Max Temp Or Max Cone?

[sloan.quinn]

So a few weeks back, I bought a used Brent wheel and an old Duncan 1029 kiln for $200 at a yard sale. A while later, I noticed the manufacturer's plate on the side of the kiln's control box says max cone 8, but max temp 2345F.

 

So which one do I pay attention to? I've never fired to cone 10, but it'd be nice to be able to give it a shot if it wouldn't destroy the kiln.

 

TIA!

Sloan

[bciskepottery]

Here is previous thread on same model kiln.

 

http://community.ceramicartsdaily.org/topic/1610-recommendations-for-a-new-used-kiln/

 

Getting to cone 10 will depend, to a large extent, on the condition of your elements.

[Mark C.]

I'll bet cone 10 will make your elements get to be toast very soon-cone 8 will be hard enough on it as thats its rating. 

How thick is the side wall 2.5 inches or 3 inches? 3 is the minimum really for any cone 10 electric these days.

my 2 cents

[sloan.quinn]

...Getting to cone 10 will depend, to a large extent, on the condition of your elements.

 

Fair statement. I can't check them out yet, since I'm waiting on hubby to run the 240v circuit and the sellers (the previous owner's daughter and SIL) didn't have 240 in their garage to fire it up.

 

On that note, I know Paragon took over supplying parts for Duncan, but do you (or anyone) know if they still MAKE the elements, should one or more need replaced? Or, if not, is there a workable substitute available? I mean, this kiln is approaching 20 years old at a minimum, so parts obsolescence could be a thing...

 

I'll bet cone 10 will make your elements get to be toast very soon-cone 8 will be hard enough on it as thats its rating. 

How thick is the side wall 2.5 inches or 3 inches? 3 is the minimum really for any cone 10 electric these days.

my 2 cents

 

I'd have to get in there again and check, but I think it's 3 inch brick. Could definitely be wishful thinking, though. I didn't really think 3 inch brick was much of a thing when this kiln was made.

 

As for "cone 8 being hard enough as thats its rating," I'm assuming that would have to do with the wear on the elements from being on long enough to get the proper heat work done? That's pretty much been my working theory here - that the kiln could get to 2345, but the heat work required to get to ^10 would fry the elements...i.e. it wouldn't like the sustained effort much at all.

 

Thanks again!

Sloan

[Mark C.]

I have a old skutt thats rated about the same as yours cone 8  on the plaque-2.5 inch wall-it will never be a cone 10 kiln as its not made for that.

I 'll bet Paragon still makes your elements if not Euclids will make them for sure.

[glazenerd]

Look at the label this way: the kiln was designed and built for cone 8 use, but has enough power to fire to cone 10 if need be.

 

A true cone 10 kiln has two design parameters that must be meet. The chamber must be a minimum of 3" K-23 IFB, but K-26 works even better because it stores and reflects heat back into the kiln. Additional fiberboard wrap is also useful for daily demands. The other issue is power: a true cone 10 should have a minimum of 1800-2000 watts per cubic foot of kiln space. My Paragon 1613-3 test kiln supplies almost 3600 watts per CF. So cone 10 kilns are either designed with 3" brick with more wattage, or 3" brick with extra fiberboard with less power.

 

That is the misconception about wattage: people see the amperage and wattage and get spooked thinking their kiln will cost a fortune to run. However, just the opposite is true: an under rated kiln can draw 50% more power trying to achieve a temp it was not really designed for. I give people this analogy to help them comprehend wattage: your outdoor water spigot has a rated pressure. Hooking up a 1/4" hose will restrict flow, a 1/2 hose will let more water out; but a 3/4 hose will let the water flow unrestricted. Hope this helps everyone to understand chamber design and wattage. I have four cone 10 kilns, all with type S thermocouples. The one that uses the most power is the first one I bought that has the bare minimum of brick and power to do the job. Have a 6.5CF custom built with 3" brick, 2" fiberboard wrap, and 9800 watts: it cost me around $7 to fire a load to cone 10. The cost of running a kiln will eat up any money you saved by buying an underrated kiln for firings it was not designed for.

 

Glaze Nerd

[Tim T]

Also, beware the possible difference between the manufacturer's claims and the reality. I bought a 2nd hand kiln (I won't give the make o spare the manufacturer's blushes) which claimed to be 6.2kW for firing at 1300.

All was fine at first for earthenware and normal stoneware, but then I started doing oil spot glazes, going to 1290 with a 2hr soak - fine for a short while but then the elements died. I bought a replacement set from the manufacturer, and the same again.

So now I've looked into it properly (get a 2nd hand copy of Electric Kiln Construction for Potters by Robert Fournier for the details). With the elements supplied, even giving the benefit of going back to when it was 240V power and not 230V, it would just do 5.8kW, and at the 230V they give us now that drops to 5.3kW. In the new year I'll get some new elements with thicker wire and a longer length, which will give me more power and also give the elements a significantly longer lifetime.