Electrical Furnace Contruction - My design and implementation

I made a new topic because the old, "Metal melting <b>propane</b> furnace contruction" didn't fit anymore after I decided to fork it by going electrical and thereby avoid the hassles of propane.

The furnace is finished, and here is the preliminary contruction log:
http://species8472.dyndns.org/tools/el_furnace/el_furnace.ht...

This topic is a continuation of the thread
http://www.sciencemadness.org/talk/viewthread.php?tid=1968

Edit1: Woot! Look at this glory hole, this is HELLFIRE!!!!! :


[Edited on 2004-6-16 by axehandle]

nice!

It's adjustable from 0 to 15A, using 220V AC. The power regulator can be seen in the contruction log, you lazy bastard...

The current coil (which I'll replace with one with lower resistance once I hotwire the power supply to the stove) has a resistance of 27 ohm. Using U=IR, that gives a maximum current of 8.7A. Using P=UI, that gives Pmax=1914W.

I don't think I've exceeded 6..7A in the dehydration step.

The maximum temperature should be close to the maximum temperature of the heating wire, 1300 degrees C, about 100 degrees lower than the MP of iron.

Edit1: As soon as I can afford a Pt/Rh thermocouple, I'll build a temperature display + thermostat circuit for integration.


[Edited on 2004-6-17 by axehandle]

Good idea, I didn't know that. If the connections fail, I can simple yank out the electrodes and do like you described.

Here is an interesting picture of a clay pot I fired in the furnace yesterday. It doesn't look very artistic, but that's beside the point. The point is that this particular clay is a white-burning one that is fired at 1200..1250 degrees C, and that it's, well, fired . It has turned white, and goes *clink* *clink* like porcelain when I knock on it.

Tonight, I will melt some brass in it.




[Edited on 2004-6-18 by axehandle]

Molten Al

Some scrap Al in a pot, slowly cooling down... beautiful.



[Edited on 2004-7-13 by axehandle]

I thought molten aluminum doesnt change colour and stays metallic silver

Are you talking about an induction furnace? I read somewhere that with a bare 15kW one could achieve temperatures of 3400 deg C!
Yes, I was thinking this would make an interesting project

Axehandle, are you using that clay crucible you described earlier? How is it holding up? I have a vague distrust of porcelain, and metal casting books say that fireclay crucibles (similar to what you are using) will not stand up to repeated uses in a furnace.

Nick F, pretty soon we are going to need a category just for furnaces.

Quote:

Originally posted by chemoleo Are you talking about an induction furnace? I read somewhere that with a bare 15kW one could achieve temperatures of 3400 deg C! Yes, I was thinking this would make an interesting project

Very true about the fire clay, had some bad experiance in my attempt at making a metal copper laser.First few runs the (induction)furnace did'nt have enough power to vaporise the copper and then it cracked and started a nasty fire killing one crow(just as well though since at that time I did'nt know yet how to discharge into the plasma )

[Edited on 23-7-2004 by IvX]

How did the fire kill a crow? Do you mean a crow as in a bird? I must be missing something.

I need a crucible for my furnace, and my thought is that if I use an iron pipe and endcap, it will melt under the heat, if I use fireclay/ any other kind of clay, it will crack at high temperatures, and I cannot use a SiC or C crucible, that would not be DIY. Ok, I might have to if there are no other options.

By the way, charcoal furnaces burn coals, coals are partially graphite. Graphite crucibles are graphite. Why will the crucible not burn?

Maybe the fireclay binder helps. Aha, to make a graphite crucible could I just mix fireclay and graphite dust? That is too easy!

Nevermore would you like to post your design on your induction furnace?
Who knows this maybe warrants a new thread... we should then have nearly all types of furnaces covered

Yes it was a bird(started a not-so-small fire-the crow must have been old anyway ).

