# Electric furnace successful melt !



## Noxx

Hello guys !
I successfully melt silver this morning with my electric furnace.
It reached 1000°C in 15 mins and this could have been faster if I wasn't taking pictures...
The furnace has two layers of Kaowool on the sides, on the top and one layer at the bottom.

Here are some pictures:

And a small video to show the heating speed from 630°C to 800°C.

http://www.goldrefiningforum.com/images/pic 057.avi


Please leave comments 8)


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## Irons

8)


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## lazersteve

Great job Noxx!


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## fixinator

Wowza....that sure heats fast!!!

I wonder what would happen if one used a furnace like this to melt the keyboard mylars??


Fix


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## Noxx

fixinator said:


> Wowza....that sure heats fast!!!
> 
> I wonder what would happen if one used a furnace like this to melt the keyboard mylars??
> 
> Fix



Probably a lot of smoke lol.


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## Noxx

I'll post more pictures soon and maybe an how-to guide if I have time.

Thanks guys.


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## Anonymous

what refactory did you use to make the interior walls and how did you form the channel for the element? 

jim


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## Noxx

I bought my refractory already mixed and wet. It contains silicates and a clay (probably Kaolin). It can support up to 1600°C but breaks very easily from thermal shock. My refractory has many many cracks but it seems to stay in place for the moment lol.

About the channels, this was for me the most challenging obstacle of the construction of the furnace. I rebuild it 7 times before I got it right...

I'm sorry to tell you that I don't know the word of the material in question. I don't even know it in french. What I know, is that it's used in mostly all houses under chairs and such to protect the floor from scratches.

Please someone, tell me how it's called !!

Here are a few pictures to help:

[img:1024:768]http://www.goldrefiningforum.com/images/pic%20031.jpg[/img]
[img:1024:768]http://www.goldrefiningforum.com/images/pic%20030.jpg[/img]

About how it was cast, I made my own cylinder made of cardboard then glued the «thing» like this: 

[img:640:480]http://www.goldrefiningforum.com/images/pic%20026.jpg[/img]

[img:640:480]http://www.goldrefiningforum.com/images/pic%20029.jpg[/img]

And then you put your refractory all around the cylinder like this: 

[img:1600:1200]http://www.goldrefiningforum.com/images/pic%20023.jpg[/img]

Then you let it dry a few days, you remove the cardboard + the «thing» and you gently burn the left over residues with a torch. 

I hope it helps.


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## Anonymous

excellent job. If I could make a suggestion about the cracks, I would work some the kaowool into the refractory to make it like fiberglass
the fibers will strengthen it. that wrap is an excellent idea.


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## Noxx

Yes, it's a good idea. I'll give it a try when I will repair it or rebuild another one...


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## fixinator

I believe it's called "felt".

Fix


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## Noxx

I've just melted gold for the first time.

It took 6 mins at full furnace capacity !

I'll post a vid and a few pictures soon.


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## aflacglobal

Good deal. :wink:


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## Noxx

Duh ! I tried to melt gold yesterday and my heating element melted ! :x 
The element was rated 1400°C and my thermocouple was showing 850°C but the element was running at full capacity and this may overheat it. Also, my thermocouple wasn't well placed in the furnace.

What I learn: Never let run full power into your heating element, don't try to reach 1100°C in 5 mins...


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## Anonymous

Do you have the coils of your element restrained in some way? If not they may move as in compress and make hot spots or touch together shorting out some of the length, effectively lowering the resistance and 
rasing the amps resulting in a melted element, this is really evedient if the melt was confinded to one small spot.

How did you calculate the length of element needed? How many amps are you drawing? 

You may need to make a custom coil to limit your amp draw to allow the heat to raise at a slower rate. As small as your heated space appears you would only need 5 or 6 amps and that Kaowool is really good at keeping the heat in. I think that most kiln controls actually cut the power on and off rapidly to keep from melting the element.

jim


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## aflacglobal

I notice the element has been straightened in the first photo.
You didn't kink or cut any lenght off the coil lowering the resistance did you ?


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## Noxx

No I did not.
I received the element with straightened end like you see in the first picture that let me connect the wire.

The wire melted at the bottom of the furnace.

I'm currently looking to buy a potentiometer (rheostat) to control the input power but I'm not sure how many ohms...


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## aflacglobal

Use a light dimmer switch.
They come in 15, 20 amp sizes.


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## lmills148

aflacglobal said:


> Use a light dimmer switch.
> They come in 15, 20 amp sizes.


 light dimmers are made of triacs not pots you may not get the control your looking for. 


Lloyd


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## aflacglobal

lmills148 said:


> aflacglobal said:
> 
> 
> 
> Use a light dimmer switch.
> They come in 15, 20 amp sizes.
> 
> 
> 
> light dimmers are made of triacs not pots you may not get the control your looking for.
> 
> 
> Lloyd
Click to expand...


good point


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## rainmaker

If you place a SSR (solid state relay) at the proper place in your control circuit it should prevent the coil from overheating. I melted my PID controller several times befor learning, and only learned by looking at how the small tabletop kiln manufatures had their controlls set up.

