Coperion Werner & Pfleiderer: four lines already sold

Only just after launching its newly developed large-scale ZSK-NT compounding technology for difficult and highly demanding compounding applications when processing polyolefins, Coperion Werner & Pfleiderer GmbH & Co. KG, Stuttgart, has achieved an extraordinary success: within only a very short time, the company has sold four such lines, two of them with rated throughputs of over 50 tonnes/hour. This is all the more astonishing considering the fact that the ZSK-NT is based on a completely new concept. These orders again underscore the technology leadership of Coperion Werner & Pfleiderer and the trust that customers place in this company’s competence in process and machine technology. The first compounding line will go into operation in 2007. The ZSK-NT technology has already been approved by several licensors for the compounding of bimodal polyethylene for film and pipe applications.
The ZSK-NT is a two-stage compounding system comprising two ZSK MEGAcompounders, each featuring a relatively short processing section. In the first stage, the plasticizing of the polymer powder is done by means of a high-speed twin-screw compounder which is relatively small considering the high throughput, e.g. a ZSK 250 Mc with a 250 diameter screw rotating at speeds of up to 600 r.p.m. The second stage, for homogenizing and discharging the melt, is equipped with a larger ZSK extruder which operates at slower speed and high degree of fill, e.g. a ZSK 350 November 2006 Mc with screw speeds of between 80 and 150 r.p.m. For each of the two stages of the ZSK-NT, Coperion Werner & Pfleiderer have developed a whole series of special screw elements. Separating the process into two stages permits the use of screw configurations and process parameters optimally adapted to the different conditions that occur in the course of the process. The end result is an outstanding product homogeneity. In comparison with a conventional system – a compounder with a long processing unit and large diameter – the ZSK-NT achieves superior homogeneity with a reduced total energy input and hence a reduced thermal stress on the melt, especially when processing difficult products. The advantages of the ZSK-NT come into their own in particular when compounding bimodal polyethylene (PE), which, as a result of the special polymerizing process, comprises polymer chains of relatively low and relatively high molecular weight. The first stage of the compounding system gently plasticizes the polyethylene powder at a high screw speed. In the second stage, the slowly rotating screws, which are equipped with special screw elements, incorporates the high-molecular-weight PE particles and disperses them gently and evenly, and at low temperature, in the lower-molecular-weight matrix of the melt. The
result is a compound that can be processed without any further homogenizing into high-quality, gel-free products, such as pipes and films.

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