[bygolly]

I have a seemingly simple question. I want to build a simple induction furnace to heat up stainless steel rods and the occasional nut/bolt. I can't find any clear plans on the internet. Can anyone help me? I have a 6kV 30mA neon sign transformer.

[the4thseal]

what about raiding stuff from an induction cook tops? i have seen some small portable versions so might it be a good moder play?

[the4thseal]

i think i was not clear....even though i wrote it. What i meant to say was is it possible to use the components from an induction range top? i have run into portable counter top models that might be what were are looking for with just a little rework and modifying? thoughts? Though i will say this thread is just great!

[ImanCarrot]

I know I asked this before, but it may have seemed like a flippant question and wasn't meant to be, but if I was to stick a hypothermia victim in a big enough induction furnace would the effect on the iron in the blood heat the core temperature and save their life?

Most research seems to state that increasing the body temperature in these cases is difficult due to cold blood flowing from the extremities back to the core causing, well, basicaly death.

Immediately attempt to rewarm the victims body core. If available, place the person in a bath of hot water at a temperature of 105 to 110 degrees. It is important that the victim's arms and legs be kept out of the water to prevent "after-drop". After-drop occurs when the cold blood from the limbs is forced back into the body resulting in further lowering of the core temperature. After-drop can be fatal.

So... if you stuck a hypothermia victim in a big eoungh induction thingy... would it heat them uniformly? if it could why isn't it used then?

(Oh I can understand NOT microwaving such cases: microwaves would heat everything in the body, probably boiling your eyeballs, but surely only heating the blood would be well, good?)

[NinerSevenTango]

Induction heating works by magnetically inducing an electrical current into a conductive material. The resistance to that current, multiplied by the square of the current, is what causes heating to take place. It's an undesirable side effect in power transmission and transformers; to get any useful effect, you need ridiculously high currents and usually, high frequencies. As particle size becomes smaller, the particles become invisible to the magnetic field, so higher frequencies are necessary. When you get to molecular particle size, you are already working in the microwave and higher frequency range anyway. In which case all heating is primarily confined close to the surface.

Particle heating in adhesives has been tried, with spotty results. Ridiculously high frequencies and power levels are necessary, and uneven heating is usually the result, with some not heating at all while other areas burn.

So no, it won't work on rust molecules in your blood. At least, not in the form generally recognized as induction heating. Microwaves work by heating water molecules, and some modified approach along those lines might work, but it's probably too dangerous. Why don't you get an industrial microwave and do testing on fresh cadavers? LOL.

Probably infrared heating through conduction is the only method the human body can withstand. Meaning, a hot bath.

--97T--

[Geof]

I know I asked this before, but it may have seemed like a flippant question and wasn't meant to be, but if I was to stick a hypothermia victim in a big enough induction furnace would the effect on the iron in the blood heat the core temperature and save their life?..

I touched on this in Post #119. The effect, as 97T points out is not on the iron in the blood but on all the conductive fluids in your system.

[NinerSevenTango]

i think i was not clear....even though i wrote it. What i meant to say was is it possible to use the components from an induction range top? i have run into portable counter top models that might be what were are looking for with just a little rework and modifying? thoughts? Though i will say this thread is just great!

Getting the power output you need will be problematic.

Take the amount of mass you want to heat, multiply by the specific heat in the units you want to use, multiply by the temperature difference, and you have the amount of heat you need to put into your mass. Then figure out how fast you need to heat it, this allows you to determine the power level you need to put into the mass. Too slow, and you will radiate all the power away at some temperature. Throw in a fudge factor for radiative power losses, and then figure somewhere around a best case of 70 percent for the efficiency of your induction coil.

What that boils down to is, maybe you could melt a thimble full of metal with it if you have excellent thermal insulation. To get more power .... the easiest way of doing it is the way manufacturers of induction heating equipment worldwide do it. The problem is that it isn't very easy or cheap. And if you deviate appreciably from tried and true design approaches, you are very likely to find yourself heading down blind alleys that have already been tried before

--97T--

[bygolly]

So apparently everybody here knows everything about induction furnaces except how to build one?

[HelicalCut]

Why build one? when they are fairly common, even in a backwater like Australia, in the last 3 years I have had the chance to aquire 8 of them from 300Kw to 1.5Kw The 300 Kw was a bit big I was outbid on a 10Kw unit but I got the 1.5Kw unit for nix, it will melt a 1" dia crucible full of copper, at least it did till the transformer took up smoking. I would like a 50Kw furnace but I have never come across one

As for using an induction furnace for treating hyperthermia victims, dielectric heating does the job very well, look up diathermy. People who worked at plants with this equipment were always warm, 27Mhz provides nice even heating, unlike the shallow heating of a microwave (2450Mhz)

[Geof]

....As for using an induction furnace for treating hyperthermia victims, dielectric heating does the job very well, look up diathermy. ...

The idea of being, effectively, the electrolyte in a high frequency electrolytic capacitor kind of sends shivers up and down my spine...but I suppose they would be warm shivers.

