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Rotary Tumbling - as a work hardener


#1

Hello,

It’s my understanding that the hardening effect is only skin deep.
That is, the surface of the metal being tumbled is hardened, but the
effect does not extend to the interior of that metal.

The variables:

Thickness of the object-My guess is that a very thin gauge of metal
would be hardened through, but a heavier piece would not.

Duration-The duration of the tumbling process might increase the
depth to which the metal object might be hardened, but still, this
would not extend through the entire object.

Type of shot-I would welcome input on whether the type of shot would
effect the completeness of the hardening.

Quantity of shot- ditto

Size of barrel- ditto. the size of the barrel relative to the
quantity of shot and number of objects being tumbled?

Whew,
Linda Kaye-Moses


#2

Hi, I recently used Argintuim silver from Rio Grande. After the
casting, the items were very soft. Big Problem. They were about 1.5mm
thick. They said to harden the silver at about 530F (call them for
exact details). I didn’t have a kiln for that temperature but I did
put them into my magnetic tumbler to clean off the cast junk surface.
When I washed them off after about 30 minutes the items were clean,
shinny and hard enough for the finished product, to my astonishment.

Good luck, Bruce.


#3

Linda - tumbling in steel in a rotary tumbler slightly hardens the
work.

You might notice that fine silver, as in bezels, gets a bit harder
in a rotary.

A couple of years ago, I did some small experiments with some
serious metalurgists on hardening jewelry. The thought was that a
harder surface would better retain a finish and help deter scratches.
When our experiments were measured with some very sophisticated
equipment, the hardening was very superficial.

The tumbler I used for this is a large rotary one turning about 50
pounds of steel shot. Yes, the amount of steel and the size of the
barrel matter.

My experience using this big boy is that it somewhat hardens money
clips, but only when run for a very long time. Most work does not
benefit from running over 30 minutes.

If you are really interested in the details, it was in a paper at
the Santa Fe Symposium about 5 or 6 years ago. Search their archives,
papers cost about $5.

Judy Hoch


#4

Hi Bruce,

I recently used Argintuim silver from Rio Grande. After the
casting, the items were very soft. Big Problem. They were about
1.5mm thick. They said to harden the silver at about 530F (call
them for exact details). I didn't have a kiln for that temperature
but I did put them into my magnetic tumbler to clean off the cast
junk surface. 

It is unfortunate that you did not receive the full details about
hardening Argentium Silver. I am going to email you privately to
find out who told you this, so that I can help inform that person.

It is surprising, because the technical advice from Rio Grande is
generally excellent. The technicians are all fully qualified
jewelers.

The fastest way is an hour at 580 F/300 C and then air cool. However,
it is also possible for heat at lower temperatures to harden. The
lowest possible temperature is 365 F/220 C.

For temperatures in between, you can use a reasonable guess on how
long to heat. It is better to heat a little bit too long than not
long enough. (But do not heat for more than 2 hours.) So, you can use
a toaster oven or any oven for these lower temperatures. A kiln is
not necessary.

Yes, I do find that tumbling with steel shot hardens AS and SS. I
find that heat hardening first, and then tumbling, results in
greater hardness. Also, hardening AS results in greater tarnish
resistance.

I find it interesting that when Judy Hoch studied the hardening
effects of tumbling, science said that the difference is minor. In
my experience, the difference is significant. She mentioned that the
difference for fine silver was more significant than for traditional
SS. So, perhaps it is also the case with Argentium Sterling.

Cynthia Eid
Cynthiaeid.com


#5

Cynthia - the studies were in 2005 and 2009. Papers are available on
both studies for a small fee from the Santa Fe Symposium.

I was not an evaluator, rather a tester. I ran the stuff in my big
tumbler, then sent it off to Stuart Grice at Hoover and Strong. The
hardening effect exists, it simply is not as pervasive as we
anticipated.

Perhaps my description misled you. If it were me, I’d do the
precipitation hardening on AS. It makes a lot more difference than
mechanical burnishing.

You can do both but the heat cycle changes the metal far more, as
you know and teach.

Judy Hoch