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Author: Subject: Homebuilt 1300°C tube furnace
macckone
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[*] posted on 16-11-2014 at 23:38


Given the size I would say it is probably a 220V rated heater element. That would be around 9KW and require a 50A circuit.

*edit*
Given a little more research it is designed to operate at 9KW
at 1200C.

[Edited on 17-11-2014 by macckone]
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metalresearcher
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[*] posted on 17-11-2014 at 00:49


Quote: Originally posted by testimento  
Silicon carbide elements are good for up to 1600C and I saw them sold in China for decent prices. Ni-chrome wire will melt at 1350C.

I'm looking for good ceramic lining material for high temp furnace. I was planning of making the body from CaSO4 because it is very cheap and withstands temps up to 1300C easily. But I was looking something more refractory for the surface, and I came up with an idea to use aluminium oxide and potassium/sodium silicate paste. Should this work?

[Edited on 16-2-2014 by testimento]


Where did you find them ? On ebay I usually find US suppliers with horrendous shipping costs extra.

Indeed CaSO4 *will* decompose and crumble, even at lower temps. Otherwise one can use plasterboard.
Even cell concrete (YTONG in EU, Hebel in AU) which is not designed as refractory, can withstand high temps up till 1400C better. When you line it with Blakite or other 1600C rated mortar, it lasts many (>10) heats is my experience.
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[*] posted on 17-11-2014 at 08:50


Quote: Originally posted by Cheddite Cheese  
At 120 V, 2.68 kW.


Do you realize that the resistance of the element is very different when it is at working temperature. Is the quoted resistance given the resistance at working temperature?

At Macckone:

Where are you getting that data?

Thanks

[Edited on 17-11-2014 by jock88]

[Edited on 17-11-2014 by jock88]

Attachment: Silicon Carbide Heater Control.html (69kB)
This file has been downloaded 836 times

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macckone
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[*] posted on 20-11-2014 at 10:14


I was able to find a similar sized element on-line that had specs.
I didn't keep the link.
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jock88
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[*] posted on 20-11-2014 at 17:13


Thanks for that.

Can anyone comment on using a motor inverter for driving a resistive load.
Feed in a 4 to 20mA (say) signal from a temperature process controller to the inverter (assuming it will take that as in input) and connect your heater to the output. The link below says something about harmonics being a problem since there is no inductance to smooth things out?
http://www.szpowerdrive.com/forum/variable-speed-drive-resis...

J88
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[*] posted on 20-11-2014 at 17:51


Basically, a PWM controller is all that it is. Driving a heating element doesn't require "smoothing things out," so you should be fine.



As below, so above.
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jock88
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[*] posted on 21-11-2014 at 15:40
Gouging rods as heating elements


Reading up on using graphite rods as heating elements shows that they are only good to about 500C when used in air.
They are good to 2000C if used with an inert gas.
Anyone care to comment on the following scheme to put gouging rods into a home furnace. The rods will be surrounded with quartz glass, the rods I have fit nicely into tubes with a small amount of play. A copper rod is machined and drilled so the the gouging rod fits up the middle and is clamped for a good connection (the copper rod being cut with a hacksaw at the back like a collette). The quarts tubes also sit into the copper end. Argon gas (very small amount) is bled into the tubes to keep the gouging rods from burning.
Cooling water could be run through the copper ends if necessary.
The diagram may explain things better and shows just one end of one element. Four elements can be run in series and the whole lot run with a pid and an oil cooled welder (or a few rewound microwave oven transformers).
The elements are ghetto and good to go to 1800C or so (until quarts starts melt).

g.gif - 8kB
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jock88
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[*] posted on 2-12-2014 at 17:00


Hi,

Is Kanthal A1 compatible with Quartz glass tubes?
Is it OK to place a wound element inside the quartz glass tubes that can be had discarded in old domestic heaters.

TIA
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JJay
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[*] posted on 25-2-2016 at 12:43


Quote: Originally posted by jock88  
Hi,

Is Kanthal A1 compatible with Quartz glass tubes?
Is it OK to place a wound element inside the quartz glass tubes that can be had discarded in old domestic heaters.

TIA


I don't see why not, but ordinarily, you would want the quartz tube to be removable.

