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Casting small round bars


#1

I have been making jewelry from jump rings from a number of years. I
have progressed to making everything from Alloying silver/gold for
solder or different carrat values, and drawing all my own wire. My
problems are all derived from the casting of the bars. I know to
watch for anything that can fold into a cast as I am working it on
the rolling mill, but regardless of how often I anneal the wire, I
am getting cracks. When I coil the wire and cut the coils, it’s not
a big deal as I remove the damaged rings adn amounts to less than
5%. But it does make the wire hard to handle and such tasks as
weaving are impossible. When I say hard to handle, It can be like
razor wire at times and I have bled more than once.

When I am finished casting a silver bar, it’s surface looks very
smooth with large snowflake pattern on it. It looks great, but never
fails to crack, at least partially, during the wire making process.
I do heat my mould, use oil and borax. If the problem is the metal
is too hot (I try not to boil it), the question is how to get the
"Right" time to pour. I wait until the molten pool can have the heat
removed and swirl for a second, then I pour through the torch flame
into the mould. I have read books on casting, but am having trouble
getting rid of this problem. Gold seems to have much less tendancy
to crack, but due to it’s cost and my lack of sales, silver is my
most used medium.

Any tips would be much appreciated.

Brian Barrett

P.S. I am a hobbyist. I make 1 or two pieces a week and have never
taken this is school.


#2

Try switching to a milling alloy. One that is designed for making
wire and sheet stock. It could solve a lot of your problems. Frank Goss


#3

Brian. I have ran into this problem when using scrap chains and such.
I found that they contained high amounts of nickel. This can be
solved by using a magnet to check them. Also if the coper content is
high it will cause the bar to crack. Although if you anneal it very
often it will not crack. Try cleaning the material prior to casting.

Regards,
Matt


#4

It would seem that perhaps your problem stems from the mold
procedure. If you do not heat your mold and maintain a gradual heat
release the metal will have a small loose crystalline structure, if
you give the metal at least 5 mins of holding heat at around 800
degrees it will make the crystal growth larger and more uniform as
it has a chance to pull itself together instead of being shocked
into freeze. This shock results in micro fractures that will not
roll together and create space for contaminant gasses to reform
making weakness…Over heating the metal can also cause serious
problems, the best marker for correct temperature is ‘when the red
streaks dance’ when you remove the heat source, if this is not
easily achieved then you are not using enough flux which will also
cause problems in the pour… hope this helps… Ringman john Henry


#5

Are you using copper to alloy your sterling silver with or are you
using a deox alloy. Some alloys are easier to work with than others
depending on what you are doing with them, milling or casting. Are
you annealing the wire enough before making the jump rings,
sometimes you may get just one area of the wire hot enough to anneal
it and miss a little section if you have a kiln you can anneal it in
there it will give you a real even annealing unlike the torch. I
have had these similar problems as well and these were some of the
solutions that I have tried, you still may set some cracking but
hopefully this helps. sincerely kevin


#6

Hi All, Casting an ingot is like casting anything else, you need a
large button on it which gets cut off before you roll it in the mill
to reduce. Roll to at least 50% end area from ingot. When rolling be
sure not to fold any “wings” or flashing back into the piece. If you
raise any burs during a rolling pass use a file to remove them before
putting it back in the mill for another pass. Aneal before pulling
through the draw plate. If you have casting equipment, consider
casting an ingot just like you would a piece of jewelry. Sprue it
with a slightly larger gate than the diameter of the ingot and use a
good size button. John, J.A.Henkel Co., Inc., Moldmaking Casting
Finishing, Producing Solutions For Jewelry Artists


#7

One of the reasons that studio metalsmiths have problems with
casting ingots is that we work with ingots that are just too small.
With these tiny little ingot molds you can’t even get the metal into
the mold before the ingot has solidified. This can be rectified by
pouring larger ingots but most of us can’t afford to pour tens to
hundreds of ounces at a time. One of the things that should be done
to castings from an ingot mold after casting and before working is
to “scalp” it that is remove a fair amount of the surface on all
sides with a coarse file, milling machine or lathe to remove any
contaminates and metal/mold reaction areas. On a small ingot like
the ones most studio metalsmiths will cast this can be anywhere
from 1/4 to 1/2 the total weight of the ingot that needs to be
removed! For small ingots of the size most of us will cast John
Henkel’s recommendation of casting it in investment like any other
small casting is not a bad way to go. You will still need to remove
the area near the sprue to get past any large shrinkage porosity but
scalping is not really necessary for the rest of the ingot. One
drawback of investment cast ingots is the large grain size that one
gets from the slow cooling in the investment. This will make for a
weak structure during the initial reduction in thickness of the
ingot so more care is required during initial forging and rolling.
The other problem with investment casting is the time factor for
doing a wax, invest, burnout and cast cycle. However if you work the
ingot carefully you can get good sheet and wire product from this
form of casting.

