Patent Report: Gneuss extruder screw protects resin properties

Extruder screw. Gneuss GmbH, Bad Oeynhausen, Germany, earned a patent for a screw for a multi-screw extruder that achieves a homogeneously molten melt while protecting the resin’s properties. 

The patent concerns multi-screw extruders that feature planetary screws in the degassing zone. In such extruders, the melt does not completely fill the degassing zone so that a large surface area is formed. The challenge with such systems is “optimizing the numerous operating parameters such as drive and melting performance, mass temperature and residence time in the metering zone,” the patent states. “An excessively high mass temperature can lead to disadvantageous changes in the plastic, whereas a low mass temperature leads to insufficient melting of the solids in the metering zone. Although a long residence time promotes melting and homogenization, it accelerates the hydrolytic degradation of the plastic, which still contains moisture in this phase.” 

Optimization is especially difficult if recycled materials are involved, which can have varying melting behaviors, allowing solid residues to increase the wear of the planetary screws and bearings, according to the patent. 

The essential idea of the screw covered in the patent is that melting and homogenizing extend further downstream than is customary, into the multi-screw section. Also key is a shorter metering zone for reduced residence times in that area, and complete filling of the chambers in the longitudinal areas of the planetary screws, which improves conveying and eliminates back pressure.  

Patent 11,141,903; issued Oct. 12