SSRs are cheep and you can find them and PID controllers on E-bay along with instructions.

Rainmaker


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## Noxx

I was using a SSR. But the thermocouple was not installed properly and the reading temp was not the actual (I guess). But I'm trying to find a way to tune down my element to 80% of it's capacity. Do you think adding a resistor in serie will do the trick ?

Thanks


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## Harold_V

Noxx said:


> I was using a SSR. But the thermocouple was not installed properly and the reading temp was not the actual (I guess). But I'm trying to find a way to tune down my element to 80% of it's capacity. Do you think adding a resistor in serie will do the trick ?
> 
> Thanks


That would be some resistor, Noxx. It would likely put out as much heat as the heating element, which is also a resistor. 

Harold


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## lazersteve

Noxx,

You want to reduce the input power to the coil so you are not melting the element. If I remember your schematic correctly, you are running it straight off of the mains power. 

Perhaps a simple rheostat in line with the mains input would allow you to control the peak power getting to the element. 

Another alternative would be to use a thyristor or SCR circuit to regulate the input power more precisely.

Lastly, a heavier element may survive the feed directly from the mains.

Steve


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## Noxx

Yes I taught about a rheostat but I can't find any cheap one which is able to handle such current.

Currently, my coil is connected to the main 120V outlet but it's controller with a PID and a SSR. 

Thanks


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## lmills148

lazersteve said:


> Noxx,
> 
> Another alternative would be to use a thyristor or SCR circuit to regulate the input power more precisely.
> 
> Lastly, a heavier element may survive the feed directly from the mains.
> 
> Steve



I would have to agree, I think ultimately the rating on the thermocouple is too low and it should probably be upgraded. 

If your trying to save $ there may be another way .
Do you know how many amps it is drawing at 120v? 

edited to add: I just seen your other post 13.3 amps at 120volts 1600 watts. The pot from an old hot plate would work. or range maybe crock pot etc


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## Bernie Foley

Hi noxx&friends,
If you look up variacs on ebay there is a company in canada that sells drills and they have variacs also. i think the 20 amp 120 volter went for about a $120.00 about as chea as one can find!! use it raise and lower the voltage going to the heating element.itself. Sorry this keyboard is skipping!
Good luck with the melter.....Bernie Foley


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## goldsilverpro

I have used Variacs all my working life. They are very handy for controlling heaters, stirrer speeds, etc.


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## Bernie Foley

Noxx&friends,
I have some good bulliten 700 relays that are 4 contacts and can be changed to no or nc.
send me a pm as i have quite a bit of stuff in that line...Trading is good...I need glass,melting dishes,erylmeyers...I'm short as hell on variacs...I can tell you who has them on ebay at good prices....I have a cnc minimill and can make simple stuff not harley
cyclinder heads.can make bullion moldsEtc...good luck Bernie


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## Refiner232121

Hi Everyone
I have been wanting to build an induction heater for a while.
I dont know if this is an induction heater.
If it is I would be intrested in making one


Also Gsp you said this and it would be nice if you could tell us more about that
Thanks



> I have used Variacs all my working life. They are so so handy for controlling heaters, stirrer speeds, etc.


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## goldsilverpro

Here's a bunch of them on Ebay
http://shop.ebay.com/items/?_nkw=variac&_armrs=1&_from=&_ipg=

The simpler ones I used looked more like this one except they were usually 15-20 amps. You simply plug the 110V, AC device you want to control, into the Variac. A 15A Variac will handle most any 110V device, since the devices are most always a max of 1500 watts, or 13 amps.The Variacs are available in a myriad of sizes and, I'm sure, voltages. Some types of motors can't be controlled in this manner, but stirrers can. They are also great for heaters, hotplates, 110V furnaces, and immersion heaters. They would probably work on power supplies, but I've never tried it. The Variac will often provide much better control on these things than the controls that came with them and you can adjust them to a gnat's a**. I usually plugged in the Variac, turned the pot on the Variac to zero, turned the control on the device to max, plugged the device into the Variac, and zeroed in on the adjustments required, using the Variac pot. 

EDIT: The Variac is sort of like a high power light dimmer switch. I also kept records of the various Variac settings needed for the various devices, so I wouldn't have to play around with it each time I used it. I think you can lower the controls on some of the devices to get better sensitivity when adjusting the Variac.
http://cgi.ebay.com/Powerstat-Variac-0-140-Volt-10-Amp-Type-116B-Fused_W0QQitemZ380141343566QQcmdZViewItemQQptZBI_Circuit_Breakers_Transformers?hash=item588230934e&_trksid=p3286.c0.m14&_trkparms=65%3A12|66%3A2|39%3A1|72%3A1205|293%3A1|294%3A50


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## Bernie Foley

Hi Gsp&friends,
The metered 20 amp units like the red ones are just fine for most any project.Most even have a fuse or circuit breaker built in!
Good luck-Bernie


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## Noxx

I never heard of variac before... I might give it a try.

