Sciencemadness Discussion Board - Homebuilt 1300°C tube furnace

Homebuilt 1300°C tube furnace

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peach - 21-6-2011 at 06:51

I thought some might be interested to know;

Pythagoras is mullite, it's a brand name Morgan Thermal Ceramics use for the refractory. MTC manufacture a huge percentage of the refractory products in the UK, like SuperWool, ceramic papers, cements and so on.

Mullite;

Quote:

Mullite or porcelainite is a rare silicate mineral of post-clay genesis. It can form two stoichiometric forms 3Al2O32SiO2 or 2Al2O3 SiO2.

- From wiki

This is interesting, as others have mentioned how nichrome like wires can not come into contact with silica glass, but there is a (sometimes large) percentage of silicates in the lower temperature refractories. I have also been on forums related to kiln building, wherein they are using nichrome or kanthal inside Quartz tubes or Quartz as a former for the element. Duralite even sell a commercial element of this design.

Pythagoras;

Quote:

Pythagoras

Most economical, Mullite material for kiln components.

Type 610 according to DIN VDE 0335
Application temperatures up to 1400 °C
Very good chemical resistance against gases free of fluorine
For kiln working under normal conditions Pythagoras has a good thermal shock resistance and good mechanical strength
Pythagoras is a very economical material being used as impervious protection sheaths and insulators for temperature measurement

- From Morgan Thermal Ceramics

The economical part will be of interest to a lot of people, as pure alumina tubes of a similar size are roughly five or ten times more expensive. As Quartz is usable to only 1100C before mechanical problems start, there is a strong incentive to avoid the pure alumina materials if at all possible.

I decided to rebuild the hotbox of my furnace, as (on opening it) I discovered it was not in a nice state inside. I am now trying to contact multiple people (I've already lost count) to investigate if it is a good idea in terms of element longevity to have them in direct contact with silicate containing refractory. I'm waiting for a phone call back from the technical boys at Morgan for some more advice on silicates and direct contact. Morgan actually have a factory about ten minutes drive from my house, so I've been trying to weedle a visit out of them thinking it might be interesting to see the products being made.

I noticed GC and Magpie were having problems getting their cement to stick to the elements and discovered an interesting snippet from this site;

Quote:

Electrical Elements
New elements have a greasy residue left from the wire manufacturing process, which may cause the ITC 213 to flake off if not removed. One method is to pre-fire elements after stretching for 5 to 10 minutes to achieve at least cherry-red glow. If this is not possible, the elements can be heated in a furnace or kiln at 700oF for 30 minutes. Allow to cool.
The ITC 213 can be applied as described above or can be applied by dipping. Using a wide shallow pan, empty the ITC 213 into the pan and add 1/3 water, mixing well. Dip the entire element except for the lead wire into the ITC 213 mixture. After dipping, shake the element to remove excess coating and hand to dry for several hours or overnight. The elements are now ready to install.

[Edited on 21-6-2011 by peach]

Magpie - 21-6-2011 at 11:14

Quote: Originally posted by peach

The economical part will be of interest to a lot of people, as pure alumina tubes of a similar size are roughly five or ten times more expensive. As Quartz is usable to only 1100C before mechanical problems start, there is a strong incentive to avoid the pure alumina materials if at all possible.

This large price difference may be a function of where you live. On this side of the pond there wasn't that much difference in price between mullite and alumina when I bought my alumina tube 3 years ago. It was $101 then.

Quote: Originally posted by peach

I noticed GC and Magpie were having problems getting their cement to stick to the elements and discovered an interesting snippet from this site;[/url]

Electrical Elements
New elements have a greasy residue left from the wire manufacturing process, which may cause the ITC 213 to flake off if not removed. One method is to pre-fire elements after stretching for 5 to 10 minutes to achieve at least cherry-red glow. If this is not possible, the elements can be heated in a furnace or kiln at 700oF for 30 minutes. Allow to cool.
The ITC 213 can be applied as described above or can be applied by dipping. Using a wide shallow pan, empty the ITC 213 into the pan and add 1/3 water, mixing well. Dip the entire element except for the lead wire into the ITC 213 mixture. After dipping, shake the element to remove excess coating and hand to dry for several hours or overnight. The elements are now ready to install.

not_important pointed out this pre-oxidizing technique on p. 4 of this thread already.

