The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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Cost and Mixing Keeps the Screw Rivalry Up & Going
Screw is the heart of an extruder. It is fact that mixing capability of a single screw is poorer than of a twin screw. More precisely, the dispersive action (breakdown) of a twin screw extruder is always better than of a single screw extruder. For producing new blends or alloys, as well as for mixing powdered feedstock or regrinds -- twin screw extruders give unparalleled dispersion. No surprise that twin screw extruders cost more than single screw extruders.
‘Plug-and-Play’ Weight Reduction Solution by Hollow Glass Microspheres
Fillers have been in use since the early days of plastics. Today’s enormous growth of the polymer industry is due to the unique properties of fillers they impart to polymers. Glass bubbles (low density hollow glass microspheres) as fillers have been incorporated into thermoset polymers for decades. They are tiny hollow spheres and are virtually inert. These glass bubbles are are compatible with most polymers. Until recently, their use with thermoplastic polymers has been limited because of high rates of bubble breakage from the high shear forces to which they are exposed during such thermoplastic processing operations as extrusion compounding and injection molding. At issue has been the strength of the glass microspheres.
Analysis of the Advantageous Process and Mixing Behaviour of Wave-Dispersion Screws in SSE
In the plastics processing industry, the improvement of the economic efficiency of extrusion lines is important. This is achieved, especially in single-screw extrusion, by an increased throughput at a constant machine size. In order to guarantee high melt quality, new screw concepts are being developed in addition to conventional screws. These include wave-dispersion screws, which are designed to break up the solid bed at an early stage so that the melting and homogeneity behavior is optimized. This paper deals with the experimental comparison of two wave-dispersion screws with a common barrier and 3-section screw. The maximum achievable throughput and in particular the melt quality with regard to thermal and material homogeneity are investigated in order to detect possible advantages of the screw concepts. Here it has been shown that both better thermal and material homogeneity with simultaneously higher possible throughputs can be achieved by wave-dispersion screws.
Application of Hybrid Modeling In Polymer Processing
For many decades, the setup and solution of polymer processing models involved use of analytical or numerical methods. These characteristics have changed with the recent digitization of polymer processes and the collection of enormous amounts of data. It is increasingly common to use data-driven modeling techniques to analyze processes, for which analytical and numerical models may not fully describe the process behavior in operational situations. These techniques have significantly extended the set of tools available to the engineer, providing new possibilities of how to develop more accurate process models. As a result, the setup of an appropriate modeling strategy more than ever requires a thorough understanding of the individual modeling techniques. This article was designed to address the potentials and limits of analytical, numerical, and data-based modeling techniques when modeling polymer processes. Moreover, we show how these methods can be combined into one hybrid approach to solve polymer process models not solvable so far. The findings are further illustrated by means of a particular use case, which models the flow of polymer melts in single-screw extruders.
Comparison of Additive and Conventional Tooling on Injection Molded Part Properties
Additive tooling can make injection molding viable for low volume production, reducing tooling cost and lead-time. This studycomparesthe final properties of injection-molded samples manufactured with a steel mold and two sets of 3D printed polymerinserts using material jetting (Digital ABSfrom Stratasys) and stereolithography(Toughfrom Formlabs). Results show thatthe Digital ABS insertsfailed after100 cycles, while the Tough insertsfailed after15 cycles. Parts producedwith steelmold and Tough and Digital ABS inserts exhibited a shrinkage of approximately3%, 6% and 9% respectively. The shrinkage and ultimate tensile strength was directly proportional to the degree of crystallinity measured using differential scanning calorimetry(DSC).
Evaluation of Mesh Interface and Immersed Boundary Models For the Optimisation of Mixing Elements
Mesh interface and immersed boundary models are presented as simplifications for the simulative design of dynamic mixing elements for single screw extruders. These simplifications have great potential to cut complexity and cost in both drafting and computation. Results for distributive mixing are compared quantitatively and qualitatively to a non-simplified 3D model. It is found that good agreement with the 3D model is achieved when the simplified models’ throughputs are adjusted for mass conservation.
Extrusion Technologies for Low Temperature Compounding
For many applications the ability to continuously compound at low temperatures can be extremely beneficial. However, many challenges prevent traditional setups from being functional, particularly for applications requiring a high degree of mixing with extreme cooling or simultaneous temperature control. This paper addresses and experimentally validates four different technologies for compounding materials at low temperatures.
Profile Extrusion Die Balancing Using Polymer Extrusion Simulation Software
The design of an extrusion die has been evaluated utilizing a 3-D polymer extrusion simulation software for optimal flow. The flow pattern, pressure, temperature, and shear rate are simulated in the software. The post-die extrudate shape is also simulated to show the improvement by balancing flow velocity in different sections. The combination of 3-D modeling and simulation decreases the time and difficulties for tuning the die during manufacturing.
