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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Simultaneous Characterization of Dispersive and Distributive Mixing in a Single Screw Extruder
Simulation of the dispersion of solid agglomerates along their trajectories in a single screw extruder with sequential tracking of parents and fragments allow us to assess conditions appropriate for dispersive mixing and simultaneously account for the spatial distribution of all particles in the system. A new mixing index based on the calculation of Shannon entropy for different size fractions of the minor component present in the system and giving preference to smaller sizes was developed.
Extrusion of BaSO4 Filled Medical-Grade Thermoplastic Polyurethane
Extrudability of 20% (vol.) BaSO4 filled medical-grade (additive free) thermoplastic polyurethanes was investigated. Filled TPU exhibits decreased shear viscosity and elasticity in comparison to unfilled TPU, generating reduced pressure drop at the die and reduced pressurization in the extruder. The moisture remaining in the BaSO4 may hydrolyze the polymer. However, hydrolysis is not sufficient and air, entrained with the filler into the extruder, reduces the viscosity and elasticity of the compounded TPU.
An Analysis of the Effect of Elongational Viscosity on the Flow in a Flat Die
The flow of a low-density polyethylene in a flat die is simulated using the axisymmetric and planar elongational viscosities estimated in an earlier publication by Beaupre and Gupta. Elongational viscosity is found to have only a limited effect on the velocity distribution at the die exit. However, the predicted pressure drop in the die and temperature distribution at the die exit changed significantly when the effect of elongational viscosity is included in the simulation.
An Optimization-Based Approach to Compute Sheeting Die Designs for Multiple Operating Conditions
A simulation-based approach is presented to optimally design polymer sheeting dies to operate over a range of operating conditions. The computational approach incorporates finite element simulations to quantify the ’goodness’ of a die design and includes a gradient-based optimization algorithm to update the die’s geometry. Examples are provided to illustrate the methodology for the creeping flow of purely viscous fluids through thin cavities that may be modeled with the Generalized Hele-Shaw approximation.
Twin Screw Extruder and Continuous Mixer Rate Limitations
An overview and general description of the fundamental parameters that limit feed rates of twin screw extruders (TSE’s) and continuous mixers (CM’s) is presented. This paper also identifies relationships that can be used to identify the key rate limiting parameters for a given TSE/CM design and set of operating conditions.
Deconvolution of Residence Time Distribution Signals to Individually Describe Zones for Better Modeling
Kinematic modeling has been shown to be important for the understanding and control of co-rotating twin screw extruders. Past techniques of kinetic modeling have dealt with the extruder as either one unit or a series of screw element wise units. In this work, multiple sensors are used to characterize the residence time distribution of an extruder. Additionally, the uncoupled signals from these sensors are deconvoluted to produce signals representative of the individual extruder zones.
A New High Speed Extruder with Melt Separation
The new extruder – project name S-Truder - surrounds the screw with a perforated sleeve to separate melt from unmelted resin. As soon as the melt develops, it flows through conically-shaped holes in the melting sleeve into the intermediate melting zone area and then with a pressure flow toward the screw tip. Therefore, the screw can then run at a higher rotation speed without overheating the polymer, and, in contrast to a “normal” screw, solid bed width is maintained. Experimental results and theoretical background will be described in this paper.
Closed-Loop Process Control Strategies for Thermoplastic Injection Molding Machines
This document outlines the advantages of a closed-loop screw cushion control system for thermoplastic injection molding machines in the production environment. It also outlines the limitations of such a system and proposes a possible path forward towards closed-loop process control, through the use of a closed-loop viscosity control system.
Impact and Utility of Volumetric Melt Density Sensors
Since variance in melt density during a molding process can infer a change of product quality, careful measurement – and subsequent management – of this factor is essential. Considering that temperature is the primary, though not only, factor in this process, injected melt temperature was measured through two means: a melt sensor installed into a machine nozzle, and a melt sensor installed into a heated insert assembly. The injected melt fill-and-pack density" was profiled for consecutive cycles and the resulting melt-flow profiles and sensing means are presented."
Artificially Balancing Geometrically Balanced Runner Systems
Artificially balancing melt delivery systems is a common practice in injection molding to compensate for filling imbalances. This artificial balance is attempted through tweaking runner and gate sizes or varying drop temperatures within melt delivery systems. These approaches at best only provide an extremely delicate pressure balance rather than address the root cause of the problem. This paper presents the results of a study that examined the robustness of artificial balancing and compares it to new advancements that address the problem that causes these imbalances.
