凝結時間包括初凝時間和終凝時間。在標準稠度下，一般初凝時間不小于6min,終凝時間不大于25min。如果在使用中初凝時間太短，小于6min,則證明石膏粉沒有炒熟夾生，或受潮內部含有生石裔，影響注模操作,表現(xiàn)為生產(chǎn)中注桶，耽誤生產(chǎn);若終凝時間太長，遠大于25tnin,則說明石膏在炒制時過燒，里面含有過燒石膏，表現(xiàn)為注模時易漏漿,甚至石膏漿不凝固，影響生產(chǎn)。

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.

這兩種情況的石膏粉在生產(chǎn)中都不能使用。故通過凝結時間的測定可判定石膏粉質量的優(yōu)劣或者決定該石膏粉在生產(chǎn)中能否使用。簡易測定方法如下：

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)按生產(chǎn)的膏水比例稱取100ml水所需的石膏粉試樣，把水注入500ml容器中，將試樣在lmin內均勻地撒入水中，并靜置30s,快速攪拌30s，并把石膏漿體立即倒進放置在玻璃板上的銅管內，隨后緩慢垂直向上提起銅管20mm,使石膏漿體平鋪成厚約5mm的試餅；

(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)用直徑約5nun的玻璃棒劃割試餅，間隔30s劃一次,每次劃后用布將玻璃棒擦凈。當劃痕兩邊的料漿剛好不再合攏時即為初凝。以試樣投入水中開始至初凝的時間間隔就是初凝時間；

(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)在測定初凝后的試餅上用大拇指以約50N的力連續(xù)按壓，間隔15s—次，當按壓至印痕邊緣沒有水分出現(xiàn)時即為終凝。以試樣投進水中開始至終凝的時間間隔就是終凝時間。

(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.

根據(jù)檢測結果與質量標準或與正常大生產(chǎn)中時的石膏粉的凝結時間數(shù)值進行對比，即可判定石膏粉質量的優(yōu)劣和決定其在生產(chǎn)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.

此外還能通過外觀上觀察和手感可初步判斷濟南石膏粉質量的優(yōu)劣。就是看石膏粉的外觀顏色，手感就是用手搓一搓石膏粉的糙細程度(細度）。外觀上看，白度高的石膏粉細度數(shù)高，質量好，價格較高；而發(fā)灰發(fā)黑、里面有黑色雜質的石膏粉質量較差。用手的拇指和食指搓捻石膏粉,手感發(fā)沙粗糙的石膏粉細度糙，質量較差、價格較低；而手感細膩的石膏粉說明細度細，質量較好，價格也會較高。

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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