is not fully soluable in the
other/parent metals. This is true with silver or gold alloys that
contain copper, as the copper is not fully soluable in the others.
But it is not true with an alloy of gold and silver, since each is
fully soluable in the other, and heating causes no separation of the
two, just annealing. As a general rule, normally the only way to work
harden metal is to work it, to distort the shape of the crystals,
which is why it’s called work hardening. Various forms of heat
treating to age harden or percipitation hard metal alloys differ
with the different alloys, and are easily more of a subject for
confusion because it’s confused often with the totally different
process of heat treating steels which happens due to a totally
different type of structural change in the steel, from what happens
with our non-ferrous jewelry metals…

Hope this helps
Peter Rowe


#5

Peter,

I recently tried to reticulate Copper, is that possible at all? As I
read your on Work Hardening, I think it is the missing
"other" which would melt and move with the flame. Would
electroforming help?

Hugs
Terrie


#6

Thanks Peter,

Your knowledge adds alot. Its too bad that this prototype can’t be
hardened easily, but it was just to figure out design, materials &
fab time. I had a large spool of the 24 ga copper, so I used it.
Ilike the idea of the berrylium copper as a useful alloy when copper
would be appropriate.

Eileen


#7
I recently tried to reticulate Copper, is that possible at all? As
I read your on Work Hardening, I think it is the
missing "other" which would melt and move with the flame. Would
electroforming help? 

Usually, the idea with reticulation is to build up a surface layer
on the metal that has a higher melting point, so it can retain
integrity as a thin surface film on the metal while the metal mass
underneath, melts and flows around. That thin film then prevents the
melted metal from smoothing over as it would do if melted all the
way, and that thin surface layer is then wrinkled and distorted as
tne metal underneath moves around, giving you the reticulated
texture. Normally, the way to get that surface layer is repeated
heating and pickling of metals where an alloy exists that will
oxidize, and pickling removes the oxide, so repeated heating and
pickling removes one componant of the surface layer, changing it’s
composition and raising it’s melting point. And example is
reticulation silver alloys, with something liek 20 percent copper,
so that with repeated pickling/heating, the surface copper is
removed. The surface then has higher silver content. You can do this
with other metal alloys where pickling or some other process
selectively removes part of an alloy, leaving a "depletion gilded"
surface with higher melting point.

Trouble with copper is that you’re not changing the composition of
the surface. I suppose it would be possible to get enough of an oxide
layer going that it might keep a surface layer, but you’d have to do
your reticulation with an oxidizing flame so as to keep the surface
oxide. I don’t know if this actually would work.

Suspect it probably wouldn’t. For one thing, copper is rather high
melting, and this would be difficult to control.

There are other ways to get a surface layer that is higher melting,
which can work for reticulation. electroplating/electroforming is one
of them. But you’d be electroforming a surface metal layer that needs
to have a higher melting point than what you’re plating for it to
work. That, and it also has to be a surface metal that will not try
to form a eutectic alloy or otherwise would combine with the base
metal underneath to melt lower. I don’t, off hand, know of something
that would work well on copper, though there may well be.

But hardening the metal does not much change the temperatures at
which it melts for most metals (all metals, perhaps, but I’m not
certain)

If you want to reticulate something easier, and still cheap, try
brass. You can build up a decent copper layer on the brass via
depletion gilding, and that can be reticulated, though it doesn’t
seem to work as well, at least for me, as do the silver/copper alloys
tuned to reticulation.

Peter


#8
Ilike the idea of the berrylium copper 

It’s interesting, yes. But don’t ignore the toxicity involved.
Especially as regards things like inhaling polishing/grinding dusts.
Also, that’s a more costly option. Simply work hardening your wire
before forming the chain links is not hard via twisting, as I
described, and would solve your problem.


#9

Peter,

Just as expected, your explanation is spot on. Guess I will get the
skin effect I am aiming for by Roller Printing onto annealed/softened
Copper. I have never been a fan of smooth shiny anything.

In my Expressive Arts class, we have created a 3D “Tree Of
Hope/Life,” I’m having fun creating leaves. Bent wires for the first
couple and affixed variety of materials to form a leaf. As all
participants are post cancer, we cannot use aerosols for fixatives,
getting around that has not been easy. I mull that over all the time.

Thanks and Hugs Peter,
Terrie


#10

Thanks, Peter, for your remarks on the technical problems of trying
to reticulate copper. Brass does reticulate, and nickel-silver is
even better. No need to build up a special surface layer at all.

Judy Bjorkman


#11

from a metallurgical point of view, Peter Rowe has it pretty much
spot on.

metals deform via a mechanism called dislocations - where a line
defect moves through the crystal.

heat treatment of an alloy works by introducing tiny particles into
the metal that hinder the movement of the dislocations. some are
really really tiny, a few atoms thick. No alloy, no defects.

The crystal size also inhibits the deformation (and hence the
hardness) - the smaller the crystal the less distance a single
dislocation can move.

if you deform a metal enough, the dislocations all bunch up on the
grain boundary, making it more disordered. ALso the grain gets
elongated. At some point the grain breaks in to smaller crystals, in
part because dislocations tend to form along the same path (because
they have a common start point/dislocation creation defect).

If you heat treat a distorted grain you get a lot of the
dislocation/grain boundary mess re-ordering, and often
reconfiguration of the grains - they grow bigger.

Work hardening makes smaller grains with disordered grain
boundaries.

precipitation hardening (heat treatment) stops grains deforming
easily by trapping the deformation mechanism.

annealing undoes all the work hardening mechanisms - and can also
grow precipitates bigger than optimal for hardening, undoing a lot of
the effect permanently - unless it’s annealed/soaked again well above
the heat treatment temperature…

shot peening works the surface, reducing grain size and increasing
surface hardness. It is only a very thin layer. (Most materials
engineering is about surfaces… bulk properties are boring, but a
lot of magic happens at surfaces)