Extrusion (processing technique)

In extrusion (comes from the Latin verb extrudere = thrust), plastics or other viscous curable materials, e.g. rubber, are pressed through a die in a continuous process. To this end, the plastic – the extrudate – is first melted by an extruder (also called a screw press or extrusion auger) by means of heating and inner friction and is homogenised. Further, the pressure necessary to flow through the die is also built up in the extruder. After leaving the die, the plastic solidifies, mostly in water-cooled sizing. Application of a vacuum causes the profile to be pressed against the sizing wall and therefore the shaping process is completed. This is often followed by a cooling section in the form of a cooled water bath. The cross-section of the resulting geometric body corresponds to that of the die or sizing used. Production tolerances within ±0.05 mm are possible. An analogous process based on the same master principle and used for the hot shaping of metals is called extrusion.

The merging of plastic melts of the same or different types before leaving the profile die is also called co-extrusion.

Extrusion can be used, for example, to produce seamless sheets, pipes and profile with a constant cross-section over their whole length , as well as for webs of plastic film or hoses of any length and mainly wound onto reels. For several years, profiles made from elastomers for vehicle seals have also been extruded with variable cross-section.

Plastic containers such as bottles or tubs, as well as fuel tanks are also made by extrusion. An extruded hose is enclosed by a mould and blown on the mould wall by means of compressed air. Which is why the term used is extrusion blowing .