Tube furnace

Cushing H. said:
Another point is that any system that a PID controller is managing must be reasonably balanced. By that I mean (sticking with the theme of controlling ovens) that the overall rate of heat input (at 100% of possible input), must be fairly close in magnitude to the rate at which heat escapes from the oven through its insulation. (for example, a nearly "perfectly" insulated oven can not be controlled by a PID, and likewise, a very poorly insulated oven will also have problems trying to control it with a PID) (again, I think some others have recently seen this when trying to get a toaster oven to work with a PID ... and did not succeed until adding more insulation to it)
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@Cushing H.
I quote your post here to not derail your topic about PID controler .... look , this is how my tube furnace work after about 15 minute soaking on 800 Celsius .....Say it is now on 803 Celsius.....I WAIT till temperature drop on 800 Celsius /that would take about minute , minute and half , maybe more / then I turn power ON and start to count .....21-22-23-24-25 and turn switch OFF . After about 10-15 sec. temperature will start to raise..very slowly ...801 ..... 802 ...803 Celsius and will stop there ......and all over again.
Can cheap Chinese PID control this behave of oven with auto tune ?
Note , HT element is from outside , so temp. from HT element must pass thru ceramic wall to get inside where TC is .....
 
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I am impressed with your tube furnace. I make nothing but folding knives. Heat treating carbon steel with a propane oven but would like to get into stainless steel. I have a ceramic tube(6" long, 2"OD, 1 1/2" ID) with a spiral groove cut on the outside. It will take 178" of 14 ga (.064) kanthal wire. This will be run on 110 volts with a PID. Would this be able to reach stainless steel heat treating temperatures?
 
coldtracker said:
I am impressed with your tube furnace. I make nothing but folding knives. Heat treating carbon steel with a propane oven but would like to get into stainless steel. I have a ceramic tube(6" long, 2"OD, 1 1/2" ID) with a spiral groove cut on the outside. It will take 178" of 14 ga (.064) kanthal wire. This will be run on 110 volts with a PID. Would this be able to reach stainless steel heat treating temperatures?
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Thanks :thumbsup: Can you calculate Watts ? It would be hard for me to do that with that USA measures .Now I have 1200 W /before was 1800W and it get to 800 celsius in 3-4 minute /in small one furnace and I have no problem to reach 1200 Celsius ....https://bladeforums.com/threads/first-san-mai-weld.1710025/
Do you have picture of that tube , i like to see grove ? How deep they are ?Maybe you can use standard spiral kanthal wire if no enough room for flat one to get Watts you need ?With only 6 inch long tube probably 600 W would be enough ......?
 
coldtracker said:
I am impressed with your tube furnace. I make nothing but folding knives. Heat treating carbon steel with a propane oven but would like to get into stainless steel. I have a ceramic tube(6" long, 2"OD, 1 1/2" ID) with a spiral groove cut on the outside. It will take 178" of 14 ga (.064) kanthal wire. This will be run on 110 volts with a PID. Would this be able to reach stainless steel heat treating temperatures?
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You can make fast test which will cost you nothing if you have already kaowool. Wind the wire on tube , wrap tube with kaowool . put some kaowool on one end to close tube and Thermocouple inside and try it ......?
 
Stacy E. Apelt - Bladesmith said:
Go ahead and build one and show us the photos after you are done.
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For some reason I don t like sound of this post :)
Bigger one , finished ............................43 cm length and 6 cm inner Dia. of pure heat :p 22 min. to 860 Celsius with 1800 W on 220V .
Now it s your turn ....... make one knife and show it to us :mad:
gANQMkj.jpg

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This time i don t think to much how to get out of heat zone :D I used 3.5mm Kanthal wire/I forged end to drill hole / as connection between HT element to get out of oven to the normal cooper wire...........
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Stainless holder for blade.............
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Now it remains to make that MF PID ........................to work :D

That is that .......... I m done with this topic .Next project for this winter is 86cm. long one ..........
 
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John mc c said:
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
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Hot spot ? Does it heat evenly ?
Inside are 52100 knife blank , can you see it ............. 830 Celsius;)
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Well .....................here it is
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I quench them all in brine....no one crack so far......... for some reason
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Nice!
If anyone stateside does this please post your sources for parts.

Thanks for the WIP, Natlek
 
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2.5” od x 2.25” id X 16” long $227.55 US.
Measurements translate to roughly
64mm od x 57mm id x 477mm long.

Not sure of the weight of the tube for watts calculation, but a guesstimate of 3lbs and a specific heat of .21 with a temp change of 2200*f looks like around 4kw +/-. Sounds like a lot, where am I going wrong??
 
DanF said:
2.5” od x 2.25” id X 16” long $227.55 US.
Measurements translate to roughly
64mm od x 57mm id x 477mm long.

Not sure of the weight of the tube for watts calculation, but a guesstimate of 3lbs and a specific heat of .21 with a temp change of 2200*f looks like around 4kw +/-. Sounds like a lot, where am I going wrong??
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There has to be time in there somewhere to get from J to W.
 
Factoring in one hour which changed nothing for w or kw in the equation
 
Here is my guesstimate: Volume about 0.25l, density 2kg/l, specific heat 1 kJ/(kg K). That gives 0.5 kJ to heat the tube by a degree Kelvin. That is 500 kJ to heat it by 1,000 degrees Kelvin. If you have a 4 kW heater, it could heat the tube in 500 kJ / 4 kW = 125 seconds.

Edit to add: The above assumes no losses. In reality, it will take a lot longer than two minutes.
 
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Thanks to Natlek’s thread, I have a starting point. I’ll be getting stuff ordered and then see what happens in real world, real time with this.
 
DanF said:
2.5” od x 2.25” id X 16” long $227.55 US.
Measurements translate to roughly
64mm od x 57mm id x 477mm long.

Not sure of the weight of the tube for watts calculation, but a guesstimate of 3lbs and a specific heat of .21 with a temp change of 2200*f looks like around 4kw +/-. Sounds like a lot, where am I going wrong??
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Did you miss this picture on first page of this thread Dan? Look at data at that picture.........
65mm inner Dia. and 550 long tube furnace use 2000 Watts element if i read that Max.power correctly ?
zUv6nxV.jpg
 
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