Extrusion Molding Extrusion Extrusion is a process in

Extrusion Molding

Extrusion: Extrusion is a process, in which polymer is propelled continuously along a screw through regions of high temperature and pressure where it is melted and compacted, and finally forced through a die shaped to give the final product.

Breaker Plate: The screens (a thick metal puck with many holes drilled through it) are reinforced by a breaker plate Functions of breaker plate: - The pressure can exceed 5000 psi (34 MPa). The screen pack/breaker plate assembly also serves to create back pressure in the barrel. - Back pressure is required for uniform melting and proper mixing of the polymer. -This breaker plate and screen pack combination also does the function of converting "rotational memory" of the molten plastic into "longitudinal memory".

Types of Extruder: 1. Single Screw Extruder. 2. Multiple Screw Extruder.

Co-extrusion: The process of extruding two or more materials through a single die with two or more orifices arranged so that the extrudates merge and weld together into a laminar structure before chilling. - Each material is fed to the die from a separate extruder. - Co-extrusion can be employed in film blowing, free film extrusion, and extrusion coating processes.

Coextrusion

Multi-manifold Die

Coextrusion Products: A film for packaging food may consist of three layers imparting, respectively, - high strength - low oxygen permeability - heat sealability

Sheet/Film Extrusion In sheet extrusion, these rolls not only deliver the necessary cooling but also determine sheet thickness and surface texture

• The molten plastic is pulled upwards from the die by a pair of nip rolls high above the die. • Around the die sits an air-ring. The air-ring cools the film as it travels upwards. • In the centre of the die is an air outlet from which compressed air can be forced into the centre of the extruded circular profile, creating a bubble. • This expands the extruded circular cross section. • The nip rolls flatten the bubble into a double layer of film. • This film can then be spooled or printed on, cut into shapes, and heat sealed into bags or other items.