Extrusion Flow Research Articles

A modified LBM for non-Newtonian effect of cement paste flow in 3D printing

Purpose The screw extruder is applied in cement-three-dimensional (3D) printing. The cement paste flow in 3D printing is the typical Herschel–Bulkley fluid. To understand the flow in the channel, the improved lattice Boltzmann method (LBM) is proposed. Design/methodology/approach For Herschel–Bulkley flow, an improved LBM is presented to avoid the poor stability and accuracy. The non-Newtonian effect is regard as a special forcing term. The Poiseuille flow is taken to discuss the detailed process of the method. With the method, the analytical solution and numerical solution are obtained and compared. Then, the effect of the initial yield stress on the numerical solution is both explored by the shear-thickening fluid and the shear-thinning fluid. Moreover, the variations of the relative errors under different lattice nodes and different power-law indexes are analyzed. Finally, the method is applied into the simulation of the flow in the extruder of cement-3D printing. Findings The results show that the improved method is effective for Herschel–Bulkley fluids, which can simulate the flow in the extruder stably and accurately. Practical implications The simulation can contribute to understand the cement paste flow in the screw extruder, which helps to optimize the structure of the extruder in the following periods. Originality/value The improve method provide a new way to analyze the flow in the extruder of cement-3D printing. Also, in the past research, LBM for Herschel–Bulkley fluid is ignored, whereas the study can provide the reference for the numerical simulation.

Particle Behaviour in Extrusion Flow of Concentrated Particle Suspensions

Particle Behaviour in Extrusion Flow of Concentrated Particle Suspensions

Variable bead width of material extrusion-based additive manufacturing

Variable bead width in material extrusion-based additive manufacturing (MEAM) is studied to enhance flexibility and capability. Discussion on associated process parameters, including the layer thickness, material flow rate, and travel feed rate is conducted to deduce their potential influence on the bead width of deposited filaments. Then the analytical models are established to analyze their effects on the bead width quantitatively. Based on the theoretical and experimental analyses, the material extrusion flow rate is selected as the input variable to control the bead width during the extrusion and deposition processes. The proposed method is implemented and verified with deposition of a multi-layer but single column thin-walled structure. Based on the implementation of several applications, it is concluded that the bead width could be achieved by adjusting some related process parameters and it can facilitate the extension and application of extrusion-based additive manufacturing technology.

Crustal Structure of Southwest China and Northern Vietnam From Ambient Noise Tomography: Implication for the Large‐Scale Material Transport Model in SE Tibet

AbstractSeveral models have been proposed to describe the tectonic evolution of SE Tibet and its marginal areas. Hence, high‐resolution crustal velocity models are essential to address this controversy. With waveform data from 73 broadband stations in southwest China and northern Vietnam, we invert for a 3‐D shear wave velocity model of the crust and uppermost mantle from ambient noise tomography. Our model reveals that the midlower crustal low‐velocity zone in the Xiaojiang Fault Zone extends farther southward across the Red River Fault to Vietnam and is approximately bounded by the Xiaojiang and Dien Bien Phu faults to the east. We suggest that the observed low‐velocity zone represents a mechanically weak zone in the mid‐lower crust, which may serve as a channel for efficient southward material transport in SE Tibet. With our results and previous evidence, we propose a combined model that integrates rigid block extrusion and crustal channel flow to describe the large‐scale material transport in SE Tibet. We further propose a two‐phase material transport model in SE Tibet after the India‐Eurasia plate collision: (1) rigid block extrusion between the right‐lateral Sagaing Fault and left‐lateral Red River Fault during the early Oligocene‐early Miocene and (2) a combined model of rigid block extrusion and material channel flow in the mid‐lower crust from the late Miocene to the present. The southward crustal material transport is likely to be diverted along two major channels around the more rigid crust beneath the inner zone of the Emeishan large igneous province.

Melt die-swell behavior of polyoxymethylene blended with ethylene-vinyl acetate copolymer and high-density polyethylene

The influence of extrusion conditions (temperature ranging from 170 to 220 °C, loads varying from 1.2 to 12.5 kg) and high-density polyethylene (HDPE) content on swelling behavior of polyoxymethylene (POM)/ethylene-vinyl acetate copolymer (EVA)/HDPE blend melts was examined. It was found the melt die-swell ratio of the blends decreased approximately linearly with rise in temperature, while it increased as a quadratic function with increasing shear rate or shear stress. The melt die-swell ratio increased with increasing HDPE weight fraction under constant test temperature, and the effect of temperature on the sensitivity of the melt die-swell ratio to the HDPE weight fraction was insignificant, while the effect of load on the melt die-swell ratio was significant. The correlation between the melt die-swell ratio of the blends and the HDPE weight fraction followed a quadratic relation. The melt extrudate swell behavior mechanisms of the blends during the die extrusion flow are discussed.

