clay lover Posted December 20, 2013 Report Share Posted December 20, 2013 One of my students has a vent on his Skutt 1027 and has this question. I don't have a vent on mine , so I thought some of you could answer this for him. He is having an issue with the top shelf being a full cone cooler than the rest of the kiln. He keeps the top shelf below 3 rings of elements or more. He has resorted to turning the vent off during firing, and using it only to cool the kiln after the peak temp is reached. With the vent off, he gets very even firings. I know the vent pulls outside air into the top of the kiln, but I don't know how the kiln keeps from having the area under the tiny vent holes from making cool spots. Any help? Link to comment Share on other sites More sharing options...
neilestrick Posted December 20, 2013 Report Share Posted December 20, 2013 Running the vent after the firing does absolutely nothing to vent fumes, since the fumes mostly come out as the temperature increases. Does the kiln have the correct quantity and size of holes for that size kiln? That kiln should have three 3/16" holes in the lid and floor. The lid holes should be spaced out, not clustered in the middle. Is the lid closing securely, or are there large gaps? A latch on the front of the lid can help keep it closed. Make sure all of the holes in the vent collection cup under the kiln are open, so it is drawing as much room air as it can. In my opinion, the greatest flaw of the Skutt and Orton vent systems is that they are not adjustable. The only adjustment is the size and number of holes, not the draw of the fan itself. The L&L vent system has an adjustable slider so you can control how much the vent is pulling from the kiln vs. the room air, so it doesn't draw an excessive amount of air into the kiln. It is made to be attached to either the bottom of an L&L kiln stand, or the side of other brands. If we can't get this figured out, it may be an option worth trying. Link to comment Share on other sites More sharing options...
clay lover Posted December 20, 2013 Author Report Share Posted December 20, 2013 His vent was factory installed, came with the kiln, new, from Scutt. The top holes are in a 10" +- circle around the latched lid. The bottom holes are close together under the cup. I can't remember how many there are. Looking back, or forward to the next order, should he have specified only 2 top holes, and added more if needed later. Holes are very small. Link to comment Share on other sites More sharing options...
Marcia Selsor Posted December 20, 2013 Report Share Posted December 20, 2013 Try placing a shelf an in or so below the lid. Marcia Link to comment Share on other sites More sharing options...
Chris Campbell Posted December 20, 2013 Report Share Posted December 20, 2013 Both my Skutt kilns have factory drilled vent holes. I do at least ten minutes hold at the end ... then, control cool the kiln as per the Ramp/Hold directions in the Skutt manual. I get very even firings top to bottom this way and often my top shelves are indeed at the top. Link to comment Share on other sites More sharing options...
clay lover Posted December 21, 2013 Author Report Share Posted December 21, 2013 Chris, what do you do with your peeps, and how big is your Skutt? Link to comment Share on other sites More sharing options...
Chris Campbell Posted December 21, 2013 Report Share Posted December 21, 2013 Chris, what do you do with your peeps, and how big is your Skutt?I have two Skutt 1227 computer controlled kilns. I leave the peeps in place all the time. I don't crack the lid or mess with anything. I load the kiln placing three witness cones on every shelf level, program the firing, hit start ... walk by and monitor the heat rise from time to time, check the details at the end of firing. It took many years to learn enough about firing my particular clay that I could make it that boring. The thrill of opening the finished firing is NEVER gone though. Link to comment Share on other sites More sharing options...
neilestrick Posted December 21, 2013 Report Share Posted December 21, 2013 When using a downdraft vent, all the peep holes should be in for the entire firing. Link to comment Share on other sites More sharing options...
clay lover Posted December 22, 2013 Author Report Share Posted December 22, 2013 Thanks, Chris. If you put cones on every shelf, does that mean that you don't use any posts shorter than 3"? I do really flat pieces often, but not identical enough to use a stack of plate sitters, so I would like to use 2" posts a lot. That is too short for self supporting cones, which I think are more accurate. Are 2" posts too short for good circulation? I use 1/2 shelves with as space between. Without a vent, I leave the top , bottom and center peeps in. Link to comment Share on other sites More sharing options...
