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Proper casting sequence


#1

When casting alone I wonder about proper sequence. Do I first get
the flask from the kiln, then heat my metal and cast, OR do I heat
the metal, pull the torch away, (causing oxygenation ?) then reheat
the metal and cast?

I’m concerned if I first pull the flask, then heat the metal, I
might over heat the investment. On the other hand if I first heat the
metal, get the flask, reheat the metal, cast, I’m concerned I will
get porosity.

What to do?

Thanks
David


#2

Hi David,

If you search the archives under the subject heading centrifigul vs,
vaccuum casting, you will find a long posting by the guy from
Racecar jewelry (Daniel…) who set up a microphone stand to hold his
torch over the crucible while he gets the flask out of the oven. I
was impressed with his method, so I built a similar setup, and it
seems to work very well. I have a stand that holds my torch in place
with the nozzle right over the crucible at the proper distance, and I
heat the metal almost to the casting stage, set the torch in the
holder, and go get my flask and pop it on the vaccuum. I’m using the
new “whip” tongs from Rio, and it works really well. With the flask
on the vac, I lift up the whip with my right hand, and, with my left
hand, I keep the torch on the crucible all the way to the mouth of
the flask, and even when pouring, the flame is on the metal coming
out. I’m also pretty new at this, but it works like a charm.

Larry Heyda


#3

David,

Each jeweler develops techniques that work for them. For me I heat
my metal in the crucible until it is shiny and rolling. I then remove
the cylinder from the oven. After the cylinder is in place I go back
to heating the metal and then release the arm.

Greg DeMark
www.natureinspiredjewelry.com


#4

I think you run a greater risk from letting that hot metal out from
under the reducing flame than you do from possibly skewing the flask
temperature from a longer time between the kiln and filling the
flask. Here is what I do working alone:

  1. Preheat the crucible.

  2. Charge the crucible with the metal.

  3. Load the flask. Quickly!!!

  4. Melt the metal without delay, keeping it constantly under the
    flame. You are right that letting it oxidize, even for a few seconds,
    is bad.

  5. Spin the caster.

I get worried about how the longer wait will affect the flask
temperature when I have a bigger charge of metal. For my torch setup
anything under 100 grams goes quickly enough that I am not worried
about the time. Over 150 grams I like to have a helper. I keep
meaning to set up an adjustable rack/holder for the torch so that I
can leave it blasting on the crucible when I go to fetch the flask,
but so far it has usually worked out OK without one.

If I have a helper, which I do about 2 times out of 3, I will time
it so that the metal is not held molten too long and risk
overheating. So if the melt is small, say 20 grams, The helper brings
the flask before I put the torch on the metal. If it is a bigger melt
I wait until the metal is almost ready to cast and then have her load
the flask, trying to time it so that it is less than a minute before
it is goes.

By coincidence I have a guy coming to my shop this morning to make a
YouTube video of our casting process, but both my apprentices have
the day off. Not quite sure how I am going to handle it. I guess you
will have to watch the video to find out.

BTW, I have a motorized centrifugal casting machine for sale. It
works with up to 4 inch flasks and was hardly ever used. The previous
owner had a growing business and bought a Inducto-Vac machine soon
after getting this machine. It is in like new condition. I would take
$500 for it, but you will have to arrange shipping or pick up.

Stephen Walker
Andover, NY
(South of Rochester,where it is very cold indeed today)


#5

I used to do quite a bit of specialty casting for 15 years in the
previous incarnation of my studio. Not anything approaching what
Daniel Grandi does on a commercial scale however (sawatdee khun
daniel ;-).

I cast very delicate wax sculptures for a select group of artists as
well as some of my own jewelry which at the time involved wax work.

My setup was a spring driven broken arm centrifuge mounted in a
galvanized washtub, bolted on a waist high countertop. Next to the
caster on the right was my kiln, elevated so that the floor of the
kiln was about the same height as the cradle in the caster.

My sequence was:
heat the crucible, add the metal, resume heating until semi-molten.

With torch held in left hand keeping flame on metal: open kiln with
right hand, remove flask (with tongs), place flask in cradle.

Close kiln door, set down tongs, pick up carbon rod, stir molten
metal, release spring arm, turn off torch.

Aside from moving my right arm to manipulate the kiln door and flask
I was standing in a stationary position and did not need to shift my
balance or make any other physical movements.

