Process of forming a continuous piece of plastic by forcing it through a shaping orifice with or without the presence of heat. The opening through which the resins are forced gives the product its form, resulting in consistent thickness and gauge control. more
Types of plastic extrusion
- Sheet Extrusion
Sheet extrusion is a technique for making flat plastic sheets from a variety of resins. The thinner gauges are thermoformed into packaging applications such as drink cups, deli containers, produce trays, baby wipe containers and margarine tubs. Another market segment uses thick sheet for industrial and recreational applications like truck bed liners, pallets, automotive dunnage, playground equipment and boats. The third primary use for extruded sheet is in geomembranes, where flat sheet is welded into large containment systems for mining applications and municipal waste disposal.
- Profile Extrusion
Rubber Profile Extrusion is accomplished 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
Pipe extrusion is defined as a process of forcing the polymer melt through a shaping die (in this case: circular). The extrudate from the die is sized, cooled and the formed pipe is pulled to the winder or a cut off device with the aid of haul off device.
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 film blowing a tubular cross-section is extruded through an annular die (usually a spiral die) and is drawn and inflated until the frost line is reached. The extruded tubular profile passes through one or two air rings to cool the material.
- Cast Film Extrusion
The cast film process differs from the blown film process through the fast quench and virtual unidirectional orientation capabilities. These characteristics allow a cast film line to operate at higher production rates while producing amazing optics. Applications in food and retail packaging take advantage of these strengths.
- Foam Extrusion
During the chemical foam extrusion process plastic resin and chemical foaming agents are mixed and melted. The chemical foaming agent decomposes liberating gas which is dispersed in the polymer melt and expands upon exiting the die. Typically foamed profile extrusions require more intense cooling than solid profiles due to the insulation properties of the foam structure.
Similar to extrusion but with much higher Strengths- even used to make road bridges. Glass or other fibres are incorporated into the extrusion and so loadings of up to 60% glass can be achieved with very good fibre alignment. Materials are generally thermosetting type materials such as epoxy.
Calendering is a process that usually uses four heated rolls rotating at slightly different speeds. Again the material is fed into the rolls, heated and melted, and then shaped into sheet or film. PVC is the most commonly calendered material.