Extrusion

Extrusion is a process used to create objects of a fixed type. A material of some form is pushed or drawn through an extruder or a machine that is capable of setting a shape to those raw materials. This process is called as extrusion.

Extrusion may be continuous (theoretically producing indefinitely long material) or semi-continuous (producing many pieces). The extrusion process can be done with the material hot or cold.

There are various types of extrusion processes like:

1. Sheet Extrusion
2. Profile
3. Pipe
4. Over- Jacketing
5. Co-Extrusion
6. Lamination and coating
7. Blown film Extrusion
8. Cast Film Extrusion
9. Foam Extrusion
10. Calendering

Sheet Extrusion
Sheet extrusion is a technique for making flat plastic sheets from a variety of resins. Another market segment uses thick sheet for recreational applications and industrial materials like automotive dunnage, truck bed liners, playground equipment, pallets, and boats. The thinner gauges are thermoformed into packaging applications such as deli containers, drink cups, produce trays, baby wipe containers and margarine tubs. Flat sheet is welded into large containment systems for mining applications and municipal waste disposal which is the third primary use for extruded sheet which is a geomembranes system.

Profile Extrusion
Rubber Profile Extrusion is produced by forcing uncured rubber through a die under heat and pressure, to form a part with a uniform cross section. This uncured rubber is then run through a heating unit to initiate the chemical cross linking reaction that causes the rubber to cure.

Pipe Extrusion
The process of forcing the polymer melt through a shaping die that is circular is defined as Pipe extrusion. The extruder from the die is cooled, sized and the formed pipe is pulled to the winder or a cut off device with the aid of haul off device.

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.

Blown Film Extrusion
In blowing film a tubular cross-section is extruded through an annular die usually a spiral die which is drawn and inflated until the frost line is reached. To cool the material the extruded tubular profile passes through one or two air rings.

Cast Film Extrusion 
The cast film process is different from the blown film process through virtual unidirectional orientation and the fast quench capabilities.These characteristics allow a cast film line to operate at higher production rates while producing amazing optics. Cast Film Applications in food and retail packaging take advantage of these strengths.

Foam Extrusion
During the chemical foam extrusion process chemical foaming and plastic resin agents are mixed and melted. The chemical foaming agent decomposes liberating gas which is dispersed in the polymer, melts and expands upon exiting the die. Due to the insulation properties of the foam structure foamed profile extrusions require more intense cooling than solid profiles.

Calendaring
Calendering is a process that usually uses four heated rolls rotating at slightly different speeds. PVC is the most commonly calendered material. Again the material is fed into the rolls, heated and melted, and then shaped into sheet or film.