I just built a fairly humble tube furnace. It is only 500 watts and 12 inches long. I simply wrapped one layer of aluminosilicate ceramic paper around a 1 inch black iron pipe and fixed it in place with wire and then wrapped it with nichrome. Then I placed several additional layers of ceramic paper around it and held them in place with wire and put it into a box made with firebrick with the power supplied by a triac dimmer. I had a similar one that was twice as big with 1/3 the wattage with less insulation up to around 850 F yesterday, so I'm quite sure that this one will get really hot. I have a couple of 120 cm quartz tubes that I can place in it. My target is 1000 C.

I bought some alumina boats, but they don't seem to quite fit into my quartz tube, and I'm not sure what to use to grind them down to size (I suppose a diamond grinder would work).

Given the simplicity of construction, I will post pictures later.

Edit: I checked the temperature at 30%, and I had to rescue my thermocouple before it was destroyed by the high temperatures (I am waiting for a better thermocouple to arrive). At the time, the temperature reading was around 730 C but rising rapidly. It looks like it will work just fine for making aluminum chloride and lithium hydride.


[Edited on 25-2-2016 by JJay]
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wg48
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[*] posted on 25-2-2016 at 15:16


Quote: Originally posted by JJay  


Snip
I just built a fairly humble tube furnace. It is only 500 watts and 12 inches long. I simply wrapped one layer of ceramic paper around a 1 inch black iron pipe and fixed it in place with wire and then wrapped it with nichrome. Then I placed several additional layers of ceramic paper around it and held them in place with wire and put it into a box made with firebrick with the power supplied by a triac dimmer. I had a similar one that was twice as big with 1/3 the wattage with less insulation up to around 850 F yesterday, so I'm quite sure that this one will get really hot. I have a couple of 120 cm quartz tubes that I can place in it. My target is 1000 C.

I bought some alumina boats, but they don't seem to quite fit into my quartz tube, and I'm not sure what to use to grind them down to size (I suppose a diamond grinder would work).

Given the simplicity of construction, I will post pictures later.


With a conductive former you risk the insulation between it and your element breaking down. Particularly so at higher temperatures, with 220V elements and only a few mm s of insulation. As the insulation starts to conduct it heats up which increases the conduction which increases the temperature. thermal runaway then create an arc melting the insulation and element.
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JJay
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[*] posted on 25-2-2016 at 18:36


LoL, it wouldn't create an arc - it would create a short circuit, which would blow out the triac long before melting the insulation. But anyway, that's actually not likely to happen with careful construction. And actually, materials become *less* effective conductors when they heat up. I'm not mocking you, but I'm not sure what makes you think you are competent to give advice on these matters... have you built a tube furnace, wg48?

I have 120v elements and yeah, only a mm or so of inside insulation and about 10mm outside plus some refractory brick. I guess I should mention that I doubled up the inner layer of ceramic paper at the ends to keep it from breaking down under the steel wire, and I didn't wrap the heating element very tightly. I think it might be possible to heat it to 1300 C but I don't have any specific plans that would require such temperatures... I think the tube furnace could be used to make phosphorus but have no plans of doing so.

Incidentally, the iron pipe / asbestos (ceramic) paper plan came straight out of Vogel's Practical Organic Chemistry, although I had to make some modifications for higher temperatures / lower voltage / less use of carcinogenic materials. I'm not saying my furnace is as good as garage chemist's, but it sure was easy to build.

Here it is running at around 800 C. I'm burning it in so that it won't fume when I use it in regular experiments (burning off pipe paint, wire coatings, masking tape, etc.). Oh and, the quartz tubing is actually pretty close to ambient temperature at 30 cm away from the heating element.

20160225_172344.jpg - 1014kB


[Edited on 26-2-2016 by JJay]
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wg48
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[*] posted on 26-2-2016 at 08:06


Quote: Originally posted by JJay  
LoL, it wouldn't create an arc - it would create a short circuit, which would blow out the triac long before melting the insulation. But anyway, that's actually not likely to happen with careful construction. And actually, materials become *less* effective conductors when they heat up. I'm not mocking you, but I'm not sure what makes you think you are competent to give advice on these matters... have you built a tube furnace, wg48?

I have 120v elements and yeah, only a mm or so of inside insulation and about 10mm outside plus some refractory brick. I guess I should mention that I doubled up the inner layer of ceramic paper at the ends to keep it from breaking down under the steel wire, and I didn't wrap the heating element very tightly. I think it might be possible to heat it to 1300 C but I don't have any specific plans that would require such temperatures... I think the tube furnace could be used to make phosphorus but have no plans of doing so.

