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In the field of polymer processing, the extrusion is one of the most common processing methods. Not only in the processing of recycled materials, also when using virgin polymers there can be contaminations during the storage or processing of the material. This may adversely affect the melt quality and by this also the quality of the final extrusion product. Examples for possible contaminations are metal particles which are caused by wear and tear of the extruder, or degradation products of the processed material itself.As a result of increasing demands on the quality of extrusion products, especially in the field of fiber and film extrusion, filtration of polymer melts is widely used and state of the art today. To remove unwanted debris out of the melt, different metal filter media is used. Some examples for typical filter media are different kinds of wire mesh, filters out of nonwoven metal fibers or sintered metal powder discs. Using this filter media, it is possible to remove foreign particles like solid particles, as well as soft components, the so called “gels” from the melt. This ensures a high quality extrusion result.In order to compare the filtering effect of different filter media and to assess the contamination and selective filtration it is necessary to develop a possibility for reproducibly rapid contamination of filter materials. In this work this should be elaborated as part of the PET processing. For this, a real filter contamination is analyzed. After this a definition of an adequate substitute dirt is effected. The focus is both on solid particles, as well as on gel contamination. With this it is possible to generate realistic and reproducible filter soiling so that pressure rise curves can be generated in order to compare the behavior of different filter media in the extrusion process.
Instrumentation and analytical methods are presented for on-line, real-time analysis of performance in single screw extrusion processes. The methodology implements analytical models for heating and cooling power for each zone, screw torque, apparent viscosity, and specific energy. In additional, numerical methods are implemented to provide real-time estimate of the process variation. The protocol defines volumetric, adiabatic, theoretical, and robustness efficiency measures useful for extrusion process engineering and optimization. Validation data is provided for general-purpose and barrier screw designs.
This paper introduces 5 different types of extrusion problems in production scale ranging from formulation issues to screw design problem. Each extrusion problem was analyzed and diagnosed by using a highly instrumented pilot-scale extruder, equipped with 14 pressure/temperature transducers along the axis of an extruder barrel. The case studies will demonstrate how pilot-scale extrusion results can be correlated with the production-scale extrusion problem, and how the measured pressure and temperature data can be used to optimize and troubleshoot production-scale extrusion problems.
A central challenge in the extrusion process is the interaction of the melt with the metallic die wall. These interactions, such as friction and adhesion, lead to a limitation of mass throughput due to high pressure drop and long material and color changeover times. Since raw material costs are price-determining with a percentage of up to 80 %, it is imperative to reduce these interactions. Extrusion dies in particular offer a very large contact area for these interactions, as the melt is formed out there with usually a large surface area. A possible solution to reduce these interactions is the encapsulation of the melt with a low viscous thermoplastic melt before entering the extrusion die. Hereby, the parabolic flow profile with wall adhesion is converted into a block-like flow profile. The pressure drop and material and color changeover times can be reduced, in this way.In this paper, the influence of the melt encapsulation with two low viscous LDPE resins on the flat film extrusion process with focus on the reduction of pressure drop and rearrangement effects is investigated. Therefor the low viscous encapsulation material, the processing temperature and the layer thickness of the low viscous encapsulation material are varied. For example, the pressure drop of the reference process at 200 °C can be significantly reduced from 47 bar to 12 bar for LDPE65 at a melt pump speed of 0.2 rpm. However, due to rheological effects a rearrangement of the low viscous material appears. This means the low viscous material accumulates in the edge area of the rectangular flow channel. As a result, the usable film width is reduced.
When modeling the melt-conveying zone of single-screw extruders, generally the flat-plate model is applied. Using a cylindrical reference frame, we investigated the effect of channel curvature on flow rate and viscous dissipation, considering a two-dimensional, fully developed, isothermal flow of a power-law fluid. Re-writing the flow equations and applying the theory of similarity revealed the existence of four independent influencing parameters: Π_(p,z), n, t/D_b , and h/D_b . Based on these, we carried out a comprehensive parametric study investigating flow rate and viscous dissipation. Our results show that the channel-height-to-diameter ratio has a significant influence on both flow rate and viscous dissipation.
