There are many kinds of gypsum powder, such as medical gypsum powder, edible gypsum powder, gypsum powder for cement, etc. the conventional detection method of general gypsum powder is to judge from the color and hand feeling: generally, gypsum powder with high whiteness has fine fineness, good quality and high price; Gypsum powder for general handicrafts requires high whiteness and hardness, while gypsum powder with gray black and black impurities is of poor quality. Twist the gypsum powder with the thumb and index finger of the hand. The gypsum powder with rough hand feel has rough fineness, poor quality and low price; The gypsum powder with fine hand feel has fine fineness, good quality and high price.

具体的石膏粉的细度如何检测呢？宇恒建材总结了以下几个步骤：

How to detect the fineness of specific gypsum powder? Yuheng building materials summarizes the following steps:

①取待测石膏粉样品约60g置于电热鼓风干燥箱中，在40±4℃下烘干至恒重，将烘干后的试样放入干燥器中冷却备用（当有效干燥时间相隔1h的两次称量之差不超过±0.2g时，即为恒重）。

① Take about 60g of gypsum powder sample to be tested, put it into the electric blast drying oven, dry it to constant weight at 40 ± 4 ℃, and put the dried sample into the dryer for cooling and standby (it is constant weight when the difference between two weighings with an effective drying time interval of 1H does not exceed ± 0.2g).

②称取50±0.1g试样石膏粉置于筛内，用手指轻轻压碎团块，盖上筛盖，套上筛盘，按以下方法进行操作：一只手拿住筛，略为倾斜，摇动筛子，使其撞击另一只手，摇动的速度为每分钟125次，筛摆的幅度约为20cm。每摇动25次应使筛子向一定方向旋转90度角，使试样均匀散开（也可采用机械振动法过筛），直到筛到1分钟内通过筛子的试样少于0.1g时为止，称取筛上物质量（筛余），数值为0.01g。

② Weigh 50 ± 0.1g of sample gypsum powder and put it in the sieve, crush the mass gently with your fingers, cover the sieve cover, put on the sieve plate, and operate according to the following methods: hold the sieve with one hand, tilt it slightly, shake the sieve to make it hit the other hand, the shaking speed is 125 times per minute, and the swing range of the sieve is about 20cm. Rotate the sieve 90 degrees in a certain direction every 25 times to make the sample disperse evenly (mechanical vibration method can also be used for sieving), until the sample passing through the sieve within 1 minute is less than 0.1g, weigh the mass on the sieve (sieve residue), and the value is 0.01g.

③按以下公式计算筛余量:C=B/A×100%

③ Calculate the screen allowance according to the following formula: C = B / A × 100%

式中：C为筛余量，%；

Where: C is sieve residue,%;

B为筛上物的质量，单位为克（g）；

B is the mass of the material on the sieve, in grams (g);

A为试样石膏粉的原始质量，单位为克（g）；

A is the original mass of gypsum powder of the sample, in grams (g);

如果某种石膏粉之前不知道其细度（目数），可采用套筛（比如80目、100目、120目、140目、160目、180目等），机械振动法过筛，检测各筛目筛余量，以确定该石膏粉的细度（目数）到底是多少，也可以反映出该石膏粉的细度（颗粒）分布。

If the fineness (mesh) of a gypsum powder is not known before, a set of screens (such as 80 mesh, 100 mesh, 120 mesh, 140 mesh, 160 mesh, 180 mesh, etc.) can be used for screening by mechanical vibration method to detect the screen residue of each mesh, so as to determine the fineness (mesh) of the gypsum powder and reflect the fineness (particle) distribution of the gypsum powder.