Plastic Extrusion process

Extrusion is a continuous process which is used to produce both solid and hollow products that have a constant cross section. Examples are tubing, pipes, profiles (like window frames, curtain track), films, sheets, insulated wires etc. Extrusion process is as follows,

 

Operation procedure,

•        Fill hopper with plastic material
•        Plastic is then heated in the barrel gradually to the state that its’ able to flow sufficiently
•        Melt plastic is forced by screw press through the die and  cooling bath
•       Letting the product cool and cut to length

Extrusion rates normally vary between nine and sixty meters per minute. Thicker cross sections are extruded slowly because more time is required for initial heating and later cooling. Extruder is the main object in the extrusion process. Its main equipments are given in the figure.

Equipments of the extruder

Functions of the extruder screw is convey the resin through the extruder, mixing the ingredient together, build pressure in the extruder (so that resin will be pushed through the die), impart mechanical energy as part of the melting process. The screw can divide in to three zones according to its function. They are feeding zone which pulls the polymer pellets from the hopper, pre heat them and convey it to other zones, transition zone which compress the material conveys from the feed zone and so it has decreasing channel depth,   metering zone which is a having constant screw depth and very shallow flight depth as homogenize the melt and supply to die.

Zones of the extrusion screw