Building tempering Oven

[joedhiggins]

Not if you run each circuit off a different hot (assuming your 240 is a four wire, has 2 hot wires, a neutral, and a ground).

If you were to power both circuits off both hot wires (or if your 240 is a 3 wire, two out of phase hots and a ground) it would double current and power output, which i think 240 usually will have at least a 30 amp breaker ( easily check by looking at the breaker, it has to be printed right on it) and so 20 amp isnt too much, assuming the elements are rated for it, but is overkill for the application. You could run all 4 in series and it would draw 5 amp and output 1200 watt which is pretty good.

This is all assuming the elements are 12 ohms each, you really need to measure this!

I think he does not live in the USA, so I am assuming that 220v is via a traditional hot, neutral, ground setup and 220 is the hot line voltage. I am unaware of any part of the world that runs 220 as standard outlet voltage with 2 110 hots. For instance, britian is one 200 hot, one neutral, one ground. I think standard amperage is 13A per line there, though I am sure this changes country to country.

 

[Natlek]

I would use high temp wire crimps on the 12 gauge (or 10 gauge) hi-temp wire and screw them tight to the elements. The front element can be wired through a small hole in the brick and down a larger hole to the bottom. A simple metal channel under the bottom to route the wires through would be a good idea. You can plug the holes in the brick with satanite or just a plug of ins-wool after everything is done and tested out. Back elements can go straight out the back. Put all the power connections and PID stuff in a metal box mounted on spacers an inch away from the back.

Sorry @stacy , my knowledge of English is limited ,especially with some specific terms so I did not explain in detail how I intend to make whole oven .I have two spare heater so I will try to bend them in 90 degree angle where is that orange line on picture and I will take off that metal part what hold heater ....That way end of both front heater will go in side wall and so it will be much easier to make/seal the door ? I think that this will work .......

 

[Natlek]

I think he does not live in the USA, so I am assuming that 220v is via a traditional hot, neutral, ground setup and 220 is the hot line voltage. I am unaware of any part of the world that runs 220 as standard outlet voltage with 2 110 hots. For instance, britian is one 200 hot, one neutral, one ground. I think standard amperage is 13A per line there, though I am sure this changes country to country.

Yes , I m in Europe .....

 

[Natlek]

I just meant an oven gasket. I used the term high temp to indicate something made of fiberglass or ceramic fiber, not traditional gasket material.

As to the blower, my worry would be properly insulating the rotating shaft. Doable, but with the combination of the partial vacuum behind the fan and an uninsulated/sealed shaft entrance, you are likely to get a meaningful temperature gradiant from front to back in the oven. I am not sure of a great way to seal the shaft other than more gasket material, but then I am unsure of how well that gasket will last in a high temp/friction environment. There is I am sure a way to do this, but I dont know off the top of my head.



Yup. Current is voltage over resistance (I=V/R) so, figure out the amperage of the circut and the specced wattage of the elements. In series, the resistance will double so if one element is 10 ohms, 2 in series will be 20. In paralell, the resistance is halved, so 2 10 ohm elements in paralell will make a 5 ohm resistor. After you have figured out the resistance of an element, determine your minimum resistance by deviding your voltage (nominally 220, but test with a multi meter) by your max current (whatever the circut is rated to. in the USA, the amperage would be printed on the breaker, not sure of code there). Take that value (in a brittish circut that would be 220V/13A or just under 17 ohms). Based on the above rules, determine what configuration of elements would give you a resistance greater than that minimum. Form there you should be good.

Double check your work by calculating the wattage of each element by dividing the voltage (nominally 220) by the resistance of your specific setup, as you measure it. That will give you your expected current draw (which should be a number smaller than your max circut amperage). Multiply your amperage by your voltage to get wattage and then divide that wattage by the number of elements in your array (assuming a symetrical array) and ensure that number is less than the watage the elements are specced for.




My suggestion on materials was mostly from an ease of construction/mounting perspective. A SS wall will stand up better than ceramic in this case as the temperatures are not high enough to cause meaningful ablation of of the steel via oxidation. You shouldn't have any concerns of shorting these elements to the stainless as long as you are concientious about your construction. And if you have to pull it all apart to replace an element of otherwise fix something, it will be much easier with a stainless internal box rather than a ceramic one. Finally, based on your design I assume you can weld stainless, so doing things like mounting the steel muffles will be much easier and more resiliant with this construction.

I don't think any of my recomendations would make it a less capable or shorter lasting oven, but maybe I am wrong, so feel free to deviate as you see fit.

