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Platinum casters [Was: Centrifugal people ]


#1

A question for the sucessful platinum casters.

Why does the platinum centrifuge swing in a vertical plane as
opposed to a horizontal plane?

The only reasons I can think of are: 1. The gal/guy that first
started casting platinum thought s/he’d put a little more mystery
into the jewelr y making process. 2. Not invented here syndrome;
I didn’t invent the horizontal centrifuge, so I won’t use it,
I’ll swing it vertically! 3. Takes up less floor space.

Thanks,

Dave


#2

The platinum casters turn on the vertical because since melted
platinum doesn’t stay fluid very long (liquidus to solidus), it
needs a quick start caster in order to fill the mold.The gravity
of the earth causes the arm to go from a standing position to a
moving one in a shorter period of time on the vertical as the arm
is essentially falling whereas in the horizontal casters used for
gold and silver, this force is constant around the arc that it
turns. Think about it a minute. :~o Regards-Ricky Low


#3

Never casted in Platinum or seen a platinum casting machine…
However, are we saying that casting platinum doe not require any
special centi casting machine for any obvious reasons??

Jim


#4

Dave: While I have not cast an ounce of platinum in my life, I
have worked my fair share of physics problems. If we look at
your question from a physics point of view we find that as the
velocity of rotation of the casting arm increses the amount of
force imparted to the liquied metal, and thus forcing it into the
flask, increses. If the arm rotates in the horizontal plane the
only source of acceleration is the sprig, but if it is in a
vertical plame you also have the extra help of gravity. Also,
gravity would help to accelerate the vertical arm to its top
speed quicker than a horizontil arm, with the same spring, could
reach its top speed. An important thing to note here is that as
the strength of the spring increse, and thus the r.p.m’s, the
effect of gravity becomes insignificant. Just to sum up all of
this mumbo-jumbo, I think it boils down to two things.

  1. Our buddy Newton comes through once again.
    
  2.  Tradition and economics.  I am sure that a caster could
    

be built to cast platinum in the horizontal, but it would
probibly cost more, and look funny. Scott


#5
The gravity of the earth causes the arm to go from a standing
position to a moving one in a shorter period of time on the
vertical as the arm is essentially falling 

Are you saying the flask & crucible are started from the top
side of the arc? If that’s the case, it would appear that the
earliest the metal coul d begin to flow into the mold was after
the arm had moved about 90 deg. Als o any extra force gravity
imparted on the down swing would be counteracted by the same
gravity on the upswing.

Dave


#6

Hi all you platinum spin doctors, As I understand, verticle
machines capitalize on gravitational force added to the potential
energy of springs to deliver the metal in the fastest manner
possible. Platinum sets up incredibly fast. But you knew that. A
horizontal broken-arm machine definately will splash less, but
loses some punch in the start up. Some people make up for this
by super heating when casting platinum horizontaly (the castings
can suffer from this). There are some lovely machines like the
Galoni that can be fitted with a platinum “kit” to address these
concerns. It will run you only $20,000.00. I like my verticle
Torit. I deal with a little splash, but I take it in stride. The
real interesting part of the process is the spruing and
investing. What would you say if I told you that from the time I
sprue to the time I cast, took 2 1/2 hrs? J.A.Henkel


#7

Hi John,

It takes 2 1/2 hrs., so…? Been doing that for almost 30 yrs.

Regards,

Skip

                                  Skip Meister
                                NRA Endowment and
                                   Instructor
                                @Skip_Meister
                                10/06/9712:04:12

#8

Are you saying the flask & crucible are started from the top
side of the arc? If that’s the case, it would appear that the
earliest the metal coul d begin to flow into the mold was after
the arm had moved about 90 deg. Als o any extra force gravity
imparted on the down swing would be counteracted by the same
gravity on the upswing.

