Back to Ganoksin | FAQ | Contact

Platinum Casting with Ney Centrifugal Machine


#1

Edward, I read with great interest your post on casting platinum
with a Ney Centrifugal caster. We have been casting gold for 20
years, but sending our platinum casting out just as long. In the
last year or so we have had to make 6 to 12 platinum pieces per
month, enough that we have begun to dabble in casting it
ourselves. After reading your post I purchased the GAAB crucible
converter and type A crucible from Rio. I ordered the Supra
investment from Gesswein. I plan on sticking with Plat/Co alloy
for casting. What I am interested in is your thoughts on burnout
cycles and flask temperatures when casting. And any tips on the
melt, casting and quenching? Is there anything we should continue
to send out? I REALLY appreciate you sharing your experience.

Mark P.
WI


#2
I plan on sticking with Plat/Co alloy for casting. 

Mark, Casters using plat/co alloy usually are using it with
induction melt casting machines that can hold the melt either
under vaccuum or under inert gas shielding. Melting pt/co in the
presence of air will cause oxidation of the cobalt, with
resulting porosity or at least, inconsistant alloy performance.
You can do it, but your results won’t be as good as that you get
from sending the castings out. I’d suggest, if you’re torch
melting, to stay with iridium platinium. You get a few more
porosity problems, and sprueing is more critical, but you also
have a much easier time fixing those problems at the bench.
fusing up, with a torch, pits in cobalt alloy isn’t easy. You
just keep getting more porosity in the fused area…

Peter Rowe


#3
I plan on sticking with Plat/Co alloy for casting. 

Mark,

Peter is correct in that you should stick with Pt/Ird to cast
with a torch. If you sprue correctly you can almost eliminate
most problems. Using one alloy gives you a lot more control of
your metal, you can take the button mill it out and fab with it,
re-cast and not be concern with mixing up metals. You can recast
and fab until its gone unlike re-casting gold alloys.

What I am interested in is your thoughts on burnout cycles and
flask temperatures when casting. 

With the Supra you will have to use the following burnout

  1. 350 F 2 hours

  2. 500 F 2 hours

  3. 750 F 1 hour

  4. Increase temp about 400 F per hour to 1650 F and hold for 1
    hour to harden investment.

  5. Lower the flask temp to 850 F for thicker items and 1000 F to
    1100 F for thinner pieces. Hold the casting temp for a minimum of
    1 hour before casting.

And any tips on the melt, 

It is very important to melt the metal as quickly as possible. I
use 65 lbs. for the oxygen and 5 lbs. for propane. The flame
must be an oxidizing flame. Crank up the torch get a very hot
hissing flame.

casting and quenching? 

After the flask is cast you should let the flask set for at
least 20 minutes. If you do not it will thermally shock the
metal making it brittle. The investment is hard to get off the
castings. You can water blast, it will take about 10 to 15
minutes. Then remove most by hand then use Hydrofluoric acid
<>> should be taken. Gessewien will be supplying a
milder investment remover that you should look into.

Is there anything we should continue to send out? 

I would send out customer jobs and one of a kind items then
practice with stock items to give you the experience of casting
before you start putting yourself under the pressure to produce a
finished product.

Edward J. Friedman
The Buehn Company
Revere Academy


#4
Then remove most by hand then use Hydrofluoric acid
<<CAUTION>>> should be taken.  Gessewien will be supplying a
milder investment remover that you should look into. 

Hi folks, In dentistry we have several investment removing
liquids. “Removsit” is the slowest but also most benign.
“No-San” and “Stripit” are hydrofluoric substitutes and will
discolor stainless steel and will totally remove porcelain when
striping a crown. Needless to say, you must use a plastic
covered beaker. These products used in the ultra-sonic will
take the investment out of the tiniest nooks and crannies. They
also clean up the castings.

