Prefire a new thermocouple?

[Dick White]

Someone just told me that Skutt told them that after installing a new thermocouple, the kiln should be prefired empty in the same manner as for new elements. I never heard of that before, but then there are a lot of things I've not heard of. Does this sound right to those of you who clearly know more than me?

Thx, dw

[neilestrick]

2 minutes ago, Dick White said:

Someone just told me that Skutt told them that after installing a new thermocouple, the kiln should be prefired empty in the same manner as for new elements. I never heard of that before, but then there are a lot of things I've not heard of. Does this sound right to those of you who clearly know more than me?

Thx, dw

I've never, ever heard that for thermocouples. It kind of makes a little bit of sense in that the metal probably builds up some oxidation that helps to protect it from the atmosphere, but I think the heat itself does far more damage to thermocouples than the atmosphere in an electric kiln. And if you've got closed protection tubes then it's really a non-issue. And if you consider the cost of an empty firing you're adding to the cost of the thermocouple change to a degree that probably outweighs the lifespan benefits of the empty firing.

[Dick White]

I thought about the same, but who am I to challenge anybody at Skutt?

[Bill Kielb]

48 minutes ago, Dick White said:

I thought about the same, but who am I to challenge anybody at Skutt?

The only thing I can remotely think of is to remove any residue or oils from the thermocouple. One could do that by wiping it off or torching it to 1000 degrees for a few seconds. I would be curious as to the reasoning ….. as thermocouples oxidize themselves to death by their function. Covering them often improves lifespan a bit. I really would love to know why the person who told you that did so, and what longevity they would attribute to that procedure. Then I guess I would form an opinion on credibility from that. I would love to know the why if you ever get an explanation.

[Mark C.]

Bad idea all around no matter where you heard it. It looses some life every fire. One more is just one less on life span.

 

[Min]

This could just be someone got their wires crossed, (yup, bad pun intended). Skutt video on replacing a TC says at the end to perform a test fire with an empty kiln to make sure the TC is working properly. The written blurb says basically the same thing using cones to verify in an empty kiln.

[rox54]

I am a relatively new potter, so I only replaced my TC one time. If I remember correctly, I think Skutt told me to fire wares I'm not too concerned about and fire bisque, not glaze.

[Bill Kielb]

18 hours ago, Min said:

The written blurb says basically the same thing using cones to verify in an empty kiln.

Even more interesting as rate would need to be included to get a meaningful temperature comparison.

[Bill Kielb]

7 minutes ago, rox54 said:

I am a relatively new potter, so I only replaced my TC one time. If I remember correctly, I think Skutt told me to fire wares I'm not too concerned about and fire bisque, not glaze.

Did they say why? After that first test fire was it ok to fire everything?

[neilestrick]

19 hours ago, Min said:

Skutt video on replacing a TC says at the end to perform a test fire with an empty kiln to make sure the TC is working properly. The written blurb says basically the same thing using cones to verify in an empty kiln.

This makes sense. New TC often give different reading than the old ones, since they drift in accuracy as they age. An empty firing would let you calibrate it without sacrificing any glaze work.

[Hulk]

When moving to a new/different thermocouple, I'd planned to set marked cones where I can see them from the peeps (wearing the proper protective glasses, of course).

However, during last glaze fire, wondering what to do if the thermocouple failed during the firing (I'm using the the single instrument), I've decided to go back to placing a marked cone where it can be seen, just in case.

For sure, if/when I get a new kiln and/or a new thermocouple, I'll be watchin' cones... 

For sure II, if/when I replace the elements in my relic kiln, I'll be watchin' cones - there's a'ready too many things that can (err, will?) go awry.

[Bill Kielb]

3 hours ago, neilestrick said:

This makes sense. New TC often give different reading than the old ones, since they drift in accuracy as they age. An empty firing would let you calibrate it without sacrificing any glaze work.

Hmm, ……….how would one calibrate by using cones in a single TC kiln?

[Morgan]

I could be wrong but that question is usually why when you replace TC or elements you replace them all. It would drive me bonkers if I had a multitude of different aged TCs. 

[Bill Kielb]

43 minutes ago, Morgan said:

could be wrong but that question is usually why when you replace TC or elements you replace them all. It would drive me bonkers if I had a multitude of different aged TCs. 

Always good to have all new but replacing them as they wear seems fine for many. If one replaces with all new do you still dry fire for calibration? In the studio we started replacing when the tip insulator started to crack knowing that it had limited firings in it till failure. The intent was to minimize unwanted down time for maintenance. The strategy worked fairly well actually.

[Min]

2 hours ago, Bill Kielb said:

Hmm, ……….how would one calibrate by using cones in a single TC kiln?

Shelf/shelves  and a cone pack in proximity to the new tc, same as for a loaded firing with a controller and programmed for a cone firing, not a peak temperature. If the aim is to test the tc with the fall of a cone it seems logical that load wouldn’t factor into it. We don't reprogram a cone firing differently for a light versus heavy load, controller adjusts heatwork to reach the target cone.

[Bill Kielb]

1 hour ago, Min said:

Shelf/shelves  and a cone pack in proximity to the new tc, same as for a loaded firing with a controller and programmed for a cone firing, not a peak temperature.

Got it,  so not a way to calibrate or check the thermocouple accuracy,  just potentially a way to recalibrate your use of your controller with a new thermocouple. I would add that cones fall based on the final rate. Often when a kiln ages it cannot make final expected or programmed rate and things begin to overfire as controllers have compensation limits and at some point the process does not work at lower energy levels. Fire an empty kiln to calibrate controller or thermocouple? Not sure that is the best representation of the kiln in actual use, especially if  it’s unable to maintain a reasonable final rate.

[neilestrick]

45 minutes ago, Bill Kielb said:

so not a way to calibrate or check the thermocouple accuracy

You calibrate with cones on a shelf where the thermocouple is located, then adjust how you load the kiln to get the rest of the kiln to match up.

[Min]

52 minutes ago, Bill Kielb said:

Not sure that is the best representation of the kiln in actual use, especially if  it’s unable to maintain a reasonable final rate.

That's the beauty of the controllers, with a cone set for the peak (not a set temperature) the controller takes the rate of climb into account and adjusts the final temp accordingly. 

 

[rox54]

On 10/9/2021 at 10:37 AM, Bill Kielb said:

Did they say why? After that first test fire was it ok to fire everything?

I think they said that the bisque is less risky than a glaze fire if it slightly over or under fires and of course, with wares you arent overly concerned about, there is even less risk. They said to put some bisque in and some furniture so the load is similiar to a typical load. It all went well and I moved forward with a glaze fire right after. I have a programmable Skutt btw

[Bill Kielb]

50 minutes ago, rox54 said:

think they said that the bisque is less risky than a glaze fire if it slightly over or under fires and of course, with wares you arent overly concerned about, there is even less risk

So it sounds like a way to confirm the new thermocouple will work within reason and not necessarily a prefire situation as in seasoning new elements. That makes sense and is consistent with the Skutt video.