# Shopping for an induction furnace



## fasTTcar (Nov 30, 2012)

Hi All.

I currently am using a RDO bench top easy melt system. I have been having some issues with it recently with keeping the heat high enough when melting over approx. 500 grams of mixed karat gold (usually about 12k). It is viscous and homogeneous but more often than not unable to be hot enough to pop the vacuum pin tube and it just melts it instead.

I have been in touch with the company and they are suspecting it is a software issue and believe it can be solved. I would need to send it back in for maintenance and thinking about my back up plan to continue to melt and assay (without resorting to my little electric job). 

One consideration is that it might be time to upgrade to a larger unit for master melts and possible silver processing and keep the original unit for day to day usage.

I have 3 phase electrical available, so that is not an issue. I need something that has a smaller footprint and can handle 5 - 10 kg lots. A tilt system would be preferred, but I am under the impression they are a big jump in price.

Currently looking at the RDO 10kg and a few others.

Any tips or suggestions would be appreciated.

Thanks,
Daniel


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## Noxx (Dec 2, 2012)

Daniel,

I currently use a propane furnace for melts up to 5kg. Have you considered using one ? It's is very efficient generates a lot of heat.

I built mine myself and it cost me only a couple of hundreds. If you ever come by Sherbrooke, I'll show you how it performs


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## glondor (Dec 3, 2012)

Mike at Toronto surplus has about 40 of them. I think he quoted me $5000. http://www.torontosurplus.com/


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## fasTTcar (Dec 3, 2012)

glondor said:


> Mike at Toronto surplus has about 40 of them. I think he quoted me $5000. http://www.torontosurplus.com/



Thanks for that. It looks like a power supply, not the furnace though.

I am not a hardware guy, but I don't believe that is what I need.


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## Dan Dement (Dec 3, 2012)

Daniel,

I have had the same exact problem and I found that I had the metal too hot and it just melts the whole end of the pin sample rod. Turn the heat down a little and I bet it solves your problem. I do business with RDO also and know them to good people. I have a small Wand Melter from another supplier and went thru the same problem. I like not having to try to handle the crucibles with thongs. I have found several Chinese melters that tilt but are overkill for my needs. 

Turning down the heat solved the problem for me and I hope it works for you.

Dan


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## fasTTcar (Dec 3, 2012)

I will give it a shot, but it seems that it is lack of heat that is the problem.

Heavy crucible loads tend to be less viscous and cool quicker when pouring.

Maybe my next melt I will dial the power back to 80% when sampling and back up to 100% when pouring. See how that works.

Thanks for the tip Dan. Also, if you want to shoot me the name of some of the tilt and pour furnaces, I would be interested in checking them out.


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## Dan Dement (Dec 3, 2012)

Daniel,

Most of the cheap ones I have found are from Google searches and they are in China. Another small suggestion, preheat the crucible until it starts to turn a dull orange before dropping in all the metal. Then drop in 40-50 grams and let that get melted and feed it in 40-50 gr lots. It actually goes a lot quicker and when it is when it's all melter, stir it and take the pin sample. I can't run my machine at 100% as it get too hot and shuts off. I try to run mine at 83%-85% and feed it. Usually takes me about 2-3 minutes to melt 500 grams.

Another tip. Try pouring into a tilting ingot form at an angle. Now this promotes solidification and pushes the high & low limits of the bar. I take 7 XRF readings with one on each short side and two on the long sides, average them, and I am within $20 of what NTR pays me. On my last 50 cashouts, it's almost always dead on! 

Dan


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## fasTTcar (Dec 3, 2012)

I do preheat the crucible and slowly add material to it.

I do not assay the bar, as that is what the pin sample is for.

My last 3 settlements with the Royal Canadian Mint were within a 10th of a gram on 100 + ounce lots.


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## Dan Dement (Dec 3, 2012)

Great,

With 100 Oz bars, you need the bigger melter. I cash out 2-3 times a week and certainly a much smaller fish. all the cheap melters I am finding are (of course) out of China. Here is the Google Search http://www.alibaba.com/trade/search?SearchText=induction+melter&IndexArea=product_en&fsb=y . I have a very tough time buying things without service. I have been seaching for a large one in 50 lb to 100 lb area for another industry that has lots of Aluminum and high chrome steels. I know RDO has a couple of tilt melters. I might have a buyer for your old machine. Just have Bob give me a call with a price and trade it back in for one of his larger machines.

Dan


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## fasTTcar (Dec 3, 2012)

Currently, I am shipping 500 gram to 1 kilo bars to the mint. They are re melting them anyway, so it really does not matter. I just would like the flexibility to handle larger bars and melt and assay silver, which is impractical with my current setup.

