I’m new to the orchid forums and i just wanted to begin by thanking
the creators and also the members for this wonderful community. I’m
a beggining jeweler and i’m just attempting to begin casting.
Right now i’ just installed my casting machine on a 250 concrete
base set in wood. When put the flask into the cradle, melt the
charge and trip the spring the silver always shoots out of the
either the sides of the casting crucible or the actual flask pops up
out of place and the silver shoots through the bottom of the
crucible.
First off the area the casting machine is bolted into is level and
very stable it does not move at all. Its set into a 250 pound
concrete base and with the pot its in it weighs close to 300 easily.
The casting machine is one i bought from santa fe jewelers (basic
buffalo dental casting machine).
When the actual silver does go in it forms incomplete castings.
(some of it shoots off the rest actualy goes in when i tie flask
down with binding wire).
I can’t figure out what the problem is. I’m doing everything by the
book: 2.5 turns, sprues are the correct size, silver is molten to
where it begins to swirl…etc. I honestly don’t have a clue why
this is happening and i’m losing a lot of silver through this
process.
There are several things that could be happening here.
First off make sure that there are no obstructions of metal or flux
in the hole of the crucible. Secondly make sure that the machine is
balanced. To do this you would extend the arm of the machine with a
crucible in place and filled with the amount of metal you will be
using. There should be a small pin hole where the arm swivels. Place
a paper clip or some other object in the hole to keep the arm out
straight.
Now place your flask filled with investment in the cradle. Release
the center screw that holds the arm of the machine onto the base. The
arm should be balanced. If not than move the weights at the back of
the arm to balance.
You should not need to do this every time if most of your castings
use a similar amount of metal. The last thing you want to do is make
sure that the hole in the crucible is lining up with the reservoir in
the flask. Most machines come with several size cradles that can
raise or lower the height of the flask.
One last thought is that you are getting a complete burnout. If you
are using wax models than this should be fairly obvious but if you
are using organic models than you may not be able to tell without
some experience and some organic objects just don’t burn out. An
example would be egg shells.
I’m not familiar with the specific machine you’re using for your
casting, but I can make a couple of suggestions as to where to look.
Check the counterbalance weight for the size of flask that you’re
using. On all centrifugal casters, you have to balance the weight of
the flask against a counter weight that’s roughly equal - otherwise,
things will go flying all over. For some machines this is simply a
matter of moving the weight on the end of the casting arm that’s
opposite where you put the flask (usually held in place by some sort
of set screw or latch).
Check the size of the saddle in which the flask rests to make
sure it’s correct for the diameter of the flask. One that’s too small
won’t hold the flask steady. One that’s too large will let the flask
roll around in it and off to one side, so the silver never gets into
the sprue hole.
To handle the issue of the flask “popping up”, we’ve used thin
brass strips (about 1/2 inch wide, probably 24 or 26 gauge, about 8 -
10 inches long), which go over top of the flask, then tuck under the
two “arms” that hold the saddle in place. Doesn’t even have to be a
really tight fit, but it’s enough to keep the flask down.
This is really a no-brainer and I’m assuming you’ve done it, but
will say it just in case. Check the alignment of the crucible’s
outflow hole against the bowl in the base of your flask. It should be
as close as possible and the crucible holder should be tucked up
against the base of the flask or as close as you can get it. There’s
less chance of metal spraying out that way.
If none of the above have any effect, take another look at how
your flasks are sprued. The bottom of the plaster should have a nice
“bowl” or cave in it, at the bottom of which is the large opening for
the center tree of your sprue. You may need to either use a larger
center trunk sprue, or enlarge the bowl feeder sprue (where the
button forms at the base of your tree).
I guess the only other thing to look at would be flask
temperature. Your flasks should be at about 900 F when you put them
in the caster and start to melt your metal. I try to direct my torch
flame during the melt process so that part of it shoots out the hole
in the crucible and into the sprue hole in the flask, which helps
keep the investment at temperature. If the flask were too cold, I can
imagine that the metal could freeze before going into the flask,
which would stop it up and could cause it to spray all over.
Hopefully, some of these will point you in the right direction to
solving your problem.
Happy casting!
Karen Goeller
No Limitations Designs
Hand-made, one-of-a-kind jewelry www.nolimitations.com
Most likely is that your are not using the right crucible or the
right rubber base for investing. The spout on the crucible needs to
be able to go into a cone shape depression in the bottom of the
flask.
