Higher Throughputs in Compounding
With the new XX Series of twin-screw extruders, Leistritz intends to increase productivity in compounding. Higher throughputs, shorter changeover times and greater flexiblity of the compounding system will form the basis for this.
The throughput of twin-screw extruders is limited primarily by the screw shaft. The larger the free volume of the screw elements, the smaller the space available for the screw shaft and the splined connection. Changing from the symmetrical DIN profile to an asymmetrical spline arrangement improves force transmittal in the new XX Series from Leistritz. As a result, the stress is distributed more uniformly at critical locations. This has been confirmed through FEM calculations and load tests, reports Richard Steiner, Marketing Director of Leistritz Extrusionstechnik GmbH, in the February issue of the magazine Kunststoffe. It has also been possible to maintain the usual safety factors. Compared to previous machine series, the volume has increased by about 30%.
The article also points out that reducing the changeover times has a geater effect on the economics of a compounding line than the energy costs, for instance. To date, between two and four hours have been estimated for this work in many facilities. For larger systems, entire production shifts can be required. With the new system, changeover times are supposed to be reduced to 15 minutes. The calculation must take into account not only the extruder, but rather the entire compounding line. Accordingly Leistritz assumes responsibility for complete integration and offers compounders a turnkey system.
Exchange of screw elements is often quite simple. In contrast, the exttruder barrel is usually less accessible and for this reason is seldom modified. The new concept provides the operator with easy access to the processing unit. Moreover, workplace hygiene is improved, since the system is easy to clean.
In order to improve performance, the cooling must also be modified. Dissipation of the increased amount of heat from the drive necessitates removal of heat during special processing steps, so that temperature limits are not exceeded. Particular attention was devoted to cooling requirements when designing the new series. The layout of cooling channels, coolant flow rates and heat exchanger systems has been improved, resulting in up to 30% more cooling.