Extrusion 4-2017

Portfolio of Pelletizers has Systems for every Type of Operation By Frank Asmuss, global product manager, BKG ® pelletizing systems, Nordson Corporation There exists a vast potential for pelletizing systems, driven by strong global growth in con- sumption of plastic products and a gathering trend toward meet- ing this demand through loca- lized polymer production. In countries where plastics con- sumption is growing most rapidly, more and more raw materials for plastic products will come from domestic resin manufacturers, compounders, and recyclers. A s the leading supplier of underwater pelletizing systems, Nordson Corporation is prepared to meet the full range of requirements that the huge and diversified global market can be expected to present. These may range from basic systems calling for minimal investment, to sophisticated and automated production lines, to fully engineered turnkey operations for high-volume producers serving multinational markets. Nord- son’s BKG ® range of underwater pelletizing systems has a tiered structure, with different types of equipment available for different levels of cost and sophistication. In addition to a comprehensive portfolio of underwater pelletiz- ing systems, Nordson offers related melt processing compo- nents as part of its Nordson Polymer Processing Systems (PPS) family of brands. These include Xaloy ® screws and barrels for extrusion and injection molding lines, BKG ® melt filtration sys- tems, melt pumps and polymer valves. Working with plastic producers and extrusion machinery OEMs, Nordson is prepared to recommend and design fully integrated underwater pelletiz- ing production operations. Underwater pelletizing: how it works In underwater pelletizing, molten thermoplastic is extruded or pumped through a die body containing holes arranged in a cir- cular pattern. The downstream die face is completely encapsu- lated in water, and as the molten material exits the die holes, it is immediately cut by a rotating cutter and quenched by the flowing water. The molten material solidifies, taking the shape of a sphere to minimize surface tension, thus creating a round pellet. These round pellets are then transported by water flow away from the cutting chamber and into a secondary step 28 Polymer Processing Extrusion 4/2017 Polygon Filter & Water Tank (Images: Nordson) where water and pellets are separated, most commonly by means of a centrifugal dryer. After exiting the dryer, the round pellets generally have very little surface moisture and are ready to be packaged in a container or transported to another pro- cess, if applicable. A consistent melt pressure is critical to maintaining a uniform pellet shape as well as avoiding freeze-off of the polymer in the die holes. In order to ensure the necessary constant melt pres- sure, Nordson can supply a BKG ® melt pump that rotates at a constant speed, metering a constant volume of polymer. This is an example of how customers benefit from the depth of pro- duct offerings within the Nordson PPS portfolio. One advantage of underwater pelletizing over the alternative method of strand pelletizing is that it can be used with materi- als over a wide range of viscosities, whereas very low-viscosity materials cannot form a strand, and highly filled materials cre- ate fragile strands. In fact, underwater pelletizing can be used not only for all thermoplastic polymers but also materials which behave like thermoplastics. Some examples include: polyole- fins, styrenics, PET, polyamides, PMMA, polycarbonate, TPEs and TPU’s, hot-melt adhesives, natural resins (e.g. chewing gum), PVC, and synthetic resins (e.g. epoxy resin). The spherical pellets formed in underwater pelletizing flow bet- ter than the cylindrical pellets created in strand pelletizing, re- melt with less energy, and package more densely. All three dif- ferences result in energy savings in comparison with strand pel- letizing. In addition, underwater pelletizing systems are more compact, and because they are totally enclosed systems, no dust or vapor emissions take place.