EuroWire Sept 2015

News Technology

Frigeco engineers redesign extruders

While the extruder is the melt supply device in most extrusion processes, the basic design has not evolved much over the last few years. Its purpose is to supply molten material at a constant melt temperature and at a constant volumetric rate. The typical extruder is made up of three geometric sections: The feed section or solids conveying, the transition or melting section, and the metering or pumping section. Frigeco has redesigned a number of areas on the Frigeco extruder:

• Feeding zone • Extruder barrel and screw profile • Thermoregulation • Stable and reactive electronics • Increased output and lower energy consumption

▲ ▲ Redesign work has been extensive from Frigeco

temperature. The next section is the transition zone, where a large amount of heat will be generated. Much of the heat necessary to plasticise the material comes from the rotation of the screw. The faster the screw rotates, the higher the surface speed of the screw, the greater amount of shear in the material and therefore an increase in melt temperature. The combination of rotational speed, adequate cooling and accurate temperature control will keep the shear rate down and prevent localised overheating. It is in this area that Frigeco engineers have done the most extensive research and redesign. Frigeco – Italy Website : www.frigeco.com

The actual melting takes place in the feeding zone. Most plastics are poor conductors of heat and are melted by shearing the material against the barrel rather than by heat conduction. Consistent flow of material into the extruder barrel is obtained by controlling the temperature of the feed throat. However, you cannot rely on plant water supply which can vary from 38ºF (3ºC) in the winter to 75ºF (24ºC) in the summer. These fluctuations in temperature will affect melt temperature and cause product variations. Therefore, controlling the temperature of the feed throat is essential to constant solids conveying. The Frigeco grooved feed throat, integral cooling jacket and closed loop water temperature control circuit provide a constant feeding zone

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September 2015