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Bad Experience With Rohde Kiln - But Is Nabertherm Any Better?

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I'm wondering if anyone else has had good or bad experiences with Rohde or Nabertherm?

 

I purchased a brand new Rohde (TE110MC+) kiln 18 months ago. On day one it would not go above 50C without konking out! The retailer insisted it was something I was doing wrong but eventually came out (after I called Rohde) and admitted the controller was faulty.

 

He replaced it but I saw his older TC304 controller which was obviously a better quality build so I suspect Rohde has been doing some cost cutting recently at the expense of quality.

 

I've also had issues of varying temperatures in the kiln (at least that is how it looks because the same pieces from the same clay with the same glaze look slightly different depending where they sit during the glaze fire.

 

Very recently the controller threw an 'over heating' error on a 1235C porcelain glaze firing. The retailer insisted it was due to my electricity supply and Rohde customer service has just been running me round in circles sometimes saying it is the controller, sometimes insisting I contact the retailer and sometimes just avoiding my calls and ignoring my emails (even though the confirm receiving them!).

 

I think the retailer wants me off his back so he has offered to buy back the kiln but refuses to replace it. He's also started saying things like "this type of kiln is not very good at firing over 1,100C".

 

At the same time I know an increasing number of people locally who are singing the praises of Nabertherm.

 

Does anyone else have any experiences, good or bad, with these two brands?

 

Thanks.

 

BTW - I know there are other brands out there but I am based in Poland and Nabertherm or Rohde are the easiest makes to get hold of.

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Hmmm. It may help people to know what part of the world you are in. Most kiln manufacturers do not ship continent to continent for rather obvious reasons.

 

 

Best,

Preston

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I don't like Nabertherm kilns because they aren't sectional. They're heavy to move into place, and replacing a brick means taking half the kiln apart. Maintenance nightmare! But if that's your only other option, and you're very gentle with your kiln, it might not be too big an issue for you.

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I've also had issues of varying temperatures in the kiln (at least that is how it looks because the same pieces from the same clay with the same glaze look slightly different depending where they sit during the glaze fire.

 

Depending on degree of difference u mean, I think this can easily be the case in any kiln's glaze firings as many additional variables including oxides on surrounding pieces, glaze thickness etc can make the look change slightly from one piece to another identical one close by with same glaze. 

 

It's actually something I like.

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I don't know anything about your kilns but I do know that in most kilns can have a noticeable temperature difference from the top to the bottom.  I can always see a difference in the same glaze  if it is placed throughout the kiln.  I have a kiln venting system and that really hasn't made any difference in pulling more heat to the bottom of the kiln. Most potters learn to work with their kilns by putting glazes on the bottom that like it a little cooler and the hotter ones on top.  A kiln with coils in the bottom would probably give you a more consistent fire, I have never fired one.    Denice

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Thanks for all the feedback so far. Many have said I should expect slight differences in temperature around the kiln but these seem to be very visible - more so than on other kilns that I have used. I have one glaze which is satin but comes out very glossy if it is in the middle of the kiln while it works perfectly at the top and bottom.

 

The kiln seems to be well insulated. It is in a fairly small room but even on a firing up to 1250C the room temperature does not go above 30C.

 

Its just that now with the retailer saying Rhode are not very good at stoneware glaze firing this is reinforcing my doubts and with a second controller acting up I'm wondering whether to jump ship on Rhode but not leap from the frying pan into the fire!.

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Hello I have a Rhoda 43L I am experiencing trouble after 18 months of trouble free firing my kiln now takes 13 hours to get up to 1240 degrees and so over fires !  I have now lost 4 full kiln loads the supplier is saying something else is taking the electricity ? my kiln has been checked for elements they are fine it generates heat at approx 100 degrees an hour until it gets to around 1100 degrees  then slows right down  the supplier does not want to get anyone out I feel very let down I live in the UK

Help and suggestions would be great thanks

Annette

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5 hours ago, Annette Shaw said:

Hello I have a Rhoda 43L I am experiencing trouble after 18 months of trouble free firing my kiln now takes 13 hours to get up to 1240 degrees and so over fires !  I have now lost 4 full kiln loads the supplier is saying something else is taking the electricity ? my kiln has been checked for elements they are fine it generates heat at approx 100 degrees an hour until it gets to around 1100 degrees  then slows right down  the supplier does not want to get anyone out I feel very let down I live in the UK

Help and suggestions would be great thanks

Annette

1250 C is cone 8 which is very tough  on elements and will decrease their firing life a whole bunch . A kiln that is slowing down is an indication that elements are wearing out, especially if the kiln has difficulty following its program and begins to fire longer for a given schedule. So wear due to firings seems to be a likely answer here.

so some observations / questions for @agafdesign and @Annette Shaw

  • Exactly how much are your elements worn? This needs to be measured with an ohm meter and compared to new. Just looking at them without having this exact value will not tell us if they are good.
  • Are you intentionally always firing to cone 8?
  • Can you publish your exact glaze fire schedule?
  • Can you  tell us what glaze you are using? Is it a cone 6 glaze, cone 8 is not as common
  • can or do you fire with cones so we know how uneven this is?
  • what does your clay body fully vitrify at?