Regards,

Skip

Skip Meister
@Skip_Meister
N.R.A. Endowment &
Certified Instructor
in all disciplines
Certified Illinois D.N.R.
Hunter Ed, Instructor


#5
    And any tips on the melt, 

and a cautionary note. Torch tips are often copper. Be careful
that the tip of your torch, while melting, is far enough from the
hot zone in the crucible. It’s pretty disheartening, when the
platinum is almost ready to cast, to suddenly have the torch
sound different, the flame look funny, and the platinum violently
react to something, and you then realize that a large chunk of
the copper at the end of your torch has just melted and dropped
into the platinum. (Seen it happen, and had it happen to me,
too.) Great way to trash a couple ounces of platinum in mere
seconds…

casting and quenching? 
   After the flask is cast you should let the flask set for at
least 20 minutes.  If you do not it will thermally shock the
metal making it brittle. The investment is hard to get off the
castings.  You can water blast, it will take about 10 to 15
minutes.  Then remove most by hand then use Hydrofluoric acid
<<CAUTION>>> should be taken.  Gessewien will be supplying a
milder investment remover that you should look into. 

Edward, are you sure about that caution? I can heat a platinum
casting quite bright and quench it, as in annealing. won’t crack
it or make it brittle. Can’t see why doing so in the investment
would be any different. Iridium platinum is pretty resiliant.
Also, the last caster I worked with (and essentially, worked for)
used a high pressure water blast cabinet to get Supra off the
castings. worked wonderfully IF you blast it while the button
is still red (not orange or hotter) hot, and the interior of the
flask hotter still. Wait longer, and the stuff got just a whole
lot harder to remove. Only thing that ever got shocked was the
investment.

Peter Rowe


#6

and a cautionary note. Torch tips are often copper. Be careful
that the tip of your torch, while melting, is far enough from the
hot zone in the crucible.

You are right Peter I have also had tips fall off. the tip
should be thick and screw onto the torch end. Some torch tips
are soldered on and fall off due to the extrem tempretures. I
use a Weldmaster torch by Meco with a #1 tip very heavy duty
torch but it is worth it. I have not had a problen with tips
falling off since and due to the thickness of the tip end they
can take alot of heat.

Edward, are you sure about that caution? I can heat a platinum
casting quite bright and quench it, as in annealing. won’t crack
it or make it brittle. Wait longer, and the stuff got just a whole
lot harder to remove. Only thing that ever got shocked was the
investment.

Peter, you may very well be right about the quench of the flask.
Being self taught on this subject I tried to eliminate any and
all possible causes for brittle castings so as to not have
thermal shock problems to contend with, I eliminated it from the
procedure. I do not have a water blaster and it would make sense
that the investment would be removed by just the steaming of the
blasting water. the reason I would let it set for at least 20
minutes is to make sure the flask is very cool. I do not place
the flask in water normally, If you do as you mentioned the
investment tends to glass up on the piece and it get much harder
to remove.

As with any and all out there it seems that what one
might read in the technical literature is not always what is
practiced in the real world. That is what makes this forum so
important, people like you helping decern fact from fiction. It
is easy to write about a subject but there is always little
things that make a big difference and when we are making comments
it is difficult to remember all of the little details. Orchid
is very lucky to have such an asset as yourself.

Keep up the good work and back to the bench for me.

Edward J. Friedman


#7

Be careful! I dont know about these particular 3 products but I
am amazed at the vendors who will tell you their product is a
"Hydrofluoric Acid Substitute" and then when you get it or look
at the MSDS sheet, you discover that it does indeed list
Hydrofluoric as one of the ingredients! If you are not 100%
sure what is in the product you are considering purchasing, be
SURE to ask them to send/fax you an MSDS (Material Safety Data
Sheet) BEFORE you buy it.

Super Strip-It for example (maybe not the same thing as the
"Strip-It" you mention) does, for example, contain Hydrofluoric.
New “Quick Set Devest” does not.

Elaine Corwin
GESSWEIN CO INC USA
Bridgeport, CT 06605
Phone: 1-800-544-2043, ext. 287