In the above paragraph I mentioned forging. You can greatly improve
the grain structure of the ingot if prior to rolling or drawing it
is forged to say 50% of its starting thickness. This will create a
grain structure that is small and tightly packed . This will help
eliminate a great majority of the cracking and imperfections in the
final wrought product.

Another area of problem for the studio metalsmith is annealing. The
majority of us over anneal our material both in getting it too hot
and doing it too often. When the metal is over annealed the grain
structure grows very large one of the visible effects of over
annealing is “orange peel” this is a grainy surface texture in your
metal that shows up when it is bent or formed or during polishing.
This grainy texture is the orientation of the actual crystals in the
metal becoming visible due to crystals of different physical
orientation moving differently due to the stress of forming or
abrading at different rates during polishing when the crystals are
too large these effects become visible These larger crystals also
greatly reduce the tensile strength of the metal so it is more
likely to break during drawing or other forming processes.

Each alloy has its own annealing temperature and time as well as an
ideal amount of reduction between anneals. Check with your alloy
supplier for their recommendation for temperature time and reduction
amount for a given alloy. As an example Sterling silver anneals at
1112-1202 F (600-650 C) in a anything other than a darkened room you
cannot see the radiant glow of the silver at these temperatures so
if you are heating until you see a glow you have overheated the
silver. And if you don’t take it up to the point where it glows then
how do you know if you got it hot enough? So if you anneal with a
torch do it in a dark room. You can anneal with a kiln but this is
not as convenient as with a torch but especially when you are
annealing lengths of fine wire a kiln is the way to go because it is
too easy to overheat or to not get a uniform anneal with the torch.
To kiln anneal set the kiln to the proper temperature and once it is
at heat coat the metal to be annealed with boric acid in alcohol
fire coat and either burn it off or let it evaporate then place the
metal in the kiln and allow it to return to temperature. Once it is
at temperature the metal typically only needs to be held there for
30-60 seconds for most gold and silver alloys so remove it and
quench in the appropriate fashion which also varies for each alloy.

Even in the commercial metals producer world most manufacturers have
moved away from ingot type casting for wire and sheet production.
The majority of commercial sheet and wire producers are using
continuous casting machines to make the plate and bar that they use
to roll/draw into stock. One of the reasons they went to these
rather expensive machines is to get away from the problems that
occur in ingot production.

Jim Binnion

James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160


@James_Binnion
Member of the Better Business Bureau


#8

I don’t know if anyone mentioned sand casting, but I usually sand
cast my ingots. No porosity, fast cooling, and a pretty decent
surface. I just make the form to cast and press sand around it. If
you have the fine grained Delft sand, even better…

Jeffrey Everett


#9
    One of the reasons that studio metalsmiths have problems with
casting ingots is that we work with ingots that are just too
small. 

Hi James, and others . . . I agree, a small ingot is a lot harder to
pull off than something larger. But frankly, I never had too much
trouble with the process, and now I’ve got a solution that works even
better and is very fast. First, the way I used to do it:

I used one of those machined steel reversible ingot molds. I’d wipe
the inside of the mold down lightly with a little machine oil. Then
I’d hold it with pliers over my jewelers torch, lit with only the gas
turned on and up high. This would soot the mold and coat it with a
fine layer of carbon. Then, handling this now quite warm mold
gingerly with gloves, clamp it together. Heat the outside of the
mold from both sides until you see that oil start to smoke a little.
Must be around 4-500 degrees, I’d guess. Then, when it comes to
metal, for gold alloys, I prefer Stuller’s alloys, the ones
formulated to make rolling stock. Not so easy to hit that ingot mold
when pouring from a dish crucible. After it’s cast, reduce it only
slightly between annealing at first, and it doesn’t hurt, as James
says, to forge the ingot all over before any rolling. But with this
method, there really isn’t any skin to remove that I’ve noticed,
unless you’re using some crappy gold that’s been melted too often.

