What Are The Main Factors Affecting The Screening Process of A Granulator Filter?

Material Characteristics

Particle Size Distribution: The particle size distribution of a material is a crucial factor. More fine particles result in higher output. The permissible particle size should not exceed 2.5-4 times the sieve aperture. The fewer difficult-to-screen and obstructive particles in the material, the higher the screening efficiency. If the content of undersize particles in the material is low, productivity will decrease significantly. For example, in processing iron ore, if the content of fine particles is high, the screening efficiency will be correspondingly higher; conversely, if the proportion of coarse particles is large, the screening difficulty will increase. A coarse screen can be used to remove excessively coarse particles before further screening to improve productivity.

Moisture Content: When the moisture content in a material reaches a certain level, fine particles agglomerate, clogging the sieve apertures and drastically reducing screening capacity. However, if wet screening is used, the water flow promotes particle passage through the sieve apertures, and the screening efficiency may even exceed that of dry screening. Taking coal screening as an example, when the coal has a high moisture content, wet screening can effectively avoid sieve clogging and improve screening efficiency.

Screen-Related Factors

Screen Hole Shape, Size, and Screen Surface Type: Different screen hole shapes have different screening efficiencies. Rectangular holes are more efficient than square holes, square holes are more efficient than round holes, and square holes offer higher screening accuracy. For screen surfaces, woven screens are more efficient than plate screens, and plate screens are more efficient than grid screens. Larger screen hole sizes result in higher screening efficiency, but smaller screen holes lead to a sharp drop in productivity. When selecting a screen, the shape, size, and type of screen hole must be considered comprehensively based on the material characteristics and screening requirements. For example, in the food processing industry, square-hole screens may be chosen to ensure screening accuracy for materials with high particle size requirements; while rectangular-hole screens may be used in applications with high output requirements.

Effective Screen Area and Screen Surface Size: The ratio of the area of the screen holes to the total area of the screen surface is called the effective screen area. A larger ratio results in higher unit productivity and screening efficiency, but an excessively large ratio will reduce screen surface strength and service life. A longer screen surface results in a longer residence time for particles, increasing their chances of passing through the screen openings and thus improving screening efficiency. However, the efficiency improvement diminishes after a certain point in screen length; therefore, industrially used screens are generally no more than 2.5-3 times their width. When designing and selecting screening equipment, it is crucial to rationally determine the screen surface dimensions and effective screen area to balance screening efficiency and equipment performance.

Equipment Operating Parameters

Screen Surface Motion Characteristics: The relative motion between the screen surface and the material is essential for screening. This motion can be divided into two types: one where particles move primarily perpendicular to the screen surface, such as in vibrating screens; and another where particles move primarily parallel to the screen surface, such as in cylindrical screens and shaking screens. Practice has shown that the motion type with higher speed results in higher screening efficiency. This is because the material's perpendicular motion to the screen surface increases the material layer's looseness and segregation rate, and also increases the probability of particles passing through the screen openings, thereby improving screening efficiency. The frequency and amplitude of the screen surface's motion also significantly affect screening efficiency, influencing the particle speed and probability of passage on the screen surface. Generally speaking, materials with smaller particle sizes are suitable for vibration with small amplitude and high frequency. The vibration conditions should be limited to prevent material particles from jumping off the screen surface. Different types of screening equipment have different screen surface motion characteristics. When selecting equipment, it is necessary to choose the appropriate equipment type and operating parameters according to the characteristics of the material, such as particle size.