lukeseall Posted March 1, 2019 Report Share Posted March 1, 2019 My pyrotechnic cones are completely melting rather than just bending. I'm a bit baffled. On my first ever glaze firing I was aiming for Cone 5 and set controller to go up to 2000 deg C. I put a 3 orton cones in (4, 5 ,6) . the firing took 13.5 hours and all the cones completely melted. I assumed that the firing was a bit slow and I was over firing. So the second ever firing, I reduced the target temperature to 1186 deg C. This time I put in 5 orton cones (4, 5, 6, 7, 8). The firing took 12 hours and still all the cones melted. Even the cone 8! I am quite new to this but surely I can't have reached cone 8 with that firing? I'm not wondering if I'm using the cones wrong or something. Any advice very welcome! Link to comment Share on other sites More sharing options...
Benzine Posted March 1, 2019 Report Share Posted March 1, 2019 If my conversion is correct, 2000 C is 3632, which is waaaay beyond normal ceramic cones. So I guess that is like setting the controller to 9999. It will basically go, as hot as it can. I have no idea, why the second firing melted the Cone 8, as 1186 C would be Cone 4. Quick question, are you sure you are using the right cones? Are you using Cone 4, 5, 6, 7 and 8 and NOT Cone 04, 05, 06, 07 and 08? Link to comment Share on other sites More sharing options...
lukeseall Posted March 1, 2019 Author Report Share Posted March 1, 2019 Sorry I meant 1200 not 2000 yes I double checked the cones are correct. That was my first thought. Link to comment Share on other sites More sharing options...
Benzine Posted March 1, 2019 Report Share Posted March 1, 2019 I know heat work can make a difference, but I can't say if it would be enough to cause that issue. What kind of kiln and firing program/ schedule are you using? Link to comment Share on other sites More sharing options...
lukeseall Posted March 1, 2019 Author Report Share Posted March 1, 2019 Electric kiln. 80 litres. 7kw. 100 degC per hour up to 600 then full speed up to full temp then 15 min hold. Then it takes about a day to cool down. Thanks for for help btw! Link to comment Share on other sites More sharing options...
Mark C. Posted March 1, 2019 Report Share Posted March 1, 2019 Are you using premade cone pads or clay pads and are the cones set at the right angle? If your cone 8 melted how did the glazes look -running ok still dry looking?? have your cones gotten wet????? Link to comment Share on other sites More sharing options...
Benzine Posted March 1, 2019 Report Share Posted March 1, 2019 I would probably get rid of that hold, on the end, for starters. Your controller is electric right? The cones are just to measure the heat work on each layer? Link to comment Share on other sites More sharing options...
lukeseall Posted March 1, 2019 Author Report Share Posted March 1, 2019 Homemade pads. I set the cones to the same angle as when the are on a flat surface. But they haven’t just bent they completely melted. Can’t see how they could have gotten wet. Had some on bottom shelf and some on top shelf. Both ended up the same. Glazes actually look look pretty good but have only fired twice so not much to compare with. Controller is electric. Wondering if temp gauge is faulty but 12 hours seems like a reasonably amount of time. And melting a cone 8 cone when I was only aiming for cone 4 temp seems too extreme. Would leaving the kiln to cool down for 24 hours cause them to melt? Link to comment Share on other sites More sharing options...
liambesaw Posted March 1, 2019 Report Share Posted March 1, 2019 10 minutes ago, lukeseall said: Homemade pads. I set the cones to the same angle as when the are on a flat surface. But they haven’t just bent they completely melted. Can’t see how they could have gotten wet. Had some on bottom shelf and some on top shelf. Both ended up the same. Glazes actually look look pretty good but have only fired twice so not much to compare with. Controller is electric. Wondering if temp gauge is faulty but 12 hours seems like a reasonably amount of time. And melting a cone 8 cone when I was only aiming for cone 4 temp seems too extreme. Would leaving the kiln to cool down for 24 hours cause them to melt? Nope, they don't bend while cooling Link to comment Share on other sites More sharing options...
neilestrick Posted March 1, 2019 Report Share Posted March 1, 2019 Is the controller set for the type of thermocouple you're using? Link to comment Share on other sites More sharing options...
lukeseall Posted March 1, 2019 Author Report Share Posted March 1, 2019 10 minutes ago, neilestrick said: Is the controller set for the type of thermocouple you're using? Errrrm. No idea. Bought the kiln second hand but the documents that came with it imply that the controller is compatible. Link to comment Share on other sites More sharing options...
neilestrick Posted March 1, 2019 Report Share Posted March 1, 2019 28 minutes ago, lukeseall said: Errrrm. No idea. Bought the kiln second hand but the documents that came with it imply that the controller is compatible. Controllers can often use more than one type of thermocouple, but you have to change the setting in the controller for whichever type you're using. Look through the manual and see what you can find out. It might just be time for a new thermocouple. How does it look? Crispy? Link to comment Share on other sites More sharing options...
Magnolia Mud Research Posted March 1, 2019 Report Share Posted March 1, 2019 3 hours ago, lukeseall said: cones are completely melting rather than just bending. Describe "melting". Photos of the "melted" cones would help us to understand what is happening. What color are the cones before they are fired? LT Link to comment Share on other sites More sharing options...
lukeseall Posted March 1, 2019 Author Report Share Posted March 1, 2019 See attached. This pad actually broke in kiln but other one was the same and intact. Cones are all different colours before depending on which cone. After they are all white. Link to comment Share on other sites More sharing options...
