Natania Posted October 4, 2014 Report Share Posted October 4, 2014 I loaded my glazed pieces in my electric kiln when they were still pretty damp and may not have candled enough as I usually do in that situation to dry the glaze. I also suspect my electric kiln does not have enough (hardly any except 2 tiny holes drilled in top with vent on) air flow, and am wondering if the water vapor in the kiln could account for the slower firing the kiln experienced yesterday. It usually takes 9-10 hours, and I turned it off at 13 (going to cone 6) because I was surprised it wasn't off. The elements are not popping out of the tracks, etc. and the inside of the kiln looks to be in great condition. It was firing like a champ previously. Has anyone experienced an delay from glazes being too damp in the kiln? I'll unload tomorrow morning and am hoping not to find a mess. Urgh! Link to comment Share on other sites More sharing options...
Foxden Posted October 5, 2014 Report Share Posted October 5, 2014 It takes a surprising amount of energy to convert water to steam. While it only takes one calorie of energy to heat one gram of water one degree C, it takes 540 calories to convert that one gram to steam. The wetter the work the more water to convert to steam. That means more energy, more watts, longer time, etc. so to answer your question, assuming nothing is wrong with your kiln, yes, a wetter load will take longer to fire. Link to comment Share on other sites More sharing options...
123pop Posted October 5, 2014 Report Share Posted October 5, 2014 My kiln did not shut off for my last bisque firing last Sunday. I knew it wasn't getting hot enough. Couldn't see the glow between the lid and the base. After wishful thinking shut it down after 17 hours. Checking with a meter found it was the top switch. Looked like it had a little nest in it. Got a new one from Cress in 2 days, installed it and today bisque fired again..off in 7 hours. I hurried it a bit since everything was almost 04 but had no idea what cone. Last glaze firing the kiln sitter cone broke and shut it down early. Everything was unfired. Orton said to tug a bit on the cone before using. Then if they are weak or cracked they will break and you won't risk an underfire. I refired and everything turned out fine. I had about 10 in the box pull apart. I think I'm due a few good firings in a row now. Hope all goes well. It could be the damp ware. I am very conservative and glaze fire very slowly 13-15hours. Link to comment Share on other sites More sharing options...
Min Posted October 5, 2014 Report Share Posted October 5, 2014 It takes a surprising amount of energy to convert water to steam. While it only takes one calorie of energy to heat one gram of water one degree C, it takes 540 calories to convert that one gram to steam. The wetter the work the more water to convert to steam. That means more energy, more watts, longer time, etc. so to answer your question, assuming nothing is wrong with your kiln, yes, a wetter load will take longer to fire. Sorry but I don't see damp pots causing the kiln to take 3 or 4 hours longer. My bet is that it's either an element gone or the electrics. Link to comment Share on other sites More sharing options...
Mark C. Posted October 5, 2014 Report Share Posted October 5, 2014 I,m with Min on this as well. Water on glazed ware in electric will not slow you down, even if the spy plugs are in. You have other issues with kiln or schedule. Mark Link to comment Share on other sites More sharing options...
oldlady Posted October 5, 2014 Report Share Posted October 5, 2014 i fire glazed greenware which feels dry all the way through and a stuffed kiln on slow glaze firing takes 10 hours which includes a very slow rise to 212 degrees. it is something wrong with the kiln. Link to comment Share on other sites More sharing options...
Bob Coyle Posted October 5, 2014 Report Share Posted October 5, 2014 If you don't have one, go buy a cheap multimeter ( harbor freight gives them away) and check the resistance of the elements in your kiln. There are a number of threads that tell you how to do this. If you are going to fire with an electric kiln, then knowing a little bit about how it works will save you a lot of grief and $$$. It ain't rocket science... and the only thing you have to know is I=E/R. A formula every potter who uses an electric kiln should be familiar with Link to comment Share on other sites More sharing options...
Natania Posted October 6, 2014 Author Report Share Posted October 6, 2014 I will get a multimeter. What will checking the resistance of the elements tell me? How well they are holding/building heat? Thnx. Link to comment Share on other sites More sharing options...
neilestrick Posted October 6, 2014 Report Share Posted October 6, 2014 Water vapor will not effect firing times. If nothing blew up, then they were dry by the time the air temp in the kiln got to 500F. You've got a kiln problem- bad element(s), switch, connections, etc. Lots of possibilities. First start it up on high and see if all the elements glow. Link to comment Share on other sites More sharing options...