The action of removing the flask from the kiln and placing it into
the cradle without moving the flame off from the metal and then
closing the kiln and releasing the spring arm was a well rehearsed
and choreographed movement. Keeping the metal under the torch at
casting temperature while placing the flask and having the melt ready
to release without the flask temp cooling was the key for me to very
consistent results.

I cast anywhere from a flask or two to perhaps a dozen at a time in
sequence without pausing in-between other than to adjust the weights
on the arm of the centrifuge or change the cradles for differing
flask sizes.

The current incarnation of my studio/classroom does not involve
casting, my casting outfit is still in a crate 4 years later.

Michael David Sturlin
www.goldcrochet.com
www.michaeldavidsturlin.com
http://michaelsturlinstudio.ganoksin.com/blogs/


#6
I think you run a greater risk from letting that hot metal out
from under the reducing flame 

Steven puts it pretty well. First - put the crucible in the kiln for
a half hour before you cast to preheat it… The core of even a small
flask will not change temperature at all in the 30 seconds it takes
to load everything up and melt even a lot of metal - if the crucible
is 900F coming out of the kiln, then a ten ounce melt will take
about 3 minutes. The outside might lower by ten degrees, but it’s
the core that matters.

Fooling around with half molten metal in air is far riskier than
letting the flask cool by a couple of degrees, if that even happens
at all.

http://www.donivanandmaggiora.com


#7

I made a clamp out of copper wire for the edge of my centrifugal
casting shield, which holds the torch handle right where it meets the
hoses. Then I also have a support made out of a copper pipe, which
clips on the shield at 2 points and makes a bridge across the circle.
This can be bent a bit to adjust to various flask lengths, and with
it I can safely leave the torch flame covering the crucible’s opening
while I load the flask. I get the flask when the metal is melted and
shiny, or just a bit before that. It’s an ugly set-up, but has worked
well for over a decade, maybe two. If I were starting out now, I
would simply get Daniel’s type of mic stand.

When I get the flask loaded, I remove the copper pipe bridge and I
hand-hold the torch, being careful to keep the crucible opening
covered at all times. Then I check the melt with a final wiggle, and
let it go.

M’lou


#8

I wonder if all these special procedures are needed for keeping a
torch on the crucible while casting. Let me explain:

I set up a 2 x 2.5 inch invested flask with a thermocouple embedded
in the center. When it was removed from the oven I found that it took
almost 5 minutes before the core temperature started to drop
significantly. This suggests that one may have much more time to
finish melting casting grain before the mold becomes too cold.

Although I usually have extra hands when teaching centrifugal or
vacuum assisted casting, I would like to suggest the following
procedure for one-person casting:

  1. Place the crucible in the oven with the burned out flasks or
    pre-heat the crucible with a torch to minimize the melting time when
    metal is added.

  2. If it makes you more comfortable with this procedure, set the
    final flask casting temperature slightly above its normal
    temperature.

  3. Install the crucible and flask in the centrifugal caster or set
    set the flask near the vacuum machine but not on the high temperature
    rubber (to save your gasket rubber). I set the open crucible on a
    firebrick near the vacuum machine. (All of this is unnecessary if you
    melt your metal in an ElectroMelt pot.)

  4. Wind up your centrifuge if necessary.

  5. Add metal to the crucible on the centrifuge or the open crucible
    on the brick and start melting. (The grain should melt relatively
    rapidly in the preheated crucible.)

  6. When the metal reaches casting temperature release the centrifuge
    as normal while keeping the torch on the metal until the last moment.

  7. For vacuum assisted casting, a little more dexterity is required.

    a.) keep torch on metal until melted while the flask remains on

    a brick near the vacuum machine.

    b.) When the grain is melted keep the flame on the metal while
    switching on vacuum pump.

    c.) Place the flask on the high temperature gasket. (The flask
    will now cool rapidly with the air being pulled into the sprue.)

    d.) Switch torch hands if necessary so that you can pour with the
    dominant hand and pour metal when you are sure it is at the right
    casting temperature.

I am reciting this from memory but I hope the sequence makes sense.
Often turning on the vacuum pump is the most complicated step and it
could be made easier by placing a knee-operated switch at a handy
place.

