Melt fi ltration | processing feature
Pat Toensmeier reports on the latest melt fi ltration systems that have been designed to meet demands for higher outputs, faster product changeovers and coping with increased contamination levels
Catching contaminants with the latest screen-changers
Many factors are infl uencing the development and use of screen-changers in applications ranging from high-output compounding to low-volume specialty operations. Most of these factors affect the design of fi ltration media, but almost every aspect of a screen- changer is being evaluated and upgraded. The developments are helping to improve contaminant removal, enhance the effi ciency of screen-changing systems and integrate them more effectively within compounding operations. “The main goal is to make certain a screen-changer is
not the weakest point in a compounding line,” comments one supplier, John Whaley, product manager at Key Filters, a business unit of Parkinson Technologies. Systems are being engineered for higher fi ltration
rates, often by expanding the amount of screening area exposed to melt without a corresponding increase in the size of screen-changing units or impediments to fl ow. Suppliers tap into a number of techniques for this, ranging from the shape and size of fi ltration media to controls that use melt-fl ow pressure to initiate purging and screen changes at optimum levels of contamina- tion. As a result, compounders are seeing ongoing improvements in fi ltration effi ciency. Another development relates to compounding volume:
the ever-present need to generate more production while maintaining energy-effi cient operations, and the recent growth of ultra-high-throughput lines. The North American shale boom is generating abundant supplies of low-cost natural gas, which contributes to a reduction of manufacturing costs in many parts of the US, notably the Gulf Coast. One effect of this, observers say, is growth in the expansion or construction of polyolefi n compounding lines with throughputs of as much as 100 tonnes/hour, double that of established lines. With these higher-volume lines comes the need for heavy-duty melt-fi ltration
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systems that are effective at such rates. Another infl uence on development is specialty
compounding, which focuses on short runs and screen-changing systems that work well with rapid changeovers of resins, additives, colours and other ingredients. For many compounders there is a related fi ltration
concern over the high use of additives in some poly- mers. Filler levels of up to 85% in some cases put extra demands on screen-changers to meet fi ltration requirements while minimizing dwell times in fl ow channels. Finally, there is recycling, an operation which is yielding more contaminants than in the past despite advances in the technology. Greater contamination of recycling streams stems from broader use of reclaimed plastics – industrial and consumer – that not long ago ended up in landfi lls.
“If anything, the quality of reclaim has been going
down,” affi rms Monika Gneuss, marketing manager and vice president of sales at Gneuss Inc., the US division of
July 2014 | COMPOUNDING WORLD 47
Maag’s CSC-BFX
screen-changer uses only two hydraulic cylinders to
fi lter recyclate
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