Dave, I don’t know who you are asking but…as you are facing
the verticle machine the crucible and waiting flask cradle are
at 9 o’clock. The metal is molten before you grab the flask from
the kiln (hopefully in the immediate vicinity). The springs are
unlike the wind up, or clock like spring found in a horizontal
centrifuge. In the verticle machine there are 4 short and stout
springs that work in concert to yank that arm into action. By
the time the flask, metal, and all have reached 3 o’clock the
story is over! The rest of the spin is cool down time. A
horizontal machine doesn’t reach full velocity for about 1 3/4
revolutions. J.A.Henkel
Thanks Skip for the addition/correction. Deguvest “Impulse” is a
high heat investment and quite easy to use with a whip-mix
machine or Degussa’s similar unit. Skip, I’ve known a couple of
dental techs and they’ve been very helpful. Their thorough
education on casting is something most jewery casters wouldn’t
have the patience for, me included! If it wasn’t for the dental
industry, jewelers would still be in the dark ages slinging hot
metal over their heads! Thanks again. J.A.
John,
I firmly believe that the old adage of “the squeaky wheel…” is
never more truthful than in the two related fields. I just
believe that we techs whine louder and longer than the jewelry
people:). I believe that we also need a greater degree of
accuracy. It is a shame that the manufacturers of our supplies
haven’t been astute enough to see the bilateral application of
their products. This is probably due to the fact that they have
separate dental and jewelry divisions whose only commonality is
the corporate ‘bottom line’. It is incumbent upon us, the
jewelers, crafters, and techs, to make them aware of the error
of their ways.
On density and grain structure, I agree with you. We in
dentistry have been using golds with a super micro fine grain
enhancer for over 30 years. As metal recrystallizes after being
molten, the grain boundaries are repositioned and the likelihood
of a gap is increased dramatically. This gap is the cause of a
thinner portion to appear to work harden quicker. What in all
likelihood has happened is that you had a grain boundary right
in the area that began to work harden and broke at that spot.
Dental golds and silver/palladium and silver/gold/palladium
alloys in dentistry all have these grain boundary enhancers.
Palladium is noted for its poor recapitalization habits and, I
suspect, would not be usable in dental applications without it.
This grain structure is so very important in dentistry because
the finest casting I or anyone can make will let the carries
bacteria waltz through the gap between tooth and crown(cap to
you tyros out there:)) holding hands 5 abreast so it is
necessary to burnish the margin(edge of the metal that touches
the tooth) both in the lab and in the mouth without breaking
or more likely flaking. One gold I used to use that is no
longer made was from Englehardt. It was 75% gold and I think 5%
platinum. It is, alas, no longer made. This metal had the
color of 18kt., was re-castable numerous times without porosity,
and was considerably harder and tougher than 10kt. gold. Very
fine detail like filigree and wax renderings were superbly
rendered and 10 yrs. of daily wear later, looked like new. It
retained its hi-shine for what seemed like forever. A quick
once-over with a polishing cloth and it looked like brand new.
I don’t remember its name but it has been gone for over 25yrs.
To all you folks out there that make marvelously detailed wax
sculptures in not only rings, but also charms and pendants etc.
that expect it to be subjected to more than the usual amount of
wear, dental gold should be considered as an option. it is
groups harder, and much more resistant to deformation, just
don’t try to hammer it a half size larger without a 3 lb. hammer
and an indestructible mandrel:). Because it is harder it will
take a shine that will dazzle you. Plaque(the gummy white stuff
you brush off of your teeth that permits the tooth decay
bacteria to grow) will stick to a not too shiny surface in the
mouth, so the hi-shineability of dental golds is really very
necessary.
Regards,
Skip
Skip Meister
NRA Endowment and
Instructor
@Skip_Meister
10/09/9710:32:38Skip:
I read your long message on the gold boundaries, etc. with great
interest. I read a fair amount in the standard jewelry texts and
I haven’t seen anything like this. . . thanks. Of course, it
brings more questions. I couldn’t see where you entioned what
these grain enhancers are . . . could jewelry casters use them?
The finer grain is better, right? Makes the metal more
workable? denser? Am I getting it?
Do you know of any way of determining which types of alloys are
going to be harder?
The gold you mention . . . was it 75% gold, 20% copper, 5%
platinum?
Hi Jess, Yes you are getting it. I’m not sure what the micro-grain
additive is in the alloy. The alloy I used was 75% Au, 5% Pt,
copper and other metals. These alloys are proprietary to the
mfgrs. but I suspect someone like Markus Ellermeier(where is he
anyway, haven’t heard from him for a while) or a metallurgist
could help us out here. Any one out there? If we don’t find an
answer in the next few days I’ll call Ney(my metals supplier)
and talk to a metallurgist there.
Regards,
Skip
Skip Meister
NRA Endowment and
Instructor
@Skip_Meister
10/10/9715:35:53