I am planning on keeping the smaller bench top for now. At the very least as a back up, but it will still be handy for the dealer lots that I have coming in.


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## fasTTcar (Dec 29, 2012)

Ended up giving Bob at RDO some business.

Purchased a 10kw benchtop induction furnace capable of melting 10kg's of gold / 7 kg of silver. Had the electrician in today working on the hookups (requires 220 3 phase). Hope to get a fume/smoke hood setup next week and hope to be going at full speed by mid January.

I am excited to be able to start melting silver, as it has been impractical for the volumes that I generate in the small furnaces that I currently have. I can get a much better handle on what I am shipping out and hopefully be able to be much more aggressive on buying at a wholesale level.

Once this is all put to bed, I am very anxious to start aggressively courting the wholesale business in South Western Ontario. I figure there is a big market here for jewellers and pawn shops that are sick of counting their fingers after shaking hands with many of the Toronto melters.


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## Dan Dement (Dec 30, 2012)

RDO are good people! Let me know how the new melter is working out for you. My little Wand Melter is really a workhorse and trying to get them to make a bigger one!

Dan


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## scrappile (Jan 1, 2013)

fasTTcar said:


> Ended up giving Bob at RDO some business.
> 
> Purchased a 10kw benchtop induction furnace capable of melting 10kg's of gold / 7 kg of silver. Had the electrician in today working on the hookups (requires 220 3 phase). Hope to get a fume/smoke hood setup next week and hope to be going at full speed by mid January.
> 
> ...




Noticed you have some induction loads and also adding this one, just wondering about the power factor . In US they will charge a power-factor penalty if it's too low.

just curious ,..


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## fasTTcar (Jan 2, 2013)

scrappile said:


> Noticed you have some induction loads and also adding this one, just wondering about the power factor . In US they will charge a power-factor penalty if it's too low.
> 
> just curious ,..



Don't believe that it will be an issue. I am in an industrial mall and have not seen any major changes in my power bills.


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## scrappile (Jan 2, 2013)

fasTTcar said:


> scrappile said:
> 
> 
> > Noticed you have some induction loads and also adding this one, just wondering about the power factor . In US they will charge a power-factor penalty if it's too low.
> ...




just thought if it was low, 
The use of synchronous motors is another method of providing power factor ... could possibly use one for the fan for fume hood, since it would be running most of the time,..??

,Rremembered doing the formulas in class . Thanks for checking


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## fasTTcar (Jan 22, 2013)

Well, I am finally up and going. Have the room built, the venting operational and the new furnace hooked up and cooking.


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## Dan Dement (Jan 23, 2013)

Nice size machine! Thanks for posting! Do you use a Crock Pot with Pickle to quick cool your bar and remove scale?

I fried my coil in my wand melter with trying to do powder with Pd in it. Every time I have trouble with an Induction Machine, it's always because of powder. I think I have learned my lesson.

dan


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## EDI Refining (Jan 23, 2013)

Congrats Daniel - Looks good


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## fasTTcar (Jan 23, 2013)

Dan Dement said:


> Nice size machine! Thanks for posting! Do you use a Crock Pot with Pickle to quick cool your bar and remove scale?
> 
> I fried my coil in my wand melter with trying to do powder with Pd in it. Every time I have trouble with an Induction Machine, it's always because of powder. I think I have learned my lesson.
> 
> dan


 
I just drop hot bars in a meatloaf pan with cool water for small melts and in a metal bucket with water for larger bars such as the one pictured.


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## Dan Dement (Jan 23, 2013)

As a suggestion, try a bigger cheap crock pot with a Pickle solution set on medium. Drop out of the mold and put it in the pickle solution. Knocks off 95 of any scale. A rotary brass wire wheel on a cheap Sears grinder will make the bars perfect.
Dan


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## fasTTcar (Jan 23, 2013)

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.


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## nickvc (Jan 24, 2013)

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.


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## nickton (Apr 8, 2018)

how much is that gold bar worth?


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## Platdigger (Apr 8, 2018)

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


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## nickton (Apr 15, 2018)

dang :!:


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## cuchugold (Apr 15, 2018)

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


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## 4metals (Apr 15, 2018)

> 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!


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## cuchugold (Apr 16, 2018)

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.


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## 4metals (Apr 16, 2018)

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


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## cuchugold (Apr 16, 2018)

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.


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## Shark (Apr 16, 2018)

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.


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## Shark (Apr 16, 2018)

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


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## 4metals (Apr 16, 2018)

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.


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## cuchugold (Apr 17, 2018)

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.


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## Lou (Apr 17, 2018)

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


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