scholarly journals Enhanced Processing of Regrind as Recycling Material in Single-Screw Extruders

Polymers ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1540
Author(s):  
Philipp Thieleke ◽  
Christian Bonten

Regrind processing poses challenges for single-screw extruders due to the irregularly shaped particles. For grooved feed zones, the output is lessened by the reduction of bulk density in comparison to virgin material. Simultaneously, the melt temperature increases, reducing the extruder’s process window. Through experimental investigations on a test stand, a novel feed zone geometry (nominal diameter 35 mm) is developed. It aligns the regrind’s specific throughput with that of virgin material. The regrind processing window is essentially increased. As the solids conveying in the novel feed zone cannot be simulated with existing methods, numerical simulations using the discrete element method are performed. Since plastic deformation occurs in the novel feed zone geometry, a new hysteresis contact model is developed. In addition to spheres, the regrind and virgin particles are modeled as superquadrics to better approximate the irregular shape. The new contact model’s simulation results show excellent agreement with experimental compression tests. The throughput of the extruder simulations is considerably underestimated when using spheres to represent the real particles than when using irregularly shaped superquadrics. Corresponding advantages can be seen especially for virgin material.

2013 ◽  
Vol 781-784 ◽  
pp. 2809-2816
Author(s):  
Liang He ◽  
Bai Ping Xu ◽  
Hui Wen Yu ◽  
Xiao Long Wang ◽  
Gang Xue

The novel geometrical configuration of embedded planetary-screws is proposed in the paper. The corresponding numerical simulation and the experimental investigation are carried out to characterize the mixing performance. Adopting commercial software FLUENT, the simplified physical model is presented with the boundary conditions imposed by UDF codes which are developed by us. Compared with the traditional single screw extruder, the flow and mixing are primarily investigated by using particle tracking technology. The sensitivity to initial positions is found in the novel screw configuration, which is caused by the periodic perturbation of planetary-screws. In contrast, the traditional laminar mixing occurs in single screw extruders. Compared with the traditional twin screw extruder, the experimental characterization of filled system of adding active nanometer CaCO3 into LLDPE matrix is conducted. No obvious difference in dispersion of CaCO3 is found when the extrusion samples are observed through scanning electron microscopy (SEM), on the condition that the both extrusion outputs are equal. The shear rate in the novel screw configuration is relatively smaller, and the extrusion characteristic is more excellent.


Polymers ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 944
Author(s):  
Raffael Rathner ◽  
Davide Tranchida ◽  
Wolfgang Roland ◽  
Franz Ruemer ◽  
Klaus Buchmann ◽  
...  

Single-screw extruders are usually operated with the screw fully filled (flood-fed mode) and not partially filled (starve-fed mode). These modes result in completely different processing characteristics, and although starve-fed mode has been shown to have significant advantages, such as improved mixing and melting performance, it is rarely used, and experimental studies are scarce. Here, we present extensive experimental research into starve-fed extrusion at feeding rates as low as 25%. We compared various operating parameters (e.g., residence time, pressure build-up, and melting performance) at various feeding rates and screw speeds. The results show a first insight into the performance of starve-fed extruders compared to flood-fed extruders. We explored starve-fed extrusion of a polyethylene material which contains a Very High Molecular Weight Polyethylene fraction (VHMWPE). VHMWPE offers several advantages in terms of mechanical properties, but its high viscosity renders common continuous melt processes, such as compression molding, ram extrusion and sintering, ineffective. This work shows that operating single-screw extruders in extreme starve-fed mode significantly increases residence time, melt temperature, and improves melting and that-in combination—this results in significant elongation of VHMWPE particles.


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