Kiln refresh questions

[moonzie]

Howdy y`all. 

I've got a small L&L E18S-3 with quads. After 192 firings, I got an error ED50 Too high above set point. After reviewing the last error details, I realized the time had come that the lower end could not keep up anymore so it was time to swap out elements. Took me a few hours longer than I expected but I got it done. I also swapped out the closed TC tubes with L&L's newer open ended ones since I was having a hard time dialing the kiln in with solid repeatable results (we pack it pretty tight). Also replaced the TC with the standard types.

Q1: How far should the TC tips recess into the open tubes? I set mine back about 3/16"

Q2: I'd like to do a seasoning fire with some shelves and maybe a bunch of stilts in it and some large witness cones in front of the peep holes so that I can dial in the adjustment all in one fire. Would this be acceptable or should I do them as two separate fires?

 

Thanks! :)

[neilestrick]

34 minutes ago, moonzie said:

Q1: How far should the TC tips recess into the open tubes? I set mine back about 3/16"

I usually do about 1/4".

35 minutes ago, moonzie said:

Q2: I'd like to do a seasoning fire with some shelves and maybe a bunch of stilts in it and some large witness cones in front of the peep holes so that I can dial in the adjustment all in one fire. Would this be acceptable or should I do them as two separate fires?

Yes, that can all be the same firing.

35 minutes ago, moonzie said:

After 192 firings, I got an error ED50

What cone are you glaze firing to? I would expect a lot more than 192 firings if you're doing cone 6 glaze and 04 bisque. Did you measure the element resistance? How old were the thermocouples?

[moonzie]

TCs were the originals from when we bought the kiln factory new. They were very blackened and charred looking. The bottom elements read 20.0 ohms (however accurate a cheap Etekcity meter is) I didn't measure the top before I pulled them. Originally, the elements measured 19.2 and that's what the new ones measured.

Always 04 bisque slow. Cone 5/6 with various holds of 2-15m. There were a handful of cone 5 Crystal Blossom (Laguna) fires with 3.5 hour holds in there. The last glaze fire I did this program. The next fire was a cone 5 glaze with 4 minute hold. It errored out just before peak temp and unfortunately, I didn't have witness cones in this load but I tested for vitrification and only one piece came out not fully vitrified.

How many firings do you usually see quads last for? I spoke with a L&L tech by phone and he said they typically see about 180 firings on average. I've been watching the screen where you can see power output and for a good while now, the bottom stays on 100% sometime after 1200f. The error occured when the top was 2190 and the bottom was 2130, but think my TC adjustments are just a touch  under value (reading cooler than what it is).

[neilestrick]

4 hours ago, moonzie said:

How many firings do you usually see quads last for? I spoke with a L&L tech by phone and he said they typically see about 180 firings on average. I've been watching the screen where you can see power output and for a good while now, the bottom stays on 100% sometime after 1200f. The error occured when the top was 2190 and the bottom was 2130, but think my TC adjustments are just a touch  under value (reading cooler than what it is).

My customers usually get about 250 firings, some more than 300. If those were the original thermocouples, then they were probably the source of the problem. I'm honestly surprised they were still functional at all after 192 firings. I would replace them every 100-125 firings to be safe. If your elements were reading 20 ohms, then they were only about 4% off. They shouldn't need changing until 10% off. It's normal for the bottom to work a lot harder and run at 100%, especially if it's a packed load and you're trying to fire fast. Which firing program do you usually use? Most kilns can't keep up with 350F/hr and fire evenly. Make sure you're not packing the bottom of the kiln tightly. Put large pieces at the bottom, small pieces in the middle/top.

[moonzie]

I usually put large stuff on the bottom so it's got plenty of surface exposure to the elements down low. I did notice last fall that when attempting a fast fire, it still took about 7 hours and the set point was off from where the kiln was at by at least 20 degrees. Usually I do medium speed glaze fires unless I'm in a hurry. The first time I did a fast fire, it only took about 4.5 or 5 hours. Maybe it was just the TC then? I thought the closed TC tubes extended the TC lifespan by quite a bit. Guess I was getting paranoid about the elements. Still learning!

[neilestrick]

2 hours ago, moonzie said:

I did notice last fall that when attempting a fast fire, it still took about 7 hours and the set point was off from where the kiln was at by at least 20 degrees.

The fast fire program is too fast for most kilns. It can get close in a small 2 section kiln, but a 3 ring kiln can't fire anywhere near that fast and stay even. A really full load will make it even more difficult, in any size kiln. I would avoid that setting altogether, because most glazes don't look as good being fired that quickly.

The TC tubes do extend their life, but not to the degree that you would expect. The heat itself is more damaging to them than the fumes in the kiln. IMO the main benefit of the protection tubes is that they keep the TC metal flakes from getting all over the inside of the kiln. Check them at 75 firings, probably replace them at 100-120. They're relatively inexpensive, and fresh ones will keep the kiln running accurately.