MRS extruder: a single-screw extruder with a multiple screw section
Compared to a conventional single-screw extruder, Gneuss’ MRS extrusion system offers many new possibilities for the efficient degassing and recycling of polymer melts. In addition, with the MRS extruder gases or fillers can be homogeneously introduced into the melt.
The MRS extruder, which is based on the technology of the single-screw extruder, has a robust design and a wide range of applications. It is particularly suitable for recycling applications, such as bottle, fiber or sheet recycling. The innovative processing unit allows post-consumer polyester (PET) to be processed directly into high-quality end products. The process takes place without pre-drying and by using a simple water ring vacuum system.
Multi Rotation System: the design of the MRS extruder
The MRS extruder is based on the conventional single-screw extruder, but is equipped with a multiple screw section, for optimum devolatilization. The polymer melt is delivered into a large single-screw drum. The drum contains several small extruder barrels, parallel to the main screw axis. Installed in these small extruder barrels are the “satellite” screws, which are driven by a ring gear in the main barrel. The satellite screws rotate in the opposite direction to the main screw while they rotate around the screw axis. This disproportionately increases the surface exchange of the polymer melt. So that the volatiles can be freely evacuated, the MRS extruder is equipped with a large opening for venting (exposing the full length of the satellite screws) which is completely under vacuum. This provides excellent and unrestricted access to the polymer melt, the surface of which is constantly replaced at an extremely high rate by the action of the satellite screws in the multiple screw section. In addition, precise control of the melt temperature is possible as the temperatures of all the surfaces in contact with the melt can be controlled accurately.
Performance comparison: MRS extruder vs. twin- & single-screw extruder
Thanks to the multiple screw section, the surface area – and the surface area exchange rate – available for devolatilization are far greater than in other extrusion systems available on the market.
The surface area of the steel parts in contact with the melt is exchanged at a rate of more than 25 times greater than with a co-rotating twin-screw extruder. Due to the opposite rotation direction and high speed of the satellite screws, the polymer surface area is increased by a factor of 100 compared to a single-screw extruder and a factor of 40 compared to a twin-screw extruder.
The MRS extruder is not only powerful, but also extremely energy efficient. Energy consumption with the MRS technology is in general 15 to 25 % lower than with conventional technologies that require pre-drying and/or a deep vacuum system.
Compared with a single-screw extruder, when recycling PET pre-treatment of the material in the form of drying and crystallizing can be avoided, thereby saving operating and maintenance costs. Compared with a twin-screw extruder, no pre-drying nor a deep vacuum are required, again saving operating and maintenance costs.
Furthermore, the MRS delivers sufficient pressure that a melt pump is not necessary to boost pressure.