Finally, my thoughts are there are too many questions here to simply say the kiln is at fault. There are many nuances to firing that can cause issues. Some of them are heat in a kiln travels primarily by radiation so no fan will ever pull the heat down. Knowing this affects how one loads a kiln.

Over firing something, let’s say a cone six glaze to cone 8 is pretty hit and miss with respect to performance and  outcome.

Most kiln programs are written so they run 60c per hour in the last 100c of the firing to finish at or near the anticipated cone temperature and to mature the glaze as the glaze designer expected. I am not certain these kilns are at fault actually.

 

 

 

Edited by Bill Kielb

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Hello Bill

Thank you for your response, I have had my elements tested they are 20 ohs which I believe are still ok I fire to 1240 generally my schedule is 100 / 300 / 0 / 150 / 1240 / 0

I have fired with an empty kiln on 2 different plugs at these settings and both times the kiln goes up fine until it reaches 950 to 1000 and it slows down considerably both firings have taken around 12.5 hours ? this kiln has worked perfectly up to now and it now over fires my pots I use sacra glazes which fire up to 1280 , 1260 and 1250 so should be fine at 1240 

I tend to fire at night so no other appliances are on this time on Friday my washing machine and tumble dryer were on all day on Saturday I had no appliances on the firing still took 12.5 hours 

 

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3 hours ago, Annette Shaw said:

Hello Bill

Thank you for your response, I have had my elements tested they are 20 ohs which I believe are still ok I fire to 1240 generally my schedule is 100 / 300 / 0 / 150 / 1240 / 0

I have fired with an empty kiln on 2 different plugs at these settings and both times the kiln goes up fine until it reaches 950 to 1000 and it slows down considerably both firings have taken around 12.5 hours ? this kiln has worked perfectly up to now and it now over fires my pots I use sacra glazes which fire up to 1280 , 1260 and 1250 so should be fine at 1240 

I tend to fire at night so no other appliances are on this time on Friday my washing machine and tumble dryer were on all day on Saturday I had no appliances on the firing still took 12.5 hours 

 

Well cone 8 will wear out the elements far quicker than cone six. It’s hard to tell from your schedule the firing rate so it’s hard to tell how long this should take.

my guess is:

  • 100C per hour to 300C = about 3 hours
  • 150C per hour to 1250 = about 8 & 1/3 hour or 8:20

so if my guess is correct and I add these up that is 11 hours 20 minutes which to me is a very long glaze schedule to start with and not very far from your reported current 12 hr firing.

Assuming I have that correct above  then my best guess is your elements have worn enough to now make this schedule overfire your glazes. There is no one perfect schedule other than the one that produces the results you like but let me present this:

Glazes and clay are generally fired to a certain cone, not necessarily a temperature. Because clay and glaze are made of silica and alumina and they will not melt (to form a glass)  below 3000F / 1650C degrees we use fluxes as a helper to get them to melt earlier. The problem with this chemical melting if you will, is it no longer occurs at a specific temperature but like baking, time and temperature are important. After all I never cook anything on the stove or in the oven strictly by temperature there is always time involved. This is what potters term heatwork.

My guess at this point is your elements have worn enough so the old schedule is a bit too long. Not to worry though we can adjust the schedule to fix this. Elements are often worn beyond use at the top temperatures when they have changed by as little as 10%.  That would mean we need to know the new value or your elements  and if it was 18 ohms, your elements are on their way to replacement as you have measured them to be 20 ohms which would be about 10%.

A little more of glaze firing though to perhaps get you to another solution and if successful, longer element life for you in the future. Generally potters use cones to show how much heatwork has been done. The cones themselves are made of glaze. So let’s assume you want to fire to cone 8 and you are not using cones but you want to approximate it as best you can with your digital control.
 

To do that if we look at the top of the cone chart it tells us to fire at 60C for  about the last 100C - 120C of the firing and the cone should bend at our magic 1250C number.

So here is a schedule to try that finishes sooner but fires at 60C per hour for the last 100C of the firing.  First  what is 100C below 1250C

1250C - 100C= 1150C

  • so room temperature slow to dry things out say 60 C  per hr. till 150C ( about 2.5 hours)
  • Then midfire 250 C per hr. till 1150C say  (about 4.6 hours)
  • Then our maturation segment of 60C per hour till 1250  (about 1.6 hours) Just like the cone chart says.

