凝结时间包括初凝时间和终凝时间。在标准稠度下，一般初凝时间不小于6min,终凝时间不大于25min。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。

Setting time includes initial setting time and final setting time. Under standard consistency, generally, the initial setting time is not less than 6min and the final setting time is not more than 25min. If the initial setting time in use is too short, less than 6min, it is proved that the gypsum powder is not cooked and mixed, or there is raw stone in the damp interior, which affects the injection molding operation, which is manifested in the barrel injection during production and delays the production; If the final setting time is too long, which is far greater than 25tnin, it indicates that the gypsum is burned during frying, which contains burned gypsum, which is easy to leak slurry during injection molding, or even the gypsum slurry does not solidify, affecting production.

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。简易测定方法如下：

The gypsum powder in both cases cannot be used in production. Therefore, the determination of setting time can determine the quality of gypsum powder or whether the gypsum powder can be used in production. The simple determination method is as follows:

（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进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；

(1) Weigh the gypsum powder sample required for 100ml of water according to the proportion of paste and water produced, pour the water into a 500ml container, evenly sprinkle the sample into the water within 1min, stand for 30s, quickly stir for 30s, and immediately pour the gypsum slurry into the copper tube placed on the glass plate, and then slowly lift the copper tube vertically for 20mm to make the gypsum slurry flat into a test cake with a thickness of about 5mm;

（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；

(2) Cut the test cake with a glass rod with a diameter of about 5nun, once every 30s, and wipe the glass rod with a cloth after each scratch. When the slurry on both sides of the scratch just no longer closes, it is the initial setting. The initial setting time is the time interval from the time when the sample is put into water to the initial setting;

（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分出现时即为终凝。以试样投进水中开始至终凝的时间间隔就是终凝时间。

(3) On the test cake after determining the initial setting, use your thumb to press it continuously with a force of about 50N at an interval of 15s. When you press it until there is no water at the edge of the impression, it is the final setting. The time interval from the time when the sample is put into water to the final setting is the final setting time.

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。

According to the comparison between the test results and the quality standards or the setting time of gypsum powder in normal mass production, the quality of gypsum powder can be determined and whether it can be used in production.

此外还能通过外观上观察和手感可初步判断济南石膏粉质量的优劣。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。

In addition, the quality of Jinan gypsum powder can be preliminarily judged by appearance observation and hand feeling. It depends on the appearance and color of gypsum powder. The feeling is to rub the roughness (fineness) of gypsum powder by hand. In appearance, gypsum powder with high whiteness has high fineness, good quality and high price; The quality of gypsum powder that is grey and black with black impurities is poor. Twist the gypsum powder with the thumb and index finger of the hand. The gypsum powder with rough hand feel is coarse in fineness, poor in quality and low in price; The gypsum powder with fine hand feel shows that the fineness is fine, the quality is good, and the price will be higher.

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