One man's insanity---the story of an induction furnace

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Patio
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Re: One man's insanity---the story of an induction furnace

Post by Patio »

To add a little technical data to the story. We did get the 3" material to heat up to about 400*+F. We initially had the charge set in the middle of the furnace, once we knew it was operating, (about 120A going into the coils of the furnace) we moved the charge up against one side of the furnace, for better inductive coupling, and the temperature in the charge started to climb more quickly. I had installed a data recorder on the input to the power supply, and will look to see what the actual in-rush current was, at a later time. Once Harold install the final lining in the furnaces,
we can actually create a melt, I expect the current entering the furnaces and the power supply from the mains, to increase significantly as the melt happens and the inductive coupling between the furnace and charge increases. We really don't know until we get there and give it a go. But for today it was a resounding success, as we now know the system functions and will not have to be sent out for scrap! Harold's dream is still alive! :)
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Harold_V
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Re: One man's insanity---the story of an induction furnace

Post by Harold_V »

neanderman wrote: Mon Jan 27, 2020 1:47 am Can we call you "Patio-H?"
Chuckle!

Well, yeah! You can call me anything except late for supper! :lol:
Great news.

Congratulations!
Thanks! I don't mind telling you it was rather satisfying, especially considering the huge amount of time that has been spent on this project. I've grown old with it. At this point in time, it is highly unlikely that it will ever get used for it's original intended purpose, but is has proven to be a very worthy adversary, and kept my mind well occupied. I've always stated that a guy needs something for which he would get out of bed in the morning. This appears to be it for me!

H
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neanderman
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Re: One man's insanity---the story of an induction furnace

Post by neanderman »

Harold, if I had half of the energy and dedication that you do, I'd consider that I had "A life well led."

I wish you only greater success!
Ed

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Patio
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Re: One man's insanity---the story of an induction furnace

Post by Patio »

neanderman wrote: Mon Jan 27, 2020 1:47 am Can we call you "Patio-H?
If the comment was directed at me, no, this is all Harold's doing! I am just a friend. I appreciate the innuendo, though. :)
I have had very little to do with the actual building or design of this unit. My part in helping Harold, is pretty much what Harold has always done for me, and that is to be another view point, to have discussions, to work out problems, concerns, and help him locate some components on the internet, as Harold's internet connection used to be horrible. He has a much better connection now, than he ever had, since I have known him.
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neanderman
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Re: One man's insanity---the story of an induction furnace

Post by neanderman »

Still, my blessings to you both.
Ed

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Patio
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Re: One man's insanity---the story of an induction furnace

Post by Patio »

Thanks Ed!
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GlennW
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Re: One man's insanity---the story of an induction furnace

Post by GlennW »

Congratulations to all involved in this project!

That is quite an accomplishment!

I too am beginning to realize that the ratio of time to projects isn't as favorable as it once seemed...
Glenn

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Re: One man's insanity---the story of an induction furnace

Post by NP317 »

Congrats! Great progress.
RussN
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Re: One man's insanity---the story of an induction furnace

Post by rrnut-2 »

Fantastic! Congratulations Harold and Patio! This has been a long and expensive project and to have this unit start and run with no problems is great! I wish I could have helped more.

What you experienced with the coupling between the load and the furnace is normal. In the foundry, to start a cold furnace, it gets packed with small size scrap such as quarter sized pieces of scrap. The "melt" will be brought up slowly in order to bake out/heat up the refractory.

When you ram the furnace, start and don't stop until it is done. If you stop ramming the refractory lets say half way up and stop, come back a few hours later and continue on, this will leave a gap that will allow the melt to leak out to the coils. I can tell you from experience that the result is always spectacular!

Jim B
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Re: One man's insanity---the story of an induction furnace

Post by Harold_V »

Jim,
You just may have answered a question I have had for a long time.

I've been aware of the idea that a "heel" is needed when firing the furnace. This heel provides a large enough mass for rapid heating, and that makes sense, but by starting with a load of small pieces, you get heating, it's just a lot slower. Is that correct?

I suspect, especially after witnessing a high amperage but low voltage, that the wattage doesn't rise until the metal is molten, or that there is a large, one piece charge. I used the largest piece I had that I was willing to heat (didn't want to heat the larger piece of 17-4 PH, for obvious reasons).

I intend to use a length of pipe as my forms. They will be melted and become a part of the first heat. For the furnace you provided, schedule 40, 6", and for the furnace I had, schedule 40, 5". I have read that the first charge should be slightly overfilled (with more added when the metal is molten) to ensure sintering of the lining above the full melt line.

Would you please address this idea, and provide further guidance?

As my primary interest is in melting steel to produce gray or ductile iron, is there a particular lining you'd advise? Also, as the top and spout are formed from a different refractory, what would you advise for that function? I hesitate to adhere to the information provided by Ajax, as it relates to technology of the early 60's, and much has changed since then.

I appreciate the tip on not stopping with the lining. I'll ensure that when I get started, I'll have enough time to complete the furnace, thanks to you.

H
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tornitore45
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Re: One man's insanity---the story of an induction furnace

Post by tornitore45 »

I know nothing about induction ovens but do know about electromagnetism.
The transformer cores are laminated to avoid eddy current losses. The idea is that as the current path is broken up the resistance increase reducing eddy currents and the power lost.

Clearly the opposite is desirable in a melting situation. In an induction oven, serious losses and heat coupling does not rise until a bird nest of small pieces coalesce into an interconnected molten mass.
Mauro Gaetano
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Re: One man's insanity---the story of an induction furnace

Post by John Hasler »

tornitore45 wrote: Wed Jan 29, 2020 7:47 am I know nothing about induction ovens but do know about electromagnetism.
The transformer cores are laminated to avoid eddy current losses. The idea is that as the current path is broken up the resistance increase reducing eddy currents and the power lost.

Clearly the opposite is desirable in a melting situation. In an induction oven, serious losses and heat coupling does not rise until a bird nest of small pieces coalesce into an interconnected molten mass.
I have no experience with induction furnaces, but looking at it from a theoretical point of view as an electrical engineer and amateur physicist here is some guesswork:

A solid block will have very low resistance when cold so it will take very high current to get much heat into it. A small diameter block will have low inductance as well as even lower resistance. Increasing diameter will obviously increase inductance, and will also increase resistance because skin depth[1] restricts most of the current to a cross-section near the surface. On the other hand the inductance of a solid block will be highest other things being equal because the average permeability is highest.

A charge of very small bits such as swarf will have high resistance because of all the contact points and so will require a lot of voltage to heat intitially, possibly more than the furnace can deliver. When melting swarf it might help to use a press to compact the charge.

A charge of medium sized chunks packed tightly may be optimum. The contact points will increase the resistance somewhat but not so much as to require more voltage than the furnace can deliver. This will also concentrate the heat so that melting starts sooner. I won't attempt to guess what size the chunks should be.

Once melting starts the effective contact area will go up but the resulting decrease in resistance will be offset by the increasing resistivity. Skin depth will be greater in the melted areas since that material is past the Curie point as well as because of the increase in resistivity.

Depending on the alloy hysteresis losses may contribute significant heating but I can't guess off the top of my head whether this effect will be significant or not. It goes away past the Curie point, of course.

I suspect that you could never melt a solid block of copper and probably not one of aluminum with your furnace. Ferritic stainless alloys might be easiest to melt.

[1] Skin depth is frequency dependent and is also affected by permeability.
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