Screening of Materials and Types of Screens...

Screening of Materials and Types of Screens Size control is done (i) to prevent undersize in the feed from blocking the next size reduction stage (scalping), (ii) to prevent oversize from moving into the next size reduction or operation stage (circuit sizing), and (iii) to prepare a sized product (product sizing). There are two methods dominating size control processes. They are (i) screening using a geometrical pattern for size control, and (ii) classification using particle motion for size control. Screening using geometrical patterns for size control (Fig 1) makes use of screening media made of bars, wires, and panels with holes usually rounds, squares, rectangle aligned to length and rectangle aligned to width. Fig 1 Geometrical patterns for the size control Screening is the process of separating solids into two or more products on basis of their size. The objective of screening is size control. The purpose of screening is to separate from a granular substance particles that are smaller than the screen opening from those that are larger. This is not as simple as it sounds, and the difficulties compound as the opening becomes smaller. This can be done dry or wet. Action of screening is aided when screen is subjected to some kind of motion, reciprocating or gyratory in the horizontal plane, or shaken with a reciprocating motion having both vertical and horizontal components. The minus particles pass through the screen at a diminishing rate until all but the particles closest to the opening size have been separated out. The time duration of the shaking to reach this stage is roughly proportional to the amount of the material on the screen. The performance of screens falls back on three main parameters namely (i) motion, (ii) inclination, and (iii) screening media. It is...