Frame Indifference: Fluid Flow in Single Screw Pumps and Extruders

Recent developments in additive manufacturing have moved towards a new trend in material extrusion processes (ISO/ASTM 52910:2018), dealing with the direct extrusion of thermoplastic and composite material from pellets. This growing interest is driven by the reduction of costs, environmental impact, energy consumption, and the possibility to increase the range of printable materials. Pellet additive manufacturing (PAM) can cover the same applications as fused filament fabrication (FFF), and in addition, can lead to scale towards larger workspaces that cannot be covered by FFF, due to the limited diameters of standard filaments. In the first case, the process is known as micro- or mini-extrusion (MiE) in the literature, in the second case the expression big area additive manufacturing (BAAM) is very common. Several models are available in literature regarding filament extrusion, while there is a lack of modeling of the extrusion dynamics in PAM. Physical and chemical phenomena involved in PAM have high overlap with those characterizing injection molding (IM). Therefore, a systematic study of IM literature can lead to a selection of the most promising models for PAM, both for lower (MiE) and larger (BAAM) extruder dimensions. The models concerning the IM process have been reviewed with this aim: the extraction of information useful for the development of codes able to predict thermo-fluid dynamics performances of PAM extruders.

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“…Investigation of the accuracy given by this kinematics assumption is addressed in different works [ 81 , 82 , 83 , 84 ].…”

Section: Models For the Materials Extrusionmentioning

confidence: 99%

Analytical and Numerical Models of Thermoplastics: A Review Aimed to Pellet Extrusion-Based Additive Manufacturing

2021

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“…The analysis developed here is based on screw rotation physics [13], and thus several other definitions are developed here. The velocities at the screw core, indicated by the subscript c, in the x and z directions are as follows:…”

Section: Simple Flow Equations For the Metering Sectionmentioning

confidence: 99%

Single-Screw Extrusion: Introduction and Troubleshooting

Campbell¹,

Spalding²

2013

Analyzing and Troubleshooting Single-Screw Extruders

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This book was written to provide the extrusion process engineer with a resource for assessing and fixing process problems associated with the use of single-screw extruders. The authors have drawn on their complementary backgrounds; both have worked with industrial extruder design, analysis, and fundamental research in the mechanism, operation, and troubleshooting of the single-screw extrusion process. The use of single-screw extruders in production processes has progressed significantly over the past several decades. As a result, the number of single-screw extruders in use has increased dramatically as has the diameter and length of the machine, especially for melt-fed extruders used in large resin production plants. In addition, resin manufacturers have developed many new resins for final products such as extruded sheet, film, pipe, fibers, coatings, and profiles. The extruder is still the process unit of choice for producing pellets in the production of polymer materials. Two types of extruders are generally used in polymer production: singlescrew extruders and twin-screw extruders. The material in this book will be confined to the analysis and troubleshooting of single-screw extruders. The rapid expansion of this part of the polymer industry has been accompanied by the need for many new extrusion engineers. Many of these engineers have not had formal training in the analysis of the extruder and screw design nor have they had extensive education in polymer materials, which would help in troubleshooting problems on production equipment.All single-screw extruders have several common characteristics, as shown in Figs. 1.1 and 1.2. The main sections of the extruder include the barrel, a screw that fits inside the barrel, a motor-drive system for rotating the screw, and a control system for the barrel heaters and motor speed. Many innovations on the construction of these components have been developed by machine suppliers over the years. A hopper is attached to the barrel at the entrance end of the screw and the resin is either gravity-fed (flood-fed) into the feed section of the screw or metered (starve-fed) through the hopper to the screw flights. The resin can be in either a solid particle form or molten. If the resin feedstock is in the solid form, typically pellets (or powders), the extruder screw must first convey the pellets away from the feed opening, melt the resin, and then pump and pressurize it for a down-

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“…Stokes flow of molten liquid in the extruder channel is essentially considered a valid assumption. Many proposed modifications were made in rectangular channels, stirred tank reactors, and extruders to achieve better mixing, often relying on the development of chaotic structures in the flowing fluids 9,13–16 . The flow field in a single‐screw extruder channel was approximated as the flow induced in a rectangular channel with one of the walls (top wall) moving as published by Middleman, 7 and Chella and Ottino 8 .…”

Section: Introductionmentioning

confidence: 99%

Chaotic mixing in a free‐helix extruder using a new solution to the biharmonic equation

Campbell

Taylor

Wetzel³

et al. 2022

AIChE Journal

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A recently published approach for modeling the cross flow in an extruder channel using a new solution to the biharmonic equation is utilized in a study of chaotic mixing in a free‐helix single‐screw extruder. This novel extruder was designed and constructed with the screw flight, also referred to as the helix, detached from the screw core. The flight‐helix had straight sides that more closely emulated rectangular channel theory than the nominal sloped sides of a conventional single screw channel. Each of the screw elements could be rotated independently to obtain chaotic motion in the screw channel. Using the new extruder, experimental evidence for the increased mixing of a dye, for both a Dirac and droplet input, with a chaotic flow field relative to the traditional residence time distribution is presented. These experimental results are compared using the new biharmonic equation‐based model. Comparing the experimental chaotic mixing with theoretical calculations was facilitated by a recently published technique for accurately placing the dye in the extruder channel. Because of the ability to periodically rotate only the flight/helix, the chaotic mixing results are minimally confounded by the existence of Moffatt eddies.

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Frame Indifference: Fluid Flow in Single Screw Pumps and Extruders

Cited by 26 publications

References 1 publication

Analytical and Numerical Models of Thermoplastics: A Review Aimed to Pellet Extrusion-Based Additive Manufacturing

Analytical and Numerical Models of Thermoplastics: A Review Aimed to Pellet Extrusion-Based Additive Manufacturing

Single-Screw Extrusion: Introduction and Troubleshooting

Chaotic mixing in a free‐helix extruder using a new solution to the biharmonic equation

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