Barrel temperature control for quality of thermoplastic polymers in the extrusion process

In this paper, the design procedure; modeling and controller design, testing are presented. Extensive tests have shown that the system reacts rapidly to changes in the operating conditions and effectively rejects disturbances due to unexpected changes in the quality of the material. This paper is the design and experimental testing of a feedback control system for the regulation of the volumetric flow in a polymer single screw extruder. Extruder temperature control is a challenging control problem. The problem becomes even more challenging when multiple barrel are included, such as in barrel temperature control for extruders. When characteristics of the system are examined, it becomes clear that a commonly used proportional plus compound plus derivative PID controller cannot meet such performance specifications for this kind of system. In order to achieve the required performance, a control strategy that utilizes techniques such as model predictive control, autotuning, and multiple parameter PID is formulated. This control strategy proves to be very effective in achieving the desired specifications.

Barrel temperature control for quality of thermoplastic polymers in the extrusion process

In this paper, the design procedure; modeling and controller design, testing are presented. Extensive tests have shown that the system reacts rapidly to changes in the operating conditions and effectively rejects disturbances due to unexpected changes in the quality of the material. This paper is the design and experimental testing of a feedback control system for the regulation of the volumetric flow in a polymer single screw extruder. Extruder temperature control is a challenging control problem. The problem becomes even more challenging when multiple barrel are included, such as in barrel temperature control for extruders. When characteristics of the system are examined, it becomes clear that a commonly used proportional plus compound plus derivative PID controller cannot meet such performance specifications for this kind of system. In order to achieve the required performance, a control strategy that utilizes techniques such as model predictive control, autotuning, and multiple parameter PID is formulated. This control strategy proves to be very effective in achieving the desired specifications.

Experimental analysis of the intensity and evolution of coal and gas outbursts

Coal and gas outburst (hereinafter referred to as “outburst”) is a complicated dynamic disaster formed in the temporal and spatial evolution process. To further improve our understanding of outburst mechanism and help more effective outburst prevention and control measures to be devised, a finite number of outburst simulation tests were carried out in the study. The results show that the contribution of the gas pressure to the energy required for an outburst is hundreds of times that of the in situ stress during the outburst. With increasing mining depths, the higher the in situ stress, the gas pressure, and the temperature; however, the temperature shows the lowest influence on the outburst intensity among various parameters such as gas pressure, the thickness of soft coal, and the temperature. The initial expansion energy of releasing gas (IEERG) is an index reflecting the influences of in situ stress, gas pressure, and coal strength on outburst intensity. The test results indicate that the potential amount of coal ejected can be predicted by measuring the IEERG of coal masses and the thickness of soft coal in outburst-prone zones. According to the failure characteristics of coal masses after an outburst, the larger the outburst intensity is, the smaller the volume of residual coal area relative to the outburst holes. The shapes of extrusive coal-gas flows after an outburst show that the outburst process is a chain of events occurring over multiple cycles as follows: preparation, initiation, development, and termination. The recorded video footage of an outburst also shows this.

Computer-aided simulation to investigate material flow in combined-radial extrusion

In this present paper, the combined-radial extrusion process at room temperature is considered. Computer-aided simulations by the rigid-plastic finite element program such as QForm 2D in two different schemes of the combined-radial extrusion process, viz, single-ended and double-ended have been used. The die schemes, die geometry parameters, axisymmetric billet dimensions and power mode parameters to investigate forming characteristics such as deformation patterns (gridlines distortion), distributions of effective strain and stress and comparisons of load–stroke curve in these processes by using various relationships have been applied. Based on the simulation results, it is concluded that the maximum forming load will occur in single-ended process and the best strain-stress distributions will be appear in double-ended process.

Effect of Filler Orientation on the Electrical Conductivity of Carbon Fiber/PMMA Composites

The electrical conductivity of extruded carbon fiber (CF)/Polymethylmethacrylate (PMMA) composites with controlled CF aspect ratio and filler fractions ranging from 0 to 50 vol. % has been investigated and analyzed. The composites were extruded through a capillary rheometer, utilizing either 1-mm or 3-mm diameter extrusion dies, resulting in cylindrical composite filaments of two different diameters. Since the average CF orientation becomes more aligned with the extrusion flow when the diameter of the extrusion dies decreases, the relationship between conductivity and average fiber orientation could therefore be examined. The room temperature conductivities of the extruded filaments as a function of CF fractions were fitted to the McLachlan general effective medium (GEM) equation and the percolation thresholds were determined to 20.0 ± 2.5 vol. % and 32.0 ± 5.9 vol. % for the 3-mm (with CFs oriented less) and 1-mm (with CFs oriented more) filaments, respectively. It turned out that the oriented CFs in the composite shift the percolation threshold to a higher value, however, the conductivity above the percolation threshold is higher for composites with oriented CFs. A novel approach based on the Balberg excluded volume theory was proposed to explain this counterintuitive phenomenon.

