1、从外观上判断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）。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。

　　1. From the appearance, 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. Visually, gypsum powder with high whiteness has a high fineness and mesh count, 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 stone tone powder indicates fine fineness, good quality, and higher price.

　　2、测定结晶水含量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。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。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%。

　　2. Determination of Crystalline Water Content: Gypsum powder is a crystalline mixture that contains gypsum, hemihydrate gypsum, and anhydrous gypsum (burnt gypsum). 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. The content of crystallization water in generally qualified gypsum powder is 4 5~5 Between 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. The method for detecting the crystal water content of gypsum powder is as follows: accurately weigh 4 (the sample mass G (usually 2-5g) cooled to room temperature after TC drying, place it in a constant weight platinum crucible (or ceramic crucible), accurately weigh its mass as G1; burn it at 230 ± 5 ° C for 2 hours, take it out and transfer it to a dryer, cool it to room temperature, and weigh its mass as G2, then its crystal water percentage content is (Gt-G2)/GX100%.

　　3、测定石膏粉的凝结时间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。如果在使用中初凝时间太短， 小于6min,则证明石膏粉没有炒熟夹生，或受潮内部含有 生石裔，影响注模操作,表现为生产中注桶，耽误生产;若 终凝时间太长，远大于25tnin,则说明石膏在炒制时过烧， 里面含有过烧石膏，表现为注模时易漏浆,甚至石膏浆不 凝固，影响生产。这两种情况的石膏粉在生产中都不能使用。故通过 凝结时间的测定可判定石膏粉质量的优劣或者决定该石 膏粉在生产中能否使用。简易测定方法为：（1)按生产的膏水比例称取100ml 水所需的石膏粉试样，把水注入500ml容器中，将试样在 lmin内均匀地撒入水中，并静置30s,快速搅拌30s，并 把石膏浆体立即倒人放置在玻璃板上的铜管内，随后缓 慢垂直向上提起铜管20mm,使石膏浆体平铺成厚约5mm 的试饼；（2)用直径约5nun的玻璃棒划割试饼，间隔30s 划一次,每次划后用布将玻璃棒擦净。当划痕两边的料浆 刚好不再合拢时即为初凝。以试样投入水中开始至初凝 的时间间隔就是初凝时间；（3)在测定初凝后的试饼上用 大拇指以约50N的力连续按压，间隔15s—次，当按压至 印痕边缘没有水份出现时即为终凝。以试样投人水中开 始至终凝的时间间隔就是终凝时间。根据检测结果与质量标准或与正常大生产中时的石 膏粉的凝结时间数值进行对比，即可判定石膏粉质量的 优劣和决定其在生产中能否使用。

　　3. The determination of the setting time of gypsum powder includes initial setting time and final setting time. The quality standard for the setting time of gypsum powder is: at 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. It is not appropriate to have a short initial setting time or a long final setting time. If the initial setting time during use is too short, less than 6 minutes, it indicates that the gypsum powder has not been cooked and mixed with raw materials, or that it has been affected by moisture and contains raw stones inside, which affects the injection molding operation and causes delays in production; If the final setting time is too long, much greater than 25tnin, it indicates that the gypsum was overheated during frying and contains overheated gypsum, which is prone to leakage during injection molding, and even the gypsum slurry does not solidify, affecting production. Both types of gypsum powder cannot be used in production. Therefore, the determination of setting time can determine the quality of gypsum powder or determine whether the gypsum powder can be used in production. The simple measurement method is as follows: (1) Weigh the gypsum powder sample required for 100ml of water according to the ratio of the produced paste to water, inject the water into a 500ml container, evenly sprinkle the sample into the water within 1 minute, let it stand for 30 seconds, quickly stir for 30 seconds, and immediately pour the gypsum slurry into the copper tube on the glass plate. Then slowly lift the copper tube up vertically by 20mm to flatten the gypsum slurry into a test cake with a thickness of about 5mm; (2) Cut the test cake with a glass rod with a diameter of about 5nm, and cut it every 30 seconds. After each cut, wipe the glass rod clean with a cloth. When the slurry on both sides of the scratch no longer closes, it is called initial setting. The time interval from the moment the sample is immersed in water to the initial setting is called the initial setting time; (3) Press continuously with your thumb at a force of about 50N on the test cake after initial setting, with intervals of 15 seconds. When there is no moisture at the edge of the imprint, it is considered final setting. The time interval between the sample being immersed in water and the final setting is called the final setting time. By comparing the test results with the quality standards or the setting time values of gypsum powder in normal large-scale production, the quality of gypsum powder can be judged and its suitability for use in production can be determined.

　　4、测定试饼直径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。实验检测时应固定水量 的大小,所采用的器具和实验方法应一致。在大生产石膏和水的比例下，若以生产中正常使用的合格石膏粉的试 饼直径为D，待检石膏粉试饼直径为d。如果d远远小于 D，甚至不流动平铺，则说明石膏粉质量不好,没有炒熟夹 生，或受潮内部含有生石膏，影响注模操作甚至不能使 用；如果d远远大于D,浆体很稀流动性强，则说明石膏 粉过烧，注模时凝结时间太长以至不凝固，也无法使用。用此方法也可以区分普通P石膏粉和高强度a石膏 粉。在同样的膏水比例下,若浆体流动性强、试饼直径大， 则证明是a石膏粉；反之，若浆体流动性差、甚至不流 动,试饼直径小,则证明是3石膏粉。

　　4. The diameter of the test cake can be determined based on the ratio of gypsum to water in production. By observing and measuring the diameter (flowability) of the test cake, the quality of gypsum powder can be judged and whether it can be used in production can be determined. The diameter of the test cake is related to factors such as water content, paste water ratio, and the quality of gypsum powder. The amount of water should be fixed during experimental testing, and the instruments and experimental methods used should be consistent. Under the ratio of gypsum to water in large-scale production, if the diameter of the test cake of qualified gypsum powder used normally in production is D, and the diameter of the test cake of the gypsum powder to be tested is d. If d is much smaller than D, or even does not flow and spread flat, it indicates that the quality of the gypsum powder is poor, it is not cooked properly, or it contains raw gypsum in the damp inner part, which affects the injection molding operation or even cannot be used; If d is much greater than D and the slurry is very thin and has strong fluidity, it indicates that the gypsum powder is overheated, and the setting time during injection molding is too long to solidify, making it unusable. This method can also distinguish between ordinary P gypsum powder and high-strength A gypsum powder. At the same ratio of paste to water, if the fluidity of the slurry is strong and the diameter of the test cake is large, it proves to be gypsum powder; On the contrary, if the fluidity of the slurry is poor or even does not flow, and the diameter of the test cake is small, it proves to be 3 gypsum powder.

　　5、生产中试注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。

　　5. During production, the trial injection is carried out according to the ratio of gypsum and water used in production, ensuring that the instruments, operators, equipment, and process methods used are consistent. A small tire master mold is selected for the trial injection of the production model, and compared with the casting process of qualified gypsum powder used normally in production. If the setting time of the tested gypsum powder is normal and reasonable, and the operation is smooth without pouring into the bucket, 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 be poured 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.

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