# Air flow amount for Electrical Muffle Furnace



## Quwannar (Aug 7, 2019)

Dear Friends; 
I am trying to built a 30 liter volume of electrical muffle furnace for carbon ashing. How much air flow should be ventilated through a furnace for a 30 liter? 
Would a observation hole at the door panel of furnace be sufficent for air intake vacuumed by a blower at the chimney of furnace? In selection of blower what capacity of blower should be? Or how the fresh air would be circulated thorough furnace? 
As for pre-heating of air inside furnace to keep heat proper level and to avoid from temperature fluctuation, what the best design of preheating apparatus should be inside furnace? Regards
Erdem 
P.S; in the drawing given below, air intake hole is shown at back panel of kiln. Any comments would be appreciated.


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## 4metals (Aug 8, 2019)

I think a powered vent would cause more issues with uniform heat. Usually furnaces have a hole in the door about 2 to 4" (5 - 10 cm) above the furnace floor and centered on the door. The hole should be the same diameter as the vent hole on top but have a simple slide baffle to close off all or a portion of the intake as needed. Let natural convection do the work.


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## anachronism (Aug 8, 2019)

There's no need to pre heat. 

Get a good control circuit and ramp your temperature to 600 degrees C and keep it there for 8 hours. That's perfect for ashing carbon.


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## rickzeien (Aug 8, 2019)

anachronism said:


> There's no need to pre heat.
> 
> Get a good control circuit and ramp your temperature to 600 degrees C and keep it there for 8 hours. That's perfect for ashing carbon.


Do you ash in an electric Kiln as well? I would think off gas would corrode the elements pretty quick. 

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## snoman701 (Aug 8, 2019)

rickzeien said:


> anachronism said:
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> 
> > There's no need to pre heat.
> ...



As long as you keep the environment mostly oxidizing, element life is good.

You can coat electric elements in ITC 213, then use them in reducing environment, but you have to derate them a bit or you end up melting them from the inside out.


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## snoman701 (Aug 8, 2019)

Also, generally a muffle furnace has the heating chamber isolated from the heat source. So it's a kiln within a kiln. 

Offers you the ability to maintain a different environment within your chamber, irrespective of your heating method.


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## rickzeien (Aug 8, 2019)

snoman701 said:


> rickzeien said:
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> > anachronism said:
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Thanks. 

Once reduced to carbon doesn't air need to be introduced to ash the carbon?

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## anachronism (Aug 8, 2019)

rickzeien said:


> anachronism said:
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> 
> > There's no need to pre heat.
> ...



Actually I'm surprised because it hasn't done that.


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## snoman701 (Aug 8, 2019)

It is.

The convection currents from the "heat rising" and "falling" are enough to draw oxygen in through the vent hole and expel carbon dioxide.


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## snoman701 (Aug 8, 2019)

anachronism said:


> rickzeien said:
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> > anachronism said:
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If you are using just a coiled kanthal wire, they are realistically pretty durable as long as you aren't trying to incinerate in it. I just keep an extra set on the shelf. The worst part is getting the old element out when it's stuck in the groove...a propane torch and needle nose pliers make it easier.


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## rickzeien (Aug 8, 2019)

anachronism said:


> rickzeien said:
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> > anachronism said:
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I am surprised as well. I may have to give it a try Thanks

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## rickzeien (Aug 8, 2019)

snoman701 said:


> rickzeien said:
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> > anachronism said:
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I just ordered some ITC 213. 

Thanks

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## snoman701 (Aug 8, 2019)

Look on google for Mel Jacobson posts on potters.org regarding itc 213 and how to apply to elements. 

Get a pid controller and use it to fire solid state relays. This stuff is dirt cheap now. You should also have a mechanical contactor to kill power set up on a limit switch basis say 50 deg c higher. Ssr’s always fail in the on position, so otherwise you’ll come in and your kiln will be cooking at 2350 f. 






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