PROCESSING | MELT FILTRATION
Right: Erema now offers Laserfilter models for PET as well as polyolefin processing
pressure consistency and particularly long screen service life,” he says. “Another benefit of the Laserfilter is that the flow-oriented working principle avoids the formation of ‘black spots’. The user also benefits from the lower melt losses which is achieved thanks to the newly developed discharge unit. Whereas the normal figure for piston filters is 1-2%, with the Laserfilter it is just a fraction of this.” Obermayr says the Laserfilter is now being used
more and more rather than the piston filter, particu- larly in the direct processing of PET flakes to make semi-finished or end products. The high process stability, which Erema attributes to its constant-pres- sure operation, is said to be a key factor in its selection. The company also says that, while the maximum level of contamination that can be handled by a piston filter lies between 0.05-0.1%, the Laserfilter processes input material with a degree of contamination of more than 1%. This means greater flexibility in being able to handle increasing contami- nated in post-consumer input material. “With the PET Laserfilter we are talking about
Below: A Gneuss GPU with MRS extruder, melt filter, and viscometer
screen life of five to twelve weeks,” Obermayr says. “You mustn’t underestimate the fact that the daily screen change by the operator which is necessary with a piston screen changer is no longer required and this reduces the risk of operating error considerably.” Gneuss says that its Gneuss Processing Unit
(GPU), which was launched several years ago, is now a proven solution for the reprocessing of bulky PET waste such as post-consumer bottle flake and industrial waste from fibre and film manufac- ture without pre-drying. The GPU consists of a
Gneuss MRS devolatilisation and decontamination extruder in combination with a Gneuss Rotary Filtration System and a VIS online viscom- eter for intelligent dynamic viscosity control.
The MRS is now also running in polyolefin and polyamide applications and is also being tested on a range of other materials. Also in the PET sector,
Nordson demonstrated the gains available from opti- mised screenchanger design
last year when it announced it had retrofitted a special version of its BKY Poly unit on a polymerisa- tion line operated by Turkish resin and packaging products maker Köksan. The company had been using a standard version of the BKG Poly screen- changer, which comprised eight flat screens supported by a breaker plate. The optimised retrofit replaced these with a new design carrying multiple filter candles, increasing the filtration area by a factor or more than 10. According to the company, the upgraded
screenchanger extends filter life by between four to eight times while reducing the number of black specks and gels and lowering shear stress. The latter benefit also extends melt pump life. “Lower delta pressure across the filter, achieved with Nordson’s POLY candle filter design even at 120 % capacity production, results in long life for the polymer pumps and its mechanical seals,” accord- ing to Peter Thomas, General Manager for PET Resin at Köksan.
Taking the pressure At the recent Fakuma show, Nordson introduced new screen packs for its BKG screen changers that withstand the pressures of extrusion – providing high filtration and optimum melt flow while ensuring a long working life. One reason for the enhanced performance of these new screen packs is a robust multi-layer structure that prevents failures caused by the pressure differential – of up to 200 bar – encoun- tered during filtration. One such example is ‘screen dimpling’, in which the mechanical stress forces screen layers into the holes of the breaker plate that supports the screen in the cavity. This distorts the screen, breaking the peripheral seal and causing contaminants to bypass the screen and become part of the end product.
26 FILM & SHEET EXTRUSION | December 2018
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www.filmandsheet.com
PHOTO: GNEUSS
PHOTO: EREMA
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