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Induction Heat used to melt glass and other metals Answered

This is the start of an intended discussion about using induction heat to melt glass and other various metal.


Glass IS a conductor, but only sensibly above about 600 C, a good glow. Tanks of liquid glass ARE heated by passing current through them resistively, with molybdenum electrodes.....

Induction heating, AFAIK could also be used at that point.


Thanks for that info. I thought glass was always a good insulator. Youtube has an experiment showing 2 bulbs in series. 1 bulb then is broken, the filament cut, and the remaining glass stem heated to red. The glass then acts as a variable resistor. I wanna share this link, but unsure how with this tablet.

The link was excellent. I've passed it round my co-workers here. We make instruments for measuring the properties of liquid glass.



There it is.

What's the conductive part, Steve? Is it the impurities? I wouldn't expect SiO2 to be conductive. However, off to Google...okay, I could use a reference. I can't find anything that tells me the conductivity of molten silica.

1Na2O : 1CaO : 6SiO2
1K2O : 1CaO : 6SiO2
1K2O : 1PbO : 6SiO2

Glass is something of the sort. It it's heated shouldn't the Na, K, whatever ions be able to move through the molten silica?

Ah! Yes, it wouldn't surprise me if some of those additives dissociated and provided conductivity. Thank you very much!

As the site physicist, I was oversimplifying "glass" to "silicon dioxide" :-)

Wow!!! I've just seen a benefit in having read a random page in the last year Chemistry book during a boring lesson.
By the way, WHY they dissociate? Liquid SiO2 should be nonpolar... Or do we need a large electric field to orientate and then tear apart molecules? That should be VERY high voltage...

I think it depends on the material in which it is found. The bond angle seems to vary from nearly waterlike (130-ish degrees, if I recall), all the way up to 180 degrees. The former can be polar, while the latter, just from symmetry, cannot.

actually the structure of SiO2 is best thought of as a net or sponge of tetrahedrons which are connected at the corners... the tetrahedron is a Si atom in the center and each corner is a O atom (where 2 tetrahedrons connect at a corner there is only 1 O not 2)... this structure seems much more logical if you start to think of SiO2 as condensed silicic acid Si(OH)4... the tetrahedrons don't allways connect with each corner to another tetrahedron, then ther is a negative charged O and obviously another ion...

Well, actually I never thought of sand as something polar, however it should be due to the tables...

One paper
I just measure it, you're the site physicist, YOU explain it - I insist we keep our demarcations..... ;-) Steve

Thanks, Steve! That was great, and the same as what Gruffalo Child pointed out -- it's the non-silica additives which provide the conductive ions.

Glass is based on sand and from sand they also make transistors and diodes.

In the cold state glass is an insulator but once it reaches the melting point it becomes conductive, almost like a giant zener diode.

You need a lot of heat to melt but to keep in that state by electricity needs surprisingly much less power.

I did some stuff with induction heating and to do it with glass you still have to melt it first.

After that you can use low frequency inductive heating but it will be hard to get an even heating.

The magnetic field concentrates in the center and the eddy currents are only small.

One approach could be to use a suitable metal crucibel filled with glass.

This group has a well organized method of getting the job done without having to melt the glass first. It relies on the conduction of heat to melt the glass... A Moly electrode is mentioned as well as a tin-filled ceramic tube. Not quite feasible without lots of testing equipment and even so, their model is 3/4 of a meter and is still expensive to run. This is not a backyard project.



5 years ago

Just some things to note.... while silicon dioxide isn't a conductor under normal instances, there are metal ions that permeate common examples of glass.

The light green color that is easily identifiable on most glass samples (especially older glass) is caused by dissolved iron; Since iron is present and ideally suited to being melted with induction current, glass probably can be melted in an induction furnace, depending on the iron content.

Graphite might be able to be used in an induction furnace. it depends on the magnetic character put into the graphite. There are a few examples of highly magnetic graphite, but that usually involves doping with a metallic ion.

Induction furnaces are a great and easy way to process some materials, but there's some instances where they don't work well.
The question is that at what point is a traditional thermal process a better idea then an induction furnace?

First point for discussion: glass is not a metal.

yeah i mean seriously. who died and made you a science teacher.....oh wait.

Science teacher? I thought he was correctly his grammer :P I.E. he needs to remove the word OTHER and then it makes sense as a sentence.

if anything, you're more of a slowly flowing solid anyway

True, but there are plenty of non-metallic conductors out there. Graphite, for example. And there are lots of conducting organic polymers these days too. I don't know if you can inductively heat them, but I don't think being metallic is necessarily a prerequisite for that.

Hello, I would like to make you a question about induction heating.
I´ve got an old induction machine to melt metals and now I want to change the system to a vacuum system. I´ve got all done, and everything work perfect but when the vacuum work at -1 bar the induction heating machine stops. Do you know why happen this? Do you know how to solve it? Are induction heating and vacuum possible together. Thansk in advance for your possible answer.

Helo again,
I have found the problem. The box is quite small, so there are a lot of metal near of the induction coil so the power is too high. I have reduced the power and now work O.K. and it can melt the metal, now I have to continue finishing the other things.


Thanks for your answer, At the end I have found the problem. When I use the machine works perfectly but when I use it under vacuum the problem appear and I have seen that there is a problem in the insulation. Tomorrow I will change this bad insulation and I´ll tell you something.

Thanks again

... and graphite is not glass (I may be wrong, but I believe it stops conducting when melted?)

Master Yoda at his best he is. :))

What language (character set) was this written in? The English translation is very strange, and not related to the topic.