Nice idea about your crucible unless the graphite/charcoal cathces fire.

ok here it is the design circuit, on the left you should put the power supply, DC from 12 to 30V at least capable of giving out 20A, the T1 should be removed and on its place two coils of thich copper wire should be used, i used 5 rounds of 4mm copper on a diameter of 10cm, the thightest the better but then the mosfet will start to get too hot and eventually die, also care that the magnetic dipole generated are opposite (that means if you make a coil turning on the right, the second should be turning on the left), that's it..the connection from mosfet to the capacitor MKP should be as short as possible also the connection to the induction coil should be short too. the induction coil should be put on top of each other, even better if they are winded together in order to concentrate the magnetic field.
If well made it drains lotsa power from the power supply BUT the mosfet remains almost cold, if they get hot something is wrong!
the circuit was not made by me, the original idea is of Vlad Mazzilli.
This circuit can use also IGBT, that will make peak current far higher, so more power, but the oscillating freq will drop alot with them, so still need to be tested (should be VERY effective too and also more reliable).
I have this circuit in working order right now, so if there is any prob ask me and i'll tell you what's wrong.

Quote:

Originally posted by Cyrus How did the fire kill a crow? Do you mean a crow as in a bird? I must be missing something. I need a crucible for my furnace, and my thought is that if I use an iron pipe and endcap, it will melt under the heat, if I use fireclay/ any other kind of clay, it will crack at high temperatures, and I cannot use a SiC or C crucible, that would not be DIY. Ok, I might have to if there are no other options. By the way, charcoal furnaces burn coals, coals are partially graphite. Graphite crucibles are graphite. Why will the crucible not burn? Maybe the fireclay binder helps. Aha, to make a graphite crucible could I just mix fireclay and graphite dust? That is too easy!

did u try using porcelain?
a coffee cup (the small one) should make an excellent job, remember the thinner the better, since is less likely there is air bubbles trapped in

I've only used it a couple of times, for "test melts". As far as I can see, it's holding up. I fired it before using it, first at approx. 400C for a couple of hours, then for approx. 4 hours at about 1100C. It goes "clink clink" like porcelain when I knock it. It's made from a fine-grained expensive kaolin-containing white burning clay I got at my trusty pottery supplier -- definitely not flower pot clay!

Make a crucible out of pure platinum. It will last forever.
(Has anyone noticed that I have a particular fondness for Pt?)


[Edited on 2004-7-24 by axehandle]

Nevermore, I thought about subjecting one of my tea cups/mugs to 1500C, but I have 3 objections.
1- I'm not that mean, I like my porcelainware in one piece.
2-If that actually works, why don't any books/websites/etc. say "instead of buying a $50 SiC crucible, you can use a tea cup" ?
3- If you look closely, the things crack after a while, just from coffee and tea, let alone molten aluminum.
I have never tried though, have you?


Axehandle, thanks for the suggestion about Pt. You are very helpful. Let me hack up one of my Pt bricks and melt it in my furnace and crucible so that I can cast it into a crucible. Nobody has noticed that you have a fetish for metals, notably Pt. Not at all.


I just got some fireclay and some firebrick sealant to seal all of the cracks in my furnace.

Does anyone know why graphite crucibles don't burn?

According to a foundry book I read, the graphite/fireclay crucibles CANNOT be made at home. That makes me all the more determined.

I don't understand the irritation in your response.
Earlier, you said a coffee cup would work fine, now you say a coffe mug will NOT work.

I guess there is a huge difference between a mug and a cup.

Either way, I'll take your word for it, and will try a thin coffee cup, making sure that it is not a mug.

Because you have tried it, I don't doubt it will work a few times, my concern for myself, and any other people following this thread, is that after many uses the cup could fail. Another problem is that a coffee/tea cup is not nearly large enough for some castings.

Maybe a tea pot would work for larger castings. (I am not serious.)

From my experience with making pottery and ceramics, the issue with thick clay crucibles (coffee mugs ) is most likely due to the comparatively extreme heating and cooling rates, creating thermal stress cracks. Ceramic kilns usually operate with 2-3 day firing cycles.

Any high-firing clay should be useable (stoneware and porcelain fire to 1250C), but porcelain is easier to use for thin walled vessels.

