What is the emissivity of a kiln's shell? I ask this because i need to know it to take infrared thermography of the surface shell of a kiln.

The emissivity of the rough oxidised kiln shell at 400 degrees C is approximately 0.9. According to my notes emissivity is dimensionless.

Thanks for your reesponse on our cracking problems. We have ordered a new cone and in the mean time we have welded the effected part and have used dye penetration test for finding the magnitude of crack. But what in I am interested is the reasons;thats why such cracks develop, either due to misappropriate operating, startup /shutdown procedures. improper jackingup the mill at the startup time, overdue servicing of trunion etc. Or only due to matelurgical/ casting failure. Furthermore please let me have the diagnoses procedure/test for the above.

The main reasons why these cracks occur are due to the high stresses that the mill end castings are subjected to and therefore metal fatigue. Most suppliers have taken steps to reduce metallurgical or casting failures as much as possible, but pre-delivery inspection and testing would be one step. Many problems are caused insufficient care by the maintenance department when welding, grinding the mill shell, or cutting bolts/drilling holes for fixing bolts. Of course there are steps you can take to during operation to mitigate against these cracks developing, (i) broken wear protection plates must be replaced immediately, (ii) temperature monitoring. Ultimately there is no alternative to frequent and rigorous inspection.