Kiln advice

[Sputnik 184]

I know some of you are pretty knowledgeable about kilns and I know very little so I’m hoping someone can point me in the right direction. I have an old Cromartie Hobbytech 45 and every so often on a 1230C glaze firing it throws up an F1 fault. Consulting the instruction manual the fault code indicates no change in temperature for 30 mins without reaching the required temperature. Suggested problems are worn elements, faulty thermocouple or a power supply issue. The glazes appear as I would expect had my temperature been achieved and Orton cones suggest Cone 8 has been reached although if the kiln ends up with a long hold as it tries to reach temperature this could indicate heat work rather than a maximum temperature. Picture below shows Orton cones 8,7,6 and 5 left to right.

I have contacted the manufacturer but they only suggested the same as the instructions and I’m reluctant to just start replacing items without knowing they’re faulty. i have inspected the elements and there are no visible signs of damage or deterioration. I’d like to check the resistance of the elements. Can anyone suggest an acceptable range for the resistance and give me any further advice? Is there a test procedure for the thermocouple if the elements issue is resolved?

Hoping somebody can help please?

 

[HorseloverFat]

I just know gas setups.. and somewhat wood.

@penumbra , however spent a good chunk of time servicing/repairing kilns....

 

[HorseloverFat]

Oh and....


...Nice cones! A-a-aaah! *Said like Pauly Shore*

 

[penumbra]

Your elements are weak. If you can get the optimal resistance for elements from the manufacturer you can use an ohm meter to find out for sure. Is cone 8 your normal firing range? Normally in the US you use 3 cones. The center one is your desired cone. For instance, if I am set up for cone 6, I use 3 witness cones. A 5, 6 and a7. At cone 6 the cone 5 cone is flat like a wet noodle. The cone 6 is bent completely over and the cone 7 is just starting to node. That is how its done in my neck of the woods.
Or you can find a kiln technician to check it out. In the mean time, take your thermocouple out and inspect it. It normally is replaced when elements are. Is it really burnt and crumbly on the end? Probably. Elements are not cheap. For my small kiln with 3 elements, they wer $55 each about 5 years ago, My large kiln's elements were about $85 each.
This is something a lot of people don't consider when they buy a kiln. Some of my customers (when I was in the bus) thought elements lasted forever.

 

[NaoTK]

Also your cone 8 is overfired... when the tip is level with the base of the cone is true cone 8, but details.
I like to use multiple thermocouples with my kilns (they are cheap), with a ceramic sleeve to protect the thermocouple from atmosphere. That way in addition to the cone you could have multiple verifications of temp.

 

[Sputnik 184]

Your elements are weak. If you can get the optimal resistance for elements from the manufacturer you can use an ohm meter to find out for sure. Is cone 8 your normal firing range? Normally in the US you use 3 cones. The center one is your desired cone. For instance, if I am set up for cone 6, I use 3 witness cones. A 5, 6 and a7. At cone 6 the cone 5 cone is flat like a wet noodle. The cone 6 is bent completely over and the cone 7 is just starting to node. That is how its done in my neck of the woods.
Or you can find a kiln technician to check it out. In the mean time, take your thermocouple out and inspect it. It normally is replaced when elements are. Is it really burnt and crumbly on the end? Probably. Elements are not cheap. For my small kiln with 3 elements, they wer $55 each about 5 years ago, My large kiln's elements were about $85 each.
This is something a lot of people don't consider when they buy a kiln. Some of my customers (when I was in the bus) thought elements lasted forever.

Thanks for your advice. I did ask the manufacturer about resistance but they omitted to answer that part of my enquiry so I guess I’ll have to get back onto them. I was aiming at a cone 6 firing and only included the 8 cone as a further check so I was rather surprised it had gone over so far. Would this happen if the temperature wasn’t reached but in trying to get there had held at a lower temperature for an extended time?

The thermocouple looks white and in good condition.

The third possibility mentioned for the fault code was insufficient power supply. I will check for voltage drop on the next bisque firing and intend trying running an uprated extension cable to the kiln for my next glaze firing.

Does this sound like a sensible course of action?

 

[penumbra]

Some kilns are set up for one thermo (most) and some for 3. L&L uses 3, Skutt uses one., and Olympic uses one. I have never seen any advantage to three personally. Its just another expense. I have never had a thermo fail but I have seen them fail when people were trying to be cheap and didn't replace them when they should have.

 

[penumbra]

Thanks for your advice. I did ask the manufacturer about resistance but they omitted to answer that part of my enquiry so I guess I’ll have to get back onto them. I was aiming at a cone 6 firing and only included the 8 cone as a further check so I was rather surprised it had gone over so far. Would this happen if the temperature wasn’t reached but in trying to get there had held at a lower temperature for an extended time?

The thermocouple looks white and in good condition.

The third possibility mentioned for the fault code was insufficient power supply. I will check for voltage drop on the next bisque firing and intend trying running an uprated extension cable to the kiln for my next glaze firing.

Does this sound like a sensible course of action?

Now you have confused me. If you were shooting for cone 6 then you overfired. You can run a kiln for days and the cone is only going to tip when it reaches the cones temperature rating. Maybe I am just need reading you clearly because now I don't understand what the problem is other than an overfire.

 

[penumbra]

The thermocouple looks white and in good condition.

The thermocouple isn't white, but the ceramic cover is. There is no way you can know the condition of the thermocouple unless you take it out of the white ceramic sleeve. Real easy, 2 screws.

