How to identify the quality of gypsum powder?

1、測定結晶水含量

1. Determination of crystal water content

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。

Gypsum powder is a crystalline mixture containing raw gypsum, hemihydrate gypsum and anhydrous gypsum (overburned gypsum). In the process of frying, raw gypsum will appear when it is under fired, or anhydrous gypsum will appear when it is over fired due to high fire and too long frying time, which will affect the setting time of gypsum and the normal use of production. Sometimes the normal use will also be affected due to the moisture of gypsum powder due to too long storage time. According to the experience and data introduction, it can be judged by measuring the content of crystal water The quality of broken gypsum powder is good or bad. Generally, the content of qualified gypsum powder crystal water is between 4.5 ~ 5.5 ^ if the content of gypsum powder crystal water is far lower than this standard value, it indicates that the gypsum powder is over burned and the setting time is too long or even does not set during injection molding; if the content of gypsum powder crystal water is far higher than this standard value, it indicates that the gypsum powder is under fire or damp and the setting time is short during injection molding. The above two cases are different Gypsum powder is unqualified and cannot be used in production.

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。

The method to detect the crystal water content of gypsum powder is as follows: accurately weigh the mass g of the sample cooled to room temperature after drying 4 (TC) (generally 2? 5g), place it in a platinum crucible (or porcelain crucible) with constant weight, and accurately weigh its mass as G1; burn it at 230 ± 5 ° C for 2h, take it out and transfer it into a dryer, cool it to room temperature, and weigh its mass as G2, then the percentage content of crystal water is (gt-g2) / gx100.

2、測定石膏粉的凝結時間

2. Determination of setting time of gypsum powder

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。

The setting time includes the initial setting time and the final setting time. The quality standard of the setting time of gypsum powder is: under the standard consistency, the initial setting time is generally not less than 6min and the final setting time is not more than 25min. The appropriate setting time is the prerequisite and necessary condition for the normal use of gypsum powder in production. Too short initial setting time or too long final setting time is not appropriate. If the initial setting time is too short in use If the final setting time is too long, much more than 25 tnin, it indicates that the gypsum is over burned during frying and contains over burned gypsum, which is easy to leak slurry during molding, or even the gypsum slurry does not solidify, affecting the production.

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。

The gypsum powder in both cases can not be used in production. Therefore, the quality of gypsum powder can be determined by measuring the setting time, or whether the gypsum powder can be used in production.

3、從外觀上判斷

3. Judging from appearance

通過外觀上觀察和手感可初步判斷石膏粉質量的優劣。觀察就是看外觀包裝袋質量情況和石膏粉的外觀顏色，手感就是用手搓一搓石膏粉的糙細程度(細度）。

The quality of gypsum powder can be preliminarily judged by appearance observation and hand feeling. Observation is to see the quality of appearance packaging bag and the appearance color of gypsum powder. Hand feeling is to rub the roughness (fineness) of gypsum powder by hand.

(1)若包裝塑料編織袋的材質質量差、松軟強度低、做工粗糙、編織稀疏(單位面積內的經緯數目不達標）、顏色發灰綠黑色、內部沒有防潮塑料袋、出現撒料現象、三無產品或外觀標識(種類名稱、生產廠家、商標、重量、聯系方式等）不齊全的石膏粉則很大可能不符合質量標準、檔次質量差，質量穩定性也不能保證。反之，那些包裝塑料編織袋用材好、做工精致、顏色發白、強度高、編織經緯密集、內部有防潮塑料袋、封口嚴密、外觀印刷清晰、標識齊全、不撒料的石膏粉一般質量較好、檔次高，質量有保證。一般使用這種包裝袋的石裔粉白度高、細度細。若石膏粉是質量上乘的、高附加值的高強度石膏粉、特種石膏粉(如母模石裔粉、原模石膏粉或樹脂石膏粉），其價格很高,是普通石膏粉的3?9倍。

(1) If the packaging plastic woven bag has poor material quality, low soft strength, rough workmanship, sparse weaving (the number of longitude and latitude per unit area does not meet the standard), gray green black color, no moisture-proof plastic bag inside, scattering phenomenon, and no product or appearance identification (type name, manufacturer, trademark, weight, contact information, etc.) incomplete gypsum powder may not meet the quality standards, poor grade quality, and quality stability can not be guaranteed. On the contrary, those packaging plastic woven bags have good materials, exquisite workmanship, white color, high strength, dense weaving longitude and weft, moisture-proof plastic bags inside, tight sealing, and clear appearance printing The gypsum powder with complete marks and no material spreading is generally of good quality, high grade and guaranteed quality. Generally, the stone powder in this packing bag has high whiteness and fine fineness. If the gypsum powder is high-strength gypsum powder and special gypsum powder with high quality and high added value (such as master mold stone powder, original mold gypsum powder or resin gypsum powder), its price is very high, which is 3-9 times that of ordinary gypsum powder.

(2)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。

(2) In appearance, the gypsum powder with high whiteness has high fineness, good quality and high price; while the gypsum powder with gray and black hair and black impurities inside is of poor quality. Rubbing and twisting the gypsum powder with the thumb and index finger of the hand, the gypsum powder with rough hand feel has rough fineness, poor quality and low price; while the stone sound powder with fine hand feel shows fine fineness, good quality and high price.

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