PROCESSING | MELT FILTERS
Right: Gneuss says filters such as it RSFgenius can maintain process
consistency at high contami- nation levels
“In terms of filtration, the only option PVC recycling companies had was either a slide plate screen- changer or a continuous mesh changer…PVC is a very sensitive material and easily degrades with higher residence times.” Canaia said that using Fimic’s PVC filtration technology, no degradation takes place during the melt filtration phase. The company has adaptated to its existing RAS technology to achieve this, including special hardening treatments on filter parts to provide greater corrosion resistance. Some components have been modified internally to enable higher melt flow. The filters were tested for two years before installations began. Fimic recently installed a melt filter for a German company recycling flexible PVC from garden hose. This involved 150 micron laser filtration, which replaced the 400 micron mesh filter installed on the previous filtration system. In a second example, the installation of an RAS400-PVC filter enabled intervals between screen changes to be increased from 15 minutes to four days on a line processing 450-500 kg/h.
Below: The latest variant of Fimic’s RAS design brings continuous scraping laser filter operation to PVC processing
Focused on quality At Gneuss, regional sales manager Andrew Prangnell also points to the drive to put PCR into high-quality final product where until recently only 100% virgin material would have been used. “But the process requires fairly fine filtration. Original equipment filtration, designed with processing virgin material in mind, very quickly becomes a bottleneck,” he said. Prangnell said that typical
screen changers offered for processing recycled material were originally developed for repelletising applications and are not so suited to final products. “Process and melt
pressure stability are of far less importance when processing
material to pellets than when manufacturing a semi-finished product,” he explained. “Gneuss offers a range of
melt filtration systems which offer
both the ability to deal with high levels of contamination whilst at the same time maintaining extremely high levels of process consistency— for example, pressure variations of less than 4 bar during
operation, together with 100% availability and a patented self-cleaning technology with unparalleled efficiency,” he claimed.
14 PIPE & PROFILE EXTRUSION | January/February 2021
Cutting losses Nordson Corporation has developed a filtration device that reduces material loss from backflush screen changers when used in the compounding and recycling of PET, it says. Backflushing is a self-cleaning feature in which a small portion of the melt is discharged in the reverse direction back through a screen to remove contaminants. It is automatically initiated when the pressure differential caused by contaminant build-up increases to a pre-set level. In one of Nordson’s BKG HiCon V-Type screen changers with four screen cavities, for example, this backflush process is performed in one cavity after another, allowing melt flow to continue through the other three cavities. To cut back on the material lost during back-
flushing, Nordson has developed a filter stack that replaces the standard screen in each cavity. Each of these filter stacks consists of two to four FlexDisc cassettes, with two screen packs in each cassette. This substantially increases filtration area and reduces material loss by reducing the amount of polymer used in the backflush cycle and the number of cycles needed in a given period of time. Nordson also offers the HiCon R-Type filtration system for recycling highly contaminated plastics. It uses a cylindrical ‘separating head’ with knives arranged on its surface in a helical pattern to move contaminant particles forward as the head rotates. Enclosing the head is a stationary filter element called a strainer tube. When contaminated melt flows into the cylindri- cal space between the rotating head and the strainer tube, the knives capture the contaminant – while the contaminant-free melt moves through the strainer into flow channels that lead to an exit port. At the same time, the rotating head turns a screw
www.pipeandprofile.com
IMAGE: GNEUSS
IMAGE: FIMIC
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