In the production process of raw material turn-to clinker, the air flow temperature inside the kiln reaches 1600℃, sometimes tops at 1800℃, the material temperature reaches 1450℃, the surface temperature of the kiln burning zone reaches 200℃ to 300℃, the installed refractory bricks and the coating protects the kiln shell, so the kiln shell will not be damaged by the ultra temperature, and it prevents or reduces the heat transmission from the internal side of kiln to the external side.

Graph 1  Schematic diagram of rotary kiln cross section

However, when the kiln coating and bricks wear out after long term burning through, or the coating and bricks deform and in bad extrusion condition, the kiln shell steel board will be affected by the high temperature and will even be damaged directly by  the flame, the color of steel board will turn to red or dark red, such phenomenon is “ red kiln” , in worse state, the steel board will soften, some parts of kiln shell will be deformed with convex and concave, in worst state the kiln shell will melt down, and the big accident of “ red kiln”occurs. In general conditions such phenomenon always occurs at burning zone or higher temperature area of rotary kiln.

Some reasons lead to the “red kiln”Phenomenon. Some as below: 1. the refractory brick selection and quality; 2. the lining quality of refractory brick; 3. the proportion formula of the raw material; 4. the operational skill to control the kiln burning process; 5. the reason of kiln shell itself, such as the shell is not round, the central line is eccentric, the poor rigid strength, the big radial deformation ( as shown in Graph 2). From the graph 2, we can see the kiln shell radial deformation due to the poor shell rigid strength, for one specific point on the kiln shell, when the kiln shell turns a cycle, it will suffer six times of convex-concave changes in the radial direction and it is the main obvious reason that will cause the kiln cushion parts loose and fall down. The worst shell deformation occurs at the tyre, and the gap between the tyre and the kiln shell poses big impact on the kiln deformation condition, it is necessary to understand and master the deformation state and the state of gap between tyre and kiln shell, when default occurs, troubleshooting actions should be taken. The usual troubleshooting method as below: according to the detected actual gap data, increase the cushion board thickness properly, and replace it with new one. For the kiln central line eccentric default, the reasons include the alignment was not done when the kiln was initial erected, the sediment, the uneven wear of each pier tyre and support roller, and the irregular kiln calibration. The relevant troubleshooting actions should be taken accordingly.

  Graph 2  Schematic diagram of kiln shell radial deformation

In order to ensure the kiln shell rigid strength and reduce the deformation, the kiln shell will be welded, the high quality steel board will be used, for example, 16Mn or QZ235C, and the thickness of kiln shell steel board ought to increase properly. Ingeneral condition, the thickness of steel board under the tyre : for ∅4M and below rotary kiln , the relative thickness σ/D=0.012/0.015, σ is thickness of steel board, D is diameter of kiln; for∅4M and above rotary kiln, the relative thickness σ/D=0.015/0.020.