cspindler

Hi Again Mark (an y one else!) I have a couple of follow-on questions from the previous discussion, if you don't mind. 1. The fibre board supplier has 25mm (1 inch) and 50mm (2 inch) 1440C / 2600F fibre board available. I assume I should I be going for the thicker one to replace the interior ceiling but could you let me know your thoughts? 2. If I'm going to replace the metal rod at the back of the kiln, is there a particular type of metal I need to be using? Many thanks. Clare

Thanks again, Bill. Appreciate all these suggestions.

Many thanks, Mark.

Thank you so much, Bill. The manual which accompanied this kiln, which was second hand, was thin on specifications and internet searches haven't turned up anything either. Not sure where else I might look! But from the feedback provided here I think we definitely need more than what we've used to date.

Thanks, Neil. Yes, cleaned out all the burner with some compressed air before we refired.

Here is a top down picture of the roof with the metal cap piece removed. The other picture is an attempt to show where the corroded metal bar was positioned. The blue arrow is pointing at the flue wall / back wall of the kiln chamber. The pink arrow is pointing at the hole where the metal bar was attached to the kiln wall with a screw (there is another hole on the opposite side of the kiln). Given that the position of this hole is very close to the top of the kiln roof, I don't think its purpose is to provide a support for the kiln chamber ceiling. But maybe is was a place for the ceramic pin wires to be attached?

Hi Neil, The original ceiling was fibre board with ceramic pins inserted which then were attached with wires to metal cross bars that spanned across the top underneath the metal roof piece. The attached pictures show 1) the interior post repair, but which is very similar to what it looked like before and 2) the top of the kiln with metal roof piece removed showing the cross bars where the pin wires were attached.

Mark, Thank you so much for your quick and thorough reply. I had only found out after doing the repair that the materials I'd been given were 1260C and thought that wasn't enough. But it's good to have your confirmation here and your suggestions on how much total thickness of insulation we should be aiming for. I'm attaching here some general images of the kiln showing 1) front on view of the exterior and hood; 2) interior view (post fix, where you can see the shrinkage and cracking in the ceiling) and 3) close up showing flue opening and hood. I will send separate messages with images of the roof, which will hopefully better explain the positioning of the corroded metal bar.

Hello. I’m a UK potter looking for help in diagnosing problems with a Laser J12N downdraft kiln, which runs off LPG and has 4 burner ports. Following a recent repair to replace a collapsing ceiling, the kiln now requires more gas to make it to temperature (cone 9/10) and the reduction has become very patchy. The interior ceiling was repaired using a piece of 25mm ceramic fibre board with a temperature resistance of 1260C. Above this, under the metal roof, we inserted a layer of 25mm ceramic fibre blanket plus a layer of 25mm ceramic fibre board, both with a temperature resistance of 1260C. When we removed the old insulation under the metal roof, we discovered the remains of a metal bar at the back of the kiln just in front of the flue opening (see photo showing position) which had corroded away. It looked like it may have supported a thin layer of ceramic board/blanket. We didn't replace this metal bar when doing the repair. Prior to our “fix” it would take us about 8-9 hours to reach cone 9/10 using one 19kg tank of LPG. We typically put the kiln into reduction at about 1000C using ceramic bricks in the flue opening. In terms of reduction achieved within the kiln, pieces on the bottom shelves would be slightly less reduced due to proximity to the burner ports but pieces above would be nicely reduced with those on the top shelves achieving the heaviest reduction. Following our “fix” we found that one 19kg tank of LPG was no longer enough to get to cone 9/10 so we purchased a changeover valve to allow for a second tank. Also the levels of reduction within the kiln are now very unpredictable. But generally, pieces on the bottom shelves are not reduced at all and neither are pieces on the top rear shelf. Pieces on the middle shelves are the only ones showing any amounts of reduction. After we had done a couple firings, we noticed that the piece of hardboard we'd used to replace the interior ceiling had shrunk from the back wall and was already showing signs of cracking. Also, our first few attempts of using the change-over valve were a bit bumpy. In both instances, the pressure/flow of gas from the first tank had already dropped quite low when we initiated the changeover. We didn’t completely lose flame before engaging the next tank but it did drop quite low for about 5 minutes. So before embarking on another fix I'm looking for some guidance on how to do it correctly. Specifically, I have the following questions: What could be the cause(s) of the need for more gas and the change in nature of the reduction within the kiln? Should we be using ceramic fibre board / blanket that has a temperature resistance higher than 1260C? Should we be using ceramic fibre board / blanket that is thicker than 25mm? Or is there a total thickness of insulation that we need to achieve? Does anyone know the purpose or importance of the metal bar at the back of the kiln? Could the issues we encountered with the cut over valve have contributed to the lack of reduction on the bottom shelves? Is there a different/ better way for us to manage the change over? Any other thoughts/comments/suggestions beyond the above are certainly welcome! Many thanks in advance for your help! Clare