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Author: Subject: Electrical Furnace Contruction - My design and implementation
Cyrus
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[*] posted on 26-7-2004 at 10:31


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. :P (I am not serious.)




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[*] posted on 26-7-2004 at 10:49


Not much more than my guess but perhaps he was'nt serious about using a coffee mug litrelly.

Say if it's just AL how about using steel?If you wanted to cast perhaps you could elctroplate something(yea I know about how long that would take).

[Edited on 26-7-2004 by IvX]
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[*] posted on 26-7-2004 at 19:43


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]
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[*] posted on 27-7-2004 at 13:27


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. :P (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 :D

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]




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[*] posted on 28-7-2004 at 09:39


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.




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[*] posted on 28-7-2004 at 11:15


What kind of frequency is your induction furnace running at? Looks like an astable monolvibrator that I have seen on simple inverters (DC>AC)-- puts out a square wave.

I have some 50amp MOSFET's lying around here some place - should do some kind of radio frequency. ???

You are using AC mains input, right?
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[*] posted on 1-8-2004 at 21:10
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.




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[*] posted on 13-8-2004 at 16:04
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? :)




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shocked.gif posted on 13-8-2004 at 16:55
Axe!


You've lost some serious weight bud!



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[*] posted on 13-8-2004 at 17:16


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]




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[*] posted on 26-12-2004 at 19:22


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]

IMG_1114.JPG - 666kB
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[*] posted on 26-12-2004 at 21:04


Quote:

Then I stumbled upon your electrical furnace, Its so beautiful!, and clean! and it

Plus it's completely silent. :)

Quote:

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

I don't know the difference between Kanthal and nichrome. AFAIK, Kanthal IS nichrome wire, but a specific brand. Perhaps someone could enlighten us? Spontaneously, I'd say that it could very likely substitute, as long as you never go above the wire's maximum rated temperature. About 1200C for Kanthal, I don't know the value for noname nichrome.

Quote:

length of wire was needed for your heating element? The control unit as stated on your

I've hooked it up to a circuit with a 10A fuse. Thus, the maximum allowable current through the coil must be slightly below 10A -- say 9A. The voltage is 230V.

Ohm's law U=RI says that R=U/I
Hence the needed resistance R=230V/9A=25.55Ω

The 0.7mm wire has a resistivity of 3.51 Ω/m

Needed length is therefore 25.55Ω/(3.51Ω/m) = 7.28m

Quote:

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

The unit on my web page has a humongous heatsink on it. The power regulator itself is very small. I won't even try to explain how it works because I'm not that versed in electronics either, but think of it as a light dimmer, only instead of a lamp you're adjusting the current through a heating coil instead of a lightbulb.

Quote:

page). Also, is this not a good project for me to under take, if I have a limited knowlege of things electrical?

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...
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[*] posted on 27-12-2004 at 07:53


From Procedures in Experimental Physics (J. Strong):

Attachment: ElectricalResistanceAlloys.djvu (53kB)
This file has been downloaded 881 times





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rift valley
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[*] posted on 27-12-2004 at 08:17


Hmmmm, stupid US outlets, they are only 120 volts with a maximum load of 15 amps (or is it 20, does someone else know?) so at nine amps you have 2070 watts of power where at 15 amps I would only have 1800 watts, and at 15 amps with 3.3ohms/m I would only be able to run 2.42m? This just doesn't sound right to me. All of the SCR (a.k.a thyristor) power controllers I am finding are either <5 amps, or some massive industrial controller that is >50amps. On a side note when are things electrical taught in american schools (if ever?) I am a senior in high school and have not be taught any of these laws.

edit: Would .7mm diameter wire be the best choice, because I could get a thicker wire, which may last longer?

[Edited on 27-12-2004 by rift valley]
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[*] posted on 27-12-2004 at 08:48


Quote:

Hmmmm, stupid US outlets, they are only 120 volts with a maximum load of 15 amps (or is it 20, does someone else know?) so at nine amps you have 2070 watts of power where at 15 amps I would only have 1800 watts, and at 15 amps with 3.3ohms/m I would only be able to run 2.42m? This just


I=15A
U=120V
=> R=U/I=120V/15A=16.67Ω

EDIT: Don't know how it happened, but it should be 8Ω

R<sub>wire</sub>=3.3Ω/m

=> L<sub>wire</sub>=16.67Ω/(3.3Ω/m)=5.05m

EDIT: and this should read 8Ω/(3.3Ω/m)=2.42m

Quote:

doesn't sound right to me. All of the SCR (a.k.a thyristor) power controllers I am finding are either <5 amps, or some massive industrial controller that is >50amps. On a

Weird. One would think that it would be much easier to get one in the US than in puny Sweden. Are you looking in the right places?

Quote:

...


Quote:

edit: Would .7mm diameter wire be the best choice, because I could get a thicker wire, which may last longer?

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]




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[*] posted on 27-12-2004 at 09:00


I=15A
U=120V
=> R=U/I=120V/15A=16.67Ω

isn't 120/15=8
so 8/3.3=2.42 meters?
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[*] posted on 27-12-2004 at 09:05


Oops. You are, ofcourse, absolutely right; I am, equally obviously, amazingly wrong. Don't know how it happened. I blame windows "calculator.exe"!



