Hi,

Has anyone considered induction heating for the extruder?

I'm interested to see if wrapping 50 to 200 windings around the head and passing 20vac or so through it generates enough heat in the extruder... 12Vac@1A / 50 windings = 0.24Vac@50A around the circumference of the barrel.

Common switchmode chips like the tl494 and sg3525 could probably be used to regulate the temperature.

Perhaps we could also check out soldering iron barrels? they're designed to stay at up to 400c for long periods of time.

Yes I have considered it and have all the parts to make one but have not had the time to do it.

Its not quite as simple as you imply. If you put 50A through a good conductor like brass that is 1.5mm thick it will not get very hot. For non ferrous metals you have to use high frequencies to exploit the skin effect so that the current only flows in a thin layer at the surface.

You need to generate something around 20-50KHz at a around 20 - 30W I would guess. A 12V supply is a bit low to do that very efficiently. I have plenty of higher voltage supplies but it is a goal of RepRap to able to run from a car battery or a PC power supply.

Another problem I anticipate is that it may induce a lot of noise onto the thermistor so some filtering may be required there, or else turn it off momentarily to take a reading.

All in all it starts to look like a sledgehammer to crack a nut. The nichrome heater works well and is very simple and cheap. Is only the JBWeld that has problems with high temperatures. BBQ paint has been reported to solve that problem.

Not sure about soldering iron barrels. Do you know of a 12V one which has a hole all the way through?

Edited 1 time(s). Last edit at 01/15/2008 05:25AM by nophead.

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[www.hydraraptor.blogspot.com]

The power supplies that drive car audio systems often run at over 100khz, and can provide thousands of watts if necessary, however it probably is quite a bit more complex than wrapping some heater wire around the barrel.

See [sound.westhost.com] if you do want to try it out

I have an arduino on the way, and several printers from which to scavenge parts

Sorry, I wasn't meaning to imply that it could not be done from 12V, only that the losses in the FETs and the induction coil would be higher with a lower voltage.

Good luck with the scavenging. I recently stripped a scanner, a printer and a couple of 8" floppy drives. The floppy drives being more than 25 years old had some nice steppers and loads of optos. The printer and scanner, being more modern, were pretty disappointing but the surprise find in the printer was a small peristaltic pump.

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[www.hydraraptor.blogspot.com]

I read about induction heater several times, but I still do not understand advantage of this method. Maybe you explain me this?

The induction coil does not have to be in contact with the thing being heated. You can have air, vacuum or a thermal insulator in between so the coil does not get hot itself.

The advantages are:-

No high temp insulation required.

The heat is generated directly in the outer layer of metal of the nozzle so less thermal resistance between the heat source and the polymer.

Less thermal mass so a faster response.

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[www.hydraraptor.blogspot.com]

Found this link on the make magazine blog [blog.makezine.com]

An induction heater:
[www.penguinslab.com]
The schematic is on this page
[www.penguinslab.com]

700 celsius at 24v,3A,300KHz.. certainly sounds like a feasible heating method to me. It would allow us to put an air gap between the barrel and coil so the wires don't need any special heat insulation, and a few extra turns near the bottom could keep the viscosity low all the way to the nozzle.

My only concern is attaching the thermistor in such a way that it doesn't get fried by the magnetic fields

woulndt it heat up all the metals around it like bolts and nuts and steel rods and motors not only the extruder barrel beware with that thing or you'll end up having one molter darwin. induction heating is usually used in high temp metal melting im not really so sure if its the best solution for a 3d printer