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Making casting grain


#1

I’ve got some ingots that I want to convert into casting grain, and
had a question. I’ve heard that you can simply pour the molten metal
into a bucket of water. I’ve also heard that this can trap water
inside the grain, causing the metal to “pop” when re-melted. Any
thoughts? How do you folks make casting grain? Anyone ever had a
problem with trapped water?

Thanks,
Jeff


#2

Jeff: The company that I have buying gold and silver casting grain
from in the last 30 years gave me a tip a couple years ago. He told
me to get a cermacic 8 oz long crucible and drill about 6 holes with
a #30 or 18 drill. Set the crucibleup with a holding clamp positioned
above a cold water contailer of about 25 to 30 gallon size. Put a
cetiline torch flame on the 8 oz crucible untilk it is red hot. Now
it is time to stert the melting process for the ingit you are to
melt. When the metal is ready to pour of in the mirrow surface state
it is ready to pour into the 98 oz crucible. The small droplets will
flow out ot the crucible and into the water and this is the process
my refiner uses to convert to granuels. try this and let me know
what the results were. Yours Billy S. Bates royalminiatures.com


#3

Hi Jeff: I have realloyed my metal and made casting shot at the same
time. I have never experienced water being trapped as you would think
the water would be a vapor that would not allow encompassment. I have
had some interesting shapes arrive during this process… the trick
is to have enough distance between your crucible and the water. I
usually stand on a chair and let it fall in to about 2’ of water.
Make sure you use a metal container. RingmanJohn


#4

Yes I have

My solution is to heat it slow in the crucible with a bushy flame.
Heating too fast will turn the water to steam and explode the nuggets
way too close to you. Also, I pour slower when making the grain so
the nuggets arent as big.

-Stanley Bright


#5

If you don’t need the nice uniform size and shape of commercially
made ones, you can do this just fine without the perforated crucible.
Just pour it slowly to get a thin stream, and it does the same
thing. A couple other comments may also help. commercially, in
addition to the perforated crucible breaking the pour into thin
streams (which then break up as it drops to fairly uniform sized
droplets), it’s common to have it set up with a reducing flame under
that crucible, so the air space between the perforated crucible (or
just the one you’re pouring from, if you do it without that
perforated crucible) lacks oxygen. That gives you less oxidation on
the grain. Or, you can simply pickle the grain after you’ve poured
it. And if you want it to look nice and bright, toss it in a tumbler
with a bit of tumbling soap. No steel shot or other media needed.
Just the metal shot, tumbling against itself will be enough to
brighten it up attractively. Not needed, but looks better, for what
that’s worth.

More useful tips are to use a deep enough water container. The
stream of molten metal drops entering the water will take a moment to
solidify, all the while sinking fast in the water. You want it to
fully solidify before it gets to the bottom. If you pour into too
shallow a container, the metal will still be molten when it gets to
the bottom of the container, and it will fuse to the metal that’s
already there, so instead of separate grain, you end up with a big
lump of fused bits. Interesting, sometimes, but not what you were
after. I’ve found I need at least about 12 inches depth to the
container, and it’s better to use more. At one point i worked for a
casting shop where we did our own grain. the setup there was a full
sized (30 gallon size) metal trash can, with a motor clipped to the
top rim, connected to a shaft going into the water at the side, and
at an angle, with a propeller on the end. The propeller caused the
water to slowly swirl in the can, and the stirring action helped
chill the grain quicker, as well as helping to keep the molten stream
from just landing on the same place at the bottom, again preventing
it all from just fusing together at the bottom. The trash can was
also fitted with a stainless steel container (just something we’d
found in kitchen supply, I think), which sat on the bottom of the
can, and could easily be lifted out, so we didn’t have to drain the
whole container to get the poured shot out. Also, whatever the
depth of the water container, be sure to pour from a good enough
height over the water surface. The metal drops take a moment from
when the stream breaks apart into separate drops, for surface tension
to pull those drops together into compact grains. Also, while the
drops don’t need to be fully solidified when they hit the water, if
they’re still too hot, the metal splashes as it hits the water, so
instead of solid grains you get little shell like shapes. That’s OK,
sometimes. In fact, sometimes they’re really pretty, and can be used
to fabricate funky stuff (though the effect is kind old… It’s been
done a lot before, so don’t expect such jewelry to seem new and
innovative). But more to the point, i it’s splashing enough so the
metal bits end up as flattened or cup shaped shell shapes, then some
of them will also likely be hollow and closed over completely. Those
can trap a bit of the water, so you end up with little bombs. If you
try and remelt those grains that have trapped water in them again,
they can sometimes explode from steam pressure, scattering your
melting metal all over the place. So unless you want to hand inspect
all your grain to pick out any bits that may seem like they’ve done
that, it’s better to try and get the melting / pouring temperature,
height of the pour, and other such factors down to the point where
you get predictable solid grains.

Poured without a perforated crucible, you end up with a wide range
of grain sizes sometimes. You can use a bit of screening to separate
out the very fine sized grains that may be harder to handle. And pick
out any large unwieldy lumps if you like. These then just go back
into the next melt and get repoured. What’s left gets pickled,
rinsed, tumbled, and you’ve then got grain good enough to sell as new
casting grain, if you like. If using it yourself, skip the tumbling.

Note that this applies mostly to sterling silver. I’d suggest that
if you’re doing standard gold casting alloys, you need to be a bit
more cautious of doing all your own grain, since unless you’re able
to control for the degree to which deoxidizers burn away, you’ll end
up with grain that can vary in casting characteristics from batch to
batch.

Hope that helps.
Peter