an idea: another extruder barrel heater

While soldering a motor controller for my reprap I had a thought about the extruder/nichrome problems that I have read about some people having. My iron has exchangeable tips and heats them with an inductive heater. It does so really fast and to very high temperatures.

Can we replace the nichrome wire with an inductive heater? This would, as far as I can tell, not require as much current as my soldering iron because we would not need to heat the barrel up to 400C.

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Robert Carpenter
[www.robertcarpenter.net]

funny...
I just asked (in the german forums) something similar [forums.reprap.org]

I thought about hacking a desoldering gun i found on ebay.
hollow barrel interchangeable tips (smalles 0.8mm unfortunately)
max temp 450

... i'm actually using and optimizing high-precision-heaters for our WLD-sensors - here i have three diferent designs with heater-transistors or -resistors, where a NTC-resistor or a PT100 acts as sensor and an OP-cascade controls the end-temperature with an accuracy of some 1/100

Quote
Viktor
with an accuracy of some 1/100

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Robert Carpenter
[www.robertcarpenter.net]

Wow, guys! Why on Earth are you getting excited about 0.01 degrees "accuracy" when you aren't putting your sensor in the molten plastic stream where the accuracy might have a meaning. It seems to be a little uselessly obsessive to brag about sensor resolution when you're not able to put the sensor close enough to what you are needing to measure to be meaningful.

Hi Forrest,

i have a PT100-resistor empedded in a 2mm thick ceramic-tube and had the idea to place it inside the heater, so it would have contact to the molten plastic or paste.

I tried with a digitally controlled soldering station, but the power wasn't enough, so when the plastic flows by it changes the temp-readout in the range of some

I still don't get it.

Does it makes any difference to the print quality if the molten filament is 0.1

i bought a couple of those car soldering irons and they just used nichrome wire as a heating element. as far as i know, induction heating needs AC power.
anyone know a good way to control AC power? triac maybe?

Quote
korndog
as far as i know, induction heating needs AC power.

Yes it does. From what I can tell, we would need to be able to control a ~100Hz, maybe 12v, but high current (any ideas?) waveform. [en.wikipedia.org]

I have no idea how to go about controlling AC power...but I bet that if some EE took apart my soldering iron they could tell me. My electronics experience and knowledge is...lacking. It does temperature regulation to about +/-5

Edited 1 time(s). Last edit at 09/30/2008 12:38PM by Robert L. Carpenter.

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Robert Carpenter
[www.robertcarpenter.net]

why would you need specifically 100hz? wouldn't a triac controlling 120v ac 60hz work and be more simple?

Quote

i bought a couple of those car soldering irons
and they just used nichrome wire as a heating element.

Well that is a pro, isn't it?
The question is, is the barrel hollow or closed at the upper end (where the nichr is connected to the powersupply)

converting 12VDC to 115VAC ?

done

'sid

Edited 1 time(s). Last edit at 09/30/2008 01:23PM by sid.

AC to DC and then to AC again? lol

the barrel is hollow, but it's not that simple to make urself unless you plan on just buying them and strapping them on to your extruder

but seriously, lets get back to induction

well, that's the plan ... no fiddling with isolation and stuff, just plug'n'play

and now back to topic,

there are two ways for having AC on the heater..
one is to take the little holes in your wall and control just a switch to turn in on and off with a relais,
the other is get the smalles DC/AC Converter that fit the needs and control and just plug'n'play.
you may choose whatever seems to be the more comfortable way

'sid

third way :
[en.wikipedia.org]
variable control, cheaper than a relay, and smaller than it.

You could drive a rheostat with a servo motor.

I not sure but i think induction heating might benifit from control of the frequency as well or certainly need the right frequency, there was a link from another posting some months ago that had a very good link to someone making a bolt red hot with and induction heater but it is not trivial. NiChrome is much much easier.

As for controlling AC a triac is very simple and works perfectly in either phase control or burst firing. But they are quite noisey in phase control mode. If burst fired (OK for a heater) then they can be switched on very close to 0 crossing and make no noise and give your heater a longer life.

