Building An Electric Kiln For Pottery

[Blue Crystal]

I intend to build an electric kiln for pottery, clay ( and other materials ) sculptures.
The internal dimensions would be 40cm(height) x 40cm(width) x 40cm(deep).
Therefore, its internal surface is 9600 cm2. I need a maximum temperature of 1300 Celsius.

1) I would like you to confirm or correct this information. I was informed that in a typical kiln the calculation of the total Electric Power necessary is given by this formula P ( Watts ) = 0.6 X Total Internal Area ( cm2). If that is true, then I would need 5760 Watts. However, I found in the internet values that are different from 0.6. So, if you are an expert please give me your informed opinion on that.

2) In order the temperature inside de kiln could be as much homogeneous as possible, its internal walls should be filled with as much heating element wires as possible. But there is a trade-off to be made. The more heating wires the bigger will be the resistance and the weaker will be the production of heat.Furthermore it may unnecessarily increase the cost of heating elements. Additionally, there will be the need to carve too many grooves on the refractory bricks to fit the elements inside which will weaken and possibly fracture them. By looking at the pictures of many different kilns it seems that the optimum distance between two parallel coiled wires is about 7cm ( axis to axis ). But if the grooves should be carved directly on the bricks and in the middle of their height then the distance between parallel grooves would be equal to their height or a multiple number of it.
Would you agree with my reasoning or do you have a different one ?

3) It seems to me that 3 resistors ( heating elements ) electrically connected in parallel is a good circuit because they would use only three relays and probably could be controlled by an electronic controller. What is you informed opinion on that ?

4) Another important aspect of the kiln design is the coiled wire ( heating element ) diameter. The bigger its diameter the bigger will be its durability. However bigger diameter reduces the resistance of the heating element and produces lesser heat. I intuitively think that a diameter of 1.30 mm would be OK. ( Of course, later on, I should also consider the coil diameter and the distance between its turns ).
Do you have a better informed proposition ?

( later on I may need further advice on the same project )

 

[Wilko]

Hi BC and welcome to the forum.
That's a challenging project to build your own kiln from scratch ! I've never built one but I can say the temp reached for any given power input depends upon the heat loss, which in turn depends on the detailed material properties and your construction technique. So no wonder the 0.6 number moves about depending who is commenting. Then there's the issue of a temp controller and safety cutouts that must be got right. Don't mean to sound like a wet rag, but why not just buy one ? Perhaps 2nd hand ?
From an electrical supply perspective it would likely be similar to a high power electric shower, with perhaps some over spec capability to allow for long periods of operation. Many Electricians here there can help with that, I'm sure.

 

[The Ghost]

Homemade Electric Kiln - http://www.instructables.com/id/Homemade-Electric-Kiln/

 

[dmxtothemax]

If you are talking about using resistance wire ( ni-chrome) of preset lengths ?
Then you don't use bigger wire to produce more heat
Instead you use more elements
so instead of three you would use four.

 

[SparkyChick]

To correct point 4, increasing the cross sectional area of a resistor will lower it's resistance allowing more current to flow. More current at a given voltage = more power dissipated by the wire which mean it will be hotter.

 

[Blue Crystal]

Hi BC and welcome to the forum.
That's a challenging project to build your own kiln from scratch ! I've never built one but I can say the temp reached for any given power input depends upon the heat loss, which in turn depends on the detailed material properties and your construction technique. So no wonder the 0.6 number moves about depending who is commenting. Then there's the issue of a temp controller and safety cutouts that must be got right. Don't mean to sound like a wet rag, but why not just buy one ? Perhaps 2nd hand ?
From an electrical supply perspective it would likely be similar to a high power electric shower, with perhaps some over spec capability to allow for long periods of operation. Many Electricians here there can help with that, I'm sure.

Thank you, Wilko. I want to enjoy the challenges of building my own kiln. Furthermore, a new kiln in the desired dimensions is quite expensive.