Being able to include the shear-thinning behavior of polymer melts in the theoretical analysis of melt-conveying and pressurization generally involves the application of numerical techniques. We have recently proposed a fast and accurate analytical approximation method for predicting the pumping characteristics of power-law fluids in three-dimensional metering channels. Removing the need for time-consuming simulations, this novel theory provides an algebraic throughput-pressure gradient relationship that can be implemented easily in real screw designs. By considering the three-dimensional geometry of the screw channel and the non-Newtonian flow behavior of the polymer melt, our model is a close representation of the actual physical process. Here, we revisit the design of the heuristic model, present further results, and validate the method against additional numerical solutions.
Post-die analysis in the polyXtrue software is enhanced to include the effect of cooling shrinkage on extrudate distortion. Extrudate distortion for two different profile dies is predicted. The effect of non-uniform exit velocity as well as that of cooling shrinkage on extrudate distortion is included in the analysis. The extrudate distortion predicted including the shrinkage analysis is compared with the distortion predictions based only upon non-uniform exit velocity. Extrudate distortion due to non-uniform exit velocity is further increased when cooling shrinkage is included in the analysis.
This capstone project consists of making a gravimetric feeder from a volumetric feeder with a speed-controlled screw. A gravimetric feeder starve-feeds material into an extruder at a constant weight per hour. A lot of extrusion companies use gravimetric feeders because it saves them a lot of money on scrap from inconsistent lines of filament. It also uses Proportional Integral Derivative (PID) controlling to monitor the weight loss and counteracts any feeding inefficiencies. Without using PID and instead using a set speed control, the screw might not feed a constant amount of material. The PID will be implemented into the system using C++ language in the Arduino software. The project will be completed using a starve-feeding hopper, a 165-lb. capacity bench scale, an Arduino Uno kit, a motor shield, and an RS-232 converter.
In this work, effect of the second to first normal stress difference ratio at the die exit, uniaxial extensional strain hardening, planar-to-uniaxial extensional viscosity ratio and Deborah number has been investigated via viscoelastic isothermal modeling utilizing 1D membrane model and a single-mode modified Leonov model as the constitutive equation. Numerical solutions of the utilized model were successfully approximated by a dimensionless analytical equation relating the normalized maximum attainable neck-in with all above mentioned variables. Suggested equation was tested by using literature experimental data. It was found that approximate model predictions are in a very good agreement with the corresponding experimental data for low as well as very high Deborah numbers. It is believed that the obtained knowledge together with the suggested simple analytical model can be used for optimization of the extrusion die design, molecular architecture of polymer melts and processing conditions to suppress neck-in phenomenon in production of very thin polymeric flat films.
This paper addresses the generation of a general valid analytic equation for estimating the initial pressure drop of woven screens in terms of polymer recycling. Therefore we performed numerical CFD Simulations as basis for heuristic modeling. Based on evolutionary heuristic algorithms, we applied symbolic regression in order to determine the pecScreen model. We performed experiments at different melt filtration systems for validation of the model using virgin as well as in-house, post-industrial and post-consumer recycling materials. It turned out that the results of the general valid analytic equation are in good agreement with the experimental determined data, yielding a coefficient of determination (R²) of 0.92.
Extrusion dies exert influence on later final product quality. Therefore it´ll make a point the dimensional and die design by using programs for calculation and simulation frequently. For the implementation of product design, it is significant to understand the flow conditions and to be able to predict the flow behavior accurately. Special rheological flow phenomena in the plastic melt as cross flows, which flow perpendicular to the main flow, should be taken into account. This phenomenon is caused by pressure gradients transverse to the direction of extrusion and both the flow distribution and the pressure consumption are influenced in the die. Network theory is a simple numerical method for a holistic one-dimensional representation (GEB) in a spreadsheet program (p.e. Excel), which can design an optimal uniform flow rate distribution and low pressure drop. The cross flow behavior can´t be described with this method as yet. Therefor a linear equation system according to the Gauss algorhythm was developed, which can calculate the cross flows in the die with rectangle cross-section. In this network crosslinks are implemented to take into account the cross flows. The equation system is set up from the network, which corresponds to the number of the desired partial volume flows in the number of established equations. Furthermore the technical measurement entry of cross flows was conduced about the evaluation of ellipsoid shape according to the flow direction and the alignment according to the flow direction. Dead-stop experiments were performed by adding a blowing agent to the extrusion process. Negatives of die with gas-filled bubbles were prepared and evaluated with image analysis software across the half width of die. Afterwards the network theory was validated by Computational Fluid Dynamics (CFD).
