Melting gold using resistive heating.

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So fiddling around a bit I found out the resistance of the crucible is less than 0.1ohms(which is the least count of my multimeter).
So directly connecting the crucible to electricity seems a no-go(without a lot of overhead).

Graphene is also a very good conductor of heat so I am planning to get a nichrome sheet use it along with the crucible.
The plan is to electrically heat the nichrome sheet which will transfer the heat to the crucible.

A couple of options here either place the crucible on top of the sheet which will create a parallel connection thus reducing the effective resistance( I am a bit sceptical of this setup).
Surround the graphite crucible with a couple of nichrome sheets, making good connection with the graphite crucible(looks like a sainer approach), the heat generated by the nichrome sheet will be transferred to the graphite crucible.

The nichrome approach has a lot less overhead, can be directly connected to the mains voltage(something that is done all the time).

Any thoughts....?
 

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So fiddling around a bit I found out the resistance of the crucible is less than 0.1ohms(which is the least count of my multimeter).
So directly connecting the crucible to electricity seems a no-go(without a lot of overhead).

Graphene is also a very good conductor of heat so I am planning to get a nichrome sheet use it along with the crucible.
The plan is to electrically heat the nichrome sheet which will transfer the heat to the crucible.

A couple of options here either place the crucible on top of the sheet which will create a parallel connection thus reducing the effective resistance( I am a bit sceptical of this setup).
Surround the graphite crucible with a couple of nichrome sheets, making good connection with the graphite crucible(looks like a sainer approach), the heat generated by the nichrome sheet will be transferred to the graphite crucible.

The nichrome approach has a lot less overhead, can be directly connected to the mains voltage(something that is done all the time).

Any thoughts....?
I don't know about how nichrome sheets are used, but this would essentially be conventional heating, so if you use nichrome wire to make a coil rather than using a sheet, you will be able to get much higher resistance because of its length. If you measure the resistance of 1m of wire you can work out the length you can use for your coil at a given voltage and current. Then for example you could double that length and run two in parallel, and so on.
 
So fiddling around a bit I found out the resistance of the crucible is less than 0.1ohms(which is the least count of my multimeter).
So directly connecting the crucible to electricity seems a no-go(without a lot of overhead).

Graphene is also a very good conductor of heat so I am planning to get a nichrome sheet use it along with the crucible.
The plan is to electrically heat the nichrome sheet which will transfer the heat to the crucible.

A couple of options here either place the crucible on top of the sheet which will create a parallel connection thus reducing the effective resistance( I am a bit sceptical of this setup).
Surround the graphite crucible with a couple of nichrome sheets, making good connection with the graphite crucible(looks like a sainer approach), the heat generated by the nichrome sheet will be transferred to the graphite crucible.

The nichrome approach has a lot less overhead, can be directly connected to the mains voltage(something that is done all the time).

Any thoughts....?
What about going to a convential electric furnace?
Save a lot of time and aggrevation.
 
What about going to a convential electric furnace?
Save a lot of time and aggrevation.
I get you point we are slowly converging to it, but the electric furnaces that I have used take close to an hour to reach the melting temprature, if I could heat only the desired part, the metal itself efficiently I can get the melts much faster something we are desperately looking for.
 
I don't know about how nichrome sheets are used, but this would essentially be conventional heating, so if you use nichrome wire to make a coil rather than using a sheet, you will be able to get much higher resistance because of its length. If you measure the resistance of 1m of wire you can work out the length you can use for your coil at a given voltage and current. Then for example you could double that length and run two in parallel, and so on.

A point of concern for me is how to connect the joints because those are the parts that fail first and inhibit the heating process.
 
A point of concern for me is how to connect the joints because those are the parts that fail first and inhibit the heating process.
You do that by folding the nichrome wire at the end so it's double, so it will have half the resistance and won't get as hot as the main part
 
I get you point we are slowly converging to it, but the electric furnaces that I have used take close to an hour to reach the melting temprature, if I could heat only the desired part, the metal itself efficiently I can get the melts much faster something we are desperately looking for.
If you want to only heat the gold and the graphite crucible, induction will do that.
 
