1、從外觀上判斷通過外觀上觀察和手感可初步判斷石膏粉質量的優劣。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目數高，質量好，價格較高；而發灰發黑、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；而手感細膩的石音 粉說明細度細，質量較好，價格也會較高。

　　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、測定結晶水含量石膏粉是一種結晶混合物，其中會含有生石膏、半水 石膏和無水石膏(過燒石膏）。在炒制過程中欠火夾生會 出現生石膏,或者火大、炒制時間過長造成過燒會出現無 水石膏，這些都會影響石膏的凝結時間,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。根據經驗和資料介紹,通過測定結晶水的含量，可 判斷石膏粉質量的好壞。一般合格的石膏粉結晶水的含 量在4. 5?5. 5%之間^若石膏粉的結晶水含量遠低于此標 準值,則說明石膏粉過燒,注模時凝結時間太長甚至不凝 固;若石膏粉的結晶水含量遠高于此標準值，則說明石膏 粉欠火或者受潮,注模時凝結時間短。以上兩種情況的石 膏粉都不合格,在生產中不能使用。檢測石膏粉結晶水含量的方法是：準確稱取4(TC 烘干后冷卻至室溫的試樣質量G (—般為2?5g),放 置于恒重的鉑金坩堝（或瓷坩堝）中，準確稱取其質量 為G1;在230±5°C下灼燒2h，取出移人干燥器內，冷 卻至室溫后稱取其質量為G2，則其結晶水百分含量為 (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、測定石膏粉的凝結時間凝結時間包括初凝時間和終凝時間。石膏粉凝結時 間的質量標準是：在標準稠度下，一般初凝時間不小于 6min,終凝時間不大于25min。適宜的凝結時間是石膏粉 在生產中正常使用的先決和必要的條件。初凝時間過短 或終凝時間過長都不合適。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,表現為生產中注桶，耽誤生產;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，表現為注模時易漏漿,甚至石膏漿不 凝固，影響生產。這兩種情況的石膏粉在生產中都不能使用。故通過 凝結時間的測定可判定石膏粉質量的優劣或者決定該石 膏粉在生產中能否使用。簡易測定方法為：（1)按生產的膏水比例稱取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 把石膏漿體立即倒人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；（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；（3)在測定初凝后的試餅上用 大拇指以約50N的力連續按壓，間隔15s—次，當按壓至 印痕邊緣沒有水份出現時即為終凝。以試樣投人水中開 始至終凝的時間間隔就是終凝時間。根據檢測結果與質量標準或與正常大生產中時的石 膏粉的凝結時間數值進行對比，即可判定石膏粉質量的 優劣和決定其在生產中能否使用。

　　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、測定試餅直徑按生產中石膏和水的比例，可通過觀察和測量試餅 的直徑大小（流動性）,來判斷石膏粉質量的優劣和決定 其在生產中能否使用。試餅直徑的大小與水量、膏水比例 以及石膏粉的質量等因素有關。實驗檢測時應固定水量 的大小,所采用的器具和實驗方法應一致。在大生產石膏和水的比例下，若以生產中正常使用的合格石膏粉的試 餅直徑為D，待檢石膏粉試餅直徑為d。如果d遠遠小于 D，甚至不流動平鋪，則說明石膏粉質量不好,沒有炒熟夾 生，或受潮內部含有生石膏，影響注模操作甚至不能使 用；如果d遠遠大于D,漿體很稀流動性強，則說明石膏 粉過燒，注模時凝結時間太長以至不凝固，也無法使用。用此方法也可以區分普通P石膏粉和高強度a石膏 粉。在同樣的膏水比例下,若漿體流動性強、試餅直徑大， 則證明是a石膏粉；反之，若漿體流動性差、甚至不流 動,試餅直徑小,則證明是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、生產中試注按生產中石膏和水的比例，確保所采用的器具、操作人員、設備和工藝方法一致，選擇一個小型胎型母模進行 生產模型的試注，與生產中正常使用的合格石膏粉的模 型澆注過程進行對比。若待測石裔粉凝結時間正常合理、 操作順利不注桶，則說明該石膏粉是合格的石膏粉;若待 測石膏粉凝結時間非正常，凝結時間太短注桶，或者凝結 時間太長甚至不凝固，這樣的石膏粉不合格，生產中絕對不能使用。

　　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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