Kiln design, heating element holders

Question

I intend to build a kiln in my free time over the next few months and am trying to avoid my past mistakes (heated too quickly, the kiln started cracking, the kanthal element melted and it was just plain terrible). So I'm thinking of using element holders. I have two ideas in mind. Either I use a ceramic tube around which the heating element is wound or I use ceramic grooves.

The second idea (Fig. 1) increases the usable space which is why I prefer it. However the price being prohibitively high (almost tripling the price of the kiln), I am considering using refractory cement to make them. It's cheap and also does not require firing the holders which is a huge advantage.

The question is three fold:

1. Should I use inset element holders such as in Fig. 1 or do offset tubes offer some advantage such as possibly quicker temperature increase due to the walls heating slower.
2. Will refractory cement survive hundreds of cycles in such close proximity/contact with the heating elements?
3. Can ceramics be used above the temperature at which they were fired without sustaining damage? Meaning, can I use the local pottery to make element holders (they can fire up to about 1350°C and I intend to be able to go to 1400°C (the bricks are supposed to be able to go to 1440°C).

If you need more specific information, I will answer the best I can. Thank you.

Best regards

Answer 1

The problem is using Kanthal ( iron base ) instead of nichrome family ( nickel base). Both have high chrome with some aluminum for oxidation resistance. Kanthal becomes brittle quickly and is weak above 2000 F. It cannot be moved after it has been heated ; too brittle. Kanthal is also attacked by silica and iron in the refractory. I am using an antique text ;Engineering Metals and Their Alloys , C H Samans 1956 . So you will not be able to find it; but trust me this stuff does not change. The only thing that changes is the advertising by the Kanthal producers. I think in F so did not recognize 1400 C = 2550 F ; you need a new plan with lower temperatures . Or silicon carbide or platinum . Nichrome will go to about 2000 F , maybe 2150 F for certain alloys.