1、从外观上判断

1. Judging from appearance

通过外观上观察和手感可初步判断石膏粉质量的优劣。外观上看，白度高的石膏粉细度目数高，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；而手感细腻的石音 粉说明细度细，质量较好，价格也会较高。

By observing the appearance and feeling, the quality of gypsum powder can be preliminarily judged. Visually, gypsum powder with high whiteness has high fineness, good quality, and high price; Gypsum powder that turns gray and black, with black impurities inside, has poor quality. Rubbing and twisting gypsum powder with the thumb and index finger of the hand, the texture of the gypsum powder is coarse and sandy, with poor quality and low price; And the delicate texture of Shiyin powder indicates fine fineness, good quality, and higher price.

2、测定结晶水含量

2. Determination of crystal 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）。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。

Gypsum powder is a crystalline mixture that contains raw gypsum, hemihydrate gypsum, and anhydrous gypsum (calcined gypsum). During the frying process, if there is insufficient heat, gypsum may appear, or if the heat is too high or the frying time is too long, anhydrous gypsum may appear, which can affect the setting time of gypsum and affect the normal use of production. Sometimes, prolonged exposure to moisture can also affect normal use of gypsum powder. Based on experience and information, the quality of gypsum powder can be determined by measuring the content of crystalline water.

3、测定石膏粉的凝结时间

3. Determining the setting time of gypsum powder

凝结时间包括初凝时间和终凝时间。石膏粉凝结时间的质量标准是：在标准稠度下，一般初凝时间不小于 6min,终凝时间不大于25min。适宜的凝结时间是石膏粉 在生产中正常使用的先决和必要的条件。初凝时间过短或终凝时间过长都不合适。

The setting time includes the initial setting time and the final setting time. The quality standards for the setting time of gypsum powder are: under standard consistency, the initial setting time is generally not less than 6 minutes, and the final setting time is not more than 25 minutes. The appropriate setting time is a prerequisite and necessary condition for the normal use of gypsum powder in production. Short initial setting time or long final setting time are not suitable.

4、测定试饼直径

4. Measure the diameter of the test cake

按生产中石膏和水的比例，可通过观察和测量试饼的直径大小（流动性）,来判断石膏粉质量的优劣和决定 其在生产中能否使用。试饼直径的大小与水量、膏水比例 以及石膏粉的质量等因素有关。

According to the ratio of gypsum and water in production, the quality of gypsum powder can be judged and its suitability for use in production can be determined by observing and measuring the diameter (fluidity) of the test cake. The size of the trial cake diameter is related to factors such as water volume, gypsum water ratio, and the quality of gypsum powder.

5、生产中试注

5. Production trial injection

按生产中石膏和水的比例，确保所采用的器具、操作 人员、设备和工艺方法一致，选择一个小型胎型母模进行 生产模型的试注，与生产中正常使用的合格石膏粉的模型浇注过程进行对比。若待测石裔粉凝结时间正常合理、 操作顺利不注桶，则说明该石膏粉是合格的石膏粉；若待 测石膏粉凝结时间非正常，凝结时间太短注桶，或者凝结 时间太长甚至不凝固，这样的石膏粉不合格，生产中绝对不能使用。

According to the ratio of gypsum and water in production, ensure that the instruments, operators, equipment, and process methods used are consistent. Select a small tire mold for trial injection of the production model, and compare it with the pouring process of qualified gypsum powder used normally in production. If the setting time of the tested stone powder is normal and reasonable, and the operation is smooth without pouring into the barrel, it indicates that the gypsum powder is qualified; If the setting time of the tested gypsum powder is abnormal, the setting time is too short to pour into the bucket, or the setting time is too long or even does not set, such gypsum powder is unqualified and cannot be used in production.