Caution Using an Induction Furnace

I was at a recent art-iron event, and talked with a person who worked for a long time in a commercial foundry.
The foundry where he worked used an induction furnace, and he said the water-cooled coils tend to fail from time to time.
I has aware of two individuals who where seriously hurt when the coil failed, allowing water to flow into the furnace/crucible full of hot iron.
The contents of the crucible are violently ejected vertically out of the furnace if a coil fails.

He said he narrowly avoided injury once when this happened.
He said "Do not under any circumstances stand over an induction furnace and look into it; even with full safety gear".

Word to the wise.

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I feel like those coils should be hydrotested regularly. It takes such a short time to hydrotest something, especially a critical part thats exposed to corrosion.

I thought the coils were outside , it would be a seriously poor design if such an accident was even possible.
Dan.

abby said:

I thought the coils were outside , it would be a seriously poor design if such an accident was even possible.
Dan.

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I am not familiar with how induction furnaces are constructed, but I thought I better pass on the information.
I was considering purchasing an induction furnace at one point, but the electrical draw is significant, and the utility company can impose a demand charge that will last for a year.

I did talk to one person who purchased a smaller induction system, for blacksmithing, and he burned out his electronic utility meter.
If the induction unit does not have a line reactor, then you can feed damaging harmonics back into the power system.

I did not think it was possible either, but that is what he said.
Perhaps an older or non-standard unit ?

Edit:
I call my diesel-fired furnace a "poor-man's induction furnace".
No demand charge; no large electrical service, I can turn on 200 (+) KW of heat in a few seconds, and maintain that as long as I have fuel.

The advantages of an induction melter are speed of melt, the ability to superheat iron if desired, and also the ability to melt steel if you decided to try that tricky endeavor.
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Me thimpfks there are very small induction furnaces that are made for jewelry and small stuff. I also thimpfks that it is not difficult to build them if you are familiar with a bit of electrical technique.

GreenTwin said:

he said the water-cooled coils tend to fail from time to time.

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I was using a small induction furnace when the crucible decided to leak molten iron. This furnace has a refractory layer between the crucible and the coils so molten metal cannot go near the coils. The electrical engineer that built this furnace was a very clever person and made spill tray underneath the furnace so if the crucible leaked all the contents of the crucible would go there instead of the floor.

Richard Hed said:

I also thimpfks that it is not difficult to build them if you are familiar with a bit of electrical technique.

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If it was that simple every one with a bit of electrical technique would build one. Just ask greentwin how easy it is to build one.

The induction melter is still in place at the Soule factory/museum in Meridian Mississippi, as is the 4 story cupola.
Theoretically either of these units could be operated, but the cupola would required a very significant amount of effort to feed with iron and coke, plus a lot of labor to tap and pour a unit that big.
I asked the Museum manager about restarting their induction unit, and he said "We looked at that, but the old electrical service has been removed, and the utility company wants $100,000.00 for a new electrical service".

The induction melting unit I considered purchasing a few years ago was 3-phase, and that was what was needed to do any significant melting.
Typically 480V, 3-phase would be used.
I ended up purchasing a building with a 200A, 208V, 3-phase service, but I doubt it is rated continuous.

They utility company will hit you with a demand charge too, and so if you run the furnace one time, they continue to charge you the same amount of money for 12 months, whether you use the furnace again or not.

I am aware of a few folks (one I think was in Australia) who used a diesel generator to power their induction furnace.
This bypasses the utility company demand charges.

My diesel burner normally operates at almost 3 gallons per hour, which is about 120 KW continuous.
You need line reactors on an induction unit, else you can damage the utility company equipment.
The less expensive induction units don't have reactors, and so while they will function, they will burn up electronic meters, and damage any other electronics connected to the same electrical service.

I know of one person who purchased an induction furnace a couple of years ago, and I think it was an Inductotherm.
I don't know the KW.
This person was speculating that perhaps he could somehow operated it off of his single-phase rural electrical service, and I correctly predicted that this would never happen.
This same person also discussed purchasing a diesel generator, but diesel generators are not exactly cheap, and there are special considerations for operating electronic loads like an induction melter (derating).

If you can mass-produce 500-1000 valuable castings per day, then you can justify a 480V 3-phase service, otherwise you are stuck with a "poor-man's induction furnace", which is an oil-fired furnace.

Another option for bulk iron melting is the reverb furnace, and examples of this can be seen on the net, used in places like Pakistan.
The reverb furnace seems to work quite well, and you let the oil burner fire directly into a chamber; sometimes round, sometimes more torpedo-shaped.
To tap a reverb furnace, you just rotate it to where a drain hole points downwards.

