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Joseph F

Upcoming 300th Firing - Kiln Repairs

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I am coming up on my 300th firing(at 280 something) and I am going to order elements soon. I assume I should order some other things along with it.

Those things being relays and thermocouples?

I would rather take out a part that might break down even if it has a few more firings than have a break down later down the line where I have a misfiring.

Sorry for the post, but I couldn't find a previous post that specified what firing number they were on. I assume every 2 element changes I should be doing these things? Is this accurate or should I wait until after I use this third set up?

Thanks!

Edited by Joseph F

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If you have never replaced your thermocouples, it's probably time for new ones. In my experience, thermocuples last a little bit longer than elements, but not twice as long. It's efficient to replace them at the same time everytime, while you've got the controller box open. 

You don't need to replace the relays unless they are obviously giving you trouble. My 13 yr old kiln is still on its original relays.

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Because I live a long way from a kiln parts store, I keep a few parts on hand.  Like pretty much everything.  I have had to replace a relay twice.  Not the same one.  But it's pretty clear when you do need to do that.  When I change the elements, I change the thermocouples.  Like Mea said, they do seem to last longer, but they are not expensive (relatively) and it's easy to do while you have everything apart. 

Roberta

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You should check your thermocouples every 50 firings or so. How long they last will depend on what type of kiln you have and what type of TC you have. Relays work until they don't. No real need to preemptively replace them. Check all your wires. Feeder wires (wires that connect to the elements) should be replaced when they start to discolor or feel crispy. Again, it depends on what type of kiln you have as to how long they'll last.

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4 minutes ago, neilestrick said:

You should check your thermocouples every 50 firings or so. How long they last will depend on what type of kiln you have and what type of TC you have. Relays work until they don't. No real need to preemptively replace them. Check all your wires. Feeder wires (wires that connect to the elements) should be replaced when they start to discolor or feel crispy. Again, it depends on what type of kiln you have as to how long they'll last.

Every 50 firings? I had no idea about this. I feel kinda silly. I assume this is glaze firings right, not bisque?

I will check the wires when I get around to ordering the elements. That way I can tell L&L which ones I need when I order. 

Thanks for this tip as well.

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Your wires will probably be fine. I've got about 1200 firings on my L&L.  Skutt feeder wires tend to crisp up sooner due to the way their control box is built. I would also order a few sets of terminal hardware, or at least run to the hardware store and get your own. Use stainless. Sometimes the nuts seize up on the bolts and you have to twist them until they snap and then replace them. It's really hard to find the hex head bolts, but you can use a pan head bolt and put a nut and lock washer on the other side to hold it tight.

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When I replaced my elements last time I ordered those extra screws or whatnot. I broke 2 of the old ones in the process. Glad I had them on hand. Planning on doing that again.

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11 hours ago, High Bridge Pottery said:

How do you check a thermocouple? I took mine out its protective casing and gave it a good mark1 eyeball test and it looked great. At a guess I think it's over 15 years old and owned by somebody else before me. Came with the second hand kiln.

Quite. The thermocouple on my (much abused) little electric kiln is of a similar age. Shows no signs of physical deterioration, and is within a couple of degrees of a second thermocouple I occasionally poke into the spyhole. It's how I get my fun.

From a quick trawl across the internet, I can see lots of evidence of (mainly American) kiln manufacturers and their associated maintenance squads advising a change of thermocouple every third full moon, but no actual evidence as to the necessity for that.

For myself, the thermocouple will get renewed when it goes wrong, and not before. I don't know anyone here in Europe who does anything other than that, to be honest.

Is it to do with the type of thermocouple used? I know that type 'S'  are considered to have much greater longevity than the often used type 'K',  although they cost a little more. Both mine are actually type 'R', similar to type 'S'. As you are in the UK, chances are yours is too.

Type 'R' (Platinum/Rhodium) - is common the the UK, 'S' (Platinum) - in the rest of Europe. Perhaps the cheaper and less long-lived type 'K' (Chromel, or Alumel) is more used in the US, and thus need changing more often, following a precautionary principle?

The only person I can think of who had an actual problem with a failing thermocouple during a firing was someone who fired without using cones, relying on the thermocouple alone. Always a mistake, IMHO.