[skmetal7]

Why build one? when they are fairly common, even in a backwater like Australia, in the last 3 years I have had the chance to aquire 8 of them from 300Kw to 1.5Kw The 300 Kw was a bit big I was outbid on a 10Kw unit but I got the 1.5Kw unit for nix, it will melt a 1" dia crucible full of copper, at least it did till the transformer took up smoking. I would like a 50Kw furnace but I have never come across one

As for using an induction furnace for treating hyperthermia victims, dielectric heating does the job very well, look up diathermy. People who worked at plants with this equipment were always warm, 27Mhz provides nice even heating, unlike the shallow heating of a microwave (2450Mhz)

oh my god, what is your electric bill!!??

[judy401]

Does anyone have an induction furnace near Loma Linda, CA 92354 that I can use to melt some silicon powder. Sillicon powder melting point is 1410 Degrees Celsius. Now the silicon powder has lots of silicon dioxide (SiO2) on the surface, one would need to melt the SiO2, thus need to go to approximatley 1700 Degrees Celsius to get the Silicon chunks. If you, or know of anyone with an induction furnace setup, please call Judy: (909)796-4796.

[Craigpat]

hello,

I havent read the whole thread but i have done a bit of research and fact finding on induction heating. I found this schematic from www.hvguy.com. The creators were very nice anwered many questions. they had it posted and was free for use so all credit goes to these gent. It is 2.5 kw using 120 VAC converts that into 12 DC and 220. So check out the attachment and i hope it helps you. I do have the 85% of the parts and have spent about 150.00 through surplus stores, online and local electronics stores.

enjoy
Craig

[NinerSevenTango]

Craigpat,

Looks like power transfer would be greatly enhanced by the right amount of capacitance across the primary of the output transformer.

--97T--

[Craigpat]

97T,

Are you answering one of my questions i asked the designers? If so thats cool i was posting to add a schematic and some info for anyone. But thanks, which question were you answering? or are you telling me an upgrade?

see this is what i get for not reading the whole thread.

thanks
Craig

[NinerSevenTango]

I just looked at the schematic, and noticed that the output circuit isn't tuned. That means whatever power makes it into the part you want to heat will be entirely by accident. I'll explain more later if that isn't clear. Gotta run now.

--97T--

[Craigpat]

ah ok Thanks
craig

[jjke]

Hi everyone on this thread.

I am in Monterrey, Mexico, and have been reading this thread. It seems to be no activity for a couple of months.

I am also working in an induction heating machine. My goal is a machine of about 3-5 KW, 20 to 100 KHz.

Some time ago, I built a circuit, as some that appear in the internet, with a transistor bridge and a choke in series with a LC resonant tank. It run more or less up to about half a kw, but the transistors failed in several ocassions.

Now I intend to use a current regulator before the bridge, as Warpspeed suggested. Also, I have purchased a couple of Celem capacitors, a C200T, 21 uF (same as Warpspeed's), an a CSP180/300, 5 uF. (for the low frequency and the high frequency ranges).

Please keep posting your advances in this subject, I intend to be posting my progress also.

Thanks,

Jose

[gombault]

Hi all
I am new to this forum. You say that a 5 Kw induction heater will melt 5Kg of steel in one hour. I contacted a company in china that makes induction heaters and they recommend I use a 120 Kw unit if I want to melt 3Kg of stainless steel. I don’t know why you guys want to make induction heaters when you can buy a new 18 Kw units from China for less than a thousand dollars.
Regards
Marcel

[JBV]

I have made some calulations for melting steel and aluminium.

First you have to calculate the energy needed to reach melting temperature:
E = c * m * (T1 - T2)
c is specific heat capacity.
m is mass in kg.
T1 is start temperature.
T2 is meltingpoint.
E in kJ.

Then you have to calculate the energy needed to melt the metal:
E = cs * m
cs is specific melting enthalpy.

So to melt 1 kg of steel:
0,45 * 1 * (20 - 1535) = 681,75 kJ
276 * 1 = 276 kJ
Total: 681,75 + 276 = 957,75 kJ
957,75 / 3600 = 0,27 kWh

And to melt 1 kg aluminium:
0,9 * 1 * (20 - 660) = 576 kJ
397 * 1 = 397 kJ
576 + 397 = 973 kJ
973 / 3600 = 0,27 kWh

Interesting that both metals need 0,27 kWh per kg to melt!

Lets say the furnace have 50% efficiency and we want it melted in 30 minutes:
0,27 / 0,5 / (30/60) = 1,08 kW per kg
Steel: 7,87 * 1,08 = 8,50 kW per liter
Aluminium: 2,70 * 1,08 = 2,92 kW per liter

And worst case? that the furnace have 25% efficiency (still in 30 minutes):
0,27 / 0,25 / (30/60) = 2,16 kW per kg
Steel: 7,87 * 2,16 = 17,00 kW per liter
Aluminium: 2,70 * 2,13 = 5,75 kW per liter

So i would say a 120 Kw unit is way overkill unless you need the melted metal in a couple of minutes. I guess they just want to make more money hehe.

I hope i have the calculations correct and that we can hit 50% efficiency I know that with BIG melts you can reach 90% but that's another story!

So how is it going? Any progress?