I didn't use ITC-100 but ITC-213. ITC-100 may have been more appropriate, but my tube furnace continues to function well. It wasn't a problem of not sticking to the kanthal wire but a problem of cracking. But since it did not spall off it seems to have been a non-issue.

For those in the US who would like to buy Kanthal wire by the foot, check the pottery suppliers.

metalresearcher - 21-6-2011 at 12:32

I got 30 meters of 1mm Kanthal A1 wire for $36 via ebay and rewired my furnace with it.

http://shop.ebay.com/i.html?_dlg=1&_jgr=1&LH_PrefLoc...

peach - 21-6-2011 at 15:14

I noticed the pre-oxidising mention earlier, but forgot whether or not it was in relation to the refractory flaking off.

$101 seems in roughly the right area for alumina. But here's a comparison on today's UK price difference between the two;

Quote:

RCA Tube 35 mm O/D X 28.8 mm I/D alumina X 1000 mm long at unit cost £36.00 (1 in stock)

Pythagoras tube 29 mm O/D X 23 mm X 760 mm long unit cost £5.50 (100 in stock)

Six times cheaper. These prices don't include VAT, which is currently 20% in the UK. 36 pounds becomes £43.20, which is about $70. Plus on the delivery, $86 ish.

[Edited on 21-6-2011 by peach]

peach - 21-6-2011 at 18:28

Quote: Originally posted by chief

Just to share 2 Ideas (not from me, but tricks of the trade) on reaching really high temoeratures:
==> up to 1700 [Celsius]: Mo-wire around Al2O3-ceramic-tube [also commercially available as furnaces]
==> up to 3000 [Celsius]: Wo-tube, current directly through the tube

The latter may be adapted,using cheaper stainless-steel-tubes (limited lifetime, but throw-away available from hardware-stores), which should hold up to 1300 [Celsius] too; then it would be only a matter of contacting them, wrapping some isolating-mat (even maybe rockwool) around them. Since the resistance rises with temperature the electrical power would be dissipated within the isolated zone, contacting therefor should be easy enough (if necessary through welding).
As power-supply: One thick additional secondary winding around the welding-transformer, eg. . Within such stainless-steel-tubes then, at lower temp., even pressure-experimentation could be done (catalysts in the tube, have fun making HNO3 etc.), since in the hardware-store there are also other stainless-steel-components available,usually to make waterpipe-connections etc. .

Maybe someone could succeed in Fischer-Tropsch-gasolining from coal-water (50 Bar, 200 [Celsius]) ?
[Edited on 8-10-2008 by chief]

[Edited on 8-10-2008 by chief]

Interesting note there on the tungsten.

Remember that all normal grades of stainless have service temperatures below 1000C. I would be grateful if they didn't start slowly sagging at that point. Pressurising them could get nasty.

Silicon carbide and moly D elements are available as tubular forms that'll manage 1400 to 1850C, but they are expensive.

I was having a click around on the Kanthal site and spotted this.

"Kanthal furnace tubes can be used at temperatures up to 1250°C (2280°F) and are available in sizes from 26 to 260 mm (1.02-10.2 inch) outside diameter."

Wonder how much they are.

One of the good things about the silicon carbide and moly D tubes, that these lack, is that they feature spiral sections for the hot zones, so the ends where they touch the refractory and wiring remain a bit cooler.

metalresearcher - 22-6-2011 at 11:26

W and Mo wires are NOT a good idea as I read earlier on this forum. Both metals oxidize quickly at those temperatures unless you have a proper vacuum or inert gas (Ar) furnace chamber.

There are also coiled MoSi2 elements up till 1900°C available from www.mhi-inc.com.

Another option is using a propane burner with forced air (using a $10 air mattress inflator suffiices). This heats to 1500oC.