Now, the latest way I make ingots for rolling into sizing stock,
wire or sheet is real simple. I just get out my Delft sand casting
kit, and using various shapes of “ingots” made from carving wax, I
make a one-shot sand mold. The hole which becomes the sprue, I’ve
found, needs to be around 1/8 inch in diameter, and a brass tube of
that diameter is great for pushing through the sand to make the hole.
I then carve a sprue cavity big enough to hit easily when pouring
from a melting dish crucible. Whereas I have a 1/8 inch hole to pour
into, on the other end of the ingot cavity is a vent hole of about
1/16 inch. Simple design, 1/8 inch sprue goes into one end of the
ingot, 1/16 inch vent comes out the other. Again, I’m using
Stuller’s alloys. I get a nice, shiny clean ingot. Rolling it down
is a piece of cake.

David L. Huffman


#10

James Binnion wrote…

you can't even get the metal into the mold before the ingot has
solidified - recommendation of casting it in investment - One
drawback of investment cast ingots is the large grain size that
one gets from the slow cooling in the investment. 

Did you consider casting in cuttlefish bone? Ok you do get a small
surface texture but cooling time is reasonable and the technique is
quick and easy.

Best Wishes,
Ian
Ian W. Wright
Sheffield UK


#11

I gave up trying to make ingots years ago. I won’t go into all the
things I tried that failed, but I found the answer at Jean Stark’s
class on chain making. We had to make our own gold wire for the jump
rings and had to start out with 4 Nines (99.99% Pure) Gold. After
she alloyed it to 22kt, she took a charcoal block and cut a groove in
it diagonally. Melt the gold on top of the block and it will run into
the groove. If it dosen’t go into the groove, use a chopstick to
guide it into the groove. I go to Chinese restaurants, eat with a
fork and save the chopsticks for my workbench……

It won’t be exactly round, but it will be close enough to run
through the mill.

As it cools, you can push it down into the groove with another
charcoal block.

If you used a 4 mm round burr to cut the groove, you will have a
half round ingot that you can roll out in your mill straight from the
charcoal block. I never have to do any cleaning with anything other
than water.

Using a large charcoal block and cutting a grove diagonally will
accommodate close to an ounce of Gold or Silver. That’s a lot of
wire at 18 or 22 gauge.

Spray the charcoal block with water to cool it off after using it as
a mold. It will last longer.

Love and God Bless
-randy
http://www.rocksmyth.com


#12

Brian. I have found more difficulties in casting silver ingots than
gold. I believe that the problems arise from the oxidation of the
copper during the melt. I have learned to pay particular attention to
the formation of oxides and tend to use a lot of flux, adding more
during the melt.

I have my own method of treating the metal mold. After trying motor
oil, WD40, “candle black” (soot) and who knows what else for mold
lubricants, I have settled for olive oil. Olive oil will help develop
a seasoned surface on the mold that consists mostly of carbon that
will absorb much of the oxygen from the melt.

Many people forge the ingot in the beginning. I use the rolling mill
to bring the round ingot square and anneal. I believe that this
serves the same purpose. Works well for me, anyway.

Good luck.
bruce


#13

I now cast my ingots in a groove (pencil-width) carved out of a
charcoal block. Doesn’t shock the metal and provides a reducing
atmosphere. They come out nice and shiny and roll out fine.

Janet in Jerusalem


#14
    Many people forge the ingot in the beginning. I use the
rolling mill to bring the round ingot square and anneal. I believe
that this serves the same purpose. Works well for me, anyway. 

Hi Bruce, The reason for forging rather than rolling is that the
rolling mill tends to not have full penetration of force. That is
that the rolling action mostly works the metal on the outside of the
bar and not the inside you can see this by looking at the end of a
piece run through the mill you will see that it develops a concave
surface. The outside of the bar is pulling the inside along with it
but at a slower rate. If you forge with an appropriate hammer size
the end of the bar will be convex indicating a full penetration of
force. The difference is that the crystals in the bar will be worked
more uniformly by forging rather than rolling and this can save your
bar from some internal cracking further on down the road in the
fabricating process. FWIW

Jim Binnion James Binnion Metal Arts Phone (360) 756-6550 Toll Free
(877) 408 7287 Fax (360) 756-2160 http://www.mokume-gane.com
@James_Binnion Member of the Better Business Bureau