The arm is horizontal prior to release. I watched a whole iris
cast in a a flask with one of the Torit machines, in sterling- it
was perfect. No vents, a couple sprues, careful investing. Won’t
forget that demonstration.

Rick
Richard D. Hamilton

Fabricated 14k, 18k, and platinum Jewelry
wax carving, modelmaking, jewelry photography

http://www.rick-hamilton.com
@rick_hamilton


#9
What would you say if I told you that from the time I sprue to
the time I cast, took 2 1/2 hrs? J.A.Henkel

ok skip and john i’ll bite the bait… how do you do that? or
are you guys just taunting us? the investment i use takes 12
minutes to mix so that would leave me about 2 hours 20 minutes
for the investment to set up. manufacter recomended set up time
is 16 hours, how do you get around that? how about burn-out? do
you guys just slap the wet (or semi wet) flask in a preheated
1600 degree oven for an hour or two??? any details you’d like
share would be great.

best regards,

geo fox


#10

What would you say if I told you that from the time I
sprue to the time I cast, took 2 1/2 hrs? J.A.Henkel

Hello John,

I think in this case I don’t have anything to say… I want to
"hear" more. I just got back to this forum, picked up this
thread and totally agree with you about spruing. Although I
think you can’t sprue well a poorly made model. I can’t rely on
any push. I don’t have the “force”. I have a very old and
unbalanced spring driven centrifugal casting machine and a 3 cfm
vacumm system (not perfurated flask). I live in Brazil, can’t
buy things around the corner. Sometimes I have good alloys from
the U.S. or Italy and sometimes I have to add plain silver and
copper. I ‘think’ I can trust the temperature reading of my
kiln. In fact, what really counts for me is a well thought model
and spruing. I have a spruing question. I have always sprued
based on having a sprue larger than any cross-section of the
piece. Is it clear? (Excuse my English). Now… Some of the
large manufacturers in this area simply don’t care about this
rule and sprue as thin as possible to make it easier afterwards
(they are very well equipped). What do you think?

Regards,

Gabriel @agv >


#11

Hi George, As Skip will tell you also, the secret is dental
investment. Ever heard of a whip-mix machine? It spatulates
under vacuum with the (small) flask on board, also under vac. 2
mins. mix, tilt and pour. Sets in 15 mins. Skip has an involved
burn-out proceedure for dental stuff, I don’t do teeth so I drop
it in at 1600. Cast in 2 hrs. J.A.Henkel


#12

Hi Gabriel, Absolutly, you have the right As the
metal is cooling, it is recrystalizing and shrinking. It wants
to be fed as this is happening. You can cast even a “bad” model
with good casting results with correct spruing (although it’s
still a bad model!) I put a sprue on all isolated “hot” spots.
Let the big guys cast anyway they want. When the customer gets a
jewelry education, they’ll find you for your quality. J.A.Henkel


#13

If you have any additional questions…just call me or ask
here
PLATINUM GUILD INTERNATIONAL USA Jurgen J. Maerz, Mgr of Tech
Edu, Cert Master Jeweler


#14

hi skip and john,

i love you guys for answering my questions! both you guys are
really generous to share this info with us!

of course there is another question: must one have the whip-mix
to use the dental investment? would it be possible to invest in
the (mix then vacuum, then pour and vacuum again) usual way? or
is there not enough time because of the fast set-up?

also, i use a neycraft horizontal to cast platinum (and really
get the platinum hot, like john says). would locking the swivel
on the arm in a ‘straight’ position speed up delivery of metal
to the flask? why have manufacters of spin casters put the
swivel on the arm any way? my guess is to reduce splash out and
maybe metal turbulence inside the flask for metals that don’t
freeze as quickly as platinum.

again, you guys are great, your thoughts and answers are greatly
appreciated.

i’ll be contacting a dental supply tommorrow.

best regards,

geo fox


#15

Hi John,

Be careful here:

