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Author: Subject: Homebuilt 1300°C tube furnace
violet sin
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[*] posted on 3-7-2013 at 20:58


nice, but why go to the trouble of building all that for just a few runs? not to be rude just seems like a waste if you don't plan on using it for a bit more than that. and by triac do you mean dimmer switch, or something you got specifically for the task?

I ask because there are a million ways to come at this if you are good at rigging stuff up to suit your needs. just look at all the stuff on youtube, f people go at it from diff angles based on what they wanna pay for. propane could be effective for you though I have grown interested with the atomized waste oil. but both my younger brothers have ford F-350 trucks that take 5gal oil per oil change. so free to me, where as propane is not.

my personal design so far calls for a hard fire brick inner face then thin foamed concrete, and probably rockwool followed by a container/structural material shell( sheet metal over hardiebacker). small and heavy. depth of all to be determined, but I am hoping to keep the rockwool from melting by keeping it just cool enough with distance. its not very far along as I have little time. but the brains coming along quite nicely, they are a shitty ebay thermocouple rigged to use an LED driver through the relay terminals( thing came unable to drive the SCR itself, jerks). reprogrammed to go as high as the thermocouple tip can handle, and have a hightemp prob on its way. its not the best idea and I am going to have to test the components of the wall together before construction commences. all in all a lot of research, little testing and buying the components on the cheap whenever they pop up. not in a hurry so I am spending the time to equip it with power & heater on indicator lights, cooling fan and replaceable portions throughout should any thing go bad. end game calls for a port to the N2 tank for some fun stuff in semi inert gas. could be upgraded to argon easily.

as it sits I have a lot of(most) components for a VERY reasonable price waiting for some attention. can't say it would be cheaper than buying a small crucible furnace, or at least by much. but it is the journey right.

* also this one isn't going up to 1300'C, planning for ~1000'C so far. thought I would add that bit while I can still edit the post


[Edited on 4-7-2013 by violet sin]
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testimento
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[*] posted on 5-7-2013 at 18:55


Well, this wouldn't be just for few uses. I was actually planning of using this for several different processes, including those with catalysts. Lead in one tube, catalyze, and lead the products out and cool. Cool. :)

I made a little adventure to my local junkyard and found a 60-liter aluminium cylindrical tank. An idea came in my mind to coat it with ceramics from inside, make holes at the bottom for the burner, a top at the middle for the canister to sit and vent holes at the top and then the lid. This would be the primary can, and I may coat this with rockwool after then.

My idea is to use common wood coal as an alternative for the gas burner. Big pack of it like 5kg costs a few quid and that should give rather nasty temperatures and kilowatt-powers when I install line fan to blow air at the bottom of the burning coal.

Another of my idea was to insert the crucible itself into this thing, which is coated with clay and stuff and has an nichrome electronics inside it, so if the outer temp is 900C, I will need only small boost with electricity to reach my 1000-1300C.

I planned on using common concrete, but it seems that it only sucks up all the heat, so I've got to look for fireclay, at least to cover the interior. Hope it aint that nasty priced shit I saw at my HW store last week... -___-
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zed
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[*] posted on 6-7-2013 at 10:32


Why re-invent the wheel? You want to attain a temperature, which in common terms is around Cone 12. Look at some furnaces that can do that, and build a copy of one.

A common method of construction of electric furnaces or kiln, is a box shape of fire-bricks, with shallow channels carve into its inner walls. Said channels, being occupied by heating elements, the whole shebang contained in a steel frame.

I suggested build, but kilns of that type are quite common, and are often available used, at inexpensive prices.
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ElectroWin
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[*] posted on 6-7-2013 at 13:00


i have run the equations and designed kilns and furnaces; max temperature and warm-up time of your kiln is highly dependent on several factors:
1) power;
2) insulation thickness;
3) type of insulation;
4) thermal mass;
5) outside surface area

it is typical for kilns of this heat range to use at least 3" thick light-weight fire brick, but check the max temperature rating for the fire brick you choose. if you use heavy fire brick, this has worse thermal conductivity and increases the warm-up time due to both thermal mass and heat loss, but heavy fire brick can be found with greater max temperature, therefore might be suitable for inside surfaces.

for lime kilns, max temp is around 950 C iirc, but you will have difficulty using electric to reach your upper range of 1300C without melting the heating coil.

if the kiln is electric, you should use a heating coil made from nichrome-A, which is rated for higher temperatures than nichrome-B. so for 2 kW, assuming nominal 120VAC, you will expect resistance equal to 7.2 ohm operating. Nichrome resistance at high temperature is about 10% higher than at ambient temperature, so wind your coil to
6.5 ohm; in common sizes of 16-AWG you can find 10 foot lengths on eBay. using these implies winding perhaps three of these coils in series. Finding wire in longer lengths is difficult. Unless they specifically say nichrome-A, it is probably nichrome-B.

