Tube furnace

[Stacy E. Apelt - Bladesmith]

I'm sure Tim will also answer, but I cut Ins-board all the time like that for forge ends. It makes assembly …. and disassembly …. very easy.

 

[Natlek]

I'm sure Tim will also answer, but I cut Ins-board all the time like that for forge ends. It makes assembly …. and disassembly …. very easy.

Thanks Stacy , that was good to hear Sharp knife , scalpel knife or scissors ? I need precisely straight cut for good fitting on both side ? Does it stretch little ? I can make inner hole little smaller to get perfect fit on ceramic tube ? Sorry for so many questions , but I know nothing about this material .....never hold in hand .

 

[Natlek]

About this oven elements .......they will not work .It is two piece ceramic insulation .One is that outer ring which is hard , but rest is to much fragile ....I try on one end to lift that wire and that ceramic? breaks down like sand ...it is probably molded , but no way it can be used for anything .Just to be clear because I mention that I can use them in this project .. .I destroy big one , and now is the right time new one in my stove to burn

 

[timgunn1962]

For circles for the ends of HT forges, I usually cut the exterior edge with a sharp (but cheap) knife. I'll usually draw round the end of the tube and cut to the line as well as I can, then put the tube onto the oversized plug that results and give it some firm(ish) taps so that it makes a "shelf" of the correct diameter, pull the tube off and use the knife again to trim the full thickness down to the diameter of the shelf. My tubes are usually thinwall 250mm (10") Stainless pipes with walls about 2mm thick. YMMV.

For the internal holes, I use a holesaw.

The shopvac gets used very freely throughout the process because it makes a lot of short fibres and I don't want them hanging around. I try to get all of my fibre cutting/trimming done in one session (even if it takes 2 or 3 days), throw away the filter along with the dust, and fit a new filter for general shopvac use.

Reusing elements has never worked well for me. I think new Kanthal A1 is probably supplied in an annealed condition and it seems to get very brittle after cycling to temperature.

 

[Natlek]

Well , thanks .............again I was thinking to use that ceramic insulation from this stove heaters not wire , @ timgunn1962 , sorry for my English
Do you think that if i make from some thin walled round pipe in right Dia. some kind of knife to push cut that inner hole , would work ?

 

[timgunn1962]

A circular knife would probably work ok. I don't have a steady enough hand to cut a consistent bevel on the inside of a pipe to try it and holesaws are readily available in useful sizes. I'd cut out as much of the waste as possible before tapping the tubular knife through, to give the displaced material somewhere to go. I have cut discs of blanket with a pipe, bevelled on the outside, several times but the board is a whole different animal.

If you can make sheetmetal endcaps and stick a couple of layers of blanket flat in the end, I'd expect that could be made to work ok, though it'll depend how you handle the electrical connections to the element. Flat blanket against the square-cut end of the blanket/tube roll should give adequate "sealing": little or no convective flow, but porous enough to allow half a litre per minute or so of Argon to flow unimpeded.

 

[Natlek]

holesaws...................right tool for right job And I repeat that in my service to younger every day ....
I like that idea about couple of layers of blanket ......
Of course that I can and will make stainless end caps.But I think it is better to finish this tube furnace , test it some time and if all work well I will make end caps .This furnace will work perfect , I m sure about that .What worry me is ceramic tube .If that part don t hold as i think that it will , stainless part will be useless with new tube which I will need to buy .There are tube very ,very close in dimension with this one from but not exact dimension...

 

[Natlek]

I was thinking on something like this .To put everything from the back side ? So from front side I have only to call it door for easy manipulating ?

 

[timgunn1962]

That’ll work.

If you only have blanket at the moment, you probably don’t even need the board on the inside. Roll a bit of blanket fairly loosely to make a plug for the other end and you’ll be good to go. Wrap it in wire and give it a wire handle and it'll work as well as any door. "Fairly loosely" because as long as it’s easier for the Argon to get out that end than the end it comes in at, you’ll have inert gas shielding the workpiece.

