machinery feature | Screen changers Nordson’s HiCon R-Type
250 transforms contaminated polyolefin or styrenic
plastics into clean, high- quality
material
exit port. At the same time, the rotating head turns a screw that guides the contaminated material through cooling sections and finally to where it is discharged into collecting bins. “This cleans much more efficiently than
commercial available filtration systems for highly contaminated polymers,” said Conrad. “The special design makes possible a uniform load on the strainer tube during the cleaning process, providing an extended lifetime for the filter and scrapers and increasing the overall efficiency of the system at far less melt loss.” The system operates at a maximum pressure of 350 bar and maximum temperature of 320°C. Throughput can range from 500 to 1,500kg/h, depending on factors such as polymer viscosity, filtration fineness and levels of contamination. As it exits the system, filtered polymer is maintained at constant pressure, ensuring uniform processing downstream. One key to the efficiency is the design of the steel
strainer tubes, which are available with micro-holes ranging from 120 to 750 microns. The holes are conical in shape, permitting passage of molten polymer while preventing blockage by contaminant. This design and the symmetrically positioned knives in the drum contribute to the long working life of the tube before it needs to be replaced. Once cleaned, the tube can be reused.
High efficiency In similar fashion, Ettlinger showcased an enhanced range of high-efficiency melt filters. Its ERF series, which is suitable for heavily contami-
Ettlinger’s ERF series of melt filters is
suitable for heavily
contaminated plastics
nated plastics, can now handle higher throughputs, while the Eco models are optimised for filtering PET and PE in film and foil lines – as well as low-viscosity thermoplastics and polyamide. The patented, continu-
ously operating ERF and Eco melt filters can be incorporated into almost any extrusion line. At the heart of both types is a rotating filter drum with conical perforations, through which the contaminated melt flows from the outside to the inside. A scraper continuously removes contaminants from the surface of the drum and feeds them to an exit screw. This enables the filter to be used continuously and fully automati- cally over long periods without
22 PIPE & PROFILE EXTRUSION | January/February 2017
having to replace the screen. The advantages of this include constant melt pressure, low melt losses, good mixing and homogenising of the melts, and short contaminant residence times on the filter surface. ERF filters, for throughputs up to 6,000kg/h, are
suitable for separating contaminants such as paper, aluminium, wood, silicones and high-viscosity plastics from heavily contaminated polyolefins and polystyrenes. Improvements to the flow channels lead to lower differential pressures, which can increase throughput rates boost productivity by up to 15%. ERF melt filters are mainly used in the extrusion of PP, HDPE, LDPE, PS and some engineering thermoplastics such as packag- ing films, yoghurt cups (web scrap), and pipes, and are processed into granulates, sheets, films or profiles.
Taking the pressure High-Technology Corp (Hitech) says that its new Model BPC screen changer that can filter under
extreme conditions – such as high processing and differential pressure – without distorting or tearing the screen media. It is designed to operate at
processing pressures up to 5,000psi and differential
pressures as high as 1,500psi. The device uses proprietary flow-channels and breaker plate geometry to form a balanced
polymer seal that promotes consistent screen displacement, says the company. Good results have been achieved
www.pipeandprofile.com
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