Extrusion

Name:
Extrusion
Detailed information:
A fundamental processing operation in many industries in which a material is forced through a metal forming die, followed by cooling or chemical hardening. The material may be liquid (molten glass or a polymer dispersion); a viscous polymer, as in injection molding; a semisolid mass, such as a rubber or plastic mix; or a hot metal billet. High-viscosity materials are fed into a rotating screw of variable pitch that forces the materials through the die with considerable pressure; a ram is used for metals at temperatures from 537 to 1093C. Film is made by passing a low-viscosity mixture through a narrow slit. Molten glass and polymer suspensions are forced through a nozzle having a tiny orifice (spinnerette); the latter are hardened after extrusion by immersion in a bath of formaldehyde or similar agent. Food items (spaghetti, etc.) are also extruded. Extrusion involves rheological principles of some complexity, critical factors being viscosity, temperature, flow rate, and die design.See Injection Molding.