Element life & decay rate

[Lizardman]

I know new elements are in my future, but I’m wondering if there is a way to estimate how soon. 

I bought a used Skutt 1027 (cone 10 version) in August 2020. I checked the element resistance when I bought the kiln — the top 2 elements and the bottom 2 elements measured between 14.3 and 14.5 ohms (Skutt says these, if new, would measure 13.6 ohms), and the middle 2 elements measured 16.9 ohms (16.3 ohms if new). 

Since then, I’ve fired it 45 times, no higher than cone 1. Firing times have been pretty consistent, but I want to do some cone 6 work soon so I thought I’d check the resistance again today.  Elements 1, 2, and 5 were 14.7 ohms, elements 3 and 4 were 17.2 and 17.3, and element 6 measured 14.7-15 ohms (couldn’t get a steady reading.)

According to the 10% rule, I think should expect to replace the elements when the resistances measure about 14.96 and 17.93 ohms. So it seems like I should be able to get to cone 6 just fine, maybe a little slowly, unless the bottom element is a problem. 

Anyways, to finally get to my questions:

1) Does element life decay at a linear rate? 

2) Is there a way to estimate how many cone 6 firings I’ll be able to do before replacing the elements? 

3) I’ve read to expect 125-150 cone 6 firings with this kiln before it needs new elements. I assume that # is actually counting the times the kiln gets up to cone 6, not ~65 times to bisque temps and another ~65 glaze firings? 

4) Is there a similar rule-of-thumb for # of low-fire firings I’d get out of new elements? 

5) Finally, I’m probably going to order new elements this week  so I have them on hand for when I need them, unless this is a bad idea for some reason. Is it?

 

 

[neilestrick]

38 minutes ago, Lizardman said:

1) Does element life decay at a linear rate? 

2) Is there a way to estimate how many cone 6 firings I’ll be able to do before replacing the elements? 

3) I’ve read to expect 125-150 cone 6 firings with this kiln before it needs new elements. I assume that # is actually counting the times the kiln gets up to cone 6, not ~65 times to bisque temps and another ~65 glaze firings? 

4) Is there a similar rule-of-thumb for # of low-fire firings I’d get out of new elements? 

5) Finally, I’m probably going to order new elements this week  so I have them on hand for when I need them, unless this is a bad idea for some reason. Is it?

1. Element decay depends on a lot of factors- firing temp, firing schedules, holds, whether or not you're using a downdraft vent, type of clays being fired, etc.

2. How many at this point? No.

3. That estimate is based on about 40% of the firings being bisque firings, and the other 60% being cone 5/6 glaze firings.

4. Low fire lifespan depends on all of the factors I listed above. I've seen them last for 200 firings, I've seen them last for 450 firings or more. However, because elements can be in really bad condition and still get to low fire temps, a lot of low fire people fire them way too long, and they're getting very inefficient firings for a long time.

5. It's a great idea to have spare elements on hand. Also have a spare thermocouple and a set of relays.

[Lizardman]

Yeah, I figured "it depends" was going to be the answer to most of those questions. I hadn’t realized that holds, type of clay, venting, etc. affect element life, but it makes sense. Thanks!

I have a set of relays and a thermocouple already on hand and will go ahead on the plan to get spare elements before I need them.  
 

Thanks for such a quick, detailed answer (and on a Sunday afternoon!)