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Ian
[www.bitsfrombytes.com]

korndog,
there's no triac that can handle serious current needed to fire up the heaters
So you need more than just that to do the job

'sid

Hi sid,

for fast (>1kHz) PWM-switching a 8Watt-diodelaser i used this part: [www2.produktinfo.conrad.com] (HALBLEITERRELAIS 1A 25A 250VAC AQN411VL) from Conrad.

It's simply triggered by 4 to 32Volts DC (i run it at 5Volt) and is able to drive until 25Amps ...

But it's a bit pricey with 32 Euros

Viktor

Edited 1 time(s). Last edit at 10/01/2008 09:24AM by Viktor.

I'm pretty sure that's not an "inductive heater" but a low-voltage high-current resistance heater connected to line voltage through a step-down transformer. At least that's the way the "soldering guns" I've taken apart worked. There may be benefits to using low voltage and high current but it would require mounting the heavy step-down transformer on the extruder head or running fat conductors from the transformer to the extruder head.



robacarp Wrote:
-------------------------------------------------------
> While soldering a motor controller for my reprap I
> had a thought about the extruder/nichrome problems
> that I have read about some people having. My
> iron has exchangeable tips and heats them with an
> inductive heater. It does so really fast and to
> very high temperatures.

sid Wrote:
-------------------------------------------------------
> korndog,
> there's no triac that can handle serious current
> needed to fire up the heaters
> So you need more than just that to do the job
>
> 'sid

I want to melt plastic, not metals.. at least not yet.
we won't need that much power to do that

fire them up, not set them ON fire
think of about 200mA for a triac.
that is about 2.4 Watts (compared to the 18 Watts with the original heater)
do you think you can melt plastic with 2 Watts?
maybe polymorph... maybe not

'sid

not sure what kind of triac you're looking at by i meant these..
[www.newark.com]
it's rated for 15amps

you could go and pass by the hardware store and pick up one a light dimmer with one of these and they're usually rated to run 300w+

I must admit that's pretty powerful with 15 Amps.

Never saw a triac even close to this
(in fact never really needed any triac )

'sid

Edited 1 time(s). Last edit at 10/03/2008 05:34AM by sid.

Do you think that a 50-60Hz would inductively heat a piece of steel tubing to the 250Degree melting range of our plastics?

From what I can tell, it needs to be down around 8-10Volts, which can be done easy enough, and that would also step up the Amperage quite a bit.

I can't reason how to calculate how much that would pull the Amperage up though...I guess you'd need the resistance of the coil we would put in through.

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Robert Carpenter
[www.robertcarpenter.net]

Inductive heating works like a transformer with a 1 turn shorted secondary. The primary current may be a few amps and hundreds turns. The secondary (your barrel) is one turn at hundreds of amps.

Normally high frequencies are used for non ferrous metals because the resistance of, say a brass tubing, would be too low to give much heat even at hundreds of amps. At high frequencies, > 20KHz, the skin effect means that the current only flows near the surface so your one turn secondary has enough impedance to generate heat.

Ferrous metals work at lower frequencies because they have a higher resistance and also have eddy current losses as well.

A normal inductive heater for non ferrous metals takes the mains, rectifies it, and switches it with a couple of power MOSFETs into a coil which has many turns of stranded wire (to counter the skin effect).

I looked into this some time ago and decided a few turns of nichrome and a thermal cement are much simpler, safer and cheaper.

Edited 1 time(s). Last edit at 10/03/2008 11:59AM by nophead.

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[www.hydraraptor.blogspot.com]

So what you're saying here, nophead, is that if we want induction heating we probably need to make the barrel out of something ferrous and/or very high electrical resistance to make it even remotely practical?

That's doable, the only reason the barrel is brass to begin with is the high heat conductance combined with easy machinability. So we add ferrous and/or high resistance to the requirements. I wonder how expensive and how machinable a chunk of 5/16" ni-chrome rod stock would be? Mild steel would certainly be easiest to get though.

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I'm building it with Baling Wire

I don't know if it is feasible to use 50Hz even with ferrous metals. Certainly cooker hobs all seem to use high frequencies.

A nice site all about it here: [www.richieburnett.co.uk]

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[www.hydraraptor.blogspot.com]