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# What is the allowable degree of Kiln ovality, and how do you [get it’s] real value ?

The maximum allowable amount of shell flexing (aka ovality) is an empirically derived value based on decades of experience and studies. Maximum allowable shell flex is seen to be a function of kiln shell diameter. The rule of thumb basically works like this; express the kiln diameter in meters e.g. 4 meters. Divide that number by 10 and attach a % sign. e.g. 0.4% That would be the mid range of the allowable relative ovality range with a tolerance of about 0.02%

In terms of actual dimensions, i.e. the absolute ovality in this example says 0.4/100 x 4000 =

16mm is the difference between the largest diameter, presumably the horizontal one and the smallest diameter, presumably the vertical one, while the kiln rotates. Further to this the maximum safe value for kilns 5 meters and larger is 0.5%.

Shell flexing values are obtained by measurement using the SFX Instrument (Avaialble from Phillips Kiln Services) as shown in the first graphic above.

Posted by Walter Gebhart