I've been thinking this way..,.....ceramic tile is not a good heat conductor so it will take heat slow , but when it reaches say 200 celsius it will not lose fast heat ? Steel will heat faster but will lose heat faster too ? So i was thinking that ceramic will have much lower oscillations in heat temp when reach set temp ? I do not know if this is right ... I'm just thinking loud.
About fan inside ..there is way to do it right ...I will explain when I start with building .

 

[Natlek]

As to the blower, my worry would be properly insulating the rotating shaft. Doable, but with the combination of the partial vacuum behind the fan and an uninsulated/sealed shaft entrance, you are likely to get a meaningful temperature gradiant from front to back in the oven. I am not sure of a great way to seal the shaft other than more gasket material, but then I am unsure of how well that gasket will last in a high temp/friction environment. There is I am sure a way to do this, but I dont know off the top of my head.

I have SIC rings for that ...they will work similar like semering/seal in auto engine water pump if you are familiar with that .............

 

[Natlek]

This is all assuming the elements are 12 ohms each, you really need to measure this!

I will measure tomorrow , my multimeter read nonsense now ..... probably need new battery .

 

[Natlek]

double post , sorry

 

[Stacy E. Apelt - Bladesmith]

DO NOT try to bend those elements. If you have a spare or bad one, cutit in half and you will see why. Inside of the metal tube is a heating element in an insulating cement.

Leave the end plates on the coils to mount them. Long thin bolts through the brick would be fine).

If you try and bend it, it will lok like this about 1 second after applying power.

 

[Natlek]

DO NOT try to bend those elements. If you have a spare or bad one, cutit in half and you will see why. Inside of the metal tube is a heating element in an insulating cement.

Leave the end plates on the coils to mount them. Long thin bolts through the brick would be fine).

If you try and bend it, it will lok like this about 1 second after applying power.

What if I heat them before bending Stacy? I mean to bend them while they are red hot ?
I watch some video how they a made.......They annealing tube before bending ? Hey , I have nothing to lose , I have two spare , they a cheap and if I succeed will be simple/safe to mount them .

 

[joedhiggins]

I've been thinking this way..,.....ceramic tile is not a good heat conductor so it will take heat slow , but when it reaches say 200 celsius it will not lose fast heat ? Steel will heat faster but will lose heat faster too ? So i was thinking that ceramic will have much lower oscillations in heat temp when reach set temp ? I do not know if this is right ... I'm just thinking loud.
About fan inside ..there is way to do it right ...I will explain when I start with building .

I think you will just see a larger overshoot (stone tends to have about double the specific heat (by mass) that steel does. That being said, steel is 2x as dense as moste stone materials, so a smaller volume of steel will have a higher heat capacity. To a large degree, you don't really want a huge thermal mass, it will just waste energy. Your goal is to have a precise temperature across the entire chamber. Thermal mass will help with this a bit, especially when you open the door, but the point of the muffle isn't to serve as thermal mass. it is to shield the knife from radiant heating from your elements. The thermal mass will help damp temperature swings, but your PID will do that by itself. That is what the PID is for.

Ideally, your muffles would be constructed from a highly thermally conductive material with a low emissivity. This would even out the temperature in the oven, providing a minimal temp gradient. Copper, brass or silver would be ideal materials. As I said, these materials should all be ideal, but I doubt there would be a noticable diference between them and steel. There will be a noticable diference between steel and insulating ceramic when it comes to temperature gradients. Also, non metals (like a cermaic muffle) tend to be more emissive than metalic elements, especially something like copper.

http://www-eng.lbl.gov/~dw/projects/DW4229_LHC_detector_analysis/calculations/emissivity2.pdf

That chart shows the emissivity of many materials. Muffle emissivity is probably not a big contributor, but I haven't given it that much thought. Muffle thermal conductivity is probably a far bigger deal.

Anyway, a steel or even better copper (once again, I doubt you can tell the difference) muffle coupled with a good pid and proper placement of the TC probe should yield great results with or without a fan.

 

[Stacy E. Apelt - Bladesmith]

"What if I heat them before bending Stacy? I mean to bend them while they are red hot ?
I watch some video how they a made.......They annealing tube before bending ? Hey , I have nothing to lose , I have two spare , they a cheap and if I succeed will be simple/safe to mount them ."


You could try. I don't know how well it will work. I would hook up power and test them out for an hour before installing them.

If they are new, and never have been heated up, then it may work. If they are used, they mat-y be brittle.