Guest JBaymore Posted December 22, 2013 Report Share Posted December 22, 2013 Are 2" posts too short for good circulation? I use 1/2 shelves with as space between. Without a vent, I leave the top , bottom and center peeps in. The prime methods of heat transfer are radiation and secondarily conduction. Convection plays a much more minor role. Without a kiln vent.... that minor role decreases even further. So the fast answer is...... yes. Radiation is "line of sight". If you happen to put one of those 2" high shelves lining up with the blank part of the wall instad of an element..... the heat peneteration into that tight space will be much slower than more open parts of the kiln. VASTLY oversimplified, in order for the interior of the shelf to get hot..... the stuff on the outer edges has to get hot and then radiate energy into the middle areas. And/or the shelves on the top and botom have to do the same. Heat slowly gets conducted thru the thickness of the clay objects and the shelves.... so that the surfaces can become radiant sources. Lacking much line of sight from a hot elelment back...... that will affect the rate of rise in the areas so affected. best, ................john Link to comment Share on other sites More sharing options...
Chris Campbell Posted December 22, 2013 Report Share Posted December 22, 2013 Thanks, Chris. If you put cones on every shelf, does that mean that you don't use any posts shorter than 3"? I do really flat pieces often, but not identical enough to use a stack of plate sitters, so I would like to use 2" posts a lot. That is too short for self supporting cones, which I think are more accurate. Are 2" posts too short for good circulation? I use 1/2 shelves with as space between. Without a vent, I leave the top , bottom and center peeps in. If I use shorter posts I simply offset the shelf a bit in order to fit them in a straight line. Witness cones are a staple for me ... you have no clue what is happening in an electric kiln without them ... unless you care to try to peek in the peepholes and try to figure out what the heck is happening. For me, the hassle of placing the wares and shelves in such a way as to have the witness cones show up in the line of sight of a peephole is just too many things to try to do while loading the kiln. Your results might vary. Link to comment Share on other sites More sharing options...
clay lover Posted December 22, 2013 Author Report Share Posted December 22, 2013 Learning more all the time! Chris, sorry, but I don't understand what you mean, you "offset the shelf". Do you mean vertically or sideways? Are you using smaller shelves to have room to shift the shelf over? Sorry, just can't figure what you mean. Thanks. John, Interesting reading. It sounds like you are saying that the use of 1/2 shelves doesn't help much? in spreading the heat if the kiln is really packed with ware. Link to comment Share on other sites More sharing options...
Chris Campbell Posted December 22, 2013 Report Share Posted December 22, 2013 This should probably come with a warning not to do this .... But I shift the shelf slightly sideways so there is an area wide enough to line up the cones in the center ... However, if I am using one inch posts I don't bother trying to wedge in witness cones ... Just go crazy and throw caution to the winds! : - ) I used to make thousands of ornaments and would have full kiln loads with one inch posts and they tended to fire very well .... I guess the combination of all those shelves and all the wares made for a packed even firing. Link to comment Share on other sites More sharing options...
Guest JBaymore Posted December 22, 2013 Report Share Posted December 22, 2013 John, Interesting reading. It sounds like you are saying that the use of 1/2 shelves doesn't help much? in spreading the heat if the kiln is really packed with ware. 1/2 shelves staggered across the kiln (so that two 1/2 shelves do not line up on the same level) certainly helps ..... but as in all things ceramic.... there are SO many cvariables that it is hard to say "do this this way" about almost anything. What IS useful is to understand why and how thngs work/happen... and then you can trouble shoot issues or prevent issues yourself. Example....... to get heat energy to penetrate into the center of a load better........ I could slow the overall rate of climb of the firing a lot. I could open up the stacking of ware to allow more radiant energy from the elements to penetrate into the interior (line of sight). I could increase the convective circulation in the chamber by increasing any availabel draft flow (vent). I could soak at the end of the firing to allow the heat energy time to move by radiant and conduction toward the center. All will work. Which is the RIGHT one to chose? Than answer depends on a bunch MORE variables that I'd have to think about a bit. If you understand how kilns work and how heat energy gets transfered.... that is a good start to understanding how to fire kilns. In ceramics, there is a lot of science underlying the art. best, ...................john Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.