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Problems casting with a centrifugal


#1

Hi i hope i’m in the right place. I need help. I have been casting
with a centrifugal for a while now and have started having problems
with flow of molten metals. I burnout over 5 hours and use an
acetalyne for melting. My metal rolls perfect and when spun wont fill
the cavities. i find if it does the rings are full of pitting and
unclean.i only use satin cast investment and I allways use clean
metals and three spins on the centrifugal and small flasks. My burnout
peeks at 1350 for two hours then drops to 800 for i hour for s/silver.
please help, i don’t know what i am doing wrong. i keep records of my
burnouts to try and find the problem but to honest i have absolutely
no idea.


#2
        Hi i hope i'm in the right place. I need help. I have been
casting with a centrifugal for a while now and have started having
problems with flow of molten metals. I burnout over 5 hours and use
an acetalyne for melting. My metal rolls perfect and when spun wont
fill the cavities. i find if it does the rings are full of pitting
and unclean.i only use satin cast investment and I allways use
clean metals and three spins on the centrifugal and small flasks. My
burnout peeks at 1350 for two hours then drops to 800 for i hour
for s/silver. please help, i don't know what i am doing wrong. i
keep records of my burnouts to try and find the problem but to honest
i have absolutely no idea. 

Hi Kellie, Your final temperature on your burnout is too low. Try 1000
or a little higher. Also if your measuring your temperature on an
analog guage (uses a needle) your temperature reading is probably not
accurate at that temperature. Ovens with analog guages for reading
the temperature are calibrated for higher temperatures depending on
the industry they are made for. If you bought yours from the jewelry
industry it would be calibrated near 1300 degrees F. So on either side
of the calibration point it will be inaccurate. The farther from the
calibration point the bigger the error in the reading and the actual
oven temperature. If you have a digital reading on your oven it would
be accurate but your flask temperature is still too low. It is
chilling the metal before it has a chance to fill the cavity.

Check your flow and melting temperatures on your alloy. You will find
they are much higher than your flask temperature. Do an experiment
with some used metal. Melt it, then take your torch away and see how
fast it starts to solidify. It will turn to slush very quickly and
this is what is happening to your castings. Simply adding more heat to
your metal will not work because you can overheat your metal very
easily when using a torch. Overheating your metal creates other very
bad problems.

One other thing, be sure to place your flask in the casting unit
right before you are ready to cast. Not when you start melting the
metal.

This should help and if you have any more questions call me toll free
at 877-262-2185 or email me at ken@mpgrepair.com

Ken Kotoski


#3

Kellie, What does your flame look like?Is your metal completley
melted?Is it boiling?How big is your sprue?What are you using for a
sprue base? J Morley Coyote Ridge Studio


#4

If nothing else has changed perhaps the calibration on your pyrometer
has changed. Might be time for a second pyrometer ot cross check
against the one you are using now… Frank Goss


#5

Hi Kellie, Your solution is simple. Raise the temp of your flask. As
a general rule, the thiner your model the hotter your flask should be.
If you try to raise the temp of the metal instead you will fry it!
That is a not-so-technical way to say you will get gas porosity and
lots of firescale. John, J.A.Henkel Co., Inc., Moldmaking Casting Finishing


#6
One other thing, be sure to place your flask in >the casting unit
right before you are ready to cast. >Not when you start melting the
metal. 

Ken-- How can a single person do this? It sounds like good advice, but
I can’t see how it could work–I’d have to shut off the torch, set it
down, get out the flask–by which time, I have to reheat my now cool
and oxidized silver. Or am I missing some clever or obvious technique?
I don’t do a lot of casting, but I guess I’ve been lucky, because I
haven’t had too much trouble, mostly. Thanks for your help!

Noel


#7

Kellie, I agree with both Daniel Grandi and Ken Kotoski. The only
advise I will give is to make your changes one at a time. The problem
with changing the metal and flask temperatures at the same time is
that you will not know what “corrected” the problem. Also, you should
calibrate your oven regularly. This will help solve some of the
system temperature issues that you might be having, especially since
the torch melting system can be a fairly inaccurate method when
melting metal. There are calibration pellets for sale from Rio Grande
(and others, I am sure) that will help you with this. If I can be of
any further assistance, please do not hesitate to contact me at
@Joe_Lovato. Sincerely, Joe Lovato Neutec/USA


#8

Hi Kellie, I’m not a bigtime caster, but had a couple thoughts after
reading your question.

The first question that comes to mind is whether there is any
discernible change in your spruing? Are you using sprue wax of a
different gauge than in the past, or have you changed the approach you
use in attaching them?

Another idea would be to attach fine vent sprues from the model back
down to the base of the flask before investing. Not to the button,
but to the base that the flask is resting on. This will give the
gasses trapped in the cavity an easier way to escape, minimizing the
build up of pressure in the mold. I haven’t normally found a need to
do this, but have a mentor who swears by it.

Hope this helps… I’m sure you will get a number of responses with
good things to think about!

Dave

Dave Sebaste
Sebaste Studio and
Carolina Artisans’ Gallery
Charlotte, NC (USA)
dave@sebaste.com


#9

Hi Noel, I use a microphone stand from Radio shack for $ 24 . to hold
my torch on the metal , which free’s both hands to do whatever is
neccessary . This has worked for me when I use vacuum casting or ( in
the past centrifugal broken arm casting). Daniel Grandi


#10

I had the same problem years ago with spin casting. I had been
casting for 10 years the same way then I could not get a fill. I
tried every temp change I could think of and it still wouldn’t fill.
I finally started vacu casting and it worked. A year or so later I
told an old time manufacturer my problem and he asked how old was the
spring in my machine. Well I said its the original spring from when
my dad bought it 15 or so years ago. So I replaced the spring and
what a difference. But, after vacu casting for a year I never went
back to spin casting.

The moral of this rambling, Try a new spring.

Good luck
Bill Wismar
www.wismargallery.com


#11

Over the years, there was a wonderful post showing to mount the torch
onto a microphone stand. In that manner it can remain focused on the
melt while the other actions come into play. I think I remember who
posted this, but in fear of being wrong, I’ll refrain from names.
Teresa


#12

Hi Terresa, I was the one who posted the note about using a torch with
a microphone stand to hold it. Starting on this page of my website,
there are pictures showing some of the lost wax process .
http://www.racecarjewelry.com/page03.html

The microphone stand/ torch holder is on the next page .This can be
used for Vacuum casting or for centrifugal casting.

Daniel Grandi


#13

Hi Noel,

Basically you will need a third hand. This could be someone to hold
the torch or someone to get the flask. It could also be a stationary
holder for the torch so you have both hands free to get the flask and
position it.

If you have any other questions please feel free to contact me by
email or toll free at 877-262-2185.

Hope this helps.

Ken Kotoski