In this way we are more certain that we are just reaching come 8  Or the proper amount of heatwork and your present elements with the current wear will likely work just fine. Plus if we  are successful with this  it only takes about nine hours and is easier for the kiln to reach top temperature, and less firing time on your elements.

Something to try a simple 3 segment program.

  1. 60C per hr.  To 150C
  2. 250C per hr. To 1150 C
  3. 60C per hr. To 1250 **cone 8**

If that works, we can discuss some of the nuances of this in another post. Copy of cone chart below with highlighting

 

E109EDA8-9CE2-4DC5-A06B-34BD381DD348.jpeg

Edited by Bill Kielb

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5 minutes ago, neilestrick said:

The downside of continuing to fire with elements that are worn is that you're wasting a lot of electricity. Your firing costs could be double depending on how worn they are.

Definite downside but since it’s firing at lower wattage the increase is mainly losses through the shell for the extra time which at this point might be an extra hour.I am not certain she is at that point with her elements  are gone that far but I did stress she needs to know the new element value.  
To add, these kilns are well insulated and sealed, they may be able to tolerate more wear than our domestic kilns.

The firing schedule to 1250 seems to have doom written all over it especially without cones to verify. She may very well get some 9 hour firings out of the current elements  probably won’t really know till she tries.

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On 1/10/2020 at 11:52 PM, Annette Shaw said:

I am experiencing trouble after 18 months of trouble free firing my kiln now takes 13 hours to get up to 1240 degrees and so over fires !

Sounds like the thermocouple(s) needs replacing since it's overfiring. It's not likely but it could also be a poor connection at the controller / thermocouple. Thermocouples drift and the hotter the temperature the more drift you can get.

When troubleshooting you want to check for the most likely and least expensive things first. If you can, as Neil suggested, find out what the resistance of the elements when new. Is this the kiln you have?

Worn out elements will take the kiln longer to fire obviously but since you are overfiring you might not know the actual temperature the kiln is reaching as the readout will be off if the thermocouple is shot. Are you using cones to verify what you are firing to?

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Hello Everyone

Thank you for all your responses I am very honoured, I fire to 1240 my kiln is electric and when I asked the supplier for cones she said the reading on the controller are precise and cones are not needed. I am a hobby potter I sell a few pots but my kiln is not fired up every week  my pottery teacher is helping me he is very experienced (45 years ) we have done graphs and he has electrically checked my elements the are all clean and look like new. I have purchased some new elements but they dont have the ohms on them I probably haven't done 100 firings on these elements and I dont pack my kiln to the gunnels. I am going to buy some cones to try just to prove to myself the kiln is firing to the correct temperature I am going to show my pottery colegue 

your comments in the morning and go from there I will let you know how I get on just disappointed in RHODA and the supplier they dont seem to be interested

Many thanks All

Annette 

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Your kiln is rated to at least cone 10, and at 150/hr to 1240 that's about cone 6. With 100 firings your elements should still be good if that's a combination of low fire bisque and cone 6 glaze. If that's all cone 6, then they could be worn out. Definitely check out your thermocouple, and all the thermocouple connections. As for something else affecting the electricity, that's not likely. Ideally you should check the voltage of your service to make sure you're not getting a voltage drop, though. Also check that your power cord isn't going bad and heating up. I had a customer's kiln just a couple of weeks ago where the plug/outlet were overheating and messing up the firing.

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9 hours ago, Min said:

Sounds like the thermocouple(s) needs replacing since it's overfiring. It's not likely but it could also be a poor connection at the controller / thermocouple. Thermocouples drift and the hotter the temperature the more drift you can get.

When troubleshooting you want to check for the most likely and least expensive things first. If you can, as Neil suggested, find out what the resistance of the elements when new. Is this the kiln you have?

Worn out elements will take the kiln longer to fire obviously but since you are overfiring you might not know the actual temperature the kiln is reaching as the readout will be off if the thermocouple is shot. Are you using cones to verify what you are firing to?

While drift can be a concern, in hobby kilns it often does not affect operation and is usually constrained to a a couple degrees C of uncertainty. Elements definitely need measuring but the firing schedule here seems  very odd as well.

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7 hours ago, Annette Shaw said:

Hello Everyone

Thank you for all your responses I am very honoured, I fire to 1240 my kiln is electric and when I asked the supplier for cones she said the reading on the controller are precise and cones are not needed. I am a hobby potter I sell a few pots but my kiln is not fired up every week  my pottery teacher is helping me he is very experienced (45 years ) we have done graphs and he has electrically checked my elements the are all clean and look like new. I have purchased some new elements but they dont have the ohms on them I probably haven't done 100 firings on these elements and I dont pack my kiln to the gunnels. I am going to buy some cones to try just to prove to myself the kiln is firing to the correct temperature I am going to show my pottery colegue 

your comments in the morning and go from there I will let you know how I get on just disappointed in RHODA and the supplier they dont seem to be interested

Many thanks All

Annette 

Since you have the new elements can you measure them and let us know how different they are from the elements in the kiln? I am also curious what your instructor says with respect to cones and a reasonable glaze fire schedule.
 

