Could one use PTFE tape...

to provide the first layer for the header for the extruder barrel (for the new bits from bytes design). The PTFE tape should allow for the temperature required, and would be easier to produce a uniform wrapped heater than trying to embed it in fire cement. I think I would still use fire cement for the outside (between the heater and the outer copper pipe).

Does this seem sensible?

I'm not sure it would work brilliantly, because the temperature of the nichrome wires is higher than the maximum temperature of PTFE. PTFE is fine for the barrel/filament guide because it is less warm, but it would quickly decompose if it touched the heater wire. I found that instead of painstakingly winding the nichrome wire around layers of fire cement it was easier to apply a huge blob of cement all around the barrel, then wind the wire tightly so it sank into the cement. After putting the copper pipe around it I managed to get a ten ohm heater working quite nicely.

I asked this same question a month or two ago. The concern is that if a little bit of extra heat got pumped into the tape (Nophead is extruding things as hot as 230C, and PTFE breaks down around 250-260C) it could potentially produce toxic fumes.

I think I may just wrap the nichrome around the heater barrel with some thermal grease and call it good enough - it seems to hold its shape pretty well on its own. Don't know if that'll work yet though.

Kyle Corbitt Wrote:
-------------------------------------------------------
>
> I think I may just wrap the nichrome around the
> heater barrel with some thermal grease and call it
> good enough - it seems to hold its shape pretty
> well on its own. Don't know if that'll work yet
> though.
>
Don't bet on that working. It will short out.

Forrest Higgs Wrote:
-------------------------------------------------------
> Kyle Corbitt Wrote:
> --------------------------------------------------
> -----
> >
> > I think I may just wrap the nichrome around the
> > heater barrel with some thermal grease and call
> it
> > good enough - it seems to hold its shape pretty
> > well on its own. Don't know if that'll work
> yet
> > though.
> >
> Don't bet on that working. It will short out.


I have the RRRF electrically insulated nichrome. That shouldn't be a problem.

Kyle Corbitt Wrote:
-------------------------------------------------------
> Forrest Higgs Wrote:
> --------------------------------------------------
> -----
> > Kyle Corbitt Wrote:
> >
> --------------------------------------------------
>
> > -----
> > >
> > > I think I may just wrap the nichrome around
> the
> > > heater barrel with some thermal grease and
> call
> > it
> > > good enough - it seems to hold its shape
> pretty
> > > well on its own. Don't know if that'll work
> > yet
> > > though.
> > >
> > Don't bet on that working. It will short out.
>
>
> I have the RRRF electrically insulated nichrome.
> That shouldn't be a problem.

Yes, it will. I originally found the "insulated" nichrome that RRRF sells and have extensive experience with it. The insulation eventually (service life measured in dozens of hours at the current ratings we use it at) perishes. When it does, it will short against your extruder barrel.

Forrest Higgs Wrote:
-------------------------------------------------------
> Yes, it will. I originally found the "insulated"
> nichrome that RRRF sells and have extensive
> experience with it. The insulation eventually
> (service life measured in dozens of hours at the
> current ratings we use it at) perishes. When it
> does, it will short against your extruder barrel.


Thanks for letting me know. That should probably be listed somewhere on the RRRF page selling it - I took the word "insulation" at face value, and I imagine others have too.

Don't misjudge it. Insulated Nichrome is great when you are assembling your extruder barrel in that it keeps loops of the nichrome from touching each other when you are winding it around the barrel. It's just that you can't depend on it instead of a permanent insulating media such as Nophead's Cerastil

[hydraraptor.blogspot.com]


or the Resbond that I am using.

[3dreplicators.com]

I think that [using PTFE tape] has been tried already.
The nichrome wire actually gets much hotter than the inner temperature, enough to burn PTFE. It's hot enough to burn JB weld.

Fire cement, or a high temperature adhesive like those made by Aremco
[www.aremco.com]
is needed to make it reliable.
[Refer to others with more experience using various materials.]

The design of the heater isn't optimal, because of thermal stresses the nichrome, and the barrel, push outward.
Most high temperature adhesives don't have very good tensile strength once cured, so they'll tend to break the covering insulation.

Eventually I intend to set up a forge to cast some things in metal.
At that point I might experiment with some Kaowool
[www.anvilfire.com]
in constructing a more reliable heater.

Edited 1 time(s). Last edit at 09/03/2008 01:55AM by Tim Attwood.

---

[olytim.blogspot.com]

Support for the fire cement is provided by an outer copper tube so it only has to stay in place and not resist and mechanical loading. copper is not the best material for the outer tube stainless steel would be better but is not so readily available or so easily worked.

---

Ian
[www.bitsfrombytes.com]

... in our local tool-store i found some high-temp 2K-silicone-rubber for mould-making (look here: [forums.reprap.org] )

This stuff is good for 350

Just picked up some 600

Hi Matthias,

... it's the same as with barbeque-paint what's Forrest used: [forums.reprap.org]

Viktor

I found that even the BBQ paint perishes after about 100-200 hours of operation.

Just got from the local hardwarestore
I got me a small pot (200grams) pyrozitur, I never heard of before, but its temperature resitance is up to 1100

Hi sid,

... if it's a white mud-like paste, then this could simply be a mixture of waterglass with ceramic dust and some additives for better stability.

So when i'll find some more time at home, i'll reactivate my experimentes with waterglass ...

Viktor

Salut Viktor,

mudlike yes, white.. unfortunately not,
it's mousegrey (that's what is written on the pot... honestly)
maybe just some sort of plaster.

'sid

[edit]
toom wenn Du dir das mal aus der N

Edited 1 time(s). Last edit at 09/03/2008 11:26AM by sid.

... OK, the dust could be cement or such ... did it smell?

I have a small probe of "Karger keramische Vergu

certainly some sort of "i was a stone or crystal once"
Could not find any information about that stuff.
But no it does not smell, not even a bit.
Not like concrete nor plaster (well.. plaster doesn't smell alot either...my nose okay? *sigh*)

Well in fact there is nothing written on it, nothing I can find on the net, nothing.. a mystery, that bottle doesn't even exist

I'll see next week I guess

'sid

This all sounds rather interesting.

I have been looking into anodizing aluminum. Aluminum oxide is apparently an excellent electrical conductor that conducts heat rather well.

A paste made from aluminium oxide and sodium silicate (waterglass) and water may be just the thing to coat the heater barrels with before winding a bare nichrome heater wire around it.

Nice and thin, electrically insulative, heating conducting. sounds too good to be true.

Topping off with a paste of vermiculite, sodium silicate (waterglass) and water. when baked out (using the element) the top layer should be a reasonable insulator and the bottom layer a good heat conductor but both good electrical insulators.

The water glass does indeed look to be very cost effective.

Question is where on earth do you get Aluminum oxide from in a powdered form ?????


what do you guys think

aka47

---

Necessity hopefully becomes the absentee parent of successfully invented children.

[www.logitech.uk.com]

Google knows all

Well, i just made a small barrel of that pyrozitur I bought the other day

from the first imression it's pretty useless.
When fully cured it's getting light grey, but it's extremely brittle,
depending on wallsize you can smash it with two fingers.

also it's conductive at least sometimes...
hard to explain;
whenn I touch it with the multimetre it shows nothing (that is more than 2000 kOhm) but when I move one of the probes it goes well below 1000 kOhms and rises again.
I'm a bit curious about that.
maybe an error of the multimetre itself, maybe some kind of capacitor (that'd be extremely strange)

Maybe I'll give it another try and be more accurate on the how to test
(fixed wallsize, fixed distance between the probes and so on)

'sid