Troubleshooting Old Duncan Kiln

[Nora Wertz]

I  finally got my garage wired for 240 to plug in my DK 820X-2 octagonal kiln. It is a lovely old kiln-sitter model and I want to start firing.

I don't think the top 4 elements are getting hot enough. There are 8 elements in all and there are two 'infinity switches', I think the top switch controls the top 4 elements and the bottom switch controls the bottom 4.

• When I turned both dials to medium I could hear the power starting but after a few moments it made a switching sound and the power sound got quieter, then a few moments later the sound revved up again, and then quieter again. This happened constantly during the 10 minute test.
  Is this loud/soft power sound typical for these kilns?

 

• The kiln started heating but I did not see the elements get red so I did a 'paper test' to check the individual elements.
• Within 3 minutes the bottom four pieces of paper were ignited by the elements and they started glowing red.
• After 8 minutes the top four pieces of paper were charing over the element but never got hot enough to ignite.
  
  I am trying to figure out whether this would be a switch problem? an element problem? Or something else (relay?) As you can probably tell I am entirely ignorant about all thing electrical.

If anyone has any experience with these kilns I would appreciate your insight.

[Norm Stuart]

Regardless of what type of controller a kiln has (kiln sitter, manual or digital), they all have relays which cycle the power to the coils on and off as they heat at the programmed rate.

So you should hear a click of the relay(s), unless your kiln has old silent mercury switches, followed by the hum of electricity slightly vibrating the heating elements at 60 cycles per second. Then a click, perhaps softer in volume, followed by silence from the coils as the electricity to the elements is shut off. This on-off cycle continues during the entire firing.

We have a very over-powered kiln and paper strips placed next to the heating elements in our kiln also char without igniting if they're good during the first 10 minutes of firing, so your kiln sounds normal to me so far.

As the kiln temperature increases the heating elements will be cycled on for a longer period than they are off. And the color they glow will be red then orange then finally yellow-white along with the interior of the kiln. You'll not see a pure white glow until cone 11.

http://www.ceramicartdaily.net/PMI/KilnFiringChart.pdf

A certain Justin Leavitt in New York has posted this photo of his kiln at peak bisque temperature around 1,888 F with the lid open - along with the good advice to NEVER open your kiln at this temperature unless you want to break the fired ceramics and possibly your kiln elements. Always good to learn from someone else's experiments.

http://justinleavittceramicart.com/wp/tag/clay/

 

[Nora Wertz]

Thank you, Norm. This information is very reassuring.  I am not ready for a bisque just yet, but I will let you know how it goes.

PS. Although I have apparently forgotten tons of kiln lore, opening the door in the middle of a firing is not something I've ever wanted to do!

PPS. We can leave that to those crazy Raku kidz. ;)

[Maggie Jones]

I don't recall what co. has Duncan now, Paragon?  You can ask Arnold Howard if so, he is very helpful.

The infinity switch is an on off situation meaning at full power it is on 100% and at half or medium setting it is on 50% and off 50%. You can time them. Some of the switches used to be able to be calibrated but I don't recall how to do that.