[Edited on 27-7-2004 by Twospoons]

Quote:

Originally posted by Cyrus I don't understand the irritation in your response. Earlier, you said a coffee cup would work fine, now you say a coffe mug will NOT work. I guess there is a huge difference between a mug and a cup. Either way, I'll take your word for it, and will try a thin coffee cup, making sure that it is not a mug. Because you have tried it, I don't doubt it will work a few times, my concern for myself, and any other people following this thread, is that after many uses the cup could fail. Another problem is that a coffee/tea cup is not nearly large enough for some castings. Maybe a tea pot would work for larger castings. (I am not serious.)

i am not irritated, i am just no english so mayeb i sound so.
There is an huge difference between a coffee mug and a coffee cup ..
this is what i mean for coffee cup
http://www.caffemako.it/images/tazzina.jpg
being the thinnest one the better, the "grandma" ones work great since usually they are good quality and very thin china, usually it breaks for thermal stress, so the thinner the better, however it will eventually break of course, but if you keep it good and don't thermally stress will last quite long.
The mugs won't work simply because they are thick, the thermal stress will crack them in 1 or 2 trials..
everything depends about how much stuff you need to melt each time and how expensive are coffee cups over there

about tea cup, if you can put your hand on 1950 china they will be probably the best crucible u can find, i have a very old japanese tea china that is so thin almost u can see tru! but if you only find the thich one then better to use coffee, less porcelain you have, less likely to find a critical defect in.


[Edited on 27/7/2004 by Nevermore]

I tried making 2 crucibles out of fireclay, I cracked one before even putting it in the furnace, and my friend cracked the other by accident. When fired up, they became crumbly and unsuitable for a crucible. My furnace ruins everything!

I think the best bet is to use an iron crucible, ie "tin" can. I know that eventually they will burn through, but if they do, the molten metal will spill in the furnace, and not on my legs. (I would only use them for a couple of runs, then change cans)

I don't have any coffee cups like that, Nevermore. I might have to go to some garage sales.

Failures

After 2 firings with very small amounts of Al, the steel food can I was using burned through. That was about 20-35 min. in the furnace lifetime. Keep that in mind before using a food can. Even though half of the bottom had dissapeared, the Al stayed in! A successful casting was made. Kind of. I had barely any "scrap" Al left, so I couldn't even fill up the cavity (~20 ml )in my sand mold.

The fireclay is still too crumbly, but only cracks a little.

The 3/2/1 cement/sand/bentonite mixture stayed hard after being fired, but the inside cracked (4 large even cracks radiating outwards) The problem with my furnace was mainly not letting it cure long enough.

Off to the ceramic store I go.

I read on a website that concrete starts to decompose and lose its strength at high temp. I forget what temp, but I know furnaces reached it. Maybe a better refractory would use fireclay in the place of cement.

Glass melt

I just melted a broken drinking glass in my furnace, and dipped an iron rod in the melt. Pulling it out, I made this:


Once cooled:


Cool or what?

Axe!

It's the camera.

But I've lost 7kg.

And I'm not FAT!!! I'm 1.75m and 78kg...





[Edited on 2004-8-14 by axehandle]

I've grown weary of my dirty char-coal fired furnace, that I have been using for the last couple of months...

Then I stumbled upon your electrical furnace, Its so beautiful!, and clean! and it doesn't require a blow dryer or char-coal!, I think an electric powered furnace would be the step in the right direction for me. I have some questions though. This .7 mm Kanthal-D wire, could 21 guage (d=.73 mm) nichrome wire be subsituted? How long of a length of wire was needed for your heating element? The control unit as stated on your web page is a 0-15 amp power regulator, I have a very limited knowledge of things electrical, could you please describe this part a little more in depth (subsequent searches on google/ebay did not lead me to anything like the unit shown on your web page). Also, is this not a good project for me to under take, if I have a limited knowlege of things electrical?

Thanks,
Rift Valley

P.S. Here is an attatched picture of my current furnace (you can see why i want to replace it!) It may not look it but the flames are close to 2m high in that picture. Warning it isn't a small picture.

Edit: This website has some interesting resistence alloys for sale (tungsten, Rh/Pt). It also has interesting links under tech. info (like pdf's on every alloy they sell) http://www.resistancewire.com

[Edited on 27-12-2004 by rift valley]

Plus it's completely silent.

