machinery feature | Screen changers Hitech’s BPC
screenchanger can handle flexible PVC
products such as tubing
the RAS400) and 50 minutes (for RAS700) – compared to a typical 90 minutes for competing technologies. “This is important if you consider that the screen
could need changing every three days, and that the line stops reduce overall production,” said the company. For this reason, Fimic has installed a line that
enables the screen to be changed without stopping the production line, using two filters in parallel. At the same time, Fimic has developed the Era filter
in applications including flexible PVC precision tubing. Until recently, continuous filtration for flexible PVC has
been limited by the polymer’s low melt temperature and high viscosity – which have led to processing challenges. The BPC screen changer has already been used by a leading manufacturer of flexible PVC tubing, says Hitech. “The success of initial trials led this processor to
retrofit all production lines at its US plant with Hitech screen changers,” said the company. At the same time, the company has developed its
latest generation of PLC touchscreen control system that can adapt to varying conditions. Optional param- eters are configured via an automation algorithm, which detects real time processing conditions and adjusts the operations of the screen changer accordingly. “These innovations deliver major enhancements with
respect to performance, integration, reliability and ease of use,” said Aline Alroy, vice president of sales for Hitech.
Filtering PVC Fimic has developed a new filter that is aimed specifi- cally at PVC processing. Its RAS technology is based on collecting a high level
Fimic has
developed the Era filter,
which filters twice in sequence
of contamination inside a hollow blade holder, and discharging it based on a pre-set pressure. It has been modified to recycle PVC electrical cables, which are difficult to recycle and contain high levels of copper, aluminium, rubber and other plastics. Because of the level of contamination – usually
above 20% – the machine is set in continuous mode. This allows the blade holder to keep slowly scraping the stainless steel screen and gradually accumulate the removed contamination. Thanks to the 150 micron laser screen and its high open area, this plastic material – usually considered unmanageable – has been success- fully processed by four separate end users. The modified Fimic filter still features fast cover opening and a rapid changeover times of between 15 (for
24 PIPE & PROFILE EXTRUSION | January/February 2017
www.pipeandprofile.com
– first seen at Plast 2015 – which filters twice in sequence. It is aimed at highly contaminated material, which requires two filtering stages in order to obtain a usable material. In the past, this required high capital investment, as it needed two filters and a gear pump or a shorter extruder in the middle. The Era is formed by two inside filtering chambers, each of them mounting a screen with different filtration level. This removes need to have two filtering machines. The first chamber is typically 400 microns – produced using punched screens – while the second chamber is a 150 micron laser screen, which refines the quality of the material. However, the screens can be modified by the customer to suit their individual needs. The two chambers are independently managed, as
they have separate discharge valves. When a set pressure is reached in the first chamber, the related valve will perform the discharge after the blade holder has collected the contamination. The quality of the material will be higher than it would from a single filtration stage, with a difference in pressure between the two chambers of around 15 bars. Both the RAS and Era models can also use the backflushing feature, which enables filtration as low as 40 microns. However, backflushing has some limits: it produces a high level of plastic waste when the mesh is cleaned (about twice that discharged in the scraping technology) and can only operate with a lower level of contamination.
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