Melting gold using resistive heating.

[Amol Gupta]

So I came across this video where individuals have used step down transformers to achieve high current flow at low voltages.



They are able to melt metal using such high currents.

I was wondering if I could use the same principle and connect the two ends of the wire to a graphite crucible which contains my metal, my intuition is it should be hot enough to melt gold without any significant metal loss.

Any thought on the idea would be appreciated.

Thanks.

 

[Amol Gupta]

I know people use induction heating furnaces which work on the principle of induced current but the machines themselves cost a lot, this seems to be a good cheap alternative.

 

[Yggdrasil]

I know people use induction heating furnaces which work on the principle of induced current but the machines themselves cost a lot, this seems to be a good cheap alternative.

As long as the Graphite are protected from most of the Oxygen it should be ok.
I guess.

 

[Amol Gupta]

As long as the Graphite are protected from most of the Oxygen it should be ok.
I guess.

I guess I'll have to sacrifice a few crucibles to check that out.
Speaking of oxidation, the induction furnaces I was talking about, the manufacturers state the machine works in vaccume but also they use argon gas to fill the chamber, never understood why argon being inert may help reduce oxidation in that case I did understand the purpose of vaccume

 

[Yggdrasil]

I guess I'll have to sacrifice a few crucibles to check that out.
Speaking of oxidation, the induction furnaces I was talking about, the manufacturers state the machine works in vaccume but also they use argon gas to fill the chamber, never understood why argon being inert may help reduce oxidation in that case I did understand the purpose of vaccume

Argon do not react with anything no matter how hot.
Most of the gases in air do.
Vacuum works too but needs powerful vacuum pumps.

 

[Amol Gupta]

Argon do not react with anything no matter how hot.
Most of the gases in air do.
Vacuum works too but needs powerful vacuum pumps.

I'm not sure if it's just me being stupid but I have seen manufacturers state the induction furnaces is a vaccum induction melting machine but I have seen argon gas tanks attached to such machines.

 

[Yggdrasil]

I'm not sure if it's just me being stupid but I have seen manufacturers state the induction furnaces is a vaccum induction melting machine but I have seen argon gas tanks attached to such machines.

There are many types.
Some have vacuum and pressure.
Another thing is that if you introduce low pressure Argon you do not need the deep vacuum needed without.
Depending on application of course.

 

[Amol Gupta]

There are many types.
Some have vacuum and pressure.
Another thing is that if you introduce low pressure Argon you do not need the deep vacuum needed without.
Depending on application of course.

Oh ok, it always bugged me how can we state the machine as vaccum operated while still introducing argon, thanks for that.

Frankly I'm pretty excited on testing out melting some metal in my graphite crucible using high current either from a transformer or a high current power supply.

 

[goldshark]

Oh ok, it always bugged me how can we state the machine as vaccum operated while still introducing argon, thanks for that.

Frankly I'm pretty excited on testing out melting some metal in my graphite crucible using high current either from a transformer or a high current power supply.

I don't know if you do much welding, and if so, have you heard of Carbon arc gouging. and the Graphite rods used. For others who do not know of this type of welding accessory, Carbon arc gouging consists of a Copper coated graphite rod. The rod is held by a typical electrode stick holder, but has the additional feature of an air port, with thumb operated on/off. This type of welding is not joining pieces of metal, but is used instead to remove welds, and cut steel. An arc is struck with the electrode, combined with the air, creating an impressive, albeit noisy, show of sparks from the metal being blown away. OK, fast forward to how this would work for melting metals. Obtain Carbon arc rods, place one in the grounding clamp, the other in the electrode holder. Strike an arc before introducing to metals in crucible. Immerse slowly, maintaining the optimum arc distance. Steel foundries use this technique. They have a jig containing the rods, set immersion speed controllers, etc.. In all, a big investment. The rods I use are typically 1/4 - 5/16 inch in diameter. I use a miller 250, which is pushing the maximum duty cycle of the welder, for this size rod. I think it runs at 24 Volts @ 250 amps. Perhaps this could be a small scale way of melting metals, that has not been explored on this forum yet. The one thing I do know, plasma obtained from this technique is very hot. Perhaps leading to excess PM losses, hence why this technique is not used.

