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Extrusion-recycling of mixed materials.

Extruding 100% recycled plastics without having to sort, wash, or pelletize is an advantage to processors of these materials. The Plastics Division of Kuhne GmbH is offering three systems that coextrude different materials, filter out impurities, and extrude quality films, sheets, or molded parts in a one-step process.

The first system is a film blowing process that primarily extrudes post industrial packaging films. The feedstock for this system consists of printed or unprinted LDPE, LLDPE, and HDPE with small amounts of PP, PS, and multilayer film. These "raw materials" can be either pressed or stretched into circular bales. Adherent contaminations and also foreign materials (such as paper labels, splinters of wood, or adhesive tapes) can be processed or filtered out during production of the film.

In the second system, the sheet extrusion process, the recycling material is treated by a compactor--not an agglomerator--in order to make it suitable for extrusion. The plastic material obtained from this process is extruded and discharged via a wide slot die. The material is given the desired thickness on a three-roll stack, and then cooled on a roll conveyor to be wound up or stacked. For this process, approximately 40% of the feed material should be a cellulose filler, such as paper waste. This filler improves the extrudability of plastic sheet by eliminating any negative influence from the various stresses of the different materials.

The "intrusion" process, the third system, is used to produce molded parts, and can use the lowest quality recycled material. This process is based on the extrusion technique of the blown film process with regard to a stuffing screw with a conical feed zone. The treated melt passes through a stationary extruder located either before or over the mold, depending on the throughput capacity. The melt is then fed to a stationary mold via a special switching valve--the only moving part. Since the molds do not rotate, no large masses have to be moved. There is no limitation of molds for rotation-symmetrical parts. Individual molds are located on the working level and are contacted in preset cycles. The molds can have any desired geometry and usually consist of top half and bottom half that are closed and opened hydraulically. The molds are water-cooled and can be equipped with an automatic ejector. The system can run with its own recycled products by using the material as a filler--hence, the recycling of recycled products. O/K International/Kuhne GmbH, Plastics Division, 490 Old Boston Post Rd., Sudbury, MA 01776; (508) 443-4696; Fax (508) 443-4787; Circle 120.
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Title Annotation:Equipment & Processing
Publication:Plastics Engineering
Article Type:Product Announcement
Date:Dec 1, 1992
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