In the compounding extrusion of recycled resins, screen changers play a key role in removing contamination, such as paper, wood, aluminum foil, rubber or other unwanted plastics, from what will end up as the pellets. Some compounders of recycled resins are investing in more effective filtration technology in an effort to add value to their products so they can better compete with low-priced virgin resin, says Mike Diletti, president of Ettlinger North America LP, Tyrone, Georgia. The challenges of processing highly contaminated reclaimed plastics also are influencing the market for melt filters and screen changers.
Some in the industry use the terms screen changer and melt filter interchangeably. Both have disposable or reusable screen packs. But screen changers involve a manual process of changing the screens, often after just a few minutes. Melt filters offer a more continuous, automated process that is gaining popularity in some circles. But melt filters represent a much bigger upfront cost.
“It’s constant filtration, and the screen will speed up or slow down automatically based on the level of contaminant that’s in the material,” says Mike DeMatto, president and chief operating officer at plastics compounder CTC Plastics LLC, based in Dayton, Ohio.
DeMatto’s firm uses multiple types of screen changers and melt filters. Slide screen changers use two screens and slide them from one side to the other. On the upside, these do not require any downtime. But the process is not without issues. “The problem with those is, if the screen pack is plugging off [contaminant catching on the screen], whatever that contaminant may be, you change screens, and there’s some dead space there. So there’s a risk of getting some contaminants through into your material.”
A four-bolt screen changer involves four screens—two of them constantly in the flow of material and two that are not. “That eliminates the risk of contaminant getting through; but still, you’re at the mercy of the type of material you want and how often you have to change those screens,” DeMatto says.
He found a continuous screen changer from Ettlinger best met CTC’s requirements. “It’s because you can run recycled resins and virgin resins. The screen changer does all the work; it keeps a nice thin pressure. It speeds up and slows down on its own. … It cleans itself. It’s a very safe way to get rid of the [contamination].”
The Ettlinger screens are expensive—$8,000 to $9,000—DeMatto says, compared with the screens in a slide-screen changer that costs less than $1. “But you’re changing them every cycle and changing them every minute. So at the end of the day [with] screen buying, the Ettlinger is a cost savings.”Ettlinger North America
Ettlinger’s Diletti says the company’s screen changers can filter out contaminants for months at a time. They can be used on a variety of plastics, such as polyolefins or polyethylene terephthalate (PET). The screens can filter to a very fine (80 micron) level to a coarse (1,000 micron) level. “It really depends on what the customer needs [and] how clean the plastic needs to be after it goes through our filter. It’s really the most important factor,” he says.
Like DeMatto, Diletti says he sees a trend in the industry toward a more automated process using continuous filters. He also is seeing a move toward higher throughputs, which the company addressed with its introduction in the past 12 months of its ERF 500 melt filter. The ERF 500’s throughput of up to 12,000 pounds per hour is twice that of other Ettlinger products.
Diletti says Ettlinger just installed its first ERF 500 in the United States. The company has three more on order in the U.S., while two currently are running in Europe. He couldn’t give much detail on the U.S. installation, however, other than it’s a high-throughput application with very contaminated polypropylene (PP).
With continuous melt filters, customers typically also can buy a lower-quality scrap resin. “Maybe they’ve got a little more paper or a little more foil, more than what a manual screen changer could practically handle,” Diletti says.
Ettlinger has a relatively new melt filter for PET resin. The product is called Eco. It’s best for PET that requires continuous, reliable filtration with minimal melt loss and a pressure-stable process. It’s well-suited for the manufacture of strapping, sheet, film and pellets. “We also see the same benefits here with the continuous melt filters—higher quality, higher throughput and less purge waste, and less operator involvement—same thing everybody’s looking for,” he says.
Fimic
Fimic Srl, Carmignano di Brenta, Italy, will showcase its ERA-model filter at the K show in Düsseldorf, Germany, in October. The filter allows the screening of plastic melt with one machine operating two passages, says Sales Director Erica Canaia.
She says the machine has been tested with low-grade material and was able to filter contaminants as small as approximately 1 millimeter. Using the ERA, the company screened material first with a 500-micron punched screen and then at 150 microns with a laser screen in the ERA’s second chamber. In that way, not only was the expensive laser screen protected because the cheaper punched screen processed the worst of the contamination, but the output material was of higher quality.
Fimic also has developed the NET filter, which will be presented for the first time at the K show, too. It’s for customers who prefer a mesh type of screen because they need to filter out particles as small as 100 microns, Canaia says.
She says she also sees an increased move toward automation and the consumption of lower-quality, lower-priced material, which leads to more contamination. Besides providing long-term savings on screen-changing costs, the automated filters are better able to handle a high level of contamination.
Next Generation Recycling Machines
For filtration issues with polyethylene (PE), Next Generation Recycling Machines Inc., Norcross, Georgia, offers the Automatic Band Melt Filter from BritAS. It meets high-quality melt requirements with tough production conditions in a cost-effective way, according to the company, which has installed more than 170 filters in Europe.
The upgraded filter, which also will be on display at the K show, makes the system easier to operate, allowing for continuous operation and lowering energy consumption, the firm says.