Edited by Sputty
Additional anecdotal evidence, there being not enough already.
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Olympic does not recommend a TC with a protective cover. I have an Olympic 2328. In the past 3 years I have replaced a type K twice. Both times the TC needed replacing because of spalling. Bits of black metal in the bottoms of pots. The kiln is at its 52nd firing. All glaze firings except 1 bisque firing. Don't know if it is the humidity getting to the TC or not. The kiln is in my pottery room, but, I leave the windows open nearly all year. BTW type K is $45.00, type S is around $300.00 in the US.

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That is crazy. I haven't examined mine. I just figured it would last a while. My kiln is slowly starting to fire a little uneven, I have been making up for it by stacking my shelves so that heat could be better distributed. I will replace the TCs and photo them when I do it and post. I have no idea what a good or bad one looks like. 

I will say that 2 TCs in 52 firings seems absurd. 

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The new TCs will be shiny metal. The old ones will be black and crusty and lumpy and flaky. When they fail its because they have crumbled apart. Pls do post a photo of new and old. That will be useful to everyone. 

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This one is really fried. I've had a few that get a crack through the welded tip way before they get as burned out as this one. Anybody have any data on K type TC's 8 gauge or 14 gauge, which lasts longer or if the gauge irrelevant?

Joseph, the temp reading can drift when the TC starts to go, weld gets weak and doesn't read properly. I wouldn't let yours get as fried as this one. It's a (relatively) cheap thing to fix.

TC.jpg.d6bfe696c6b81ea102d303d7967ebabf.jpg

 

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@Sputty I have a type S, the kiln was made in the Netherlands and made it's way to the UK somehow. I do have a friend with 2 type R that are 20 years old and well used, still seem to be reading great. 

I have noticed in the US they don't like protective tubing. I have never seen a bare metal thermocouple end anywhere in the UK. Maybe it is down to being type K.

Here is a picture of mine, hard to get it to focus because the end is about the size of a pin head... Small tube goes in the big tube.

ThermoS.JPG.ac6560e816dd7b96d43de13b9234bc57.JPG

 

 

Edited by High Bridge Pottery
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1 hour ago, High Bridge Pottery said:

@Sputty I have a type S, the kiln was made in the Netherlands and made it's way to the UK somehow. I do have a friend with 2 type R that are 20 years old and well used, still seem to be reading great. 

I have noticed in the US they don't like protective tubing. I have never seen a bare metal thermocouple end anywhere in the UK. Maybe it is down to being type K.

Here is a picture of mine, hard to get it to focus because the end is about the size of a pin head... Small tube goes in the big tube.

 

Yes - the tip of mine looks identical. Nice and shiny, and in no way degraded. I think the evidence against type 'K' is mounting...

Interestingly, I used to use the second of my two thermocouples when I was salt-glazing. I would brush a thin layer of salt-resistant kiln-wash over the protective sheath before each firing. It survived with no damage to the sheath at all. A great boon to firing salt, when the cones are less than reliable because of the action of the salt on them.

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4 hours ago, dhPotter said:

 BTW type K is $45.00, type S is around $300.00 in the US.

How much!?!? $300 ?!?!

Have a look at some of the UK/European potters' supply websites - you'll be astonished at the difference. 'S' and 'R' available at less than half that price.

Out of interest, do you know why Olympic don't  recommend thermocouples with a protective cover? All of the kilns I have seen over here are fitted as standard with sheathed thermocouples.

Edited by Sputty
'cos I is illiterate, apparently.

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The L&L kilns in the US do have protective tubes. Which I think is why mine has lasted this long. Although who knows when I open it up I bet it will look similar to the one Min posted.

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Type K is standard in the US. They are cheap, and good enough for what 99% of potters do with their kilns. Type S are worth it for people who fire to cone 10, or who do long, high temp holds like for crystalline glazes, or if they need a greater degree of accuracy. Type S last a lot longer, and are more accurate, but if you break one it's an expensive fix. L&L charges $230 for one. A type K is only $16.50. So you can go through 14 type K's for the same price as one S. Does the type S last 14 times as long as a K? I'm not sure, but I doubt it. You'd have to go at least 2000 firings with a type S for it to even come close to coming out the same for someone doing the typical bisque and cone 6 firings. But again, for cone 10 or work that requires greater accuracy, type S is worth it.

