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.

　　结晶水含量

　　Crystalline water content

　　石膏粉是一种结晶混合物，由于炒制工艺的不同，其内会含有生石膏(CaSO4·2H2O)、半水石膏(CaSO4·0.5H2O)和无水石膏(CaSO4，也称过烧石膏)。在炒制过程中欠火发嫩有生石膏，或者火大、炒制时间过长形成过烧有无水石膏，这都影响石膏的凝结时间，影响消费正常运用。有时由于石膏粉放置时间过长受潮，也影响正常运用。经过测定结晶水的含量，可判别石膏粉质量的优劣。普通合格的石膏粉结晶水的含量在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响到其运用寿命和坯体的质量。由于模型在运用中不时地挤压、擦模、泥浆腐蚀，会使工作面磨损，呈现麻面，招致模型报废。丈量模型外表硬度的办法有划痕硬度法和耐磨耗性两种。划痕硬度是在丈量尺寸稳定性后，用划痕硬度实验机，测定荷重50g时被划起伤痕的幅度，数值愈小，表示资料的外表硬度愈高。耐磨耗性是在丈量尺寸稳定性后，将其试体外表往复平磨30次，测定其重量减少率，数值愈小，阐明试样的外表硬度愈高。普通石膏模在规范稠度下的划痕硬度在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.

　　其实，依据石膏粉的结晶水含量与外表硬度也能间接的判别石膏粉的好坏，这关于采购检验石膏粉质量的人来说，也算是一个方法。

　　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.