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Centrifugal casting problem


#1

Hello every orchidians, i’ve encountered a little problem since i
have change my casting method from vassum to centrifugal.i have
bought a neycraft centrifugal machine that comes with a crucible
capable (that’s what the manufacturer says) of holding up to 5 onces
of silver if i am coorect that should be arround 155 grams exept
that i needed a crucible able to contain at least 250 grams so i
bought a progress crucible able to contain 11 onces meaning 330grams
aproximatly. the problem is here. i have cast a couple of times with
270 grams inside the crucible , resulting by a lost of at least 30
grams that fly out side the crucible and going on to the exterior
side of the cylinder… is there an explanation… my therie is that
since it is a short arm , the swing of the release is to fast
resulting that the metal slips over the side of the crucible .
could that be an option. if somebody out there is able to help me
please let me know.

Syd


#2

Syd,

(A) make sure that the neck of the crucible is up against the flask.

(B) make sure that the crucible hole lines up with the sprue hole of
the flask.

© make sure that the cavity in the casting ring is capable of
accepting the amount of metal that you have melted, example, (you
can’t put an ounce of metal into a cavity that can only accept a half
an ounce, it has to go somewhere.

(D) make sure that the swing section of the arm is at a right angle
to the weighted section of the arm.

(E) and make sure that the arm is balanced, an un-balanced arm will
result in a miscast.

Sincerely, Richard Lucas…
http://community.webtv.net/lucadent


#3

Dear Syd, You are best off pouring that much metal by vacuum casting.
The pour allows the metal a little more time to enter and flow into
your flask. Spin Casting is an immediate introduction with a lot of
force of all material into the flask. Spin casting will fill up the
spru button reservoir right away. It then flies out the bottom of the
flask in a spill if the spru reseverour is not adequate. Your cast
may only allow a certain amount through the sprus. My rule is to spin
most things under 100 dwt. and vac cast anything over 100 dwt. It’s
much safer that way. This is the case most of the time. If you can’t
change techniques, attach your sprus off a super large rubber base.
The part that needs to be enlarged is the center black round section
of the spru base. That should hold all your metal at once. It will
travel there when spun and travel to the rest of the cast. I don’t
think there is a base large enough to buy so you will have to modify
one by building it up with wax or try to make you own some how.

Best Regards,
Todd Hawkinson
www.trhawkinson.com
www.ajt-online.com
T.R. the Teacher
www.mctc.mnscu.edu/jewelry.com


#4

Hi Syd, You might have an alignment problem. Put a cold dummy flask
in the cradle and the new crucible and see if the hole on the
crucible aligns with the center of the flask funnel. If you need to,
you can make a cradle from some sheet metal that will hold your flask
just right. A question… after you cast is the button level with the
funnel edge of the flask? Centrifugal casting Rocks (and rolls!)
John, J.A. Henkel Co.,Inc. Moldmaking Casting Finishing, Producing
Solutions For Jewelry Artists


#5

Just curious…, why did you change your casting method from
vacuum casting to centrifugal casting? I don’t think you would have
this problem with vacuum casting. Also, I agree with your idea that
you probably have too much metal for the size of the crucible that
you are using. Try backing off two ounces and see if this solves your
problem.

Glenn
Shardan Jewelry


#6

after trying out a couple of more cylinder it seems that i have
found the problem… casting with more then 180 grams will result
in lost of metal on the side of the flask. but i cant understand why
when i tryed with a bigger crucible the lost of metal was even more
important! could it be that the crucible wasn’t ment for that
machine… i would love to ear on that.

Syd


#7

Hi Syd, I can think of following situations that could result in the
problem you describe:

  1. The holes in your crucible and investmentflask are not aligned

  2. The passage between flask and crucible is blocked

  3. Too much silver in the crucible. Remember: the weight of the
    wax-tree times 10, plus 20 grams for the button.

  4. Your wax tree-trunk too thin.

  5. Flasktemperature too high, especially if you are casting big
    chunks.

  6. Flasktemperature too low, if you are casting small items with
    fine details (filigran).

  7. Inadequate burnout.

  8. Centrifugal force incorrectly adjusted.

Hope this will help.
Jon Holm
INSULA BURGUNDI MARE BALTICUM
@Jon_Holm


#8

That makes it sound even more likely what someone else has already
said; that you just don’t have a hole (or a conical depression) large
enough to admit all that metal that was thrown into it all at once!

Margaret


#9

Hi Syd,

could it be that the crucible wasn't ment for that machine... i
would love to ear on that." 

I believe you mentioned you are using a Neycraft, if so, you should
probably use the Neycraft crucible, they are a different shape.
Also, they have spru e bases that are a bit different shape. And, be
sure that you are putting the weight that comes with your machine in
the heavy slot for large flasks.

Marta


#10

Syd, just maybe the bigger crucible that you used is not lining up
with the flask!!!

Just because the bigger crucible looks like the one that came with
the machine, does not mean that it was made for your machine.

Many crucibles that seem to look alike, may actually have different
heights to the neck of the crucible, check it out or even better,
why don’t you try contacting the manufacturer of the casting machine,
which I believe you said was NEY.

For the amount of money that you spent on this casting machine, I
would think that they should be able to help you.

Sincerely,

Richard Lucas
Lucas Dental Co
18 Herkimer Place
Brooklyn, NY 11216
http://community.webtv.net/lucadent


#11
You are best off pouring that much metal by vacuum casting. 
Todd, 	 		

I cast 250-350 grams, 166-233 dwt, regularly with a kerr long arm
centrifical. Kerr makes crucibles that hold 20 ounces for
centrifical.I would also like to mention that Marc Robinson’s method
of hot water investment has been working really well at Denver’s
altitude. It does require paying attention, I have had less surface
irregularities. I used to have small bubbles and some little surface
blemishes that disappeared. Thanks Marc! Isn’t it interesting that
it seems that for every procedure, someone is successful and some
have failure? Richard in Denver


#12

Dear Richard,

I do prefer spin casting my large heavy weight class rings. On those
casts I usually throw about 180 dwt. I cast the flask at about 500 to
550 F and use the doughnut shaped spru bases. The quick
solidification from spin casting minimizes porosity.

Best Regards,

Todd Hawkinson


#13

Do I remember correctly that you are using a Neycraft spin-caster ?
If so you should have read the specifications carefully. It is
designed for safety and works wonderfully if you stay within the
proper limits. It has only one type of crucible and you must use it
and not a substitute. It uses only certain sizes and diameters of
flasks - again, you must use those that fit into the grooves on the
back-plate securely. My recollection is that the crucible may not
melt more than six and a half troy ounces of silver - adjust for
other metals accordingly. This is a fine machine when used correctly
and the only reason for spills are those that others have mentioned,
but the most likely is simply melting more than the machine is
capable of. Re-calculate your metal needs by carefully weighing the
waxes, allowing for the sprue button, and not overfilling the
crucible. Also, carefully place the counter weight in one of the two
slots designed for it. Closest to the handle for the larger flasks,
closest to the center for lighter. None needed at all for very small
ones.

Please respect your equipment by understanding it thoroughly before
use. We’d like to see you stick around and cast successfully with all
your body parts and equipment in good condition.

Pat