Her my video:

<iframe sandbox width="425" height="349" src="http://www.youtube.com/embed/Z2wGV6g7I6E" frameborder="0" allowfullscreen></iframe>

[Edited on 2011-6-22 by metalresearcher]

peach - 22-6-2011 at 13:40

Thanks for the video MR!

Graphite is used in commercial furnaces that need to reach 3000C and where a direct arc, plasma or flame aren't acceptable.

That is a ridiculous temperature for the majority of what people on here will want to do, and expensive to cater for (it'll boil aluminium oxide and melt magnesium oxide & zirconium dioxide

).

<object width="560" height="349"><param name="movie" value="http://www.youtube.com/v/DWrisy1_8_U?version=3&hl=en_GB"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/DWrisy1_8_U?version=3&hl=en_GB" type="application/x-shockwave-flash" width="560" height="349" allowscriptaccess="always" allowfullscreen="true"></embed></object>

[Edited on 22-6-2011 by peach]

metalresearcher - 23-6-2011 at 00:49

@peach:

I performed experiements with the electric arc including melting MgO and boiling metals.

www.metallab.net/arcmelt.php

The graphite heating is used in graphitizing coke with the Acheson furnace, heating coke pressed in rods to 3000oC.

[Edited on 2011-6-23 by metalresearcher]

Thor - 25-7-2011 at 10:49

Quote: Originally posted by peach

Quote:

RCA Tube 35 mm O/D X 28.8 mm I/D alumina X 1000 mm long at unit cost £36.00 (1 in stock)

Pythagoras tube 29 mm O/D X 23 mm X 760 mm long unit cost £5.50 (100 in stock)

Six times cheaper. These prices don't include VAT, which is currently 20% in the UK. 36 pounds becomes £43.20, which is about $70. Plus on the delivery, $86 ish.

[Edited on 21-6-2011 by peach]

Could you tell me the source of these prices? Have tried a few suppliers and the price's seem to differ hugely.

peach - 25-7-2011 at 12:06

Are you in the UK? Because shipping would probably make the difference between your local prices and mine not all that much if you're in the US.

http://www.almath.co.uk/ has it, but only in specific sizes.

I bought mine from Anderman, who seem to have more than one site. The one I initially contacted was something like 'Technical Ceramics'. Here's another with the name Anderman in their emails. http://www.earthwaterfire.com/

I was pissed off to discover the postage was going to be £15. The tube it's self was about £10 I think, and just over a foot long. So it would have gone in one of those poster tubes and the royal mail could have sent it for about a quid.

I've since tried Garage Chemists nichrome wrap method as well, using this tube, and it works a charm.

Keep in mine that cutting this stuff yourself is extremely difficult. It's so hard HSS hacksaw blades don't even scratch it, they just leave a shiny mark where the blade has worn down. I tried using a diamond disc in a tile cutter, but it continually shattered a scrap piece I was using. Get them to cut if it needs chopping down, they have special high speed diamond saws with precise guides to hold it in place as it goes.

{edit}Do any of the US guys know of any companies who still do by ground international shipping? USPS seems to have dropped that 4-6 week service, so I keep getting insane 'express by air' quotes on stuff to the UK. Some of them aren't far off the amount it'd cost for me to get on a plane, fly across the ocean for seven hours and collect things in person. It's funny, imagining things I've bought sitting on a seat in the plane on their own, being served drinks with their safety belt on.

[Edited on 25-7-2011 by peach]

garage chemist - 25-7-2011 at 12:48

I have a method for cutting pythagoras tubes at home.
It involves two persons, one is holding a powerful angle grinder with a disc for cutting concrete, grinder sitting on the ground and disc facing upwards, and the other one holds the tube to the spinning disc while constantly rotating the tube, slowly cutting deeper with each rotation. There is a little chipping at the cut, but after cleaning up the cuts with a diamond grinding bit only about 1cm of tube is lost.
I agree that you should always let the supplier do the cutting if possible as this method is obviously somewhat dangerous both for the tube and for the workers, though I've made several cuts this way and never broke a tube.

