MELT FILTRATION | MACHINERY
Increasing
demand for melt filters capable of processing highly contaminated recycled polymers is advancing screen changer developments, writes Mark Holmes
PHOTO: NORDSON POLYMER PROCESSING SYSTEMS Cleaning up in melt filtration
With quality demands intensifying, melt filtration is being used increasingly widely across the compounding industry. To ensure the most cost-effective production, melt filter and screenchanger manufacturers work hard to ensure their hardware integrates seamlessly within the compounding line. However, they are also being asked to deliver increased output, achieve finer filtration, and to be able to process ever more demanding materials. And, with the use of recycled polymer feedstocks rapidly increasing, screenchangers for compounding applications will need to be capable of handling higher levels of contamination than in the past. Designing screen changers and melt filters for plastics compounding applications presents a number of special issues, according to Dr Oliver Schmidt, Manager Product Management at Gneuss Kunststofftechnik. “Frequent colour and material changes in the compounding process require filtration systems with excellent purging properties and/or a design that allows easy mechanical cleaning,” he says. “In addition, sensitive polymers need good rheological properties in order to avoid any degradation during the filtration process,” Schmidt says. “Combined recycling and compounding is another important area for filtration, where high exchange rates for the screen area are required. Filter changes must not affect the upstream
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compounding process, through back pressure effects, as well as the downstream process. Finally, direct compounding – combined compounding and production to the final product – also requires a filtration system that does not affect the production process during screen change.” Gneuss highlights several trends and customer
requests for its filtration equipment for compounding. These include the need for higher throughputs and for finer filtration, as well as an increasing need to process recycled material and demand for filtration systems able to accommodate direct compounding. The company says that if two or more of these requests are combined, then the limits of conventional screen changers can be exceeded. Filtration systems with large filter areas and high
filter exchange rates, as well as a high process consistency, are typically required by the compounding industry. Gneuss says it has developed newly designed and optimised filtration systems for the continuously changing compounding market, and it will be presenting these at the K show in Germany in October.
Optimised packs Nordson Corporation has developed a new series of high performance screen packs for its BKG screen changers that can withstand higher extrusion pressures and provide maximum filtration and optimum melt flow while ensuring longer working
July 2019 | COMPOUNDING WORLD 27
Main image: Nordson BKG’s optimised four-layer screen packs combine durability with high levels of melt filtering and
permeability
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