Good knifemakers tend to be a bloody nightmare to deal with, IME, because they always really, really want things to look and be "right". Try to put that aside for now. Let’s get it working first, then you can make it look pretty and add bells and whistles to your hearts content.

Confession time: I’m much too rough to be a knifemaker and consequently have enormous respect for those who can do it. On the upside, I can usually get technical things to work.

If you are worried about the tube holding up, a really slow ramp-up should help. Starting with the controller in manual and setting the output to 10% or so until the temperature is above the start-of-ramp setpoint should avoid any initial thermal shock.

 

[Natlek]

@ timgunn1962 I don t know anymore how to thank you for helping me out with this
Now I have another problem ??? I have contacted Kanthal to ask some question about A-1 wire and how much A-1 wire I need to get 3000W from 1.5mm wire .Then they start to ask me what where how you plan to use that wire ...............I explain them what I'm going to do and I get this answer ..........IF Kanthal wire is mounted in spiral on ceramic tube they have this rule ...... Dia. of wire x 12/14 = MAXIUM radius of ceramic tube on which A1 wire can be spiral mount .IF I use 1.5mm A-1 wire ..1.5 x 14 = 21mm diameter of ceramic tube .
They say this too................

The design of industrial heaters is influenced by many factors. It is not a problem to calculate how much wire is needed to get a certain amount of heaters, but it has to be taken care of and many other factors, all in order to get efficient oven with an acceptable lifetime of the heaters themselves. Care must be taken of the wattage on the heater itself and in the furnace itself, on the temperature control, the diameter of the spiral, and the like.

Now I really have no idea what to do ? I'm kind of embarrassed to ask them what will happen If I still do that ? DO you or anybody have any idea what will happened ?? If it is only for longevity of A1 wire i have no problem with that ??? They give me this data for 1.5mm A-1 wire .... for 3000W I need 22,49m/0,28 kg Kanthal A1 ...
There was solution to this ...to make heaters just as how Carbolite do that , but will complicate building

 

[Natlek]

This is Kanthal catalog , page 13 is about this ....

https://www.kanthal.com/globalasset...-elements/resistance-alloys_s-ka041-b-eng.pdf

 

[Natlek]

I found answer to my question here ....http://www.joppaglass.com/elements/dudleys_element_paper_2015.pdf

There are several reasons for stretching your new element: a) for letting the heat out of the coils; b) for fitting the element to the kiln; & c) if you don’t, the electricity can arc across the touching loops and burn the element out. A good rule of thumb is to have a minimum distance of 3 to 5 diameters of wire distance between coils. Thus for 15 or 16 gauge wire this translates into roughly 1/4” spacing. There is no maximum distance. The coils can be stretched straight with no harm done. In fact, it is a common practice in Japan to pin straight wire elements all around the interior of the kiln. We use coils to condense this process and put the elements in grooves or on rods, but this is only a Western kiln practice, not universal.

Well guys , I have luck Friend of mine have small company for casting some parts from Al and steel ...... last year they renovated furnaces and some material left them ... I pay him 40$ for this kaowool ,6.2m lenght .And I get for free 25kg bag with casting refractory + this monster kanthal elements I found this 304L tube in scrapyard for 10$ .Dia is 27cm. and 60cm lenght which is perfect for this . I'm waiting to arrive this set of electronics on picture ....Better one, Omega will get my USA friend in spring .Then , if everything works fine I will switch electronic.This one I will use for my tempering oven ,so no loss . A1 1.5mm wire is little problem for now ...But now I have most of material so I can start with some work ....

 

[Natlek]

I would have thought that 3 KW oven with a relatively small volume would heat up quite a lot faster. The cork at the end probably cant be too tight of a fit.

Well , with 30cm long and 5cm Dia tube and 2800W power it take three /3/ minutes to red color inside/magnet don t stick on steel/ and 5 minute to glow like sun .......Even color is up to that white line you see on picture where you see other ceramic tube on working one /almost all tube /. Finally I find time to make some test with this .So far I like it .... it's amazing how long it remains on temp. when I switch off power .First I try only with bricks , it take more then 20 minutes to get dull red inside ..... When I wrap tube with ceramic blanket ...... HT element is connected direct on 220V ,no PID control.I will make lot of changes from original idea ......there was better way to do all this

This is after about one and half minute .....

