CactusPots Posted March 27, 2019 Report Share Posted March 27, 2019 My kiln is a home made ceramic fiber down draft, 36 cubic ft. There are 4 propane burners on each side and I load 2 18x18 shelves on each side with a gap between them. My firing is perfectly acceptable, glazes especially shinos look good, even reduction everyone, usually a half cone between top and bottom, 12 hours to cone 10. Reduction at 1600 top. Now for the fun part. at about 2000 degrees on my pyrometer, the reading switches where the bottom reads hotter that the top and continues that way until the end. Final reading will have the bottom about 100 degrees hotter than the top, but the cones will show that the top had more heat/work. I think what's happening is that the draw from the bottom is actually pulling the heat down more, but once the kiln is closed up the heat rises and finishes off the top more. There isn't really much of a problem here, I'm just into fine tuning. I think the flue pull is slightly too strong, a combination of the damper and the opening into the flue, which can be adjusted. Opinions? Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 27, 2019 Report Share Posted March 27, 2019 It is not uncommon to see various gas kilns display more heat on the bottom than the top generally there is more mass there and late in the firing most of the heating is done by radiation. Since the burners are situated at the bottom generally more radiant heat is generated there. You have good results in your firings so I would not obsess over it. Cones bend on temperature if they are heated a certain speed in about the last 250 degrees of their rating. Think of it as cooking something, warming it at 110 degrees forever will not likely ever get your pizza cooked. So there is a very real range where the work is relevant and that before it, not so much. If you look at the Orton cone chart below the cone 10 will bend at 2345 F if the kiln rate is 108 degrees per hour for about the last 250 degrees of the firing but bends at an entirely different temperature if the rate is different, say 27 degrees per hour gets you cone ten at 2284. Folks often notice this when firing one cone lower with a hold. Cone temps are not evenly spaced in temperature and that rate for the last 250 degrees complicates things. It becomes difficult to fire several cones lower with a longer hold time that intuitively makes sense. just my opinion but you get reasonable results and reasonable heatwork with your method. How your glazes finish is everything as long as you are not firing several cones above. Link to comment Share on other sites More sharing options...
CactusPots Posted March 27, 2019 Author Report Share Posted March 27, 2019 Lots of variables, to be sure. My thinking is to go as slowly as possible from 2000 to finish to give the glazes as much time in the melt zone as possible. The kiln is only climbing 50-60 degrees per hour. By my meter, I never get above 2150, but get a full bend on cone 10. Cone 11 if I want it. An easy half cone comes after the kiln is shut off, but it has a full 12 inch fiber module lid. Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 27, 2019 Report Share Posted March 27, 2019 Agreed but you get the results you want so that is everything in my view so I would keep doing what you know works. Link to comment Share on other sites More sharing options...
neilestrick Posted March 27, 2019 Report Share Posted March 27, 2019 Ignore the pyrometer for anything other than approximate rate of climb. Trust the cones, trust your glazes. The pyrometer is just a guideline, and unless it's a Type S, it won't be accurate at cone 10. Link to comment Share on other sites More sharing options...
Mark C. Posted March 28, 2019 Report Share Posted March 28, 2019 If the glazes are working and the temps are even enough do not change a thing. As Neil say thermocouples are a crude guide at best. since yours is reading very cool it could be slowing dying(is it in protection tube-if not then its going to have short life at cone 10. Just use it for a general climb up. as you noted the last time in the fire is when the glaze is melting so slow is better here. Fiber kilns are notorious fast cooling surfaces as they do not hold heat they reflect it. Link to comment Share on other sites More sharing options...
liambesaw Posted March 28, 2019 Report Share Posted March 28, 2019 6 minutes ago, Mark C. said: If the glazes are working and the temps are even enough do not change a thing. As Neil say thermocouples are a crude guide at best. since yours is reading very cool it could be slowing dying(is it in protection tube-if not then its going to have short life at cone 10. Just use it for a general climb up. as you noted the last time in the fire is when the glaze is melting so slow is better here. Fiber kilns are notorious fast cooling surfaces as they do not hold heat they reflect it. I think 12 inches thick of fiber would hold heat pretty good. Unless i misread that! Link to comment Share on other sites More sharing options...
