1、 Accurate debugging of core parameters of equipment

The airflow system is the foundation for ensuring the fluidization state of materials and the prerequisite for uniform coating. Firstly, it is necessary to optimize the inlet air parameters: the inlet air velocity should be controlled within the range that allows the material to form a stable "boiling bed", generally 0.5-1.2m/s. If the air velocity is too low, it can easily cause material deposition, while if it is too high, it may cause excessive particle collision and damage. Suggest conducting a wind speed gradient test to determine the optimal value for material fluidization without significant entrainment. At the same time, it is necessary to regularly clean the air inlet filter and distribution plate to avoid blockage and uneven airflow distribution. Pulse blowback devices can be used to improve cleaning efficiency.

The commissioning of the spray system directly affects the contact effect between the droplets and materials. The atomization pressure needs to be adjusted according to the viscosity of the coating liquid, usually 0.2-0.4 MPa. When the viscosity is high, the pressure should be appropriately increased to ensure uniform droplet size (ideal range 10-50 μ m). The nozzle height and angle are equally critical. The nozzle should be located at the center of the fluidized bed, 15-25cm away from the material bed surface, and the angle should be adjusted to 30-45 ° to avoid direct impact of liquid droplets on the equipment wall or concentrated spraying in local areas. In addition, adopting a multi nozzle layout can expand the spraying coverage range, especially suitable for large equipment, and it is necessary to ensure that the flow rate of each nozzle is consistent.

2、 Adaptation and pretreatment of material characteristics

The inherent characteristics of the material have a significant impact on the uniformity of the coating. Excessive differences in particle size can lead to "graded fluidization", with large particles settling at the bottom and small particles suspended at the top, resulting in uneven coating. Therefore, before feeding, the material needs to be screened to control the particle size distribution RSD ≤ 20%, and if necessary, the particle shape can be optimized through pre granulation. At the same time, the moisture content of the material should be controlled between 5% and 10%. If it is too high, it may cause particle agglomeration, while if it is too low, it may affect the adsorption effect of the coating solution.

The optimization of the formula for coating solution cannot be ignored. Film forming materials with good compatibility with the material should be selected, such as hydroxypropyl methylcellulose, polyvinylpyrrolidone, etc., and the solid content of the coating solution should be controlled at 10% -20%. If the solid content is too high, it will increase the difficulty of atomization, and if it is too low, multiple sprays will be required to extend the production cycle. Adding an appropriate amount of plasticizer (such as polyethylene glycol) can enhance the flexibility of the coating layer and reduce the risk of cracking; Adding anti adhesive agents (such as talcum powder) can prevent particle adhesion and ensure smooth fluidization.

3、 Fine control of production process

Real time monitoring of material bed temperature is required during the production process, generally controlled at 40-60 ℃. Excessive temperature may cause rapid drying of the coating solution, resulting in rough skin; If the temperature is too low, it will cause excessive penetration of the coating solution, affecting the film-forming effect. It is recommended to use a PID temperature control system, combined with the linkage adjustment of inlet air temperature and induced draft air volume, to maintain stable bed temperature.

The material loading capacity needs to match the equipment capacity, usually 30% -60% of the effective capacity of the equipment. Insufficient loading capacity can lead to excessive material fluidization and severe particle collisions; Excessive flow will limit the space for material movement and result in insufficient fluidization. During the production process, the material fluidization status can be observed through a sight glass, and if necessary, the inlet air speed can be adjusted or additional materials can be added. In addition, the spraying rate should be reasonably controlled, following the principle of "slow fast slow". The initial slow spraying allows the material to adapt, the mid-term stable spraying ensures uniformity, and the later deceleration avoids excessive spraying.

Regular maintenance of equipment is the key to ensuring long-term uniformity of coating. Regularly check the wear of nozzles and replace clogged or damaged nozzles in a timely manner; Clean up residual materials on the inner wall of the equipment to avoid cross contamination; Verify temperature, pressure and other detection instruments to ensure accurate data. At the same time, establish a production process parameter database to record the optimal parameter combinations of different products, providing reference for subsequent production.