My main point is that one can leave even a small flask on a fire
brick or in a centrifugal casting machine for several minutes without
having the temperature drop significantly. Much more time may be
allowed on larger flasks due to the additional thermal mass.

Hope this helps,
Fred


#9

If you are melting a large load of silver and need a “third” hand to
hold the torch while it heats up, Daniel Grandi (Racecarjewelry) has
developed an excellent technique. He uses a microphone stand and
holder from Radio Shack to hold the torch body. They are cheap,
readily available, and very adjustable. It enables you to do other
things while the load heats up and yet quickly releases torch when
needed. Radio Shack sells several versions of the microphone holder
so make certain that the one you buy will clamp around the size
torch you are using. The torch I use for melting is particularly
large and has heavy hoses, so I add use an additional plastic clamp
(from Harbor Freight) to hold the torch securely in the microphone
holder.

Here is Daniels explanation from 2002 orchid,

You buy a $29 microphone stand from Radio shack. this will be
your torch holder... make sure you bring your torch so that you
get the correct plastic microphone holder for it... there are 3
different ones. They cost about $3. Now, You buy the ceramic
crucible holder/ handle from Contenti supply (800-343-3364)
there are 2. a large capacity and a smaller one. This is about
$15. The large ceramic crucible fits the larger handle. Crucible
is about $ 8 and last a year or more... depending on use and how
you treat it. Get some flux and flux the crucible. The large
crucible is capable of melting just over 700 grams of silver and
the torch can have that ready to cast in under 5 minutes Pre heat
the crucible for 3 minutes at high heat with the torch. Put your
metal in the crucible, slight amount of flux added and melt
away... If you are melting 400 grams, you will be ready to pour
in about 2 1/2 minutes or less... so don't leave. As the metal is
approx. 3/4 melted, Move quickly as this is crucial.. Now, You
are ready to cast... With the microphone stand holding the torch,
you have both hands free... Reach into the oven ( with tongs)
remove the selected flask, Place it on the vacuum table( seal in
place) turn the vac. on. You can now remove the torch from the
mic stand, Pick up the crucible holder, keeping the flame on the
metal.... As soon as the surface of the metal is clear and bright
(looks like Liquid Mercury) pour the metal into the flask. 

Mitch Adams


#10

I do not know if how I cast alone is proper but following has worked
for me with a Kerr Centrifuge:

  1. Place cradle and crucible in the centrifugal casting machine for
    the size flask being cast and wind up the centrifuge. Crucible
    opening should be line up near center of button area of flask NOTE -
    It is important to have the crucible opening and flask opening facing
    each other with the crucible in the holder and crucible opening
    facing toward the outside of the casting machine - students have
    gotten this mixed up with some interesting results - usually metal
    splattered around the inside of the casting machine shroud.

  2. Put a piece of rebar across the centrifuge shroud - bend rebar to
    hold the torch flame

above the crucible where it will melt the metal in the crucible but
not melt the torch tip (I have some partially melted Prestolite
tips).

  1. Place the crucible in the centrifuge and pre-heat the crucible.

  2. Remove flask from kiln with tongs and place hot flask in the
    centrifugal caster cradle.

NOTE - It is important to have the crucible opening and flask
opening facing each other with the crucible in the holder and
crucible opening facing toward the outside of the casting machine -
students have gotten this mixed up with some interesting results -
usually metal splattered around the inside of the casting machine
shroud.

  1. Add metal to the crucible.

  2. Push crucible holder to flask with tongs. Balance the centrifuge
    arm.

  3. When the metal gets near casting temperature, sprinkle some
    borax, preheat carbon rod then stir molten metal with it

  4. When the metal reaches casting temperature, lift torch enough to
    remove rebar.

  5. Lower torch flame back where it was and pull centrifuge arm to
    drop the holding pin keeping the torch flame on the molten metal…

  6. Release the centrifuge arm while lifting the torch. (At this
    point if all was right in the universe and the casting deity of
    choice had been properly appeased, the centrifuge arm will be
    spinning and molten metal will have flowed into the flask.

  7. Let machine spin, then slow down and stop.

  8. Remove flask from casting machine with tongs and let cool until
    button is not red.

  9. Quench flask in water keeping flask below top surface of water
    and out of investment that may already be in the bottom quench
    bucket. Remove flask and pieces from quench water. I think I got that
    awl ritten rite - HAVE FUN