The main causes of longitudinal cracks in the rotary kiln shell are caused by insufficient rigidity of the shell, large temperature stress and additional stress. Therefore, in the design and manufacture process of the rotary kiln, the thickness of the cylinder shell should be appropriately increased. According to the relevant information, the thickness of the kiln shell under the tyre should not be less than 1.5% of the nominal diameter of the cylinder. The thickness of the stopper of the floating pad should not be greater than 50% of the thickness of the cylinder, and the width of the stopper should not be greater than 200mm, to reduce the additional stress and temperature stress caused by uneven deformation of the cylinder because of the support reaction force. The area of the pad should not be lower than 60% of the internal control surface area of the tyre, and the height of the weld of the stopper and the cylinder should be controlled at about 60% of the thickness of the stopper. And there shall be no defects such as undercuts to avoid local stress concentration and damage on cylinder.

In the installation process, not only the cold state accuracy should be considered, but also the hot state accuracy during operation. Predict the operating temperature of the tyre at each gear, calculate the amount of center rise in the hot state of each gear, and make installation adjustment, to make the force on the rotary kiln at each gear in the long-term operation is close to the design level, avoiding excessive cracking due to the increase of the center of a certain gear; in the production and maintenance, protect the kiln skin and the refractory brick, to prevent the cylinder from the large axial and axial temperature difference which will cause the cylinder to bend, and result in the additional stress because of limited expansion and contraction of local cylinder. When the rotary kiln is faulty, such as the watt heat, it must not be unloaded regardless of the cause, causing the cylinder to deviate from the center line. It is also impossible to cool the cylinder sharply when the red kiln or cylinder temperature is too high.

 

In order to prevent the circumferential crack, the thickness of the cylinder should be fully considered in the design and manufacture. The thickness of the transition cylinder should be close to the average of the thickness of the lower cylinder and the thickness of the intermediate cylinder to facilitate the smooth deformation, and the stress is easy to spread and reduce the stress concentration. The key to prevent the crack at the weld between the cylinder and the spring plate of the large ring gear is to ensure that the rigidity of the cylinder is greater than the stiffness of the spring plate. The thickness of the cylinder under the large ring gear should not be lower than the 1% of the nominal diameter, the thickness of the spring plate should be about 60% of the thickness of the cylinder, which is beneficial to digest the external force through the deformation of the spring plate, to alleviate the damage of the external force to the weld; in the production and maintenance, we must also ensure the longitudinal temperature of the cylinder The circumferential temperature difference is less than 50 °C, which reduces the additional bending stress and temperature difference stress. 

 

The main reason of cracks on the transition zone is that the cylinder is thinned by the corrosion of alkaline gas and alkaline materials in the kiln. Therefore, we must first consider the isolation of alkaline materials from the metal cylinder to reduce corrosion. There are several aspects of the measures. First, the high-temperature anti-corrosion coating can be painted on the inner surface of the cylinder; the second is to grout the wet refractory brick to eliminate the brick joint and isolate the alkaline material from the metal cylinder to prevent or relieve stress and chemical corrosion and prolong the life of the cylinder. It is also possible to extend the life of the cylinder by increasing the thickness of the cylinder (e.g., increasing the thickness of the cylinder to 0.7% of the nominal diameter of the cylinder).