 Hi George, As Skip will tell you also, the secret is dental
investment. Ever heard of a whip-mix machine? It spatulates
under vacuum with the (small) flask on board, also under vac.
2 mins. mix, tilt and pour. Sets in 15 mins. Skip has an
involved burn-out proceedure for dental stuff, I don't do teeth
so I drop it in at 1600. Cast in 2 hrs. J.A.Henkel

All dental investments are not high heat! Kerr Lustre Cast and
Whipmix Beauty Cast are just 2 of the investments that will
probably explode at 1600. Be sure that it is a high heat
investment
. John uses a Degussa product and I use Jelenko
Complete. There are a number of investments out there in
dentalland that are suitable. Be sure that it is high heat
investment suitable for casting ceramic gold(a gold that will be
veneered with porcelain at 1800 deg.F not literally ‘ceramic
gold’, we’re not alchemists you know:) and not an investment
for chrome cobalt, which is for casting partial dentures.

My burnout is not complicated, John misunderstood me I think. I
sent a post earlier today that hasn’t appeared yet but will beat
this one, so look for it or E-mail me: @Skip_Meister

Regards,

Skip

                                  Skip Meister
                                NRA Endowment and
                                   Instructor
                                @Skip_Meister
                                10/08/9700:49:54

#16

Hi George,

John and I both use dental investment that is made for high
speed processing, in addition to high heat golds. John uses a
German made product from Degusa(a great alloy supplier in dental
alloys anyway). His product is ready for the oven in 15 min.
and can be put into a 1600F oven. The product that I use is
Jelenko Complete. I spatulate with a Whip-Mix brand combination
unit vacu-vestor(vertical kind in dental catalog) under vacuum
for 15 sec. I hand mix 'til investment is thoroughly wet before
power vacuum mixing. I fill the flask by vibrating on a
separate vibrator and let the vibrator run while the investment
sets up. Just before it goes into its exothermic state(gives
off heat) I scrape the top because all the little tiny
particles float to the top giving it a glazed appearance that
effectively seals the investment and doesn’t permit trapped
gasses from burnout and casting to exit. When the mold is room
temp. in about 45-60 min. I put it into a cold oven(Ney computer
controlled) and run it up at 32F degrees per minute to 1500
deg.F(46 min.). I heat soak for 1 hr. on 2 1/2" and smaller
casting rings and add 10min. for larger rings or 10 min. each
for multiple rings. I never exceed 2 hrs. total if I can help
it. When casting silver, jewelry gold, or regular dental gold I
take the ring and put into the cradle on the casting machine
before I start the melt. For high heat dental gold and
palladium-silver-gold alloys( used for veneering porcelain at
1750-1800 deg.F) I melt first.

I can cast pieces as thin as .2mm with all metals except the
high heat pal. alloy with 100% success.(O.K.99.9999999…). The
pal. alloy requires .4mm. For fun once, I took some store
bought filigree ring patterns that had wax flash so thin I
couldn’t measure it with my wax calipers without breaking it. I
cast one in 14k and one in sterling. The flash was there in
both castings. Another thing about dental investments is that I
believe that they are more accurate than jewelry investments.
Our castings need to be accurate to .001" in many situations and
this is why I make that statement.

If anyone has any more questions you can post it in Orchid or
feel free to E-mail me personally. I’d be happy to help if I
can. BTW everyone, thanks for the stone setting info.

Regards,

Skip

                                  Skip Meister
                                NRA Endowment and
                                   Instructor
                                @Skip_Meister
                                10/07/9718:28:37

#17

Hi George,

If you have a power mixer for the investment (1500rpm or more)
you can mix it and then vacuum, vibrate the investment into the
flask, and return to the vac source. Be sure to scrape the top
when the investment is about 80% set(hard but scrape able). If
your power mixer is faster say 3200 rpm’s, spatulate for 10 sec.
Make sure that your mixing container is cool or cold, the
liquid is cold, and the room is not hot. These factors will
retard the setting time. The age of the investment also matters.
Older investment will set faster for some reason. This info is
for Jelenko Complete but will probably be the same for Johns
Degussa investment. The whip mix makes it so much more
convenient.

