The purchase of gypsum powder only depends on the scope of gypsum powder manufacturers? In fact, otherwise, the selection of gypsum powder is comparable and exquisite, there are also parameters to refer to, can be selected according to my needs, today we will understand the crystalline water content and surface hardness of gypsum powder.

　　結晶水含量

　　Crystalline water content

　　石膏粉是一種結晶混合物，由于炒制工藝的不同，其內會含有生石膏(CaSO4·2H2O)、半水石膏(CaSO4·0.5H2O)和無水石膏(CaSO4，也稱過燒石膏)。在炒制過程中欠火發嫩有生石膏，或者火大、炒制時間過長形成過燒有無水石膏，這都影響石膏的凝結時間，影響消費正常運用。有時由于石膏粉放置時間過長受潮，也影響正常運用。經過測定結晶水的含量，可判別石膏粉質量的優劣。普通合格的石膏粉結晶水的含量在5.2%～6.2%。

　　Gypsum powder is a kind of crystalline mixture. Because of the different stir-frying process, it will contain raw gypsum (CaSO4.2H2O), hemihydrate gypsum (CaSO4.0.5H2O) and anhydrous gypsum (CaSO4, also known as burnt gypsum). In the process of stir-frying, there are raw gypsum under fire and tender, or over-heated and over-stir-frying for too long to form anhydrous gypsum, which affects the setting time of gypsum and the normal use of consumption. Sometimes the plaster powder is damped for too long time, which also affects its normal use. The quality of gypsum powder can be judged by determining the content of crystalline water. The content of crystalline water in common qualified gypsum powder ranges from 5.2% to 6.2%.

　　外表硬度

　　Surface hardness

　　石膏模的外表硬度直接影響到其運用壽命和坯體的質量。由于模型在運用中不時地擠壓、擦模、泥漿腐蝕，會使工作面磨損，呈現麻面，招致模型報廢。丈量模型外表硬度的辦法有劃痕硬度法和耐磨耗性兩種。劃痕硬度是在丈量尺寸穩定性后，用劃痕硬度實驗機，測定荷重50g時被劃起傷痕的幅度，數值愈小，表示資料的外表硬度愈高。耐磨耗性是在丈量尺寸穩定性后，將其試體外表往復平磨30次，測定其重量減少率，數值愈小，闡明試樣的外表硬度愈高。普通石膏模在規范稠度下的劃痕硬度在0.21mm左右，耐磨耗性在13.4%左右。

　　The surface hardness of gypsum mould directly affects its service life and the quality of green body. Because the model is extruded, scratched and mud corroded from time to time in use, the working face will be worn out, showing a hemp surface, which will cause the model to be abandoned. There are two methods to measure the surface hardness of the model, scratch hardness method and wear resistance method. Scratch hardness is the extent of scratch when the load is 50g measured by scratch hardness testing machine after measuring dimensional stability. The smaller the value, the higher the surface hardness of the data. The wear resistance is to grind the surface of the specimen 30 times after measuring the dimensional stability, and determine the weight reduction rate. The smaller the value, the higher the surface hardness of the specimen. The scratch hardness of plaster mould is about 0.21 mm and the wear resistance is about 13.4% under the standard consistency.

　　其實，依據石膏粉的結晶水含量與外表硬度也能間接的判別石膏粉的好壞，這關于采購檢驗石膏粉質量的人來說，也算是一個方法。

　　In fact, the quality of gypsum powder can also be indirectly judged based on the crystalline water content and surface hardness of gypsum powder, which is also a method for purchasing and testing the quality of gypsum powder.