外观判断

　　Appearance judgment

　　通过外观上观察和手感可初步判断石膏粉质量的优劣。就是看石膏粉的外观颜 色，手感就是用手搓一搓石膏粉的糙细程度(细度）。

　　The quality of gypsum powder can be preliminarily judged by observing its appearance and feel. It depends on the appearance and color of the gypsum powder, and the feel is the roughness (fineness) of the gypsum powder when rubbed by hand.

　　外观上看，白度高的石膏粉细度数高，质量好，价格较高；而发灰发黑、里面有黑色杂质的石膏粉质量较差。用手的拇指和食指搓捻石膏粉,手感发沙粗糙的 石膏粉细度糙，质量较差、价格较低；而手感细腻的石膏粉说明细度细，质量较好，价格也会较高。

　　Visually, gypsum powder with high whiteness has a high degree of fineness, good quality, and a relatively high price; The quality of gypsum powder that turns gray and black with black impurities inside is poor. Rub and twist gypsum powder with the thumb and index finger of your hand. Gypsum powder that feels sandy and rough to the touch has a coarse fineness, poor quality, and lower price; The delicate texture of gypsum powder indicates fine fineness, good quality, and higher price.

　　测定结晶水含量

　　Determination of Crystalline Water Content

　　石膏粉是一种结晶混合物，其中会含有生石膏、半水石膏和无水石膏(过烧石膏）。

　　Gypsum powder is a crystalline mixture that contains gypsum, hemihydrate gypsum, and anhydrous gypsum (burnt gypsum).

　　在炒制过程中欠火夹生会出现生石膏,或者火大、炒制时间过长造成过烧会出现无水石膏，这些都会影响石膏的凝结时间,影响生产的正常 使用。有时由于石膏粉放置时间过长受潮,也会影响正常使用。根据经验和资料介绍,通过测定结晶水的含量，可判断石膏粉质量的好坏。一般合格的石膏粉结晶水的含 量在4.5?5.5%之间^若石膏粉的结晶水含量远低于此标 准值,则说明石膏粉过烧,注模时凝结时间太长甚至不凝 固;若石膏粉的结晶水含量远高于此标准值，则说明石膏粉欠火或者受潮,注模时凝结时间短。以上两种情况的石膏粉都不合格,在生产中不能使用。

　　During the frying process, insufficient heat can lead to the formation of raw gypsum, or excessive heat and frying time can result in the formation of anhydrous gypsum, which can affect the setting time of gypsum and the normal use of production. Sometimes, due to prolonged exposure to moisture, gypsum powder can also affect its normal use. Based on experience and information, the quality of gypsum powder can be determined by measuring the content of crystal water. What is the content of crystallization water in generally qualified gypsum powder at 4.5? Between 5.5% ^ If the crystalline water content of gypsum powder is much lower than this standard value, it indicates that the gypsum powder is overheated, and the setting time during injection molding is too long or even not solidified; If the crystalline water content of gypsum powder is much higher than this standard value, it indicates that the gypsum powder is undercooked or damp, and the setting time during injection molding is short. The gypsum powder in both of the above situations is unqualified and cannot be used in production.

　　检测石膏粉结晶水含量的方法是：精确称取4(TC 烘干后冷却至室温的试样质量G (—般为2?5g),放 置于恒重的铂金坩埚（或瓷坩埚）中，精确称取其质量 为G1;在230±5°C下灼烧2h，取出移人干燥器内，冷 却至室温后称取其质量为G2，则其结晶水百分含量为 (Gt—G2)/GX100%。

　　The method for detecting the crystal water content of gypsum powder is to accurately weigh 4 (the mass G of the sample cooled to room temperature after TC drying is generally 2-5 g), place it in a constant weight platinum crucible (or porcelain crucible), and accurately weigh its mass as G1; Burn at 230 ± 5 ° C for 2 hours, transfer to a dryer, cool to room temperature, and weigh its mass as G2. The percentage of crystal water is (Gt-G2)/GX100%.

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