 

[Sputnik 184]

Also your cone 8 is overfired... when the tip is level with the base of the cone is true cone 8, but details.
I like to use multiple thermocouples with my kilns (they are cheap), with a ceramic sleeve to protect the thermocouple from atmosphere. That way in addition to the cone you could have multiple verifications of temp.

Thanks for the information.Are you suggesting it went above a cone 8 or could this have been caused by the extended hold at a lower temperature doing extra heat work?

It is a pretty small kiln. I don’t know how easy it would be to fit multiple thermocouples?

 

[Sputnik 184]

Now you have confused me. If you were shooting for cone 6 then you overfired. You can run a kiln for days and the cone is only going to tip when it reaches the cones temperature rating. Maybe I am just need reading you clearly because now I don't understand what the problem is other than an overfire.

That’s really helpful. This now makes me suspect the thermocouple. Is there any other check for the thermocouple other than just visual which I will do as you’ve suggested?
If the elements were failing would they still reach cone 8?

 

[NaoTK]

Thanks for the information.Are you suggesting it went above a cone 8 or could this have been caused by the extended hold at a lower temperature doing extra heat work?

It is a pretty small kiln. I don’t know how easy it would be to fit multiple thermocouples?

The cone says more heat work than 8 was put in there, but i don't suspect much more. At any rate its way more than 6!

I drilled a ~3/8" hole through the metal sheeting and through the kiln brick at the top and bottom of my kiln, so I have a top and bottom temp. There is a 1/2 cone/20F delta for example.

They have published tables for the expected voltage for your thermocouple type

 

[penumbra]

When I want to know the temperature inside a kiln I put a thermocouple through the bottom peep hole and then the top peep hole. The thermocouple on my Skutt kiln is solely for the auto control device. I haven't had to check top vs bottom in years because I have very even firing. When I did check it in 2018 there was an 8 degree F difference which is negligible.

 

[sorce]

When web searching "Cromartie Hobbytech 45".


Rock on.

How long is it taking to reach those cones?

Seems not an element problem. If because it's the most work to replace. Unless it takes over 14ish hours.

Thermocouple is the cheapest and easiest.

Power source the most dangerous iffin you start a fire cuz of a short.

Therm first with a cautious eye for no fires.

Power source next cuz, you know, dying and all.

Elements last cuz f that work.

Don't die.

It's the thermocouple.

Sorce

 

[michaelj]

This is the part that stresses me out about becoming a real potter and not relying on my community college studio and especially its kiln resources. Even more so than having to buy and store my own slip and glaze components.

 

[JeffS73]

From the Orton Cones Firing PDF:

Kiln uniformity normally improves as the temperature increases in the kiln due to radiant heat. With electronic controllers, the kiln can be held (soaked) at a temperature. This allows time for heat to move into all areas of the kiln and ware, greatly increasing temperature uniformity. As a guide:

• lowering the firing temperature by 18°F (10°C) requires about 20 minutes of hold time to add the same heat to a cone or body
• lowering the firing temperature 36°F (20°C) requires 40 to 60 minutes of hold time
• lowering the firing temperature 54°F (30°C) requires about 2 hours of hold time

My elements are going, it takes hours to get to 1250c, but when it does, my C10 cone is down, and 11 has moved plenty. Elements are expensive, it's enough to make me want to fire at cone 6 while I'm on electric.

 

[HorseloverFat]

It should take MANY hours to get that hot, friend... Think 10-12...

I CAN fire to c6/7 in 4-5 hours... IF I WANTED.... I DON'T want, though..

I candle overnight (8-10 hours)at just under 200F

Then the gas is on for 8-12 hours...

Reeeeeeeeeeeaaalllll sloooooooow.

 

[Sputnik 184]

From the Orton Cones Firing PDF:

Kiln uniformity normally improves as the temperature increases in the kiln due to radiant heat. With electronic controllers, the kiln can be held (soaked) at a temperature. This allows time for heat to move into all areas of the kiln and ware, greatly increasing temperature uniformity. As a guide:

• lowering the firing temperature by 18°F (10°C) requires about 20 minutes of hold time to add the same heat to a cone or body
• lowering the firing temperature 36°F (20°C) requires 40 to 60 minutes of hold time
• lowering the firing temperature 54°F (30°C) requires about 2 hours of hold time

My elements are going, it takes hours to get to 1250c, but when it does, my C10 cone is down, and 11 has moved plenty. Elements are expensive, it's enough to make me want to fire at cone 6 while I'm on electric.

Thanks. I was concerned about the combination of temperature and soak and how this could be affecting things. Just out of interest what kiln are you running and if you’re bisque firing how long does it take and at what temperature?

 

[Sputnik 184]

I was convinced after reading last night’s posts I was going to find a thermocouple problem rather than elements but now I’m not so sure. After the kiln cools from the bisque firing that I have in it at the moment I will inspect the thermocouple closely and take it from there.

 

[JeffS73]

Thanks. I was concerned about the combination of temperature and soak and how this could be affecting things. Just out of interest what kiln are you running and if you’re bisque firing how long does it take and at what temperature?

Mines a Rohde ecotop 43L. I bisque to cone 04, 950c, as recommended by Matt Katz from CMW. It takes an age, like 36-48hrs including cooling. I candle for 12hrs at 80c, and I take it very slow between 700 and 900, 34c per hr, 7hrs just on that. My kiln fires fine at those temps and rates. At 1150 to 1250c it climbs at about 10c an hour!