you will wind the heating coil on a form about pencil thickness, with a small inter-loop gap, and rest it on narrow dadoes that you have cut into the fire brick inside the kiln walls. The coil becomes very brittle during use, so do not stress it.

if you tell me inside dimensions i can run calculations on max temperature.
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violet sin
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[*] posted on 6-7-2013 at 21:49


ya I wasn't trying to reinvent the wheel. but I deffinitely plan on finding out first hand as a learning experience. planned on cutting the hard firebricks in half, like 2 thinner bricks w/ same side dimensions. just to hard face it in there. and ya they were the cheapest and most heat resistant material I found pre-fabed to a reliable shape. so no forms, pouring or having to learn a whole new trade to get the material usable. I have the nichrome A, as well as a nice pile of large wall heater elements. basically the only thing I'm gambling on is the diff layers of insulation sandwich. no too bad if you ask me. I am a ways off with no time to spare for a while, but I will be posting a write up of how it went when done, if any one is interested.
-Violet Sin-
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[*] posted on 7-7-2013 at 13:30


Hey, guys. I heard about the tube furnace a while back, and it was praised to the skies, and it seems like there are guys here that have one at home and using it.

I like the DIY stuff, and i have a question to those who have built one or have experience with it in any way, if i some day am able to make a fully functioning t-furnace at home?

Have a great day.
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testimento
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[*] posted on 9-7-2013 at 18:51


Sorry I make two threads but Im gonna make this oven:

-I use 8-12 firebricks
-I mortar them together with fire clay in square form
-I will put nichrome wire worth of 2kW inside and glue them with al2o3 paste to the walls
-The bottom and cover will be made out of 60mm thick plates of fire clay
-The bottom have insert for gas burner and air holes for roasting coal
-The container that goes inside is stainless steel or clay. It will be coated with al2o3 paste, wrapped with its own nichrome wires and coated with clay again.
-So you can use the electric only heater, the container heater and the gas burner or coal. This should bring the thing over 1000C.
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testimento
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[*] posted on 10-7-2013 at 01:36


Well, fuck. My great-looking patent of that glue-like al2o3 paste just failed miserably. And it looked so fine when it was wet. ;___;

Any ideas how can I glue stuff that can hold up at 1300C? Clay layer is fine for me and that'll go if no better ideas come by.
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watson.fawkes
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[*] posted on 10-7-2013 at 02:54


Quote: Originally posted by testimento  
My great-looking patent of that glue-like al2o3 paste just failed miserably. And it looked so fine when it was wet.
Of course it failed. No one glues heating elements to the inside of a furnace, because it doesn't work. A basic understanding of thermal coefficients and rates of heat transfer would make this clear.

Perhaps reading about how other people do it would be a good next step. There are plenty of ways, all of which require some amount of fabrication effort (or purchase, if you use someone else's fabrication).

Edit: Put back the excerpted quotation that bfesser took out.

Warning: Do not do that again. I am perfectly capable of choosing what I am replying to in a quotation.

[Edited on 2013-7-11 by watson.fawkes]
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ElectroWin
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[*] posted on 10-7-2013 at 13:42


as i wrote, above, the heating coils should be resting on dadoes;
if you look in kilns you will see they are not glued to anything
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testimento
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[*] posted on 11-7-2013 at 22:27


I'll do so then. Had it in my mind on the way. :P
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batsman
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[*] posted on 30-7-2013 at 06:18


What did you insulate it with? I have heard that you can use asbestos paper, but there has to be some substitute to it that you used, right?
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watson.fawkes
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[*] posted on 30-7-2013 at 09:43


Quote: Originally posted by batsman  
I have heard that you can use asbestos paper, but there has to be some substitute to it
The magic search terms are "ceramic fiber paper" and "ceramic fiber cloth". Major brand names are Fiberfrax and Kaowool.
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testimento
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[*] posted on 5-8-2013 at 02:13


I built one furnace just recently. Its as crude as it is, consisting only some 18 firebricks and a top cover, air duct and line fan. I use 500m3 fan with dimmer to inject air into it. I made a test run with charcoal and the furnace consumed the steel sheets I fed to it within minutes. I also made about 3kg of calcium oxide, which indicates very strong alkalinity and reaction when mixed with water at litmus. During this process I managed to blow(it literally flew up from the furnace) one clay pot and melt down one stainless steel pot. Second one this week already. Ahh, time to visit to my junk dealer again... It indicates the core temps of the furnace rise well over 1500C since it took only some 5-10 minutes to liquidate the SS pot. The fan is way too powerful and only 1/3 to 1/2 is well enough to heat up the thing. The inner dimensions are about 300x300x400mm.

Will post pics soon when I make the system a LITTLE more aesthetic. Now it's technically just a bunch of bricks with steel tube that has fan attached to it with duct tape. But at least it works.

