A woven, fabriclike structure made of intersecting strands of wire or plastic, usually mounted in a steel frame. They are available in a wide range of sizes, weaves, and meshes from as coarse as 25 to as fine as 400. The mesh is the number of apertures per square inch; it is the square of the number of strands of metal or plastic per linear inch. The strands can be made of any suitable metal (copper, nickel), alloy (steel, bronze), or synthetic (nylon, PVC). Some types of screen are mechanically vibrated or gyrated to facilitate solids separation; fine mesh screens require application of force, such as a stream of water, to effect separation. Screens are used for filtration, clarification of suspensions, separation and classification of solids, and removal of contaminants from semisolid materials. Lab sizes are available. A special application is the wire of a fourdrinier papermaking machine; it may be 38–60 inches. wide and 55–85 mesh; it moves continuously over return rolls, the sheet being formed upon it by filtration of wood pulp slurry.See Filter Medium.