Design of A Novel Free-Rotating Mixing Sleeve For Single-Screw-Extrusion
This paper will present the conceptual design of a novel free-rotating mixing sleeve for single screw applications. In contrast to most of the currently available free rotating mixing rings (e.g. the TMR) which primarily have a distributive mixing effect, the mixing sleeve presented in this paper will focus on dispersive mixing. The variety of requirements on dispersive mixing make the structural design and the geometrical layout very complex. Therefore, a method is introduced to couple a full parametric 3D-CAD master model of the mixer with a 3D-CFD-simulation. The aim is to describe a set-up of an automated process to design and optimize the novel mixing element by defining several target figures.
Effect of Shear Rate and Draw Down Ratio on tensile Properties of Thermally Conductive Polymer
The use of thermallyconductivepolymersto replaceconventionaltubingmaterialshas the potentialto improveefficiencyof heat exchangedevices. Inthis study,a designof experimentswas conductedto understandthe effectsofextrusionon physicalpropertiesof thermallyconductivetubingfor an MCS.Shearrates and draw downratioswere independentlyvaried,and the tensilepropertiesof the resultingtubingwere measuredand comparedto determinethe effectof each.It was foundthat, in accordancewith previousliterature,shearrate had no substantialeffecton tensilepropertieswhile draw downratiohad a positiverelationshipwith tensileproperties
Effect of Ultrasonic Extrusion On Properties of Colloids Containing Epoxidized Soybean Oil and Clay
Colloid prepared with epoxidized soybean oil (ESO) and organically modified montmorillonite (OMMT) has been processed using an ultrasonic twin-screw extruder under various ultrasonic amplitudes and screw rotation speeds. Ultrasonic treatment has significantly increased OMMT dispersion in ESO, according to WAXD and rheological data. Yield strength, storage and loss modulus, complex viscosity and relaxation time of the colloid have been increased with increase of ultrasonic amplitude. Under certain high ultrasonic amplitudes, increase of one to two orders of magnitude have been observed. Creep and recoverable compliance have been decreased with the increase of ultrasonic amplitude. The tremendous changes in rheological properties of the colloid is a result of significantly improved OMMT dispersion with the aid of ultrasonic treatment. With no or low ultrasonic treatment, a higher screw rotation speed has improved OMMT dispersion since it brings more mixing effect. However, at high ultrasonic amplitudes, a higher rotation disrupts jet flow and has led to less dispersion improvement compared with the same colloid extruded at a lower rotation speed.
Energy Transfer Single-Screw Extruder Design For Peroxide-Containing Polyolefin Compositions
Peroxide-containing ethylenic polymers are used in many power cable applications. The processes involve extrusion of the polymer compositions to form one or more layers on a conductor, followed by crosslinking in a continuous vulcanization step. To extrude the composition, it is critical to maintain a low discharge temperature so that the peroxide does not decompose significantly during the extrusion process, so as to prevent premature crosslinking. However, with a low discharge temperature, the rate is usually reduced; for some formulations, the rate reduction is dramatic. This paper describes an energy transfer (ET) screw design that enables high rates at acceptably low melt discharge temperatures, or alternatively, yields significantly lower melt discharge temperatures at a given rate than a conventional Maddock mixing screw. The design simulations of the new ET screw were validated experimentally.
Fatigue Resistance of Structural Adhesives
Adhesive selection in high dynamic load environments relies heavily on mechanical adhesive properties, including shear, peel and compressive strength. Over time and in the life a part, fatigue can occur to metals, plastics and adhesives. Fatigue weakens the overall strength of these components and can lead to premature failure. In the case of adhesives, shear strength values may depreciate an order of magnitude, from thousands to hundreds of psi due to a life of wear and dynamic movement, which can lead to failure. When selecting an adhesive for bonding a joint, the likely first choice is the adhesive with the highest shear strength with the assumption that the higher the shear strength the longer the part will last. However, upon testing, higher shear strength does not directly correlate to a longer part life. In the case of hybrid adhesives (Loctite® HY4090GY™ and HY4070™) compared to epoxies (Loctite® E-20HP™), the epoxy greatly outperformed the hybrids in shear strength, but the hybrids greatly outperformed the epoxy in limit of endurance. Overall, the methyl methacrylate (MMA) adhesive (Loctite® H8003™) proved to be the most fatigue resistant adhesive tested.
Use of Gradually Changing Profile Shape in Extrudate Sizers for Simplification of Die Design
Simulation of the flow and extrudate deformation in two extrusion dies with gradually changing profile shape in successive sizers is presented. The change in the profile shape in sizers is used to employ a simpler die geometry and then deform the extrudate in sizers to the required final product shape. Effect of non-uniform exit velocity, cooling shrinkage and shape of sizer profiles on extrudate deformation is included in the simulation. The predicted extrudate shape and layer structure is found to match accurately with those in a coextruded product.
