# melting silver into bars in graphite molds



## jackoa (Feb 17, 2022)

I am wondering if I can just measure 20ozt in grain, put it in a bar mold and put the mold into an induction furnace/oven? then let it cool. will it create uniform bars?


----------



## Gwar (Feb 17, 2022)

Nice question, but I believe the graphite may hold the heat needed for such action, ( Following )


----------



## jackoa (Feb 17, 2022)

Gwar said:


> Nice question, but I believe the graphite may hold the heat needed for such action, ( Following )


I currently melt in a graphite crucible in a lid type furnace, then pour into graphite bar mold. I am just wondering if I can skip the pour step and melt directly in the bar mold, if I have an oven style furnace?


----------



## cejohnsonsr1 (Feb 17, 2022)

I’ve seen that done with gold. Don’t remember exactly where, but it was a video demonstration by a company that sells the furnaces. Not sure what the mold was made of either, but they sold those too. Google is probably a better friend than me for further information.


----------



## GoIdman (Feb 18, 2022)

jackoa said:


> I am wondering if I can just measure 20ozt in grain, put it in a bar mold and put the mold into an induction furnace/oven? then let it cool. will it create uniform bars?


Hi Jackoa,

If you want to do shiny uniform bars the most important thing is the heat profile of the melt. If you have an electric furnace with temperature controller, try to make a heat profile for your melt. When the heat profile is made, make sure you put an accent to the cooling part which you have to do by reducing the temperature gradually for the first 200C (from 1150 to 950 step by step with a 10 degree steps). after that you can do 25-50 degree steps until you reach 600C after that 50-75 degree steps until you reach 200C after that you can leave it to cool by itself.
You need to have min 30 sec. between each step to let the material stabilize to the heat.
This is mostly a guide, you have to experiment it with your furnace to see what is working best for you.
I do not pour my PM`s, i am melting it in the mold directly in the furnace with heat profile.
Note that this process usually eat the molds very fast.

If you have the time and patience to do what i have described above you will have some really uniform shiny bars, almost mint quality.

Be safe

Pete.


----------



## goldshark (Feb 18, 2022)

Any body know how well a plaster of Paris mold holds up? Or what the material is a jeweler uses for casting?


----------



## Yggdrasil (Feb 18, 2022)

It is called investment casting or lost wax casting.
It is done with "investment" which is a mix of different high temp refractory oxides and binders for each application. Silver, gold platinum, steel and so on.
Time consuming and expensive for pouring since they are one time use.
Excellent for complicated dentistry and jewelry, not so much for bars.


----------



## FrugalRefiner (Feb 18, 2022)

When I was a teenager we collected rocks, cut and polished them, and made some crude jewelry, including some casting. The material used to make molds for lost wax casting is called "investment". In lost wax casting, it is a one-time use material. Once the metal is poured and has frozen, the flask is put into a bucket of water. The boiling action of the water hitting the still very hot flask/investment/casting causes the investment to pretty much disintegrate. It I don't know if it could hold up to more than one firing.

Dave


----------



## nickvc (Feb 19, 2022)

To follow on from Dave’s comments , no it will only be a one use only method and the finish will not be mirror finish as the powder particle pattern will transfer onto the bar.


----------



## orvi (Feb 19, 2022)

jackoa said:


> I am wondering if I can just measure 20ozt in grain, put it in a bar mold and put the mold into an induction furnace/oven? then let it cool. will it create uniform bars?


Yes, it is done like this. Precise ammount of shot is measured, put into graphite mold, close the mold with lid and place it into the closed furnance deprived of oxygen. Get it to the temperature, hold it for enough time to melt all the gold, then cool down.
In amateur setup it is bit harder to do it like this - heating the rectangular mold in induction heater will be somewhat tricky. Heating the mold with gold in regular furnance will be also difficult - graphite will slowly burn away as you will heat the mold. Furnance should be sealed from the air, to slow down erosion of graphite.


----------



## goldshark (Feb 19, 2022)

What about taking a bar shape, imbedding it in the investment, one side open to the furnace, let set. Weigh out a given amount of shot, heat till melt, then let cool in mold, at set heat reduction schedule. Would natural contraction of cooled metal be enough to release from mold, or would a pre applied mold release be required? Obviously minimal cast side detail to facilitate ease in removal from investment. Side exposed to furnace would be rough, but investment side may be clean to perfect? Just built a couple of assay furnaces, so haven't been able to get them outside to test my own ideas. Still winter here at 10,000 ft.. In other words, using an open top, reusable investment. Much like the graphite mold, but made of investment.


----------



## Yggdrasil (Feb 20, 2022)

goldshark said:


> What about taking a bar shape, imbedding it in the investment, one side open to the furnace, let set. Weigh out a given amount of shot, heat till melt, then let cool in mold, at set heat reduction schedule. Would natural contraction of cooled metal be enough to release from mold, or would a pre applied mold release be required? Obviously minimal cast side detail to facilitate ease in removal from investment. Side exposed to furnace would be rough, but investment side may be clean to perfect? Just built a couple of assay furnaces, so haven't been able to get them outside to test my own ideas. Still winter here at 10,000 ft.. In other words, using an open top, reusable investment. Much like the graphite mold, but made of investment.


An investment is designed to disintegrate after cooling. You have to do a burnout cycle with a scheduled heating cooling.
From the moment you start mixing it with water the investment have a very limited lifespan, you have to cast it within a very short time 15min-1h ish after burnout since it is already breaking down in a way.
It can be done but you will only get one cast of each investment.
It would be better to use an iron mould for silver, cover it in carbon from oil, WD 40, CRC 556 or acetylene torch and cast in it.


----------

