Hi Gerry; It has been my limited experience that yes, a smaller
crysal lattice in the metal does result in a stronger and more
ductile metal, as for speed of cooling if I’m casting stones in place
I imeadiatley put the flask back into the oven and ramp down about
200 degrees per hour, (probably a better way but thats the way I was
taught and I haven’t fogged a stone of late.,) My idea of allowing a
flask to cool slowly is to cast my silver flasks at 1150 to 1250
degrees for thin pieces this is quite a bit below the liquidus stage
of the metal (DeOx Silver) a good 600 degrees or more. Then let the
flask cool until there is no visible color on the button, this can
take from 10 min. to as much as 25 if it were a flask with a large
button, some one here on the board recomended placing a just cast
flask on some discarded wax and then covering the button with wax as
well, and I tried it ONCE and only onece, after I got the flame out
and the smoke and residue out of the shop I promised not to try that
again, it’s amaxing how low the flash-point of injection wax is when
placed on an 1600 degree surface.
Now on assumption number 2, I tend to go in a different direction,
My Theroy is that the longer the metal is at it’s liquidus state
which is sometimes near the point of becoming gaseous as with some
of the anti firescale alloys, ( remeber solid to liquid to gas) you
actually want the initial 600 degree for thin parts to 850- to 1000
degree difference to start cooling quickly to stop gaseius
entrapments which will turn into gas pockets and form porosity (or
even worse denditic porosity whilst it can evoke some lovely
patterns reminicent of fine lace agate) Many clients find this
unacceptable. so let your temperature drop a bit at the end of your
burn out cycle. but please remember that different alloys do react
differently,
Number 3
Not so Some how given the difference of the atomic weights and
crystal latice structures of some of the new alloy materials like
Indium, Boron, Silicon and several other modern alloy materials I
don’t think they could help but change the not just the size of the
molecular grain but the lattice structure as well, We have a couple
chemical and Scientific heavyweights on the board, Mr Ballard from
Precious Metals West and our very own Man from Down Under John
Burgess, These gentelmen can actually shed some true scientific
knowlege on the subject. My knowlege just comes from alot of years of
casting and making changes, Though I’m not sure Mr Burgges is up to
it yet. (sure am glad to hear he’s recovering so well)!
Number 4
That sounds so nice and I wish it were always true but alass this is
a less than perfect world, and unless you are operating extreemly
sophisticated closed environment induction melting system it will
happen most of the time, and some times you may get lucky and not
scorch the metaL I’ve used a ker Electro melt with mixed results,
even an old Hoover melting system, and I’ve run Induction systems,
as well as Oxy Accet., Induction has the best chance of yielding a
homogenous mixture, but with care and practice you can get pretty
close with a big gas torch…
( DON’T YOU WISH WE COULD ALL PLAY WITH SILLY PUTTY AND ROCKS FROM
THE SIDEWALKS?)
Kenneth Ferrell
www.shadras.com