Coperion's knife rotor minimises dust content of PVC pellets

Coperion's latest type of knife rotor of eccentric pelletising systems (EGR) makes it possible to produce extremely low-dust PVC pellets.

Rotating directly on the die plate of the EGR, the rotor permits particularly smooth and gentle cutting of temperature and shear-sensitive plastics such as medical grades. This greatly improves the quality and further processability of the pellets produced as compared to the types previously available.   

To achieve this progress, Coperion specified a special metal alloy and design for the production of both the new rotor and the knives mounted on it. Due to these technical optimisations the knives remain in particularly close contact with the die plate during operation. The result is very high cutting quality that forms the basis for achieving the desired substantial reduction of the proportion of fines in the pellets. 

Proportion of fines reduced down to detection limit 

As a general rule, the occurrence of such fines essentially depends on the PVC recipe used and the knife arm speed required to attain a particular pellet length. In practice it is possible to reduce the quantity of fines by adjusting the knife rotor, but not avoid them altogether. The consequences of these fines becoming detached during pneumatic conveying of the pellets is both increased waste and severe contamination of the conveying pipes and the cooler. A good deal of work and time may then be required for cleaning to avoid contamination on next product change. 

By contrast, Coperion's knife rotor/knife combination makes it possible to reduce the proportion of fines almost down to the detection limit across the whole spectrum of throughput rates and cutting speeds.  

Established and reliable compounding and pelletising technology  

Coperion developed the EGR eccentric pelletiser especially for operation in conjunction with its Kombiplast KP two-stage processing systems. With the combination of a twin screw extruder ZSK and a single-shaft discharge screw ES-A, these ensure the gentle build-up of pressure required by shear-sensitive compounds being pressed through the die plate of the EGR. All this adds up to a reliable, proven technology for the gentle and economical processing and pelletising of hard and plasticised PVC recipes, as well as of HFFR recipes or elastomer-based compounds. Coperion can draw on decades of experience in the design and construction of complete plants for the processing of temperature and shear-sensitive materials – from material handling and feeding, to dry blend production, compounding, and pellet cooling, to storage and filling.