Flow Simulation of A Microcapillary Cast Film Die
A relatively wide (610 mm) lab-scale microcapillary cast film die was fabricated to aid in the development of this unique film processing technology. Due to the approach used to create microcapillary channels, standard die design techniques for maintaining uniform film gauge (e.g. die lip adjusters) are not applicable. A series of modifications were made to the original die design to improve film gauge. One such modification was the use of computational fluid mechanics (CFD) to improve flow uniformity across the die. Due to the multitude of air pins located near the die outlet, it is impractical to perform direct CFD simulations based on the actual flow geometry. Instead, the flow geometry associated with the comb-like structure of the air pin region is replaced by a porous medium with an equivalent viscous resistance. The primary focus of this paper is a description of the porous medium CFD technique used in the design of the 610 mm wide die.
Improving Thermoforability of IPP Through Multilayer Coextrusion
While the flow forces governing primary melt-based polymer processing techniques, such as extrusion and injection molding, have been extensively studied, characterization of forcesin secondary processes such as thermoforming is limited. In this work we utilize multilayer coextrusion to create an extruded film with 100s of alternating linear low density polyethylene (LLDPE) and isotactic polypropylene (iPP) layers; and by extension, 100s of interfaces. The combination of LLDPE, iPP, and these interfaces decreases the elastic storage modulus (E’) and broadens the rubbery plateau observed via dynamic mechanical analysis (DMA). The broadening of the rubber plateau is correlated with an observed improvement in LLDPE/iPP multilayer thermoformability compared to the homopolymer LLDPE and iPP films.
Machine Learning and Multi-Objective Optimization of Industrial Extrusion
A three-level multivariate control system is described that transforms a vector of machine inputs to a vector of virtual process states, and then these virtual process states to key performance objectives. The multivariate system is implemented on a 150 mm (6 inch) screw diameter producing approximately 500 kg/hr of polyvinyl chloride (PVC) film having a nominal width around 1 m (37 inch) and a nominal thickness of 0.38 mm (0.149 inch). Validation is performed with respect to modeling and optimization of three performance objectives including production rate, energy efficiency, and process capability. The results suggest significant gains with respect to the Pareto optimality (efficient frontier) of energy efficiency and process capability.
Modeling the Non-Isothermal Conveying Characteristics In Single-Screw Extrusion By Application of Network Analysis
This paper deals with the modeling of the conveying behavior of polymer melts in single-screw extruders based on a network-analysis approach. The polymer-melt rheology is strongly temperature-dependent and hence the temperature profile affects the pumping capability. In this work, we propose an approach to predicting the non-isothermal, coupled axial pressure and temperature profiles. We present the fundamental background of the implemented pumping and dissipation models and the network theory for modeling the axial pressure and temperature profiles. The simulation procedure for calculating the non-isothermal conveying characteristics is shown and a few exemplary simulation results are presented. The novel algorithm provides fundamental insights into the non-isothermal extrusion characteristics and enables screw design and process optimization in single-screw extrusion.
New Development in Adhesion Promotion Using Flame Plasma Surface Treatment - Tutorial
Adhesion promotion technologies have wide application in the numerous industries for a wide range of plastic parts, such as those made of PE, PP, PET, etc. One method used to modify the surface of these and other polymer products to promote adhesion of coatings and adhesives is flame plasma. This paper describes the theory behind natural gas, propane or LPG fired flame plasma surface treatment to promote adhesion of water based inks, coatings, adhesives, labels and other substrate laminates to polyolefin based substrates. Critical parameters in flame treatment are, flame chemistry, flame geometry, plasma output and distance of the burner to the part. The interrelationship between these variables, and how to control them for optimum surface treatment, will be discussed. The use of Schliren imaging technology, high speed photographs of the flame geometry, used to develop new burner designs, as well as advances in equipment technology will be presented. A completely new patented process design has been developed and successfully implemented providing significantly improved control of the flame chemistry, while at the same time simplifying the process control and mechanical hardware required. In addition, the new design improves the overall efficiency of the flame treating process Troubleshooting & maintenance of flame plasma surface treating systems will be discussed.
Optimization of Processing Properties of Co2 Rubber Compounds
In order to reduce the carbon footprint, carbon dioxide (CO2) can be used as a raw material for synthesizing innovative rubber materials. In the following, the process of testing and improving CO2-based rubber compounds is described. The substitution of parts of the polymer chain by CO2 contributes to a sustainable rubber industry. A wide range of different raw materials is provided by the manufacturer, compounded and then tested. In order to improve processability, compound recipes are modified and improved. The investigations focus on static and dynamical mechanical properties and caloric properties. After the ability to be processed in an internal mixer is proven and improved by the use of processing aids, the compounds are tested for extrusion and vulcanization. It is shown, that CO2-rubber compounds can be processed on a rubber extruder and can be vulcanized by using hot air and infrared radiation.
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