NYCOA TOPICS: Pelletization Technologies
A series of small colored plastic pellets.
Nylon polymerization is a fascinating intersection of chemistry, process optimization, and polymer performance. In many cases, the properties of specialty, engineered nylon resins are defined in the polymerization reactor; however, to deliver that value to their final application, they must be extruded into a final form - often, this means small pellets, round or oblong in shape and smaller than a pencil eraser. The means of producing these pellets also have important implications on their performance and usability, as these pellets are used around the world to be transformed through processes such as monofilament extrusion, foaming, injection molding, film extrusion, yarn threading, and fiber extrusion. In this post we want to share some introductory information about the world of pelletization, and how the process method for making resin pellets is an important choice.
Underwater pelletizers are a big investment, and often one of the more complex system options. Underwater pelletization is a submerged die-face pelletizer. The polymer is cut into pellets after being extruded through round die holes in a molten state. The process water then transports the spherical pellets from the cutting chamber to an agglomerate chamber which removes clumps of plastic. Then they are moved into a centrifugal dryer. Meanwhile the water exposed to the high temperature polymer is tempered to bring it back down in temperature. A potential downside is “die freeze off”. Where a disruption upstream in polymer flow causes polymer to harden inside the die and thus solidify clogging the die. The complexity of this system relates to the management of water temperature, bath composition, die condition, die geometry and die hole arrays - all can be changed to help optimize the extrusion of polymer
However, underwater pelletization running correctly has a number of benefits to offset the cost and complexity of the equipment. Underwater pelletization has higher throughput, the most automation options, a smaller footprint, and high consistency of pellet shape and size distribution. Additionally, thanks to the fact that they are spherical and cut in a liquid phase there is minimal dusting and an extremely low tendency towards clogging in hoppers or feeder chambers.
Water ring pelletization is a similar process that creates rounded but flat shapes like an aspirin tablet. Water ring pelletization is more compact and doesn’t suffer from die freeze. However, the production yield may be lower and the shape may be more prone to dusting and jamming in hopper feeds than the spherical shape of underwater pelletization.
Strand pelletization takes cooled polymers that have been extruded through a strand die and then cooled with water and cuts them once solidified into pellets. The pellets therefor have a cylindrical shape and flat ends. This technology is cheaper but has a lower throughput and a higher clogging potential and more dusting because the material is being sheared once it’s already solid. However, it has a low cost and is compatible with a wide variety of polymers. Strand pelletization also has more limitations in pellet size, as moving the stranded without breakage becomes extremely difficult past a certain size.
Conveyor belt pelletization deals with one of these issues. Instead of extruding the strands into a water bath they are extruded directly onto a conveyor belt. This allows extremely fragile strands to be transported to cutting blades without breakage, alleviating some of the risk of certain pellet sizes and allowing a wider range of strand pelletization.
Flake Barrel Production is slightly different from true pelletization, and may be something you observe in chemistries that may not be able to easily hold a pellet shape. In flake barrel production, a large cylinder is cooled and the chemical substrate is spread over it’s outer surface area. As it chills, the substrate solidifies and coats the cylinder. Finally, the cylinder is brought into close proximity to a blade or bar that shaves or “flakes” off the substrate, now solid, in a manner that can be conveyed and packed.
The exact methods of pelletization are going to vary depending on your material needs, your hopper feeds, how much dusting your machines can handle and your throughput. These factors along with many others will result in you getting the most out of your pellets in your manufacturing process. Hopefully, after reading this you have a better understanding of the current pelletization technologies and the different ways in which they are used and the applications for which they are most suited.
About NYCOA
NYCOA (the Nylon Corporation of America) commercially manufactures many grades of specialty engineered nylon, including nylon 6, nylon copolymers, filled and super-tough grades, nylon 6,10 and 6,12, and unique long-chain polyamide family NXTamid , and our unique flexible PEBA Nylon Ny-Flex. All NYCOA products are made in the USA, manufactured in our ISO plant located in Manchester, NH. NYCOA is dedicated to plastics engineering, plastics innovation, and a consistent quality earned through operational excellence. NYCOA is dedicated to its customers, and produces specialty engineered polymers for industries and partners around the world, and has plastics compounding capabilities to produce a variety of reinforced grades.
Nylon manufactures for many industries and applications, including fasteners, hook and loop, extruded parts, injection molding, athletic accessories, military and transportation applications, foamed components, monofilament, powders, and wire and cable jacketing.
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