Extrusion Temperature and Flow Rate Effects on Tensile Properties of Additively Processed Poly(Ethylene-<i>co</i>-Trimethylene Terephthalate)

This study investigated the effects of the extrusion temperature and volumetric flow rate settings in a fused filament fabrication (FFF) process on the tensile properties of specimens made of poly(ethylene-co-trimethylene terephthalate). The tensile strength almost doubled from 13.5 MPa at 230°C to 26.7 MPa at 260°C extrusion temperature, while the elongation at break improved to 5.4% and the tensile modulus rose to 641.8 MPa at the highest temperature. Similar observations were made when the extrusion flow rate was augmented to 115% of the initial value, with part strength greatly improving to 795.9 MPa and part elasticity increasing by 22%. These results illustrate two effective strategies to enhance the mechanical properties of components made in an engineering material that is increasingly being utilized in filament-based 3D printing.

Research on Extrusion of Rubber Composites Reinforced by Short Fibers Orientation Based on FEA

In recent years, rubber composites reinforced by short fibers has been researched deeply, because of its good performances such as higher wear resistance, higher cut resistance and so on. Some research results indicated that if short fibers get orientation in rubber composites, the performances of rubber products could be promoted greatly. But how to make short fibers get orientation in rubber matrix during extrusion is still a real problem. And there are many parameters affect the short fibers orientation. So, in this paper, the effects of die structure including expansion-die and dam-expansion-die on extrusion flow field of short fiber and rubber composite material during extrusion process has been researched by Polyflow. And the FEA results about the pressure field, velocity field and the velocity vector of the rubber composites flow field indicate that, comparing with expansion-die and the dam-expansion-die, the latter one is better for the extrusion process of rubber composites and making short fibers get radial orientation in rubber matrix.

Observation of Particle Behavior in Two Dimensional Extrusion Flow of Concentrated Particle Suspension

Observation of Particle Behavior in Two Dimensional Extrusion Flow of Concentrated Particle Suspension

Numerical simulation and experiment on effect of ultrasonic in polymer extrusion processing

The influence of ultrasonic wave on the flow field parameters and the precision of extruded products are studied. Firstly, the effect of vibration power on the average velocity of the outlet, the average viscosity of the die section, the average shear rate and the inlet pressure of the die section were studied by using the Polyflow software. Secondly, the effects of ultrasonic strength on the die temperature and the drop of die pressure were studied experimentally by different head temperature and different screw speed. Finally, the relationship between die pressure and extrusion flow rate under different ultrasonic power were studied through experiments.

Effect of Screw Rotation Speed on Extrudate Flow Rate and Pressure Drop

Effect of Screw Rotation Speed on Extrudate Flow Rate and Pressure Drop

Mayer Kangri metamorphic complexes in Central Qiangtang (Tibet, western China): implications for the Triassic–early Jurassic tectonics associated with the Paleo-Tethys Ocean

The Mesozoic orogeny in Central Qiangtang Metamorphic Belt, northern Tibet, provides important insights into the geological evolution of the Paleo-Tethys Ocean. However, the Triassic–early Jurassic tectonics, particularly those associated with the continental collisionstage, remains poorly constrained. Here we present results from geological mapping, structural analysis, P–T data, and Ar–Ar geochronology of the Mayer Kangri metamorphic complex. Our data reveal an E–W-trending, ~2 km wide dome-like structure associated with four successive tectonic events during the Middle Triassic and Early Jurassic. Field observations indicate that amphibolite and phengite schist complexes in this complex are separated from the overlying lower greenschist melange by normal faulting with an evident dextral shearing component. Open antiform-like S2 foliation of the footwall phengite schist truncates the approximately north-dipping structures of the overlying melange. Microtextures and mineral chemistry of amphibole reveal three stages of growth: Geothermobarometric estimates yield temperatures and pressures of 524 °C and 0.88 GPa for pargasite cores, 386 °C and 0.34 GPa for actinolite mantles, and ~404 °C and 0.76 GPa for winchite rims. Peak blueschist metamorphism in the phengite schist occurred at ~0.7–1.1 GPa and ~400 °C. Our Ar–Ar dating of amphibole reveals rim-ward decreasing in age bands, including ~242.4–241.2 Ma, ≥202.6–196.8, and 192.9–189.8 Ma. The results provide evidence for four distinct phases of Mesozoic tectonic evolution in Central Qiangtang: (1) northward oceanic subduction beneath North Qiangtang (~244–220 Ma); (2) syn-collisional slab-break off (223–202 Ma); (3) early collisional extension driven by buoyant extrusion flow from depth (~202.6–197 Ma); and (4) post-collision contraction and reburial (195.6–188.7 Ma).