I am perfectly content with my oil-fired iron furnace, and it is basically maintenance-free.
I patch the interior of my furnace from time to time using plastic refractory, but the Mizzou hot face I use is very durable, and while it may crack sometimes, it will not degrade significantly over time at iron temperatures.

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Here is a small induction melter, and it has water-cooled coils, and water-cooled electronics.
So a break in any of those waterlines would produce some serious fireworks.
This unit is used in the blacksmith shop, and is a very quick way to bring steel shapes to red hot heat in perhaps 15 seconds.
Within 30 seconds, you can melt the end of a steel bar completely off.

A chiller is required to cool and pump the cooling water.

You can tell from looking at this unit, and its chiller, that it will have a finite lifetime, and then one of its many components will fail.
For this smith shop, they can justify the cost of the induction melter and chiller, due to how much it speeds up the work process.

Induction melters have come down in price over the years, but I can vouch for their reliability.
I can vouch for the fact that some of them will burn up an electronic utility electric meter, which can cause a lot of damage to the service entrance (sometimes a burndown).
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Here is a video of this unit in operation.

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I recall induction heating of significant parts of stub axles for cars - heat treatment necessary for the right hardness/strength in the right places. Parts are heated in a furnace, forged, then machined, heat treated with induction heating coils, air blast chilled, finish ground where required, etc. and 100% crack checked. Zero warranty in my time on that job. (I just checked the manufacturer actually did what he said he was doing, not just 100% but audit testing and inspection as well). A coil lasted just a couple of hours before it was changed for a new one. I can't remember why... (30 years back). I do know that getting the heat treatment wrong meant the stub axles broke!
K2

100model said:

If it was that simple every one with a bit of electrical technique would build one. Just ask greentwin how easy it is to build one.

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I am not so sure, maybe it depends on what "a bit" means. (pacemakers, radio, grid reactions come to mind)

abby said:

I thought the coils were outside , it would be a seriously poor design if such an accident was even possible.
Dan.

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Sort of yes and not.
When the refractory lining wears down to the coil, I assume it can get nasty. I guess repairing the lining is on the long run cheaper than wasting the coil. Running equipment as long as possible, or beyond. If the coil fails it possibly becomes a mixture of cannon and vulcano.
Assumption: monitoring the water temperature should give a good indication if something is going to happen.... I am guessing.

Just so you all know, when I said an amateur could build and induction furnace, I also stated "for jewelry and other small items". That would be about a teaspoon of metal. I have seen, (I thimpfk I have seen this) a utub vid of someone making one. Maybe it is just my imagination (I have a good one that I use all the time) that I saw it. I believe someone used a transformer and some other easily available parts.

As for radio which Big Timo mentions, when I was a kid (last week) my cousin and I were interested in all things electronic. No-one was around to teach us, infact we didn't have books or magazines on the subject--we just did it. However, we didn't know the theory of any of the parts we were fiddling with. When I went to college I found out the theory. It's unfortunate for our sh*tty schools that they don't teach this stuff. Truthfully, tubes (valves in Britain), capacitors, basic transistors, resistors, etc. are all quite simple. But like finance and anything to do with banking, if kept secret, it is like a mystery to everyone not in the know.

About 40 years ago I worked 2nd shift as a Machine Repairman/Electrician in a plant that made hydrostatic transmissions for everything from Cub Cadets up to John Deere crawlers. One night I was assigned the job of repairing the 50KW induction hardener in the Heat Treat department. That induction heater was used to harden the splines on all the motor/pump shafts that the plant produced. This was a 480V, three phase unit and the control cabinet was almost big enough to walk into. I checked through the prints and determined that we probably had a bad tube, and replaced it. (That's a valve for you folks that live across the pond.) Not having worked in the plant for very long I carefully followed the break-in instructions included with the tube. A couple of hours later my boss came looking for me wondering why I was still working on what should have been a 1/2 hour job. I handed him the instructions and said we still had an hour to go in the break-in cycle.

The cycle time on that induction hardener was only about 10-15 seconds. It would go through hundreds/thousands of parts before the heating coil was changed. And then the only reason they changed the coil was because they needed to heat treat a shaft requiring a different coil configuration. The coils were liquid cooled, and that cooling system was checked at least 3 times a day.

Working on an induction heater is not that hard, building one that works isn't that hard. Designing and maintaining one that works well, year after year - 24/7, is hard.

Don

Richard Hed said:

I have seen, (I thimpfk I have seen this) a utub vid of someone making one

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Here is a video I made using a home made induction furnace about twenty years ago, it works from a domestic power point (240v 10amp 2400 watts). It takes about two hours to melt 2 kgs of cast iron. If it was so easy to build one they would be so many videos on youtube but it is very rare to find a video showing one working let alone giving detailed instructions on how to build one. If you noticed greentwin never said it was easy to build one but only mentioned the problems installing and running one.

ddmckee54 said:

Designing and maintaining one that works well, year after year - 24/7, is hard.

