Extrusion

Extrusion is the process of forming a raw material into a product of uniform shape and density by forcing it through an orifice or die under controlled conditions. An extruder consists of two distinct parts: a delivery system which transports the material and sometimes imparts a degree of distributive mixing, and a die system which forms the material into the required shape. Extrusion may be broadly classified into molten systems under temperature control or semisolid viscous systems. In molten extrusion, heat is applied to the material in order to control its viscosity to enable it to flow through the die. Semisolid systems are multiphase concentrated dispersions containing a high proportion of solids mixed with a liquid phase.

Extrusion is achieved by formulation to control the viscosity of the semisolid mass.
Extrusion is a continuous process that affords a consistent product at high throughput rates. The process has diverse applications in a range of industries utilizing extrusion equipment specifically designed or adapted to form a particular product. A description of the different types of extruders is given here, along with details that illustrate the versatility of extrusion
processing.