Melting gold using resistive heating.

[Amol Gupta]

Most Multi meters have a function to measure resistance directly.

I did that the readings were not consistent.
The lowest resistance reading I got was 1 ohm everyother reading was north of that

 

[Yggdrasil]

I did that the readings were not consistent.
The lowest resistance reading I got was 1 ohm everyother reading was north of that

That simply means you do not have a consistent pressure/contact at one of the elctrodes

 

[Amol Gupta]

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....?

 

[haveagojoe]

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.

 

[Yggdrasil]

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.

 

[Amol Gupta]

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.

 

[Amol Gupta]

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.

 

[haveagojoe]

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

 

[haveagojoe]

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.

 

[Amol Gupta]

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.

 

[Amol Gupta]

If you want to only heat the gold and the graphite crucible, induction will do that.

I could heat it using nichrome wire at a fraction of the cost.