By observing the appearance and feeling, the quality of gypsum powder can be preliminarily judged. Visually, gypsum powder with high whiteness has high fineness, good quality, and high price; Gypsum powder that turns gray and black, with black impurities inside, has poor quality. Rubbing and twisting gypsum powder with the thumb and index finger of the hand, the texture of the gypsum powder is coarse and sandy, with poor quality and low price; And the delicate texture of Shiyin powder indicates fine fineness, good quality, and higher price.
Gypsum powder is a crystalline mixture that contains raw gypsum, hemihydrate gypsum, and anhydrous gypsum (calcined gypsum). During the frying process, if there is insufficient heat, gypsum may appear, or if the heat is too high or the frying time is too long, anhydrous gypsum may appear, which can affect the setting time of gypsum and affect the normal use of production. Sometimes, prolonged exposure to moisture can also affect normal use of gypsum powder. Based on experience and information, the quality of gypsum powder can be determined by measuring the content of crystalline water.
The setting time includes the initial setting time and the final setting time. The quality standards for the setting time of gypsum powder are: under 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. Short initial setting time or long final setting time are not suitable.
According to the ratio of gypsum and water in production, the quality of gypsum powder can be judged and its suitability for use in production can be determined by observing and measuring the diameter (fluidity) of the test cake. The size of the trial cake diameter is related to factors such as water volume, gypsum water ratio, and the quality of gypsum powder.
According to the ratio of gypsum and water in production, ensure that the instruments, operators, equipment, and process methods used are consistent. Select a small tire mold for trial injection of the production model, and compare it with the pouring process of qualified gypsum powder used normally in production. If the setting time of the tested stone powder is normal and reasonable, and the operation is smooth without pouring into the barrel, 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 pour 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.