Segmented Extruder Screw Toothing for High-Torque Durability
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Solution Overview
Problem
Extruder screws experience plastic deformation and damage at the hub toothing due to high torque transmission, particularly from stress peaks arising from differences in torsional stiffness between the worm shaft and screw elements, leading to undesirable deformation and potential failure.
Innovation Solution
The extruder screw design incorporates recesses in the external toothing, forming separate gear rings with alternating axial spacing, allowing the internal toothing of screw elements to engage only within these rings, reducing stress peaks by introducing torque away from the hub edges and using asymmetric tooth flanks to accommodate torsional changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a shaft-hub toothing connection is used to transmit high torque, then torque transmission capability is improved, but plastic deformation and damage occur at the hub toothing due to stress peaks
Solution Approach 1:
The continuous external toothing on the worm shaft is segmented into multiple separate ring gears spaced axially apart. This segmentation creates discrete engagement zones along the axial length, allowing the internal toothing of screw elements to engage with specific ring gears while leaving gaps (recesses) between them. This reduces stress concentration at any single toothing location and prevents plastic deformation by distributing the torque transmission load across multiple separated engagement points.
2Power
If the internal toothing of screw elements engages with the external toothing along the entire length, then torque transmission is maximized, but stress peaks arise at the hub edges due to stiffness discontinuity
Solution Approach 1:
The harmful engagement at the hub edges is eliminated by removing material to create recesses between the ring gears. The internal toothing of screw elements extends axially beyond the ring gears, but the recesses prevent engagement at these critical hub edge locations. This extraction of the problematic engagement zones eliminates the stress peaks that would otherwise occur at the hub edges due to stiffness discontinuity, while torque transmission is maintained through the engaged portions of the toothing.
3Reliability
If recesses are provided in the external toothing to reduce stress peaks, then toothing durability is improved, but the complexity of manufacturing increases
Solution Approach 1:
The external toothing is segmented into discrete ring gears with recesses between them, which can be manufactured using standard gear cutting or forming processes. The recesses are simple axial gaps that require no special finishing operations, making the design easier to manufacture than continuous toothing with complex stress relief features. The segmented structure allows for modular manufacturing and assembly, reducing overall manufacturing complexity while improving durability.
Data Source
AI summary
An extruder screw having a worm shaft and a plurality of screw elements that are releasably plugged or pluggable thereon, wherein each screw element has a defined axial minimum length or a length that corresponds to a multiple of the minimum length. The worm shaft has an external toothing and the screw elements have an internal toothing engaging therewith. The external toothing has, forming individual gear rings extending around the circumference, a plurality of recesses extending around the circumference in an offset manner along its axial length, which are spaced apart from one another by the minimum length, such that the internal toothing of each screw element extends, at both axial ends, into the region of the recess, and the ends of the internal toothing are not engaged with the external toothing.