The two most common types of type K in the US are the 8ga unsheathed and the pyrocil (metal) sheathed. The pyrocil sheathed last about as long (maybe a little less) than an 8 gauge in a protection tube, but they cost $40 rather than $16.50. The nice thing about the 8ga is that you can see if the thermocouple is degraded. You can't tell in the metal sheathed until is stops working.

HERE is a thermocouple test done by L&L.

It seems that kiln brands that don't use mullite protection tubes all say that they don't work. Yet every brand that does use them have no problems with them (not just L&L). They are very common in industrial applications. To me, there are several problems with not using the protection tube. First, the thermocouple will shed all over the inside of the kiln. You'll get black stuff on your shelves and on your pots. I get this complaint from my customers all the time. To fix the problem, you either have to use a protection tube or replace the thermocouple long before its useful lifespan is over. Second, a significant percentage of the thermocouples I replace for my customers have been broken by getting hit with a shelf during loading/unloading. The protection tubes prevent this from happening. Third, the thermocouples last longer when they're in the tubes, like 50% longer. The protection tube does require that you adjust the setting in the controller to compensate for the fact that the tube does slightly insulate the thermocouple, about 18 degrees. But with that they work just fine. And if you find the kiln is not firing accurately, you can adjust the thermocouple offset as needed, just like you often need to in a kiln without protection tubes. I have done almost 2000 firings over the last 9 years with protection tubes, and have never had accuracy issues.

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Am I looking at the wrong part for my TC? My price is $34 each. I need 2. http://hotkilns.com/thermocouple-k-standard. I am guessing you get a better price Neil because your a fancy dancy super tech. :wub:

I am still pretty ok with that price considering that's like selling a few pots and I got almost 300 firings out of it before I started having issues. Although I will just always replace them with my elements in the future. I am probably not gonna fire again because I just unloaded some pots and the middle was overfired slightly, which has only been a problem in the last 20 or so firings. So I am betting one of the TC's is probably on the brink!!!

Going to order everything tomorrow. Will follow up with pictures of new and old as promised next week.

 

Edited by Joseph F

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12 minutes ago, Joseph F said:

Am I looking at the wrong part for my TC? My price is $34 each. I need 2. http://hotkilns.com/thermocouple-k-standard. I am guessing you get a better price Neil because your a fancy dancy super tech. :wub:

I am still pretty ok with that price considering that's like selling a few pots and I got almost 300 firings out of it before I started having issues. Although I will just always replace them with my elements in the future. I am probably not gonna fire again because I just unloaded some pots and the middle was overfired slightly, which has only been a problem in the last 20 or so firings. So I am betting one of the TC's is probably on the brink!!!

Going to order everything tomorrow. Will follow up with pictures of new and old as promised next week.

 

You don't need a new block unless it's all corroded. You can just get the TC http://hotkilns.com/type-k-8-ga-thermocouple-element

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When I called Olympic about another TC, I asked them about a protection tube. They said they do not recommend and they said what Neil said, Would make the firnigs off and would have to offset the TC. Also the brick wher the TC goes thru would probably need drilled larger. 

Well if they do not recommend, I let them be the expert. But, I wish I had gotten a protective tube and done the right thing. The black specks, spalling, is horrible. 

When the first TC was replaced I did not test fire, just went right on my happy way/ BUT, when the 2nd TC was replaced I fired and the load was about 1/2 a cone underfired. Have TC offset by 20*F. Cones are back to normal.

The pic on top is the original TC. It really did not affect firings but rather spitting black specks everywhere. The pic on the bottom is the new one for replacing the original when I did this back in 2015. When this TC had to be replaced it was black and crusty. Odd thing, I never had bisqued fired in this kiln. This TC had about 20 firings on it and was not spalling at all. Then I did a bisque in this kiln. The TC spit all over the place. Worse I had ever seen. Why would a lower temp, ^04 bisque, do damage to the TC when the ^6 glaze firings did not?

 

TC.JPG

New_TC.JPG

Edited by dhPotter

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10 minutes ago, dhPotter said:

Well if they do not recommend, I let them be the expert. But, I wish I had gotten a protective tube and done the right thing. The black specks, spalling, is horrible. 

(cough, cough, cough, Aug 09th email...:rolleyes:)

One of my kilns doesn't have protection tubes (ConeArt) I use one of those synthetic dusters and gently brush the tips before glaze firing.

 

Not my idea (or kiln) but this might help 7ae3a46a36349871a943c13198643290--potter

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