TypicalGirl Posted December 18, 2011 Report Share Posted December 18, 2011 OK - more help please... 3rd firing of my new kiln. Olympic DD9 downdraft, propane. I WAY overfired my last load so am being more cautious this time. I'm using this as a guide: http://clayarts.websitetoolbox.com/post?id=1263521 I was at 1600f, with the 2 upper peeps closed and the lower one open. I can tell I'm having a big issue in temp difference top to bottom. The outside of the kiln is hot to touch on the top half, but cool to the touch on the lower half. I can even put my finger in that lower peep hole. I've been closing the flue periodically trying to get some air/flame circulation top to bottom and now have it closed about 3/4, which seems like too much (this is not a redux firing, and this clay body does not like an early redux), but I am not smelling anything that smells like its reducing, and I don't seem to be getting circulation. Gage is at 3.5 psi and the flames are blue going in but yellow inside the kiln. How can I even out the temp? Later, the next day... Well, that was a less-than-spectacular firing. Cones 8 and 9 down on top, 10 bending. No cones down on the bottom. 1 exploded mug (on the top shelf of course, so it could rain down on lower pieces) and 2 cracked foot rings. 1/2 the pieces underfired. sigh... Link to comment Share on other sites More sharing options...
Marcia Selsor Posted December 19, 2011 Report Share Posted December 19, 2011 I tried four times to save a detailed explanation of how to fire this kiln but it got "OOPS" four times. Sorry. I get this quite often and it really is a pain. Marcia Link to comment Share on other sites More sharing options...
Natas Setiabudhi Posted December 19, 2011 Report Share Posted December 19, 2011 Ya the good kiln is number one consider before you decide making ceramics, especially if ceramic as your profession. If every time the under fired pieces 1/2, absolutely just waiting for bankruptcy. The principle one is good gas burner. Useless good kiln, if your burner got trouble. Second one may be the display of your works in the kiln. Third one may the process of increasing the temperature. As theory first step slowly, medium faster, last slowly again. Another thing may be you must arrange between gas and air. Good combustion is well balanced between them. Sometime the problem of the kiln make us frustrate. So welcome to the club.. Link to comment Share on other sites More sharing options...
Benhim Posted December 19, 2011 Report Share Posted December 19, 2011 Sounds like you need to balance air and gas with your damper and burner controls. You'll probably have to put it in at least light reduction to get the kiln to even out. You shouldn't need to have your lower ports open to get even temperature. If anything having those ports open will draw cool air straight across the bottom to your stack effectively cooling off the bottom half of your kiln. You should be able to adjust your damper and burners until the ports are spitting fire and black smoke. This is too much reduction, what you want is back pressure with out much black smoke. When you pull the top port the flame should push out briefly and then pull back inside. The lower port will probably have a smaller flame, but it should also push out briefly. This is how almost all downdraft kilns I've fired work. If your flame is continuously pushing out your ports your damper is slightly to far in. If you have no visible flame (visible in darkness, as the flame can be very light) then your damper is not in far enough. Adjusting your primary and and secondary air on your burners is a whole other conversation. What you're looking for from your burners is flame color. An orange flame is rich with fuel and a blue flame is efficiently oxidized. Adjusting the primary air to get a flame that is blue has given me the best results in most kilns. This blue flame is sucking in enough oxygen to burn the flame until the damper is closed to create reduction. If your burners are shooting orange flames you'll have a problem getting even heating because your fuel is not going to burn. One way to find the most efficient configuration is to open the primary air until the burner blows out or starts popping. Turn the air back down until it stops popping and holds a steady strong full blue flame. This advice is my experience with Downdraft kilns in college. Be safe use all safety gear, and seek advice from the manufacturer if possible about your burner configuration and general firing guidelines. Best of luck, Ben Link to comment Share on other sites More sharing options...
Marcia Selsor Posted December 19, 2011 Report Share Posted December 19, 2011 I agree with Benhim. Use your damper more. I would keep it shut more than 1/2 closer to 3/4 during the firing. When reducing cut the primary air on your burners and shut the damper as much as you can...maybe as much as 7/8 without getting back pressure on your burner tips. You want to get a licking flame or harder coming out of the bottom peep hole. But keep the plug in the peephole when you are not checking the reduction or cones. You can hold a stick in front of the peephole. If it doesn't burn in the flame, you have a reduction atmosphere. Marcia Link to comment Share on other sites More sharing options...
bciskepottery Posted December 20, 2011 Report Share Posted December 20, 2011 A really good book on firing is The Art of Firing by Nils Lou. A wealth of information. Another excellant source is Mel Jacobson's 21st Century Kilns. Link to comment Share on other sites More sharing options...
Marcia Selsor Posted December 20, 2011 Report Share Posted December 20, 2011 I agree Nils' book is a great asset to firing reduction...but every kiln, at every altitude, with every climate variation is a challenge. Link to comment Share on other sites More sharing options...
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