What is the maximum continuous shell temperature a kiln stands without permanent damage to the shell?
By: Nael Shabana email@example.com
The maximum recommended kiln shell temperature varies by plant, by country and by kiln manufacturer, despite the fact that most kiln shells are made of low alloy carbon steel. Age of the kiln shell, distance between the tires, and structure of the shell are some important points should be considered before deciding what the maximum allowable temperature for a kiln is. Let us explain these points briefly:
- Age and condition of the kiln shell: Old kilns shells have been exposed to creep for a long time and are more prone to develop fatigue cracks than newer shells.
- Distance between tires: The longer the shell span, the less it will resist high temperatures without sagging. Therefore, longer spans have more tendencies to develop permanent deformation than shorter spans.
- Kiln shell structure: Kiln shells are made with structural rolled steel plate, such as A.S.T.M. A36. The tensile strength of this type of steel at room temperature is 50,000 to 80,000 psi. As stated before shell strength is measured at a room temperature. Figure-1 is showing how shell strength drops considerably as its temperature is raised. It is interesting to notice that there is a gain in strength between room temperature and 200 °C, followed by a sharp loss in strength as the temperature goes up. At 430 °C the ultimate strength of the steel drops from 75,000 psi to 50,000 psi (a hefty 33%) loss. Some investigators report a 50% strength loss for the same temperature range.