Back when I was a young pup of a dental tech, I saw a film on
casting put out by Aderer Dental golds. They had a marvelous
segment that showed an actual side view of a flask being cast.
During this segment, they explained that even the tinyest and
thinnest segments of the casting are cast within the first 1/20
sec. and the broken arm accelerates the metal more rapidly.
When I cast gold or silver I use 3 full winds on my casting
machine(Kerr Centrifigo) and for high heat Palladium alloys, I
use 4 winds. I always use the broken arm.

Regards,

Skip

                                  Skip Meister
                                NRA Endowment and
                                   Instructor
                                @Skip_Meister
                                10/08/9713:24:01

#18

Hi Geo, If Skip doesn’t get to this before I do,…don’t do it!.
I mean, DON’T lock your horizontal broken arm centrifuge into a
straight position!. As someone mentioned earlier, one of the
reasons for a verticle spin is that you won’t get splashed with
molten platinum. I occationaly have some splash with my
verticle, but I take that in stride. I scrape it off the sheild
and save it for the refiner. To answer your other question, yes
you do need the whip-mix or similar unit to take advantage of
the dental investment. Skip might know of another way, but the
stuff sets up real quick. I’m done working with it in two mins.
As Skip pointed out, it has to be a “high heat” investment. J.A.


#19

Geo, The whip-mix unit I have has an on-board vibrator. They sell
a power mixing bowl that has a rubber top flask pad off to one
side on the top of the bowl. You place your flask open end down
(special hard sprue base) on that pad. Using a "high heat"
investment you then can spatulate, tip, pour, and vibrate, all
under vacuum. No need for extra steps. Skip’s idea of scraping
the top of the investment is a good tip. As for the burnout, I’m
not fitting jewelry into folk’s mouth, so I’ll stick to the one
step process. Although, there is a lot to be said for sticking to
a well researched and rehearsed burnout schedule with any
casting. J.A.


#20

Hi John,

I have had too many bubbles with the vacu-vest container with
the spot to fit the flask, besides, I use Ney tapered casting
rings for the most part that won’t fit into the hole. I use the
mixing container that has a solid top and the slotted nut for
the slow speed mix. The investment requires not only
spatulation, but also time to become thoroughly ‘wet’ and mixed.
The longer that you mix and at higher speeds you decrease your
setting time by much more than just the extra time that you
spent mixing. I often mix and invest three 1/3/4" ring flasks
at one time. I think that I will put the invested rings into a
clean mixing container and vacuum it next time to see how it
works.

John, you may wish to look into the tapered rings, they make
de-flasking a breeze. When cool, you can push them out with
your thumb. Another thing is that the regular flasks are
nothing more than standard size seamless stainless tubing
available from any steel jobber. You can buy several ft. of the
sizes you need and have it cut at a local machine shop. Have
them remove the burrs from cutting and slightly ream both the
I.D. and O.D. for you. You can have a supply of casting rings
in non-stock lengths. I don’t know how much it will cost
because I got mine from my Dad, a tool and die maker, who is now
retired. He worked for Elkay stainless steel sink mfg. and
would save the scrap small pieces and make me the rings on his
lunch hr.

If you have a Dental Supply catalog look up the Belle-de Saint
Clare casting system. It uses narrow oval flasks and a runner bar
sprueing system that enables you to set-up a series of
rings/pieces like ducks-in-a-row. You can also cast larger flat
pieces and forego the runner bar. It really saves on investment
costs. The kit comes complete with sprue former, flask and
cradle for your casting machine.(maybe not yours)

Regards,

Skip

                                  Skip Meister
                                NRA Endowment and
                                   Instructor
                                @Skip_Meister
                                10/09/9711:40:09