The particle size range of powder coatings and the proportion of particles of various sizes in the total amount are called particle size distribution.
Sieve: The size and aperture of the sieve shall comply with the provisions of GB000e-85 "Test Sieve". A circular sieve with a diameter of 200mm and a depth of 50mm is recommended for storage. The aperture and quantity of the sieve shall be selected according to requirements.
Industrial balance: Sensitivity 0.5g.
Seal sieves, catch pans and soft brushes.
Weigh out 100g, 0.5g powder sample, which can be sieved by stacked sieve or single-division sieve.
①Stacked sieves: Stack the selected group of sieves up and down in order of aperture size, with the smallest aperture at the bottom. The powder sample is poured into the top sieve.
②Single sieve sieving: pour the powder into the selected sieve with the smallest aperture for sieving, and the residue from the sieve is then put into a sieve with one size larger aperture for subdivision until all the sieves are used.
Stacked sieves or single sieves are installed under the receiving tray, and the amount is placed on top of it. It can be held with one hand when sieving, if it is too heavy, it can be installed on the product rack of the patient's arm, and the sieve surface should be kept at an inclination angle of 10°20°. Lift the sieve lightly by hand. Beat about 120 times per minute. After every 30 times, place the sieve in a horizontal position. After turning a 90° angle, re-pat the sieve frame with your hands or give periodic vertical vibrations. You can also shake it by hand. . If the powder is not easy to sieve out, you can lightly brush the bottom of the screen with a brush to help the powder fall.
The sieving time should be determined through experiments according to the type, thickness and decoration method of the powder. When the passing amount of the powder is less than 1% of the feed amount within 1 minute, it will be used as the end point of the sieving.
After sieving, the decoration or plate and the powder in it can be weighed together, and then the mass of the sieve or plate itself can be subtracted; the powder sample can also be taken out and weighed separately, but care should be taken to brush away the sticky powder.
Calculate the percentage of the remaining powder on each sieve to the total powder sample, and indicate the loss percentage of the stacked mass (including the powder weight in the pan). The loss should not exceed 2%, otherwise the weighing process should be carefully checked and retested if necessary.
吕仕铭 杜长森 周华 - 《《涂料用颜料与填料》》