Innovative Developments in Single Screw Extrusion

In single-screw extrusion, bettering economic efficiency is a priority for extrusion companies, in fact it is among the major production objectives for machine suppliers also. High economic effectiveness is achieved by low specific expense costs �i.e. related to melt throughput �and low operating costs. Optimum melt throughput with good melt quality for a given machine size, in addition to the ability to method a wide range of recycleables with the same screw, are factors which contribute to the economy of a machine. Different important aspects include low energy intake and low maintenance costs.

Innovative developments also contribute to greater economy in single-screw extrusion. From this background, this content presents a range of extruder pieces and process controls which enable the melt throughput to be increased for a wide range of thermoplastics and also ensure good melt quality. It addresses, on the one hand, the chance of increasing the melt throughput of polyolefins through a substantial go up in the screw quickness and, on the additional, increasing the melt throughput of engineering thermoplastics by processing them on a grooved barrel extruder. The trials were completed on a grooved barrel extruder built for these tests specially.

The design of the screw is explained in greater detail in another article being presented as of this conference. Two factors of particular importance in connection with the trials completed here are the superior melting capability of the barrier section, and the consistent implementation of the principle of a well balanced axial pressure account with low pressure by the end of the grooved feed section, that is achieved by a high conveying productivity of the subsequent barrier section and homogenizing components. For optimum material feed, the machine has an asymmetrical feed beginning with a feed pocket. The purpose of this screw design was to create it suitable for processing a broad spectrum of thermoplastics over a broad speed range. Table 1 shows the technical data of the test extruder.

With single-screw extruders of confirmed screw diameter, the melt throughput could be increased both by raising the precise through ghput per revolution and by increasing the screw swiftness. The torque which can be transmitted at the end of the screw, and the melting potential, however, limit the utmost specific throughput. The figures given by many extruder suppliers are nowadays more or less the same, and only small increases in specific throughputs can be expected nowadays.

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