Nah, I'd say "go for it". As long as you avoid electrocuting yourself, an electrical coil furnace is probably as safe as furnaces get, heh. The power controller I used was this one, in case you want to check out the manufacturer's homepage: http://www.elfa.se/elfa-bin/setpage.pl?http://www.elfa.se/el...

You'll have to replace the coil periodically. I've had to replace the coil twice so far. It's very easy to overheat it, plus it gets <b>very</b> brittle once it's been used. Right now I'm using a 0.5mm Kanthal-D wire -- I don't think there's any obvious (dis-)advantage compared to a 0.7mm wire, but it's less blistering on the hands winding the coils by hand.

[Edited on 2004-12-27 by axehandle]

[Edited on 2004-12-27 by axehandle]

Well my birthday is next week and since I don't trust my knowledge of electrics I bought a nice little power regulator, for eighty bucks. I know it isn't in the spirit of science madness, but I am afraid starting an electrical fire, or getting electrocuted. The Kanthal D wire is on its way, I already have the refractory, all I need is some tubing and a container. Speaking of which would anyone have any ingenious ideas for a container, I think I might just use metal ducting intended for a home furnace. Midterms next week, to bad I have a feeling that I won't be studying

P.S. Axehandle have you only used your furnace for the melting of metal, or have you used it for any experiments. Recently I have been thinking that an electrical furnace would be perfect for a phosphorus synth. or will it not get hot enough?

rift valley, that power controller looks very good, even having a dial going from 0 to 100. I have to make something similar for my power controller

From the specs it seems to be good up to 15A. Just as you said, adding a fan in addition to the built-in heatsink is probably necessary, especially since you're going to use it at the top of its rating, I believe you mentioned 14A at 110V.

Please tell us of your progress with the furnace ---- it's very interesting, and although the web has lots of pictures and plans of and for home built furnaces, they are typically all gas fired.

Incidentally, I'm in the "acquiring parts stage" for another, <b>much</b> bigger electrical furnace. It will be capable of melting aluminum, brass, silver, zink etcetera, firing pottery and serving as muffle furnace for chemical processes. Perhaps cooking pot roasts as well, although that might be overkill. This time I got some off-the-shelf industrial grade insulation, a 7 meter roll of SuperWool 607 ceramic blanket (less unhealthy alternative to Kaowool, specs at http://www.607max.com).

I intend to include a thermostat this time. The thermocouple won't be cheap though *shudder*.

The stove in the apartment/house is probably hooked up to its own, separate 16A fuse. I know mine is, at least. You may be able to steal power from it, although you'll probably be unable to cook while using the furnace.

On a side note, and yes, I'm blabbering -- I may just have located a source for Kanthal-A1 wire. Maximum temp 1400C as opposed to 1300 for Kanthal-D. Could be useful... although the thinnest one they carry is 1.1mm. Incidentally, if max current is 9A, and the coil diameter is 8mm, the number of turns needed is, according to my calculations, 666 (!). Weird. Get it? 666. Fire. Hell. Pretty funny.


[Edited on 2005-1-10 by axehandle]

My wire finally arrived, technically its for my birthday (tomarrow) but I managed to cut off a little piece to test it out. My mom thinks I ask for the oddest things for my birthday, "What do you need all that wire for? You're not making a bomb are you?" I swear sentence my mom speaks to me ends with "You're not making a bomb are you?" I got close to five hundred feet of the wire so I think that I'm set for now. (If any members want a piece send me a U2U) Here are a couple of pictures.

Is it possible to place more then one attachment on to a post? Here is the other photograph.