Mark C. Posted March 28, 2019 Report Share Posted March 28, 2019 Ok yes 12 inches is great amount to insulate but its the thermo mass of the load that holds that heat-in a brick kiln some of that hot mass is the bricks bag walls etc. I a fiber kiln its the stack-pots and furniture not much in the way of bricks. My brick car kiln is much different than my friends Geil fiber car kiln for example in cooling even though my bricks are IFB mostly and a hard brick floor and bag walls.I get better crystal growth by far as the slow cool helps that. It sounds like the OP has a slow firing schedule so this is not a problem . Link to comment Share on other sites More sharing options...
CactusPots Posted March 29, 2019 Author Report Share Posted March 29, 2019 It's a fun topic anyway. I try to get as much mass down low as I can. The bottom shelves are 1" mullite and the bottom post are hard brick soaps. The rest of the shelves are silicon carbide with one set of advancers for the top. Otherwise there are some big pots on the bottom, say 4 @25 lbs wet, plus filler pots. The results are good. I still want to learn as much as I can even if it's not all useful. I don't have an oxyprobe, so I don't really know if I could get better results with less reduction. The probes are in tubes and I replaced them when I started wondering about this. It seems odd to me that the bottom would read hotter than the top at any stage of firing. I just switch the meter to the bottom probe and go by that. I agree, all it's really good for is watching the rate of climb to not waste a bunch of time. The cones are show time. Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 29, 2019 Report Share Posted March 29, 2019 51 minutes ago, CactusPots said: It's a fun topic anyway. I try to get as much mass down low as I can. The bottom shelves are 1" mullite and the bottom post are hard brick soaps. The rest of the shelves are silicon carbide with one set of advancers for the top. Otherwise there are some big pots on the bottom, say 4 @25 lbs wet, plus filler pots. The results are good. I still want to learn as much as I can even if it's not all useful. I don't have an oxyprobe, so I don't really know if I could get better results with less reduction. The probes are in tubes and I replaced them when I started wondering about this. It seems odd to me that the bottom would read hotter than the top at any stage of firing. I just switch the meter to the bottom probe and go by that. I agree, all it's really good for is watching the rate of climb to not waste a bunch of time. The cones are show time. If you think in terms of radiant heat it helps as line of sight is super relevant and traditionally gas firing folks raise and lower the centerline of their flame tips to even this out. As far as heating rate, knowing more is tremendous. Most folks Do not really measure and as a result often have interesting views on rates. We can get a really decent reduction complete with carbon trapping etc.... in our underpowered 16 cu ft Alpines in about eight hours at cone 10 / 11. I have watched the final rate so many times that I can usually guess within a few degrees when cones 9 , 10 will start to fall. We have a custom monitor which details the rate of heating updated at five minute intervals so watching the last 200 degrees or so becomes easy and tells me which column of the cone chart will reflect my final cone bend temperature on the pyrometer. Definitely the more ya watch and think the more ya can learn though. At our studio We have a sort of 101 reduction video that we encourage newbies to watch to get them thinking about reduction and rates and asking questions. You may find it too simplistic but it has helped folks get inquisitive. Link to comment Share on other sites More sharing options...
CactusPots Posted March 29, 2019 Author Report Share Posted March 29, 2019 I would love to have something like this data panel on my kiln. Is it based on the Data Logger? When I'm firing, I constantly use the stop watch function on the meter to compute the temp rise. Can I get some info from you about how to set this up? Thanks Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 29, 2019 Report Share Posted March 29, 2019 5 hours ago, CactusPots said: I would love to have something like this data panel on my kiln. Is it based on the Data Logger? When I'm firing, I constantly use the stop watch function on the meter to compute the temp rise. Can I get some info from you about how to set this up? Thanks Absolutely, as I say in the video, for those able, build your own, We will help. it’s standard PLC stuff which ends up to be super easy.. I have a couple coming next weekend just to see it and are contemplating adding it to their new startup pottery business. Anyone can do this, message me with your background and at some point we should verbally discuss just to be sure you are fine. The unit in the video is very economical plug together PLC industry stuff. Probably 500.00. - 800.00 bucks worth of parts. The most expensive piece was the size of the touch screen. It logs, it serves up web page access, serves two kilns and really has way more power than that. Both kilns can operate normally even if it’s turned off, so no worries about down time. The deal I have made others is the software is written already, free for,personal,use at a single site, just not re-sellable Link to comment Share on other sites More sharing options...
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