Shopping for an induction furnace

[fasTTcar]

As much as I like the look of pristine bars, they all end up in Royal Canadian Mints furnaces after I finish my melt and assay.

As long as I have the slag knocked off of them and have a accurate weight and assay, I really don't care much about the appearance.

 

[nickvc]

Dan and to all others who do regular melts, make sure you re run your fluxes there are several compounds which can be added to thin them out and give them a good long hot soak in your furnace, I wouldn't recommend an induction furnace though, an old pot is fine for this, and pour ideally ino a cone mould or failing that a large mould and just powder the resultant flux bar and recover the beads. I do mine every time I accumulate enough flux to fill a large crucible 2 - 3 times it holds around 4-5 kilos of silver, if you have volumes of flux it's worth crushing and assaying especially at today's prices you just have to find a reasonable deal to be able to sell it, I get around 80% of spot for mine if I send 10 kilos+ with an assay, I have also added them to my floor sweeps at times when the volumes have been too small to bother with, every penny counts.

 

[nickton]

how much is that gold bar worth?

 

[Platdigger]

Well the day the post was made, about 136 thousand.
At todays price about 107 thousand.
Pretty nice chunck I would say.

 

[nickton]

dang :!:

 

[cuchugold]

I also was smitten with "induction furnaces", till I built an arc furnace at a very small fraction of the cost. Instead of tilting you can use a tundish type crucible. Beautiful solution really. :G

 

[4metals]

till I built an arc furnace at a very small fraction of the cost. Instead of tilting you can use a tundish type crucible.

Could you go into some detail about your tundish fed arc furnace. Always open to new ideas here the GRF!

 

[cuchugold]

Sure 4metals. The 'tundish' idea I got from you in one of our discussions about the atomizer, etc.

Basically you drill a hole near the wall of a ceramic crucible, and use a ceramic plug to make a tundish. In the opposite wall you have the electric arc.

This guy in the video is a maniac, but he makes good videos. I suggest some discretion on the safety issues, but the technology is there to have an electric furnace for less than $1,000 that will melt 400 Oz gold bar in minutes with no problem at all, and no tilting mechanism needed.

https://www.youtube.com/watch?v=VTzKIs19eZE

I'm surprised that nobody has done it here.

edit: To clarify: Let's say we pick an AP green size 14 crucible and drill a 3/8" hole in the bottom near the wall, and taper the hole conically from the inside, then a weighed graphite rod with a slightly less than 3/8 diameter plug and a conical seat is the plug. The crucible can seat inside a small furnace made of same material as the guy in the video. Drill some holes for the carbon rods near the top, and some simple metal structure to hold it all together. After the melt is liquid, one lifts the weighed rod, and the gold discharges from the bottom. I don't have photos, except for the crucible. It is really simple.

 

[4metals]

I think this discussion would benefit from other members who have some practical experience in fabrication and electrical systems. The video from the King of Random is a good example of a small arc furnace but scaling up to a 10-20KG charge would require more detail and research.

My interest is in using this type furnace is for the smelting of copper, it may work, may not. But the only way to determine that is by more detailed discussion. The issue of mixing of the melt comes into play and I am not sure a simple tundish can fit the bill. Classically the arc furnaces rock back and forth to stir the pot, and good mixing is important.

If this thread takes off we can split it off into its own thread about making an arc furnace. Let's see it there is enough interest.

I found this website by searching and this could be more along the size we would be looking for and he goes into good detail as well. http://hildstrom.com/projects/electric_arc_furnace/index.html

 

[cuchugold]

I used an old electric welder for the arc, 300 Amp If I remember well, and the graphite rods were bigger, but it really cranks, and the metal gets so hot, that really no stirring is needed, but it wouldn't hurt. If the metal is not pure, or it oxidizes like copper, then maybe stirring is a must.

 

[Shark]

I have been interested in building an arc furnace for a while. And as 4metals mentioned I also am thinking copper for my smallish cells. I did some research on youtube for a while and while there are many videos mimicking the king of randoms there seems to be only a few related to the larger sizes. The one that caught my eye (and now I can't find again) was a large size that used a 1 1/2 to 2 inch carbon rod directed toward the bottom of the furnace which held a (supposedly) 20Kg crucible. Almost all of the videos related to larger builds were from Southeast Asia. At least the ones that I could find some translation to.

The thing that could make a workable smaller version is the use of a large arc welder as mentioned. I have a small 110 arc welder that really surprised me with the amount of heat produced by using two gouging rods. From there I haven't got up the courage to try larger rods in my big welder yet.

I would love to see more information come out this post as well. Thanks for bringing it back up.

 

[Shark]

Some basic videos, hope it gives someone some ideas.

Indirect melting furnace
https://www.youtube.com/watch?v=BFyAF-GKWDA

Water cooled arc furnace on a small scale
https://www.youtube.com/watch?v=mtxlIp52L9Y&t=13s

Brazing with a carbon arc toarch.
https://www.youtube.com/watch?v=SVKZZN_W5cU

 

[4metals]

The first video, the indirect melting furnace is a nice design. I have used large gas furnaces with the same pour and feed principle which is rocking to mix the charge and rocking to a more extreme degree so the melt pours out. Using the arc for the heat may not be too difficult. Maybe some of the welders in our group can chime in.

 

[cuchugold]

Interesting videos. Certainly for a copper furnace one needs a much bigger furnace, to make it worth the time. I was thinking that for gold, a simpler furnace, with a graphite crucible and a graphite cathode rod that arcs into the charge, would be the simplest design, add some insulation, and that's it. Pour the 12 kg bar manually with a large tong. Even 25 Kg can be handled manually. 2 bars. Few will pour more than that at a time. I remember that a 12 kg bar was liquid in less than 4 minutes.

 

[Lou]

Conductive as gold is, I’d still be worried about volatilization and the turbulence that arcs can have.