There are many performance testing methods for powder coatings. This article mainly introduces the surface fineness testing method.
(1) Definition Apparent density refers to the mass of powder per unit volume.
(2) Instruments Fineness board, density cup.
(3) Test procedure Place the funnel vertically, with the lower opening directly above the measuring tube, with a distance of 25-30mm, and the two are coaxial.
Loosen the powder to be tested, measure out 110~120mI (more if necessary) powder sample with a measuring cup, block the lower opening of the hopper with a sealing plate, and pour the powder sample into the hopper. Quickly remove the sealing plate to let the powder sample flow into the measuring cylinder. If necessary, use a small stick to loosen the powder sample in the funnel to help flow out. When the graduated cylinder is full, level the surface with a ruler. Use a balance to weigh the mass of the powder, accurate to 0.1g, and repeat the measurement 2 times. (Related instrument: specific gravity cup)
(4) Results The apparent density of the tested paint was calculated according to the following formula:
①Stacked sieve screening Place the selected set of sieves up and down in order of aperture size, with the smallest aperture at the bottom, and pour the powder sample into the uppermost sieve.
②Single sieve: Pour the powder sample into a sieve with a smaller aperture for sieving, and then pour the residue into a sieve with a larger aperture for sieving, until all the sieves are used.
Load the receiving tray under the sieve or single sieve, put the cover on it, and hold it with one hand when sieving. If it is too heavy, it can be installed on the most pipe hanger, and the screen surface should be kept at an inclination angle of 10°~20°, and the screen should be tapped lightly by hand, about 120 times per minute. After every 30 times, place the sieve in a horizontal position, and then re-pat the sieve frame by hand after turning a 90° angle or give periodic vertical vibration; it can also be held and shaken 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, composition and sieving method of the powder, and the sieving end point is judged by 1% of the amount of the minority seed feed of the powder within 1 min.
After sieving, the sieve or pan and the powder therein can be weighed together, and then the mass of the sieve or pan 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.
