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Old 10-09-2018, 03:04 PM
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Heating Refractory

My furnace is off right now due to either a loose wire, controller failure, or thermocouple problem.

Symptom: it was holding idle temp no problem (1900F). When I'd get ready to blow, I'd ramp up to 2100. At 2000, the temperature display suddenly flipped from actual to UUUU (so one of the above most likely causing it). This shut off the power to the elements until things dropped to under 2000, then it would come back on and try and recover. As I was there, I watched it happen a few times then shut it off as I was near my annual maintenance window anyway.

The most obvious suspect based on what happened is a loose thermocouple wire or connection. These things can work their way loose over time.

My plan is to tighten the connections on all the wires, and then fire up the furnace. Basically if it's a high temp (over 2000F) problem, no amount of low temp fussing will find it.

The elements have been checked and are all fine, as is power to the elements.

I want to bring the furnace up to 2100 quickly.

The crucible is out of the furnace right now as part of the overall maintenance, so the furnace is just K23, fiberfrax and alumina board.

Can I fire this up to 2000 without stopping for hours at the inversion point (900-1300F)? That is, does refractory also need to be babied through the quartz inversion or can I just crank it up? Is there a 'best ramp rate" to follow with just refractory?
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Old 10-09-2018, 03:09 PM
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Might also check that your controller does not have an upper limit governor on it. The last time I had this happen to me my K-type had burned up.

Last edited by Scott Novota; 10-09-2018 at 03:17 PM.
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Old 10-09-2018, 03:26 PM
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If nothing inside (no crucible just an empty kiln) let 'er rip. IFB and fiberfrax can take it. I assume the alumina board is outside.
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Old 10-09-2018, 04:31 PM
Rick Kellner Rick Kellner is offline
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I think the alumina board is the top baffle, which isolates the elements from the glass fumes.
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Old 10-09-2018, 05:51 PM
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solid castings should be treated with respect and go thru inversion with at least a wink and nod to expansion. Otherwise, it doesn't matter much. With the pot in, you need to behave.
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Old 10-09-2018, 05:57 PM
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You should be fine. Sounds like a TC problem. Could be something lose or cracked anywhere from the thermocouple junction itself all the way back to the controller. If you are cold right now you can take the thermoucouple out of its sheath and inspect it.
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Old 10-09-2018, 09:50 PM
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Quote:
Originally Posted by Rick Kellner View Post
I think the alumina board is the top baffle, which isolates the elements from the glass fumes.
Correct. I could always remove it for the test.
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Old 10-09-2018, 09:52 PM
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Quote:
Originally Posted by Pete VanderLaan View Post
solid castings should be treated with respect and go thru inversion with at least a wink and nod to expansion. Otherwise, it doesn't matter much. With the pot in, you need to behave.
The only casting is my rammable gathering port in the maintenance lid. It's removable so I can do that for the test. I'll probably just set the lids on rather than connect up all the hinges until it's working properly.
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Old 10-09-2018, 09:58 PM
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Quote:
Originally Posted by Jordan Kube View Post
You should be fine. Sounds like a TC problem. Could be something lose or cracked anywhere from the thermocouple junction itself all the way back to the controller. If you are cold right now you can take the thermoucouple out of its sheath and inspect it.
For sure. Loose/broken wire or loose connecting screw. I'll check the main power connections at the same time. Repeated heating/cooling cycles has been known to loosen even really tight connections.

The only odd thing is the UUUU reading (beyond upper limit). Since this controller upper limit is set to 2400F (by me) and since it was not even 2100 when it did this, it suggests either a bad connection or controller failure. I say UUUU is odd because usually broken wire will read LLLL (no signal).

Worst case I have a spare controller of another brand that I can swap in and see what happens between 2000 and 2100.
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Old 10-11-2018, 12:32 PM
Cecil McKenzie Cecil McKenzie is offline
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On my equipment when i have had failed thermocouples the controllers always max out and shut the whole thing down. Not sure if this is always the case.
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Old 10-18-2018, 03:59 PM
Brendan Miller Brendan Miller is offline
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all UUUU's usually means means thermocouple is burnt out or a leg of the thermocouple is open. Some Controllers will read LLLL or UUUU but both can be thermocouple problems.
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