EDIT: just got into college, now I can abandon school work and focus on this project

[Edited on 12-1-2005 by rift valley]

Here is my long overdue electrical resistance furnace. The first thing I noticed is how much easier this furnace it to operate then my old POS charcoal blast furnace. I would like to thank Axehandle, his furnace was a great model to build off of. Also the refractory composisition was fantastic to work with (Silica sand, Portland cement, Perlite and bentonite clay). Thank you also for helping me along with the electrical aspect since I have never been taught any of the electrical laws. The pictures might be a little decieving since there is nothing to guage the size of the furnace with. It is a rather small furnace about 15 inches tall, the body is made out of two 5 quart cans for painting I found at home depot. My only regret is that I made the lid a little too thick IMO but that is just a little detail. It is surprising how efficent this furnace it, it helps that the air/gases are not constantly being replaced like in a propane/charcoal furnace. If I grow some balls maybe I will attempt some phosphorus extraction ideas that I have been having. The winters are long in New England so I really will not be able to give this thing a run for its money until spring comes, although I could run this indoors but I don't want to burn my house down (had a close call once but thats a different story). Well I'm babbeling again so I'll just show you the pictures.

This is just a picture of the completed system as a whole


I ripped the guts out of the power controller I bought and created a new housing for it with a fan (although at this time it isn't powered)


This is the inside of the beast, when drying it out i got some cracks but fortunatly they did not seem to weaken the structure that much.


Is this what hell looks like? Just a picture of the furnace when its heated up. I melted a piece of copper in it so I know it gets up to at least 1100C/2000F unfortunatly I didn't take a picture because I was afraid of frying my dads camera, I wish I did though it looked mean.


Thanks again Axehandle and the whole sciencemadness community, if it wasn't for this website I'd still be the kewl I once was.

Nice work!
How did your furnace look after your first run? Many cracks? How long did it take to take on red heat inside, i.e. the the walls of the furnace inside would glow?

Re. the copper - did it truly melt, or just become soft? Where did you place it inside the furnace? I am wondering due to my own experiences, it would have to be white heat inside (correct me if wrong) for it to reach 1100 deg C. In the pic it didnt look like it though

I am just curious because with my charcoal i did melt stainless steel, but only in small places, and only when it directly contacted the brightly white glowing coal, but not elsewhere.

I going to make my own heating applications after these 2 wonderfull examples of what experimentialism can accomplish.

In place of spending alot of hard earned cash on an expensive power regulator, I made my own. Capable of regulating 16 Amperes (3.5 KW on 240 V), it will suffice for most things.

It can be made with under 10€ electronic parts.


Schematic:




First tests with it seem very promising.
A RBF heating mantle will be my first project

An action shot of the above construction:



Notice the old cpu cooler the BT139 triac is mounted on.

The setup is mounted on a simple piece of wood now, but this is only to show the simplicity and size of the cirquit.

Any electronics shop should have these components.
I got mine from a Velleman shop.

Most components are dirt cheap (a few cents), only the printboard, variable resistor and BT139 triac where a bit more expensive.
About €3 for the print, €2 for the varistor and €2 for the triac. The rest of the part cost is less then €1.

The complexity for the scheme is low enough to be feasable to make for amateurs in the electronic science, and can (as you see) make a big difference in price.
Money that could be better spent on some quality glassware

Conrad has them too:

Thanks for the info, I do not plan on building a large furnace anyway, I just need something to melt small ammounts of powdered antimony, to consolidate it into any other form, and likely for melting other metals as well. However, for such a small use, it would be a shame to have to buy so much wire from resistancewire.com, anyone have a source for smaller ammounts?

http://www.used-line.com/c4452597s1424-Ohmite_VT8.htm
This is the one I found, it just needs a new cord(I found it without one). 150$ piece of working equipment for free...wow...

I've just finished my own furnace
Here is the link for the pictures.

http://www.picturetrail.com/gallery/view?p=999&gid=88977...

As you can see, It's made of an welded steel frame with heat resistant stones inside. The heating wire is wrapped around some ceramic sticks to give stability to the heating wires at high temperature. The ceramic sticks are holded by cramps made of Kanthal wire which are jamed into the heat resistant stone. The isolation is mineral wool.
At the beginning I heated the oven with 220V. At 220V the furnace had 220V*2 coils*6A=2600W which wasn't enough. It only went up to appr. 700°C. So I hoped that the fuse would hold and connected the furnace at 380V. Surprisingly the fuse hold 380V*2*10,5A=8200W and the furnace went up to 1150°C after only 5 minutes.
I don't know yet why the fuse hold it, because 380V are 3phases and I had to connect one phase to both two coils and one coil pulls 10,5A but my fuse is only rated for 16A.
Now I need to build a temperature controller and then I'll try to reduct some phosphate to white phosphorous ( big scale of course)
All the temperatures I measured with an IR radiation thermometer.