The Effect of Mold Surface Topography on Plastic Part In-Process Shrinkage in Injection Molding
An experimental study of the effect of mold surface roughness on in-process in-flow linear part shrinkage in injection molding has been carried out. The investigation is based on an experimental two-cavity tool, where the cavities have different surface topographies, but are otherwise identical. The study has been carried out for typical commercial polystyrene and polypropylene grades.
Mechanical Properties and Microstructure Enhancement of Injection Molded Parts via Push-Pull Processing
Push-pull injection molding is a live in-mold manipulation method used for enhancing the orientation of molecules and fillers. It implements an alternating shear field induced by a coordinated action of two injection units to create multiple oriented layers across the thickness of moldings. In this work design of experiment was used to analyze the processing parameters in push-pull molding of polypropylene homopolymer. The microstructure and the flexural and impact properties of the produced parts were assessed.
Injection Molding Process Optimization and Documentation
Though molding for decades, we have yet to develop a scientific method of developing an optimized process. The established process is often poorly documented and cannot be transferred to another machine. This paper outlines a scientific process optimization based on data and defines the necessary variables to establish a reproducible consistent process. The procedure along with the resulting setup sheet, that will work on any appropriate machine (hydraulic or electric) are presented.
Design and Analysis of Model-Based Iterative Learning Control of Injection Molding Process
Despite several researchers have reported excellent performance of iterative learning controls for injection molding process, a serious work remains, namely, stability guarantee of the learning controllers. This work presents the first effort on theoretical analysis of iterative learning injection molding control. Specifically, analysis of a filling velocity learning control is conducted. The analysis adopts Lyapunov’s indirect method. Experiment evaluation is carried out on a commercial injection molding machine.
Automatic Injection Velocity Initialization for Computer-Assisted Injection Molding Setup
Modern systems for computer-assisted injection molding use data acquired from sensors and feedback from operators to setup the injection-molding process, to automate optimization of process parameters and to provide a statistical process control. A good initial starting point greatly streamlines injection molding setup and increases its robustness. Here we describe an algorithm for initial determination of injection velocity based on rheological calculations of the melt flow inside the mold cavity.
Measuring Clamping Force with Piezoelectric Strain Transducers
Strain gauges are one of the best measures of clamping force on the toggle clamp units. By means of FEA-calculations, it will be demonstrated that a problem with this kind of clamping force measurement lies with the superposition of strain and bending in the tie bars. In addition, FEA-results will show that only parts of the toggle are elongated, and therefore measuring at these parts will lead to higher precision. In the following paper, measurements of clamping forces with the new Kistler piezoelectric strain transducers will be presented and compared to measurements of a strain gauge.
Geometric Variation of Micro-Features in Injection Molding Experiment
Micro features were produced on inserts for a macroscopic polymer injection mold. The inserts were produced using traditional machining and micro machining techniques. The inserts were installed and subsequent moldings were examined to measure the accuracy of replication of the micro features. The molding conditions were varied to identify the processing window available for accurate production of the micro features.
Numerical Simulation and Experimental Validation of the Filling Stage in the Co-Injection Molding Process
In this work, a three-dimensional finite element flow analysis code is used to solve sequential co-injection molding problems. Non-Newtonian, non-isothermal flow solutions are obtained by solving the momentum, mass and energy equations. Two additional transport equations are solved for tracking polymer/air and skin/core polymers interfaces. Solutions are shown for a rectangular plate filled with polypropylene. The numerical solutions are compared with experimental results.
Flow Prediction in the Presence of Inserts for the Injection Over-Molding Process
Injection over-molding involves injection of molten polymer into complex cavities over solid inserts to form fabricated parts. This process is non-isothermal and the flow is strongly affected by the presence of the insert, and its thermal and mechanical properties. This paper compares the three dimensional flow simulation results of metal and polymer inserts and reviews their effects on filling pattern with experimental data. Furthermore, a two shot over-molding simulation is also presented.
A Genetic Optimization of Shrinkage by Runner Balancing
A new approach to runner balancing is proposed which identifies and deals with limitations associated with the traditional approach to runner balancing. The runner diameters are varied by a multi-objective genetic algorithm, which simultaneously optimizes the product shrinkage and cost. The results suggest that balanced runner systems, which exhibit large differences in cavity pressure, have lower product costs than systems characterized by similar fill times and cavity pressures. The optimization of the secondary runner lengths also reduced costs significantly.
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