Thursday, March 3, 2011

Element Life Test

According to the experts, there are 2 factors that play a major role in how quickly elements wear out: how hot the kiln is fired, and how many times the elements cycle on and off (assuming the same number of firings).

Kilns with computer controllers increase the heat in the kiln by cycling the elements on and off. They are either all the way on, or all the way off. To heat the kiln slowly, they turn on for a few seconds or minutes, then turn off for a few seconds, then turn back on. There are no low, medium and high settings like on a manual kiln. The hotter the kiln gets, the longer the elements must stay on to increase the temperature. At the high end of a cone 6 firing, they are on almost continuously. This cycling puts wear and tear on the elements. The same is true for light bulbs and other electrical systems. The big question is whether this cycling is more detrimental than firing temperature. I decided to do my own un-scientific test in my small kiln to find out.

To test which is worse, the current set of elements in my kiln have been used with a different firing schedule than the previous sets. Rather than fire all the way up to cone 8 as I used to, I have only been firing to cone 6 then adding a 40 minute hold to get to cone 8 (see HERE for an explanation of how cones work).

When firing all the way up to 8, the elements were having to go hotter, but they weren't cycling on and off as much. As I said before, at the high end of the firing they don't cycle much at all. With the current firing schedule they don't go as hot, but in order to hold temperature for 40 minutes they have to cycle more than before.

So which is better? The previous 2 sets of elements each lasted about 10 months. Right now my current elements are at the 9 month mark, and they are still going strong. They are showing some signs of wear when tested with an Ohm meter, but they are still well within the normal range. Visually, the elements look a lot better at this point than the last set did. I know that's not very scientific, but you can tell a lot about an element by looking at it.

I should also mention that in addition to the changes discussed above, I have also been adding a slow-cooling step to the end of the firing. Rather than just shutting down after the 40 minute hold, the kiln cools at a rate of 175 degrees per hour down to 1600 degrees. This adds about 4 hours to the total firing time, and adds a lot of cycles to the elements. I think it's also safe to say that I fire more often than before, since the studio is busier than last year.

At this point it appears that the higher firing temperature shortens element life more than cycling on and off. I'll post a note when the current elements have to be replaced, and we'll see if it's a significant difference.

One last note: even if it didn't extend the life of my elements, my glazes look better. That long soak really has a nice effect on them. It's worth doing it for that reason alone!

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