Know more about Extrusion machinery

Extrusion is a process that differs from molding in that it is a continuous process in which products such as tubes, profiles, filaments and films are formed by forcing plasticized material through a forming orifice called a spinneret. It is used for thermoplastics as well as for elastomers and thermosets. The plasticizing extruder has three functions: first, it extracts the material in granules from the feeding system and conducts it at the time it compresses it and, at times, degasses it; secondly, it mixes and produces a homogeneous melt, and, third, it develops enough pressure to overcome the flow resistance of the open row, so that the profile emerges from the row continuously.

Extruders are also used to mix and granulate complexes, to form preforms for blow molding and to feed other machines, such as calendars. Some types are designed to combine polymerization, compounding and production in a single unit.

Hydraulic extruders are used for thermoplastics with very high melt viscosity, as in the case of PTFE piston extrusion. The Engel process uses two twin pistons that work in cycles to plasticize the mass adiabatically at pressures of 1000 N / mm in the shortest time. They can be used in some cases, for a very precise extrusion, gear pumps interposed between the extruder and the die that relieve the extruder of the work of generating sufficient pressure to supply a regular fusing current.

Extruders of one and several screws

The screw extruders can be equipped with one or more screws working in coordination. Its construction and size are designated internationally through numerical codes. According to Euro map 20, the first number gives the number of screws, the second its diameter in mm and the third the effective length of the screw as a multiple of the diameter. Thus, the denomination 2-90-20 indicates a two-screw extruder with 90 mm diameter and 1,800 mm effective length of the screw. The additional letter V indicates degassing cylinder. Multi-screw extruders require more gears and thrust bearings in the mechanism box and a cylinder section suitable for the type of screw. Otherwise, they have the same components as a single screw extruder. Power is supplied by infinitely variable switching motors or controlled by thrusters that control their speed. The hydraulic drive is used very infrequently. For more info click here.

Another system uses two extruders in cascade: the melt is fed from the first extruder, usually with a filter to eliminate impurities, while the second extruder effects the homogenization and the generation of pressure. The feed hopper is a separate component with water cooling around the feed neck. Those with one or two stages under vacuum, which can be heated for pneumatic feeding, allow obtaining significant increases in quantity and quality.