Also, do you think triacs could also work ?


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## Refiner232121

Hi Gsp & Friends 
Thanks for your replies
I think I would have to spend at least one day to really understand this subject in debt


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## goldsilverpro

Bernie,

A question. The pots on the Variacs I used all went to 140 volts. I usually avoided pegging them, especially with motors. Could 140 volts damage any of the devices or cause any other problems?


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## nicknitro

Hi all,

I thought Variacs regulated voltage, with a constant amperage? How would this help control the output to the coils?

Sorry all you electrical engineers if this is a dumb question. LOL Hey Bernie.

Thanks,

Nick


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## Bernie Foley

Hi Gsp,
running 120 volt units on 140 volts usually does no harm unless overspeeding would cause something to go out of balance.
Electric motors usually run cooler at higher voltages as long as they are up to speed.Voltage allowance is 10 % so if we add
12to 120=132 which is darn close to 140volts.I always used the 208 tap on welders&power supplies to include spotwelder&
plating supplies when running on 240 volts. They just plain run better and more efficiently! Very good question!
Something like a microgram scale or a delicate measuring instrument run it exactly as told!....Have a great day!...Bernie


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## Chumbawamba

Hi GSP.

I'll jump in here though I may not know what I'm talking about. I don't think you want to feed anything 140V unless it's protected up to that spec. It's up to you to not send an over-voltage into your device.

Here's a good tutorial on variacs that I just found:

http://www.elect-spec.com/variac_tutorial_xref.pdf

I actually have several, and in fact just pulled one from an old dentist's x-ray controller yesterday. I'm not sure what amperage it's capable of as I haven't checked it out in detail yet. I also have a couple smaller lab variacs, along with my primary variac, which I think can handle 30A. I bought it at a ham swap years ago for something like $30 (deal of the century).

Let me know if you're interested in a trade for one of my other variacs. I'm interested in lab equipment and knowledge


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## Bernie Foley

Hi Nicknitro&friends,
With amperage is the result of resistance verses voltage...simply the more load the more amperage-ohms law.
one volt,one ohm=1 watt...2 volts 1 ohm=2 watts.....at half the voltage the resistance must double to equal the same wattage.
The only stupid question i know of is one that does'nt get asked!
With people that we have on the forum i don't think there is any question that can't be answered...althougt somtimes a
foolish answer is a dam good laugh!!!!.....Bernie


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## Anonymous

Bernie Foley said:


> Hi Nicknitro&friends,
> With amperage is the result of resistance verses voltage...simply the more load the more amperage-ohms law.
> one volt,one ohm=1 watt...2 volts 1 ohm=2 watts.....at half the voltage the resistance must double to equal the same wattage.



At half the voltage, the amperage must double for the same wattage. One volt, through one ohm of resistance is one amp, do that for 1 sec and you have one watt.
If you half the voltage, and double the resistance at the same time you will get 1/4 the amperage also reducing the wattage to 1/4.

jim


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## Anonymous

Noxx,
did you get this fixed? I buy 20 amp infinite switches for taco bell units that are analog and last for a long time.

Jim


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## Noxx

No, it is not fixed yet...

What are these switches ?


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## Anonymous

Noxx,
they are the turn style knob switch, they actually cut the power on and off to reduce the power, control the temp.

I will see if I have an extra, if I do I will PM you if you like.

They are like the switches used on electric ranges (in the old days).

Mine run 1200-5000w elements.

Jim


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## nicknitro

Thanks all,

I think I see how one is proportional to the other now in an autotransformer.

Nick


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## Bernie Foley

Hi James 122964&friends,
That control may be just what Noxx needs.Not to get too technical i believe these switches work by turning on+off+on+off
proportional to the setting and maybe even better for this use than a variac and they will not use any extra wattage that the variac
does.I believe it should be used between the controller+ the element .Very good idea James!!!! We have some of the very best
people on the forum!!! Noxx we will get you back up better than ever! Good luck!....Bernie


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## Anonymous

Noxx,
Search infinite switch on ebay, they have tons of them, as low as 10.00

Jim


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## butcher

http://en.wikipedia.org/wiki/Infinite_switch

http://www.coastalacsupply.com/servlet/the-14/5500-dsh-202-INFINITE-SWITCH/Detail

http://cgi.ebay.com/WB21X5243-GE-Electric-Range-Burner-Infinite-Switch-NEW_W0QQitemZ380135601351QQcmdZViewItemQQimsxZ20090706?IMSfp=TL090706114009r1628


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## Higashi

i wish the pics are still available


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## qst42know

Did you search ebay *"infinite switch"*.

Many pages of them.


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## butcher

alot of stove equiptment use infinite switch's
http://www.google.com/images?hl=en&source=imghp&q=infinite+switch&btnG=Search+Images&gbv=2&aq=f&aqi=&aql=&oq=&gs_rfai=


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## Noxx

Fixed few pictures in my initial post...


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## Higashi

thanks Noxx.


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