Upper Austrian plastics machine manufacturers MAS Maschinen- und Anlagenbau Schulz GmbH will be bringing the world's largest melt filter to Fakuma this autumn.
MAS
Fig 1.
Both companies strive to bring innovation to improve efficiency in extrusion and recycling technology. These include the gentle plasticising co-rotating conical twin screw extruder offering high throughput rates, the waterless working DRD-cleaning and drying systems for film flakes, as well as the CDF-rotating-disk-melt-filter.
At Fakuma MAS will bring the latest and largest of its filter series for continuous melt filtration, with a filter area of 6.560 cm² representing a new size and throughput record.
Melt filtering rethought
The MAS approach to melt filtration is the latest technical solution on the market. It differs considerably in significant details, thereby offering advantages in long-term use, as well as at periodic cleaning and maintenance. Its central element is a shaft-driven, rotating sieve carrier and supports an interchangeable round mesh plate. The perforated plate is made of surface-hardened steel and available, depending on the application, with a filter-hole pattern in the range of 100 to 750 microns. The rotating filter unit is running against a stationary squeegee, which collects the foreign particles retained by the filter disc, such as paper, wood, aluminium, rubber, or non molten plastic particles and diverts them to a discharge screw. A significant advantage of this arrangement is that the highest amount of foreign particles (it goes up proportionally with the disc diameter) is nearest to the material discharge. This minimises filter blockages or filter disc wear by abrasion. The contact pressure of the squeegee is controlled by the melt pressure via a mechanical piston-lever system. The melt inflow is lateral into the filter housing, passes through the filter disc and flows as pure melt centrally through the drive shaft and thereafter to the lateral outlet (Fig.1).
Since the material combination of the functional filter components consists of a hardened filter plate and a "soft" squeegee, it offers the best conditions for a long service life. Any exchange of the filter disc is easy, because the filter housing is divided vertically and both halves are pivotally connected together by a hinge. The change process itself is very simple and can be performed
with conventional tools in approximately 45-50 minutes (Fig.2).
The CDF filter series - modular and record-breaking efficiency
The CDF(Continuous Disc Filter)-series is modular. It comprises four sizes. The smallest size CDF 300 uses a 300 mm disc with 704 cm² filtration area, for about 300 - 700 kg polymer melt per hour. All other sizes are working with one or more 510 mm filter discs, in concrete terms the CDF 500 one disc with a filter area of 1,640 cm² for 700 - 1600 kg / h and the CDF-500-D two parallel disks with a total filter area of 3,280 cm² for 1300-2000 kg/h (Fig.3). The now presented largest filter unit with the type designation CDF-500-D-P consists of two parallel CDF-500-D units with a total of 4 filter disks and a usable filter area of 6.560 cm² (Fig.4). With a possible melt throughput of up to 4000 kg per hour polyolefin-melt the new filter system is geared to the throughput levels of large recycling plants and currently the most powerful unit on the market.
MAS
Fig 3.
Enhanced MAS-extruders
The conical co-rotating extrusion system developed by MAS combines the known good plasticisation and homogenisation of a parallel twin-screw extruder with the specific advantages of the conical twin-screw extruder in one machine. The latter provides through the system-
specific large feed opening optimum processing conditions for materials with a low bulk density and large intake volume. In addition, the MAS-extruder scores over single screw extruders, which are generally used for recycling, with superior handling and homogenisation performance, a particularly gentle material treatment and a stable mass pressure. Accordingly a melt pump for pressure stabilisation and pressure build-up is usually not required. The thus more homogeneous plastic melt produced offers the best conditions for an effective melt filtration and degassing, which for processing of recycled materials is just as important as the fact, that the polymer structure is only minimally stressed in a MAS-extruder. That is confirmed by the comparison of the physical characteristics of the starting material with the recycled material: The material characteristics, such as viscosity, elongation at break and tensile strength remain maximally preserved.