You do that by folding the nichrome wire at the end so it's double, so it will have half the resistance and won't get as hot as the main part

I have heard of it, the connection to the power supply can be done by folding but the connection to the graphite crucible will be hot even if it is doubled since this is the part which will be doing majority of the heat transfer.

Any advice with respect to insulating the nichrome wire since I do not want the wire to radiate the heat but to transfer it to graphite crucible.
 
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.
Argon gas turns into Argon Plasma and helps with the induction process as it displaces other gasses. I use it for my ICP-OES burn chamber and it is great for the initial clearout before the burn begins.
 
Argon gas turns into Argon Plasma and helps with the induction process as it displaces other gasses. I use it for my ICP-OES burn chamber and it is great for the initial clearout before the burn begins.
or the Argon Gas to turn into plasma you need to heat it beyond the electron threshold.
Which is way hotter than any furnace
Anyway many use Argon to immerse the melt in so there will not form oxides or other unwanted products.
That is why a Tig-welder use Argon as well.
 
or the Argon Gas to turn into plasma you need to heat it beyond the electron threshold.
Which is way hotter than any furnace
Anyway many use Argon to immerse the melt in so there will not form oxides or other unwanted products.
That is why a Tig-welder use Argon as well.

A graphite crucible creates a reducing atmosphere around the molten metal is argon still required in such circumstances....?
 
A graphite crucible creates a reducing atmosphere around the molten metal is argon still required in such circumstances....?
No not really but again that depends on the application and production.
Argon is usually used in jewlry production in the casting first and foremost to reduce casting errors.
 
No not really but again that depends on the application and production.
Argon is usually used in jewlry production in the casting first and foremost to reduce casting errors.

Also with respect to casting I've heard if the investment is not of good quality it starts oxidising at high temperatures argon would be a lot more helpful in such environments.
 
Also with respect to casting I've heard if the investment is not of good quality it starts oxidising at high temperatures argon would be a lot more helpful in such environments.
Of course one need to use the appropriate investment and follow the procedures for that particular investment.
But when the burnout cycle has been done and one is ready to cast that should not have much to say as long as temperatures are within safe parameters.
 
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I could heat it using nichrome wire at a fraction of the cost.
I have just learned that nichrome wire is not ideal as it won't survive long above 900degrees Celcius, and suffers from gradual oxidization which causes the wire to get thinner over time. A better option is "Kanthal D" which can operate up to 1300deg C and does not suffer so much from oxidization. However it is more expensive.
 
I have just learned that nichrome wire is not ideal as it won't survive long above 900degrees Celcius, and suffers from gradual oxidization which causes the wire to get thinner over time. A better option is "Kanthal D" which can operate up to 1300deg C and does not suffer so much from oxidization. However it is more expensive.

Nichrome wire has multiple variants as well but the name of the game in this case is to control the resistance of the wire when it is in contact with the crucible.

One needs to control the resistance of the entire system in order for things to be safe.

The greater the contact of the wire with the crucible the lower will be the resistance but also greater power used for heating and better the heat transfer. But lower the contact will result in lesser heat transfer.

This is a double edged sword and a trade-off that needs to be managed
 
Nichrome wire has multiple variants as well but the name of the game in this case is to control the resistance of the wire when it is in contact with the crucible.

One needs to control the resistance of the entire system in order for things to be safe.

The greater the contact of the wire with the crucible the lower will be the resistance but also greater power used for heating and better the heat transfer. But lower the contact will result in lesser heat transfer.

This is a double edged sword and a trade-off that needs to be managed
I think in most small furnaces the coil does not touch the crucible, it's mounted on the inside of the insulating surround, with a small air gap, and so it heats the crucible through radiation. That way the crucible can be removed for pouring without disconnecting or damaging the wires. There are quite few videos on youtube for DIY mini furnaces and they all seem to do it that way.
 

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