Ventilation ducts are mostly thin-walled and large painted products, which often experience warping and deformation issues during production and use. The main reasons are as follows: four points:

(1)鎂水泥的體積是在自然固化條件下的連續膨脹過程。線膨脹率為0.1-0.2%，體積膨脹率約為1%。

(1) The volume of magnesium cement is a continuous expansion process under natural curing conditions. The linear expansion rate is 0.1-0.2%, and the volume expansion rate is about 1%.

(2)在服務燃燒過程中不可避免地發生菱鎂礦的局部過燒，導致部分MgO處于死燃狀態。過度燃燒的MgO的水合過程非常緩慢。當具有強度的水泥石中的MgO再次被水水合時，形成Mg(OH)2，并且體積膨脹為120%。

(2) In the process of service combustion, local overburning of magnesite inevitably occurs, resulting in some MgO being in a dead burning state. The hydration process of excessively burned MgO is very slow. When MgO in high-strength cement paste is hydrated again by water, it forms Mg (OH) 2 and has a volume expansion of 120%.

(3)輕度燃燒氧化鎂中游離CaO的體積在水化過程中增加了90%，而SO42-存在于鹽水片中。當Ca(OH)2轉化為石膏時，固體體積將增加兩倍以上，導致產品變形。這也是限制輕微燃燒的氧化鎂和鹽水薄片中的SO42-中游離CaO含量的原因。

(3) The volume of free CaO in lightly burned magnesium oxide increased by 90% during the hydration process, while SO42- was present in saline solution. When Ca (OH) 2 is converted into gypsum, the solid volume will increase by more than twice, leading to product deformation. This is also the reason for limiting the free CaO content in SO42- in slightly burned magnesium oxide and salt water flakes.

(4)MgO-Mg-C12-H2O體系的水化過程是一個強烈的放熱反應過程，生產管道的體積很大。如果環境溫度高，則反應溫度升高。片材的整體溫度太高并且反應不充分，導致更大的結晶應力和熱膨脹應力，以及產品的體積膨脹。

(4) The hydration process of the MgO-Mg-C12-H2O system is a strong exothermic reaction process, and the volume of the production pipeline is large. If the ambient temperature is high, the reaction temperature increases. The overall temperature of the sheet material is too high and the reaction is not sufficient, resulting in greater crystallization stress and thermal expansion stress, as well as volume expansion of the product.

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