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Author: Subject: Homebuilt 1300°C tube furnace
JJay
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[*] posted on 11-3-2016 at 08:37


You can use an iron pipe wrapped with ceramic paper. Note that not everyone likes this approach. Also, ceramic paper is a little hard to find, but many places that sell/service fireplaces should have it.
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Macom24guitar0
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[*] posted on 13-3-2016 at 14:53
A simple electric oven temperature control and thermo sensor placed inside the pipe but outside the blankets will control theses devices. Just
recalibrate the temperature marks with the melting points of lead, tin, silver etc


Quote: Originally posted by Magpie  
PID (proportional-integral-derivative) controllers can be had for very low cost off e-bay.

I built a control circuit for a small relatively low temperature furnace using a PID controller and a solid state relay. It works quite well. You can see it in my last picture at:

http://www.sciencemadness.org/talk/viewthread.php?tid=2171&p...
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Arbetarn
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[*] posted on 18-3-2016 at 19:01


Yes, i searched for a ceramic tube about a year ago and found it here in my country, but i passed becouse it was about 80-100 euros, before shipping.

Thanks for your response. :)
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yobbo I
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[*] posted on 20-3-2016 at 14:58




Quarts tubes here. About 14 quid for 40mm by a foot or 30cm.

http://www.aquatix-2u.co.uk/pif600b-pisces-quartz-sleeves.ht...

Info came from here.
http://imajeenyus.com/mechanical/20151127_quartz_sleeve/inde...

Yob

[Edited on 20-3-2016 by yobbo I]
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JJay
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[*] posted on 27-3-2016 at 19:52


After running several trials to determine its temperature profile, I plugged my furnace directly into the wall current, and it was quickly destroyed. So I built another one. Unfortunately, this time I used a different brand of ceramic paper, and it appears that it wasn't as good an electrical insulator, and it was destroyed on its first trial. I rebuilt it using the same brand of ceramic paper, and the same thing happened (the other kind came from oneworldonedream on eBay and is very delicate and easy to tear but does function well).

So I soaked a cardboard tube in sodium silicate and smeared a layer of perlite/sodium silicate paste around it and then dried it with a heat gun. Then I wrapped some nichrome around it. I limited the maximum wattage to 350 so that the maximum theoretical temperature at 100% power is 1200 C (according to a chart I saw in some trade publication... obviously this is just a rough estimate). I dried out the tube and then cemented it into a cube of firebrick, and right now I am burning out the cardboard. I don't think it is safe to take this furnace up to 1300 C, but it should be able to do 1000 C, and it has a large enough diameter to hold two of my quartz tubes.

Edit: Right now it is holding 700 C at just over 50% power. That's good enough for me.

[Edited on 28-3-2016 by JJay]
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[*] posted on 27-3-2016 at 21:51


Grr I went a little too hot and now the wire is sagging... I'm going to have to try something else... and it appears that molten silica gel actually etches quartz... ugh.

[Edited on 28-3-2016 by JJay]
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JJay
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[*] posted on 28-3-2016 at 15:49


Here is a stoneware tube that I made by putting successive layers of slip onto cardboard. It is crudely constructed, will shrink when fired, and is surely not as heat resistant as fused alumina or pure mullite, but I think it will do the job.

[Edited on 28-3-2016 by JJay]

20160328_154405.jpg - 794kB
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JJay
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[*] posted on 29-3-2016 at 20:32


The stoneware tube is performing well so far. At maximum power (slightly over 300 watts, considerably less than the ones I made previously), it is glowing yellowish orange, and the inside of the quartz tube inserted into it is has a peak temperature of just under 700 C. The stoneware shrank slightly when heated, which was expected. Also, the cardboard tube burned to ashes.I'm going to try to pick up some rockwool tomorrow to see if I can't heat the stoneware to cone 10 without a kiln.
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[*] posted on 30-3-2016 at 09:01


I let the apparatus cool all night, and this morning discovered that while it has maintained its form, the tube is cracked pretty severely. In a couple of places, the cracks actually go all the way around the tube, so I had to handle it carefully. There are a few reasons as to why these cracks occurred.. for one, it was constructed by an amateur who has never done any pottery. Also, the tube was made with unadulterated high-firing stoneware clay flour (adding grog, which is flour made from fired clay, would probably reduce cracking). In addition, the tube was not kiln-fired prior to winding it with nichrome.
--

I sealed the cracks with slip, which is now drying. I'll heat it again later. It will probably crack some more but less severely.