Magnolia Mud Research Posted March 2, 2019 Report Share Posted March 2, 2019 OK, I now understand that all the cones are 'flat' and that the upper right corner cone is almost melted (my definition of "melted"). My conclusion is the kiln is hot, at a temperature in the range of cone 8+/-. All of which are hotter than the temperature being reported by the thermocouple. I am not surprised that the cones, probably located on a middle level kiln shelf, are hotter than the thermocouple probe located near a wall of the kiln and having a direct line-of-sight to the lid and floor of the kiln - the two coolest areas of the kiln. From my experience working with industrial furnaces, it is not unusual for thermocouples to be significantly different from the actual temperature of the surrounding gaseous environment and nearby solids, and a single thermocouple located near a kiln wall, will almost always produce a reading that is colder than the true temperature of the objects being processed. ["Transport Phenomena", 2nd edition, Bird, Stewart, and Lightfoot, 2002, Example 10.7-1 "Error in Thermocouple Measurement", page 309-10 has a good explanation of why.] I have seen 100+ C differences in the thermocouple reading and the actual object temperature. The important question is: are the wares in the kiln meeting your requirements in maturity and other specifications? You stated: "Glazes actually look pretty good" and "I was only aiming for cone 4 temp" implies that the ware met your expectations". also... "but 12 hours seems like a reasonably amount of time." Assuming that the pots were heated to about cone 8, the pots are telling you that the clay body and the glaze can withstand the conditions that were in the kiln. I would accept that the setup you have is over firing, but not excessively with regards to the ware; i.e. panic is not needed. Next step might be to lower the thermocouple target number in your next firing by another 25 degrees and using the same or similar glazes and clay body and see what happens. Let the pots tell you when they are not hot enough to meet your requirements. Keep using a wide spread of cones to provide the temperature feed back. If spy holes are available, add a cone pack that can be seen from a spy hole near the ware to provide visual insights into what is happening. LT Link to comment Share on other sites More sharing options...
oldlady Posted March 2, 2019 Report Share Posted March 2, 2019 MMR, luke said the cones were near the top and near the bottom. does that change your answer? Link to comment Share on other sites More sharing options...
Magnolia Mud Research Posted March 2, 2019 Report Share Posted March 2, 2019 Oldlady, Not really; the principles are the same. The magnitude of the offsets might be different. Focus on the ware, not on a temperature reading that is located separately from the item being fired. (Even if the thermometer is embedded in one item of the ware the reading is not necessarily the same throughout the item or in all the items. ) If the ware is Ok, the rest is an optimization issue. All the pottery made prior to Seger’s and Orton’s Cone were fired by evaluating the ware; measurements are helpful, but best evidence is the ware. LT Link to comment Share on other sites More sharing options...
lukeseall Posted March 2, 2019 Author Report Share Posted March 2, 2019 Thank you so much for taking the time to help me, especially MMR! Much appreciated. One question - if I fired the kiln empty with just furniture and cones, would it heat significantly different to when it’s full? I’m thinking about just doing a few test fires to try and narrow down what cone I’m actually achieving. Link to comment Share on other sites More sharing options...
liambesaw Posted March 2, 2019 Report Share Posted March 2, 2019 Yeah it will fire faster, has a small affect on the cones Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 2, 2019 Report Share Posted March 2, 2019 @lukeseall Cones bend at different temperatures based upon approximately the last 250 f of your firing. At 27:degrees per hour rise cone six will bend approximately 2165 F at 270 degrees per hour the cone will bend at 2269 F. You have a 7kw kiln, which is not a bunch of energy, your kiln cools in a day so it has a fair amount of losses. What’s the point of all this? 100c to 600 is about five hours + with the balance to 12 hours. My guess is this kiln goes extremely slow at the last 250 degrees and therefore these cones are performing as prescribed meaning they will fall at significantly lower temperature. Common glaze firing to cone six, 5- 8 hrs is usually plenty. The important part, the firing rate for the last 250 degrees. So my sophisticated wild guess: your kiln cannot go fast enough in the last 250 f of your firing. I have watched kilns go from 7 hours with new elements to 20 hours with elements that have lost 10-20% of their capacity after a couple hundred firings. Guess what, all the cones were smashed to smithereens and the controller errored out and never made it to cone 04! you likely have a lack of available heat very likely due to the age of your elements. 7kw is not a bunch of power in a moderately insulated kiln. I would immediately accurately check the elements to see how far out of specification they have become. At 7kw you may need all you can get at the top end of firing in this kiln. Link to comment Share on other sites More sharing options...
NotJo Posted March 2, 2019 Report Share Posted March 2, 2019 Yep, I'd say heatwork, too. My small 2-phase kiln can't get past 1215 according to the controller (and new thermocouple) but the last temperatures take so long to reach that the heat work is enough to mature my cone 9 glazes (at least, they seem so). When first firing my (newly received very old kiln) I totally overfired it trying to reach 1280 on the readout, and all of my cones totally melted, even the cone 10. Now I put them near the spy hole and when the kiln alarm goes off (which I assume is due to not being able to reach the temp in a reasonable approximation of the programmed ramp) I see if they're properly deformed, and if so, then let it cool. Good luck figuring out how to bake in your new oven! Don't forget it takes a lot of energy to heat up those kiln shelves alone. Link to comment Share on other sites More sharing options...
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