測定石膏粉的結晶水含量

Determination of crystal water content of gypsum powder

濟南石膏粉是一種結晶混合物，含有生石膏、半水合物和硬石膏（超煅石膏）。在炒制過程中，在火下會出現石膏，或者火太大、炒制時間過長會出現無水石膏，影響石膏的凝固時間，影響生產的正常使用。有時由于石膏粉放置時間過長受潮，也會影響正常使用。

Jinan gypsum powder is a crystalline mixture containing raw gypsum, hemihydrate and anhydrite (super calcined gypsum). In the process of frying, gypsum will appear under the fire, or anhydrous gypsum will appear if the fire is too large and the frying time is too long, which will affect the setting time of gypsum and the normal use of production. Sometimes the gypsum powder will be affected by damp due to its long storage time, which will also affect its normal use.

據經驗和資料介紹，石膏粉的好壞可以通過測定結晶水的含量來判斷。一般合格石膏粉的結晶水含量在4.5-5.5%之間。如果石膏粉的結晶水含量遠低于這個標準值，說明石膏粉過燒，注塑時凝固時間過長甚至不凝固；石膏粉的結晶水含量遠高于這個標準值，說明石膏粉在火或潮濕下，注塑成型時凝固時間短。以上兩種情況的石膏粉不合格，不能用于生產。

According to experience and information, the quality of gypsum powder can be judged by measuring the content of crystal water. Generally, the crystal water content of qualified gypsum powder is between 4.5-5.5%. If the crystal water content of gypsum powder is far lower than the standard value, it indicates that the gypsum powder is burned, and the solidification time is too long or even does not solidify during injection molding; The crystal water content of gypsum powder is much higher than this standard value, which indicates that the solidification time of gypsum powder during injection molding is short under fire or humidity. The gypsum powder in the above two cases is unqualified and cannot be used in production.

石膏粉結晶水含量的檢測方法如下：精密稱取試樣質量G（一般為2-5g），經40℃干燥后冷卻至室溫，置于鉑坩堝（或瓷坩堝）中)恒重。準確稱量其質量為G1；在230±5℃下燒2h，取出轉移到干燥器中，冷卻至室溫后稱重質量為G2，其結晶水百分比為（Gt-G2）/GX100%。

The test method for the crystal water content of gypsum powder is as follows: accurately weigh the sample mass g (generally 2-5g), dry it at 40 ℃, cool it to room temperature, and place it in a platinum crucible (or porcelain crucible) for constant weight. Accurately weigh its mass to G1; Burn it at 230 ± 5 ℃ for 2h, take it out and transfer it to a dryer. After cooling to room temperature, the weight is G2, and the percentage of crystal water is (gt-g2) /gx100%.

測定石膏粉的凝結時間

Determination of setting time of gypsum powder

濟南石膏粉的凝固時間包括初凝時間和終凝時間。標準稠度下，一般初凝時間不小于6min，終凝時間不大于25min。使用中初凝時間過短，小于6min，說明石膏粉未熟，或潮濕中含有生石，影響注塑操作，表現為生產時注桶，延誤生產;如果終凝時間過長，遠大于25tnin，說明石膏在油炸過程中過燒，其中含有過燒石膏，在注塑成型時容易漏漿，甚至石膏漿也會漏漿。不凝固，影響生產。

The setting time of Jinan gypsum powder 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. The initial setting time in use is too short, less than 6min, indicating that the gypsum powder is not mature, or there is green stone in the wet, which affects the injection molding operation, which is manifested as barrel injection during production, delaying production; If the final setting time is too long, which is far greater than 25tnin, it indicates that the gypsum is burned during the frying process, which contains burned gypsum. It is easy to leak slurry during injection molding, and even the gypsum slurry will leak slurry. No solidification, affecting production.

兩種情況下的石膏粉都不能用于生產。因此，凝固時間的確定可以判斷石膏粉的質量，也可以決定石膏粉能否用于生產。簡單的測量方法如下

In both cases, gypsum powder cannot be used for production. Therefore, the determination of setting time can determine the quality of gypsum powder and whether gypsum powder can be used in production. Simple measurement methods are as follows

(1)按制得的膏體與水的比例稱取100ml水所需的石膏粉試樣，將水倒入500ml容器中，1min內將試樣均勻灑入水中，靜置30s，快速攪拌30s，立即將石膏漿倒入放置在玻璃板上的銅管中，然后將銅管慢慢垂直向上提起20mm，使石膏漿壓平成約5mm厚的試餅；

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

(2)用直徑約5nun的玻璃棒切試餅，每30s一次，每劃一次后用布擦拭玻璃棒。當劃痕兩側的漿液剛剛不再合攏時，即為初凝狀態。試樣放入水中至初凝的時間間隔為初凝時間；

(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 is no longer closed, it is in the initial setting state. The time interval between putting the sample into water and initial setting is the initial setting time;

(3)初凝后的試餅，用大拇指以約50N的力連續按壓，間隔15s，當壓印邊緣無水分時，即為終凝。終凝時間是從樣品開始入水到終凝的時間間隔。

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

根據檢測結果與質量標準或石膏粉在正常規模化生產中的凝固時間值的比較，可以判斷石膏粉的質量是否可以用于生產。

According to the comparison between the test results and the quality standards or the setting time of gypsum powder in the normal large-scale production, we can judge whether the quality of gypsum powder can be used in production.

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