peach - 25-7-2011 at 14:08

Quote: Originally posted by garage chemist

I have a method for cutting pythagoras tubes at home.
It involves two persons, one is holding a powerful angle grinder with a disc for cutting concrete, grinder sitting on the ground and disc facing upwards, and the other one holds the tube to the spinning disc while constantly rotating the tube, slowly cutting deeper with each rotation. There is a little chipping at the cut, but after cleaning up the cuts with a diamond grinding bit only about 1cm of tube is lost.
I agree that you should always let the supplier do the cutting if possible as this method is obviously somewhat dangerous both for the tube and for the workers, though I've made several cuts this way and never broke a tube.

That's pretty much what I tried with the RCA.

I managed to make a good, clean groove in it, but it was so easy for it to chip back an inch or so. I tried on some scrap a few times, but could never get a nice, clean edge on the diamond tile saw.

I think one of those diamond blades Dremel sell might have a better chance, but I'd still go with, "get them to do it". Most of them will do it 50p or free, saving you the possibility of loosing pounds on mullite or tens of pounds on alumina.

[Edited on 25-7-2011 by peach]

Magpie - 25-7-2011 at 14:20

Quote: Originally posted by peach

It's funny, imagining things I've bought sitting on a seat in the plane on their own, being served drinks with their safety belt on.

That's damn funny, peach.

I've cut the tops off assay crucibles (mullite?) using a masonry/concrete blade in my table saw. This gave a fairly clean cut.

[Edited on 25-7-2011 by Magpie]

peach - 25-7-2011 at 14:40

Quote:

It wasn't a problem of not sticking to the kanthal wire but a problem of cracking.

I have also noticed cracking, despite pre-oxidising the wire and leaving the cemented result overnight and then in the oven all day, gradually increasing the temperature from 70C to 250C to cure the cement. Solution? Bake and then re-cement with a thinner layer? Must be water loss and shrinkage.

This reminds me of rendering the garden. A week of mixing half a ton of render by hand, troweling it on by hand in the hottest summer on record, stuff cracks in the lower parts my brother did; lack of PVA / SBR / admix? Render is a magical thing.

The tubes that cracked for me on diamond cutting were pure alumina. Maybe Mullite is less prone to it. I didn't give it a try. I have some iron ladle bricks and damn......! They're tough!

[Edited on 25-7-2011 by peach]

Magpie - 25-7-2011 at 15:00

I've never "rendered" anything (had to look up the meaning as this seems to be one of those many UK terms not generally used in the US). I have done some concrete work occasionally, though. Along with getting the right water:cement ratio it is important to keep the concrete wet until it has developed sufficient strength through hydration. I usually covered it with plastic film, or cotton towels kept wet, for about 7 days. Have never had any cracking, but this was bulk material for foundations, not thin layers.

I don't know if any of this would apply to the commercial product I put on my tube furnace, however. I just followed directions, which did not include keeping it wet, IIRC.

Thor - 26-7-2011 at 03:56

Peach: I'm in the UK, so these companies are ideal. Anderman is one that I have contacted, no reply yet though. Is there any particular size of tube, my hood is quite small, so if i can use a smaller length of tube then that would be better suited. Also will need to try and source a quartz tube with ground glass joints too, which never seems to come up on ebay UK.

peach - 26-7-2011 at 05:43

Nah, you're not getting a decent formed, taper quartz tube with caps via eBay any time soon!

The average 'home chemist' is far more interested in making kEwL thermite than doing anything involving quartz.

My mullite tube is about 29mm ID I think, and it's 460mm long. They usually come as 760 or a metre. Most companies only do things by the stick or sheet; even though they'll chop it up, you have to pay for the whole length.

I am about to order a quartz liner myself and the guy who's making it is doing it for a reasonable price. If you can decided what size you want yours to be within a week or two, I may be able to get him to do it cheaper by adding more to the order. He also has quartz wool, can make the custom tubing adaptors, boats and all that stuff to go with it. I think mine is around a hundred pounds for the tube, caps and some wool.