I may see if I can get some anthracite, it's a lot cheaper than the charcoal and much denser. 1kg of wood coal will easily fill up the bottom of the furnace, meaning that one will need to add charcoal every 15 minutes.

[Edited on 5-8-2013 by testimento]

[Edited on 5-8-2013 by testimento]

[Edited on 5-8-2013 by testimento]
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testimento
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[*] posted on 13-9-2013 at 12:06


Suitability of porcelain on furnace kiln material?

Porcelain seems to bear up at temps to 1200-1400C which would be suitabe for coal heated furnace suitable for my needs. Has anyone performed high temp tests with porcelain products?

Some pot-type porcelain containers and common food plates should form suitable kiln for several processes?
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[*] posted on 24-10-2013 at 13:03



Has anyone any thoughts on these babys. (Molybdenum Disilicide MoSi2 Heating Elements )

http://www.ebay.co.uk/itm/Moly-D-Molybdenum-Disilicide-MoSi2...

What would you need to make the acutal walls of the furnace from? Silica tube?
Graphite bricks with a flow of inert gas? Would high temperature kiln bricks (from local pottery store) hold up for long?
I have no clue but just a Moly D fettish.

I presum that Moly D could be run from a variac so long as you kept an eye on the temperature and adjusted the variac untill the whole thing stabalized at a working temperature otherwise you are getting into complicated control circuitry.
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watson.fawkes
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[*] posted on 25-10-2013 at 07:12


Quote: Originally posted by jock88  
I presum that Moly D could be run from a variac
Unlikely with just a variac. These elements run at rather high currents and low voltages. Variacs are current limited, so you don't want to use also as a step-down transformer. The small size of commercially available element has a hot-zone diameter of 3 mm and maximum current of 75 A at startup (when resistance is lowest). Standard variacs have a current limit of 10 A. The highest current I've seen at prices less than $1K is 30 A. Find a 10:1 (or so) step-down transformer and put that between the variac and the heating element. Don't expect it to be too cheap; it's a lot of copper to get a 100 A (you'll need a safety margin) rating on a transformer.

There's a reason why MoSi2 is not found in small equipment. The fixed costs of using it only start to become effective when the cost of element replacement for other materials is more than the cost of supplying MoSi2 with appropriate current.

A vendor these elements has a good page of engineering information.
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testimento
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[*] posted on 28-10-2013 at 07:00


I use direct 220VAC for 0.5mm heating elements with good success. I thought the idea of using transformer to lower the voltage, but the need for thicker resistance wire and the power restriction with such a large transformer needed(2kW) that I have designated for electrolysis cell use, I didn't bother.
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[*] posted on 23-1-2014 at 21:30


I'm hoping to build a furnace capable of near 1400C in an N2 atmosphere.
Small, low thermal mass inner shell. possibly double wall.
Kanthal A-1 datasheets say 1400C use/1500C melt. Less pre-oxidized in N2.
Fleaker on page2 of this thread mentioned Kanthal A-1 is good to 1450C - can anyone else confirm?

Anyone tried homemade graphite-copper/graphite rod/plate elements?
or an inexpensive commercial source for reactions @1500C
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testimento
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[*] posted on 15-2-2014 at 17:36


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]
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[*] posted on 27-2-2014 at 11:37


why not just use Alundum?

That's what it is made for.




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jock88
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[*] posted on 17-5-2014 at 15:30



Some Silicon carbide tubes here.
They are a bit short. Could you make a heating element from one?

http://www.ebay.co.uk/itm/FOUR-INCH-LONG-HEXOLOY-SILICON-CAR...
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[*] posted on 3-10-2014 at 09:11


Hi - I'm in the process of working on a tube furnace which will be used for heating and annealing under inert gas. I plan to use pythagoras tube with kanthal wound around it, and a 2" quartz process tube, closed at one end, for the inner chamber. My question is, what kind of clearance does there need to be between the quartz tube and the ceramic one? Will differences in expansion coefficient require a certain minimum clearance? Secondly, for annealing under inert gas, it seems to me that having a vertical system with only one end open would be easier as far as the gas connections, and more efficient thermally. What is the benefit of a horizontal design for a tube furnace? Finally, can I use the quartz tube as the chamber in every case or does one have to have a graphite or platinum boat for higher temps? Thanks for your replies!
Sincerely,
Mike Nolley
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jock88
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[*] posted on 16-11-2014 at 17:43



What do ya all think of this one?

http://www.ebay.co.uk/itm/Silicon-Carbide-Heating-Element-1-...

It is a Silicon Carbide heating element 5.37 ohms , 1.25 inches diameter and about 15 inches long (I think). and costs 100 bucks
What power would it put out?

TIA

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[*] posted on 16-11-2014 at 18:24


At 120 V, 2.68 kW.



As below, so above.
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