Thermocouple Question

[Gage]

Malcoa has it right with the plugs, sockets and training the production workers.

Be honest do you have to do anything other than reconnect the new unit? Check it’s working is about the sum total.

Didn't know there was more furnace men on here. Who's going to the brew house with the bucket?

Never been near a kiln though.

 

[Richard Burns]

Is the problem with the sheath expanding and contracting against the thermocouple, because really even though type K may be a bit susceptible to this sort of thing I would have thought they would survive for a few months at least even if they are cooled and heated. Are the breakdowns when it is rapid cooling but shutdowns are slow controlled reductions?
Type N may help but I think there is something else odd here, though if bits of furnace are falling on them this could cause problems of a different nature!

 

[Gage]

Is the problem with the sheath expanding and contracting against the thermocouple, because really even though type K may be a bit susceptible to this sort of thing I would have thought they would survive for a few months at least even if they are cooled and heated. Are the breakdowns when it is rapid cooling but shutdowns are slow controlled reductions?Type N may help but I think there is something else odd here, though if bits of furnace are falling on them this could cause problems of a different nature!

There isn't a way to rapidly cool the furnace. It just has a fan blow through it and it takes about 24-30 hours to cool to ambient. And inconel is highly resistant to expansion/contracting/distortion. But my theory is that the actual junctions themselves do not like being cooled to ambient after so long at High temp. And when heated back up, start to crack.

The thermocouples are embedded in the wall of the furnace however not inside the hearth/chamber. Nothing ever falls off and hits them but the walls do expand and contract. However again...the sheath is perfectly fine when these thermocouples break.

 

[Marvo]

The more you say about them the more I'm convinced you should try another manufacturer. It does sound at least partially like a quality issue.

 

[Gage]

The more you say about them the more I'm convinced you should try another manufacturer. It does sound at least partially like a quality issue.

All their other types of thermocouples are perfectly fine, absolutely fantastic in fact. The price is right. The service is right. It would seem odd if every single one of these thermocouples they send us is dodgy. (I've received close to 30). And it's not as easy as just finding another supplier lol.

 

[Knobhead]

Gadge,

The refractory linings the thermocouples are embedded in, are they multi layer brick?

On shut down cooling some of ours could shift especially with new linings until the inner had surface had really fused.

We would be running the after burner 4 days at 1300/1500°C, 1 day cooling followed by 1½ days at ambient, then ½ day warm through. The usual time for a failure would be on our “pre burn” before the furnace burden was charged in. The temperature would rise from 200°C to 900°C in ½ hour, the lining could shift again.

Just an idea.




Temperature inside the furnace? Forget it! An optical pyrometer through the port holes was the only way to get a temperature. The burden could wear 3” of the inner refractory in a week.

Won’t be the first time the refractory has fallen out on start up. Then it is panic stations!

 

[Gage]

Gadge,

The refractory linings the thermocouples are embedded in, are they multi layer brick?

On shut down cooling some of ours could shift especially with new linings until the inner had surface had really fused.

We would be running the after burner 4 days at 1300/1500°C, 1 day cooling followed by 1½ days at ambient, then ½ day warm through. The usual time for a failure would be on our “pre burn” before the furnace burden was charged in. The temperature would rise from 200°C to 900°C in ½ hour, the lining could shift again.

Just an idea.




Temperature inside the furnace? Forget it! An optical pyrometer through the port holes was the only way to get a temperature. The burden could wear 3” of the inner refractory in a week.

Won’t be the first time the refractory has fallen out on start up. Then it is panic stations!

Just pretty basic furnace bricking I'm afraid. It's layed out like this:

Furnace walls -> Layer of furnace bricks -> Space & Thermocouple tip -> Workzone & Custom made brick shapes of which I don't know the material.

 

[malcoa]

I would call in a rep from the manufacturer, i think they should really be lasting longer and they dont appear to be an an envirnment alien to them, maybe they have advice on alternatives

 

[Bobster]

I know the thermocouples we used on the cyclones had a knack to fitting them. We slid the probe out of its protective sheath and put a slight bend in it, just enough so when it was put back into the sheath it was 'held in' if that makes sense.

Doing this stopped vibration from rattling them round inside the sheath and breaking them. We also had two probes in the same locations and programmed the plc to take an average, so if one failed it wouldn't matter.

1800degC alkali dust being blown over the probes used to wear them away fairly regularly.

 

[Knobhead]

There was no point trying to taking the sheath out once it failed. I had a dolly to knock them in.

Pre heat cyclones must be one of the harshest environments possible.