Significant interest has been growing around the properties and potential applications arising from 2D materials. Molybdenum disulfide (MoS2) is a well-known transition metal dichalcogenide (TMD) that can exhibit tunable electrical, optical, and catalytic characteristics based on its method of preparation. Here we have prepared optical plaques of poly(methylmethacrylate) containing hydrothermally synthesized MoS2 nanoflowers, both neat and complexed with reduced Graphene Oxide (rGO), using a laboratory scale twin screw extruder and injection molder. Filler dispersion, composite optical properties, and thermal properties have been assayed as a function of MoS2 characteristics and loading.
Three dimensional (3D) flow simulation though twin screw extruders are inherently difficult. This is due to the transient nature of the flow, the non-Newtonian behavior of the polymer, the fact that the screws are never fully filled in addition to other flow physics that may also be present (e.g. viscous heating or chemical reaction). Current flow simulation technology limited the scope of flow simulation to fully filled twin screw extruders which is seldom a realistic scenario. In the current work, the newly developed Overset Mesh technique for modeling moving part in general is employed to simulate such complex motion of a twin screw extruder. The fact that the extruder is starve-fed is taking into account and thus the flow field represents both the liquid polymer as well as the air (gas) within the extruder. Emphasis is placed on the flow visualization within the twin screw, velocity field, polymer volume fraction, shear rates and mixing index developed. The overset mesh technique is also compared with the long standing mesh superposition technique (MST) typically used to model fully filled twin screw extruders. Results for a simple 2D fully filled system compared very well between the overset mesh and the superposition mesh techniques. Similarly, a 3D comparison between the fully filled system using MST and the partially filled system using overset mesh have been carried out and the differences have been highlighted.
The co-rotating fully intermeshing twin-screw extruder has evolved significantly in the 60 years since it was commercialized in 1957. While this equipment might be considered a “mature” technology, it has not experienced a decline in new developments as might be expected, but rather a significant number of advancements. The technology continues to evolve. For example in the last 20 years several significant developments have been introduced. These include a) the implementation of high torque (power) designs, b) the use of increased screw rpm in conjunction with high torque for improved operating flexibility and productivity, and c) a breakthrough technology for feeding difficult to handle low bulk density materials. However, one area of twin-screw technology that has not evolved as much is screw elements geometry. Conveying elements and kneading blocks have remained essentially the same since the original Erdmenger design patents filed in the late 1940’s and early 1950’s. However, to take advantage of increased torque and power transmission capacity introduced in the newest generation of twin-screw compounding extruders, solids feed conveying and melt/mixing capacity in, for example, some highly filled compounds, had to be improved. Coperion has developed special involute screw and kneading elements with a new (Patent: EP 2 483 051 B1) cross section design to help achieve this objective. This paper will focus on the comparison of standard kneading blocks vs new involute kneading elements, specifically looking at some significant aspects related to performance.
The application of micro-structures enables the integration of new functionalities on product surfaces. Though some applications have successfully been introduced on the market, widespread use of the full potential is depending on efficient and economical production processes. For plastics films the variothermal extrusion embossing process enables a quick and cost efficient replication of micro-structures on large areas.To achieve high quality replication, the process has to be finely tuned to the desired geometry. In this paper, the effects of the processing parameters on the replication quality inside previously established processing windows are investigated for two polycarbonate materials. The replication quality is evaluated for three different micro-structures.The experiments confirm strong interdependencies between the processing parameters, the material behavior and the geometric features of the micro-structures. These lead to partly contrary effects on the replication quality for different micro-structures and make the prediction of the optimal processing parameters for any given geometry very difficult.