Bob Coyle Posted October 6, 2014 Report Share Posted October 6, 2014 The resistance of an element tells you how much current(amps) it will pass at a specific voltage. the formula I =E/R means that amps = line voltage/ total resistance of all elements. So to measure the resistance of all of the elements you unplug the kiln, turn all of the elements to high, set the kiln sitter on, and measure the total resistance across the plug. (This is assuming the elements are not held open by internal relays.) So if you have a 30 amp kiln plugged into 240 volts the resistance should be around R=E/I or 240/30 around 8 ohms If you don't get a resistance reading at the plug because the circuit is open inside the controller are you can measure the resistance of each element where it goes into the controller from the inside of the kiln. You will have to know what you are looking for to do this. You have to be careful not to lean in and break the refractory at the top of the kiln and not disturb the elements. If you feel that this is getting too complicated you may have to get help from someone who is a little more familiar with electricity and kiln wiring. If you want to forge ahead , and have to measure resistance of individual elements then first year algebra is required. Assuming all elements are wired in parallel to each other the way to calculate the total is.... see the attachment. The volt meter can also be used to measure output of the thermocouple, if you have one which could eliminate another source or error and requires you to download a chart of temperature Vs thermocouple voltages.It's good to do spot checks every once and a while. Link to comment Share on other sites More sharing options...
neilestrick Posted October 6, 2014 Report Share Posted October 6, 2014 The easiest thing to do is call the manufacturer and find out the element resistance. Since most brands use graded elements (different resistance in different parts of the kiln) you have to do this anyway. Then, unplug the kiln, open the control box and take an ohm reading where the elements come through the wall. It can be difficult to get a reading form inside the kiln itself since the elements will have a thick layer of oxidation that prevents good contact with the meter. If the thermocouple looks nasty, change it. I'm assuming you have a manual kiln, Natania, since it fired so slow and you didn't mention an error code? Link to comment Share on other sites More sharing options...
Natania Posted October 6, 2014 Author Report Share Posted October 6, 2014 Thanks very much Neil and Bob. I will get an ohm meter and try using it. Knowing how an electric kiln works is one of my goals...Yes, my kiln is manual. The odd thing is that I refired it today and it went off (reached temperature) in the regular 9.5 hours. Neil - could it be that the extra water vapor just made it take longer to get to 500F? I have had this happen before (ok, so I have a bit of a problem with being impatient and loading wet glazed ware) with a different kiln, which also fired fine when the ware was good and dry...or maybe there was a bigger draw on the electric grid that day (it was very rainy but not particularly hot or cold out though...)? Anyway,Thanks again for your help. I'll save your suggestions if problems persist in the future.... Link to comment Share on other sites More sharing options...
neilestrick Posted October 7, 2014 Report Share Posted October 7, 2014 A voltage drop could affect the speed slightly, but I wouldn't expect a 30% difference. The density of the load will have a greater effect. Link to comment Share on other sites More sharing options...
Natania Posted October 7, 2014 Author Report Share Posted October 7, 2014 It was a denser load than I typically have, but I didn't change it at all (except to put in a new cone) for the refire which was fine. Odd...... Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted October 7, 2014 Report Share Posted October 7, 2014 Is that a thing in America to use E for voltage? Link to comment Share on other sites More sharing options...
neilestrick Posted October 7, 2014 Report Share Posted October 7, 2014 Hard to say what's going on without getting my hands on it. When you shut down the kiln at 13 hours, was it glowing hot like it was close to getting to temp? Is the kiln sectional, with interbox plugs (plugs on the control boxes that plug together when you stack the sections)? What brand/model? Link to comment Share on other sites More sharing options...
Natania Posted October 7, 2014 Author Report Share Posted October 7, 2014 The kiln was glowing bright orange when I shut it down. I did let it cool and looked at the ware before refiring, and it looked like it maybe reached cone 3 or 4 instead of 6. Glaze was hard but crusty and not shiny. I will look in the sectional and report back...Thanks! Link to comment Share on other sites More sharing options...
neilestrick Posted October 8, 2014 Report Share Posted October 8, 2014 The kiln was glowing bright orange when I shut it down. I did let it cool and looked at the ware before refiring, and it looked like it maybe reached cone 3 or 4 instead of 6. Glaze was hard but crusty and not shiny. I will look in the sectional and report back...Thanks! The reason I ask about the connections is because sometimes the interbox plugs don't make good contact and you end up with a section that's not getting power. It can happen if the sections shift a little when you're leaning into the kiln during loading, or just from raising and lowering the lid. Link to comment Share on other sites More sharing options...
Natania Posted October 9, 2014 Author Report Share Posted October 9, 2014 ah. It turns out that my kiln is not sectional. It is an old Gare kiln. That would make sense, though, and I'll remember it when loading the kiln I use at the school where I teach, which is sectional... Link to comment Share on other sites More sharing options...
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