[Edited on 20-12-2005 by hinz]

Yay, I got an old waffle iron out of the trash today with about 1m(when coiled) of around .4mm resistance wire. As soon as I can get the refractory ingredients I will be able to make my micro-furnace.

Well the furnace is done, it is currently drying at 40v outside. It turned out OK, not as good as I had hoped due to the following reasons:
-I used a big thick wooden dowel to make the hole, removing it took me several hours with a hammer, chisel and power drill. As a result some of the indents for the resistance wire were badly damaged.
-I used 5 year old cement in the refractory
-Ended up making 2 batches of refractory, the second perhaps a bit too fast as I did not make enough the first time.

EDIT: Cost to me: around 20$ I had most things lying around except bentonite and the nuts and threaded rod. And I keep blowing the 8A fuse in the variable transformer

EDIT: All galvanized parts(threaded rod and nuts, not the paint can it is in) that will be exposed to high temps were soaked in HCl until major bubbling stopped, hopefully most of the zinc was removed this way.


[Edited on 7-1-2006 by rogue chemist]

The fuse blows at 8A, or whenever I turn the power up to 130-140v. If the furnace doesent reach the temp needed to melt Sb and Al, I guess I will switch to a higher amp rated fuse or if I am feeling crazy...just bypass the fuse...Let the beakers limit me instead.

EDIT: I am probably kidding about bypassing the fuse...probably...

EDIT: The lid for the furnace is about 1.5" thick, I put a metal strip around it, to hold a handle in place. The metal strip was found in a construction site, but the refractory should keep any heat away from it if the metal contains zinc...I hope.

Also, the furnace is currently running at around 60v, nice glowing coil inside, and steam coming out of the furnace like mad.

Any zinc that was missed by the acid wash should hopefully be burnt out while the furnace is running outside, as the furnace will ideally be used indoors when the drying is complete.

[Edited on 8-1-2006 by rogue chemist]

Nice stuff. Check out www.backyardmetalcasting.com for furnace designs and help,

alsohttp://www.dansworkshop.com/ he built an aluminum melting 240V furnace. He also sells instructions, which I bought, and they are very detailed. I am thinking of making this furnace soon.

I recently bought that controller from payne engineering. I think they meant "pain" engineering because of the 111 dollar cost total for thier 240V controller

To run my 240V furnace, I had to make a 240V extension cord out of 1 plug, one receptacle, and 10 gauge wire ( had to wrestle it) to get a 240 supply outside of the garage from the dryer outlet. MY controller came with a 15A fuse so it can handle moderately heavy loads.

I recently rewound the secondary coil an old microwave transformer with 12-guage wiring hoping to power my furnace with tons of amps from a 120 supply, this failed. Apperently the windings deliver enough current but not enough volts to get across the coil, you could hold it with your bare hands (it was only about 100 degrees).

What happened: 120 In, 27 out. I can't measure the amps because my multimeter only goes to ten.
Mabey I wil make a small spot welder with it or something.

Don't overload the 15 amp rating on the 240 controller. I burned mine out, and had to manually bypass the fuse

[Edited on 18-3-2006 by MetalCastr]

That's called reactance, and depends on the inductance, which depends on the turns and whatnot. The equation you are thinking of is probably something like L = N^2 + R^2 / (9R + 10X), where N is turns, R is radius, X is length and L is in microhenries or something. (Seems to me there should be a constant in there, too.) Eh, Google it.

Unless you're cooking an utterly massive chunk of ferrite (which is a ceramic ), inductance is negligible.

Tim

Yeah well I have been googling for this, it's that I do not trust what I found. In fact, I know a book which is somewhere in my basement which describes it. Finding that book, though, isn't as easy as it seems Assuming that nichrome has almost the susceptibility of vacuum, I still get a significant inductive effect on 50 Hz from the googled formula...

But if everyone else simply uses AC and has no problems whatsoever, then the correct formula isn't so important