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macckone
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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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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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jock88
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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 1138 times
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macckone
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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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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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Metacelsus
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Basically, a PWM controller is all that it is. Driving a heating element doesn't require "smoothing things out," so you should be fine.
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jock88
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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).
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jock88
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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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| 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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| 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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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]
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wg48
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| 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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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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| 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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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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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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JJay
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| 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.
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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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| 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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JJay
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...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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ParadoxChem126
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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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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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wg48
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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.
[Edited on 4-3-2016 by wg48]
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Sulaiman
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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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Magpie
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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.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Arbetarn
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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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