Tube furnace

[Natlek]

Are you saying you have Kanthal wire as the power wire in the ceramic insulation beads? That is a bad idea. You want high temperature power wire, not Kanthal. If you use Kanthal as the power wire it will heat up inside the ceramic insulation beads.

Yes ....I have doubled and twisted 1mm Kanthal wire inside beads .Was thinking that I need that there exactly for that reason because higher temp inside oven ? Are you referring to use this kind of wire , like this one on picture ? It is silicone wire for high temp ..or one reinforced with fiberglass , only kind I know ?

 

[Stacy E. Apelt - Bladesmith]

Use 10 gauge fiberglass insulated high temperature wire with high temperature lugs crimped on the ends. It won't get hot like the kanthal. It won't hurt to slip some ceramic insulator beads on the first inch or so if they fit over the insulated wire..

https://www.ebay.com/itm/High-tempe...197505&hash=item3d7784c296:g:UuEAAOSw4Gdbyoml

 

[Natlek]

Use 10 gauge fiberglass insulated high temperature wire with high temperature lugs crimped on the ends. It won't get hot like the kanthal. It won't hurt to slip some ceramic insulator beads on the first inch or so if they fit over the insulated wire..

https://www.ebay.com/itm/High-tempe...197505&hash=item3d7784c296:g:UuEAAOSw4Gdbyoml

I try that Stacy ,and heat was gone from wire,only first two inch was hot . But it will not work in this furnace .....look at first picture , almost all tube was heated .Now if I close that side /call it back side/ with ceramic blanket ALL tube will be on same temp. so cooper wire will not last 5 minutes . So I use four strands of 1mm Kanthal /but shorter this time for one leg and / and after 4-5 minutes which is max. time I can hold HT element on before tube start glow white / I can hold with hand 3 inch far from connector ..... I don t see other way to do this and I think that this problem is solved ,will work .

Here's what I did........... four strands of Kanthal wire in ceramic beads , rest is hi/temp silicone wire ...

Now , I found source for that cracking sound ...It was not ceramic tube ,ceramic tube is fine. It was that brown ceramic paint.. whatever it is over tube .It little melt/soften somehow /probably when I push temp to white glow tube....I notice that when I try to put steel inside ..I felt how it stick to something.... Good thing is that now HT strip is glued on tube so it will not move , one more less thing to worry .In normal use I will never get furnace on that much high temp. , so no problem there .
Other thing , this piece of file is soaked and quenched maybe more then 30 times .I can t see ANY decarb. on surface which is little strange or it is not ?

I wrap another one layer of ceramic blanket so now after one hour holding tube on over 800 C degrees surface is pleasant worm on hand ...In build I will use another one layer for peace in mind . I have a feeling that SSR will have little work , this thing don t want to cool down even how it is now ......without insulation on both side I don t know what else I can say or to test .If anyone have any suggestion...........

 

[Natlek]

A few thoughts:

The rate of heating may be limited by the thermal gradient the tube can tolerate. Diameter, wall thickness, Thermal Conductivity, Thermal Expansion Coefficient and mechanical properties will all factor in. If you make it heat faster than the tube can safely take, the chances are it'll break.

45 min to 1100 degC, 2012 degF, does not seem unusual: probably faster than many conventional HT ovens out there. There was a thread on warm-up times fairly recently:

@timgunn1962 , what do you think about what I done so far? This thing heat up extremely fast . I don t notice any problem on tube with that ? Tube was 28cm long and 5cm.out Dia. and HT element is 1800 W . Is it wise to use lower Watts Ht element , heat time is not that important to me ? It heat fast because Watts or because ceramic insulation/low thermal mass/ ... most likely of both ? Is there any difference in power between round HT wire and this in strip one or watts are watts ?
Edit to add ...I ask because I can use this approximate data for calculation for Watts for HT element on bigger tube I intend to use . . . .

 

[Stacy E. Apelt - Bladesmith]

You can strip the insulation off 100mm to 150mm of the wire and put the ceramic insulators over that part.

 

[Natlek]

I do just that , sorry I didn't mention that in my previous post . . . I have not high temperature crimp lugs in the moment and was afraid that if ever I use stainless temp. cooper wire would be very close to melting point inside that closed chamber....maybe I overthink this , this is first time I work on this kind of tool so I have no idea what can I expect. I know that after HT element get hot Watts go down so that mean less heat on terminal if I m correct ? Anyway ,I think it s time to connect PID and see how this would work with auto control of temperature . .

