Screw Extruder

An extruder is basically a screw pump; the screw rotates in a tightly fitting stationery barrel. The semi moist feed or dry powder/grit or plastic is introduced into the extruder, usually at a constant rate of mass or volume employing a feeding mechanism. The material thus moves forward by the rotation of the screw. Heat is usually supplied externally to the extruder barrel, and is partly produced by viscous dissipation of mechanical energy. The control of temperature is required at different sections of the extruder and at the die end. The material thus undergoes several unit operations like mixing, compression, shearing, and cooking inside the extruder, and is finally shaped in the die through which the material is forced to exit under pressure. The extruder may also be considered as a continuous chemical or biochemical reactor. It can be involved in the conversion of a plasticized biopolymer based formulation into a uniformly processed viscoelastic mass that is appropriate for forming or shaping into products by a die. Sequential reactions/changes in a controlled manner may be obtained in specially designed modular machines like an extruder. It is one of the most versatile and well-recognized machines in the food and plastic industries for the last 40 years.