Flow visualisation and modelling of solid soap extrusion

Ram extrusion of a solid granular soap was studied using three geometrically identical but differently-scaled extruders. The experimental design revealed deviation from the Benbow and Bridgwater (1993) extrusion model due to non-ideal, scale-dependent effects. Typically these effects, linked to the shear rate in the extruder, are absorbed into the model’s material pseudo-properties. The data were able to be represented using the Basterfield et al. (2005) model for extrusion flow which does include a shear rate as a variable.Flow visualisation in conjunction with fluid dynamics-based simulations showed, however, that the assumptions underlying the Basterfield et al. model are not appropriate for soap extrusion, despite the good agreement of the model with the experimental extrusion data. This highlights a need for care in interpretation of extrusion data, in that the limited information gathered about any given experiment, typically just the extrusion pressure, can lead to the generation of spurious parameters if the wrong model is applied.

Particle migration in planar die-swell flows

We present a numerical study on particle migration in a planar extrudate flow of suspensions of non-Brownian hard spheres. The suspension is described as a Newtonian liquid with a concentration-dependent viscosity, and shear-induced particle migration is modelled according to the diffusive flux model. The fully coupled set of nonlinear differential equations governing the flow is solved with a stabilized finite element method together with the elliptic mesh generation method to compute the position of the free surface. We show that shear-induced particle migration inside the channel leads to a highly non-uniform particle concentration distribution under the free surface. It is found that particle migration dramatically changes the shape of the free surface when the suspension is compared to a Newtonian liquid with the same bulk properties. Remarkably, we observed extrudate expansion in the Newtonian and dilute suspension flows; in turn, at high concentrations, a die contraction appears. The model does not account for normal stress differences, and this result is a direct consequence of variations in the flow stress field caused by shear-induced particle migration.

Numerical simulation and experimental research of metal dynamic flow in cold extrusion under the electric-hydraulic vibration

With thick-wall cylinders as the researched object, the paper adopts a novel cold-extrusion technology, namely electro-hydraulic cold-extrusion, to apply vibration signals into a traditional cold extrusion technology. With volume effects of vibration processing as the theoretical basis, Deform-3D software was used to conduct numerical simulation of metal materials under a traditional extrusion type and an extrusion mode with vibration respectively. Evolution processes of metal flow lines and metal grid flow under two kinds of extrusion types were analyzed and compared in details. Through experimental research, computational results of numerical simulation were verified. Metal flow lines at corners of molded parts were observed and analyzed in particular. Researched results show that the metal flow velocity increased and the bending level of cross-section flow lines of the metal decreased after applying vibration signals compared with the traditional extrusion type. The research indicated that vibration promoted metal flow, reduced resistance of the metal flow, and obtained more uniform deformation of metal materials during plastic molding. Research achievements obtained in this paper provide important theoretical and practical engineering values for effectively applying vibration in mechanical processing fields.

Linking particle properties to dense suspension extrusion flow characteristics using discrete element simulations

Extrusion is a widely used process for forming suspensions and pastes into designed shapes, and is central to the manufacture of many products. In this article, the extrusion through a square‐entry die of non‐Brownian spheres suspended in Newtonian fluid is investigated using discrete element simulations, capturing individual particle‐particle contacts and hydrodynamic interactions. The simulations reveal inhomogeneous velocity and stress distributions, originating in the inherent microstructure formed by the constituent particles. Such features are shown to be relevant to generic paste extrusion behavior, such as extrudate swell. The pressure drop across the extruder is correlated with the extrudate flow rate, with the empirical fitting parameters being linked directly to particle properties such as surface friction, and processing conditions such as extruder wall roughness. Our model and results bring recent advances in suspension rheology into an industrial setting, laying foundations for future model development, predictive paste formulation and extrusion design. © 2016 American Institute of Chemical Engineers AIChE J, 63: 3069–3082, 2017