And I just realized that rockwool will melt at around 1200 C, so I'm not going to be able to reach cone 10 (1330 C) with it.

Vermiculite starts to sinter at cone 10 and might work as insulation in a pinch... I feel like a caveman working with these primitive materials....
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[*] posted on 31-3-2016 at 17:15


I am pleased to announce that I have successfully made aluminum chloride with my tube furnace.
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[*] posted on 31-3-2016 at 17:36


Quote: Originally posted by JJay  
I am pleased to announce that I have successfully made aluminum chloride with my tube furnace.


A write-up would be far more interesting than an announcement. :)




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JJay
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[*] posted on 31-3-2016 at 18:32


Ok....
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yobbo II
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[*] posted on 28-4-2016 at 05:58


Why are high temperature high Alumina bricks so expensive? It's only Alumina?

http://www.ebay.co.uk/itm/INSULATION-BRICKS-230-x-114-x-76mm...

The seller has HR 180 bricks available (good to 1800C) for 25 sterling a brick.
Are there any other alternatives.
Would these bricks cut in half (the long way) do in front (the hot side) of more cheaper bricks.
I would suppose that Magnesium Oxide boards used for lining walls of houses etc would fall apart. They contain other things besides MgO.
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[*] posted on 28-4-2016 at 10:45


I would first have to say that might be eBay prices. I have never purchased them, but things tend to be cheaper in person.
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[*] posted on 4-5-2016 at 08:04


Is it possible to use the quartz tubes that can be found inside the infrared heaters (common household appliances)?
According to wikipedia, some heaters operate at 1500 °C. They emmit infrared. I think it is quartz glass right?
Also the lamp inside the heater is called "qurtz heat lamp".

Typical tubes are 30cm length with 1cm diameter. Maybe they can be repurposed to be used in a tube furnace.
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[*] posted on 4-5-2016 at 12:14


Quote: Originally posted by experimenter_  
Is it possible to use the quartz tubes that can be found inside the infrared heaters (common household appliances)?
According to wikipedia, some heaters operate at 1500 °C. They emmit infrared. I think it is quartz glass right?
Also the lamp inside the heater is called "qurtz heat lamp".

Typical tubes are 30cm length with 1cm diameter. Maybe they can be repurposed to be used in a tube furnace.


I think you can use such quartz tubes and I have been collecting as many as I can find. There are similar ones in some powder type photocopiers used to heat the fusing roller. They can be 500mm long.

I think the wiki article you quote is probably referring to the tungsten element temperature not the quartz temperature. From memory quartz starts to devitrify at about 1200C and for loading bearing applications 1000C is quoted. Both are temperature and time dependent and may refer thousands of hours of use. In any case if you are using Kanthal heating element its max temperature is about 1300C.

I think the advantage of a quartz tube is it isolates the heating element from the insulation and atmosphere of the furnace.
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[*] posted on 5-5-2016 at 06:42



The tubes you speak of are translucent, as opposed to transparent.
I have attempted to bend these tubes using a homemade oxy propant torch but was unable to get a good bend. The torch was a grid of holes about 4 inches long and 1/2 an inch wide. The noise coming from it was scary. The heat was a dread. It would heat the tube to white heat ok but as soon as you would go to bend it you had to remove it partially from the flame and it cooled down very very rapidly and that put an end to the bending.
I have little skill regarding glass work anyways.