 

[John mc c]

Does it heat evenly with no hotspot natlek
Or maybe your design might have cool spots at ends and hot spot in middle
Don't know if you have a way of testing that

 

[Natlek]

Does it heat evenly with no hotspot natlek
Or maybe your design might have cool spots at ends and hot spot in middle
Don't know if you have a way of testing that

I can t see how that would happen ? It is tube wrapped with heat element all around so heat is evenly distributed on tube from all sides.Watch this clip on tube ....
pay attention on 1,50 min.They must to use insulation plugs at ends that goes INSIDE tube and that change length of even temperature inside because they drag temperature from tube . / I highly recommend to everyone who have classic HT oven and HT elements only on side walls to put at least half inch ceramic blanket on door and back side and on the roof if it is possible and see what would happen with heat uniformity inside oven / . In my case sealing would be done at the END of tube from outside which will give more even temperature until the end of tube .Plus HT elements start almost from the end of tube /10mm/in my build so that helps for more even temp.Don t forget that all would be surrounded with thick ceramic insulation so heat can t escape nowhere .

You know what ? I think that I would finish this in real furnace All I need to finish is stainless tube 10 inch Dia. It will be nice for making test with steel ..... + most knives I make are under 10 inch and will fit inside this tube so it will be very economic and fast for small and single blade .

Just two brick at the end of tube make difference ,huge difference in heating time and even color inside ...This will work ,I have no doubt about that .My concern is durability . . . .

 

[Natlek]

Does it heat evenly with no hotspot natlek
Or maybe your design might have cool spots at ends and hot spot in middle
Don't know if you have a way of testing that

It can be tested , I can buy/they are cheap/ temperature measuring device with four probe and sacrifice one tube in name of science But I don t see that it is necessary..... I do same thing as they do in Carbolite Gero tube furnace so ......
Look , this thing need exactly 35 sec. to heat 2.5mm thick , 2cm. wide and about 18cm. long spring steel to not magnetic ..I do that zilion times this days...I see beautiful even color on all length of that steel

 

[Natlek]

I make some progres with this thing . . . Take me one afternoon to cut that tube straight from both side , to cut piece for door and for side covers and to get to this stage . . . I left the outer tube a little longer from back side so in future I can use bigger tube .I hope that this weekend I will finish it .

To lock the door I will make something very simple like on this sketch

Now ... I do not know if I should cry or to be happy .My friend in his machine shop have several HT ovens ......One of them he do not use for several years . I asked him to sell me that HT oven many times in past and he always says .........NO Yesterday I had some rear axle from one bike for repair and I went to his work shop .He was not there , went to Germany ...... one of employed who work on lathe repaired what I need and just as I came out to go someone call me back........ I went to him and he say to me ... follow me , the boss left something for you ....you can take that if you have 300 euros What ????????? To shorten ...now I have my own HT oven, and it is good one And that s way I don t know should I cry or be happy I've spent a lot of time and work on this one oven and sand pot oven ....
It is made from stainless steel

What s wrong with this Imgur ????????

 

[A.McPherson]

Nice!!! A Cheap oven is awesome!

I also wonder if you might be getting a little induction heating too from your tube oven...
obviously I don’t know much of anything about inductance heating, but it does make me wonder!

 

[Natlek]

Nice!!! A Cheap oven is awesome!

I also wonder if you might be getting a little induction heating too from your tube oven...
obviously I don’t know much of anything about inductance heating, but it does make me wonder!

Induction heating is another story . . .you need electromagnet ....etc

Induction heating is the process of heating an electrically conducting object (usually a metal) by electromagnetic induction, through heat generated in the object by eddy currents. ... The rapidly alternating magnetic field penetrates the object, generating electric currents inside the conductor called eddy currents

I finished this open/close thing.............and it works

Now knob................... on ugly oven you need something pretty to distract attention

This thing need legs to It easier to make baby then furnace

 

[Natlek]

Almost there ..................

I will rework this , they are too long and will be between ceramic layer ..

I weld some simple legs too

Now...........this thing is crazy I put some blank inside /cold oven,first start / and turned on the power........after 5 minutes I open the door and you would not believe this ....blade was missing inside That is the first thing I thought ,then I start to look around for blade and then tang start to be visible inside . Steel was literally not visible inside ..all was one color Picture is taken when I get to my self ,maybe after one or more minute from door opening.I like it so far ... it gives me the will to go back to study that Chinese PID s----

Total it was ON for about 15 minutes , cold from outside ....after one hour surface get warm ,maybe over 50 celsius .........And this thing really don t want to cool down ... it was warm inside this morning .

