AG115M is the alloy from legor which is mixed with silver to give
sterling silver. The sterling silver is cast & the jobs are then
processed using centrifugal disc finishers. The process involved
is wet grinding using cermamic cones & pyramids. corn cobs, &
walnut shell susequently. The problem with this is the prong get
damaged. We have now started using age hardening process for
hardening the pieces for avoiding the scratches. We are also
planning to coat it with polymer based liquid to avoid the tarnish
Umesh - I would offer the following comments from experience -
The centrifugal disc finishers are really tough on silver. If you
have small easily bendable parts such as prongs, the force of the
disc finishers will distort them when used in batch. They are also
hard on fabricated work with fine silver bezels.
These are the ways that I would suggest around the problem - if you
must use disc finishers for silver, you need to fixture your pieces
so they don't impinge on each other or the sides of the container. Or
you can run very small batches to avoid impingement. An easier answer
would be to use a large vibratory tumbler. The vibratory tumblers are
gentle on sterling, and I've never seen them damage a prong. For cast
pieces, I'd use two step process - medium and then fine abrasive.
While I know the vibratory tumblers take longer - in the range of 4
hours each cycle, you can put an enormous amount of work in a large
vibratory tumbler. Disc finishers require much smaller batches and
when you figure the unloading and cleaning time for small batches in
the disc finisher, the time shouldn't be such a concern. You also
avoid the ongoing maintenance of disc finishing - all the cleaning
to avoid getting bits of media stuck under the spinning disc.
I don't have a problem with steel in a rotary tumbler damaging
parts. Or in a properly loaded vibratory tumbler either.
As to hardening the silver to avoid damage - a research project that
I worked on with Gary Dawson and others for the Santa Fe Symposium a
couple of years back showed only minimal surface depth hardening. Not
enough to help prongs. If you are using one of the new-tech
sterlings, it is possible to increase hardness well beyond regular
cast material, but not enough to help prongs in a disc finisher. I
would be interested in your experience in age hardening - are you
using heat or what?
An alternate finishing method for you might be to try the new dry
medias from Diamond Pacific. My experience is that they finish
beautifully in a Vibra-sonic machine and not in other devices. The
run times are significant - measured in days. Their dry media with
50,000 diamond does work well for cleaning everything in a retail
environment - jewelry set with everything - opals, amber, pearls -
but run singly in a machine for 20 minutes - to remove light tarnish
and clean. Again, impingement is a problem - thus the advice to run
one at a time at take-in. This could be a quick finish for problem
pieces in a production environment.