The other problem could be the cradle that holds the flask is not at
the right height.The spout on the crucible holds the flask in place
and that is how the metal goes in without spilling. Any questions,
e-mail me or call.
Are you balancing the arm with the flask in place? This is easiest
prior to burn out so that it’s set up and ready to go. Improper
balancing can lead to a bent pivot point. If not balanced correctly,
the flask can actually fly out of the cradle at a high velocity.
Are you sure the crucible and flask are properly aligned and in
good contact? Sounds like this may be your problem.
Everything is well lined up, but i’m not sure what you mean by
contact. My crucible and the flask at best are not very close to
each other. The sprue hole is at least an inch, perhaps two from the
flask when they are closest to each other.
Silver is correct amount and the flask is hot (lightly glowing red)
Right now the rubber base that i use is the sprue tree type so its
fairly shallow and cone shaped. The tip of the crucible though comes
nowhere near the actual sprue hole. There is about a one inch gap
between the two. I’ll continue troubleshooting. Right now i’m
focusing on flask temperature (incomplete castings) and perhaps a new
crucible. Any more advice would be greatly appreciated.
This may sound dumb. Is this a broken arm casting machine? If so,
the arm needs to be in the “broken” position at the start of it’s
spin. Otherwise, it will slam into the broken position, spilling
metal. You might not see it, but I think that you should hear it.
Tell us how you solved it.
Bruce D. Holmgrain
JA Certified Master Benchjeweler
One reason for incomplete castings is an incomplete melt. If a chunk
of unmelted alloy sticks in the exit point this could potentially
cause the rest of the material to exit in unexpected directions.
Re the flask eject problem: I didn’t get in on what brand or style
of machine you have but I’ve used a little Neycraft machine for
decades. One of the first problems I faced was the crucible carriage
not staying tight against the flask prior to casting. I’d be half way
through a melt when the front of the flask would drop down onto the
slides. I solved this very efficiently by using a style of paper
fastening clip that you can get at Staple or Office Max in a variety
of sizes. The clip is a piece of springy sheet metal with little
handles on either side that you squeeze to part the edges of the
spring sheet. I found a size that snaps perfectly over the slide bars
that the crucible carriage moves on.
When I place the flask in the casting machine I simple slide the
carriage up tight against the flask the place the clips over the
slide bars and tight against the underside of the carriage. No more
slipping flasks.
The sprue hole is at least an inch, perhaps two from the flask when
they are closest to each other.
This is your problem. The crucible should actually be right against
the flask, with its protruding lip right in the flask’s sprue button
hole. Maybe you can build up the back of your flask cradle or
something. This flask and crucible fit is not correct.
The cradle that holds the crucible has a metal plate that the spout
of the crucible goes through, The metal plate must be against the end
of the flask with the spout inside the flask where the sprue base
was.
Perhaps the cradle that holds the flask is in the wrong place, or it
is to wide. If you need pictures, e-mail me off line. It is not flask
temp or metal temp that is the problem.
Everything is well lined up, but i'm not sure what you mean by
contact. My crucible and the flask at best are not very close to
each other. The sprue hole is at least an inch, perhaps two from
the flask when they are closest to each other.
They should be much closer, mouth of the crucible should be in the
sprue hole. This is probably the basic cause of your problem.
One of your problems is the crucible is too far away from the flask
when I use a centrifugal caster the nose of the crucible is inside
the investment cone. This will also help with incomplete castings
because you are not getting enough metal to the mold. I hope this
helps
The crucible should actually be right against the flask, with its
protruding lip right in the flask's sprue button hole.
M’lou is absolutely right! I saw that in your post last night and
had to shake my head. I thought someone might catch it and M’lou did.
My opinion is that you really need to get someone who has experience
centrifuge casting to walk you through a casting session. Sounds like
you are in a little over your head.
I had a problem of a similar nature and it turned out that the
crucible I was using was designed for casting gold, which is denser
than silver and the molten metal couldnt pass through the spout fast
enough and was acting as a slug and then going over the open top. I
bored out the crucible hole a bit and it was fine. Note: this worked
for this particular set up so would speak to your supplier to make
sure that you dont have a similar problem before attacking your
crucibles with a drill as you may end up throwing silver through the
bottom of your investment flask instead!