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dhPotter

Thermocouple Spitting Metal Flakes

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Or Something else is in the glaze kiln. The 23 x 27 Olympic kiln with computer controller just finished its 19th glaze firing to cone 6 oxidation. For most of those firings I have found small bits of something metallic in the bottom of 1 or 2 bowls or mugs. I think it is metallic. I scraped the trash in the bottom of the tumbler with a plastic handle and it cut the handle. This past firing, the tumbler was in the middle of a half shelf on the bottom. 2 other pots were closer to the wall with the TC and they did not get contaminated. The middle shelf was about an 1 inch lower than TC. If the trash did come from the TC, it is amazing, at least to the novice, how far it traveled.

 

Notice the picture of the TC. 1 side is much thinner than the other.

Is the trash in the bottom of the tumbler metal flaking off of the TC? If not what is it? How to fix this problem?

 

Thanks in advance for your help.

 

 

post-13363-0-10712100-1431981923_thumb.jpg

post-13363-0-10712100-1431981923_thumb.jpg

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Your thermocouple is contaminated and that is what happens to a type K exposed to the atmosphere in a kiln.  You need to replace the thermocouple. The T/C mounted in the top of the kiln is going to flake all over the kiln like it has.  If you are only firing in oxidation you might consider using a protecting tube, but that tends to slow down its response.  You don't have to be using a 8 gauge T/C.  You can get a 14 gauge element in a protecting tube that would be about the same size and last longer because of the protecting tube..  Check www.omega.com   Almost all kiln manufacturer's use open thermocouples and they are prone to this problem.  If you want to respond to me directly hdwoodin@gmail.com  I use a high response type K in a protecting tube.

Is this a gas or electric kiln ?  What is the model number maybe the thermocouple can be relocated?

David 

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Go to Omega.com type in part # KQXL-14U-6.  This is 1/4 inch diameter by 6" long and enclosed in a high temp.sheath   I usually get between 120 and 150 firings out of this.  When it fails it fails fast so the accuracy stays  stable with no drift until a pinhole develops in the sheath. I use them in gas or electric kilns. Your spare from Olympic costs $45.00 this costs $38.00.  As far as flaking goes you will eventually see some black area under the probe on the shelf but you normally don't but a pot under the thermocouple, and it is only into the kiln about 1 1/2 inches.  You may not like the quick connect junction they have another transition junction with extension wire. I use the ungrounded just in case there is electrical noise being picked up. You can always talk to someone about it at Omega.

David

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Your thermocouple is in really bad shape for only having 19 firings. I have to think Olympic isn't using a very high quality TC. And if they are charging $45 for a thermocouple, then they're robbing you. L&L and Skutt both sell them for around $15. You do not need to buy the entire block assembly, just the thermocouple itself. Most manufacturers have gone to the open type 8 gauge because the last longer than the thin metal sheathed type they used to use. I have no trouble getting 150 firings out of my TCs, but they are in protection tubes. The tubes do not affect the accuracy if you set the appropriate offset. If you need greater accuracy than that, you should be using type S TCs. See HERE for the test L&L did.

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I am glad to see that L & L has addressed this situation.  There tests didn't mention if they tested Omegaclad which is not Inconel.   It would be a lot easier to use what L&L or some of the other kiln mfg use that have protecting tubes, because of trying to adapt  connections to the various controllers.  One big plus for me with the Omega is the rapid response of these 1/4 inch diameter thermocouples and 150 firings is a very conservative estimate.

David

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All this TC talk reminded me of strange readings last fire in car kiln-so I just put in a new 12 inch thermocouple in my protection tube while loading todays bisque load.I always keep a few  new ones of various lengths handy as I tend to go thru these over time at a steady rate.

If you want great readings get a S -thermocouple-these are made for longer life and are way more acurate but cost more.

I have a platinum oxygen thermocouple in the car kiln as well-it also gives great readings and as you may have guessed cost more than S-Thermocouples.

If you are just firing oxidation fires to cone 6 I doubt you need any fancy thermocouples-but a protection tube will make it last longer.

Mark

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Neil: The kiln sat idle for 6 years in a temperature controlled room. Would this have any affect on the TC?

 

Can an L & L protection tube and TC work with my Olympic kiln?

 

Fellas, thanks a lot for your quick and informative responses.

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Neil: The kiln sat idle for 6 years in a temperature controlled room. Would this have any affect on the TC?

 

Can an L & L protection tube and TC work with my Olympic kiln?

 

Fellas, thanks a lot for your quick and informative responses.

 

It's possible it corroded a bit from humidity. Yes, an L&L tube will work. Any protection tube will work, you just have to drill out the brick. You can use a cheap round wood rasp to file it out. It would be cheaper than buying a large drill bit. Once it's really close you can use the tube itself as a drill bit to grind away the last little bit. You'll probably need to program a TC offset of about 10 degrees to compensate for the insulation provided by the tube. You want the computer to fire 10 degrees cooler, since the actual inside of the kiln will be 10 degrees hotter than what the TC is reading.

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Now I am as confused as a rat in a maze.

 

I talked with a person at Omega. When I mentioned 8 gauge, he pointed me to this model #  DH-1-8-K-12. Am I making this more difficult than need be?

 

David, can the model number you suggested be placed in a protection tube? What are these that he suggested on these web pages?

 

http://www.omega.com/pptst/BARE_SH_DH_OV_ELEMENTS.html    and

http://www.omega.com/temperature/pdf/BARE_SH_DH_OV_ELEMENTS.pdf

 

I do not know what I am looking at. Unfortunately, everything will be ordered sight unseen, except for the pictures. We do not have ceramic supply houses in Mississippi.

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Now I am as confused as a rat in a maze.

 

I talked with a person at Omega. When I mentioned 8 gauge, he pointed me to this model #  DH-1-8-K-12. Am I making this more difficult than need be?

 

David, can the model number you suggested be placed in a protection tube? What are these that he suggested on these web pages?

 

http://www.omega.com/pptst/BARE_SH_DH_OV_ELEMENTS.html    and

http://www.omega.com/temperature/pdf/BARE_SH_DH_OV_ELEMENTS.pdf

 

I do not know what I am looking at. Unfortunately, everything will be ordered sight unseen, except for the pictures. We do not have ceramic supply houses in Mississippi.

The model I suggested and use doesn't need a protecting tube and therefore has a high response time and needs no offset for the lag of a large mullite protecting tube.  If you were to go with the Omega you need a way to mount it and I can tell you what I use. The DH-1-8-K-12 is a replacement thermocouple for what you now have except it is 12 inches long you would have to cut it shorter. The other web page I couldn't open and probably shows a complete assy. with protecting tube.  So yes you are getting into deep waters.  If you want the mullite protecting tube, you might ask Olympic about it and tell them of the problems you are having.  As to how long does the one I use last, I have some in use since 2009 but I am not a production potter.

David

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David,

 

I have not torn apart the controller so I don't know what I'm looking at as far as connections. I did read that the model # KQXL-14U-6 has Excellent Oxidation, Carburization and Chlorination Resistance.

 

Yes point me in the right direction for connecting/ mounting this model.

 

Thanks

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David,

 

I have not torn apart the controller so I don't know what I'm looking at as far as connections. I did read that the model # KQXL-14U-6 has Excellent Oxidation, Carburization and Chlorination Resistance.

 

Yes point me in the right direction for connecting/ mounting this model.

 

Thanks

I think rather than taking up the forum's time it would be better to contact me off line hdwoodin@gmail.com  The kilns I have didn't have a controller so I decided to buy one controller and use it to control three different kilns.  I also would need a picture of the inside of the control panel.

David

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