Ventilation  pipes are mostly thin-walled, large-scale painting of the product, in  the production and use of the process often appear warping deformation  problems. The main reasons are the following four points:

① Magnesium cement in the natural conservation conditions, its volume  is a continuous expansion process, the linear expansion rate of 0.1 to  0.2%, the volume expansion rate of about 1%;

②  magnesite in the process of burning will inevitably produce local  overcooling, so that part of the MgO was dead burning state, over the  burning of the MgO hydration process is very slow, when the formation of  the strength of the cement in the MgO and then water for water , The formation of Mg (OH) 2, the volume expansion of 120%;

(3)  When the Ca (OH) 2 is converted into gypsum, the solid volume will  increase by more than 2 times, resulting in deformation of the product,  which is Limiting the free CaO content in the light burned magnesium oxide, the reason for the SO42- content in the halogen film;

④  MgO-Mg-C12-H2O system hydration process is a strong exothermic reaction  process, and the production of the pipe volume is large, if the ambient  temperature is high, the reaction temperature process, the plate body  temperature is too high, the reaction is not sufficient, resulting in Larger crystal stress and thermal expansion stress, so that the product volume expansion.