Incidentally, the iron pipe / asbestos (ceramic) paper plan came straight out of Vogel's Practical Organic Chemistry, although I had to make some modifications for higher temperatures / lower voltage / less use of carcinogenic materials. I'm not saying my furnace is as good as garage chemist's, but it sure was easy to build.

Here it is running at around 800 C. I'm burning it in so that it won't fume when I use it in regular experiments (burning off pipe paint, wire coatings, masking tape, etc.). Oh and, the quartz tubing is actually pretty close to ambient temperature at 30 cm away from the heating element




[Edited on 26-2-2016 by JJay]


Well apparently we agree one thing it may be possible to run it at 1300C. Why not try it if you think its not risky. The question is how long will the few mm's of ceramic insulation hold off the voltage. Perhaps you will be lucky.

I suggest you swot up on the behaviour of insulators with temperature.
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JJay
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[*] posted on 26-2-2016 at 20:48


Umm... let's see here....

The coefficient of resistance of both quartz and alumina is extremely close to 0. There is minimal risk of loss of resistance from temperature.

I haven't run it at 1300 C because my thermocouple would disintegrate long before reaching that temperature. Also, 1300 C is pushing the service temperature of the nichrome wire (I've read that Kanthal is a bit better at high temperatures). The melting point of the pipe is probably around 1400 C. While it could withstand a temperature of 1300 C for a limited time, its service life would be limited, and the quartz might not do so well at that temperature either. The furnace was cheap and easy to construct, but I don't have a specific reason to use such high temperatures.

I thought the alligator clamp/120V plug cable was a nice touch, but of course that would be considered an unholy abomination around children or in the workplace.

I usually use game theory type analysis instead of SWOT analysis, but it does depend on what exactly I'm trying to accomplish.
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wg48
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[*] posted on 28-2-2016 at 16:07


Quote: Originally posted by JJay  
Umm... let's see here....

The coefficient of resistance of both quartz and alumina is extremely close to 0. There is minimal risk of loss of resistance from temperature.

Snip .


Ok so your swotting was not very good. Take alumina as a typical high temperature ceramic. Depending on its composition and structure it will have a room temperature resistance of about 10*14ohm.m that's a reasonable insulator. But it drops drastically as the temperature increases. At 1300C it's only about 10*2. That's a change of 1000,0000,0000,0000 fold. (looks more impressive as a regular number lol)

The above is for a high performance alumina ceramic not your your alumina silicate which is probably not as good.

The bottom line is having the heating element insulated from a steel tube with a few mm of almost any common ceramic including quartz risks failure Increasingly with temperature and time. From my experience even 800C is pushing it but then I am in 240v land.

Sorry I have lost the ref link to the above. I am on a phone since my pc died.
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wg48
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[*] posted on 28-2-2016 at 16:36


I found the link
http://www.vtt.fi/inf/pdf/tiedotteet/1996/T1792.pdf
Page 11 starts the electrical data

Thinking about it if you don,t ground the tube (I don't recommend that) it will approximately half the voltage across the tube insulation. If you have an ohm meter you could check the resistance between the tube and element cold and hot dis connected from the mains of cause.
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JJay
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[*] posted on 28-2-2016 at 20:31


The breakdown voltage is more than 1000 volts / mm at 1400 C.

The surface area between the nichrome wire and the ceramic paper is tiny, so the volume resistivity changes, while interesting, are not significant enough to lead to problems, even at 220 V. Please stop spreading disinformation.
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[*] posted on 28-2-2016 at 22:23


Quote: Originally posted by wg48  
I found the link
http://www.vtt.fi/inf/pdf/tiedotteet/1996/T1792.pdf
Page 11 starts the electrical data

Thinking about it if you don,t ground the tube (I don't recommend that) it will approximately half the voltage across the tube insulation. If you have an ohm meter you could check the resistance between the tube and element cold and hot dis connected from the mains of cause.


You really have no idea what you are talking about & I certainly hope no one lets you do any electrical wiring.
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wg48
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[*] posted on 1-3-2016 at 17:16


Quote: Originally posted by JJay  
The breakdown voltage is more than 1000 volts / mm at 1400 C.

The surface area between the nichrome wire and the ceramic paper is tiny, so the volume resistivity changes, while interesting, are not significant enough to lead to problems, even at 220 V. Please stop spreading disinformation.


Thermal runaway is a different phenomena from voltage break down though it may be the end result of thermal runaway.

Its actually the volume of the insulation between wire and steel tube that may thermally runaway because the conduction path is shortest and hence will have the lowest restance and therefore the greatest additional heating.