 

[mete]

Ceramic materials , by their very nature , conduct heat slowly. They do not like thermal shock or fast thermal cycling . Use of ceramic is to reduce thermal cycling in the oven.
This will work better than any metal.
Cost ? I already have the tile !
Other materials depend on the temperature max you might use. Kitchen oven temperatures will take 300* C so silicone will work . High temperatures will require ceramic wool.
I assume you will be working not much more than 300* C ??

 

[Natlek]

Well , for now not much more then 300 ....... Thanks for taking time to answer mete !

 

[joedhiggins]

Ceramic materials , by their very nature , conduct heat slowly. They do not like thermal shock or fast thermal cycling . Use of ceramic is to reduce thermal cycling in the oven.
This will work better than any metal.
Cost ? I already have the tile !
Other materials depend on the temperature max you might use. Kitchen oven temperatures will take 300* C so silicone will work . High temperatures will require ceramic wool.
I assume you will be working not much more than 300* C ??

Dude, ceramic is not what you want here for your muffles. You have three goals.

1: Stable temperature. This will be handled by the thermal mass of the oven and the PID. nothing to really do here. It will just work.

2: protection of the blade from radiant heat. As I said earlier, any muffle will do this well enough. Copper, silver, etc will do this better than ceramic. Reference the above chart. but we want to minimize emissivity.

3: the smallest possible temperature gradient across the oven. This is where a metal muffle is most ideal. Ceramic has poor thermal conductivity, as do most nonmetallic solids. as such, the muffles, if made of say copper, will have a very even temperature across the entire piece of copper. Regardless of the inconsistencies of the elements behind them, (which there will be big gradient, cooler near the contacts, hotter on the looped end), a thermally conductive muffle is ideal.

I am not arguing he should build the insulation out of metal, just the bits of the oven that would best be made from metal.

 

[Natlek]

Beauty of home made tools is that it can be build much better then any commercial unit. We have no labor cost , we not build for profit so we can use best available materials............If we know/find which they are obviously
OK , this heaters have mark on them which I don t see at first......230 V 350 W .......... I intend to use four so I have total 1400 W in chamber with dimension 500 x 12 x 15 cm. are 1400 W enough ?

 

[Stacy E. Apelt - Bladesmith]

I agree with Joe.

The oven shell and insulation will be fine the way you have them drawn (overbuilt, but perfectly good).

The muffle only needs to shield the blade from the coils and radiate the heat out more evenly. Thin metal plates will work fine. Copper would technically be the best, but I doubt you could tell the difference if using steel.

The PID control will regulate the internal temperature and after the oven has soaked ( come to an even temperature), it will stay that way.

The circulation fan is needed on larger ovens for circulating the hot air, but probably is a waste of time on a small tempering oven. IT won't harm your oven, but I don't think it will make it significantly more efficient.

 

[Natlek]

I agree with Joe.


The muffle only needs to shield the blade from the coils and radiate the heat out more evenly. Thin metal plates will work fine. Copper would technically be the best, but I doubt you could tell the difference if using steel.
Thin metal plates will work fine. Copper would technically be the best, but I doubt you could tell the difference if using steel.

Stacy , when you say muffle you think on that parts which on my picture are marked as ceramic glass ? Not on ceramic tile chamber, right ?

 

[Randy3000]

Beauty of home made tools is that it can be build much better then any commercial unit. We have no labor cost , we not build for profit so we can use best available materials............If we know/find which they are obviously
OK , this heaters have mark on them which I don t see at first......230 V 350 W .......... I intend to use four so I have total 1400 W in chamber with dimension 500 x 12 x 15 cm. are 1400 W enough ?

1400 watt is plenty. The only way to get 1400 watt will be to connect all 4 elements in parallel.

 

[Natlek]

1400 watt is plenty. The only way to get 1400 watt will be to connect all 4 elements in parallel.

Thank you very much my friend I have one more question.....can I use three thermocouple in parallel connection , furnace is quite long ?
Like this ? yellow color represent three thermocouple ?

 

[Randy3000]

Thank you very much my friend I have one more question.....can I use three thermocouple in parallel connection , furnace is quite long ?

A pid usually only handles one thermocouple, so it would take 3 pid's and that is a little overboard.

The ssr is just a switch, and is in the main power circuit. So your hot wire(s) from the power cord connect to one terminal on the ssr and then you will need a hot wire from the other terminal on the ssr to branch in to 4 wires. Each of these 4 wires will go on one end of each element. Then you need a wire going from the neutral on the power cord, braching into 4 wires, each connecting to the remaining end of the elements.