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Annealing and Cold Work


#1

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Hi John and Alan,

So, how does hitting silver with a nylon mallet compare to
striking/reducing/raising with a metal hammer, when it comes the
need to anneal? Thanks!

Jim Binnion is Mr. Science - I mean that sincerely, and he can
answer in his inimitable way. On a practical level, you are dealing
with the deformation of metal. More deformation=more hardness. It
doesn't matter, really, whether it's bending, twisting, or
smashing. An exaggeration: if you sit there and pound on a piece of
silver with your finger nails all day long, it will not harden,
because you're not deforming the metal, even though you are
pounding on it. A nylon mallet will harden some - depending how hard
you hit with it - it's not the hammer so much as the bending of your
bracelets that's doing it, though. 

Mr Science here :slight_smile: John you hit the nail on the head of course. Cold
work is manipulating the metal by bending, hammering, twisting,
rolling, drawing etc. When trying to define how much cold work has
been done forging, rolling or drawing are easy to determine you just
measure the starting thickness vs the thickness after working and
you can determine how much stress you put into it. However bending
and twisting are much harder to figure out as they don’t reduce the
section of the work much relative to the amount of work you put into
the metal. Alan, in the process of bending your bracelet you are
compressing the inner surface of the metal and stretching the outer
surface. This does indeed produce significant cold work and the
resulting work hardening and they can possibly require annealing
before you can complete the work. Unfortunately there is no simple
way to determine when you have put enough work into an object by
bending to get an optimum crystal restructuring during the anneal.
So you must rely on your hard won experience of just how far you can
push the metal before it breaks then anneal just before you reach
that point. From my experience a bracelet in most silver and gold
alloys should not need several anneals to bend it round the mandrel.
What you may be experiencing is the stiffening of the metal as it
begins to work harden makes it harder to bend and you may need a
bigger hammer or a different system of leverage to bend the
material.

If you anneal too hot or too often (or both) you will end up with
metal that has an orange peal surface and is not as strong and
ductile as properly annealed metal. This will show up in working and
also in polishing as orange pealed over annealed surfaces don’t take
as good a polish as properly handled ones (correctly annealed and
left in a hard state before polishing).

Hope this helps,

Jim

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550


#2

Hi Allan,

I think we can change the subject heading - lets see if this works!

Work hardening happens when the metal is deformed in some way, the
more the metal is deformed the more it is work hardened. Hammering
with a mallet does not deform the metal much, it will smooth out
kinks which is the same as doing a little bending, and this does only
a little work hardening. If you manage to actually hammer the metal
thinner with a mallet, then the metal is work hardened more.

My rules of thumb for gold and silver:

-for heavy reduction (eg rolling an ingot) anneal after deforming the
metal by 50%.

-delicate bending/forming when fabricating, anneal before forming
even if the metal is only slightly hard. -a sharp bend of 90 degrees
= more than 50% deformation at the bend.

The final product can be more serviceable with a certain hardness
left in it. Eg an open bangle that will be bent by the owner to put
on the wrist should be finished fully annealed; a closed bangle can
be left hardened so that it is stronger and keeps its shape.

Alastair


#3
Eg an open bangle that will be bent by the owner to put on the
wrist should be finished fully annealed; a closed bangle can be
left hardened so that it is stronger and keeps its shape. 

And rings and ring shanks should always be annealed, unless you have
some real reason otherwise…

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