Sorry about the 1250 number but in one of these threads the number was used.  1240C is still cone 7 and in a long firing without cones and not firing your final rate as published in the cone chart hard to understand how to regularly predict where this will end up with respect to heatwork.

It will be interesting to hear his opinion.

Edited by Bill Kielb

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1 hour ago, Bill Kielb said:

Sorry about the 1250 number but in one of these threads the number was used.  1240C is still cone 7 and in a long firing without cones and not firing your final rate as published in the cone chart hard to understand how to regularly predict where this will end up with respect to heatwork.

She said that her ramp was 150 to 1240, which puts it at cone 6.

2 hours ago, Bill Kielb said:

While drift can be a concern, in hobby kilns it often does not affect operation and is usually constrained to a a couple degrees C of uncertainty. Elements definitely need measuring but the firing schedule here seems  very odd as well.

Thermocouple wear can cause drift of a cone or more, I see it all the time. It can also cause problems in the firing schedule if it's not reading properly. It's not just a matter of it working or not, it can be reading improperly, and cause the controller to respond in ways that cause the firing schedule to go funky as the controller tries to deal with inconsistent readings. Replacing the thermocouple would be the cheapest, simplest fix the try.

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36 minutes ago, neilestrick said:

She said that her ramp was 150 to 1240, which puts it at cone 6.

Thermocouple wear can cause drift of a cone or more, I see it all the time. It can also cause problems in the firing schedule if it's not reading properly. It's not just a matter of it working or not, it can be reading improperly, and cause the controller to respond in ways that cause the firing schedule to go funky as the controller tries to deal with inconsistent readings. Replacing the thermocouple would be the cheapest, simplest fix the try.

Hmm, never seen one drift excessively in the hobby kiln environment.  Have checked many in industry just for this issue in process equipment though and have measured this drift within a few degrees but at that point we are referencing much more precise control equipment. How far have you seen these drift and is there a testing protocol you prefer?

and  Yes, 150 to 1240, I see now. I Keep mixing the two threads. If she has the new elements on hand It will be interesting what the actual measurement is. It will also be interesting if there is or is not a heatwork component. 11 - 12 hour glaze firings  vs. say a 9 hour cost more from the get go due to the standby losses as well. Unless there is a specific look, I am not sure why one would do it for normal wares. Generally we see the last segment firing rate used for the last segment ( last 100 degrees C) not the previous as well.

Edited by Bill Kielb

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"...reading on the controller are precise and cones are not needed."

Cones (should) provide consistent and accurate feedback.

I've found one cone pack on each shelf  has been helpful for sorting out loading and shelf arrangement (to even out heat work); also gives me an idea how accurate the thermocouple is.

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14 hours ago, Bill Kielb said:

Hmm, never seen one drift excessively in the hobby kiln environment.  Have checked many in industry just for this issue in process equipment though and have measured this drift within a few degrees but at that point we are referencing much more precise control equipment. How far have you seen these drift and is there a testing protocol you prefer?

The drift is evident in the pots. My kilns always fire hotter when I put in new thermocouples if I let them wear down too far. There's no scientific test to determine how far is too far, but if they're looking nasty and have decreased in diameter a bit I replace them. I certainly don't let them get super skinny. Type K thermocouples are cheap.

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10 hours ago, neilestrick said:

The drift is evident in the pots. My kilns always fire hotter when I put in new thermocouples if I let them wear down too far. There's no scientific test to determine how far is too far, but if they're looking nasty and have decreased in diameter a bit I replace them. I certainly don't let them get super skinny. Type K thermocouples are cheap.

Drift is a function of the thermocouple output drifting downward. Through age they move upward as well, but not to the extent of the downward move known as drift. Old thermocouples would drift downward by a few degrees per year so that would cause your controller to over fire with old thermocouples and normal fire with new so I am not sure I am reading your first statement correctly.

My direct Industry experience with thermocouples and to a lesser degree hobby or studio kilns is that drift is one of the last things I would emphasize to most pottery folks. Calibration can be done and there are several reasonable methods and compensation often necessary in many precise processes that we do on a normal basis so calibration and measurement is a  regular doable daily thing that occurs.

kilns aren’t nearly as vulnerable to micro volt level changes, so my experience would be this is a rare issue for most, something I would not advise as a primary source of concern and for the average potter if drift is suspected  just switch one zone with another as a simple indicator Else replace the single thermocouple with new. 

I do agree that reasonable replacement is practical since we know they and will fail in 100-150 firings.  If your kiln is over or under firing there are many more likely causes to check first, this one is pretty rare for small kilns in my opinion.

Edited by Bill Kielb

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