Filling ratio, resin pressure and resin temperature are important process parameters related to the residence time distribution and thermal history of resin in a twin-screw extruder. This study presents a series of experimental results of these parameters and compares them with the values obtained from the 2.5D Hele-Shaw model calculation developed in our group recently for a twin screw extruder. Homo polypropylene with melt flow rate of 7.0 g/10-min was feed to a ϕ 26 mm co-rotating twin screw extruder. Temperature and pressure of resin were measured using sheathed temperature sensor and pressure transducer contacting to molten resin. Fill ratio distribution was measured by our laser light section method. The experimental results of resin pressure, temperature and fill ratio agreed well with the simulation results. It was validated that the Hele-Shaw model is valid for co-rotating twin screw extruder.
Loss of molecular weight due to shear and hydrolytic degradation resulting in lower Intrinsic Viscosity (IV) is a matter of importance while working with PET resin. In applications that demand high levels of dispersion, for instance, addition of Carbon Black, drop in IV has been an unfortunate compromise to achieve the necessary dispersion, which is measured using a Filter Pressure Value (FPV). This study uses an advanced screw design to compare viscosity retention and effective dispersion of carbon black in Poly(ethylene terephthalate) (PET) resin against a screw design used for many years as an industry standard. The advanced screw design attempts to eliminate the presence of peak shear, which is considered as the leading factor for the degradation of PET and the resultant reduction in IV. PET was blended with carbon black and dispersed in the extruder at a barrel temperature of 220°C to 260°C with screw speeds of 200, 250 and300 rpm. The screw configuration resulting in reduced degradation of PET and the retention of molecular weight was evaluated along with the dispersionpotential. These observations were evidenced from IV measurements on a Ubbelohde viscometers and Filter pressure value (FPV) for dispersion rating on a Collins FPV tester. Melt transducers were used to track melt temperature and pressure.Specific Mechanical Energy (SME) and extruder screw speed were also recorded from the extruder.
We present a systematic approach based on networks that uses tensor algebra and numerical methods to model and calculate selected double wave screw geometries in terms of pressure-throughput behavior. Due to the extreme diversity of their geometries, describing the flow behavior is difficult and rarely done in practice. Three-dimensional CFD methods (finite-element or finite-volume) are well capable of calculating the flow behavior in complicated geometries, but they require vast computational power, large quantities of memory, and consume considerable time to create a geometric model created by computer-aided design (CAD). Consequently, a modified 2.5-dimensional finite-volume method, termed Network Simulation Method (NSM) is preferable.The main goal of this study was to compare the results of the NSM with CFD. The results for isothermal melt-dominant flow correlated well. With recently developed pressure-/throughput models for two- and three-dimensional flow of shear-thinning fluids the accuracy of NSM could be further improved. This makes network analysis a valid and easy-to-use tool for screw calculations in practice.
Water-assisted mixing extrusion was used to prepare thermal conductive poly(vinylidene fluoride)/graphene oxide (PVDF/GO) nanocomposites. The injected water not only improves the GO dispersion in the PVDF matrix, but also promotes in situ thermal reduction of the GO. As a result, the intrinsic thermal conductivity of the GO is significantly increased. The interfacial interaction between the GO and PVDF facilitates the nucleation of crystallites at the PVDF-GO interfaces, leading to reduced interfacial thermal resistivity. The thermal conductivity of PVDF/GO nanocomposites prepared with water injection is significantly improved. The nanocomposite with 1.0 wt% GO exhibits a thermal conductivity of 0.475 W/mK, which is much higher than those of the PVDF (0.206 W/mK) and the nanocomposite prepared without water injection (0.335 W/mK).
The image analysis of the investigation of the melting process, as Maddock has already done in 1959, is further developed by means of modern image analysis. The experiments are carried out on the two most common screw types in the plastics industry: the general-purpose screw and barrier screw. Control of the residence time is essential for the production of high-quality products and is also important for biodegradable and other time-sensitive polymers. The results indicate that both the general- purpose screw and the barrier screw have significant stagnation zones and broad residence time distribution.
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