Melt Filtration Products
The featured product line from Melt Filtration Products (MFP) LLC, Charlotte, North Carolina, is the AutoScreen continuous screen changer. To create it, MFP took a screen concept known as the Kalman design, which was developed in the 1960s in the United Kingdom, and added new features designed to improve the control of pressure, polymer temperature and screen movement, Managing Director Bob Phillips says.
The extrusion pressure control system uses feedback from pressure transducers to control the change in flow pressure on either side of the screen. This allows for extrusion control within a tight pressure range without deviations because of changes in material bulk density or contamination level. The AutoScreen automatically introduces a fresh filter screen when it is required for maintaining consistent extrusion pressures.
New features include a low filter ribbon indicator and on/off indicator lights for the filter screen exit heater, Phillips says.
Gneuss
Gneuss Inc., Matthews, North Carolina, is attempting to deal with a wider range of materials, which presents new challenges for its equipment. The company is managing projects with new materials such as nylon, thermoplastic polyurethane (TPU), polybutylene terephthalate (PBT) and polymethyl methacrylate (PMMA), as well as with specially formulated resins. “Each material comes with its own challenges,” says Monika Gneuss, the company’s vice president of sales and marketing manager. “These applications continuously push us to make our filtration systems even better.”
The company will present updated products at the K show.
Gneuss’ top model, its RSFgenius, has an integrated self-cleaning feature. It works automatically with screens being backflushed up to 400 times. It requires much less operator interaction than side screen changers, for example.
Gneuss says she sees a trend toward bigger lines. “If in the past our biggest screen changers were used in polymerization plants, we now see RSFgenius 250s, 330s and even 400s on extrusion lines.” Also, she says she sees more use of reclaim, “which is, of course, good for anybody manufacturing screen changers. A lot of plants are trying to avoid any type of waste; everything is supposed to go back into the process, so the need for filtration is certainly higher today.”
Gneuss also says she is seeing a movement toward finer filtration. “We have screen changers in PET bottle flake applications filtering as fine as 40, 30, 20 microns [400, 500, 600 mesh] and finer, depending on the end product. In a lot of cases, the intermediate step of repelletizing is being skipped, so the requirements on the filtration system/screen changer in regard to process stability and quality are very high.”
But the quality of reclaim is going down in many cases, she says, while conversely end-product quality requirements increase, necessitating finer filtration. That presents challenges to the filtration system in many ways. “On one hand, that might be an opportunity for a bigger screen changer; but, on the other hand, sometimes the contamination level is just too high to make cleaning via melt filtration economical.”
High-Technology
High-Technology Corp. (HiTech), Hackensack, New Jersey, specializes in continuous belt-type screen changers. It offers a filtration system that is fully integrated with the entire extrusion process, says Aline Alroy, vice president of sales.
HiTech has developed a new generation of programmable logic touch-screen controls designed to provide maximum flexibility to varying processing conditions. Both operational parameters and hardware are continuously monitored, Alroy says.
The firm has developed a new stainless steel screen changer to address filtration of flexible polyvinyl chloride (PVC). That material has presented a challenge because of PVC’s thermally unstable characteristics, such as low melt temperature and corresponding high viscosity.
Finally, HiTech completed a project recently that integrated continuous filtration technology for a demanding three-layer PE cast film application, with the dual challenge of high concentrations of calcium carbonate and the need for fine filtration using multilayer screen media, Alroy says.
Nordson Corp.
Nordson Corp., Münster, Germany, is introducing its BKG HiCon R-Type 250 filtration system, designed for highly contaminated polyolefins or styrenics, at the K show.
Nordson says the central concept involves the use of a cylindrical “separating head” that has knives arranged on its surface in a helical pattern. It is designed to push contaminants forward as the head rotates. A stationary filter element known as a strainer tube encloses the head. When the contaminated melt flows into the cylindrical space between the head and the tube, the knives catch contaminants. The melt moves through the strainer into flow channels leading to an exit port. Simultaneously, the rotating head turns a screw, guiding contaminated material through cooling sections before discharging it into collection bins.
This design allows for a uniform load on the strainer tube during cleaning, which means an extended lifetime for the filter and scrapers and better overall efficiency of the system at far less melt loss, says Sven Conrad, business unit director of Nordson Polymer Processing Systems (PPS).
The steel strainer tubes’ design is another key to efficiency. The tubes are available with micro-holes ranging from 120 to 750 microns. The conically shaped holes allow molten polymer to pass through and prevent blocking from contaminants. Nordson says the design and the symmetrically positioned knives in the drum contribute to the long working life of the tube. Also, once cleaned, tubes can be reused.
Several Siemens control and monitoring units regulate the system. This allows for a visualization of all process parameters. With an onboard Ethernet/Profibus interface, it is possible to integrate with other devices. Users can collect and record production data and perform remote maintenance.
“A network of several Siemens Simatic control and monitoring units contributes to the high level of automation and ease of use,” says Rolf Schultheis, Nordson PPS manager of electrical engineering. “The Siemens control system is intuitive, instantly providing a visualization of all process parameters. The onboard Ethernet/Profibus interface opens the possibility of integrating communication with other devices, collecting and recording production data and even performing remote maintenance.”
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