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Richard Huntrods 10-09-2018 03:04 PM

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?

Scott Novota 10-09-2018 03:09 PM

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.

Greg Vriethoff 10-09-2018 03:26 PM

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.

Rick Kellner 10-09-2018 04:31 PM

I think the alumina board is the top baffle, which isolates the elements from the glass fumes.

Pete VanderLaan 10-09-2018 05:51 PM

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.

Jordan Kube 10-09-2018 05:57 PM

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.

Richard Huntrods 10-09-2018 09:50 PM

Quote:

Originally Posted by Rick Kellner (Post 141533)
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.

Richard Huntrods 10-09-2018 09:52 PM

Quote:

Originally Posted by Pete VanderLaan (Post 141534)
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.

Richard Huntrods 10-09-2018 09:58 PM

Quote:

Originally Posted by Jordan Kube (Post 141535)
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.

Cecil McKenzie 10-11-2018 12:32 PM

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.

Brendan Miller 10-18-2018 03:59 PM

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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