As far as Anderman go, I think you'd be better firing up your fingers on the phone's keypad. The guy I spoke to also gave me the wrong email address over the phone.

I've had the vacuum people on the phone three times now, to repeat my card number. My last experience with another vacuum company was the same, and then I got a letter from my bank telling me they wanted money I'd already given them. Some companies have not joined the high tech era of the pen and paper note. :mad:

[Edited on 26-7-2011 by peach]

jock88 - 30-5-2013 at 06:15

Bump.

I have not read the thread completely.
Has anyone tried using those quartz tubes in domestic heaters as elements in a furnace. The tubes have a coil of Nichrome (I presume) in them.
I am going to construct a furnace. Not very high temperature, perhas up to 1100 C.
Are these quartz tubes resistent to hot water vapour? I am not putting the hot tubes in contact with cold steam or water BTW. The tubes in question are not clear as they contain little air bubbles, I believe.

I would love to purchase a Moly Sci element to play with.

http://www.duralite.com/store/scripts/prodList.asp?idCategor...

The price is a bit hot too!!

[Edited on 30-5-2013 by jock88]

Furnace up to 1200-1300C

testimento - 3-7-2013 at 12:32

I need to make a furnace that can reach temps up to 1300C MAX. It could run on electricity, but I would like having it with propane burner, wherever this could be possible to make. I need it for making calcium oxide from calcium carbonate and calcinating and other processes too.

There is furnace on this thread mentioned:

https://www.sciencemadness.org/whisper/viewthread.php?tid=14...

What materials could the reactor be made of to hold up for this? I have no zirconia and other stuff available, so common structural materials, fireclay, fire mortar (cement used to make fireplaces), common clay and this kind of stuff are to go.

I can have resistance wire, but could I use 6kW propane burner to reach temps up to 1300C? The volume I'd like to have for the pot would be 3-5 liters.

Could stainless steel (MP 1510C) used for max. 1300C processes? It would be easiest to put a pot of stainless into fireclay, wrap resistance wire around it and make a cover for it.

watson.fawkes - 3-7-2013 at 12:55

The Kiln Book, by Frederick L. Olsen.

testimento - 3-7-2013 at 16:42

How much temperature would an 2kW induction heater generate, would it reach 1000C without trouble if I put one under the oven and insulate it with double ceramic layer?

I think SS crucible would be enough to hold CaO and other processes which limit to 1000C.

bfesser - 3-7-2013 at 16:53

I don't think he gets it, <strong>watson.fawkes</strong>.

<strong>testimento</strong>, what we was undoubtedly implying is that your questions are more complex than you realize, and cannot be simply answered. You'll need to do some further research, perhaps studying the book he has recommended.

testimento - 3-7-2013 at 17:47

Yeah, I understand Im looking a simple solution for complex task. I dont need pharmaceutical performance though, I just need reduce some calciums and other stuff which should go in quite harsh conditions, compare to mining industry.

I have following design in mind (ATTACHMENT)

a steel cooking pot in
cover it with clay of 1-2cm thick
put charcoal in the mantle
add another layer of clay of 0.5-1cm thick

Cover the lid with same structure

Would this reach 1000-1200C temp with LPG gas burner? Should the bottom be covered with clay layer too, would this hinder the delivery of energy into the container?

violet sin - 3-7-2013 at 18:30

dont remember which thread it was but I remember reading a comment by one of the sci mad members saying stainless oxidizes above ~600/650'C. I lucked out and got a nice big quartz tube 147mm x 152mm optical grade for 11$ + 11.95$ s&h off ebay. so <25$ was a great purchase. what you going to use to monitor temp, control temp? did you calculate how much wire and all that you are gonna need( if you go electrical)? you don't wanna pull so many amps you blow a breaker every time it turns on. it's a big project to get there and not a lot is easy about it. I am in the process of building mine, in scant spare time, but slowly it is happening.

instead of charcoal liner you could try rockwool. I haven't done the heated tests yet but they sell cubes for transplanting seedlings and clones in a garden supply shop. they come all stuck together in small rectangles that are easily cut. might make a better insulator, might melt to a pile of goo, don't know yet.

http://en.wikipedia.org/wiki/Rockwool

the wiki page says 700-850'C so may not be great for you unless they are shielded a bit from the core temp. but something to think about.

testimento - 3-7-2013 at 20:04

Yes I considered rockwool and glass wool and other wools, but they do have limited temps of 400-800C, and some few ceramic special wools can hold up to 1300C. Asbestos was another one, but that is obviously a rather too nasty one for this purpose.