2.5mm spring steel blade was iniside...take minute to get to temp . Nice even color , it is finished blade ,even sharpened and while I take picture edge cool down little which is normal .... I quenched it again in pure cold water and it s survived

 

[John mc c]

Looks good natlek
I thought of this design after,and I stress after,I got my own oven up and running and saw its design flaws
I put a 1/2" of firebrick all around my elements and stretched the coil at the back wall out fully so it's just a wire
When my elements go I will do something like yours
Well done

 

[Natlek]

Looks good natlek
I thought of this design after,and I stress after,I got my own oven up and running and saw its design flaws
I put a 1/2" of firebrick all around my elements and stretched the coil at the back wall out fully so it's just a wire
When my elements go I will do something like yours
Well done

Thanks Well it can not be simpler, cheaper and probably more accurate and far away more even temperature then ordinary commercial HT oven on market .Only negative is it can not be HT at once multiple blade....But in bigger tube which I will use for build I can HT three blade at once if I want to do that .I will test this tube tonight little longer to see how will hold ... I make mistake in previous post,HT element is 1800W not 2800 W .It is from this stove element which I destroyed trying to get that ceramic insulation

But before I build this one I need to finish my sand pot oven .I can no longer look at the parts scattered around my shop which I have prepared for making it I think that I found right solution for HT elements ...... I will use 3 or it was 3.5mm thick Kanthal A1 wire for base.First I will make a spiral with 5 inch Dia. long enough for tube I will use , then I will string on it billions of ceramic insulation beads and over that long spiral of HT element from 1.5mm thick A1 kanthal and of course stainless tube filled with sand inside that vulcano ....problem solved .I will do this because that way I can use ceramic blanket for insulation because it is more efficient then bricks . I make some test and that 3mm wire is stiff even when glow yellow so I think that will hold for what I think to do .
big circle on picture ..........blue is ceramic blanket insulation , red is HT element and black is stainless/inconel tube ....
small circle on picture ......black is 3mm kanthal wire ,blue are ceramic insulation beads and red is HT element .....I hope it is clear what I plan to do .

 

[John mc c]

I think I get it.
No doubt I would have lots of questions before I'd start mine tho
I would love to see how it tests for even heat throughout when it's finished

 

[Natlek]

I think I get it.
No doubt I would have lots of questions before I'd start mine tho
I would love to see how it tests for even heat throughout when it's finished

I don t worry about that , even heat throughout tube would be great ....Even in this setup it is good .When everything get closed/insulated temperature would be even more constant inside . I make more test this two days .Maybe more than four hours total .I leave tube to heat to almost white color and it hold . I use piece 4 inch long and thick file for test ..... Next day when I test it again I put inside tube that piece /COLD/ file I heard the sound of cracking . . . . I repeated that test several time and every time I heard that sound .Tube was bright yellow inside .I know that because i leave file inside every time till get color of tube ...On lower normal temperature no sound .I know it that it is ceramic tube and ceramic don t like cold when it is very hot ,but need to see what would happen. I can t see any crack but they are must be there ..... I will continue to test when ever I have time ....

After all this run test ..

It s safe from inside , this is ceramic part in which that small/M4/ stainless steel bolt seat deep inside ceramic so steel can not touch it...In real build I would use high temperature silicon /1500 celsius/ to seal that place from inside for even better protection.

 

[Natlek]

One more thing ....First I try with normal spiral HT element . It heat tube maybe five time slower then with this corrugated one wire HT element..........same power both ..

 

[Natlek]

What I m most impressed is how FAST steel get heat inside .....I will try to forge some steel this afternoon , if my son agree to plays PID
One more thing , this ceramic insulation ring get hot when HT element are on power ? Hot that you can t touch them with hand , is it normal or I should use thicker wire ? Now it is doubled and twisted 1mm kanthal wire ?

 

[Stacy E. Apelt - Bladesmith]

The ceramic insulation on the power leads will get hot from heat of the power lug/bolt.

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.