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The electrical engineer that designed and built his induction furnace had problems with the mosfets which convert 50Hz to 30Khz. At the time ( 35 years ago ) they were the highest rating transistor he could buy so when you wanted a quicker melt running them to the maximum rating they would fail sometimes. Today you have so many options to buy higher rated transistors.

timo_gross said:

When the refractory lining wears down to the coil, I assume it can get nasty

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That drawing can be a bit misleading as it shows the crucible wall being very thin as compared to the bottom of the crucible. As the crucible wall gets thinner over time it is getting closer to the work coils. A compromise has to be made in having the coils too far from the crucible (slow heating) or very close to the crucible (short crucible life) and quicker heating.

FOR THE third tyme: for SMALL things like jewelery

I struggled with my electronics classes in school, and while I could understand the basic concepts, I found it very difficult to actually design transistor circuits that functioned well, and especially circuits that would handle any appreciable power.

I ended up joining a firm working for an old guy who had spent 50 years designing and repairing medium voltage power distribution systems, and so that is what I learned, along with PLC control systems.

One of the types of projects I use to work on was airport lighting, and those were 5KV series circuits, with stepdown transformers at each light fixture. The larger airports used imbedded electronics that operated via a superimposed high frequency control signal, and that signal was used to control stop bars, wig-wags, etc.
There were approach lights that will tell you if you are on the correct glide path, and also end of runway lights, and lights on the corners of the runway.

I talked to a guy who manufactured the end of runway corner lights, and asked him how he managed to keep his corner lights at the same output intensity even as the runway lighting overall was stepped up or down by the pilots, via clicking on the microphone button.
He said he designed an electronic circuit to sense I think line amperage, and adjust his light output to a constant value.
He mentioned that he learned medium voltage electronics at one of the big companies, I forget which one.

Had I gone to work for the medium voltage power guy, I am sure I would be well versed with power electronics, but I went with power distribution instead. So of the folks with more brain power than me (many for sure) can do it all, but my knowledge is somewhat compartmentalized, to include power distribution up to 35kV, and automated control/SCADA systems.

Part of being capable at electronic design is having a good knowledge of commercially available power electronic devices; who makes them, what their operating characteristics are, and how they can be applied to a variety of applications. I don't have that database of knowledge.
One also has to have a knowlege of microcontrollers, since those generally have to control current flow, etc.

If I were going to design an induction furnace (which I am not), I would find some proven design, with some reliable and readily available components, and go from there.
A buddy of mine purchases a used Inductotherm (tm) furnace, and that would be one way to go if setting up a furnace, assuming you could purchase repair parts.
A second option would be to purchase a new tilting induction furnace, and I have looked at those.
Cost is one factor with an induction furnace, but then there is the 3-phase electric service that is required (I have 200 A at 208V), and then utility company demand charges, harmonics potentially fed back to the power company, and finally being able to source spare parts for the electronics that will eventually begin to fail over time.
An electronic component failure in mid-melt could do a lot of damage if you are not able to clear out the partial melt from the furnace and/or crucible.

My oil-fired furnace takes about 1 hour to melt a #10 full of iron (perhaps 25 lbs of iron), and with an induction furnace, I could probably reach pouring temperature in 15 minutes.
My oil burner is simple, and while it is a typical siphon-nozzle design, I designed it to operate without an o-ring, so there is no posibility of the o-ring failing if the burner tube ever overheats (generally when one forgets to withdraw the burner tube from the furnace after the burner is turned off).
I have never had a problem with my siphon nozzle burner, and it performs extremely consistently, which is what is needed when melting iron.
If there ever was a problem with my burner, the tip could easily be replaces for a few dollars.
I have two (actually more) siphon nozzle burners, and so even if one fails in mid-melt, I can change it out and have another burner operating in a few minutes.
There is really not much to fail in my burner.
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Here is the Inductotherm website.

https://www.inductotherm.com/product_categories/induction-melting-furnaces/

A "Mini-melt" system is good for up to about 50 lbs, but I would consider that too small.

The "Rollover" system is what I think I would want, otherwise known as a tilting furnace.

These are Inductotherm's iron melting products.

https://www.inductotherm.com/applications/induction-iron-melting/


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Here is another company, with a "lift-and-swing" melter, and from a small operation standpoint, this would make more sense, and would be less expensive than a tilting furnace.

I would want one that would handle up to a #100 crucible.

https://inductiontech.com/wp-content/uploads/2022/07/Lift-Large-And-Swing-1-front.pdf

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