I guess your not going to get/accept it. Put less effort in to trumping and learn more physics a lot more.
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[*] posted on 2-3-2016 at 14:39


...I only brought up voltage breakdown because of your concerns about arc generation.

You got snippy and brought up ill-founded criticisms of my humble apparatus. I feel like the kid who built a tree fort who was confronted by a home inspector saying that it doesn't meet building codes--and then discovers that it does.
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[*] posted on 3-3-2016 at 13:51


JJay, nice work and congratulations on building a functioning tube furnace! The firebricks and quartz tube are a nice touch.

wg48 does have a point, however. It is true that insulators actually become more conductive (occasionally significantly so) at very high temperatures. If you have several layers of insulating paper, you might be just fine, but it is something to keep in mind.

I don't really see where wg48 has necessarily been "snippy" or given "ill-founded criticisms" of your work. Your furnace is impressive, and his advice on high-temp insulation failure was genuine. His commentary does not seem particularly offensive to me.

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JJay
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[*] posted on 3-3-2016 at 13:58


He did have a couple of good points on insulation at high temperatures, and obviously the behavior of insulators with respect to temperature doesn't really follow a first order equation as is commonly taught. But I'm still sure I can take the furnace to 1300 C.

[Edited on 3-3-2016 by JJay]
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[*] posted on 3-3-2016 at 18:47
Ready made furnace elements ((reporposed)


Below is a pic of a heating element extracted from an old ceramic hob. Presumable good to red heat temperature perhaps higher if the watts is reduced. It could be repurposed as the heating elements of a furnace.

Sorry a bit off topic but is related.

This is my second attempt to post. Does attempting to post two pics crash the system?

The glass (possibly fused quartz) tube across the diameter of the element had me intreaged. It appears to be a thermal cut out operated by the deferential expansion of the glass tube to a metal bar inside the tube. I surprised the difference can operate the micro switch type of mechanism at the end of the glass tube.



WP_20160303_23_43_17_Pro.jpg - 1.6MB

[Edited on 4-3-2016 by wg48]
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[*] posted on 5-3-2016 at 23:48
NoobTube Furnace.


I have been sucked into the furnace fever but I don't want it to be a major project / cash burner,
also, I have no space for a permanent setup and I can not carry heavy stuff,

so, approaching this project impetuously, I now have 10m 20awg (0.81mm) Kanthal A1 wire, which is c2kW at 240 Vac.

My plan is to wrap the wire around the centre part of a quartz tube, 26 mm id x 893mm long, c100 turns, c200mm winding length.
http://www.ebay.co.uk/itm/160998873534?_trksid=p2060353.m143...
and rely on the poor thermal conductivity of quartz and air,
supporting the quartz tube horizontally at its ends with some kind of heat transfer/cooling (tbd)
I expect radiated heat loss to limit the maximum temperature to below 1000 C (I may try insulation later)
Anyone tried quartz tubing meant for uv tubes ?
Is there any reason to doubt that these tubes are fused quartz ?

My main problem (apart from no experience and little research) is measuring and controlling the temperature.
I have a Rex C-100 temperature controller with 40A triac that would suit, but which thermocouple to use?
Type-K (1350 C max) would be simplest.
Can anyone recommend a CHEAP/eBay thermocouple that is likely to survive say 1000 C for extended periods ?
The wire and junction are not a problem, I can make my own, its the insulation that's a problem.
Worst case I'll just physically separate the wires.

If I change my mind about the quartz tube
then the Kanthal wire will probably be used as a heater for either flasks or a fractionating column,
or just rest amongst other project seeds ;)

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[*] posted on 6-3-2016 at 18:55


What is the wall thickness of your quartz tube? The only reason I ask is that a tube meant for lighting might be rather thin-walled and therefore somewhat delicate. Maybe with careful handling this won't be a problem.

I use a K type thermocouple for my furnace and have taken it up to 1000°C quite a few times. I think it is a good choice as I have no need to go hotter. Those who routinely expect to go to 1300°C probably should have one of those very expensive R or S type thermocouples using platinum and platinum-rhodium. Also the elements would likely have to be MoSi2.

I use a Kanthal wire that is ~1mm in diameter. I also coated it with a special coating which probably increases its lifetime greatly by preventing oxidation.

You likely have already seen my construction shown upthread.





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[*] posted on 11-3-2016 at 04:43


Im sure someone already asked this but i have for a long time now been planning to make a tube furnace like this, but i wonder if i can substitute the ceramic tube with something more readily available?

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