Speaking of very high temperatures.
Can anyone suggest where you can obtain some cheap rhodium platinum + platinum wire for a thermocouple.
There is some on sale here. It is 0.005 of an inch. 40 swg. (glorified hair).
http://www.ebay.co.uk/itm/Platinum-13-Rhodium-Thermocouple-W...

http://www.ebay.co.uk/itm/LCD-Non-Contact-High-Temperature-I...

Also high temp. pyrometer above.

I wonder would the cheapter thungsten rhenium t couples do if sheated with something available for cheap.
Any suggestions?

Can pyrometers like the one above be used continously?
If they had an electrical output you could use them as the measureing device to control the furnace temperature by having a peep hole with the device constantly looking the the furnace.
Perhaps just better to buy that thermocouple.

Yob


[Edited on 5-5-2016 by yobbo II]
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[*] posted on 19-9-2016 at 15:47


Quote: Originally posted by yobbo II  
Why are high temperature high Alumina bricks so expensive? It's only Alumina?

http://www.ebay.co.uk/itm/INSULATION-BRICKS-230-x-114-x-76mm...

.


Good afternoon Yobbo II.
Let me tell ya that the reason that the higher temperature bricks are much more expensive is that the materials used to make them have to be more pure that the stuff in the lower temperature rated bricks.

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[*] posted on 19-9-2016 at 18:57


Am I missing something...Why are you quoting and replying to yourself in the second person?



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[*] posted on 20-9-2016 at 06:43


Sur everyone else is ignoring me
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[*] posted on 19-7-2017 at 08:52


Using a quartz resistance from a toaster oven/microwave grill, removing the resistance from the inside, and wapping it arround the outside of the oven, then drilling a hole the size of the tube in a refractory brick, and inserting it along with a thermocouple, a really cheap, but small one (my tubes are 1cm diameter, and 30cm long)

However, to me it seems to good to be true, and since im such a beginner in all of this, asking seemed like a smarter option than going ahead and doing it.
So, what is the wrong thing with this idea that would make me fail? :)

The resistance wire may need to be changed so that it doesnt melt.

[Edited on 19-7-2017 by ficolas]
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JJay
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[*] posted on 19-7-2017 at 09:23


You can use nichrome or Kanthal wire to make heating elements. Kanthal is capable of reaching slightly higher temperatures and is more costly, but neither is very expensive.



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[*] posted on 19-7-2017 at 10:01


Also, what can I use to cover both sides, as plugs, or as metal tube joint (for passing methanol through), so that the different coefficients of expansion dont shatter the quartz?
making a quartz-metal joint doesnt seem easy.
The outter part of the quartz tube, the part that sticks out of the refractory brick, what max temperature should that reach? And how do I acomplish that? Maybe adding some sort of cooling to it, and not worrying too much about the joint shattering, or using vinyl tubing if the temperature is low enough?
Aluminium cooling fins and a fan? That looks like a big botch, and maybe it cools it too much... No idea, have to try. However, the quartz shouldnt shatter because of temperature differences in it I dont think, because of how low quartz thermal expansion coefficient is?

I cant seem to find a good thermocouple to buy that isnt too expensive tho...
Also, could the temperature be controled more or less good enough (not preciselly, but good enough to not fall certain value, and not melt the resistances) using just a relay, not a PID? For formaldehyde I only need ~600º, but I will probably try something non toxic and higher temp to see if the setup stands it before the formaldehyde, something like calcium oxide from calcium carbonate.

Too many botches probably.

[Edited on 19-7-2017 by ficolas]
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JJay
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[*] posted on 19-7-2017 at 14:06


I've seen cheap high-temperature thermocouples on eBay... I destroyed one at around 1100 C not knowing that its cable was not capable of withstanding such high temperatures, but the thermocouple itself was still intact and worked fine. You can also get infrared thermometers.

I've tried corks soaked with sodium silicate to plug the ends of a quartz tube, but I don't consider this approach to be entirely satisfactory. Jointed quartz tubes are available. As long as the tube isn't too hot at the joint, you can interface it directly with borosilicate, but borosilicate-to-quartz transition pieces are also available.




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