Maximum allowed weight on a kiln shelf

[Bill Kielb]

1 minute ago, Cristobal said:

I just checked and I can move the end posts 1' away from the edge and still fit 4 full and one short brick on the shelf.

Nice investigative work,  I think you will be fine with the amount of due diligence. Next time you look up at some building structural framing you can point out a center member that is much smaller than the end members and proclaim its double cantilever and they are using the end loads to offset the center load.

Best of luck!

[Cristobal]

I realized that my shelves are not cordierite, but regular high alumina.

I resquared brick posts and made them more uniform in height. The old ones that I was using in the torch zone, under the first shelf, got shrunk by 2-3 mm from repeated firings and I cut new ones. I measured distances to the walls and used clay wads covered in kiln wash on two middle posts only. One middle post was too high (or shelf sagging a little in that spot) and I ground it with a diamond file to prevent any rocking. I loaded only 4 bricks per shelf, because the distance between middle posts was only 176 mm and my short bricks are 183. I have 168 mm bricks also and they would fit, but did not want to spend more time on painting them with the enamel.  So I fit 4 * 2 * 3 = 24 bricks and am firing now. The pyrometer is showing 520 C.

[Cristobal]

I have finished firing before midnight on Sunday. Usually I open the kiln on the morning of the next next day, so after 34 hours. In this case I had to wait longer, because even on Tuesday evening the pyrometer was still showing 55 C and I usually open when it's showing the room temperature (which is outside temperature in my case), probably because of large thermal mass of the glazed bricks. Only today morning, so after 58 hours it finally showed 27 C. The bricks on top shelf did not get (as usually) enough heat, but they will not be really visible in the project I'm making them for and I just glazed them translucent. Middle and bottom shelf got gorgeous deep cobalt blue. The bottom shelf got the 06 cone collapsed, so probably it reached 05 to 04. The bricks were still warmer than all other fired objects that I took out from the cooled down kiln in previous firings.

Shelves were fine, but will inspect them in the daylight. It means that one 5/8 high alumina shelf with 4 posts could hold 29 lbs of material at cone 05. Next firing will have a little bit heavier load, because I will add shorter 5 lbs brick between middle posts. I still have to do 10 more firings. With the longer kiln cooling time I will be able to do it every third day, instead of every second one.

I will post some pictures later.

[Bill Kielb]

@Cristobal  very nice, congratulations! 29 pounds distributed evenly across approx. 300 square inches per section a long way from your 10 PSI finding. I did find this from L&L a day or so ago (thinking of this issue), It gives some guidance over a really evenly loaded kiln floor. (Bottom shelf right on the kiln brick) You would probably need to look at these models and find the most similar configuration. Anyway, this may help someone in the future. I don’t believe I have ever seen this question here, so all interesting knowledge actually.  https://hotkilns.com/support/pottery-kiln-knowledgebase/how-much-weight-can-go-kiln#:~:text=For Easy-Fire%2C Jupiter%2C,100 X 3.54 %3D 354 pounds.

Edited September 5 by Bill Kielb

[Cristobal]

I have finished the third firing. On the second one I have put 36 lbs on bottom and medium shelves. For bottom shelf 06 and 05 cones are fully collapsed. I'm waiting for the kiln to cool to see the results of the third firing which included some bricks with both stretcher and header (vertical) glazed. Tomorrow I will do the fourth one.