The stainless will form an oxide layer at high temps but as long as no mechanical forces are applied, it just sits there, as far as I have tested. The surface layer flakes off when you cool the pot, so in the end after a couple of hundred runs, the reactor bottom may just fall off. I believe I will not be conducting more than a few dozen runs with the reactor until it goes to dump yard so I dont concern about that a lot.

I use triacs with potentiometers to control the power of the heaters. I have controllers that limit max power to 2000, 3000 and 3800 wats, respectively, so it will just sit there at the designated temp. I have one with my 2kW chlor-alkali cell too and it works like a clock.

I'll give a try for this reactor type and see if I can get it hot enough. The propane should give 2000C temp at the flame core and melting lead with it is a minute job, but I made a test today where I used CaCO3 in a steel pot with double radiation shieldings and the temperature went so high the plastic knob on top of the lid of the pot self-ignited and charred into carbon so the temp was at least 500-600C, but IDK will it reach 1000C. If it wont, I will consult my electric company via nichrome.

[Edited on 4-7-2013 by testimento]

violet sin - 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]

testimento - 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... -___-

zed - 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.

ElectroWin - 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.

violet sin - 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-

batsman - 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.

testimento - 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.

testimento - 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.

watson.fawkes - 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]

ElectroWin - 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

testimento - 11-7-2013 at 22:27

I'll do so then. Had it in my mind on the way.

batsman - 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?

watson.fawkes - 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.

testimento - 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]

testimento - 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?

jock88 - 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.

watson.fawkes - 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.

testimento - 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.

sinterin - 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

testimento - 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]

Maya - 27-2-2014 at 11:37

why not just use Alundum?

That's what it is made for.

jock88 - 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...

miken277 - 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

jock88 - 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

Metacelsus - 16-11-2014 at 18:24

At 120 V, 2.68 kW.

macckone - 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]

metalresearcher - 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.

jock88 - 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)
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macckone - 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.

jock88 - 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

Metacelsus - 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.

Gouging rods as heating elements

jock88 - 21-11-2014 at 15:40

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).

jock88 - 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

JJay - 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]

wg48 - 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.

JJay - 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.

[Edited on 26-2-2016 by JJay]

wg48 - 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.

JJay - 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.

wg48 - 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.

wg48 - 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.

JJay - 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.

JJay - 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.

wg48 - 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.

JJay - 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.

ParadoxChem126 - 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.

JJay - 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]

Ready made furnace elements ((reporposed)

wg48 - 3-3-2016 at 18:47

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]

NoobTube Furnace.

Sulaiman - 5-3-2016 at 23:48

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

Magpie - 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.

Arbetarn - 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?

JJay - 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.

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

Macom24guitar0 - 13-3-2016 at 14:53

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&a...

Arbetarn - 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.

yobbo I - 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]

JJay - 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]

JJay - 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]

JJay - 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]

JJay - 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.

JJay - 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....

JJay - 31-3-2016 at 17:15

I am pleased to announce that I have successfully made aluminum chloride with my tube furnace.

blogfast25 - 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.

JJay - 31-3-2016 at 18:32

Ok....

yobbo II - 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.

Loptr - 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.

experimenter_ - 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.

wg48 - 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.

yobbo II - 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]

yobbo II - 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.

NedsHead - 19-9-2016 at 18:57

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

yobbo II - 20-9-2016 at 06:43

Sur everyone else is ignoring me

ficolas - 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]

JJay - 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.

ficolas - 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]

JJay - 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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