 

[Stacy E. Apelt - Bladesmith]

Really interesting project.

 

[Brian Stucker]

What kind of ceramic tube are you using?

 

[Natlek]

What kind of ceramic tube are you using?

This one is from 115KV High-voltage fuse . Google .....ceramic tube for furnace

 

[Natlek]

Really interesting project.

Indeed ! I think that it is worth the time and effort I spend on build .This small oven would have some advantages ..like economy ,blade is equally heated from all side , heat uniformity inside , precise temperature , no direct radiation from HT element to steel, temperature don t drop when i open the door ...I can put blade in cold oven and start proces /no thermal shock on cold blade inserting in 800 degrees oven .....And most probably I can HT more blade at a certain time then in classic HT oven, while it comes to the temperature I will already have several completed I can t wait to see how fast would go from 800 to say 1150 Celsius which is important in some case ...and to see should this tube handle that temperature for half hour ....... Now I think that this corrugated HT element is /unintentionally/ a real hit compared to round one and it is one of a reason why oven get so fast on temperature .. More heat is transferred from direct contact between element and tube compared to round wire which radiate heat in all direction equally...
I ordered this thermometer , it is excellent tool to see how fast will temperature raise + I think that I will need it that to check/compare with PID ....

 

[Natlek]

Really interesting project.

Wait , I m not done with this
This oven have 1800 Watts HT element and reach 830 Celsius in about 5 min.
Question ............
Now I m ready to complete bigger one .I have no idea how much watts HT element to use ? Any suggestion ? You can see on picture difference in size , what do you think ? Bigger tube is little over 17 inch long .I m ok if it take little longer time to reach temperature ? What do you think about 2500 Watts ?

Next project this winter will be to make another oven ..... third one ...........with two tube jointed ........for swords

 

[Natlek]

What kind of ceramic tube are you using?

Here how they look ...they are used in transformer in settlement ? is right word ? When they activated they are useless after that so you can get them for free if you know someone who works on maintenance ....and they have lot of pure silver /most a flat wire / wire inside ... and is excellent to mix it in marble carbon.....

 

[Natlek]

Does it heat evenly with no hotspot natlek
Or maybe your design might have cool spots at ends and hot spot in middle
Don't know if you have a way of testing that

Well , now I think that I can answer this question ................
Absolutely not hot or cold spot ....when moving thermocouple inside tube all I can see on screen is 2-4 Celsius difference .I mean from one end of tube to other end...
And I know why ..............
In conventional tube furnaces /Like Carbolite Gero mentioned earlier in this topic/ the temperature is generally uniform over only the central third of the heated length. Outside this region, the temperature decreases significantly due to heat loss at the ends , because the tube goes outside the insulation.....
In my case tube is FLOATING wrapped with ceramic blanket insulation from all sides and whole tube get same temperature all over ...
I finished bigger one with 65mm inside Dia. tube and 43 centimeters long .Now I see that I have no pictures of
completely finished oven , but all in all it is same as first one .Only change I make was that i used that 1800W HT elements from first/small one for this big one .On first one I have 1200W now ..It take one -two minute longer to get to temperature but I m ok with that ..
ONE more thing ...........@Stacy .......with only on/of switch I LEARN to keep temperature on 800-803 Celsius forever if necessary .Of course I will use PID on this bigger one IF our friend @Cushing H. make good tutorial for PID ... Stainless steel need long soak so siting there half hour and playing with on/of switch I suppose would not be funny anymore
Tube ready to be wrapped.....

This summer i will make another one .......last one with two tube jointed for swords , 86 cm long is enough ..
PS . What do you think is there difference between horizontal and vertical HT furnace ? I mean steel lies on the spine horizontally in the furnace or hanging inside tube ? This furnace can be used in both way ?
PSS .I didn't mention it here that I used small one for welding san mai ....It is amazing how fast steel get to temperature ,especially after being put back in again when the forging temperature drops... I can keep door open and there is absolutely no drop of temperature , only first inch, inch and half is little cooler . I didn t see any problem using it on 1200 celsius .Max. temp. I try was 1250 and tube hold just fine ...