(1 Scope
This standard specifies the determination method for the fluidity of powder/air mixture. This method reflects the commercial practice of powder spraying.
The conclusion obtained through the study is that the factors affecting fluidity include the component density, particle size and particle size distribution of powder materials, as well as the properties of particles coagulating and accepting frictional charges.
(2) Principle
A measured quantity of powder coating is placed in a container under dry conditions. Under the air pressure and temperature conditions specified in the standard, use clean dry air to fluidize, measure the height of the powder during and after fluidization and the velocity when the fluidized powder flows through a specific orifice.
The fluidization factor and the powder flow rate (flow factor) R, which define the powder delivery and sprayability, are calculated by the determination method.
(3) Equipment
① The equipment for testing fluidity is composed of a fluidization container with an annular powder outlet on the wall and an instrument for testing the powder height in the container. It also includes an instrument for weighing the amount of powder flowing through the nozzle.
Figures 6-13 are suitable designs, which are described below. Settings that give similar results can also be used.
A typical design is composed of each unit described below.
a. Fluidized powder container (container A): the outer diameter is about 110mm, the inner diameter is about 100mm, and the height is not less than 200mm. It is made of transparent polymethacrylate. The bottom is composed of a copper disc with uniform pores. The pore size is about 40µm0.
The bad-shaped powder outlet D with an outer diameter of 4mm can be plugged with a plug E, and its position on the container wall should be suitable, generally 10mm above the disc of the casting collar hole.
b. Air conditioning unit B: Use flow meter F to adjust the air flow.
c Container C: It must have sufficient volume to hold the powder that flows out during the test powder flow rate (see Figure 6-13).
②Supply of dry air: There must be enough supply for the test.
③Timer: accurate to ls.
④Analytical balance: the maximum weighing value is 500g, and it can weigh up to 0.lg.
⑤Test container: the equipment for powder height in A, the scale is in mm.
⑥ Paint scraper.
(4) Sampling
Follow the method described in lS08130-9 to take a representative sample of the test product.
Sufficient sample size should be taken for three tests with 0.
(5) Operation steps
①Equipment calibration
Calibrate the instrument at a temperature of 23°C and a pressure of 101.3kPa (see Appendix A).
② Fluidity test: Parallel test is carried out.
Plug the powder outlet D with the plug E, and fill the container A with 250g ± 10g powder coating sample.
Introduce clean and dry air through the bottom of the cast copper gap plate, the flow rate is subject to the good fluidization effect of the powder, usually (200L±10L)/h, pay attention to the air flow rate indicated on the flow meter F. To prevent flow grooves and air bubbles during fluidization, stir the powder with a paint scraper until the height of the powder fluidized bed remains constant at 0 during the stirring process.
For example, when the air flow rate is within the range of 190L/h to 200L/h, the fluidization effect of the powder is better, and an appropriate flow rate should be selected.
It is meaningless to directly compare the fluidization effect of powders when the air velocity is different.
Measure the fluidized height h of the fluidized bed powder, accurate to 2 mm, turn off the air flow and the powder is still (it takes 1 to 2 minutes), and measure the height h of the still powder. Accurate to within 2mm.
Fluidize the powder again at the same air flow rate, stir to help fluidize, wait until the fluidized powder reaches a constant level, pull the plug E from the powder outlet D, and press the timer at the same time. Collect the powder coming out of the powder outlet within 30s±1s, plug the powder outlet D with plug E, and weigh the collected powder (m) to the nearest 0.1g.
(6) Indication of results
① Calculation of fluidization factor is expressed by formula (612):
Arithmetic mean of the result. If the deviation between the first test result and the previous test result is greater than 5%, the phenomenon and individual results shall be recorded in the report.
Appendix A
Notes on equipment and operations
①The structure of the equipment: In order to prevent the difficulty of cleaning or the blocking of the special copper pore plate, it is strongly recommended that the air inlet part G (the bottom of the pore of the container A) should be detachable.
② Calibration: Usually the flowmeter F is calibrated with air under the temperature and pressure conditions specified in the standard. However, the flowmeter is not used under the conditions stipulated in the standard in most cases, so it is necessary to correct it in order to obtain the real flow rate of 200L/h. Assuming that c is the correction factor and g. is the required flow rate [such as 200I/h ± 10L/h is given in (5)②], then the flowmeter reading gf can be expressed by formula (6-14):