 

[Yggdrasil]

I don't know if you do much welding, and if so, have you heard of Carbon arc gouging. and the Graphite rods used. For others who do not know of this type of welding accessory, Carbon arc gouging consists of a Copper coated graphite rod. The rod is held by a typical electrode stick holder, but has the additional feature of an air port, with thumb operated on/off. This type of welding is not joining pieces of metal, but is used instead to remove welds, and cut steel. An arc is struck with the electrode, combined with the air, creating an impressive, albeit noisy, show of sparks from the metal being blown away. OK, fast forward to how this would work for melting metals. Obtain Carbon arc rods, place one in the grounding clamp, the other in the electrode holder. Strike an arc before introducing to metals in crucible. Immerse slowly, maintaining the optimum arc distance. Steel foundries use this technique. They have a jig containing the rods, set immersion speed controllers, etc.. In all, a big investment. The rods I use are typically 1/4 - 5/16 inch in diameter. I use a miller 250, which is pushing the maximum duty cycle of the welder, for this size rod. I think it runs at 24 Volts @ 250 amps. Perhaps this could be a small scale way of melting metals, that has not been explored on this forum yet. The one thing I do know, plasma obtained from this technique is very hot. Perhaps leading to excess PM losses, hence why this technique is not used.

He wants to use the resistive heating of the crucible only.
No arc.
Just clamp conductors on the crucible and heat it direcly.

 

[Amol Gupta]

I don't know if you do much welding, and if so, have you heard of Carbon arc gouging. and the Graphite rods used. For others who do not know of this type of welding accessory, Carbon arc gouging consists of a Copper coated graphite rod. The rod is held by a typical electrode stick holder, but has the additional feature of an air port, with thumb operated on/off. This type of welding is not joining pieces of metal, but is used instead to remove welds, and cut steel. An arc is struck with the electrode, combined with the air, creating an impressive, albeit noisy, show of sparks from the metal being blown away. OK, fast forward to how this would work for melting metals. Obtain Carbon arc rods, place one in the grounding clamp, the other in the electrode holder. Strike an arc before introducing to metals in crucible. Immerse slowly, maintaining the optimum arc distance. Steel foundries use this technique. They have a jig containing the rods, set immersion speed controllers, etc.. In all, a big investment. The rods I use are typically 1/4 - 5/16 inch in diameter. I use a miller 250, which is pushing the maximum duty cycle of the welder, for this size rod. I think it runs at 24 Volts @ 250 amps. Perhaps this could be a small scale way of melting metals, that has not been explored on this forum yet. The one thing I do know, plasma obtained from this technique is very hot. Perhaps leading to excess PM losses, hence why this technique is not used.

You have stated the reason for not using arc furnaces, the heat coming from the arcs is hot enough to vaporize precious metals, the whole premise of such resistive heating is to reduce the losses in melting.

 

[haveagojoe]

I think to reach the temperature needed to melt gold in a resistive crucible would require enormously high current, it would be very inefficient and pretty dangerous. Induction is the way to go, there are quite cheap kits available these days from China or it would even be possible to build a custom one, I'd say 3kW would be ideal for small amounts. I think the trick used with induction is to melt a small amount of gold powder first and then add more to it when it's up to melting temperature.

 

[Yggdrasil]

I think to reach the temperature needed to melt gold in a resistive crucible would require enormously high current, it would be very inefficient and pretty dangerous. Induction is the way to go, there are quite cheap kits available these days from China or it would even be possible to build a custom one, I'd say 3kW would be ideal for small amounts. I think the trick used with induction is to melt a small amount of gold powder first and then add more to it when it's up to melting temperature.

There is not much need for induction with Gold.
Any electric or gas driven furnace can do that.
And yes you need very high Amps to heat it enough.

 

[Amol Gupta]

I think to reach the temperature needed to melt gold in a resistive crucible would require enormously high current, it would be very inefficient and pretty dangerous. Induction is the way to go, there are quite cheap kits available these days from China or it would even be possible to build a custom one, I'd say 3kW would be ideal for small amounts. I think the trick used with induction is to melt a small amount of gold powder first and then add more to it when it's up to melting temperature

Fiddling around with 3kw power is more dangerous than applying small alternating current for 700 Amps at 2V.
This is an experiment I wish to conduct I'm guessing I will be able to melt close to 100gm gold using this technique.

 

[haveagojoe]

Fiddling around with 3kw power is more dangerous than applying small alternating current for 700 Amps at 2V.
This is an experiment I wish to conduct I'm guessing I will be able to melt close to 100gm gold using this technique.

3kw is the input. It puts about 50A through the coil so about 60V.
700A x 2V = 1400W so still quite a lot of power.
Mr Electron on Youtube has done it your way to melt aluminum here, it seems dangerous to me and even for a very small amount of aluminium it did not melt it very well. I would be very surprised if you can melt 100g of gold, maybe I'm wrong.