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[*] posted on 27-12-2004 at 18:26


rift valley,

Unfortunately, you'll only learn electrical laws if you take physics this year (often an elective) or if you took another electricity/electronics class earlier in your HS career. Such classes are deemed over-and-above what is necessary for a general education, and as such are offered as electives. When given a choice between having an extra study (screw-off) period or taking another ‘optional’ class, many students decide to use their time smoking blunts in the parking lot.


Also, in most houses the circuit breaker is either 15 or 20A. The breaker is what limits the amount of current flowing through the wire on that circuit. Breaker boxes in the US are wired for both 110V/220V, but a service has to be run especially for the 220V receptacle (dryers). If you know an electrician, they can easily install a 220V service in your garage, or somewhere more appropriate than your laundry room, for a kiln.
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[*] posted on 27-12-2004 at 19:13


Thanks, yeah I am taking physics this year but not a single word has been mentioned about electrical laws I doubt we will cover it, we will spend the whole year on useless force diagrams (God I hate HS physics).

I am going to be purchasing 150 meters of 1 mm diameter kanthal D resistance wire (It is sold by the pound with a min. order of $50 US) If I am feeling generous I wouldn't mind giving away (just pay for shipping) a few meters to people interested in making their own furnaces.
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[*] posted on 27-12-2004 at 21:20


Just make sure you actually have room for all the coiled wire inside the furnace. I think 1mm wire sounds awfully thick. My first coil was 0.7mm wire, and I found that the needed wire length was almost too long to fit inside the furnace even with it coiled in a spiral 8mm in diameter.

Btw, could anyone tell me why 110V was chosen as the standard household AC in the US? It's curious considering that most of the rest of the world uses 230.


[Edited on 2004-12-28 by axehandle]
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[*] posted on 27-12-2004 at 23:56


Or rather, why did the rest of the world choose to use 230?

Even the IEEE doesn't know:

http://www.ieee.org/organizations/history_center/faqs.html

Most houses here get 230-240 V, with two hot wires - L1 and L2, 240 V across them - and a neutral. There is 115-120 V between neutral (or ground) and L1 or L2, and this is wired accordingly at the breaker/fuse box to put the appropriate voltage to the outlets where it is supposed to go.

But in the older areas, some houses only have 1 line with potential, a neutral, and ground. They can only use 120 V appliances, which blows for them.

So my question is: is Euro home 230 power coming in from the transformer as 1 230 V hot wire and a neutral, or two hot lines with no neutral (common here, but not going into houses), or what?

Some people managed to take and pass physics, electricity, electronics, and burn (well, this was before blunts) in the parking lot.

Everyone should take all of the shop/trade electives that you can, unless you want to be a clueless Suit.
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[*] posted on 28-12-2004 at 07:30


I just read the other thread, the one that came before this one. I see in one shot you had two electrodes sticking out of the top, I thought I only needed one, or does the other serve some other function? How did you attatch the heating coil to the electrode, just by wrapping it around it? I will be taking into consideration the thick diameter of my wire, I choose it because I imagine the thicker wire will be more durable. You had to jam 7.3 meters of wire into two meters of tunneling.

120V / 14 amps = 8.6
8.6ohm / 1.77 ohm/m = 4.6 meters

So I figure about two meters of tunnels should be sufficent to house my coil. I will be using this for my refractory, I spied it at the local home depot and since I got a giftcard there for xmas I can't resist buying it.
http://www.rutland.com/sfp4/link4.htm#600

Rift Valley

P.S. Does anyone know if US outlets are 120 or 110 volts I keep hearing and seeing both, I always thought it was 120.
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[*] posted on 28-12-2004 at 13:11


I am not american , but I have seen 115 V, but that is probably just laziness (230 V European standard /2)

as for the question regarding the voltage: Europe usually have a 3 phase system, with 4 or 5 wires in. 3 phases, earth and neutral. Neutral is made by connecting all the three phases, so it can be omitted, earth and neutral is often connected in the fuse board.

Potential from one phase to ground is 230 V which gives 400 V between any two phases. (RMS value). Fusing is typically 10 A on 230 V, and 16 A on 400 V but it depends a lot .

In a typical house/apartment the oven/warm water tank /electrical elements(as typical in sweden electrictiy is used for heating since it was/is cheap) and other large consumers are split equally between the three phases, so the power plant generator is loaded equally. The same goes for the outlets, they can be on different phases in different rooms.

/rickard
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[*] posted on 28-12-2004 at 13:13


There was only one electrode on the top, and one on the bottom. Bad idea with the iron electrodes actually, they lost connection with the Kanthal coil after a while due to oxidation. My solution was to pull them out through the refractory and discard them and make the 2nd heating coil have a section of straight non-spiraled wire at both ends, protruding through the holes left from the iron electrodes and connected to the copper wires from the power regulator using normal screw-strips (or whatever they're called, those usually white plastic things with two screws and two holes for wires)).
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[*] posted on 28-12-2004 at 16:30


The standard domestic supply in the UK is 240 V 50 Hz single phase at 100 A. The standard socket ring main rated at 30 A and each socket on it is rated at 13 A. You can draw up to 3.12 kW from a standard 13 A socket.

Edit: There are 2 wires - live and neutral. The domestic earth is connected to neutral and a local earthing bar at the consumer unit. The neutral is also connected to earth at several points on the way from the substation (multi-point earthing).

[Edited on 29-12-2004 by HRH_Prince_Charles]




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